A TWO-STAGE AIR-GAS MIXING UNIT FOR AN AIR-GAS MIXTURE BURNING APPLIANCE

Abstract

 In a two-stage air-gas mixing unit (110) that comprises an air inlet (113), an air flow channel (250), a gas inlet (117), an air-gas outlet (132), a gas valve (240), a first stage air-gas mixer (210), and a second stage air-gas mixer (220), the gas valve (240) being adapted for regulating a flow of gas (119) based on the pressure of a flow of the air (111) received at a reference pressure port (242), the first stage air-gas mixer (210) being adapted for mixing the gas (119) from the gas valve (240) with a first portion of the air (111) to form a preliminary air-gas mixture (230), and the second stage air-gas mixer (220) being adapted for mixing a second portion of the air (111) with the preliminary air-gas mixture (230) from the first stage air-gas mixer (210) to form a combustible air-gas mixture (130).

Description

Background of the Invention

[0001] The present invention relates to a two-stage air-gas mixing unit for mixing of air with gas to form a combustible air-gas mixture for a burning unit of an air-gas mixture burning appliance. The two-stage air-gas mixing unit comprises an air inlet, an air flow channel, a gas inlet, a gas valve with a reference pressure port, a first stage air-gas mixer, a second stage air-gas mixer, and an air-gas outlet. Furthermore, the present invention relates to an air-gas mixture burning appliance with such an air-gas mixing unit.

[0002] From the state of the art, an air-gas mixing unit having an air inlet, a gas inlet, an air-gas outlet, and an air-gas mixing section for mixing air with gas to form a combustible air-gas mixture is known. More specifically, known air-gas mixing units such as venturi mixers take in separate gas (fuel) and air (oxidizer) streams and provide a pre-mixed (or aerated) air-gas mixture for the burning unit at a desired concentration or ratio.

[0003] A venturi mixer typically contains a converging channel to accelerate the air stream in order to create a decreased pressure in the throat of the mixing unit. This decreased pressure, which is sometimes also referred to as suction pressure, in the throat causes a suction effect on the gas stream, which causes the gas stream to flow into the air-gas mixing unit and mix with the air stream. The upstream side of the gas stream is usually controlled by a gas valve, which regulates the gas pressure relative to the air pressure measured at some location in the air-gas mixture burning appliance.

[0004] Current air-gas mixture burning appliances usually include a controller that controls the amount of gas and the amount of air that enter the air-gas mixing unit.

[0005] Moreover, the air-gas mixing units of such appliances are often designed to operate with a predetermined gas that has certain properties, which are determined by a combination of density, viscosity, heating value, heat input, and air-gas ratio. Furthermore, the air-gas mixing units are often very sensitive to changes in gas quality levels, including the level of impurities such as nitrogen or carbon dioxide in the gas.

[0006] Conventional air-gas mixing units that are designed for a certain air-gas ratio have a predetermined pressure drop in the gas channel that, when combined with the setting of the gas valve regulator, precisely results in the target air-gas ratio. However, if a different fuel gas is used, the pressure drop in the gas channel changes. This results in a different air-gas ratio for the venturi mixer. As a result, a venturi designed for one fuel gas may no longer be suited to operating on another type of fuel gas.

[0007] In the remainder of this description, the term "gas" refers to any fuel in gaseous form that, when mixed with air, forms a combustible air-gas mixture. Examples for such a gas include hydrogen, propane, butane, methane, liquefied petroleum gas, etc. Moreover, the term "air" refers to any suitable oxidizer that may be mixed with a fuel gas to form a combustible air-gas mixture.

[0008] The concentration of the combustible air-gas mixture, which is sometimes also referred to as the air-gas ratio or the air to gas ratio, is the mass of air per mass of gas in the air-gas mixture. A complete combustion takes place when all the gas of the combustible air-gas mixture is burned. In other words, the exhaust gas is free of unburned gas. The air-gas ratio of a complete combustion is referred to as the stoichiometric air-gas ratio, and the ideal gas-air ratio is called stoichiometric gas-air ratio.

[0009] Document DE 10 2018 119 457 A1 describes a method for regulating a mixing ratio of fuel gas and air for a heating device. Initially, an air mass flow is subdivided and mixed with the fuel gas mass flow to form a premix via a partial flow. Material properties of the premix are detected by a sensor and the mixing ratio of fuel gas and air is calculated therefrom.

[0010] Document US 2016/018105 A1 describes a burner and a tile for producing a flame in a furnace. The burner includes a pre-mixer with a venturi that mixes fuel with a first portion of combustion air. The mixture of the fuel and combustion air is passed through the tile. The tile also passes additional portions of combustion air there through. The tile may include a wall to form a staged fuel tile with flow channels splitting the mixture of fuel and combustion air so that some exits the tile inside of the wall, and some exits the tile outside of the wall. The tile may be two pieces. Also described is a process for improving a flame produced by such a burner with a tile.

