HYBRID DUCT DEVICE FOR HEATING AN AIR FLOW

Abstract

A hybrid device for heating an air flow, with duct, provided with a main direction and characterized by the presence of an electric heater for the preheating of the process air, with a gas burner for the completion of the heating of the process air and with a control system for the management of the parameters of interest and for the optimization of the process.

Description

The present invention relates to a hybrid duct device for heating a process air flow to an optimal temperature.

In the industrial realm, hot air is used in numerous applications, exploiting the different temperatures thereof that may be obtained. Hot air can come from the environment or derive from a process: in this case, it can be preheated and can have characteristics such as a high moisture and carbon dioxide content and low oxygen content; the steam content and other elements depend on the upstream processes.

To date, the systems commonly used to heat large amounts of air are fossil fuel burners, which allow high-temperature exhaust gas to be obtained; these are duct devices, in which one or more gas burners are arranged in line with the process air flow.

This type of device, starting from a flow of incoming process air, yields an air flow heated to a given outlet temperature. A typical heating duct is made up of a metal casing inside which one or more burners and a gas supply line with associated delivery valves are located.

Thanks to the combustion of the supply gas, high-temperature exhaust gas is obtained: the amount of heat released by the burner is proportional to the length and design of the burner itself. In order to obtain the desired temperature of the air flow, the heated gas is mixed and appropriately diluted by the process air flow so as to obtain the desired temperature, suitable for its use.

This class of systems, however, shows some limitations and critical aspects: in particular, these are very costly processes from the standpoint of gas consumption; moreover, they release a large amount of polluting carbon dioxide as a waste product.

Alternatively, in the sector of burners, there are known hybrid systems which comprise two distinct heating chambers, separated, for example, by a metal wall. Such prior art devices are configured to heat process air by means of a process called indirect heating.

In detail, the first chamber is configured to heat the process air according to a first heating mode, preferably by means of an electric heater; the second chamber, separate from the first, is configured to generate heat by means of a gas burner or another type of device, and to exchange heat with the first chamber through the separating wall. If a gas burner is present, the second chamber will have its own channel for discharging the exhaust gas produced during combustion. In other words, the exhaust gas and the process air are not mixed during the phases of heating the air.

This second type of prior art heaters, however, could certainly be improved from the standpoint of air heating efficiency. In fact, the physical separation between the two chambers renders the heat exchange between the first and second chambers poorly efficient, making the process costly from the standpoint of the time consumed and of the resources necessary.

The aim of the present invention is to improve the currently available heating devices.

The object of this invention is a hybrid device for heating a process air flow to an optimal temperature: the device is a heating duct, whose main elements are:

• • an electric heater;
  • at least one gas burner;
  • a control system for managing the electric component and the gas component. Essentially, the object of the present invention combines a gas burner with an electric heater positioned upstream of the same: the two systems, placed in series, allow a hybrid air heating solution to be obtained.

The invention in question has the advantage of preheating the process air by means of an electric heater, before it reaches the gas burners, in order to decrease the amount of gas necessary to obtain the desired heating.

A further advantage of the present invention is that, thanks to the lower gas consumption, it is possible, accordingly, to decrease the amount of carbon dioxide released by the process as a waste product, thus making the system less polluting.

Moreover, thanks to the presence of a control system and a management algorithm, it is possible to modulate the parameters related to the carbon dioxide emissions and fuel consumption.

A further 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 an eye to saving energy and reducing pollution, and to choose fully electric or fully gas air heating to satisfy particular production process requirements.

Moreover, the hybrid heating duct is an easy-to-use device, thanks to the “plug-and-play” usage mode.

Finally, the present invention makes it possible to use a casing already present in a production line by replacing the main components, in particular the burner modules, and inserting an electric heater with a design that is compatible with the available space; by working on these two elements, it is possible to change the type of heating of the air flow without increasing the space occupied by the heater, in particular the length occupied. The already existing devices operating in a production line can be converted without impacting on the space occupied by them; this characteristic can also be exploited where it is desired to adapt a completely new hybrid system in the presence of particular spatial limitations. In other words, the device according to the present invention makes it possible to avoid increasing the required dimensions already applied by the commonly used air heating systems: this aspect of the invention is particularly advantageous, above all for production lines of industrial processes in which there are spatial limitations and in which it is not possible to move machinery or reorganise the space dedicated to the heating system.

