CONTROL SYSTEM FOR A BURNER WITH PERFORATED FLAME HOLDER

Abstract

 A combustion system includes a perforated flame holder, a preheating fuel distributor, a main fuel distributor, an oxidant source, an array of sensors, and a controller. The oxidant source outputs an oxidant. The preheating fuel distributor supports a preheating flame configured to preheat the perforated flame holder by outputting a preheating fuel when the combustion system is in a preheating state. The main fuel source outputs a main fuel in the standard operating state. The perforated flame holder is configured to support a combustion reaction of the main fuel and the oxidant in the standard operating state. The sensors are configured to sense parameters of the preheating flame and the perforated flame holder and to output sensor signals to the controller. The controller executes software instructions that include adjusting the flow of the main fuel, the preheating fuel, and the oxidant responsive to the sensor signals.

Description

SUMMARY

[0001] Embodiments include a combustion system including a perforated flame holder. The combustion system is configured to operate in a preheating state and in a standard operating state. In the preheating state, the combustion system supports a preheating flame with a preheating fuel and an oxidant. The preheating flame is positioned to heat the perforated flame holder to an operating temperature. In the standard operating state, the perforated flame holder holds a combustion reaction of a main fuel and an oxidant. Optionally, the main fuel and the preheating fuel may be the same fuel. According to some embodiments, the main fuel and/or the preheating fuel may include fuel mixtures. In an embodiment, the main fuel and the preheating fuel are natural gas.

[0002] According to an embodiment, combustion system includes a preheating flame sensor configured to sense a condition of the preheating flame and to output sensor signals indicative of the condition of the preheating flame. The combustion system includes a perforated flame holder sensor configured to sense a condition of the perforated flame holder or a combustion reaction held by the perforated flame holder and to output sensor signals indicative of the condition of the perforated flame holder or the combustion reaction. The combustion system includes a controller configured to receive the sensor signals from the preheating flame sensor and the perforated flame holder sensor. The controller is configured to execute software instructions stored on a non-transitory computer readable medium to automatically adjust parameters of the combustion system and to automatically transition the combustion system between the preheating state and the standard operating state responsive to the sensor signals from the perforated flame holder sensor and the preheating flame holder sensor and/or to engage alternate methods, or devices to maintain stable and safe combustion or stable and safe states other than the preheating state and the standard operating state. The controller adjusts the combustion system and transitions between states by controlling one or more actuators configured to adjust components of the combustion system.

[0003] According to an embodiment, a flame stability sensor is positioned to sense a flame condition (e.g., the presence or absence of a flame) in a region between the (e.g., main) fuel nozzles and the perforated flame holder, said region being found by the inventors to characterize a main combustion reaction instability. For example, the flame stability sensor may be positioned half way between the fuel nozzles and the perforated flame holder. The controller may, upon receipt of an instability signal from the flame stability sensor corresponding to at least transient presence of a flame in the positioned region and responsively execute a logical decision that the combustion reaction instability exists, at least transiently. The controller may responsively write an incident of combustion reaction instability to a log file and/or cause an electronic display state corresponding to the incident o be provided to an operating engineer or the like. Optionally, the controller may cause one or more actuators to modify an operating condition to increase main combustion reaction stability. For example, the controller may cause actuation of a flame blow off apparatus to increase fluid flow velocity or fluid cooling between the fuel nozzles and the perforated flame holder, cause a damper to open to increase air volume delivery, cause a blower to increase power to increase air volume delivery, cause a valve to momentarily pause fuel delivery, and/or cause a perforated flame holder heater to activate.

[0004] One embodiment is a combustion system including a perforated flame holder. The combustion system is configured to operate in a preheating state and in a standard operating state. In the preheating state, the combustion system supports a preheating flame with a preheating fuel and an oxidant. The preheating flame is positioned to heat the perforated flame holder to an operating temperature. In the standard operating state, the perforated flame holder holds a combustion reaction of a main fuel and an oxidant. The combustion system includes a preheating flame sensor configured to sense a condition of the preheating flame and to output sensor signals indicative of the condition of the preheating flame. The combustion system includes a perforated flame holder sensor configured to sense a condition of the perforated flame holder and to output sensor signals indicative of the condition of the perforated flame holder. The combustion system includes a controller configured to receive the sensor signals from the preheating flame sensor and the perforated flame holder sensor. The controller is configured to execute software instructions stored on a non-transitory computer readable medium to output messages on a display prompting an operator of the combustion system to adjust parameters of the combustion system and to transition the combustion system between the preheating state and the standard operating state responsive to the sensor signals from the perforated flame holder sensor and the preheating flame holder sensor.

[0005] One embodiment is a combustion system including a perforated flame holder. The combustion system is configured to operate in a preheating state and in a standard operating state. In the preheating state, the combustion system supports a preheating flame with a preheating fuel and an oxidant. The preheating flame is positioned to heat the perforated flame holder to an operating temperature. In the standard operating state, the perforated flame holder holds a combustion reaction of a main fuel and an oxidant. The combustion system includes a preheating flame sensor configured to sense a condition of the preheating flame and to output sensor signals indicative of the condition of the preheating flame. The combustion system includes a perforated flame holder sensor configured to sense a condition of the perforated flame holder and to output sensor signals indicative of the condition of the perforated flame holder. The combustion system includes a controller configured to receive the sensor signals from the preheating flame sensor and the perforated flame holder sensor. The controller is configured to execute software instructions stored on a non-transitory computer readable medium to adjust parameters of the combustion system and to transition the combustion system between the preheating state and the standard operating state responsive to the sensor signals from the perforated flame holder sensor and the preheating flame holder sensor. The controller is configured to output messages on a display prompting an operator of the combustion system to approve adjusting parameters of the combustion system or transitioning between the preheating state and the standard operating state responsive to the sensor signals. The controller adjusts the combustion system and transitions between states by controlling one or more actuators configured to adjust components of the combustion system if the operator indicates approval of the adjustment or the transition. The controller can also maintain desired combustion within the perforated flame holder via control of actuators in accordance with sensor signals output by the various sensors of the combustion system. Additionally, or alternatively, the controller may be configured to operate in an automatic mode wherein the controller automatically controls the one or more actuators. In the automatic mode, the controller preferably creates a log file to indicate sensed parameters and/or actuations performed under automatic control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] 

FIG. 1

is a block diagram of a combustion system including a perforated flame holder perforated flame holder, according to an embodiment.

FIG. 2

is a simplified diagram of a combustion system including a perforated flame holder configured to hold a combustion reaction, according to an embodiment.

FIG. 3

is a side sectional diagram of a portion of the perforated flame holder of FIGS. 1 and 2, according to an embodiment.

FIG. 4

is a flow chart showing a method for operating a burner system including the perforated flame holder of FIGS. 1-3, according to an embodiment.

FIG. 5A

is a simplified diagram of a combustion system including a reticulated ceramic perforated flame holder configured to hold a combustion reaction, according to an embodiment.

FIG. 5B

is a side sectional diagram of a portion of the reticulated ceramic perforated flame holder of FIG. 5A, according to an embodiment.

FIG. 6

is a block diagram of components of a combustion system, according to an embodiment.

FIG. 7

is a flow diagram of a process for operating a combustion system, according to an embodiment.

FIG. 8

is a flow diagram of a process for operating a combustion system, according to an embodiment.

FIG. 9

is a flow diagram of a process for operating a combustion system, according to an embodiment.

FIG. 10A

is a diagram of a combustion system, according to an embodiment.

FIG. 10B

is a diagram of the combustion system of FIG. 10A in a preheating state, according to an embodiment.

FIG. 10C

is a diagram of the combustion system of FIG. 10A in standard operating state, according to an embodiment.

FIG. 11

is a diagram of a combustion system, according to an embodiment.

FIG. 12A

is a diagram of a combustion system including a perforated flame holder and an electrocapacitive tomography device, according to an embodiment.

FIG. 12B

is a top view of the perforated flame holder and the electrocapacitive tomography device, according to an embodiment.

DETAILED DESCRIPTION

[0007] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

[0008] As used herein, the term electrocapacitive tomography (ECT) shall be understood as described. ECT sensing may be fundamentally capacitive, or may additionally or alternatively be made to actually measure a conductance, a resistance, an impedance, or other electrical parameter. ECT may include a plurality of sensor channels, such as may be produced by moving a sensor or using a sensor array, such as may be seen in more familiar (e.g., medical) tomography systems. Additionally or alternatively, an ECT system may include a range of sensor channels as low as a single channel defined by two electrodes positioned relative to a sensed region (e.g., a flame-holding region, a blow-off region, a flash-back region, a flue gas region, a pilot flame region, etc.). Unless context dictates otherwise, disclosure and claims herein shall be accorded this broad meaning.

[0009] FIG. 1 is a diagram of a combustion system 100 including a perforated flame holder (perforated flame holder) 102, according to an embodiment. The combustion system 100 is configured to preheat the perforated flame holder 102 to an operating temperature at which the perforated flame holder 102 can sustain a combustion reaction of a main fuel and an oxidant at least partially within the perforated flame holder 102. Thus, the combustion system 100 is configured to operate in two general operating conditions: a preheating state and a standard operating state. In the preheating state, the combustion system 100 preheats the perforated flame holder 102 to the operating temperature. When the perforated flame holder 102 has reached the operating temperature, the combustion system 100 transitions to the standard operating state in which the perforated flame holder 102 holds a combustion reaction of the main fuel and the oxidant at least partially within the perforated flame holder 102. In one embodiment, in the standard operating state the perforated flame holder 102 holds a majority of a combustion reaction of the main fuel and oxidant within the perforated flame holder 102.

[0010] In one embodiment, the combustion system 100 utilizes an oxidant source 104, a preheating fuel distributor 106, and a preheating fuel source 108 in the preheating state. In the preheating state, the oxidant source 104 outputs an oxidant into the furnace volume in which the perforated flame holder 102 is positioned. The preheating fuel source 108 supplies a preheating fuel to the preheating fuel distributor 106. The preheating fuel distributor 106 outputs the preheating fuel into the furnace volume. The preheating fuel and the oxidant mix together in the furnace volume. The combustion system 100 utilizes an igniter to ignite the mixture of the preheating fuel and the oxidant, thereby generating a preheating flame. The preheating flame is positioned between the preheating fuel distributor 106 and the perforated flame holder 102. The preheating flame preheats the perforated flame holder 102 until the perforated flame holder 102 reaches the operating temperature. When the perforated flame holder 102 reaches the operating temperature, the combustion system 100 transitions to the standard operating state.

[0011] In one embodiment, in the standard operating state the combustion system 100 utilizes the main fuel distributor 110, the main fuel source 112, and the oxidant source 104 to support a combustion reaction at least partially within the perforated flame holder 102 during a standard operating state. In the standard operating state, the main fuel source 112 supplies a main fuel to the main fuel distributor 110. The main fuel distributor 110 outputs the main fuel with a trajectory to be received by the perforated flame holder 102. The main fuel and the oxidant mix as the main fuel travels toward the perforated flame holder 102. The perforated flame holder 102 receives the mixture of the main fuel and the oxidant within the perforated flame holder 102. Because the perforated flame holder 102 has been heated to the operating temperature, the perforated flame holder 102 supports a combustion reaction of the main fuel and the oxidant at least partially within the perforated flame holder 102.

[0012] In one embodiment, the oxidant source 104 includes multiple sources of oxidant. In the preheating state, the oxidant source 104 may supply oxidant from all sources of oxidant, e.g., through slots in a barrel register and from a common upstream supply. In the standard operating state, the barrel register can be closed so that all oxidant comes from upstream the slots of the barrel register.

[0013] In one embodiment, the oxidant source 104 includes dampers whose positions can be adjusted to direct all of the flow of the oxidant closer in proximity to a location of the main fuel distributors during the standard operating state and during transition to the standard operating state. During the preheating state, the dampers position of the dampers can be adjusted to enable flow of the oxidant proximal to the preheating fuel distributors 106.

[0014] In one embodiment, various conditions can arise during the preheating state, the standard operating state, and the transition between the preheating state and the standard operating state. The conditions in the combustion system 100 can indicate that the preheating state is progressing normally, that the time to transition to the standard operating state has arrived, or that the combustion system 100 is operating as expected in the standard operating state. However, in some cases the conditions can indicate a problem with one or more components, processes, or operations of combustion system 100. The conditions within the combustion system 100 can indicate that one or more parameters of the combustion system 100 should be adjusted in order to bring operations to a desired state, that the combustion system 100 should revert from a standard operating state to the preheating state, or that the combustion system 100 should shut down.

[0015] In one embodiment, the combustion system 100 utilizes a sensor array 114, a controller 116, actuators 118, and a display 120 in order to monitor and address the conditions within the combustion system 100. In particular, the sensor array 114 includes multiple sensors configured to sense various parameters of the combustion system 100. The sensors of the sensor array 114 can provide sensor signals to the controller 116. The controller 116 receives the sensor signals, identifies conditions within the combustion system 100, and controls the actuators 118 to adjust the conditions within the combustion system 100. The sensor signals can indicate that the preheating state is progressing normally, that the time to transition to the standard operating state has arrived, or that the combustion system is operating as expected in the standard operating state. The sensor signals can also indicate a problem with the conditions or components of the combustion system 100. The controller 116 can adjust the components or conditions of the combustion system 100 in response to the sensor signals by controlling the actuators 118 to physically adjust components or parameters of the combustion system 100. The display 120 can indicate the present conditions within the combustion system 100 in accordance with the sensor signals, can indicate that the controller 116 is taking one or more corrective actions, or can indicate that an operator of the combustion system 100 should operate one or more manual controls 123 in order to adjust conditions within the combustion system 100.

[0016] In one embodiment, the sensor array 114 includes a preheating flame sensor 124. The preheating flame sensor 124 senses parameters relating to the preheating flame during the preheating state of the combustion system 100. The preheating flame sensor 124 provides sensor signals to the controller 116 indicating the conditions of the preheating flame. Based on the sensor signals provided by the preheating flame sensor 124, the controller 116 can adjust parameters of the combustion system 100.

[0017] In one embodiment, the preheating flame sensor 124 detects whether the preheating flame is present during the preheating state. When the combustion system 100 enters the preheating state, the controller 116 controls one or more of the actuators 118 to cause the oxidant source 104 to output the oxidant into the furnace volume. The controller 116 can also control the actuators 118 to operate a valve or other mechanism enabling the preheating fuel source 108 to supply the preheating fuel to the preheating fuel distributor 106. The controller 116 can then cause an ignition mechanism, such as a sparker, to ignite the preheating fuel and the oxidant, thereby initiating the preheating flame. The preheating flame sensor 124 senses whether the preheating flame is present during the preheating state. The preheating flame sensor 124 provides sensor signals to the controller 116 indicating whether or not the preheating flame is present. If the sensor signals indicate that the preheating flame is not present, the controller 116 can take action such as causing the igniter to generate additional sparks in order to ignite the preheating fuel and the oxidant. If the preheating flame sensor 124 indicates that the preheating flame is still not present, then the controller 116 can control the actuators 118 to attempt to cause the oxidant source 104 to supply oxidant or to attempt to cause the preheating fuel source 108 to supply the preheating fuel to the preheating fuel distributor 106. This can be followed by causing the igniter to generate additional sparks. If the sensor signals continue to indicate that the preheating flame is not present, the controller 116 can indicate that a system fault has occurred that requires that the combustion system 100 be shut down until an operator can inspect the oxidant source 104, the preheating fuel source 108, preheating fuel distributor 106, the valves connecting the preheating fuel distributor 106 and the preheating fuel source 108, and the actuators 118 in order to identify and correct any faulty conditions with these components. The operator can then inspect the various components and correct any issues.