Summary of the Invention

[0011] The present invention relates to a two-stage air-gas mixing unit for mixing of air with gas to form a combustible air-gas mixture for a burning unit of an air-gas mixture burning appliance. The two-stage air-gas mixing unit comprises an air inlet for providing a flow of the air, an air flow channel that is arranged downstream of the air inlet, a gas inlet for providing the gas, a gas valve that is arranged downstream of the gas inlet and comprises a reference pressure port, wherein the air flow channel is adapted for providing the flow of the air to the reference pressure port, and wherein the gas valve is adapted for regulating the flow of the gas based on the pressure of the flow of the air at the reference pressure port, a first stage air-gas mixer that is arranged downstream of the gas valve and adapted for mixing the gas from the gas valve with a first portion of the air to form a preliminary air-gas mixture, a second stage air-gas mixer that is arranged downstream of the first stage air-gas mixer and the air inlet, wherein the second stage air-gas mixer is adapted for mixing a second portion of the air from the air inlet with the preliminary air-gas mixture from the first stage air-gas mixer to form the combustible air-gas mixture, and an air-gas outlet that is adapted for providing the combustible air-gas mixture to the burning unit.

[0012] Accordingly, the inventive two-stage air-gas mixing unit may be able to control the pressure drop in the gas channel as a result of a changing density and/or viscosity of the gas, thereby making the air-gas mixing unit suitable for mixing different gas types, for reacting promptly to changes in gas quality, and for providing a uniform combustible air-gas mixture at the air-gas outlet.

[0013] Optionally, the two-stage air-gas mixing unit may include an additional air flow channel that is arranged upstream of the air flow channel and adapted for providing the first portion of the air to the first stage air-gas mixer.

[0014] Thus, air from upstream of the air flow channel may beneficially be provided to the first stage air-gas mixer.

[0015] Optionally, the two-stage air-gas mixing unit may include an additional air flow channel that is arranged downstream of the air flow channel and adapted for providing the first portion of the air to the first stage air-gas mixer.

[0016] Accordingly, air from downstream of the air flow channel may advantageously be provided to the first stage air-gas mixer.

[0017] Optionally, the two-stage air-gas mixing unit may include a restricting device that is arranged in the additional air flow channel and adapted for regulating the first portion of the air to the first stage air-gas mixer.

[0018] Thus, the amount of air that mixes with the gas in the first stage air-gas mixer may be restricted such that the preliminary air-gas mixture remains non-flammable.

[0019] According to one embodiment, the restricting device may be adapted for regulating the first portion of the air based at least on the type of the gas.

[0020] Thus, the two-stage air-gas mixing unit may be adjusted to allow for the use of different gas types and to react to different levels of impurities in the gas.

[0021] Optionally, the two-stage air-gas mixing unit may include a second additional air flow channel that is arranged downstream of the air inlet, and an additional first stage air-gas mixer that is arranged downstream of the gas valve and adapted for mixing the gas from the gas valve with a third portion of the air from the second additional air flow channel to form the preliminary air-gas mixture.

[0022] Accordingly, the two-stage air-gas mixing unit may be able to provide a combustible air-gas mixture for at least two different predetermined gas types.

[0023] Optionally, the two-stage air-gas mixing unit may include a second additional air flow channel that is arranged downstream of the air inlet, and an additional first stage air-gas mixer that is arranged downstream of the first stage air-gas mixer and adapted for mixing the preliminary air-gas mixture from the first stage air-gas mixer with a third portion of the air from the second additional air flow channel to form a second preliminary air-gas mixture.

[0024] Accordingly, the two-stage air-gas mixing unit may be able to provide a combustible air-gas mixture for at least two different predetermined gas types.

[0025] Optionally, the two-stage air-gas mixing unit includes at least one of a first restricting device or a second restricting device, wherein the first restricting device is arranged in the additional air flow channel and adapted for regulating the first portion of the air to the first stage air-gas mixer, and wherein the second restricting device is arranged in the second additional air flow channel and adapted for regulating the third portion of the air to the additional first stage air-gas mixer.

[0026] Thus, the amount of air that mixes with the gas in the first stage air-gas mixer may be restricted for at least one of the two different predetermined gas types such that the preliminary air-gas mixture remains non-flammable.

[0027] Preferably, the first restricting device is adapted for regulating the first portion of the air based at least on the type of the gas, and the second restricting device is adapted for regulating the third portion of the air based at least on the type of the gas.

[0028] Accordingly, the two-stage air-gas mixing unit may react to different levels of impurities in the gas of at least one of the two different predetermined gas types.

