Combustion System

Abstract

To simply execute O2 trimming.SOLUTION: A combustion system is equipped with a combustor (burner 112), an air supply path 232 connected to the combustor, a gas supply path 212 connected to the combustor, a trimming valve 256 provided in the air supply path 232, an oxygen sensor that measures oxygen concentration in exhaust gas generated in the combustor, and an opening adjusting portion 142 that adjusts an opening of the trimming valve 256 on the basis of a measurement value of the oxygen sensor.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a combustion system such as an industrial furnace or a boiler. [Background technology]

[0002] An air supply passage provided with a butterfly valve and a gas supply passage provided with a needle valve are connected to a combustion appliance such as an industrial furnace or a boiler. The openings of the butterfly valve and the needle valve are set so that the flow rate ratio of air to gas supplied to the combustion appliance is a fixed value based on a target air ratio.

[0003] However, when the air temperature changes, the amount of air per unit volume fluctuates. Therefore, if the flow rate ratio of air to gas is fixed, the air ratio fluctuates with the change in air temperature. For example, if a fixed value is determined based on the target air ratio when the air temperature is high, such as in summer, the air ratio will increase when the air temperature is low, such as in winter. Similarly, if a fixed value is determined based on the target air ratio when the air temperature is low, such as in winter, the air ratio will decrease when the air temperature is high, such as in summer. If the air ratio becomes higher than the target air ratio, misfires may occur or the combustion efficiency may decrease. On the other hand, if the air ratio becomes lower than the target air ratio, incomplete combustion may occur.

[0004] Therefore, O2 trimming has been developed, which controls the flow rate ratio of air and gas based on the oxygen concentration in the exhaust gas generated in the combustion appliance (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-169483 A Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need to develop technology that can easily perform O2 trimming.

[0007] An object of the present invention is to provide a combustion system that can easily perform O2 trimming. [Means for solving the problem]

[0008] In order to solve the above problems, the combustion system of the present invention includes a combustion appliance, an air supply passage connected to the combustion appliance, a gas supply passage connected to the combustion appliance, a flow rate control valve provided in the air supply passage, a trimming valve provided in the air supply passage between the flow rate control valve and the combustion appliance, a pressure equalizing valve that equalizes the pressure in the air supply passage and the gas supply passage, an oxygen sensor that measures the oxygen concentration in exhaust gas generated by the combustion appliance, and an opening adjustment unit that adjusts the opening rate of the trimming valve based on the measurement value of the oxygen sensor and adjusts the opening rate of the flow rate control valve based on the furnace temperature of the combustion appliance, wherein the flow rate control valve is provided upstream of the pressure equalizing valve, and the trimming valve is provided downstream of the pressure equalizing valve. The air supply passage has a first passage in which a fixed valve is provided, and a second passage connected to the first passage, bypassing the fixed valve, and in which a trimming valve is provided. do.

[0010] The combustion system may include a first shutoff valve provided upstream of the fixed valve in the first flow path, and a second shutoff valve provided upstream of the trimming valve in the second flow path, and the first flow path may have a flow path cross-sectional area approximately equal to that of the second flow path.

[0011] The second flow path may have a smaller cross-sectional area than the first flow path. Effect of the Invention

[0013] According to the present invention, O2 trimming can be easily performed. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a combustion system according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a fuel supply unit according to the first embodiment. [Diagram 3]FIG. 4 is a diagram illustrating control by an opening degree adjusting unit according to the first embodiment. [Figure 4] 4 is a flowchart illustrating control by an opening degree adjusting unit according to the first embodiment. [Diagram 5] FIG. 6 is a diagram illustrating a fuel supply unit according to a second embodiment. [Figure 6] 10 is a flowchart illustrating control by an opening degree adjusting unit according to a second embodiment. [Figure 7] 13A and 13B are diagrams illustrating a fuel supply unit according to a modified example. [Figure 8] 10 is a flowchart illustrating control by an opening degree adjusting unit according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present invention are not shown.

[0016] [First embodiment: combustion system 100] Fig. 1 is a diagram illustrating a combustion system 100 according to a first embodiment. In Fig. 1, dashed arrows indicate the flow of signals. As shown in Fig. 1, the combustion system 100 includes a combustion appliance 110, a fuel supply unit 120, an oxygen sensor 130, and a central control unit 140.