[0018] In one embodiment, the preheating flame sensor 124 may sense the position of the preheating flame. For example, the preheating flame may be present and may not be in the desired position. The sensor signal can indicate that the preheating flame is too close to the perforated flame holder 102 or too far from the perforated flame holder 102, i.e., too close to the preheating fuel distributor 106. In response to these conditions, the controller 116 can adjust the flow of oxidant into the furnace volume by increasing or decreasing the flow of oxidant into the furnace volume. In response to these conditions, the controller 116 can adjust the flow of the preheating fuel into the furnace volume by increasing or decreasing the flow rate of the preheating fuel, or by increasing or decreasing the velocity of the preheating fuel. By adjusting the flow of the oxidant and the preheating fuel, the controller 116 can adjust the position of the preheating flame relative to the perforated flame holder 102.

[0019] In one embodiment, the preheating flame sensor 124 can indicate a temperature of the preheating flame. The preheating flame may be generating more or less heat than desired for the preheating of the perforated flame holder 102. The sensor signals can inform the controller 116 of the temperature of the preheating flame. In response, the controller 116 can adjust the parameters of the flow of oxidant and preheating fuel in order to adjust the temperature of the preheating flame during the preheating state.

[0020] In one embodiment, the preheating flame sensor 124 can include multiple sensors. The preheating flame sensor 124 can include one or more of a flame scanner, a flame rod, a temperature sensor, an image capture device, a flame rod or other kinds of sensors for detecting the presence and parameters of the preheating flame.

[0021] In one embodiment, the sensor array 114 can include a perforated flame holder sensor 122. The perforated flame holder sensor 122 can monitor the parameters of the perforated flame holder 102. The perforated flame holder sensor 122 senses parameters of the perforated flame holder 102 during the preheating state entering the standard operating state. The perforated flame holder sensor 122 generates sensor signals and provides them to the controller 116. The controller 116 receives the sensor signals from the perforated flame holder sensor 122 and can take action to adjust the parameters of the combustion system 100 based on the conditions of the perforated flame holder 102.

[0022] In one embodiment, the perforated flame holder sensor 122 includes a temperature sensor configured to sense the temperature of the perforated flame holder 102 during the preheating state. During the preheating state, the combustion system 100 supports a preheating flame positioned to heat the perforated flame holder 102 to the operating temperature. Throughout the preheating state, the perforated flame holder sensor 122 monitors the temperature of the perforated flame holder 102. If the sensor signal indicates that the perforated flame holder 102 has not yet reached the operating temperature, then the controller 116 keeps the combustion system 100 in the preheating state, thereby causing the preheating flame to continue to heat and increase the temperature of the perforated flame holder 102. If the sensor signals indicate that the perforated flame holder 102 has reached the operating temperature, then the controller 116 can cause the combustion system 100 to transition to the standard operating state.

[0023] In one embodiment, the controller 116 causes the combustion system 100 to transition to the standard operating state by removing the preheating flame. The controller 116 can remove the preheating flame by causing the actuators 118 to stop the preheating fuel source 108 from supplying the preheating fuel to the preheating fuel distributor 106. The controller 116 can cause the preheating fuel source 108 to stop providing the preheating fuel to the preheating fuel distributor 106 by closing one or more valves that connect the preheating fuel source 108 to the preheating fuel distributor 106. When the preheating fuel distributor 106 no longer outputs the preheating fuel, the preheating flame will be extinguished. The controller 116 continues the transition from the preheating state to the standard operating state by causing the main fuel source 112 to supply the main fuel to the main fuel distributor 110 by controlling the actuators 118 to open one or more valves that enable the flow of fuel from the main fuel source 112 to the main fuel distributor 110. The main fuel distributor 110 outputs the main fuel into the furnace volume. The oxidant source 104 continues to output oxidant into the furnace volume during the transition to the standard operating state. The main fuel and the oxidant mix as they travel toward the perforated flame holder 102. The perforated flame holder 102 receives the mixture of the main fuel and the oxidant. Because the perforated flame holder 102 has reached the operating temperature, the perforated flame holder 102 outputs heat sufficient to ignite the mixture of the main fuel and the oxidant at the perforated flame holder 102. In the standard operating state, the perforated flame holder 102 supports a stable combustion reaction of the main fuel and the oxidant at least partially within the perforated flame holder 102. In this way, the controller 116 can cause the transition of the combustion system 100 from the preheating state to the standard operating state responsive to the sensor signals from the perforated flame holder sensor 122.

[0024] In one embodiment, the perforated flame holder sensor 122 continues to monitor the perforated flame holder 102 in the standard operating state and to output sensor signals to the controller 116. The perforated flame holder sensor 122 can detect the presence or absence of the combustion reaction within and adjacent to the perforated flame holder 102. If the perforated flame holder sensor 122 indicates that the combustion reaction of the main fuel and the oxidant is not present at the perforated flame holder 102, then the controller 116 can take corrective action. The controller 116 can cause the actuators 118 to adjust or reopen the valves that enable the flow of the main fuel from the main fuel source 112 to the main fuel distributor 110. The controller 116 can output a message on the display 120 indicating to an operator to check whether the main fuel source 112 is supplying the main fuel to the main fuel distributor 110 and to take corrective action, if necessary, by operating the manual controls 123. If, after the controller 116 has taken corrective actions, the perforated flame holder sensor 122 indicates the absence of a combustion reaction of the main fuel and the oxidant, the controller 116 can cause the combustion system 100 to enter a fault state in which all fuel sources shut down so that neither the main fuel nor the preheating fuel is output into the furnace volume.

[0025] In one embodiment, the perforated flame holder sensor 122 can indicate that the combustion reaction of the fuel and oxidant is localized below the perforated flame holder 102 or in an otherwise undesirable location. The controller 116 can take actions such as adjusting the flow of the main fuel, adjusting the output of oxidant, or adjusting of the parameters of the components of the combustion system 100 in order to adjust the position of the combustion reaction of the main fuel and the oxidant. Alternatively, the controller 116 can output messages on the display 120 indicating to an operator of the combustion system 100 that the combustion reaction is not properly held by the perforated flame holder 102 and that the operator should take corrective action.

[0026] In one embodiment, the perforated flame holder sensor 122 can indicate that the temperature of the perforated flame holder 102 has fallen below the operating temperature. In this case, the controller 116 can cause the combustion system 100 to reenter the preheating state. Additionally, or alternatively, the combustion system 100 may include a heater separate from the preheating fuel distributor 106 and the preheating fuel source 108. The heater can be positioned adjacent to or on the perforated flame holder 102. If the perforated flame holder sensor 122 indicates that the temperature of the perforated flame holder 102 is below the operating temperature, the controller 116 can activate the heater in order to heat the perforated flame holder 102 to the operating temperature. The controller 116 can cause the main fuel distributor 110 to again output the main fuel in order to reenter the standard operating state in which the perforated flame holder 102 sustains a combustion reaction of the main fuel and oxidant.

[0027] In one embodiment, the perforated flame holder sensor 122 includes one or more of a flame scanner, a flame rod, a temperature sensor, a visible light sensor, an infrared light sensor, an ultraviolet light sensor, an electrocapacitive tomography device, an image capture device that captures images in one or more of the visible light spectrum, the infrared light spectrum, or the ultraviolet light spectrum, or any other type of sensor that can detect parameters of a combustion reaction. The perforated flame holder sensor 122 can include multiple sensors of the same type. The perforated flame holder sensor 122 can include multiple sensors of different types, such as those set forth above. Thus, while FIG. 1 indicates a single perforated flame holder sensor 122, the perforated flame holder sensor 122 can include multiple individual sensors of different kinds or of the same kind.

[0028] In one embodiment, if neither the preheating flame sensor 124 nor the perforated flame holder sensor 122 indicate the present of a preheating flame or combustion reaction, the controller 116 can stop the flow of all fuel into the furnace volume.

[0029] In one embodiment, the preheating flame sensor 124 includes one or more of a flame scanner, a flame rod, a temperature sensor, a visible light sensor, an infrared light sensor, an ultraviolet light sensor, an electrocapacitive tomography device, an image capture device that captures images in one or more of the visible light spectrum, the infrared light spectrum, or the ultraviolet light spectrum, or any other type of sensor that can detect parameters of a combustion reaction. The preheating flame sensor 124 can include multiple sensors of the same type. The preheating flame sensor 124 can include multiple sensors of different types, such as those set forth above. Thus, while FIG. 1 indicates a single preheating flame sensor 124, the preheating flame sensor 124 can include multiple individual sensors of different kinds or of the same kind.

[0030] In one embodiment, the sensor array 114 includes sensors other than the perforated flame holder sensor 122 and the preheating flame sensor 124. For example, the sensor array 114 can include one or more of a bridge wall temperature sensor, a CO monitor, an NOx monitor, an O2 monitor, a process monitor, a draft pressure sensor, a dynamic pressure sensor, a pressure differential sensor, or other kinds of sensors. Some of the sensors can be included in the perforated flame holder sensor 122 or the preheating flame sensor 124. All the sensors of the sensor array 114 provide control signals to the controller 116. The controller 116 can take actions to adjust conditions in the combustion system 100 responsive to the sensor signals from the various sensors of the sensor array 114.

[0031] In one embodiment, the controller 116 includes a non-transitory computer readable medium and one or more processors. The non-transitory computer readable medium can include one or more memories and store instructions encoded in software for controlling the combustion system 100. The one or more processors are configured to execute the instructions. The instructions can include data related to the various operating conditions of the combustion system 100. The instructions can include data related to both faulty or undesirable operating conditions and proper or desirable operating conditions. The instructions can include actions to be taken by the controller 116 responsive to the sensor signals received by the controller 116. The actions can include adjusting conditions of the combustion system 100 by causing the actuators 118 to adjust, activate, or deactivate various components of the combustion system 100. The actions taken by the controller 116 can also include outputting messages to a display 120. The messages can include data indicating the current conditions of the combustion system 100. The messages can also include data prompting an operator of the combustion system 100 to take various actions in order to maintain or adjust the conditions of the combustion system 100. The messages can include prompts to approve an action proposed by the controller 116 to adjust or maintain conditions in the combustion system 100. The controller 116 can also output data via wired or wireless connections to one or more other computing systems. The data can include data related to current conditions of the combustion system 100, data related to actions taken by the controller 116, data related to actions proposed by the controller 116, or prompts to an operator of the combustion system 100 to take actions or to approve proposed actions.

[0032] In one embodiment, the software instructions include one or more algorithms, state diagrams, decision trees, or other instructions by which the controller 116 makes decisions to adjust the parameters of the combustion system 100. The controller 116 can also include a state machine that determines actions to be taken by the controller 116 responsive to the sensor signals.

[0033] In one embodiment, the actuators 118 include mechanisms that can control, adjust, or otherwise affect physical components of the combustion system 100. The actuators 118 can include motors, motivators, electrical switches, electrical connectors, electrical transmitters, or other types of mechanisms that can physically affect or manipulate components of the combustion system 100. For example, the actuators 118 can include motors or switches for physically opening, closing, or otherwise adjusting valves that control the flow of fuel or oxidant into the furnace volume. The actuators 118 can include mechanisms that control the movements of a stack damper. The actuators 118 can include mechanisms that activate an igniter to ignite the preheating flame or the main combustion reaction. The actuators 118 can include mechanisms that adjust the mixture of fuels included in the preheating fuel or the main fuel by increasing or decreasing the concentration of various components of the preheating fuel or the main fuel. The actuators 118 can include mechanisms for adjusting, activating, or the activating the oxidant source 104. The actuators 118 can include other kinds of mechanisms for physically manipulating components of the combustion system 100 other than those set forth above. These other kinds of mechanisms can also include mechanisms for controlling components of the combustion system 100 not shown in FIG. 1 or expressly described herein.

[0034] In one embodiment, the manual controls 123 enable an operator of the combustion system 100 to physically manipulate components of the combustion system 100 in order to adjust conditions of the combustion system 100. The manual controls 123 can include switches, buttons, dials, levers, keypads, touchscreens, keyboards, or other types of mechanisms that can enable an operator to manipulate the components of the combustion system 100. The manual controls 123 can include manual devices for opening and closing valves. The manual controls 123 can include the valves themselves. The manual controls 123 can enable an operator to activate, deactivate, or adjust the oxidant source 104, the main fuel source 112, the preheating fuel source 108, the main fuel distributor 110, the preheating fuel distributor 106, the igniter, the heater, the stack damper, or any other components of the combustion system 100.

[0035] In one embodiment, the manual controls 123 can control the actuators 118. The manual controls 123 can control some or all of the same actuators 118 that can be controlled by the controller 116. The manual controls 123 can also control actuators 118 that cannot be controlled by the controller 116. In some cases, the manual controls 123 include some or all of the actuators 118. In one embodiment, the manual controls 123 enable an operator to shut down the combustion system 100 entirely or to override actions taken by the controller 116.

[0036] FIG. 2 is a simplified diagram of a burner system 200 including a perforated flame holder 102 configured to hold a combustion reaction, according to an embodiment. As used herein, the terms perforated flame holder, perforated reaction holder, porous flame holder, porous reaction holder, duplex, and duplex tile shall be considered synonymous unless further definition is provided.

[0037] Experiments performed by the inventors have shown that perforated flame holders 102 described herein can support very clean combustion. Specifically, in experimental use of burner systems 200 ranging from pilot scale to full scale, output of oxides of nitrogen (NOx) was measured to range from low single digit parts per million (ppm) down to undetectable (less than 1 ppm) concentration of NOx at the stack. These remarkable results were measured at 3% (dry) oxygen (O2) concentration with undetectable carbon monoxide (CO) at stack temperatures typical of industrial furnace applications (1400 - 1600 °F). Moreover, these results did not require any extraordinary measures such as selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), water/steam injection, external flue gas recirculation (FGR), or other heroic extremes that may be required for conventional burners to even approach such clean combustion.

[0038] According to embodiments, the burner system 200 includes a fuel and oxidant source 202 disposed to output fuel and oxidant into a combustion volume 204 to form a fuel and oxidant mixture 206. As used herein, the terms fuel and oxidant mixture and fuel stream may be used interchangeably and considered synonymous depending on the context, unless further definition is provided. As used herein, the terms combustion volume, combustion chamber, furnace volume, and the like shall be considered synonymous unless further definition is provided. The perforated flame holder 102 is disposed in the combustion volume 204 and positioned to receive the fuel and oxidant mixture 206.

[0039] FIG. 3 is a side sectional diagram 300 of a portion of the perforated flame holder 102 of FIGS. 1 and 2, according to an embodiment. Referring to FIGS. 2 and 3, the perforated flame holder 102 includes a perforated flame holder body 208 defining a plurality of perforations 210 aligned to receive the fuel and oxidant mixture 206 from the fuel and oxidant source 202. As used herein, the terms perforation, pore, aperture, elongated aperture, and the like, in the context of the perforated flame holder 102, shall be considered synonymous unless further definition is provided. The perforations 210 are configured to collectively hold a combustion reaction 302 supported by the fuel and oxidant mixture 206.