[0029] Preferably, the additional air flow channel and the second additional air flow channel are arranged hydraulically parallel to each other and adapted for providing different quantities of the flow of the air to the first stage air-gas mixer and to the additional first stage air-gas mixer, respectively.

[0030] Thus, the additional air flow channel may be adapted to provide air to the first stage air-gas mixer, and, in parallel, the second additional air flow channel may be adapted to provide air to the additional first stage air-gas mixer.

[0031] Preferably, the additional air flow channel and the second additional air flow channel are operable independent of each other.

[0032] Accordingly, the additional air flow channel and the second additional air flow channel may be adjustable independent of each other, for example to adjust for different levels of impurities in the gas.

[0033] Optionally, the two-stage air-gas mixing unit may include an additional air inlet that is adapted for providing the air directly to the first stage air-gas mixer.

[0034] Thus, air may be provided from outside the two-stage air-gas mixing unit directly to the first stage air-gas mixer.

[0035] Optionally, the two-stage air-gas mixing unit may include a fan that is arranged upstream of the air flow channel and adapted for propagating the flow of the air towards the first and second stage air-gas mixers.

[0036] Accordingly, the fan may propel air from the air inlet towards the first and second stage air-gas mixers.

[0037] Optionally, the two-stage air-gas mixing unit may include a fan that is arranged downstream of the second stage air-gas mixer and adapted for propagating the combustible air-gas mixture towards the air-gas outlet.

[0038] Accordingly, the fan may propel the combustible air-gas mixture from the second stage air-gas mixer towards the air-gas outlet.

[0039] Optionally, the two-stage air-gas mixing unit may include a gas sensor that is arranged upstream of the gas valve and adapted for detecting the type of the gas.

[0040] Thus, the two-stage air-gas mixing unit may advantageously detected the type of the gas upstream of the gas valve.

[0041] Furthermore, an air-gas mixture burning appliance includes an air inlet for providing air, a gas inlet for providing gas, a burning unit for burning a combustible air-gas mixture, and the two-stage air-gas mixing unit described above.

[0042] Accordingly, the inventive air-gas mixture burning appliance may be suitable for being operated with different gas types using the same air-gas mixing unit and for reacting promptly to changes in gas quality.

Brief Description of the Drawings

[0043] Exemplary embodiments of the present invention are described in detail hereinafter with reference to the attached drawings. In these attached drawings, identical or identically functioning components and elements are labelled with identical reference signs and they are generally only described once in the following description.

Fig. 1

shows a schematic view of an air-gas mixture burning appliance with a two-stage air-gas mixing unit according to the present invention,

Fig. 2

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan downstream of a second stage air-gas mixer and an air flow channel to a first stage air-gas mixer downstream of an air flow channel to the reference pressure port of a gas valve,

Fig. 3

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan downstream of a second stage air-gas mixer and an air flow channel to a first stage air-gas mixer upstream of an air flow channel to the reference pressure port of a gas valve,

Fig. 4

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan downstream of a second stage air-gas mixer and ambient air pressure at the reference pressure port of a gas valve,

Fig. 5

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan downstream of a second stage air-gas mixer and ambient air pressure at the reference port of a gas valve and at the first stage air-gas mixer,

Fig. 6

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan downstream of a second stage air-gas mixer, an air flow channel to the reference pressure port of a gas valve, and ambient air pressure at the first stage air-gas mixer,

Fig. 7

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan upstream of an air flow channel to the reference pressure port of a gas valve that is up-stream of an air flow channel to a first stage air-gas mixer,

Fig. 8

shows a schematic view of the air-gas mixture burning appliance of Fig. 1, with a two-stage air-gas mixing unit having a fan upstream of an air flow channel to a first stage air-gas mixer that is upstream of an air flow channel to the reference pressure port of a gas valve, and

Fig. 9

shows a schematic view of a two-stage air-gas mixing unit having an air flow channel to the reference pressure port of a gas valve that is up-stream of two hydraulically parallel air flow channels to a first stage air-gas mixer and an additional first stage air-gas mixer.

Detailed Description

[0044] Fig. 1 shows an exemplary air-gas mixture burning appliance 100. By way of example, the air-gas mixture burning appliance 100 may be used in any application that requires the use of a heat exchanger. For example, the air-gas mixture burning appliance 100 may be used in a building heating system or a water heater.

[0045] As shown in Fig. 1, the air-gas mixture burning appliance 100 may include an air inlet 105 for providing air 111, a gas inlet 107 for providing gas 119, and a flue outlet 150 for the evacuation of exhaust gas 152. Illustratively, the air-gas mixture burning appliance 100 may further include an air-gas mixing unit 110, a burning unit 120, and a heat exchanger 140.