The following description aims to detail elements and features, as well as further advantages, of two embodiments of the invention in question; the appended figures, together with the description, illustrate these embodiments of the invention by way of non-limiting example.

FIG. 1 shows a diagram relating to a first embodiment of the invention.

FIG. 2 shows a diagram relating to a second embodiment of the invention.

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 can comprise a fan (F), if not present elsewhere in the plant, arranged upstream of the inlet zone (C), which is arranged so as to introduce an air flow along the duct (1) from the inlet zone (C) towards the outlet zone (H).

Considering the elements introduced, 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) for the heated gas.

The device further comprises an electric heater (2), located inside the duct (1a), and a gas burner (3), likewise located inside the duct (1a) downstream of the electric heater (2) with respect to the direction of the air flow.

The air flow passes through the duct (1a) from the inlet zone (C) to the outlet zone (H). The air initially meets the electric heater (2) and subsequently the gas burner (3) for the final heating of the air flow: the electric heater (2) advantageously brings about a preheating of the air, so that the latter, upon reaching the burner (3), requires a smaller contribution of heat, and hence a lower consumption of gas, in order to be brought to the desired temperature. The gas burner (3) is supplied by a gas line (4) provided with opening and closing valves (5) for controlling the delivery of gas; safety sensors and flame detection sensors are also present. Depending on type, the device can have a single burner (3) or a number of burners (31) placed inside a combustion chamber (7). The combustion of the gas causes the air flow to be heated through the mixing of the exhaust gas produced by combustion by the burner (3) with the incoming air flow prior to the exit from the combustion chamber (7).

In other words, the heating device according to the present invention is configured to bring about a direct heating of the air flow using the electric heater (2) and the gas burner (3) inside a same chamber, delimited by the casing (1).

Unlike prior art heating devices, that is, unlike the devices configured for indirect heating, the heating device according to the present invention is configured to bring about the mixing of the process air preheated by the electric heater (2) with the exhaust gas produced by the burner (3).

Advantageously, this mixing of preheated process air and exhaust gas brings about a heating of the process air that is more rapid, less costly, and thus more efficient compared to the prior art heating devices.

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 outgoing flow will have the desired temperature, usable in the subsequent phases along the line.

The preheating process according to the invention has, in addition to the others mentioned above, the advantage of reducing the length of the flame coming out of the burner (3): the reduction of the flame length advantageously allows for increasing the stability of the flame itself and, simultaneously, decreasing the length of the combustion chamber, thus limiting the size of the device.

Advantageously, the gas burner (3) comprises a plurality of combustion modules (31), associated with each other according to a predetermined configuration.

Among the numerous advantages that will be better illustrated below, the use of a plurality of combustion modules makes it possible to convert, in a very effective manner, a gas heating device having a critical length (L) and a total heating power (P), into a hybrid heating device which substantially maintains the same total heating power (P) and the same critical length (L).

Essentially, 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 of said heating power (Pe) and said nominal heating power (Pn) is equal to said total heating power (P), it is possible to carry out the following steps:

• • to reduce the nominal heating power (Pn) of the burner modules (31) by approximately (Pe/P) ⅔;
  • to increase the number (N) of burner modules (31) by 1/(1-(Pe/P)⅔); in order to maintain the desired critical length (L). This is because, as already pointed out, reducing the nominal heating power (Pn) of the combustion modules (31) means reducing, in practice, the length of the flame produced. In this manner, the total length defined by the electric heater (2) and the burner (3) can be made equivalent to the desired critical length (L).

In other words, considering a hybrid heater, the length of the electric heater (2) depends on the heating power of the electric component Pe, whereas the length of the combustion chamber (7) depends on the heating power of the combustion modules (31). It is thus possible to reduce the critical length (L) by reducing the heating power of the burner modules (31).