[0017] The combustion appliance 110 is a furnace that burns fuel. For example, the combustion appliance 110 is a furnace that constitutes a boiler, an industrial furnace, etc. The combustion appliance 110 includes one or more burners 112.

[0018] The fuel supply unit 120 supplies fuel gas and air to the burner 112. The fuel gas is, for example, a gaseous fuel such as a hydrocarbon such as methane, ethane, propane, or butane, carbon monoxide, hydrogen, or ammonia. In this embodiment, a fuel supply unit 120 is provided for each burner 112. A fuel gas supply source 122 is connected to the fuel supply unit 120. A main shutoff valve 124 is provided between the fuel gas supply source 122 and the fuel supply unit 120. The main shutoff valve 124 opens and closes a flow path formed between the fuel gas supply source 122 and the fuel supply unit 120. During operation of the combustion system 100, the main shutoff valve 124 is maintained in an open state. Details of the fuel supply unit 120 will be described later.

[0019] The oxygen sensor 130 measures the oxygen concentration in the exhaust gas produced by the combustion appliance 110 .

[0020] The central control unit 140 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 140 reads out programs and parameters for operating the CPU from the ROM. The central control unit 140 manages and controls the entire combustion system 100 in cooperation with a RAM as a work area and other electronic circuits.

[0021] In this embodiment, the central control unit 140 functions as an opening degree adjustment unit 142. The opening degree adjustment unit 142 controls the fuel supply unit 120. The opening degree adjustment unit 142 will be described in detail later.

[0022] [Fuel supply section 120] 2 is a diagram illustrating the fuel supply unit 120 according to the first embodiment. In FIG. 2, the dashed arrows indicate the flow of signals. As shown in FIG. 2, the fuel supply unit 120 includes a gas supply unit 210 and an air supply unit 230.

[0023] The gas supply unit 210 supplies fuel gas to the burner 112. The gas supply unit 210 includes a gas supply passage 212, a pressure regulator 214, main shutoff valves 216a, 216b, a pressure equalizing valve 218, and a fixed valve 220.

[0024] The gas supply path 212 is a path that connects the main shutoff valve 124 and the burner 112. The gas supply path 212 has a smaller flow path cross-sectional area than an air supply path 232 described later. The pressure regulator 214, the main shutoff valves 216a, 216b, the pressure equalizing valve 218, and the fixed valve 220 are provided in the gas supply path 212.

[0025] The pressure regulator 214 regulates the pressure of the fuel gas supplied downstream to a preset pressure. The main shutoff valves 216a, 216b are provided downstream of the pressure regulator 214. The main shutoff valves 216a, 216b open and close the gas supply passage 212. During operation of the combustion system 100, the main shutoff valves 216a, 216b are maintained in an open state.

[0026] The pressure equalizing valve 218 is provided, for example, downstream of the main shutoff valve 216b. The pressure equalizing valve 218 equalizes the pressure between the air supply path 232 and the gas supply path 212. By providing the pressure equalizing valve 218, the pressure downstream of the flow rate adjustment valve 242 in the air supply path 232 (between the flow rate adjustment valve 242 and the burner 112) and the pressure downstream of the pressure equalizing valve 218 in the gas supply path 212 (between the pressure equalizing valve 218 and the burner 112) can be made substantially equal (for example, 2 kPaG). The pressure equalizing valve 218 may be provided upstream of the main shutoff valve 216a.

[0027] The fixed valve 220 is provided downstream of the pressure equalizing valve 218. The fixed valve 220 is maintained at an opening (set value) that is set when the combustion system 100 starts operating. The set value is, for example, an opening that can avoid incomplete combustion and misfire. The fixed valve 220 is, for example, a needle valve.

[0028] The air supply unit 230 supplies air to the burner 112. In this embodiment, the air supply unit 230 includes an air supply passage 232, a blower 240, a flow rate adjustment valve 242, a first shutoff valve 250, a fixed valve 252, a second shutoff valve 254, and a trimming valve 256.

[0029] The air supply passage 232 is a passage that connects the blower 240 and the burner 112. In this embodiment, the air supply passage 232 includes a first passage 234 and a second passage 236. The first passage 234 is a passage that connects the blower 240 and the burner 112. A first shutoff valve 250 and a fixed valve 252, which will be described later, are provided in the first passage 234. The second passage 236 is a passage that bypasses the first shutoff valve 250 and the fixed valve 252 and is connected to the first passage 234. In this embodiment, the first passage 234 and the second passage 236 have approximately the same passage cross-sectional area.