[0046] The gas 119 may be any gas such as hydrogen, propane, butane, methane, liquefied petroleum gas, etc. Illustratively, the gas 119 may have a certain gas quality range. The gas quality range may be specified by the gas distributer. Thus, the gas 119 may contain other, usually non-flammable, species besides the pure fuel itself. These other species in the gas 119 are called impurities. Typical impurities are nitrogen or carbon dioxide.

[0047] The density and viscosity of the pure fuel are different from the density and viscosity of the typical impurities. When the gas quality changes, within limits as allowed by the gas quality standards, the concentration of impurities in the gas 119 will change. This results in a change in density and viscosity of the gas 119. Consequently, the flow rate of gas 119 drawn in by the air-gas mixing unit 110 changes. As a result, the heat input and air-gas ratio of the air-gas mixture burning appliance will change. The larger the difference in density and viscosity between the gas 119 before the gas quality change and after the gas quality change, the larger the change in heat input and air-gas ratio of the air-gas mixture burning appliance at the moment of the gas quality change.

[0048] The air-gas mixing unit 110 is preferably adapted for mixing of air 111 and gas 119 to form a combustible air-gas mixture 130. Preferentially, the combustible air-gas mixture 130 is a homogenous mixture of the air 111 and the gas 119. To adapt to different gas types and/or to different gas quality ranges, the air-gas mixing unit 110 is preferably embodied as a two-stage air-gas mixing unit 110 as shown in Fig. 2 to Fig. 9.

[0049] By way of example, the air-gas mixing unit 110 includes an air inlet 113 that receives air 111 from the air inlet 105 of the air-gas mixture burning appliance 100 and a gas inlet 117 that receives gas 119 from the gas inlet 107 of the air-gas mixture burning appliance 100.

[0050] Illustratively, the combustible air-gas mixture 130 is formed in the two-stage air-gas mixing unit 110 from the air 111 received at the air inlet 113 and the gas 117 received at the gas inlet 117. In the two-stage air-gas mixing unit 110, a first stage air-gas mixer may mix a portion of the air 111 from the air inlet 113 with the gas 117 from the gas inlet 117 to produce a preliminary air-gas mixture. The preliminary air-gas mixture may have a predetermined air-gas ratio. For example, the preliminary air-gas mixture may have an air-gas ratio such that the preliminary air-gas mixture is non-flammable.

[0051] By way of example, a second stage air-gas mixer may mix the remaining air 111 from the air inlet 113 with the preliminary air-gas mixture to produce a combustible air-gas mixture 130. The combustible air-gas mixture 130 is provided via the air-gas outlet 132 to the burning unit 120.

[0052] Illustratively, the burning unit 120 is provided with a burner surface 124 that is arranged downstream of the air-gas mixing unit 110 such that the combustible air-gas mixture 130 that is formed in the two-stage air-gas mixing unit 110 flows towards the burner surface 124. If desired, a fan may drive the combustible air-gas mixture 130 towards the burner surface 124.

[0053] The combustible air-gas mixture 130 is burned by the burning unit 120 and, more specifically, at the burner surface 124. The heat exchanger 140 may transfer the heat that is generated at the burner surface 124 to another medium. For example, the heat exchanger 140 may transfer the heat that is generated at the burner surface 124 to water in a water circuit. The flue outlet 150 may evacuate the exhaust gas 152 from the air-gas mixture burning appliance 100.

[0054] Fig. 2 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 1 with a two-stage air-gas mixing unit 110. The two-stage air-gas mixing unit 110 is suitable for mixing of air 111 with gas 119 to form a combustible air-gas mixture 130 for burning unit 120 of air-gas mixture burning appliance 100.

[0055] As shown in Fig. 2, the two-stage air-gas mixing unit 110 includes an air inlet 113 for providing a flow of the air 111, a gas inlet 117 for providing the gas 119, and an air-gas outlet 132 that is adapted for providing the combustible air-gas mixture 130 to the burning unit 120. Preferably, the flow of the air 111 is unregulated. For example, the flow of the air 111 may have an ambient air pressure. Thus, the air inlet 113 may be adapted for providing an unregulated flow of the air 111.

[0056] The two-stage air-gas mixing unit 110 further includes an air flow channel 250 that is arranged downstream of the air inlet 113 and a gas valve 240 that is arranged downstream of the gas inlet 117. The gas valve 140 may include a reference pressure port 242.

[0057] Preferably, the air flow channel 250 is adapted for providing the flow of the air 111 to the reference pressure port 242, and the gas valve 240 is adapted for regulating the flow of the gas 119 based on the pressure of the flow of the air 111 at the reference pressure port 242.

[0058] Illustratively, the two-stage air-gas mixing unit 110 may include a first stage air-gas mixer 210 that is arranged downstream of the gas valve 240. The first stage air-gas mixer 210 may be adapted for mixing the gas 119 from the gas valve 240 with a first portion of the air 111 to form a preliminary air-gas mixture 230.