[0040] The fuel can include hydrogen, a hydrocarbon gas, a vaporized hydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered or pulverized solid. The fuel can be a single species or can include a mixture of gas(es), vapor(s), atomized liquid(s), and/or pulverized solid(s). For example, in a process heater application the fuel can include fuel gas or byproducts from the process that include carbon monoxide (CO), hydrogen (H2), and methane (CH4). In another application the fuel can include natural gas (mostly CH4) or propane (C3H8). In another application, the fuel can include #2 fuel oil or #6 fuel oil. Dual fuel applications and flexible fuel applications are similarly contemplated by the inventors. The oxidant can include oxygen carried by air, flue gas, and/or can include another oxidant, either pure or carried by a carrier gas. The terms oxidant and oxidizer shall be considered synonymous herein.

[0041] According to an embodiment, the perforated flame holder body 208 can be bounded by an input face 212 disposed to receive the fuel and oxidant mixture 206, an output face 214 facing away from the fuel and oxidant source 202, and a peripheral surface 216 defining a lateral extent of the perforated flame holder 102. The plurality of perforations 210 which are defined by the perforated flame holder body 208 extend from the input face 212 to the output face 214. The plurality of perforations 210 can receive the fuel and oxidant mixture 206 at the input face 212. The fuel and oxidant mixture 206 can then combust in or near the plurality of perforations 210 and combustion products can exit the plurality of perforations 210 at or near the output face 214.

[0042] According to an embodiment, the perforated flame holder 102 is configured to hold a majority of the combustion reaction 302 within the perforations 210. For example, on a steady-state basis, more than half the molecules of fuel output into the combustion volume 204 by the fuel and oxidant source 202 may be converted to combustion products between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, more than half of the heat or thermal energy output by the combustion reaction 302 may be output between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the terms heat, heat energy, and thermal energy shall be considered synonymous unless further definition is provided. As used above, heat energy and thermal energy refer generally to the released chemical energy initially held by reactants during the combustion reaction 302. As used elsewhere herein, heat, heat energy and thermal energy correspond to a detectable temperature rise undergone by real bodies characterized by heat capacities. Under nominal operating conditions, the perforations 210 can be configured to collectively hold at least 80% of the combustion reaction 302 between the input face 212 and the output face 214 of the perforated flame holder 102. In some experiments, the inventors produced a combustion reaction 302 that was apparently wholly contained in the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, the perforated flame holder 102 can support combustion between the input face 212 and output face 214 when combustion is "time-averaged." For example, during transients, such as before the perforated flame holder 102 is fully heated, or if too high a (cooling) load is placed on the system, the combustion may travel somewhat downstream from the output face 214 of the perforated flame holder 102. Alternatively, if the cooling load is relatively low and/or the furnace temperature reaches a high level, the combustion may travel somewhat upstream of the input face 212 of the perforated flame holder 102.

[0043] While a "flame" is described in a manner intended for ease of description, it should be understood that in some instances, no visible flame is present. Combustion occurs primarily within the perforations 210, but the "glow" of combustion heat is dominated by a visible glow of the perforated flame holder 102 itself. In other instances, the inventors have noted transient "huffing" or "flashback" wherein a visible flame momentarily ignites in a region lying between the input face 212 of the perforated flame holder 102 and the fuel nozzle 218, within the dilution region DD. Such transient huffing or flashback is generally short in duration such that, on a time-averaged basis, a majority of combustion occurs within the perforations 210 of the perforated flame holder 102, between the input face 212 and the output face 214. In still other instances, the inventors have noted apparent combustion occurring downstream from the output face 214 of the perforated flame holder 102, but still a majority of combustion occurred within the perforated flame holder 102 as evidenced by continued visible glow from the perforated flame holder 102 that was observed.

[0044] The perforated flame holder 102 can be configured to receive heat from the combustion reaction 302 and output a portion of the received heat as thermal radiation 304 to heat-receiving structures (e.g., furnace walls and/or radiant section working fluid tubes) in or adjacent to the combustion volume 204. As used herein, terms such as radiation, thermal radiation, radiant heat, heat radiation, etc. are to be construed as being substantially synonymous, unless further definition is provided. Specifically, such terms refer to blackbody-type radiation of electromagnetic energy, primarily at infrared wavelengths, but also at visible wavelengths owing to elevated temperature of the perforated flame holder body 208.

[0045] Referring especially to FIG. 3, the perforated flame holder 102 outputs another portion of the received heat to the fuel and oxidant mixture 206 received at the input face 212 of the perforated flame holder 102. The perforated flame holder body 208 may receive heat from the combustion reaction 302 at least in heat receiving regions 306 of perforation walls 308. Experimental evidence has suggested to the inventors that the position of the heat receiving regions 306, or at least the position corresponding to a maximum rate of receipt of heat, can vary along the length of the perforation walls 308. In some experiments, the location of maximum receipt of heat was apparently between 1/3 and 1/2 of the distance from the input face 212 to the output face 214 (i.e., somewhat nearer to the input face 212 than to the output face 214). The inventors contemplate that the heat receiving regions 306 may lie nearer to the output face 214 of the perforated flame holder 102 under other conditions. Most probably, there is no clearly defined edge of the heat receiving regions 306 (or for that matter, the heat output regions 310, described below). For ease of understanding, the heat receiving regions 306 and the heat output regions 310 will be described as particular regions 306, 310.

[0046] The perforated flame holder body 208 can be characterized by a heat capacity. The perforated flame holder body 208 may hold thermal energy from the combustion reaction 302 in an amount corresponding to the heat capacity multiplied by temperature rise, and transfer the thermal energy from the heat receiving regions 306 to heat output regions 310 of the perforation walls 308. Generally, the heat output regions 310 are nearer to the input face 212 than are the heat receiving regions 306. According to one interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via thermal radiation, depicted graphically as 304. According to another interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via heat conduction along heat conduction paths 312. The inventors contemplate that multiple heat transfer mechanisms including conduction, radiation, and possibly convection may be operative in transferring heat from the heat receiving regions 306 to the heat output regions 310. In this way, the perforated flame holder 102 may act as a heat source to maintain the combustion reaction 302, even under conditions where a combustion reaction 302 would not be stable when supported from a conventional flame holder.

[0047] The inventors believe that the perforated flame holder 102 causes the combustion reaction 302 to begin within thermal boundary layers 314 formed adjacent to walls 308 of the perforations 210. Insofar as combustion is generally understood to include a large number of individual reactions, and since a large portion of combustion energy is released within the perforated flame holder 102, it is apparent that at least a majority of the individual reactions occur within the perforated flame holder 102. As the relatively cool fuel and oxidant mixture 206 approaches the input face 212, the flow is split into portions that respectively travel through individual perforations 210. The hot perforated flame holder body 208 transfers heat to the fluid, notably within thermal boundary layers 314 that progressively thicken as more and more heat is transferred to the incoming fuel and oxidant mixture 206. After reaching a combustion temperature (e.g., the auto-ignition temperature of the fuel), the reactants continue to flow while a chemical ignition delay time elapses, over which time the combustion reaction 302 occurs. Accordingly, the combustion reaction 302 is shown as occurring within the thermal boundary layers 314. As flow progresses, the thermal boundary layers 314 merge at a merger point 316. Ideally, the merger point 316 lies between the input face 212 and output face 214 that define the ends of the perforations 210. At some position along the length of a perforation 210, the combustion reaction 302 outputs more heat to the perforated flame holder body 208 than it receives from the perforated flame holder body 208. The heat is received at the heat receiving region 306, is held by the perforated flame holder body 208, and is transported to the heat output region 310 nearer to the input face 212, where the heat is transferred into the cool reactants (and any included diluent) to bring the reactants to the ignition temperature.

[0048] In an embodiment, each of the perforations 210 is characterized by a length L defined as a reaction fluid propagation path length between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the term reaction fluid refers to matter that travels through a perforation 210. Near the input face 212, the reaction fluid includes the fuel and oxidant mixture 206 (optionally including nitrogen, flue gas, and/or other "non-reactive" species). Within the combustion reaction region, the reaction fluid may include plasma associated with the combustion reaction 302, molecules of reactants and their constituent parts, any non-reactive species, reaction intermediates (including transition states), and reaction products. Near the output face 214, the reaction fluid may include reaction products and byproducts, non-reactive gas, and excess oxidant.

[0049] The plurality of perforations 210 can be each characterized by a transverse dimension D between opposing perforation walls 308. The inventors have found that stable combustion can be maintained in the perforated flame holder 102 if the length L of each perforation 210 is at least four times the transverse dimension D of the perforation 210. In other embodiments, the length L can be greater than six times the transverse dimension D. For example, experiments have been run where L is at least eight, at least twelve, at least sixteen, and at least twenty-four times the transverse dimension D. Preferably, the length L is sufficiently long for thermal boundary layers 314 to form adjacent to the perforation walls 308 in a reaction fluid flowing through the perforations 210 to converge at merger points 316 within the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. In experiments, the inventors have found L/D ratios between 12 and 48 to work well (i.e., produce low NOx, produce low CO, and maintain stable combustion).

[0050] The perforated flame holder body 208 can be configured to convey heat between adjacent perforations 210. The heat conveyed between adjacent perforations 210 can be selected to cause heat output from the combustion reaction portion 302 in a first perforation 210 to supply heat to stabilize a combustion reaction portion 302 in an adjacent perforation 210.

[0051] Referring especially to FIG. 2, the fuel and oxidant source 202 can further include a fuel nozzle 218, configured to output fuel, and an oxidant source 220 configured to output a fluid including the oxidant. For example, the fuel nozzle 218 can be configured to output pure fuel. The oxidant source 220 can be configured to output combustion air carrying oxygen, and optionally, flue gas.

[0052] The perforated flame holder 102 can be held by a perforated flame holder support structure 222 configured to hold the perforated flame holder 102 at a dilution distance DD away from the fuel nozzle 218. The fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant to form the fuel and oxidant mixture 206 as the fuel jet and oxidant travel along a path to the perforated flame holder 102 through the dilution distance DD between the fuel nozzle 218 and the perforated flame holder 102. Additionally or alternatively (particularly when a blower is used to deliver oxidant contained in combustion air), the oxidant or combustion air source can be configured to entrain the fuel and the fuel and oxidant travel through the dilution distance DD. In some embodiments, a flue gas recirculation path 224 can be provided. Additionally, or alternatively, the fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant and to entrain flue gas as the fuel jet travels through the dilution distance DD between the fuel nozzle 218 and the input face 212 of the perforated flame holder 102.

[0053] The fuel nozzle 218 can be configured to emit the fuel through one or more fuel orifices 226 having an inside diameter dimension that is referred to as "nozzle diameter." The perforated flame holder support structure 222 can support the perforated flame holder 102 to receive the fuel and oxidant mixture 206 at the distance DD away from the fuel nozzle 218 greater than 20 times the nozzle diameter. In another embodiment, the perforated flame holder 102 is disposed to receive the fuel and oxidant mixture 206 at the distance DD away from the fuel nozzle 218 between 100 times and 1100 times the nozzle diameter. Preferably, the perforated flame holder support structure 222 is configured to hold the perforated flame holder 102 at a distance about 200 times or more of the nozzle diameter away from the fuel nozzle 218. When the fuel and oxidant mixture 206 travels about 200 times the nozzle diameter or more, the mixture is sufficiently homogenized to cause the combustion reaction 302 to produce minimal NOx.

[0054] The fuel and oxidant source 202 can alternatively include a premix fuel and oxidant source, according to an embodiment. A premix fuel and oxidant source can include a premix chamber (not shown), a fuel nozzle configured to output fuel into the premix chamber, and an oxidant (e.g., combustion air) channel configured to output the oxidant into the premix chamber. A flame arrestor can be disposed between the premix fuel and oxidant source and the perforated flame holder 102 and be configured to prevent flame flashback into the premix fuel and oxidant source.

[0055] The oxidant source 220, whether configured for entrainment in the combustion volume 204 or for premixing, can include a blower configured to force the oxidant through the fuel and oxidant source 202.

[0056] The perforated flame holder support structure 222 can be configured to support the perforated flame holder 102 from a floor or wall (not shown) of the combustion volume 204, for example. In another embodiment, the perforated flame holder support structure 222 supports the perforated flame holder 102 from the fuel and oxidant source 202. Alternatively, the perforated flame holder support structure 222 can suspend the perforated flame holder 102 from an overhead structure (such as a flue, in the case of an up-fired system). The perforated flame holder support structure 222 can support the perforated flame holder 102 in various orientations and directions.

[0057] The perforated flame holder 102 can include a single perforated flame holder body 208. In another embodiment, the perforated flame holder 102 can include a plurality of adjacent perforated flame holder sections that collectively provide a tiled perforated flame holder 102.

[0058] The perforated flame holder support structure 222 can be configured to support the plurality of perforated flame holder sections. The perforated flame holder support structure 222 can include a metal superalloy, a cementatious, and/or ceramic refractory material. In an embodiment, the plurality of adjacent perforated flame holder sections can be joined with a fiber reinforced refractory cement.

[0059] The perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least twice a thickness dimension T between the input face 212 and the output face 214. In another embodiment, the perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least three times, at least six times, or at least nine times the thickness dimension T between the input face 212 and the output face 214 of the perforated flame holder 102.

[0060] In an embodiment, the perforated flame holder 102 can have a width dimension W less than a width of the combustion volume 204. This can allow the flue gas recirculation path 224 from above to below the perforated flame holder 102 to lie between the peripheral surface 216 of the perforated flame holder 102 and the combustion volume wall (not shown).

[0061] Referring again to both FIGS. 2 and 3, the perforations 210 can be of various shapes. In an embodiment, the perforations 210 can include elongated squares, each having a transverse dimension D between opposing sides of the squares. In another embodiment, the perforations 210 can include elongated hexagons, each having a transverse dimension D between opposing sides of the hexagons. In yet another embodiment, the perforations 210 can include hollow cylinders, each having a transverse dimension D corresponding to a diameter of the cylinder. In another embodiment, the perforations 210 can include truncated cones or truncated pyramids (e.g., frustums), each having a transverse dimension D radially symmetric relative to a length axis that extends from the input face 212 to the output face 214. In some embodiments, the perforations 210 can each have a lateral dimension D equal to or greater than a quenching distance of the flame based on standard reference conditions. Alternatively, the perforations 210 may have lateral dimension D less than a standard reference quenching distance.

[0062] In one range of embodiments, each of the plurality of perforations 210 has a lateral dimension D between 0.05 inch and 1.0 inch. Preferably, each of the plurality of perforations 210 has a lateral dimension D between 0.1 inch and 0.5 inch. For example the plurality of perforations 210 can each have a lateral dimension D of about 0.2 to 0.4 inch.

[0063] The void fraction of a perforated flame holder 102 is defined as the total volume of all perforations 210 in a section of the perforated flame holder 102 divided by a total volume of the perforated flame holder 102 including perforated flame holder body 208 and perforations 210. The perforated flame holder 102 should have a void fraction between 0.10 and 0.90. In an embodiment, the perforated flame holder 102 can have a void fraction between 0.30 and 0.80. In another embodiment, the perforated flame holder 102 can have a void fraction of about 0.70. Using a void fraction of about 0.70 was found to be especially effective for producing very low NOx.

[0064] The perforated flame holder 102 can be formed from a fiber reinforced cast refractory material and/or a refractory material such as an aluminum silicate material. For example, the perforated flame holder 102 can be formed to include mullite or cordierite. Additionally, or alternatively, the perforated flame holder body 208 can include a metal superalloy such as Inconel or Hastelloy. The perforated flame holder body 208 can define a honeycomb. Honeycomb is an industrial term of art that need not strictly refer to a hexagonal cross section and most usually includes cells of square cross section. Honeycombs of other cross sectional areas are also known.

