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(11) | EP 4 382 823 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | HYBRID DUCT HEATING DEVICE FOR AIRFLOW |
| (57) Hybrid device for heating an air flow, with duct, provided with a main direction
(X) and characterized by the presence of an electric heater (2) for the preheating
of the process air, with a gas burner (3) for the completion of the heating of the
process air and with a control system (8) for the management of the parameters of
interest and for the optimization of the process.
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[0001] The present invention relates to a hybrid duct device for heating a process air flow to an optimal temperature.
[0002] In the industrial field, the hot air is used in numerous applications taking advantage of the different obtainable temperatures. The hot air can come from the environment or result from a process: in this case, it can be preheated and can have characteristics such as a high humidity and carbon dioxide content and low oxygen content; steam content and other elements depend on the upstream processes.
[0003] To date, the systems commonly used to heat large quantities of air are fossil fuel burners, which allow to obtain high temperature exhausted gas; these are duct devices, in which one or more gas burners are arranged in line with the process air flow.
[0004] This type of device, starting from a flow of inlet process air, returns a flow of heated air at a certain outlet temperature. A typical heating duct is composed of a metal casing inside which one or more burners are located and a gas supply line with relative delivery valves.
[0005] High temperature exhausted gas is obtained thanks to the combustion of the supply gas: the amount of heat released by the burner is proportional to the length and to the design of the burner itself. To obtain the desired temperature of the air flow, the heated gas is mixed and suitably diluted by the process air flow, so as to obtain the desired temperature, functional to its use.
[0006] This class of systems, however, has some limitations and criticalities: in particular, they are very onerous processes from the point of view of gas consumption; in addition, they release a large amount of polluting carbon dioxide, as a waste product.
[0008] This invention relates to a hybrid device for heating a process air flow to an optimal temperature: said device is a heating duct, the main elements of which are:
- an electric heater;
- at least one gas burner;
- a control system for the management of the electrical component and of the gas component. In essence, the object of the present invention combines a gas burner with an electric heater positioned upstream thereof: the two systems, placed in series, allow to obtain a hybrid air heating solution.
[0009] The invention in question has the advantage of preheating the process air by means of an electric heater, before it reaches the gas burners, so as to decrease the amount of gas necessary to obtain the desired heating.
[0010] A further advantage of the present invention is that, thanks to the lower gas consumption, it is possible to consequently decrease the amount of carbon dioxide released from the process as a waste product, thus making the system less polluting.
[0011] In addition, thanks to the presence of a control system and of a management algorithm, it is possible to modulate the parameters relating to the carbon dioxide emissions and to the fuel consumption.
[0012] Another advantage of the control system is the possibility of exploiting the hybrid nature of the air heating device: it is possible both to combine the two sources, with a view to energy saving and less pollution, and to choose totally electric or totally gas air heating, to meet particular needs of the production process.
[0013] The hybrid heating duct is also an easy-to-use device, thanks to the "plug and play" mode of use.
[0014] Finally, the present invention makes it possible to use a casing already present in a production line, replacing the main components thereof, in particular the burner modules, and inserting an electric heater with a design compatible with the available space; by working on these two elements, it is possible to change the type of air flow heating, without increasing the space occupied by the heater, in particular the occupied length. The already existing devices operating in a production line can be converted without affecting the space they occupy; this feature can also be exploited if it is wished to adapt a hybrid system ex novo, in the presence of particular spatial limitations. In other words, the device according to the present invention allows not to increase the dimensions required and already used by the commonly used air heating systems: this aspect of the invention is particularly advantageous, especially for those production lines of the industrial processes in which spatial limitations are present and in which it is not possible to move machinery or reorganize the space dedicated to the heating system.
[0015] The following description is intended to detail elements and characteristics, as well as further advantages of two embodiments of the invention in question; the attached figures, together with the description, illustrate by way of non-limiting example, such embodiments of the invention.
[0018] The air heating device according to the first embodiment of the present invention extends along a main direction (X). The device comprises a duct (1a), contained in a casing (1), which has an inlet zone (C) and an outlet zone (H). The device may comprise a fan (F), if not present elsewhere in the plant, arranged upstream of the inlet zone (C), which is arranged to introduce an air flow along the duct (1) from the inlet zone (C) towards the outlet zone (H).