[0059] By way of example, the two-stage air-gas mixing unit 110 may include a second stage air-gas mixer 220 that is arranged downstream of the first stage air-gas mixer 210 and the air inlet 113. The second stage air-gas mixer 220 may be adapted for mixing a second portion of the air 111 from the air inlet 113 with the preliminary air-gas mixture 230 from the first stage air-gas mixer 210 to form the combustible air-gas mixture 130.

[0060] As shown in Fig. 2, the two-stage air-gas mixing unit 110 includes a fan 270. The fan 270 may be arranged downstream of the second stage air-gas mixer 220, if desired. The fan 270 may propagate the combustible air-gas mixture 130 towards the air-gas outlet 132.

[0061] Preferably, the first portion of air 111 that mixes with the gas 119 from the gas valve 240 in the first-stage air-gas mixer 210 to form the preliminary air-gas mixture 230 is controlled such that the preliminary air-gas mixture 230 remains above the upper flammability limit of the gas 119.

[0062] Illustratively, the two-stage air-gas mixing unit 110 may include an additional air flow channel 260. The additional air flow channel 260 may provide the first portion of the air 111 to the first stage air-gas mixer 210. By way of example, the additional air flow channel 260 may control the first portion of air 111 (e.g., through the dimensions of the additional air flow channel 260) such that the preliminary air-gas mixture 230 remains non-flammable. If desired, the additional air flow channel 260 may be arranged downstream of the air flow channel 250.

[0063] Fig. 3 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 2 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0064] However, in contrast to the two-stage air-gas mixing unit 110 of Fig. 2, the additional air flow channel 260 to the first stage air-gas mixer 210 in the two-stage air-gas mixing unit 110 of Fig. 3 is arranged upstream of the airflow channel 250 to the reference pressure port 242 of gas valve 240. Moreover, the two-stage air-gas mixing unit 110 of Fig. 3 includes a gas sensor 310 and a restricting device 320.

[0065] The gas sensor 310 may be adapted for detecting the type of the gas 119. Illustratively, the gas sensor 310 may be arranged upstream of the gas valve 240. If desired, the gas sensor 310 may be arranged between the gas valve 240 and the first stage air-gas mixer 210.

[0066] The restricting device 320 may be adapted for regulating the first portion of the air 111 to the first stage air-gas mixer 210. Preferably, the restricting device 320 may be arranged in the additional air flow channel 260. If desired, the restricting device 320 may regulate the first portion of the air 111 based at least on the type of the gas 119. Thus, the two-stage air-gas mixing unit 110 may adapt to the use of different gas types.

[0067] Fig. 4 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 2 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0068] However, the two-stage air-gas mixing unit 110 of Fig. 4 differs from the two-stage air-gas mixing unit 110 of Fig. 2 in that the air flow channel 250 to the reference pressure port 242 of gas valve 240 is decoupled from the air inlet 113. Instead, the reference pressure port 242 of gas valve 240 is subjected to ambient air pressure, for example from outside the air-gas mixture burning appliance 100. If desired, the reference pressure port 242 of gas valve 240 may be subjected to ambient air pressure from inside the enclosure of the air-gas mixture burning appliance 100.

[0069] Fig. 5 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 4 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0070] However, in contrast to the two-stage air-gas mixing unit 110 of Fig. 4, the additional air flow channel 260 to the first stage air-gas mixer 210 of the two-stage air-gas mixing unit 110 of Fig. 5 is decoupled from the air inlet 113. Instead, the two-stage air-gas mixing unit 110 includes an additional air inlet 513 that is adapted for providing the air 111 directly to the first stage air-gas mixer 210. In other words, the first stage air-gas mixer 210 receives the air 111 from the ambient air within the enclosure of the air-gas mixture burning appliance 100 at an ambient air pressure.

[0071] Fig. 6 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 2 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0072] However, in contrast to the two-stage air-gas mixing unit 110 of Fig. 2, the additional air flow channel 260 to the first stage air-gas mixer 210 of the two-stage air-gas mixing unit 110 of Fig. 6 is decoupled from the air inlet 113. Instead, the two-stage air-gas mixing unit 110 includes an additional air inlet 513 that is adapted for providing the air 111 directly to the first stage air-gas mixer 210. In other words, the first stage air-gas mixer 210 receives the air 111 from the ambient air within the enclosure of the air-gas mixture burning appliance 100 at an ambient air pressure.

[0073] Fig. 7 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 2 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0074] The two-stage air-gas mixing unit 110 of Fig. 7 differs from the two-stage air-gas mixing unit of Fig. 2 in that the fan 270 of Fig. 2 is removed, and, instead, a fan 770 is arranged upstream of the air flow channel 250. Fan 770 is adapted for propagating the flow of the air 111 towards the first and second stage air-gas mixers 210, 220.