[0065] The inventors have found that the perforated flame holder 102 can be formed from VERSAGRID ® ceramic honeycomb, available from Applied Ceramics, Inc. of Doraville, South Carolina.

[0066] The perforations 210 can be parallel to one another and normal to the input and output faces 212, 214. In another embodiment, the perforations 210 can be parallel to one another and formed at an angle relative to the input and output faces 212, 214. In another embodiment, the perforations 210 can be non-parallel to one another. In another embodiment, the perforations 210 can be non-parallel to one another and non-intersecting. In another embodiment, the perforations 210 can be intersecting. The perforated flame holder body 208 can be one piece or can be formed from a plurality of sections.

[0067] In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from reticulated ceramic material. The term "reticulated" refers to a netlike structure. Reticulated ceramic material is often made by dissolving a slurry into a sponge of specified porosity, allowing the slurry to harden, and burning away the sponge and curing the ceramic.

[0068] In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from a ceramic material that has been punched, bored or cast to create channels.

[0069] In another embodiment, the perforated flame holder 102 can include a plurality of tubes or pipes bundled together. The plurality of perforations 210 can include hollow cylinders and can optionally also include interstitial spaces between the bundled tubes. In an embodiment, the plurality of tubes can include ceramic tubes. Refractory cement can be included between the tubes and configured to adhere the tubes together. In another embodiment, the plurality of tubes can include metal (e.g., superalloy) tubes. The plurality of tubes can be held together by a metal tension member circumferential to the plurality of tubes and arranged to hold the plurality of tubes together. The metal tension member can include stainless steel, a superalloy metal wire, and/or a superalloy metal band.

[0070] The perforated flame holder body 208 can alternatively include stacked perforated sheets of material, each sheet having openings that connect with openings of subjacent and superjacent sheets. The perforated sheets can include perforated metal sheets, ceramic sheets and/or expanded sheets. In another embodiment, the perforated flame holder body 208 can include discontinuous packing bodies such that the perforations 210 are formed in the interstitial spaces between the discontinuous packing bodies. In one example, the discontinuous packing bodies include structured packing shapes. In another example, the discontinuous packing bodies include random packing shapes. For example, the discontinuous packing bodies can include ceramic Raschig ring, ceramic Berl saddles, ceramic Intalox saddles, and/or metal rings or other shapes (e.g., Super Raschig Rings) that may be held together by a metal cage.

[0071] The inventors contemplate various explanations for why burner systems including the perforated flame holder 102 provide such clean combustion.

[0072] According to an embodiment, the perforated flame holder 102 may act as a heat source to maintain a combustion reaction even under conditions where a combustion reaction would not be stable when supported by a conventional flame holder. This capability can be leveraged to support combustion using a leaner fuel-to-oxidant mixture than is typically feasible. Thus, according to an embodiment, at the point where the fuel stream 206 contacts the input face 212 of the perforated flame holder 102, an average fuel-to-oxidant ratio of the fuel stream 206 is below a (conventional) lower combustion limit of the fuel component of the fuel stream 206-lower combustion limit defines the lowest concentration of fuel at which a fuel and oxidant mixture 206 will burn when exposed to a momentary ignition source under normal atmospheric pressure and an ambient temperature of 25° C (77° F).

[0073] The perforated flame holder 102 and systems including the perforated flame holder 102 described herein were found to provide substantially complete combustion of CO (single digit ppm down to undetectable, depending on experimental conditions), while supporting low NOx. According to one interpretation, such a performance can be achieved due to a sufficient mixing used to lower peak flame temperatures (among other strategies). Flame temperatures tend to peak under slightly rich conditions, which can be evident in any diffusion flame that is insufficiently mixed. By sufficiently mixing, a homogenous and slightly lean mixture can be achieved prior to combustion. This combination can result in reduced flame temperatures, and thus reduced NOx formation. In one embodiment, "slightly lean" may refer to 3% O2, i.e., an equivalence ratio of ∼0.87. Use of even leaner mixtures is possible, but may result in elevated levels of O2. Moreover, the inventors believe perforation walls 308 may act as a heat sink for the combustion fluid. This effect may alternatively or additionally reduce combustion temperatures and lower NOx.

[0074] According to another interpretation, production of NOx can be reduced if the combustion reaction 302 occurs over a very short duration of time. Rapid combustion causes the reactants (including oxygen and entrained nitrogen) to be exposed to NOx-formation temperature for a time too short for NOx formation kinetics to cause significant production of NOx. The time required for the reactants to pass through the perforated flame holder 102 is very short compared to a conventional flame. The low NOx production associated with perforated flame holder combustion may thus be related to the short duration of time required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 102.

[0075] FIG. 4 is a flow chart showing a method 400 for operating a burner system including the perforated flame holder shown and described herein. To operate a burner system including a perforated flame holder, the perforated flame holder is first heated to a temperature sufficient to maintain combustion of the fuel and oxidant mixture.

[0076] According to a simplified description, the method 400 begins with step 402, wherein the perforated flame holder is preheated to a start-up temperature, TS. After the perforated flame holder is raised to the start-up temperature, the method proceeds to step 404, wherein the fuel and oxidant are provided to the perforated flame holder and combustion is held by the perforated flame holder.

[0077] According to a more detailed description, step 402 begins with step 406, wherein start-up energy is provided at the perforated flame holder. Simultaneously or following providing start-up energy, a decision step 408 determines whether the temperature T of the perforated flame holder is at or above the start-up temperature, TS. As long as the temperature of the perforated flame holder is below its start-up temperature, the method loops between steps 406 and 408 within the preheat step 402. In decision step 408, if the temperature T of at least a predetermined portion of the perforated flame holder is greater than or equal to the start-up temperature, the method 400 proceeds to overall step 404, wherein fuel and oxidant is supplied to and combustion is held by the perforated flame holder.

[0078] Step 404 may be broken down into several discrete steps, at least some of which may occur simultaneously.

[0079] Proceeding from decision step 408, a fuel and oxidant mixture is provided to the perforated flame holder, as shown in step 410. The fuel and oxidant may be provided by a fuel and oxidant source that includes a separate fuel nozzle and oxidant (e.g., combustion air) source, for example. In this approach, the fuel and oxidant are output in one or more directions selected to cause the fuel and oxidant mixture to be received by the input face of the perforated flame holder. The fuel may entrain the combustion air (or alternatively, the combustion air may dilute the fuel) to provide a fuel and oxidant mixture at the input face of the perforated flame holder at a fuel dilution selected for a stable combustion reaction that can be held within the perforations of the perforated flame holder.

[0080] Proceeding to step 412, the combustion reaction is held by the perforated flame holder.

[0081] In step 414, heat may be output from the perforated flame holder. The heat output from the perforated flame holder may be used to power an industrial process, heat a working fluid, generate electricity, or provide motive power, for example.

[0082] In optional step 416, the presence of combustion may be sensed. Various sensing approaches have been used and are contemplated by the inventors. Generally, combustion held by the perforated flame holder is very stable and no unusual sensing requirement is placed on the system. Combustion sensing may be performed using an infrared sensor, a video sensor, an ultraviolet sensor, a charged species sensor, thermocouple, thermopile, flame rod, and/or other combustion sensing apparatuses. In an additional or alternative variant of step 416, a pilot flame or other ignition source may be provided to cause ignition of the fuel and oxidant mixture in the event combustion is lost at the perforated flame holder.

[0083] Proceeding to decision step 418, if combustion is sensed not to be stable, the method 400 may exit to step 424, wherein an error procedure is executed. For example, the error procedure may include turning off fuel flow, re-executing the preheating step 402, outputting an alarm signal, igniting a stand-by combustion system, or other steps. If, in decision step 418, combustion in the perforated flame holder is determined to be stable, the method 400 proceeds to decision step 420, wherein it is determined if combustion parameters should be changed. If no combustion parameters are to be changed, the method loops (within step 404) back to step 410, and the combustion process continues. If a change in combustion parameters is indicated, the method 400 proceeds to step 422, wherein the combustion parameter change is executed. After changing the combustion parameter(s), the method loops (within step 404) back to step 410, and combustion continues.

[0084] Combustion parameters may be scheduled to be changed, for example, if a change in heat demand is encountered. For example, if less heat is required (e.g., due to decreased electricity demand, decreased motive power requirement, or lower industrial process throughput), the fuel and oxidant flow rate may be decreased in step 422. Conversely, if heat demand is increased, then fuel and oxidant flow may be increased. Additionally, or alternatively, if the combustion system is in a start-up mode, then fuel and oxidant flow may be gradually increased to the perforated flame holder over one or more iterations of the loop within step 404.

[0085] Referring again to FIG. 2, the burner system 200 includes a heater 228 operatively coupled to the perforated flame holder 102. As described in conjunction with FIGS. 3 and 4, the perforated flame holder 102 operates by outputting heat to the incoming fuel and oxidant mixture 206. After combustion is established, this heat is provided by the combustion reaction 302; but before combustion is established, the heat is provided by the heater 228.

[0086] Various heating apparatuses have been used and are contemplated by the inventors. In some embodiments, the heater 228 can include a flame holder configured to support a flame disposed to heat the perforated flame holder 102. The fuel and oxidant source 202 can include a fuel nozzle 218 configured to emit a fuel stream 206 and an oxidant source 220 configured to output oxidant (e.g., combustion air) adjacent to the fuel stream 206. The fuel nozzle 218 and oxidant source 220 can be configured to output the fuel stream 206 to be progressively diluted by the oxidant (e.g., combustion air). The perforated flame holder 102 can be disposed to receive a diluted fuel and oxidant mixture 206 that supports a combustion reaction 302 that is stabilized by the perforated flame holder 102 when the perforated flame holder 102 is at an operating temperature. A start-up flame holder, in contrast, can be configured to support a start-up flame at a location corresponding to a relatively unmixed fuel and oxidant mixture that is stable without stabilization provided by the heated perforated flame holder 102.

[0087] The burner system 200 can further include a controller 230 operatively coupled to the heater 228 and to a data interface 232. For example, the controller 230 can be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold the start-up flame when the perforated flame holder 102 needs to be pre-heated and to not hold the start-up flame when the perforated flame holder 102 is at an operating temperature (e.g., when T ≥ TS).

[0088] Various approaches for actuating a start-up flame are contemplated. In one embodiment, the start-up flame holder includes a mechanically-actuated bluff body configured to be actuated to intercept the fuel and oxidant mixture 206 to cause heat-recycling and/or stabilizing vortices and thereby hold a start-up flame; or to be actuated to not intercept the fuel and oxidant mixture 206 to cause the fuel and oxidant mixture 206 to proceed to the perforated flame holder 102. In another embodiment, a fuel control valve, blower, and/or damper may be used to select a fuel and oxidant mixture flow rate that is sufficiently low for a start-up flame to be jet-stabilized; and upon reaching a perforated flame holder 102 operating temperature, the flow rate may be increased to "blow out" the start-up flame. In another embodiment, the heater 228 may include an electrical power supply operatively coupled to the controller 230 and configured to apply an electrical charge or voltage to the fuel and oxidant mixture 206. An electrically conductive start-up flame holder may be selectively coupled to a voltage ground or other voltage selected to attract the electrical charge in the fuel and oxidant mixture 206. The attraction of the electrical charge was found by the inventors to cause a start-up flame to be held by the electrically conductive start-up flame holder.

[0089] In another embodiment, the heater 228 may include an electrical resistance heater configured to output heat to the perforated flame holder 102 and/or to the fuel and oxidant mixture 206. The electrical resistance heater 228 can be configured to heat up the perforated flame holder 102 to an operating temperature. The electrical resistance heater 228 can further include a power supply and a switch operable, under control of the controller 230, to selectively couple the power supply to the electrical resistance heater 228.

[0090] An electrical resistance heater 228 can be formed in various ways. For example, the electrical resistance heater 228 can be formed from KANTHAL® wire (available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden) threaded through at least a portion of the perforations 210 defined by the perforated flame holder body 208. Alternatively, the heater 228 can include an inductive heater, a high-energy beam heater (e.g., microwave or laser), a frictional heater, electro-resistive ceramic coatings, or other types of heating technologies.

[0091] Other forms of start-up apparatuses are contemplated. For example, the heater 228 can include an electrical discharge igniter or hot surface igniter configured to output a pulsed ignition to the oxidant and fuel. Additionally, or alternatively, a start-up apparatus can include a pilot flame apparatus disposed to ignite the fuel and oxidant mixture 206 that would otherwise enter the perforated flame holder 102. The electrical discharge igniter, hot surface igniter, and/or pilot flame apparatus can be operatively coupled to the controller 230, which can cause the electrical discharge igniter or pilot flame apparatus to maintain combustion of the fuel and oxidant mixture 206 in or upstream from the perforated flame holder 102 before the perforated flame holder 102 is heated sufficiently to maintain combustion.

[0092] The burner system 200 can further include a sensor 234 operatively coupled to the control circuit 230. The sensor 234 can include a heat sensor configured to detect infrared radiation or a temperature of the perforated flame holder 102. The control circuit 230 can be configured to control the heating apparatus 228 responsive to input from the sensor 234. Optionally, a fuel control valve 236 can be operatively coupled to the controller 230 and configured to control a flow of fuel to the fuel and oxidant source 202. Additionally or alternatively, an oxidant blower or damper 238 can be operatively coupled to the controller 230 and configured to control flow of the oxidant (or combustion air).

[0093] The sensor 234 can further include a combustion sensor operatively coupled to the control circuit 230, the combustion sensor being configured to detect a temperature, video image, and/or spectral characteristic of a combustion reaction 302 held by the perforated flame holder 102. The fuel control valve 236 can be configured to control a flow of fuel from a fuel source to the fuel and oxidant source 202. The controller 230 can be configured to control the fuel control valve 236 responsive to input from the combustion sensor 234. The controller 230 can be configured to control the fuel control valve 236 and/or oxidant blower or damper 238 to control a preheat flame type of heater 228 to heat the perforated flame holder 102 to an operating temperature. The controller 230 can similarly control the fuel control valve 236 and/or the oxidant blower or damper 238 to change the fuel and oxidant mixture 206 flow responsive to a heat demand change received as data via the data interface 232.

[0094] FIG. 5A is a simplified perspective view of a combustion system 500, including another alternative perforated flame holder 102, according to an embodiment. The perforated flame holder 102 is a reticulated ceramic perforated flame holder, according to an embodiment. FIG. 5B is a simplified side sectional diagram of a portion of the reticulated ceramic perforated flame holder 102 of FIG. 5A, according to an embodiment. The perforated flame holder 102 of FIGS. 5A, 5B can be implemented in the various combustion systems described herein, according to an embodiment. The perforated flame holder 102 is configured to support a combustion reaction 302 of the fuel and oxidant mixture 206 at least partially within the perforated flame holder 102. According to an embodiment, the perforated flame holder 102 can be configured to support a combustion reaction 302 of the fuel and oxidant mixture 206 upstream, downstream, within, and adjacent to the reticulated ceramic perforated flame holder 102.

[0095] According to an embodiment, the perforated flame holder body 208 can include reticulated fibers 539. The reticulated fibers 539 can define branching perforations 210 that weave around and through the reticulated fibers 539. According to an embodiment, the perforations 210 are formed as passages through the reticulated ceramic fibers 539.

