Burner unit, furnace and method of operation

Abstract

The invention relates to a burner unit (23) for a furnace, in particular a continuous furnace, tunnel furnace or the like, a furnace (13) and a method for operating a furnace, wherein the burner unit has at least two burners (14) designed for the combustion of a fuel gas, wherein the burner unit has a gas line and an air line (15) for supplying the burners with fuel gas, wherein the burner unit has at least one gas metering valve in the gas line and at least one air metering valve (21) in the air line, wherein the gas metering valve and the air metering valve are controllable by means of a common control device, wherein the gas metering valve is a solenoid valve and the air metering valve is a solenoid valve (25, 26).

Description

[0001] The invention relates to a burner unit for a furnace, in particular a continuous furnace, tunnel furnace, chamber furnace, bogie hearth furnace or the like, as well as a furnace and a method for its operation, wherein the burner unit has at least two burners which are designed to burn a fuel gas, wherein the burner unit has a gas line and an air line for supplying the burners with fuel gas, wherein the burner unit has at least one gas metering valve in the gas line and at least one air metering valve in the air line, wherein the gas metering valve and the air metering valve are controllable by means of a common control device, wherein the gas metering valve is a solenoid valve.

[0002] Such burner units or furnaces with burner units are well known in the art. In continuous furnaces or tunnel furnaces, a material to be treated, for example, ceramic products, is moved through the furnace continuously or periodically at time intervals; in chamber furnaces or bogie hearth furnaces, the burner output can be adjusted. The material to be treated is exposed to a predefined temperature profile, for example, in designated zones of the furnace for preheating, heating, and cooling, or the temperature profile is created solely in one zone of the furnace. So-called gas burners are used as burners. The burners are fuel dosing devices that are self-ignited at permanently prevailing temperatures above an ignition limit temperature. A burner unit and a method for operating a furnace with the features of the preamble of claim 1 and claim 9, respectively, are known from US 2016 / 348904 A1.

[0003] Since furnaces for the mass production of goods are comparatively large, a plurality of burners is always required to achieve the required temperature within the furnace. The burners are arranged in a burner unit at a designated position on the furnace; the burner unit with the burner remains fixed to the furnace as the material is moved relative to the burners. A furnace can be constructed with a plurality of burner units, each of which, in turn, contains a plurality of burners. Each of the burner units has a gas line and an air line to supply the respective burner with a fuel gas. Since the material composition of the air within the furnace is uncertain, gas is always introduced into the furnace via the respective burner together with air.This prevents incomplete combustion of the gas inside the furnace due to a lack of oxygen, which could have a detrimental effect on the product being produced, and thus creates a risk of explosion.

[0004] To meter the gas or fuel gas via the burner in the furnace, a gas metering valve can be provided on the gas line, which is controlled by a control device. The gas metering valve can be a solenoid valve. Such solenoid valves are known, for example, from EP 2 192 336 and are designed with a displaceable piston arranged in a valve housing, which blocks two chambers from one another and can be actuated by means of an electromagnet. The gas can be metered to the burner by actuating the piston. An air metering valve can be provided in the air line, which can also be controlled by the control device. The air metering valve can be designed as an actuatable flap, for example driven by a servo motor or pneumatically. Depending on the amount of fuel gas required, the control device can open or close the flap in the air line.into a partially open position so that a sufficient amount of air required for complete combustion can be supplied to the burner when fuel gas is introduced into the furnace for combustion. A disadvantage of the furnaces described above, however, is that their operation is expensive due to the constantly rising cost of gas.

[0005] The present invention is therefore based on the object of proposing a burner unit, a furnace and a method for operating a furnace with which cost-effective operation is possible.

[0006] This object is achieved by a burner unit having the features of claim 1, a furnace having the features of claim 8 and a method having the features of claim 9.