[0019] Considering the introduced elements, it is possible to define a critical length (L), which corresponds to the distance between a first end (C1) of the inlet zone (C), and a second end (H1) of the outlet zone (H) of the heated gas. The device further comprises an electric heater (2), located inside the duct (1a), and a gas burner (3), also located inside the duct (1a) downstream of the electric heater (2) with respect to the direction of the air flow.
[0020] The air flow runs through the duct (1a) from the inlet zone (C) to the outlet zone (H). The air first meets the electric heater (2) and then the gas burner (3) for the final heating of the air flow: the electric heater (2) advantageously causes the preheating of the air, so that this, once the burner (3) is reached, requires a lower heat input, and therefore a lower gas consumption, in order to be brought to the desired temperature. The gas burner (3) is fed by a gas line (4), provided with opening and closing valves (5) for controlling the gas delivery; there are also safety sensors and flame detection sensors. Depending on the type, the device may have a single burner (3) or more burners (31) placed inside a combustion chamber (7). The combustion of the gas causes the heating of the air flow by mixing with it before the outlet. In the combustion chamber (7) the gases exiting from the burners are cooled by the air flow to a lower temperature: at the end of the duct (H) the outflow will have the desired temperature, which can be used in the subsequent steps of the line.
[0021] The preheating process according to the invention in question has, in addition to the others mentioned above, the advantage of reducing the length of the flame exiting from the burner (3): the reduction of the flame length advantageously allows to increase the stability of the flame itself and, at the same time, to decrease the length of the combustion chamber, thus containing the dimensions of the device.
[0022] Advantageously, the gas burner (3) comprises a plurality of combustion modules (31), associated with each other according to a predetermined configuration.
[0023] Among the numerous advantages that will be better illustrated below, the use of a plurality of combustion modules allows, in a very effective manner, to convert a gas heating device, having a critical length (L) and a total heating power (P), into a hybrid heating device which maintains substantially the same total heating power (P) and the same critical length (L).
[0024] In essence, given a nominal heating power (Pn) of the combustion modules (31), and given a heating power (Pe) of the electric heater (2) such that the sum between said heating power (Pe) and said nominal heating power (Pn) is equal to said total heating power (P), it is possible to perform the following steps:
- reducing the nominal heating power (Pn) of the burner modules (31) by approximately (Pe/P)2/3;
- increasing the number (N) of burner modules (31) by 1/(1-(Pe/P)2/3);
[0025] In other words, considering a hybrid heater, the length of the electric heater (2) depends on the heating power of the electric component Pe, while the length of the combustion chamber (7) depends on the heating power of the combustion modules (31). It is therefore possible to reduce the critical length (L) by reducing the heating power of the burner modules (31).
[0026] In the event that:
- the maximum heating power of the hybrid system coincides with P, i.e. the maximum heating power of the gas burner, i.e. of a burner without an electric heater (2);
- Pe represents less than 60% of P;
[0027] Consequently, the use of combustion modules (31) makes it possible to adapt the shape of the burner to numerous construction needs. In particular, in order to obtain a given overall power of the burner (3), it is possible to use a number of combustion modules (31) of reduced power, each of which emits a flame of relatively small length. A given overall power of the burner (3) can thus be obtained from a predetermined number of combustion modules (31), but by reducing the length of the flame produced below a limit length, established on the basis of the length available for the casing (1). In other words, by juxtaposing multiple burners of lower capacity, it is possible to maintain the same heating power as a traditional burner, but with a shorter flame length. In this way a combustion chamber (7) of shorter length is sufficient.
[0028] The reduction of the power of each module (31) can be obtained, for example, but not exclusively, by reducing the diameter of the holes of the burners and by decreasing the spatial frequency of the holes on the surface of the burner (3).
[0029] A practical way, by way of not exclusive example, of how to intervene on the burners is as follows: by decreasing the diameter of the holes from 2.3mm to 2mm or by increasing the distance between the holes from 6-7mm to 8-10mm, in order to pass from a capacity of 5MW per m^2 of section of the module (measured in the direction of the process flow) to a capacity of 2-4 MW/m^2; then increasing the number of modules in parallel makes it possible to obtain the starting heating power with a shorter flame length. The burner (3) comprising a plurality of combustion modules (31) may be configured to make room for the electric heater (2).