[0096] According to an embodiment, the reticulated fibers 1239 are formed as a reticulated ceramic foam. According to an embodiment, the reticulated fibers 1239 are formed using a reticulated polymer foam as a template. According to an embodiment, the reticulated fibers 539 can include alumina silicate. According to an embodiment, the reticulated fibers 539 can be formed from extruded mullite or cordierite. According to an embodiment, the reticulated fibers 539 can include Zirconia. According to an embodiment, the reticulated fibers 539 can include silicon carbide.

[0097] The term "reticulated fibers" refers to a netlike structure. According to an embodiment, the reticulated fibers 539 are formed from an extruded ceramic material. In reticulated fiber embodiments, the interaction between the fuel and oxidant mixture 206, the combustion reaction 302, and heat transfer to and from the perforated flame holder body 208 can function similarly to the embodiment shown and described above with respect to FIGS. 2-4. One difference in activity is a mixing between perforations 210, because the reticulated fibers 539 form a discontinuous perforated flame holder body 208 that allows flow back and forth between neighboring perforations 210.

[0098] According to an embodiment, the reticulated fiber network is sufficiently open for downstream reticulated fibers 539 to emit radiation for receipt by upstream reticulated fibers 539 for the purpose of heating the upstream reticulated fibers 539 sufficiently to maintain combustion of a fuel and oxidant mixture 206. Compared to a continuous perforated flame holder body 208, heat conduction paths 312 between reticulated fibers 539 are reduced due to separation of the reticulated fibers 539. This may cause relatively more heat to be transferred from the heat-receiving region 306 (heat receiving area) to the heat output region 310 (heat output area) of the reticulated fibers 539 via thermal radiation 304.

[0099] According to an embodiment, individual perforations 210 may extend from an input face 212 to an output face 214 of the perforated flame holder 102. Perforations 210 may have varying lengths L. According to an embodiment, because the perforations 210 branch into and out of each other, individual perforations 210 are not clearly defined by a length L.

[0100] According to an embodiment, the perforated flame holder 102 is configured to support or hold a combustion reaction 302 or a flame at least partially between the input face 212 and the output face 214. According to an embodiment, the input face 212 corresponds to a surface of the perforated flame holder 102 proximal to the fuel nozzle 218 or to a surface that first receives fuel. According to an embodiment, the input face 212 corresponds to an extent of the reticulated fibers 539 proximal to the fuel nozzle 218. According to an embodiment, the output face 214 corresponds to a surface distal to the fuel nozzle 218 or opposite the input face 212. According to an embodiment, the input face 212 corresponds to an extent of the reticulated fibers 539 distal to the fuel nozzle 218 or opposite to the input face 212.

[0101] According to an embodiment, the formation of boundary layers 314, transfer of heat between the perforated flame holder body 208 and the gases flowing through the perforations 210, a characteristic perforation width dimension D, and the length L can be regarded as related to an average or overall path through the perforated flame holder 102. In other words, the dimension D can be determined as a root-mean-square of individual Dn values determined at each point along a flow path. Similarly, the length L can be a length that includes length contributed by tortuosity of the flow path, which may be somewhat longer than a straight line distance TRH from the input face 212 to the output face 214 through the perforated flame holder 102. According to an embodiment, the void fraction (expressed as (total perforated flame holder 102 volume - reticulated fiber 539 volume)/total volume)) is about 70%.

[0102] According to an embodiment, the reticulated ceramic perforated flame holder 102 is a tile about 1" x 4" x 4". According to an embodiment, the reticulated ceramic perforated flame holder 102 includes about 100 pores per square inch of surface area. Other materials and dimensions can also be used for a reticulated ceramic perforated flame holder 102 in accordance with principles of the present disclosure.

[0103] According to an embodiment, the reticulated ceramic perforated flame holder 102 can include shapes and dimensions other than those described herein. For example, the perforated flame holder 102 can include reticulated ceramic tiles that are larger or smaller than the dimensions set forth above. Additionally, the reticulated ceramic perforated flame holder 102 can include shapes other than generally cuboid shapes.

[0104] According to an embodiment, the reticulated ceramic perforated flame holder 102 can include multiple reticulated ceramic tiles. The multiple reticulated ceramic tiles can be joined together such that each ceramic tile is in direct contact with one or more adjacent reticulated ceramic tiles. The multiple reticulated ceramic tiles can collectively form a single perforated flame holder 102. Alternatively, each reticulated ceramic tile can be considered a distinct perforated flame holder 102.

[0105] FIG. 6 is a block diagram of components of a combustion system 600, according to an embodiment. The combustion system 600 includes a controller 116, a set of sensors 114, a set of actuators 118, a display 120, a heater 668, and a control input 670. The set of sensors 114, the set of actuators 118, the control input 670, the display 120, and the heater 668 are communicatively coupled to the controller 116 such that the controller 116 can send, or receive signals, instructions, or data from the components. These components are utilized to monitor, control, and adjust operation of the combustion system 600 with respect to holding a combustion reaction 302 in a perforated flame holder 102 (see FIGS. 1-3, 5A, 5B).

[0106] In one embodiment, the set of sensors 114 includes a bridgewall temperature sensor 640, a preheating flame scanner 642, a CO monitor 644, a NOX monitor 646, an O2 monitor 648, a dynamic pressure sensor 649, a perforated flame holder flame scanner 650, a pressure differential sensor 651, a process monitor 652, a camera 653, a pressure sensor 654, and a perforated flame holder temperature sensor 655. These sensors monitor various parameters of the combustion system 600 and output sensor signals to the controller 116. The sensor signals indicate various parameters of the combustion system 600. The set of sensors 114 can include fewer sensors, more sensors, or different kinds of sensors than those shown in FIG. 6.

[0107] In one embodiment, the set of actuators 118 include a stack damper actuator 656, a main fuel actuator 658, a preheating fuel actuator 660, an oxidant source actuator 662, a process actuator 664, an igniter actuator 666, and a heater actuator 668. The set of actuators 118 receive electrical commands and instructions from the controller 116. The set of actuators 118 activate, control, or adjust components of the combustion system 600 responsive to the commands from the controller 116. Additionally, or alternatively, the set of actuators 118 can be operated manually by an operator of the combustion system 600.

[0108] In one embodiment, the display 120 displays messages, data, or other indications from the controller 116. An operator or technician of the combustion system 600 can receive information via the display 120. The controller 116 can output messages via the display 120 indicating various parameters of the combustion system 600 as measured by the set of sensors 114. The controller 116 can output messages via the display 120 indicating operations that the controller 116 will undertake, such as transitioning from a preheating state to the standard operating state or controlling one or more of the set of actuators 118 responsive to the sensor signals. The display 120 can also display prompts requesting input from an operator of the combustion system 600 requesting that the operator provide approval or permission to execute one or more proposed actions. Upon receiving input from the operator, the controller 116 can undertake actions or refrain from action in accordance with the instructions received from the operator.

[0109] In one embodiment, the control input 670 enables an operator of the combustion system 600 to enter commands to the controller 116. The control input 670 can include one or more of the keypad, a keyboard, a touchscreen, buttons, switches, a mouse, a trackpad, or any other suitable way for an operator of the combustion system 600 to input data or commands to the controller 116. The control input 670 can communicate with the controller 116 via any suitable data transfer interface. In one embodiment, when the controller 116 outputs a message on the display 120 requesting input from an operator to proceed with a proposed adjustment to the combustion system 600, the operator can include a command to the controller 116 via the control input 670 responsive to the message on the display 120. The operator can also utilize the control input 670 to override actions taken by the controller 116 in controlling the combustion system 600.

[0110] In one embodiment, the bridgewall temperature sensor 640 senses the temperature of the furnace bridgewall. The temperature of the furnace bridgewall provides an indication of whether a process of the furnace is ready for operation. As the perforated flame holder 102 sustains a combustion reaction 302, the temperature of the bridgewall will increase. When the bridgewall of the furnace has reached a selected threshold temperature, the combustion system 600 can initiate a process.

[0111] In an embodiment, the controller 116 receives the temperature of the bridgewall from the bridgewall temperature sensor 640 and takes one or more actions based on the temperature of the bridgewall and on one or more algorithms, state machines, or other software instructions implemented by the controller 116. In one example, if the sensor signal from the bridgewall temperature sensor 640 indicates that the temperature of the bridgewall is above the threshold temperature, then the controller 116 can send the signal to the process actuator 664. The process actuator 664 can activate a process, such as initiating the flow of a working fluid to be heated by the furnace. In one embodiment, if the bridgewall temperature sensor 640 indicates that the temperature of the bridgewall is below the threshold temperature, then the controller 116 refrains from activating the process actuator 664. In one embodiment, if the process is already active, and the sensor signal from the bridgewall temperature sensor 640 indicates that the temperature of the bridgewall has fallen below the threshold temperature, then the controller 116 can take measures to increase the heat output by the perforated flame holder 102 by operating the main fuel actuator 658 to adjust flow of the main fuel, the oxidant source actuator 662 to adjust the flow of oxidant, the stack damper actuator 656 to adjust the stack damper, or any other actuators that can adjust a parameter of the combustion system 600 to increase output from the perforated flame holder 102. The controller 116 can also cause the process actuator 664 to adjust or stop the process until the temperature of the bridgewall increases beyond a threshold temperature.

[0112] In one embodiment, the preheating flame scanner 642 monitors parameters of the preheating flame while the combustion system 600 is in the preheating state. The preheating flame scanner 642 can detect whether the preheating flame is present. The preheating flame scanner 642 can detect the position of the preheating flame. The preheating flame scanner 642 outputs a sensor signal to the controller 116 indicating the presence, absence, position, or other parameters of the preheating flame.

[0113] In one embodiment, when the controller 116 receives the sensor signal from the preheating flame scanner 642, the controller 116 takes one or more actions based on the parameters of the preheating flame. If the sensor signal from the preheating flame scanner 642 indicates that the preheating flame is not present, then the controller 116 can send command signals to the oxidant source actuator 662 to adjust the flow of oxidant, to the preheating fuel actuator 660 to adjust the flow of the preheating fuel, and to the igniter actuator 666 to ignite the preheating flame by generating sparks or in any other suitable way.

[0114] In one embodiment, if the sensor signal from the preheating flame scanner 642 indicates that the position of the preheating flame is too far from the perforated flame holder 102 or too close to the perforated flame holder 102, then the controller 116 can output control signals that cause the preheating fuel actuator 660 to adjust a flow rate of the preheating fuel, or to adjust a fuel mixture of the preheating fuel. The controller 116 can also issue commands to the oxidant source actuator 662 causing the oxidant source actuator 662 to increase or decrease the flow of oxidant.

[0115] In one embodiment, the CO monitor 644 monitors the concentration of CO and flue gases generated by the combustion reaction 302 of the main fuel and the oxidant in the standard operating state. The CO monitor 644 outputs sensor signals to the controller 116 indicating concentration of CO in the flue gases generated by the combustion reaction 302 held by the perforated flame holder 102. The controller 116 receives the sensor signals and takes one or more actions based on the CO concentration as indicated by the sensor signals from the CO monitor 644.

[0116] In one embodiment, if the concentration of CO in the flue gas is below an acceptable value, then the controller 116 may not adjust any parameters of the combustion system 600 in order to maintain the current state of the combustion reaction 302. If the concentration of CO in the flue gas is higher than an acceptable value, then the controller 116 can send signals to the main fuel actuator 658, the oxidant source actuator 662, the heater actuator 668, or the stack damper actuator 656 in order to adjust the combustion reaction 302 of the main fuel and the oxidant. The controller 116 can cause the main fuel actuator 658 to adjust the flow of the main fuel or the mixture of fuels that make up the main fuel in order to cause the combustion reaction 302 of the main fuel and the oxidant to generate less CO. The controller 116 can also cause the oxidant source actuator 662 to adjust the flow of oxidant into the furnace in order to reduce the concentration of CO in the flue gas.

[0117] In one embodiment, the NOX monitor 646 senses the concentration of NOX in the flue gas generated by the combustion reaction 302 of the main fuel and the oxidant held by the perforated flame holder 102 in the standard operating state. The NOX monitor 646 outputs a sensor signal to the controller 116 indicating the concentration of NOX in the flue gas. The controller 116 can take one or more actions based on the concentration of the NOX in the flue gas as indicated by the sensor signal.

[0118] In one embodiment, if the sensor signal from the NOX monitor 646 indicates that the NOX concentration is higher than a threshold value, for example higher than 10 ppm, then the controller 116 can take actions to reduce the concentration of NOX in the flue gas. In one embodiment, the controller 116 can control the oxidant source actuator 662 to increase the flow of oxidant from the oxidant source. Additionally, or alternatively, the controller 116 controls the main fuel actuator 658 to decrease the flow of fuel or to otherwise adjust parameters of the flow of the main fuel in order to decrease the concentration of NOX in the flue gas.

[0119] In one embodiment, the O2 monitor 648 monitors the presence of O2 in the flue gas. The O2 monitor 648 outputs a sensor signal to the controller 116 indicating the concentration of O2 in the flue gas. The controller 116 receives the sensor signal from the O2 monitor 648 and undertakes one or more actions based on the concentration of O2 in the flue gas.

[0120] In one embodiment, it is desirable that the concentration of O2 in the flue gas fall within a selected range, e.g., greater than or equal to 2% and less than or equal to 5%. If the sensor signal from the O2 monitor 648 indicates that the concentration of O2 is below the selected range, then the controller 116 can control the oxidant source actuator 662 to increase the flow of oxidant into the furnace. Additionally, or alternatively, the controller 116 can increase the concentration of O2 in the flue gas by decreasing the flow of fuel into the furnace. If the sensor signal from the O2 monitor 648 indicates that the concentration of O2 is greater than the selected range, then the controller 116 can cause the oxidant source actuator 662 to decrease the flow of fuel into the furnace. Additionally, or alternatively, the controller 116 can cause the main fuel actuator 658 to increase the flow of the main fuel into the furnace in order to decrease the concentration of O2 in the flue gas. In some cases, a higher than desired concentration of O2 can be the result of incomplete fuel burn. Thus, the controller 116 can control the main fuel actuator 658 to reduce the velocity of the main fuel in order to more completely combust the main fuel.

[0121] In one embodiment, the dynamic pressure sensor 649 detects changes in pressure with time at one or more locations in the combustion environment. The dynamic pressure sensor 649 generates sensor signals indicative of the change in pressure in the furnace over time or of the draft of the oxidant. The sensor signals from the dynamic pressure sensor 649 can indicate a slope or derivative of the pressure with respect to time and/or may be converted to frequency domain to detect audible or inaudible noise caused by pressure waves. The inventors note that the dynamic pressure sensor 649 produces a signal indicative of stability of a combustion reaction in the perforated flame holder 102. When the combustion reaction is stable, there is relatively constant pressure at the dynamic pressure sensor 649. When the combustion reaction is unstable, the dynamic pressure sensor 649 produces a signal corresponding to rapid fluctuations in pressure, a condition that has been noted by the inventors to correspond to relatively high audible noise produced by the flowing gas in the furnace. The controller 116 can undertake one or more actions to adjust the pressure or other combustion parameters responsive to the sensor signal from the dynamic pressure sensor 649.