[0007] The burner unit according to the invention for a furnace, in particular a continuous furnace, tunnel furnace, chamber furnace, bogie hearth furnace or the like, has at least two burners which are designed to burn a fuel gas, wherein the burner unit has a gas line and an air line for supplying the burners with fuel gas, wherein the burner unit has at least one gas metering valve in the gas line and at least one air metering valve in the air line, wherein the gas metering valve and the air metering valve are controllable by means of a common control device, wherein the gas metering valve is a solenoid valve, and wherein the air metering valve is also a solenoid valve.

[0008] The gas metering valve and the air metering valve are controllable by the control device, so that the opening and closing of the gas metering valve and the air metering valve can be controlled via the control device. The fact that the air metering valve and the gas metering valve are each solenoid valves makes it possible to coordinate the opening and closing of the gas metering valve and the air metering valve relatively precisely. This allows the opening and closing to occur essentially synchronously.

[0009] This is not the case with the prior art, particularly when a different type of valve, such as a flap with a servomotor or a pneumatic drive, is used as the air dosing valve. In this case, operating costs are comparatively high and actuation of the valve in question is comparatively slow, so synchronization of the gas dosing valve and the air dosing valve is not easily possible. Because the gas dosing valve and the air dosing valve can now be opened and closed synchronously, energy can be saved. This results from the fact that the volume of air required for combustion can now be metered into the furnace with relative precision. When using a different type of valve for the air dosing valve, a larger volume of air regularly enters the furnace than would be necessary to ensure complete combustion of the gas.Therefore, according to the state of the art, air is continuously introduced into the furnace during rapid opening and closing of the gas metering valve, since an air damper, for example, operated by a servomotor as an air metering valve, can only be operated comparatively slowly. However, since the air drawn in from the surroundings of a furnace has a significantly lower temperature than the atmosphere inside a furnace, the air introduced into the furnace must be heated, which consumes energy and thus gas. If more air is introduced into the furnace than needed, this air must also be heated accordingly, which in turn requires a larger volume of gas.Because the solenoid valve allows the air dosage in the furnace to be adjusted more precisely to the amount of gas introduced into the furnace, the overall amount of gas consumed can be reduced, which can result in significant cost savings during continuous operation of the furnace.

[0010] The burner unit can comprise a control device of the control apparatus, which can be designed to synchronize a respective operating state of the gas metering valve and the air metering valve. The control device and the control apparatus can, for example, be formed in a common structural unit, for example by a programmable logic controller, a computer with software executed thereon, or the like. Alternatively, however, the control device and the control apparatus can also be formed by two separate structural units, for example each by a computer. An operating state of the gas metering valve and the air metering valve is understood here to mean a position of the respective valve, open or closed. The control device can then synchronize the gas metering valve and the air metering valve such that they are either open or closed at essentially the same time.A slight advance and / or retardation of one of the two valves may be possible, for example, in a range of < 3 to 0.05 seconds. This ensures that no more air is introduced into the furnace than is required for complete combustion of the gas.

[0011] The gas line and the air line can branch to the respective burners, whereby the burners can be connected in parallel to the gas line and the air line. Branches can therefore be formed on the gas line and the air line, each from the gas line and the air line to the respective burners. This ensures that the burners are supplied evenly with gas and air. In principle, however, a series connection of burners to the gas line and / or air line would also be possible. The pressure in the respective lines can range from 1 bar to 3 bar.

[0012] According to the invention, the burner unit has a gas metering valve for each burner and an air metering valve assigned to the gas metering valve. If each burner is supplied with fuel gas via a dedicated gas metering valve and an air metering valve, the output of the burners can be individually adjusted. This allows a particularly uniform temperature distribution within the furnace. This also enables particularly precise metering of fuel gas. The burner unit can have a shut-off valve in the gas line and / or the air line for each burner and / or for the entire burner unit. For example, a shut-off valve can be provided in a branch of the gas line and / or the air line leading to the burner. The shut-off valve can be a manually operated valve.This makes it possible to easily replace a single burner if it should become defective, without having to shut off the entire gas line and the air line for all burners. However, the burner unit can have a central shut-off valve in the gas line and / or the air line for the entire burner unit, allowing the burner unit to be completely shut off.