[0030] In a particularly advantageous embodiment, the electric heater (2) comprises a series of projections (21), which extend substantially parallel to the main direction (X). The combustion modules (31) can be arranged so as to define spaces within which the projections (21) of the electric heater (2) are housed. In a very advantageous way, the electric heater (2) can therefore be positioned not only upstream of the burners (3), but between or around the combustion modules (31), as indicated below in one of the possible embodiments.
[0031] By adopting these modifications, the heating power of the system and the critical length (L) remain unchanged compared to the non-hybrid devices. Advantageously, therefore, by adequately designing the electrical component and the gas component, it is possible to find solutions applicable to any type of pre-existing casing (1), so to facilitate the conversion of the supply system from gas to hybrid, thus favouring the adaptation of a less polluting type duct heating, thanks to the introduction of the electrical component, with all the advantages already indicated of a hybrid supply type.
[0032] For example, by exploiting the characteristics and the processes described above, it is possible, in a very advantageous way, to design the electrical component and the gas component in such a way as to convert a heater with a pre-existing gas-supplied duct, without having to replace the casing thereof (1) or maintaining the same critical length (L) of the non-hybrid system, within a production line. The trivial union of electrical component and gas component, according to the currently used heaters, necessarily implies an increase in the space required by the heater. According to the method in question, however, it is possible to perform two actions: to reduce the length of the combustion chamber (7) and, at the same time, to modify the design of the electric heater (2).
[0033] The desired temperature in output from the device according to the present invention is obtainable thanks to a control system (8), provided with an algorithm to optimize the energy requirements. The control module is substantially arranged to regulate the power delivered by the electric heater (2) and the power delivered by the burner (3). To this end, the control module (8) is connected to the electric power supply of the electric heater (2) and to the gas supply of the burner (3). For example, the control module (8) is connected to the opening and closing valve (5) to regulate the opening thereof and consequently vary the gas flow rate sent to the burner (3).
[0034] The control module (8) is also connected to one or more functional sensors arranged to regulate, directly or indirectly, operational data, relating to one or more of the following heating parameters:
- the amount of carbon dioxide produced;
- the fuel consumption;
- the electric energy consumption
- the power of the gas burner and the power of the electric heater.
[0035] Through an algorithm, the control module (8) receives the operational data coming from the functional sensors in input, performs a processing of the functional data and produces a command signal configured to regulate the power delivered by the electric heater (2) and the power delivered by the burner (3).
[0036] The control module is then able to modulate parameters such as the amount of carbon dioxide produced, the fuel consumption, the electric energy consumed, the power of the gas burner and the power of the electric heater. Advantageously, the control module (8) is also configured to receive economic parameters in input, such as the gas and energy price data: by making this information accessible to the algorithm, it is possible to modulate the use of the two energy sources in order to obtain the combination with greater economic savings.
[0037] Finally, the algorithm of the aforementioned control system (8) allows not only to optimize the process, minimizing the production of carbon dioxide and the consumption of gas, but also to take advantage of its hybrid nature: the air can be heated by simultaneously activating the electric heater and the gas burner, modulating the percentage of activation, or by activating only the electric heater or only the gas burner, to meet specific needs and to face particular conditions in which the heating device can be involved. A control panel (9), connected to the control module (8), allows to choose between the following delivery modes, depending on the parameters set and the needs of the process:
- 1-BOOSTER: 100% gas burner and 100% electric heater
- 2-E-COL: gas at the minimum power required
- 3- ELE-ENERGY SAVING: gas up to 100% of power, electricity if necessary
- 4-Custom: percentage of gas and percentage of electric set at will by the operator
- 5- Fully Gas: from 0% to 100% of power of the gas burner, no electric heater
- 6- Fully Electric: from 0% to 100% of power of the electric heater, no gas burner
[0038] A second embodiment, represented in Fig. 2, shows the presence of a further supply channel (10) for the combustion air, interposed between the electric heater (2) and the burner modules (3): a second fan (11) allows to introduce into the duct (10) a further flow of comburent air, to be provided to the burner together with the fuel to heat the process air already pre-heated by the electrical resistors.