[0122] In one embodiment, the controller 116 can increase or decrease the pressure by controlling the oxidant source actuator 662 to adjust the flow of oxidant responsive to the sensor signals provided by the dynamic pressure sensor 649. The controller 116 can adjust the pressure by causing the stack damper actuator 656 to adjust the stack damper. The controller 116 can adjust the pressure by causing the main fuel actuator 658 to adjust the flow of the main fuel. The controller 116 can also undertake other actions to adjust the pressure responsive to sensor signals provided by the dynamic pressure sensor 649.

[0123] In one embodiment, the pressure differential sensor 651 detects pressure differentials or differences across two locations or more in the furnace, such as across the perforated flame holder 102. The controller 116 can undertake one or more actions to adjust the pressure or other combustion parameters responsive to the sensor signal from the pressure differential sensor 651.

[0124] In one embodiment, the controller 116 can increase or decrease the pressure by controlling the oxidant source actuator 662 to adjust the flow of oxidant. The controller 116 can adjust the pressure by causing the stack damper actuator 656 to adjust the stack damper. The controller 116 can adjust the pressure by causing the main fuel actuator 658 to adjust the flow of the main fuel. The controller 116 can also undertake other actions to adjust the pressure responsive to sensor signals provided by the dynamic pressure sensor 649.

[0125] In one embodiment, the perforated flame holder flame scanner 650 monitors parameters of the combustion reaction 302 of the main fuel and the oxidant held by the perforated flame holder 102. The perforated flame holder flame scanner 650 outputs a sensor signal to the controller 116 indicating the parameters of the combustion reaction 302 held by the perforated flame holder 102 in the standard operating state.

[0126] In one embodiment, the perforated flame holder flame scanner 650 can detect whether the combustion reaction 302 of the main fuel and oxidant is present at the perforated flame holder 102. If the sensor signals output by the perforated flame holder flame scanner 650 indicate that the combustion reaction 302 of the main fuel and oxidant is not present, then the controller 116 can undertake one or more actions. For example, the controller 116 can cause the heater actuator 668 to provide additional heat to the perforated flame holder 102 so that the perforated flame holder 102 is at a sufficient temperature to initiate a combustion reaction 302 of the main fuel and the oxidant. The controller 116 can cause the combustion system 600 to revert back to the preheating state by controlling the main fuel actuator 658, the preheating fuel actuator 660, the oxidant source actuator 662, and the igniter actuator 666 to cease the flow of the main fuel, to adjust the flow of the oxidant, to initiate a flow of the preheating fuel, and to ignite the preheating flame until the perforated flame holder 102 has reached the threshold temperature.

[0127] In one embodiment, if the sensor signals output by the perforated flame holder flame scanner 650 indicate that the combustion reaction 302 of the main fuel and the oxidant is concentrated too far upstream from the perforated flame holder 102 or too far downstream from the perforated flame holder 102, then the controller 116 can control the main fuel actuator 658 to adjust the flow rate, the velocity, the mixture, or other parameters of the main fuel. The controller 116 can also cause the oxidant source actuator 662 to adjust the flow of the oxidant in order to cause the combustion reaction 302 of the main fuel and the oxidant to be held by the perforated flame holder 102.

[0128] In one embodiment, the perforated flame holder flame scanner 650 can indicate how much heat is generated by the combustion of the main fuel and the oxidant. If the sensor signals from the perforated flame holder flame scanner 650 indicate that the combustion reaction 302 of the main fuel and the oxidant is generating too much heat or too little heat, then the controller 116 can take one or more actions. For example, the controller 116 can adjust the flow or mixture of the main fuel by controlling the main fuel actuator 658. The controller 116 can also cause the oxidant source actuator 662 to adjust the flow of oxidant to increase or decrease the temperature of the combustion reaction 302 of the main fuel and the oxidant.

[0129] In one embodiment, the process monitor 652 measures parameters of the process, such as the transfer of heat from the combustion reaction 302 of the main fuel and the oxidant to a working fluid. The process monitor 652 outputs sensor signals to the controller 116 indicating the parameters of the process. The controller 116 can take one or more actions to adjust parameters of the process responsive to the sensor signals.

[0130] In one embodiment, the controller 116 can control the process actuator 664 in order to adjust one or more aspects of the process responsive to the sensor signal from the process monitor 652. Additionally, or alternatively, the controller 116 can control one or more other actuators to adjust parameters of the combustion reaction 302 of the main fuel and the oxidant in order to adjust parameters of the process.

[0131] In one embodiment, a camera 653 monitors one or more conditions within the furnace and outputs sensor signals indicative of the monitored condition. The camera 653 can include a charge coupled device (CCD) camera, a CMOS camera, or other types of cameras. The camera 653 can be part of one or more other sensors in the sensor array 114. The camera 653 can monitor visual parameters of the perforated flame holder 102, the combustion reaction 302 within the perforated flame holder 102, the preheating flame, flashback of the combustion reaction 302, the physical condition of components, actuators, sensors, or other conditions within the furnace. The controller 116 can take one or more actions in response to the sensor signals from the camera 653. The camera 653 can detect UV wavelengths, IR wavelengths, and/or visible light wavelengths. The camera 653 can include a video camera or other kinds of cameras.

[0132] In one embodiment, the camera 653 can convert the field of view with a phase mask and detect a signal with a planar CCD or a CMOS array, not as an image of the field of view, but as matrix data that can be decoded to focus at a range of focal planes.

[0133] In one embodiment, the sensor array 114 can include a flashback sensor configured to detect flashback of the combustion reaction 302 from the perforated flame holder 102 towards the main fuel distributors. The flashback sensor can be part of one or more other sensors in the sensor array 114. The flashback sensor can include one or more of a camera, an infrared sensor, a flame rod, a UV sensor, a CCD camera, thermocouples, photo cells, electrodes, or other kinds of devices capable of sensing flashback.

[0134] In one embodiment, the controller 116 can control the turndown ratio in the furnace response to sensor signals from one or more of the sensors in the sensor array 114 or from sensors not shown or described herein. The controller 116 can control or adjust the turndown ratio by operating one or more actuators 118 to adjust parameters of the combustion environment such as fuel flow parameters, oxidant parameters, operating state parameters, or other parameters.

[0135] In one embodiment, the combustion system 600 can include multiple perforated flame holders 102. The combustion system 600 can include multiple main fuel distributors 110, multiple oxidant sources 104, multiple preheating fuel distributors, and multiple other components to operate the multiple perforated flame holders 102. The combustion system 600 can include multiple of the various sensors 114 to sense the parameters related to the multiple perforated flame holders 102. The controller 116 can adjust the parameters related to the multiple perforated flame holders 102 in response to the sensor signals from the various sensors 114. The sensors can control the operations related to the multiple perforated flame holders 102 based on huffing, instability, and turndown as indicated by the sensors of the sensor array 114. The controller 116 can also cease operation of one or more of the perforated flame holders 102 or can select which and how many of the multiple perforated flame holders 102 should be in operation. The controller 116 can control the set of actuators 118 to control, operate, select, or stop operations related to the multiple perforated flame holders 102.

[0136] The combustion system 600 can also be a multi-fuel system that utilizes multiple fuels or kinds of fuel in holding a combustion reaction 302 in one or more perforated flame holders 102. The controller 116 can control the flow of the multiple fuels, select which fuels to use, or select mixtures or blends of fuel based on the sensor signals from the various sensors of the sensor array 114.

[0137] In one embodiment, the pressure sensor 654 monitors pressure in the furnace or the draft pressure of the oxidant. The process sensor 654 sensor signals and outputs into the controller 116 a signal indicative of the pressure in the furnace or of the draft of the oxidant. The controller 116 can undertake one or more actions to adjust the pressure responsive to the sensor signal from the pressure sensor 654.

[0138] In one embodiment, the controller 116 can increase or decrease the pressure by controlling the oxidant source actuator 662 to adjust the flow of oxidant. The controller 116 can adjust the pressure by causing the stack damper actuator 656 to adjust the stack damper. The controller 116 can adjust the pressure by causing the main fuel actuator 658 to adjust the flow of the main fuel. The controller 116 can also undertake other actions to adjust the pressure responsive to sensor signals provided by the pressure sensor 654.

[0139] In one embodiment, the perforated flame holder temperature sensor 655 monitors the temperature of the perforated flame holder 102. The perforated flame holder temperature sensor 655 generates sensor signals indicating the temperature of the perforated flame holder 102 and transmits them to the controller 116. The controller 116 can undertake one or more actions to adjust the temperature of the perforated flame holder 102 based on the sensor signals from the perforated flame holder temperature sensor 655.

[0140] In one embodiment, the perforated flame holder temperature sensor 655 monitors the temperature of the perforated flame holder 102 during the preheating state of the combustion system 600. Thus, as the preheating flame of the preheating fuel and the oxidant heats the perforated flame holder 102, the perforated flame holder temperature sensor 655 monitors the temperature of the perforated flame holder 102. If the sensor signal indicates that the temperature of the perforated flame holder 102 is below the threshold temperature or an operating temperature, then the controller 116 causes the combustion system 600 to remain in the preheating state in which the preheating flame remains present and continues to heat the perforated flame holder 102. If the sensor signal from the perforated flame holder temperature sensor 655 indicates that the temperature of the perforated flame holder 102 has reached the threshold temperature or the operating temperature, then the controller 116 can control the preheating fuel actuator 660 and the main fuel actuator 658 to transition from the preheating state to the standard operating state by ceasing the flow of the preheating fuel and initiating the flow of the main fuel.

[0141] In one embodiment, the perforated flame holder temperature sensor 655 continues to monitor the temperature of the perforated flame holder 102 during the standard operating state. If the sensor signal from the perforated flame holder temperature sensor 655 indicates that the temperature of the perforated flame holder 102 has dropped below the threshold temperature or the operating temperature, then the controller 116 can take one or more actions. For example, the controller 116 can cause the heater actuator 668 to begin heating the perforated flame holder 102. Additionally, or alternatively, the controller 116 can cause the combustion system 600 to revert to the preheating state by ceasing the flow of the main fuel and initiating the flow of the preheating fuel.

[0142] In one embodiment, the controller 116 automatically controls the various actuators 118 responsive to the sensor signals from the set of sensors 114 in accordance with one or more sets of software instructions, algorithms, state machines, or other protocols that indicate what actions the controller 116 will take based on the values of the sensor signals generated by the set of sensors 114. In one embodiment, the controller 116 does not automatically control one or more of the actuators 118 responsive to the sensor signals. Instead, the controller 116 outputs prompts or instructions via the display 120 to an operator indicating that the operator should manually adjust components of the combustion system 600 based on the sensor signals. The controller 116 can also prompt an operator to approve actions to be undertaken by the controller 116 so that the controller 116 can control the various actuators 118. The controller 116 can use a mixture of automatic controlling actuators 118, prompting an operator to control the actuators 118, and prompting an operator to approve proposed actions of the controller 116.

[0143] FIG. 7 is a flow diagram of a process 700 for operating a combustion system in a preheating state, according to an embodiment. The process 700 can be controlled by a controller 116 executing process steps in accordance with one or more algorithms, sets of software instructions, or state machines. The controller 116 can implement a process 700 by utilizing one or more processors to execute instructions stored on a non-transitory computer readable medium.

[0144] At step 702, the process 700 begins by pre-purging a furnace of the combustion system. The pre-purging process includes purging gases, particulates, or debris from the furnace. The pre-purging process can include controlling an oxidant source to flow an oxidant through the furnace in order to clear unwanted gases, particulates, and debris from the furnace. Additionally, or alternatively, the pre-purging process can include passing an inert gas into the furnace in order to remove unwanted gases, particulates, and debris from the furnace. Once the furnace has been purged, the process 700 can proceed to step 704.

[0145] In one embodiment, at step 704, the process 700 opens the preheating fuel valve in order to initiate a flow of preheating fuel into the furnace. If the process 700 has not yet begun flowing oxidant into the furnace, then the process 700 can control an oxidant source to begin flowing oxidant into the furnace. From step 704, the process 700 proceeds to step 706.

[0146] At step 706, the process ignites the preheating flame of the preheating fuel and the oxidant. In one embodiment, the process may ignite the preheating flame by generating a spark. In another embodiment, the process may ignite the preheating flame by generating a gliding arc. In another embodiment, the process may ignite the preheating flame by controlling a pilot burner, such as by deflecting or not deflecting the pilot flame, to ignite the preheating fuel. In another embodiment, the process may ignite the preheating flame by dissipating current through a hot surface ignitor. In particular, the controller can control an igniter or pilot burner in order to ignite the preheating flame. From step 706, the process 700 proceeds to decision step 708.

[0147] In one embodiment, at decision step 708, the process determines whether or not the preheating flame is present. If the preheating flame is not present, then the process 700 can revert to step 706 and can attempt again to initiate the preheating flame. If the preheating flame is present at decision step 708, then the process 700 can proceed from decision step 708 to step 710.

[0148] In one embodiment, at step 710 the process 700 preheats the perforated flame holder positioned in the furnace. In particular, the perforated flame holder is positioned to receive heat from the preheating flame. The preheating flame heats the perforated flame holder, causing the temperature of the perforated flame holder to increase. From step 710, the process 700 proceeds to step 712.

[0149] In one embodiment, at step 712 the process 700 measures the temperature of the perforated flame holder. From step 712, the process proceeds to decision step 714.

[0150] In one embodiment, at decision step 714, if the temperature of the perforated flame holder TPFH is less than a threshold or operating temperature TTH, then the process 700 returns to step 710 and continues to preheat the perforated flame holder. At decision step 714, if the temperature of the perforated flame holder is greater than the threshold or operating temperature, then the process 700 proceeds to step 716. Typically, the threshold temperature TTH is at or above the autoignition temperature of the preheating fuel at the conditions of the system (temperature, humidity, atmospheric pressure). The inventors have noted a very slight transient reduction in perforated flame holder temperature TPFH when cold fuel is first introduced to the perforated flame holder. The inventors have found it advantageous, therefore, to set the threshold temperature TTH slightly above the preheating fuel autoignition temperature.

[0151] In one embodiment, at step 716, the process 700 transitions from the preheating state to the standard operating state. In the standard operating state, the preheating flame is extinguished and a combustion reaction of the main fuel and oxidant is held by the perforated flame holder.

[0152] FIG. 8 is a flow diagram of a process 800 for operating a combustion system in a standard operating state, according to an embodiment. The process 800 can be controlled by a controller 116 executing process steps in accordance with one or more algorithms, sets of software instructions, or state machines. The controller 116 can implement the process 800 by utilizing one or more processors to execute instructions stored on a non-transitory computer readable medium.

[0153] In one embodiment, at step 802, the process 800 transitions from a preheating state to the standard operating state by opening the main fuel valve. With the main fuel valve open, the main fuel is output into the furnace. If the oxidant source is not already supplying oxidant to the furnace, then at step 802 the process 800 can also cause the oxidant source to supply oxidant into the furnace. The main fuel and the oxidant travel towards the perforated flame holder and mix together as they travel toward the perforated flame holder. The perforated flame holder receives the mixture of the main fuel and the oxidant into the perforations or channels of the perforated flame holder. Because the perforated flame holder has been heated to the operating temperature or threshold temperature, the perforated flame holder ignites a combustion reaction of the main fuel and the oxidant. The perforated flame holder holds a portion of the combustion reaction within the perforated flame holder. Portions of the perforated flame holder can also occur downstream and upstream from the perforated flame holder. From step 802, the process 800 proceeds to step 804.

[0154] In one embodiment, at step 804, the process 800 closes the preheating fuel valve. Closing the preheating fuel valve ceases the flow of the preheating fuel into the furnace, thereby extinguishing the preheating flame. Alternatively, the preheating fuel valve can be closed prior to opening the main fuel valve. From step 804, the process 800 proceeds to step 806.