[0075] Fig. 8 shows a schematic view of the air-gas mixture burning appliance 100 of Fig. 7 with air inlet 105, gas inlet 107, burning unit 120, heat exchanger 140, flue outlet 150, and a two-stage air-gas mixing unit 110.

[0076] However, in contrast to the two-stage air-gas mixing unit 110 of Fig. 7, the additional air flow channel 260 to the first stage air-gas mixer 210 in the two-stage air-gas mixing unit 110 of Fig. 8 is arranged upstream of the air flow channel 250 to the reference pressure port 242 of gas valve 240. In other words, the additional air flow channel 260 connects an opening at the output of fan 770 upstream of an opening of air flow channel 250 with the first stage air-gas mixer 210 such that a first portion of air 111 from the fan output may arrive at the first stage air-gas mixer 210.

[0077] Fig. 9 shows a schematic view of a two-stage air-gas mixing unit 110. The two-stage air-gas mixing unit 110 is suitable for mixing of air 111 with gas 119 to form a combustible air-gas mixture 130 for a burning unit of an air-gas mixture burning appliance (e.g., burning unit 120 of air-gas mixture burning appliance 100 of Fig. 1).

[0078] As shown in Fig. 9, the two-stage air-gas mixing unit 110 includes an air inlet 113 for providing a flow of the air 111, a gas inlet 117 for providing the gas 119, and an air-gas outlet 132 that is adapted for providing the combustible air-gas mixture 130 to the burning unit. Preferably, the flow of the air 111 is unregulated. For example, the flow of the air 111 may have an ambient air pressure. Thus, the air inlet 113 may be adapted for providing an unregulated flow of the air 111.

[0079] The two-stage air-gas mixing unit 110 further includes an air flow channel 250 that is arranged downstream of the air inlet 113 and a gas valve 240 that is arranged downstream of the gas inlet 117. The gas valve 140 may include a reference pressure port 242.

[0080] Preferably, the air flow channel 250 is adapted for providing the flow of the air 111 to the reference pressure port 242, and the gas valve 240 is adapted for regulating the flow of the gas 119 based on the pressure of the flow of the air 111 at the reference pressure port 242.

[0081] By way of example, the two-stage air-gas mixing unit 110 may include an additional air flow channel 260. The additional air flow channel 260 may provide a first portion of the air 111 to the first stage air-gas mixer 210. The additional air flow channel 260 may be dimensioned to control the first portion of air 111 such that the preliminary air-gas mixture 230 remains non-flammable. If desired, the additional air flow channel 260 may be arranged downstream of the air flow channel 250.

[0082] Illustratively, the two-stage air-gas mixing unit 110 may include a first stage air-gas mixer 210 that is arranged downstream of the gas valve 240. The first stage air-gas mixer 210 is adapted for mixing the gas 119 from the gas valve 240 with the first portion of the air 111 to form a preliminary air-gas mixture 230.

[0083] As shown in Fig. 9, the two-stage air-gas mixing unit 110 may include a second additional air flow channel 960 that is arranged downstream of the air inlet 113. Illustratively, the additional air flow channel 260 and the second additional air flow channel 960 may be arranged hydraulically parallel to each other. If desired, the additional air flow channel 260 and the second additional air flow channel 960 may be adapted for conveying different quantities of the flow of the air 111. Preferably, the additional air flow channel 260 and the second additional air flow channel 960 are operable independent of each other.

[0084] Illustratively, the two-stage air-gas mixing unit 110 may include an additional first stage air-gas mixer 910. The additional first stage air-gas mixer 910 may be arranged downstream of the first stage air-gas mixer 210 and mix the preliminary air-gas mixture 230 from the first stage air-gas mixer 210 with a third portion of the air 111 from the second additional air flow channel 960 to form a second preliminary air-gas mixture 230.

[0085] If desired, the additional first stage air-gas mixer 910 may be arranged downstream of the gas valve 240 and mix the gas 119 from the gas valve 240 with the third portion of the air 111 from the second additional air flow channel 960 to form the preliminary air-gas mixture 230.

[0086] Preferably, the additional air flow channel 260 and the second additional air flow channel 960 may be adapted for providing different quantities of the flow of the air 111 to the first stage air-gas mixer 210 and to the additional first stage air-gas mixer 910, respectively. As an example, the additional air flow channel 260 may be closed such that no air 111 is flowing from the air inlet 113 to the first stage air-gas mixer 210 of Fig. 9. As another example, the second additional air flow channel 960 may be closed such that no air 111 is flowing from the air inlet 113 to the additional first stage air-gas mixer 910.