[0039] Considering the main direction (X), the heating of the process air according to this embodiment takes place by following the steps described herein: the process air is introduced into the duct and is subjected to first heating by means of an electric heater (2); the pre-heated air is then conveyed towards the combustion chamber (10), where one or more burner modules (3) supplied by the gas line (4) and by the combustion air of the second fan (11) cause the combustion of the gas itself, with consequent heating of the air flow. In the combustion chamber (7) the air heated by the electric heater is diluted by the combustion gases to obtain an outflow (H) at the desired working temperature.
[0040] This embodiment, thanks to the additional air supplement, is particularly convenient and advantageous in cases where the process air flow is low in oxygen or has high humidity levels.
[0041] In other possible embodiments, in particular in the forms of adaptation of the heating device to a pre-existing casing (1), the electric heater (2) can also be totally or partially interposed between the comburent air supply channel (10) and the combustion chamber (7) where burner modules are placed in parallel (3) suitably dimensioned to reduce the capacity of each, maintaining the overall heating power. The heating elements can, as illustrated above, be designed to optimize the space available between the burners, allowing the insertion of the electric heater (2) designed ad hoc for the space available inside the specific duct heater.
[0042] In the latter configuration, the speed of the process flow increases at the level of the burners, resulting in a better combustion, with lower emission of carbon dioxide and a shorter flame length.
[0043] The second embodiment, illustrated in figure 2, is provided with a control module (8) substantially analogous to that already described in relation to the embodiment of figure 1. In the case of the second embodiment, the control module (8) is also connected to the second fan (11), to regulate the air flow rate introduced into the comburent air supply chamber (10).
1. A duct heating device for process air flow, comprising a casing (1), which delimits
a duct (1a) provided with a main direction (X), an electric heater (2), a gas burner
(3), wherein the casing (1) has a first end (C1), arranged in an inlet zone (C), and
a second end (H1), arranged in an outlet zone (H) of the heated gas, and wherein the
casing (1) has a critical length (L) measured parallel to the main direction (X) as
a distance between the ends (C1, H1), characterized in that, inside the duct (1a), the electric heater (2) is located upstream of the burner
(3) with respect to the air flow and adjacent to the burner (3).
2. The heating device according to claim 1 comprising a plurality of combustion modules
(31) associated with each other according to a predetermined configuration, wherein
the power of each combustion module (31) is established so that, for a given overall
power from the burner (3), the length of the flame produced by the burner (3) is less
than a limit length.
3. The heating device according to claim 1 provided with an auxiliary air supply (10,
11).
4. The heating device according to claim 1, wherein the chamber (10) is located between
the heater (2) and the gas burner (3).
5. The heating device according to claim 1, wherein the electric heater (2) is partially
or totally interposed between the chambers (10) and the gas burner (3)
6. The heating device according to claim 1 or 2 provided with a control system (8) and
an integrated algorithm, for the direct or indirect regulation of heating parameters.
7. The heating device according to claim 6 wherein the heating parameters regulated by
the control system are one or more of the following: amount of carbon dioxide produced,
fuel consumption, electricity consumption, gas burner power and electric heater power.
8. The heating device according to claim 6 provided with a control panel (9) connected
to the control module, which allows the selection of the parameters of interest and
of the delivery modes.
9. The heating device according to one or more of the preceding claims, configured to
operate in electric-gas hybrid mode, in fully electric mode and in fully gas mode.
10. A method for converting a gas heating device having a critical length (L) and a total
heating power (P) into a hybrid heating device which maintains substantially the same
total heating power (P) and the same critical length (L), wherein:
- the gas heating device comprises a casing (1), delimiting a duct (1a) provided with a main direction (X), a gas burner (3) comprising a number (N) of combustion modules (31) having a nominal heating power (Pn);
- wherein the casing (1) has a first end (C1), arranged in an inlet zone (C), and a second end (H1), arranged in an outlet zone (H) of the heated gas, and wherein the casing (1) has a critical length (L) measured parallel to the main direction (X) as a distance between the ends (C1, H1);
the method comprising the following steps:- defining a heating power (Pe) of an electric heater (2) such that the sum between said heating power (Pe) and said nominal heating power (Pn) is equal to said total heating power (P);
- reducing the nominal heating power (Pn) of the burner modules (31) by approximately (Pe/P)2/3;
- increasing the number (N) of burner modules (31) by 1/(1-(Pe/P)2/3).