If:

• • 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; advantageously, it will be possible to reduce the nominal heating power of the burner modules (31) by approximately (Pe/P)⅔ and increase the number of gas burner modules by 1/(1-(Pe/P)⅔) compared to the corresponding non-hybrid solution, in order to maintain the same heating power (P) and the same critical length (L) of the previous non-hybrid gas burner.

Consequently, the use of combustion modules (31) allows the form of the burner to be adapted to numerous construction requirements. In particular, in order to obtain a given overall power of the burner (3), it is possible to use a certain number of combustion modules (31) with a reduced power, each of which emits a flame of a relatively limited length. A given overall power of the burner (3) can thus be obtained by a predetermined number of combustion modules (31), while reducing the length of the flame produced to below a limit length, established based on the length available for the casing (1). In other words, by placing several burners of a lower capacity side by side, it is possible to maintain the same heating power as a traditional burner, but with a shorter flame length. In this manner, a combustion chamber (7) of a shorter length is sufficient.

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 decreasing the spatial frequency of the holes on the surface of the burner (3).

By way of non-exclusive example, a practical way of how one can intervene on the burners is the following: by decreasing the diameter of the holes from 2.3 mm to 2 mm or increasing the distance between the holes from 6-7 mm to 8-10 mm, in order to pass from a capacity of 5 MW per m{circumflex over ( )}2 of the module section (measured in the direction of the process flow) to a capacity of 2-4 MW/m{circumflex over ( )}2; by then increasing the number of modules in parallel, it is possible to obtain the starting heating power with a shorter flame length.

The burner (3) comprising a plurality of combustion modules (31) can be configured to make space for the electric heater (2).

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 in such a way as to define spaces inside which the projections (21) of the electric heater (2) are accommodated. Very advantageously, the electric heater (2) can thus be positioned not only upstream of the burners (3), but also between the combustion modules (31) or around them, as indicated below in one of the possible embodiments.

When these modifications are adopted, the heating power of the system and the critical length (L) will remain unchanged compared to non-hybrid devices.

Advantageously, therefore, by suitably designing the electric component and the gas component, it is possible to find solutions applicable to any type of pre-existing casing (1) so as to facilitate the conversion of the supply system from gas to hybrid, thus favouring the adaptation of a less polluting type of duct heating, thanks to the introduction of the electric component, with all the already specified advantages of a hybrid type of supply.

For example, by exploiting the characteristics and processes just described, it is possible, very advantageously, to design the electric component and the gas component in such a way as to convert a pre-existing gas duct heater within a production line, without having to replace the casing (1) thereof or maintaining the same critical length (L) as the non-hybrid system. The standard combination of an electric component and a gas component, according to the heaters presently used, necessarily implies an increase in the space required by the heater. According to the method in question, by contrast, it is possible to carry out two actions: to reduce the length of the combustion chamber (7), and simultaneously modify the design of the electric heater (2).

The desired outlet temperature of the device according to the present invention is obtainable thanks to a control system (8) provided with an algorithm for optimising the energy demands. The control module is substantially configured to regulate the power delivered by the electric heater (2) and the power delivered by the burner (3). For this purpose, the control module (8) is connected to the 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) in order to regulate the opening thereof and vary, accordingly, the flow rate of the gas sent to the burner (3).

The control module (8) is also connected to one or more functional sensors configured to regulate, directly or indirectly, operating data related to one or more of the following heating parameters:

• • the amount of carbon dioxide produced;
  • the fuel consumption;
  • the electricity consumed;
  • the gas burner power and the electric heater power.

By means of an algorithm, the control module (8) receives as input the operating data coming from the functional sensors, carries out 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).

The control module is thus able to modulate parameters such as the amount of carbon dioxide produced, the fuel consumption, the electricity consumed, the gas burner power and the electric heater power. Advantageously, the control module (8) is also configured to receive as input economic parameters, such as gas and energy price data: by making this information available to the algorithm, it is possible to modulate the use of the two energy sources so as to obtain the combination with the highest energy savings.

Finally, the algorithm of the aforesaid control system (8) makes it possible not only to optimise the process, thereby minimising the production of carbon dioxide and consumption of gas, but also to exploit the hybrid nature thereof: the air can be heated by simultaneously activating the electric heater and the gas burner, modulating the percentage of activation, or activating only the electric heater or only the gas burner, to satisfy specific requirements and deal with particular conditions under which the heating device can be found.