[0030] The suction side of the blower 240 is open to the atmosphere. The discharge side of the blower 240 is connected to the air supply path 232 (first flow path 234). The blower 240 supplies air to the burner 112 through the air supply path 232.

[0031] The flow rate adjustment valve 242 is provided in the first flow path 234 between the burner 112 and a branch point of the second flow path 236. The flow rate adjustment valve 242 is, for example, a butterfly valve with a control motor. The opening degree of the flow rate adjustment valve 242 is adjusted by the opening degree adjustment unit 142.

[0032] The first shutoff valve 250 and the fixed valve 252 are provided between a branch point of the first flow path 234 to the second flow path 236 and a reconnection point of the second flow path 236. In other words, the second flow path 236 branches off from between the flow rate adjustment valve 242 and the first shutoff valve 250 in the first flow path 234, and is reconnected between the fixed valve 252 and the burner 112. The first shutoff valve 250 opens and closes the first flow path 234.

[0033] The fixed valve 252 is provided downstream of the first shutoff valve 250. The fixed valve 252 is maintained at an opening (set value) that is set when the combustion system 100 starts operating. The set value is, for example, an opening that can avoid incomplete combustion and misfire. The fixed valve 252 is, for example, a butterfly valve.

[0034] The second shutoff valve 254 and the trimming valve 256 are provided in the second flow path 236. The second shutoff valve 254 opens and closes the second flow path 236.

[0035] The trimming valve 256 is provided downstream of the second shutoff valve 254. The trimming valve 256 is, for example, a butterfly valve with a control motor. The opening of the trimming valve 256 is adjusted by the opening adjustment unit 142.

[0036] [Control by opening adjustment unit 142] Next, the control of the flow rate adjustment valve 242, the first shutoff valve 250, the second shutoff valve 254, and the trimming valve 256 by the opening adjustment unit 142 according to this embodiment will be described.

[0037] FIG. 3 is a diagram for explaining the control by the opening adjustment unit 142 according to the first embodiment. As shown in FIG. 3, when performing O2 trimming, the opening adjustment unit 142 closes the first shutoff valve 250 and opens the second shutoff valve 254. When performing O2 trimming, the opening adjustment unit 142 adjusts the opening of the trimming valve 256 based on the measurement value of the oxygen sensor 130. For example, the opening adjustment unit 142 adjusts the opening of the trimming valve 256 so that the measurement value of the oxygen sensor 130 is maintained within a predetermined target oxygen range. Therefore, when performing O2 trimming, air is supplied to the burner 112 through the second flow path 236. The target oxygen range is a range of oxygen concentration in the exhaust gas in which the combustion efficiency of the combustion device 110 is equal to or greater than a target value.

[0038] On the other hand, when O2 trimming is not performed, the opening adjustment unit 142 opens the first shutoff valve 250 and closes the second shutoff valve 254. Therefore, when O2 trimming is not performed, air is supplied to the burner 112 through the first flow path 234. Also, when O2 trimming is not performed, the opening adjustment unit 142 does not adjust the opening of the trimming valve 256. Therefore, when O2 trimming is not performed, air is supplied to the burner 112 at a flow rate according to the preset opening of the fixed valve 252.

[0039] FIG. 4 is a flowchart illustrating the control by the opening degree adjustment unit 142 according to the first embodiment.

[0040] 4, the opening adjustment unit 142 determines whether or not an operation input to execute O2 trimming has been received (step S110). As a result, when it is determined that an operation input to execute O2 trimming has been received (YES in step S110), the opening adjustment unit 142 closes the first shutoff valve 250 and opens the second shutoff valve 254 (step S112), and proceeds to step S110.

[0041] On the other hand, if it is determined that an operation input to perform O2 trimming has not been received (NO in step S110), the opening adjustment unit 142 determines whether an operation input to not perform O2 trimming has been received (step S114). As a result, if it is determined that an operation input to not perform O2 trimming has been received (YES in step S114), the opening adjustment unit 142 opens the first shutoff valve 250 and closes the second shutoff valve 254 (step S116), and proceeds to step S110.