[0087] Illustratively, a gas sensor 310 may be arranged upstream of the gas valve 240 or between the gas valve 240 and the first stage air-gas mixer 210. The gas sensor 310 may exemplarily be adapted for detecting the type of the gas 119. If desired, the gas sensor 310 may sense other properties than the type of the gas 119. As an example, the gas sensor 310 may measure the pressure drop in the gas channel between the gas inlet 117 and the gas valve 240. As another example, the gas sensor 310 may measure the viscosity of the gas 119. As yet another example, the gas sensor 310 may measure the amount of impurities in the gas 119.

[0088] By way of example, the two-stage air-gas mixing unit 110 may include at least one of a first restricting device 320 or a second restricting device 920. The first restricting device 320 may be arranged in the additional air flow channel 260 and adapted for regulating the first portion of the air 111 to the first stage air-gas mixer 210. The second restricting device 920 may be arranged in the second additional air flow channel 960 and adapted for regulating the third portion of the air 111 to the additional first stage air-gas mixer 910.

[0089] As an example, the first restricting device 320 may be adapted for regulating the first portion of the air 111 based at least on the type of the gas 119. As another example, the second restricting device 920 may be adapted for regulating the third portion of the air 111 based at least on the type of the gas 119.

[0090] For example, a controller may receive information about the type of the gas 119 from the gas sensor 310. The controller may be coupled to the first restricting device 320 and adjust the first portion of air 111 that flows through the additional air flow channel 260 from the air inlet 113 to the first stage air-gas mixer 210. If desired, the controller may be coupled to the second restricting device 920 and adjust the third portion of air 111 that flows through the second additional air flow channel 960 from the air inlet 113 to the additional first stage air-gas mixer 910.

[0091] Illustratively, the two-stage air-gas mixing unit 110 may use the additional airflow channel 260 and provide a first portion of air 111 to the first stage air-gas mixer 210 for one type of gas 119, and the two-stage air-gas mixing unit 110 may use the second additional air flow channel 960 and provide a third portion of air 111 to the additional first stage air-gas mixer 910 for another type of gas 119.

[0092] For example, the two-stage air-gas mixing unit 110 may close the second additional air flow channel 960 when the additional air flow channel 260 is providing the first portion of the air 111 to the first stage air-gas mixer 210, and the two-stage air-gas mixing unit 110 may close the additional air flow channel 260 when the second additional air flow channel 960 is providing the third portion of the air 111 to the additional first stage air-gas mixer 910. Thus, the two-stage air-gas mixing unit 110 may use a first subset of the air channels for one type of gas 119 and a second subset of the air channels for another type of gas 119.

[0093] By way of example, the two-stage air-gas mixing unit 110 may include a second stage air-gas mixer 220 that is arranged downstream of the first stage air-gas mixer 210 and the air inlet 113. The second stage air-gas mixer 220 is adapted for mixing a second portion of the air 111 from the air inlet 113 with the preliminary air-gas mixture 230 from the first stage air-gas mixer 210 and/or the additional first stage air-gas mixer 910 to form the combustible air-gas mixture 130.

[0094] Preferably, the preliminary air-gas mixture 230 that is provided to the second stage air-gas mixer 220 is controlled such that the preliminary air-gas mixture 230 remains above the upper flammability limit of the gas 119. In other words, the first portion of air 111 that mixes with the gas 119 from the gas valve 240 in the first-stage air-gas mixer 210 and/or the third portion of air 111 that mixes with the gas 119 or the preliminary air-gas mixture 230 from the first stage air-gas mixer 210 in the additional first stage air-gas mixer 910 to form the preliminary air-gas mixture 230 that is provided to the second stage air-gas mixer 220 is controlled such that the preliminary air-gas mixture 230 remains non-flammable.

[0095] If desired, the two-stage air-gas mixing unit 110 may include a fan. The fan may be arranged downstream of the second stage air-gas mixer 220 and propagate the combustible air-gas mixture 130 towards the air-gas outlet 132. Alternatively, or in addition, the two-stage air-gas mixing unit 110 may include a fan that is arranged between the air inlet 113 and the air flow channel 250.

[0096] It should be noted that air flow channel 960 is shown to be wider than air flow channel 260. However, air flow channel 960 may be wider than air flow channel 260, if desired.