[0013] The opening cross-section of the air dosing valve can be larger than the opening cross-section of the gas dosing valve. This means that a significantly larger volume flow of air can be metered via the air dosing valve than the volume flow of gas. This enables combustion in an essentially stoichiometric ratio. The cross-section of the gas line can also be significantly smaller than the cross-section of the air line. Furthermore, the pressure in the gas line can be significantly higher than the pressure in the air line. This also enables the use of a fan to suck in and convey the air in the air line, thus eliminating the need for compressed air, which would be expensive to provide.

[0014] The burner unit can have at least 3, 4, 5, 6, 7, 8, or more burners. Preferably, the burner unit can have an odd or even number of burners. The burner unit can be designed symmetrically with regard to the arrangement of the burners on the furnace.

[0015] The burner unit can be equipped with a fan for conveying air into the air duct or can be connected via the air duct to a central air distribution duct of a furnace. The fan can be arranged at one end of the air duct and draw in air from the area surrounding the furnace and blow it into or convey it into the air duct. A burner unit with a dedicated fan enables flexible arrangement of the burner unit on the furnace and its replacement without affecting other burner units in the furnace. Alternatively, the air duct can be connected to an air distribution duct, to which a similar fan is connected. The air distribution duct then makes it possible to convey air to the burners via a number of air ducts that branch off from the air distribution duct.

[0016] The furnace according to the invention, in particular a continuous furnace, tunnel furnace, chamber furnace, shuttle furnace, or the like, comprises at least one burner unit according to the invention. However, the furnace can also comprise a plurality of burner units, in particular burner units according to the invention or burner units of different types. For example, the furnace can have 5, 10, 15, 20, or more burner units. The burner units can be arranged above a furnace interior, for example, on a furnace or its ceiling, or on the side of a furnace or a furnace interior.

[0017] In the method according to the invention for operating a furnace, in particular a continuous furnace, tunnel furnace, chamber furnace, bogie hearth furnace or the like, a fuel gas is burned using at least two burners of a burner unit of the furnace, wherein the burners are supplied with the fuel gas via a gas line and an air line, wherein at least one gas metering valve in the gas line and at least one air metering valve in the air line are controlled by means of a common control device, wherein a regulating device of the control device opens and closes the gas metering valve and the air metering valve synchronously. The burner unit comprises the gas line, the air line, the gas metering valve, the air metering valve and the control device. For the advantages of the method according to the invention, reference is made to the description of the advantages of the burner unit according to the invention.

[0018] The operating state of the air dosing valve can be controlled based on the operating state of the gas dosing valve, for example, open or closed, as a reference variable. This makes it possible to always adjust the air requirement relatively precisely to the amount of gas blown into the furnace. For this purpose, the control device can, for example, comprise a PID controller. Alternatively, it would also be possible to operate the gas dosing valve and the air dosing valve in parallel or synchronously using the control device, without controlling the air dosing valve after the gas dosing valve.

[0019] The control device can regulate the fuel gas in a stoichiometric ratio. Accordingly, the air dosing valve can then meter the exact amount of air required for stoichiometric combustion into the gas. Excess air introduced via the burners, which would then have to be unnecessarily heated inside the furnace, is then eliminated. Burners in large-capacity furnaces do not always have the task of introducing as stoichiometric a fuel gas or fuel gas mixture as possible into the furnace chamber. This is because the basic operating mode of the furnace always means that there is sufficient air available in the furnace chamber. However, it cannot always be fully utilized for combustion. The burner air therefore serves more of a role than simply covering areas where oxygen is depleted, contributing to the cooling of the burner lances and being available as a premix with the fuel gas.