[0155] In one embodiment, at step 806, the process 800 checks measurables or parameters of the combustion system. These measurables can include whether the combustion reaction of the main fuel and oxidant is present, the location of the combustion reaction of the main fuel and oxidant, the concentration of various gases in the flue gas, pressure in the furnace, the temperature of the bridgewall of the furnace, parameters of the process receiving heat from the combustion reaction, or other parameters of the combustion system. From step 806, the process 800 proceeds to decision step 808. At decision step 808, the process 800 determines whether the measured conditions of the combustion system are acceptable. If the measured conditions of the combustion system are not acceptable, the process 800 proceeds to step 810. If the measured conditions of the combustion system are acceptable, the process 800 proceeds to step 812.

[0156] In one embodiment, at step 810, the process 800 takes corrective action to adjust the parameters of the combustion system. The corrective actions can include adjusting the flow of the main fuel, adjusting the flow of the oxidant, adjusting the stack damper, activating a heater, adjusting a mixture of the main fuel, shutting down the combustion system, reversing to the preheating state, or other kinds of corrective actions. From step 810, the process 800 proceeds to step 806.

[0157] In one embodiment, at step 812 the process 800 maintains the present conditions of the perforated flame holder and of the combustion system in general. From step 812, the process 800 can proceed back to step 806 for the measurables to be checked again. Alternatively, if the combustion system has accomplished the desired work, the process 800 can proceed to step 814.

[0158] In one embodiment, at step 814 the process 800 shuts down the combustion system.

[0159] FIG. 9 is a flow diagram of a process 900 for operating a combustion system in a standard operating state, according to an embodiment. The process 900 can be controlled by a controller 116 executing process steps in accordance with one or more algorithms, sets of software instructions, or state machines. The controller 116 can implement a process 900 by utilizing one or more processors to execute instructions stored on a non-transitory computer readable medium.

[0160] In one embodiment, at step 902 the process 900 checks the measurables of the combustion system. These measurables can include whether the combustion reaction of the main fuel and oxidant is present, the location of the combustion reaction of the main fuel and oxidant, the concentration of various gases in the flue gas, pressure in the furnace, the temperature of the bridgewall of the furnace, parameters of the process 900 receiving heat from the combustion reaction, or other parameters of the combustion system. From step 902, the process 900 proceeds to decision step 904. At decision step 904, the process 900 determines whether the measured conditions of the combustion system are acceptable. If the measured conditions of the combustion system are not acceptable, the process 900 proceeds to one or more of steps 906, 908, 910, or 912. If the measured conditions of the combustion system are acceptable, the process 900 proceeds to step 914.

[0161] In one embodiment, at step 906 the process 900 adjusts the stack damper responsive to the measured parameters of the combustion system. In one embodiment, at step 908 the process 900 adjusts the oxidant flow responsive to the measured parameters of the combustion system. In one embodiment, at step 910 the process 900 adjusts the main fuel flow responsive to the measured parameters of the combustion system. At step 912, the process 900 re-transitions to the preheating state, responsive to the measured parameters of the combustion system.

[0162] In one embodiment, at step 914 the process 900 maintains the present conditions of the perforated flame holder and of the combustion system in general. From step 912, the process 900 can proceed back to step 902 for the measurables to be checked again. Alternatively, if the combustion system has accomplished the desired work, the process 900 can proceed to step 916.

[0163] In one embodiment, at step 916 the process 900 shuts down the combustion system.

[0164] FIG. 10A is a diagram of the combustion system 1000, according to an embodiment. The combustion system 1000 includes a furnace 1071 defining a furnace volume 1073. The combustion system 1000 includes a perforated flame holder 102 positioned within the furnace volume 1073. The combustion system 1000 includes main fuel distributors 110, a preheating fuel distributor 106, an igniter 1077, a preheating flame sensor 124, and the perforated flame holder sensor 122 positioned within the furnace volume 1073. The combustion system 1000 includes an oxidant source 104, the controller 116, actuators 118, a display 120, a control input 670, manual controls 123, the main fuel source 112, and the preheating fuel source 108. The combustion system 1000 includes one or more main fuel valves 1074 controlling a flow of main fuel from the main fuel source 112 to the main fuel distributors 110. The combustion system 1000 includes one or more preheating fuel valves 1076 controlling a flow of the preheating fuel from the preheating fuel source 108 to the preheating fuel distributor 106. The combustion system 1000 includes a stack damper 1084 positioned in a flue of the furnace 1071. The combustion system 1000 further includes a bridgewall temperature sensor 640 and a gas composition sensor 1072.

[0165] In one embodiment, the controller 116 receives sensor signals from the preheating flame sensor 124, the perforated flame holder sensor 122, the bridgewall temperature sensor 640, the gas composition sensor 1072, and the pressure sensor 654. The controller 116 is coupled to actuators 118. The various actuators 118 are capable of physically adjusting the main fuel valves 1074, the preheating fuel valves 1076, the oxidant source 104, the main fuel distributors 110, the preheating fuel distributor 106, and the stack damper 1084. In one embodiment, the controller 116 is configured to control the actuators 118 to adjust various parameters of the combustion system 1000.

[0166] In one embodiment, the controller 116 is configured to output messages, sensor readings, prompts, warnings, alerts, or other types of data on the display 120. An operator of the combustion system 1000 can view the data output on the display 120 and can operate the combustion system 1000 responsive to the data output on the display 120.

[0167] In one embodiment, the operator of the combustion system 1000 can utilize manual controls 123 to operate the components of the combustion system 1000. The manual controls 123 can control the actuators 118 to adjust the parameters of the combustion system 1000. Alternatively, or additionally, the manual controls 123 can enable the operator to physically adjust components of the combustion system 1000 separate from the actuators 118.

[0168] In one embodiment, the control input 670 enables an operator of the combustion system 1000 to input commands or data to the controller 116. In one embodiment, the controller 116 can output requests for the user to approve one or more actions proposed by the controller 116 responsive to sensor signals provided by the various sensors. The operator of the combustion system 1000 can input selections or commands approving or disapproving the proposed actions of the controller 116 via the other control inputs 670.

[0169] FIG. 10B is a diagram of the combustion system 1000 of FIG. 10A in the preheating state, according to an embodiment. In the preheating state, the combustion system 1000 generates a preheating flame 1075 to preheat the perforated flame holder 102 to an operating temperature. When the perforated flame holder 102 has been heated to the operating temperature, the combustion system 1000 can transition to the standard operating state.

[0170] In one embodiment, in the preheating state the controller 116 controls one or more of the actuators 118 to open the preheating fuel valves 1076. With the preheating fuel valves 1076 open, the preheating fuel source 108 supplies the preheating fuel to the preheating fuel distributor 106. The preheating fuel distributor 106 outputs the preheating fuel into the furnace volume 1073. In one embodiment, the preheating fuel distributor 106 includes one or more preheating fuel nozzles each coupled onto the end of a preheating fuel riser. The preheating fuel is output from orifices in the fuel nozzles.

[0171] In one embodiment, in the preheating state the controller 116 controls one or more of the actuators 118 to cause the oxidant source 104 to supply oxidant into the furnace volume 1073. The oxidant source 104 supplies the oxidant into the furnace volume 1073. The oxidant mixes with the preheating fuel in the furnace volume 1073.

[0172] In one embodiment, the oxidant source 104 includes a barrel register. The barrel register includes apertures that can be opened to a selected degree in order to draft an oxidant into the furnace volume 1073. The actuators 118 can control the degree to which the apertures are open, and thus the degree to which the oxidant is drafted into the furnace volume 1073.

[0173] In one embodiment, the controller 116 controls one or more of the actuators 118 to cause the igniter 1077 to ignite the preheating flame 1075 from the preheating fuel and the oxidant. The controller 116 can cause the igniter 1077 to generate sparks in the presence of the mixed preheating fuel and oxidant. The sparks cause ignition of the preheating fuel and the oxidant, thereby initiating the preheating flame 1075.

[0174] In one embodiment, the preheating flame sensor 124 monitors the parameters of the preheating flame 1075 and provides sensor signals to the controller 116 indicating the sensed parameters of the preheating flame 1075. The preheating flame sensor 124 can sense whether the preheating flame 1075 is present. The preheating flame sensor 124 can also sense the position of the preheating flame 1075. The preheating flame sensor 124 can also sense the temperature of the preheating flame 1075. The preheating flame sensor 124 outputs sensor signals to the controller 116 indicative of the parameters of the preheating flame 1075.

[0175] In one embodiment, the controller 116 can adjust the parameters of the preheating flame 1075 responsive to the sensor signals provided by the preheating flame sensor 124. For example, if the preheating flame sensor 124 signals indicate that the preheating flame 1075 is not present, then the controller 116 can control one or more of the actuators 118 to generate additional sparks from the igniter 1077, to adjust the distribution of the preheating fuel into the furnace volume 1073, or to adjust the flow of the oxidant into the furnace volume 1073. The controller 116 can also control the flow of the preheating fuel and the oxidant in order to adjust the position of the preheating flame 1075 responsive to the sensor signals from the preheating flame sensor 124.

[0176] In one embodiment, the perforated flame holder sensor 122 measures the temperature of the perforated flame holder 102 during the preheating state and provides sensor signals to the controller 116 indicating the temperature of the perforated flame holder 102. If the sensor signals from the perforated flame holder sensor 122 indicates that the temperature of the perforated flame holder 102 is below an operating or threshold temperature, then the controller 116 allows the preheating flame 1075 to continue to heat the perforated flame holder 102. If the sensor signals from the perforated flame holder sensor 122 indicate that the temperature of the perforated flame holder 102 is equal to or greater than the operating or threshold temperature, then the controller 116 can cause the combustion system 1000 transition to the standard operating state.

[0177] In one embodiment, an operator of the combustion system 1000 can activate, operate, or adjust the various components of the combustion system 1000 during the preheating state by operating the manual controls 123. The operator can adjust the parameters of the combustion system 1000 responsive to messages provided by the controller 116 via the display 120.

[0178] FIG. 10C is a diagram of the combustion system 1000 in the standard operating state, according to an embodiment. In the standard operating state, the combustion system 1000 sustains a combustion reaction 1086 of the main fuel and oxidant at the perforated flame holder 102.

[0179] In one embodiment, the combustion system 1000 transitions to the standard operating state by first extinguishing the preheating flame 1075. The controller 116 extinguishes the preheating flame 1075 by causing one or more of the actuators 118 to close the preheating fuel valves 1076, thereby ceasing the flow of the preheating fuel to the preheating fuel distributors 106. When the preheating fuel distributor 106 ceases to output the preheating fuel, the preheating flame 1075 is extinguished.

[0180] In an embodiment, the controller 116 causes the combustion system 1000 to enter the standard operating state by causing one or more of the actuators 118 to open the main fuel valves 1074, thereby enabling the main fuel to flow from the main fuel source 112 to the main fuel distributors 110. The main fuel distributors 110 output the main fuel toward the perforated flame holder 102. The controller 116 can also cause the oxidant source 104 to output the oxidant into the furnace volume 1073, if the oxidant source 104 is not already outputting the oxidant into the furnace volume 1073. The main fuel entrains and mixes with the oxidant as it travels toward the perforated flame holder 102. Because the perforated flame holder 102 is at the operating temperature, the perforated flame holder 102 ignites and sustains a combustion reaction 1086 of the mixture 206 of the main fuel and the oxidant. In one embodiment, the perforated flame holder 102 holds a portion of the combustion reaction 1086 within the perforated flame holder 102. The perforated flame holder 102 can also sustain a portion of the combustion reaction 1086 upstream and downstream from the perforated flame holder 102.

[0181] In one embodiment, in the standard operating state, the perforated flame holder sensor 122, the pressure sensor 654, the bridgewall temperature sensor 640, and the gas composition sensor 1072 output sensor signals to the controller 116. The perforated flame holder sensor 122 monitors parameters of the combustion reaction 1086, including the position, distribution, and temperature of the combustion reaction 1086. The bridgewall temperature sensor 640 senses the temperature of the bridgewall of the furnace 1071 and the pressure sensor 654 senses the pressure within the furnace volume 1073. The gas composition sensor 1072 senses the concentration of various gases, such as NOX, CO, and O2 in the flue gases 1082 and exit through the flue of the furnace 1071.

[0182] In one embodiment, the controller 116 can cause the actuators 118 to adjust the flow of the main fuel, the flow of the oxidant, the orientation of the stack damper 1084, and other components of the combustion system 1000 in order to adjust the parameters of the combustion system 1000. The controller 116 can control the flow of oxidant and the main fuel, as well as a position of the stack damper 1084 to adjust the concentration of gases in the flue gas 1082, to adjust the location and distribution of the combustion reaction 1086, to adjust the pressure within the furnace volume 1073, or to adjust other parameters of the combustion system 1000.

[0183] FIG. 11 is a diagram of a combustion system 1100, according to an embodiment. The combustion system 1100 is substantially similar to the combustion system 100 of FIG. 1, except that the sensor array 114 of the combustion system 1100 includes a flashback sensor 1123.

[0184] In one embodiment, the flashback sensor 1123 is configured to sense flashback of the combustion reaction held by the perforated flame holder 102 toward the main fuel distributor 110 during the standard operating state. Flashback is a potentially dangerous condition in which the combustion reaction travels upstream, igniting the fuel stream closer than desired to the main fuel distributor 110. The flashback sensor 1123 senses the flashback and transmits sensor signals to the controller 116 indicating the presence of flashback. The controller 116 can then take one or more actions to stop the flashback condition.

[0185] In one embodiment, the controller 116 stops the flashback condition by increasing a velocity of the flow of the main fuel from the main fuel distributor 110. The increased velocity of the flow of the main fuel inhibits the combustion reaction from traveling upstream because the fuel travels faster than the combustion reaction can travel upstream. The controller 116 can operate one or more of the actuators 118 to adjust the flow of the main fuel from the main fuel distributor 110 responsive to the sensor signals from the flashback sensor 1123. Alternatively, the controller 116 can output an indication on the display 120 prompting an operator to manually adjust the flow of the main fuel to inhibit flashback.

[0186] In one embodiment, the controller 116 stops the flashback condition by stopping the flow of the main fuel, thereby bring the combustion system 1100 out of the standard operating state. The controller 116 can operate one or more of the actuators 118 to stop the flow of the main fuel from the main fuel distributor 110 responsive to the sensor signals from the flashback sensor 1123. Alternatively, the controller 116 can output an indication on the display 120 prompting an operator to manually stop the flow of the main fuel to inhibit flashback. The controller 116 can shut down the combustion system 1100 entirely when flashback occurs.

[0187] In one embodiment, the controller 116 can take other actions than those described above in order to deal with a flashback condition.

[0188] In one embodiment, the flashback sensor 1123 senses flashback during the preheating state of the combustion system 1100. In particular, in the preheating state the flashback sensor 1123 detects flashback of the preheating flame toward the preheating fuel distributor 106. The controller 116 can respond to the flashback condition in the preheating state by increasing the flow of the preheating fuel, by stopping the flow of the preheating fuel, or in any other suitable manner.

[0189] In one embodiment, the flashback sensor 1123 is positioned to sense flashback between the input face 212 of the perforated flame holder 102 and the main fuel distributor 110. Thus, in a vertically fired combustion system 1100, the flashback sensor 1123 can have a vertical position between the perforated flame holder 102 and the main fuel distributor 110. In a laterally fired combustion system 1100, the flashback sensor 1123 can have a lateral position between the perforated flame holder 102 and the main fuel distributor 110.