A control panel (9), connected to the control module (8), allows for choosing between the following delivery modes, according to the set parameters and process needs:

• • 1-BOOSTER: 100% gas burner and 100% electric heater
  • 2-E-COL: gas at the minimum necessary power
  • 3-ELE-ENERGY SAVING: gas up to 100% of the power, electricity if necessary
  • 4-Custom: percentage of gas and percentage of electric set as desired by the operator
  • 5-Fully Gas: from 0% to 100% of gas burner power, no electric heater
  • 6-Fully Electric: from 0% to 100% of electric heater power, no gas burner 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 the introduction into the duct (10) of a further flow of combustion air, to be supplied to the burner together with the fuel in order to heat the process air already preheated beforehand by the electrical heating elements.

Considering the main direction (X), the heating of the process air according to this embodiment is carried out by following the steps described here: the process air is introduced into the duct and undergoes a first heating by means of the electric heater (2); the preheated air is then conveyed towards the combustion chamber (10), where one or more burner modules (3) supplied by the gas line (4) and the combustion air of the second fan (11) bring about the combustion of the gas itself, with a 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.

This embodiment, thanks to the further supplement of air, is particularly convenient and advantageous in cases where the process air flow is low in oxygen or has high levels of moisture.

In other possible embodiments, in particular in the embodiments of the heating device adapted to a pre-existing casing (1), the electric heater (2) can also be totally or partially interposed between the combustion air supply channel (10) and the combustion chamber (7) where burner modules are arranged in parallel (3) and suitably dimensioned so as to reduce the capacity of each, while maintaining the overall heating power. The heating elements, as illustrated previously, can be designed to optimise the available space between the burners, thus enabling the insertion of the electric heater (2) designed ad hoc for the space available inside the specific duct heater.

In the latter configuration, the velocity of the process flow increases at the level of the burners, thus bringing about a better combustion, with a lower emission of carbon dioxide and a shorter flame length.

The second embodiment, illustrated in FIG. 2, is endowed with a control module (8) that is substantially similar to the one already described in relation to the embodiment in FIG. 1. In the case of the second embodiment, the control module (8) is also connected to the second fan (11) in order to regulate the flow rate of the air introduced into the combustion air supply chamber (10).

Claims

1. A duct heating device for process air flow, comprising a casing, which delimits a duct provided with a main direction, an electric heater, a gas burner, wherein the casing has a first end, arranged in an inlet zone, and a second end, arranged in an outlet zone of the heated gas, and wherein the casing, has a critical length measured parallel to the main direction-as a distance between the ends, wherein, inside the duct, the electric heater is located upstream of the burner with respect to the air flow and adjacent to the burner.

2. The heating device according to claim 1 comprising a plurality of combustion modules associated with each other according to a predetermined configuration, wherein the power of each combustion module is established so that, for a given overall power from the burner-, the length of the flame produced by the burner is less than a limit length.

3. The heating device according to claim 1 provided with an auxiliary air supply.

4. The heating device according to claim 1, wherein the chamber is located between the heater and the gas burner.

5. The heating device according to claim 1, wherein the electric heater is partially or totally interposed between the chambers and the gas burner.

6. The heating device according to claim 1, provided with a control system 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 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 claim 1, 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 and a total heating power into a hybrid heating device which maintains substantially the same total heating power and the same critical length, wherein:

the gas heating device comprises a casing, delimiting a duct (provided with a main direction, a gas burner comprising a number of combustion modules having a nominal heating power;

wherein the casing has a first end, arranged in an inlet zone, and a second end, arranged in an outlet zone of the heated gas, and wherein the casing has a critical length measured parallel to the main direction as a distance between the ends; method comprising the following steps:

defining a heating power of an electric heater such that the sum between said heating power and said nominal heating power is equal to said total heating power;

reducing the nominal heating power of the burner modules by approximately (Pe/P)⅔;

increasing the number of burner modules by 1/(1-(Pe/P)⅔).