[0020] The control device can control the gas metering valve based on a request for a burner output and / or a furnace temperature as a reference variable of the control device. Thus, the burner output and / or the furnace temperature can be processed by the control device based on a specification from the control device. A controlled variable can be determined, for example, by means of a sensor, in particular a temperature sensor, of the control device. In addition to this control loop, the control device can also comprise a plurality of control loops, for example, cascaded control loops and / or control loops for the burner unit and individual burners of the burner unit.

[0021] Opening and closing can occur at a rate of at least 50 cycles / minute, preferably 100 cycles / minute, particularly preferably 200 cycles / minute, up to 400 cycles / minute. The opening and closing of the gas dosing valve and the air dosing valve can therefore occur comparatively quickly. This rapid cycle is only possible through the use of solenoid valves. One cycle can be at least 50 ms. Other types of valves, for example those with an actuatable flap, would be hardly suitable for this purpose and wear out comparatively quickly compared to solenoid valves, which would require costly repairs. Furthermore, it has been shown that this cycle can achieve particularly strong turbulence of the fuel gas within the furnace and thus a more even combustion. The resulting more uniform temperature distribution within the furnace leads to improved quality of the material treated in the furnace.This allows a more even firing result to be achieved with ceramics, for example.

[0022] The control device can initiate a sequence of opening and closing cycles when a lower furnace temperature is undershot and can end the sequence of cycles when an upper furnace temperature is exceeded, wherein the control device can preferably regulate burner output by varying cycle intervals and / or cycle lengths. Thus, a respective burner can be started up by executing the sequence of cycles. A cycle can have an unchanged length. When the respective burner is switched off, the sequence of cycles is ended. The respective burners can be started up when the control device detects the lower furnace temperature, and switched off when the control device detects the upper furnace temperature. The lower furnace temperature and the upper furnace temperature thus define a temperature range in which the furnace can be operated.By varying a clock frequency depending on a temperature setpoint, the temperature setpoints are only rarely exceeded or undershot in the event of exceptional disturbances.

[0023] Air at a temperature of below 100°C, preferably below 70°C, can be metered through the air metering valve, whereby a temperature of up to 400°C, preferably up to 700°C, particularly preferably up to 1,000°C or higher can be achieved in the furnace. Because air that is comparatively cold compared to the temperature in the furnace is metered through the air metering valve, it is possible to keep the volume flow of the air metered through the air metering valve as small as possible. If, on the other hand, hotter air were used, the temperature difference between the air and an atmosphere in the furnace would be smaller, but due to the volume expansion of the hotter air, a much larger volume flow of air would have to be pumped into the furnace. The structural measures then required, as well as the energy costs for pumping, for example for fans, would exceed any potential gas savings or costs.A furnace can therefore be operated particularly cost-effectively in the specified ratios of air temperature and temperature of the furnace atmosphere.

[0024] Further embodiments of the method emerge from the descriptions of the features of the subclaims which refer back to device claim 1.

[0025] A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawings.

[0026] They show: Fig. 1: an embodiment of a burner unit according to the prior art; Fig. 2: another embodiment of a burner unit; Fig. 3: an embodiment of a solenoid valve in a sectional view; Fig. 4: a diagram showing the operating states of solenoid valves in a burner unit.

[0027] The Fig. 1 shows a burner unit 10 as is known from the prior art. The burner unit 10 is positioned on a furnace roof 11 of a tunnel 12 of a furnace 13 and is shown here in a plan view. The burner unit 10 essentially comprises burners 14, which are shown only symbolically here and by means of which a fuel gas is introduced into an interior of the furnace 13, which is not shown here, and burned there. The burner unit 10 also comprises an air line 15 and a gas line, which is not shown here and supplies the burners 14 with gas. The gas line has gas metering valves, each of which is assigned to a burner 14 and meter a volume flow of gas to the burners 14. The gas metering valves are formed by solenoid valves.