[0190] In one embodiment, the flashback sensor 1123 can include one or more of a camera, an infrared sensor, a flame rod, a UV sensor, a CCD camera, thermocouples, photo cells, electrodes, an electrocapacitive tomography device, or other kinds of devices capable of sensing flashback.

[0191] In one embodiment, the flashback sensor 1123 includes an electrocapacitive tomography device, such as the electrocapacitive tomography device 1205 of FIG. 12A and FIG. 12B. The electrocapacitive tomography device can include a first set of electrodes, including multiple pairs of electrodes, positioned laterally around the perforated flame holder 102 in order to sense a parameter of the perforated flame holder 102. The electrocapacitive tomography device can also include a second set of electrodes positioned upstream from the perforated flame holder 102. The first set of electrodes can sense a capacitance or other parameter in a vicinity of the perforated flame holder 102. The second set of electrodes can sense a capacitance or other parameter upstream from the perforated flame holder 102. The controller can compare the capacitance or other parameter sensed by the first set of electrodes to the capacitance or other parameter sensed by the second set of electrodes in order to detect flashback.

[0192] In one embodiment, the perforated flame holder sensor 122 includes an electrocapacitive tomography device. The perforated flame holder sensor 122 and the flashback sensor 1123 can share use of the first set of electrodes described in relation to the flashback sensor 1123. In this case, the first set of electrodes including pairs of electrodes positioned laterally around the perforated flame holder 102 can act as both the perforated flame holder sensor 122, and a portion of the flashback sensor 1123.

[0193] In one embodiment, the preheating flame sensor 124 includes an electrocapacitive tomography device 1205. The preheating flame sensor 124 and the flashback sensor 1123 can share use of electrodes positioned upstream from the perforated flame holder 102 or laterally around the perforated flame holder 102. Two or more of the preheating flame sensor 124, the flashback sensor 1123, and the perforated flame holder sensor 122 can share electrodes of an electrocapacitive tomography device.

[0194] FIG. 12A is a diagram of a combustion system 1200 including a perforated flame holder 102 and an electrocapacitive tomography device 1205, according to an embodiment. The combustion system 1200 includes a fuel and oxidant source 202, a perforated flame holder 102, a controller 116, an electrocapacitive tomography device 1205, and a memory 1207. The fuel and oxidant source 202 can include the main fuel distributor 110 and the oxidant source 104. Additionally, the fuel and oxidant source 202 can include the preheating fuel distributor 106.

[0195] According to an embodiment, the fuel and oxidant source 202 includes, for example, a fuel nozzle configured to output the main fuel and oxidant onto the perforated flame holder 102. The perforated flame holder 102 sustains a combustion reaction of the fuel and oxidant primarily within the perforated flame holder 102.

[0196] According to an embodiment, the electrocapacitive tomography device 1205 is an image capture device that includes a plurality of electrodes 1220 positioned at selected locations adjacent to the perforated flame holder 102. The electrocapacitive tomography device 1205 is configured to make images of the perforated flame holder 102 based on the capacitance between the electrodes 1220. The images represent slices of the perforated flame holder 102 based on the capacitances between the electrodes 1220. The capacitance between pairs of electrodes 1220 depends, in part, on the dielectric constant of the material(s) between the pairs of electrodes 1220. In particular, the dielectric constant within the perforations of the perforated flame holder 102 can change based on the characteristics of the combustion reaction within the perforations. Therefore, the images produced by the electrocapacitive tomography device 1205 can give an indication of a temperature within the perforations or a concentration or flow of fuel, oxidant, and flue gasses at various locations in the perforated flame holder 102 based on the dielectric constant at the various locations of the perforated flame holder 102. The controller 116 can analyze the images and adjust the combustion reaction based on the images.

[0197] According to an embodiment, the controller 116 is configured to cause the electrocapacitive tomography device 1205 to capture one or more images of the combustion reaction. In one embodiment, the controller 116 is further configured to analyze the one or more images and to adjust the characteristics of the combustion reaction based on the analysis of the one or more images.

[0198] FIG. 12B is a top view of the perforated flame holder 102 and the electrocapacitive tomography device 1205, according to an embodiment. The electrocapacitive tomography device 1205 includes multiple pairs of electrodes 1220 positioned laterally around the perforated flame holder 102. Each pair of electrodes 1220 includes two electrodes 1220 directly facing each other, with the perforated flame holder 102 positioned between the pair of electrodes 1220. The controller 116 controls each pair of electrodes 1220 to make a plurality of images of the perforated flame holder 102, according to an embodiment.

[0199] In one embodiment, the electrodes 1220a and 1220a are a pair, the electrodes 1220b and 1220b are a pair, the electrodes 1220c and 1220c are a pair, the electrodes 1220d and 1220d are a pair, the electrodes 1220e and 1220e are a pair, and the electrodes 1220f and 1220f are a pair. The electrocapacitive tomography device 1205 can generate electrocapacitive tomography images based on a capacitance between the pairs of electrodes 1220.

[0200] In one embodiment, the plurality of electrodes 1220 includes one or more first pairs of electrodes 1220 facing each other in a first orientation substantially perpendicular to a primary direction of a flow of the fuel and oxidant toward the perforated flame holder 102. In one example, the first pairs of electrodes 1220 can include the pair of electrodes 1220a and the pair of electrodes 1220b. The first pairs of electrodes 1220a and 1220b sense the capacitance of the perforated flame holder 102 along an X direction substantially perpendicular to a primary direction of flow of the main fuel and oxidant toward the perforated flame holder 102. The primary direction of flow of the main fuel and oxidant toward the perforated flame holder 102 can correspond to a Z direction.

[0201] In one embodiment, the plurality of electrodes 1220 includes one or more second pairs of electrodes facing each other in a second orientation substantially perpendicular to the first orientation and a primary direction of a flow of the main fuel and oxidant toward the perforated flame holder 102. In one example, the second pairs of electrodes 1220 can include the pair of electrodes 1220c and the pair of electrodes 1220d. The second pairs of electrodes 1220c and 1220d sense the capacitance of the perforated flame holder 102 along a Y direction substantially perpendicular to the primary direction of flow of the main fuel and oxidant and substantially perpendicular to orientation of the first pairs of electrodes 1220a and 1220b.

[0202] In one embodiment, the plurality of electrodes 1220 can include pairs of electrodes 1220 oriented transverse to both the first pairs of electrodes 1220a and 1220b and the second pairs of electrodes 1220c and 1220d. The transverse pairs of electrodes 1220 can include the pair of electrodes 1220e and the pair of electrodes 1220f.

[0203] Although the views of FIG. 12A and FIG. 12B have shown the electrocapacitive tomography device 1205 including the electrodes 1220 positioned laterally around the perforated flame holder 102, an electrocapacitive tomography device in accordance with principles of the present disclosure can include pairs of electrodes positioned in configurations other than laterally around a perforated flame holder 102. An electrocapacitive tomography device can include pairs of electrodes positioned upstream from the perforated flame holder 102, downstream from the perforated flame holder 102, or in other locations depending on the particular aspect of a combustion system that the electrocapacitive tomography device is intended to sense or monitor. Accordingly, other sensors of the sensor array 114 described in relation to FIGS. 1-11 can include electrocapacitive tomography devices where suitable.

[0204] Those of skill in the art will recognize, in light of the present disclosure, that the combustion system in accordance with principles of the present disclosure can include sensors and actuators other than those disclosed herein, other combinations of sensors and actuators, as well as other kinds of actions to be taken by the controller 116 responsive to sensor signals. All such other sensors, actuators, combinations, and actions fall within the scope of the present disclosure.

[0205] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A combustion system, comprising:

- an oxidant source configured to output an oxidant into a furnace volume;

- a preheating fuel distributor configured to support a preheating flame by outputting a preheating fuel into the furnace volume during a preheating state;

- a main fuel distributor configured to output a main fuel into the furnace volume during a standard operating state;

- a perforated flame holder positioned in the furnace volume to be preheated by the preheating flame during the preheating state and to support a combustion reaction of the main fuel and oxidant at least partially within the perforated flame holder during the standard operating state;

- a preheating flame sensor configured to sense a condition of a preheating flame and to output a sensor signal indicative of the condition of the preheating flame;

- a perforated flame holder sensor configured to sense a condition of the perforated flame holder and to generate a sensor signal indicative of the condition of the perforated flame holder;

- one or more actuators configured to adjust a flow of the main fuel from the main fuel distributor, to adjust a flow of the preheating fuel from the preheating fuel distributor, and to adjust a flow of the oxidant from the oxidant source; and

- a controller communicatively coupled to the actuators, the preheating flame sensor, and the perforated flame holder sensor, the controller being configured to receive the sensor signals from the preheating flame sensor and the perforated flame holder sensor and to control the actuators to adjust the flow of the preheating fuel, the main fuel, and the oxidant responsive to the sensor signals and in accordance with software instructions stored in a non-transitory computer readable medium coupled to the controller.

2. The combustion system of claim 1, further comprising a bridgewall temperature sensor configured to sense a temperature of a bridgewall and to output sensor signals to the controller indicative of the temperature of the bridgewall, wherein the controller is configured to control the actuators to adjust conditions in the furnace volume responsive to the sensor signals from the bridgewall temperature sensor by controlling the actuators.

3. The combustion system of claim 1, further comprising an ignitor configured to generate sparks wherein the controller is configured to control one or more of the actuators to cause the ignitor to generate sparks to ignite the preheating flame if the preheating flame sensor indicates that the preheating flame is not present and all safety interlocks are met.

4. The combustion system of claim 1, further comprising a CO monitor sensor configured to sense a concentration of CO in flue gases generated by the combustion reaction and to output sensor signals to the controller indicative of the concentration of CO in the flue gases, wherein the controller is configured to control the actuators to adjust the flow of the main fuel and/or the oxidant if the sensor signals indicate a higher than acceptable concentration of CO in the flue gases.

5. The combustion system of claim 1, further comprising a NOX monitor configured to sense a concentration of NOX in flue gases generated by the combustion reaction and to output sensor signals to the controller indicative of the concentration of NOX in the flue gases, wherein the controller is configured to control the actuators to adjust the flow of at least one of the main fuel and the oxidant if the sensor signals indicate a higher than acceptable concentration of NOX in the flue gases.

6. The combustion system of claim 1, further comprising an O2 monitor configured to sense a concentration of O2 in flue gases generated by the combustion reaction and to output sensor signals to the controller indicative of the concentration of O2 in the flue gases, wherein the controller is configured to control the actuators to adjust the flow of the main fuel and/or the oxidant if the sensor signals indicate a concentration of O2 in the flue gases outside an acceptable range.

7. The combustion system of claim 1,
wherein the perforated flame holder sensor includes a perforated flame holder flame scanner configured to sense a condition of a combustion reaction of the main fuel and oxidant and to output sensor signals indicative of the condition of the combustion reaction, wherein the controller is configured to receive the sensor signals from the perforated flame holder flame scanner and to cause the actuators to adjust one or more of the flow of the main fuel and the flow of the oxidant responsive to the condition of the combustion reaction.

8. The combustion system of claim 1, further comprising a process monitor configured to sense a condition of a process that receives heat from the combustion reaction and to output sensor signals indicative of the condition of the process, wherein the controller is configured to receive the sensor signals from the process monitor and to cause the actuators to adjust one or more of the flow of the main fuel and the flow of the oxidant responsive to the condition of the process.

9. The combustion system of claim 1, further comprising a pressure sensor configured to sense a pressure in the furnace volume and to output sensor signals indicative of the pressure, wherein the pressure sensor includes one or more of a pressure change microphone, a static pressure sensor, a dynamic pressure sensor, and a differential pressure sensor, wherein the controller is configured to receive the sensor signals from the pressure sensor and to cause the actuators to adjust one or more of the flow of the oxidant, the flow of the main fuel, or a stack damper responsive to the condition of the process.

10. The combustion system of claim 1,
wherein the perforated flame holder sensor includes a perforated flame holder temperature sensor configured to sense a temperature of the perforated flame holder and to output sensor signals indicative of the temperature of the perforated flame holder, wherein the controller is configured to receive the sensor signals from the perforated flame holder temperature sensor and to cause the actuators to adjust one or more of the flow of the main fuel, the flow of the oxidant, or a stack damper responsive to the condition of the process.

11. The combustion system of claim 10,
wherein the controller is configured to control one or more of the actuators to activate a heater to heat the perforated flame holder if the sensor signals from the perforated flame holder temperature sensor indicate that the temperature of the perforated flame holder has dropped below an operational temperature.

12. The combustion system of claim 1, further comprising a display coupled to the controller, wherein the controller is configured to output messages on the display related to conditions in the furnace volume.

13. The combustion system of claim 1, further comprising a flashback sensor configured to detect flashback of the combustion reaction from the perforated flame holder toward the main fuel distributor and to output sensor signals to the controller indicating the occurrence of flashback.

14. The combustion system of claim 13,
wherein the flashback sensor includes an electrocapacitive tomography device.

15. The combustion system of claim 14,
wherein the electrocapacitive tomography device includes:

- a first set of electrodes positioned laterally around the perforated flame holder and configured to sense a parameter in a vicinity of the perforated flame holder; and

- a second set of electrodes positioned upstream from the perforated flame holder and configured to sense a parameter upstream from the perforated flame holder.

16. The combustion system of claim 1,
wherein the wherein the perforated flame holder is a reticulated ceramic perforated flame holder.

17. The combustion system of claim 1,
wherein the perforated flame holder sensor includes an electrocapacitive tomography device.

18. A computing system implemented method for operating a combustion system, the method comprising:

- receiving, during a preheating state of a combustion system, sensor signals from a preheating flame sensor indicating a condition of a preheating flame in a furnace volume supported by a flow of preheating fuel and an oxidant;

- receiving, during the preheating state, sensor signals from a perforated flame holder sensor indicating a temperature of a perforated flame holder positioned in the furnace volume to be preheated to an operating temperature by the preheating flame during the preheating state;

- outputting control signals to control one or more actuators to adjust the flow of the preheating fuel, to adjust the flow of the oxidant, or to generate sparks to ignite the preheating flame responsive to the sensor signals from the preheating flame sensor and in accordance with software instructions stored on a non-transitory computer readable medium;

- outputting control signals to control one or more actuators to transition the combustion system from the preheating state to a standard operating state if the sensor signals from the perforated flame holder sensor indicate that the perforated flame holder has reached the operating temperature, the standard operating state corresponding to supporting a combustion reaction of a main fuel and the oxidant in the perforated flame holder and in accordance with the software instructions stored on the non-transitory computer readable medium;

- receiving sensor signals from the perforated flame holder sensor during the standard operating state indicating a condition of the perforated flame holder; and

- outputting control signals to control one or more actuators to adjust a flow of the main fuel or to adjust the flow of the oxidant responsive to the sensor signals from the perforated flame holder sensor during the standard operating state and in accordance with the software instructions stored on the non-transitory computer readable medium.

19. The computing system implemented method of claim 18, further comprising outputting control signals to shut down the combustion system if the sensor signals indicate a fault condition.

20. The computing system implemented method of claim 18,
wherein receiving sensor signals from the perforated flame holder sensor includes receiving electrocapacitive tomography signals from the perforated flame holder sensor.

Drawing