Claims

1. A two-stage air-gas mixing unit (110) for mixing of air (111) with gas (119) to form a combustible air-gas mixture (130) for a burning unit (120) of an air-gas mixture burning appliance (100), comprising:

an air inlet (113) for providing a flow of the air (111);

an air flow channel (250) that is arranged downstream of the air inlet (113);

a gas inlet (117) for providing the gas (119);

a gas valve (240) that is arranged downstream of the gas inlet (117) and comprises a reference pressure port (242), wherein the air flow channel (250) is adapted for providing the flow of the air (111) to the reference pressure port (242), and wherein the gas valve (240) is adapted for regulating the flow of the gas (119) based on the pressure of the flow of the air (111) at the reference pressure port (242);

a first stage air-gas mixer (210) that is arranged downstream of the gas valve (240) and adapted for mixing the gas (119) from the gas valve (240) with a first portion of the air (111) to form a preliminary air-gas mixture (230);

a second stage air-gas mixer (220) that is arranged downstream of the first stage air-gas mixer (210) and the air inlet (113), wherein the second stage air-gas mixer (220) is adapted for mixing a second portion of the air (111) from the air inlet (113) with the preliminary air-gas mixture (230) from the first stage air-gas mixer (210) to form the combustible air-gas mixture (130); and

an air-gas outlet (132) that is adapted for providing the combustible air-gas mixture (130) to the burning unit (120).

2. The two-stage air-gas mixing unit of claim 1, further comprising:
an additional air flow channel (260) that is arranged upstream of the air flow channel (250) and adapted for providing the first portion of the air (111) to the first stage air-gas mixer (210).

3. The two-stage air-gas mixing unit of claim 1, further comprising:
an additional air flow channel (260) that is arranged downstream of the air flow channel (250) and adapted for providing the first portion of the air (111) to the first stage air-gas mixer (210).

4. The two-stage air-gas mixing unit of claim 2 or 3, further comprising:
a restricting device (320) that is arranged in the additional air flow channel (260) and adapted for regulating the first portion of the air (111) to the first stage air-gas mixer (210).

5. The two-stage air-gas mixing unit of claim 5, wherein the restricting device (320) is adapted for regulating the first portion of the air (111) based at least on the type of the gas (119).

6. The two-stage air-gas mixing unit of claim 2 or 3, further comprising:

a second additional air flow channel (960) that is arranged downstream of the air inlet (113); and

an additional first stage air-gas mixer (910) that is arranged downstream of the gas valve (240) and adapted for mixing the gas (119) from the gas valve (240) with a third portion of the air (111) from the second additional air flow channel (960) to form the preliminary air-gas mixture (230).

7. The two-stage air-gas mixing unit of claim 2 or 3, further comprising:

a second additional air flow channel (960) that is arranged downstream of the air inlet (113); and

an additional first stage air-gas mixer (910) that is arranged downstream of the first stage air-gas mixer (210) and adapted for mixing the preliminary air-gas mixture (230) from the first stage air-gas mixer (210) with a third portion of the air (111) from the second additional air flow channel (960) to form a second preliminary air-gas mixture (230).

8. The two-stage air-gas mixing unit of claim 6 or 7, further comprising:
at least one of a first restricting device (320) or a second restricting device (920), wherein the first restricting device (320) is arranged in the additional air flow channel (260) and adapted for regulating the first portion of the air (111) to the first stage air-gas mixer (210), and wherein the second restricting device (920) is arranged in the second additional air flow channel (960) and adapted for regulating the third portion of the air (111) to the additional first stage air-gas mixer (910).

9. The two-stage air-gas mixing unit of claim 8, wherein the first restricting device (320) is adapted for regulating the first portion of the air (111) based at least on the type of the gas (119), and the second restricting device (920) is adapted for regulating the third portion of the air (111) based at least on the type of the gas (119).

10. The two-stage air-gas mixing unit of any one of claims 6 to 9, wherein the additional airflow channel (260) and the second additional air flow channel (960) are arranged hydraulically parallel to each other and adapted for providing different quantities of the flow of the air (111) to the first stage air-gas mixer (210) and to the additional first stage air-gas mixer (910), respectively.

11. The two-stage air-gas mixing unit of any one of claims 6 to 10, wherein the additional airflow channel (260) and the second additional air flow channel (960) are operable independent of each other.

12. The two-stage air-gas mixing unit of claim 1, further comprising:
an additional air inlet (513) that is adapted for providing the air (111) directly to the first stage air-gas mixer (210).

13. The two-stage air-gas mixing unit of any one of the preceding claims, further comprising:
a fan (770) that is arranged upstream of the air flow channel (250) and adapted for propagating the flow of the air (111) towards the first and second stage air-gas mixers (210, 220).

14. The two-stage air-gas mixing unit of any one of claims 1 to 12, further comprising:
a fan (270) that is arranged downstream of the second stage air-gas mixer (220) and adapted for propagating the combustible air-gas mixture (130) towards the air-gas outlet (132).

15. The two-stage air-gas mixing unit of any one of the preceding claims, further comprising:
a gas sensor (310) that is arranged upstream of the gas valve (240) and adapted for detecting the type of the gas (119).

16. An air-gas mixture burning appliance (100) comprising:

an air inlet (105) for providing air (111);

a gas inlet (107) for providing gas (119);

a burning unit (120) for burning a combustible air-gas mixture (130); and

the two-stage air-gas mixing unit (110) of any one of the preceding claims.

Drawing