[0028] The burner unit 10 further comprises a fan 16, which is arranged at one end 17 of the air line 15 and draws in air from an environment 18 of the furnace 13 and conveys it into the air line 15. The air line 15 branches via branches 19 to the respective burners 14 so that the burners 14 can be supplied with air. Shut-off valves 20 are arranged in the respective branches 19 of the air line 15. These shut-off valves can be manually operated and enable the air line 15 to be completely shut off at this point. Furthermore, an air metering valve 21 is provided, which here is arranged essentially at the end 17 of the air line 15 downstream of the fan 16 in the direction of air flow. The air metering valve 21 is formed with a servomotor 22 and a flap (not shown in detail here) within the air line 15. The air dosing valve 21 can be used to adjust the volume flow of air supplied to the burners 14.By means of a control device of the burner unit 10 (not shown here), the air metering valve 21 is adjusted so that sufficient air is always available for complete combustion of the gas within the furnace 13.

[0029] The Fig. 2 shows a burner unit 23 in which, in contrast to the burner unit from Fig. 1 The fan 16 is connected directly to the air line 15 at the end 17 of the air line 15, without the interposition of a valve. On the other hand, an air metering valve 24, formed by a solenoid valve 25, is provided on the air line 15 or the branches 19 specifically for each burner 14. The air blown into the air line 15 via the fan 16 can then be directed to the respective burner 14 via the air metering valve 24.

[0030] The Fig. 3 shows, by way of example, a solenoid valve 26 which can be used for the burner unit 23. Depending on the size or line cross-section 27 of the solenoid valve 26, it can be used as an air metering valve or a gas metering valve. The line cross-section 27 is comparatively larger in an air metering valve than in a gas metering valve. The solenoid valve 26 is designed with a valve housing 28 and an actuating device 29. The actuating device 29 comprises a piston 30 and an electromagnetic coil 31. The valve housing 28 forms a first chamber 32 and a second chamber 33, which serve for connection to media lines not shown here. In the exemplary embodiment, a preferred flow direction of a medium from the chamber 32 to the chamber 33 is provided, indicated by an arrow 34.Furthermore, a valve seat 35 is formed in the valve housing 28, which can be closed with a valve sealing device 36 arranged on a piston 30. The piston 30 is pressed against the valve seat 35 by means of a spring 37 with the valve sealing device 36, such that the solenoid valve 26 is closed. The solenoid valve 26 is opened by actuating the piston 30 by means of the electromagnetic coil 31 and thus by lifting the valve sealing device 36 from the valve seat 35. A gaseous medium can then flow from the first chamber 32 to the second chamber 33. The actuation can occur in a sequence of cycles by opening and closing the solenoid valve 26. The piston 30 has a bypass bore (not shown here) with a diameter of a few millimeters. Purge air flows through this bypass bore, which protects a burner mouth from overheating when the piston 30 is in the closed position.

[0031] The Fig. 4 shows a diagram with a first sequence 38 of cycles of opening and closing a gas metering valve, as it is in a burner unit according to the Fig. 2 is used, based on a temporal progression. A line 39 represents an open position 40 and a closed position 41 of the respective gas metering valve. Furthermore, a sequence 42 of cycles of opening and closing of an air metering valve according to the prior art, as is the case, for example, with the burner unit according to the Fig. 1 can be used. Opening and closing is only possible slowly here, so that during the closed position 41 of the gas metering valve, air can continue to flow through the air metering valve, thus allowing excess air to enter the interior of a furnace, which must be additionally heated to maintain the desired furnace temperature. Furthermore, a sequence 43 of cycles of opening and closing an air metering valve is shown, as is the case with the burner unit according to the Fig. 2 can be used. Here, the sequence of 43 cycles is synchronized with the sequence of 38 cycles to such an extent that an optimal amount of air for combustion is introduced into the furnace. Heating of excess air in the furnace is then no longer necessary, resulting in significant cost savings.

Claims

1. A burner unit (23) for a furnace (13), in particular a continuous furnace, a tunnel furnace, a chamber furnace, a bogie hearth fu-nace or the like, the burner unit having at least two burners (14) which are configured for burning a combustion gas, the burner unit having a gas pipe and an air pipe (15) for supplying the burners with combustion gas, the burner unit having at least one gas metering valve in the gas pipe and at least one air metering valve (24) in the air pipe, the gas metering valve and the air metering valve being controllable by means of a shared control device, the gas metering valve and the air metering valve being a magnet valve (25, 26), characterized in that the burner unit has a gas metering valve and an air metering valve assigned to the gas metering valve per burner.

2. The burner unit according to claim 1, characterized in that the burner unit (23) comprises a regulating apparatus of the control device, the regulating apparatus being configured for synchronizing a corresponding operating state of the gas metering valve and the air metering valve (24).

3. The burner unit according to claim 1 or 2, characterized in that the gas pipe and the air pipe (15) is branched toward the corresponding burner (14), the burners being switched parallel at the gas pipe and the air pipe.

4. The burner unit according to any one of the preceding claims, characterized in that the burner unit (23) has a check valve (20) in the gas pipe and / or the air pipe (15) per burner (14) and / or for the entire burner unit.

5. The burner unit according to any one of the preceding claims, characterized in that an opening cross section (27) of the air metering valve (25, 26) is larger than an opening cross section of the gas metering valve.

6. The burner unit according to any one of the preceding claims, characterized in that the burner unit (23) has at least 3, 4, 5, 6, 7, 8 or more burners (14).

7. The burner unit according to any one of the preceding claims, characterized in that the burner unit (23) has a fan (16) for conveying air into the air pipe (15) or is connected to a central air circulation pipe of a furnace using the air pipe.

8. A furnace (13), in particular a continuous furnace, a tunnel furnace, a chamber furnace, a bogie hearth furnace or the like, having at least one burner unit (23) according to any one of the preceding claims.

9. A method for operating a furnace (13), in particular a continuous furnace, a tunnel furnace, a chamber furnace, a bogie hearth furnace or the like, a combustion gas being burned using at least two burners (14) of a burner unit (23) of the furnace, the burners being supplied with the combustion gas via a gas pipe and an air pipe (15), at least one gas metering valve in the gas pipe and at least one air metering valve (24) in the air pipe being controlled by means of a shared control device, a regulating apparatus of the control device synchronously opening and closing the gas metering valve and the air metering valve characterized in that the burner unit has a gas metering valve and an air metering valve assigned to the gas metering valve per burner.

10. The method according to claim 9, characterized in that an operating state of the air metering valve (24) is regulated as a reference variable according to the operating state of the gas metering valve.

11. The method according to claim 9 or 10, characterized in that the regulating apparatus regulates the combustion gas in a stoichiometric relationship.

12. The method according to any one of the claims 9 to 11, characterized in that the regulating apparatus regulates the gas metering valve according to a requirement of a burner performance and / or a furnace temperature as a reference variable of the control device.

13. The method according to any one of the claims 9 to 12, characterized in that an opening and a closing is executed at a stroke of at least 50 strokes / minute, preferably 100 strokes / minute, particularly preferably 200 strokes / minute, up to 400 strokes / minute.

14. The method according to any one of the claims 9 to 13, characterized in that the control device initiates a sequence of strokes of an opening and closing when a lower furnace temperature is not met and terminates the sequence of the strokes when an upper furnace temperature is exceeded, preferably the regulating apparatus being able to regulate a burner performance by varying stroke time and / or stroke duration.

15. The method according to any one of the claims 9 to 14, characterized in that air at a temperature of below 100 °C, preferably below 70 °C, is metered via the air metering valve (24), a temperature of up to 400 °C, preferably up to 700 °C, particularly preferably 1,000 °C or higher, being generated in the furnace (13).

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