[0042] If it is determined that an operation input to not perform O2 trimming has not been received (NO in step S114), the opening adjustment unit 142 determines whether O2 trimming is being performed (step S120). If it is determined that O2 trimming is being performed (YES in step S120), the opening adjustment unit 142 determines whether the measurement value of the oxygen sensor 130 (oxygen concentration in the exhaust gas) exceeds the upper limit of the target oxygen range (step S122).

[0043] As a result, when it is determined that the measurement value of the oxygen sensor 130 exceeds the upper limit value (YES in step S122), the opening adjustment unit 142 reduces the opening of the trimming valve 256 (step S124), and the process proceeds to step S110.

[0044] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not above the upper limit value (NO in step S122), the opening adjustment unit 142 determines whether the measurement value of the oxygen sensor 130 is below the lower limit value of the target oxygen range (step S126). As a result, if it is determined that the measurement value of the oxygen sensor 130 is below the lower limit value (YES in step S126), the opening adjustment unit 142 increases the opening of the trimming valve 256 (step S128) and proceeds to step S110.

[0045] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not less than the lower limit (NO in step S126), that is, if it is determined that the measurement value of the oxygen sensor 130 is within the target oxygen range, the opening degree adjustment unit 142 proceeds to step S110.

[0046] Moreover, when it is determined that O2 trimming is not being performed (NO in step S120), the opening adjustment unit 142 advances the process to step S110.

[0047] Returning to Fig. 3, the opening adjustment unit 142 adjusts the opening of the flow rate adjustment valve 242 based on the measurement value of a temperature sensor (not shown) that measures the furnace temperature of the combustion appliance 110, regardless of whether O2 trimming is performed. For example, when the measurement value of the temperature sensor is less than the target temperature, the opening adjustment unit 142 increases the opening of the flow rate adjustment valve 242. Also, when the measurement value of the temperature sensor is greater than the target temperature, the opening adjustment unit 142 decreases the opening of the flow rate adjustment valve 242.

[0048] As described above, the combustion system 100 according to this embodiment includes the oxygen sensor 130, the opening adjustment unit 142, the second flow path 236, the first shutoff valve 250, the second shutoff valve 254, and the trimming valve 256. This allows the combustion system 100 to easily perform O2 trimming. Therefore, the combustion system 100 can prevent misfire or incomplete combustion in the burner 112, and can improve combustion efficiency.

[0049] In addition, the combustion system 100 is capable of easily performing O2 trimming by simply adding the oxygen sensor 130, the opening adjustment unit 142, the second flow path 236, the first shut-off valve 250, the second shut-off valve 254, and the trimming valve 256 to a conventional air supply mechanism that does not have an O2 trimming function.

[0050] Moreover, the air supply unit 230 includes a second flow path 236 and a second shutoff valve 254, and includes a trimming valve 256 downstream of the second shutoff valve 254 in the second flow path 236. This allows combustion by the burner 112 to continue even if the trimming valve 256 fails. More specifically, even if the trimming valve 256 fails, it is possible to supply air from the first flow path 234 to the burner 112 by closing the second shutoff valve 254 and opening the first shutoff valve 250.

[0051] Furthermore, in the combustion system 100, a trimming valve 256 whose opening is adjusted when performing O2 trimming is provided in the air supply passage 232. In other words, when performing O2 trimming, the combustion system 100 can change only the air ratio while maintaining the amount of fuel gas (combustion amount) supplied to the burner 112. Therefore, the combustion system 100 can reduce interference with temperature adjustment inside the furnace of the combustion appliance 110.

[0052] The combustion system 100 also includes a trimming valve 256 downstream of the pressure equalization valve 218. The trimming valve 256 can thereby change the air ratio.

[0053] [Second embodiment: fuel supply unit 320] 5 is a diagram illustrating a fuel supply unit 320 according to the second embodiment. Components substantially the same as those in the fuel supply unit 120 are denoted by the same reference numerals and will not be described. In the second embodiment, the configurations other than the air supply unit 330, such as the combustion appliance 110, the fuel gas supply source 122, the main cutoff valve 124, the oxygen sensor 130, the central control unit 140, and the gas supply unit 210, are substantially the same as those in the first embodiment.

[0054] 5, the fuel supply unit 320 includes an air supply unit 330 and a gas supply unit 210. The air supply unit 330 includes an air supply passage 232, a blower 240, a flow rate adjustment valve 242, a fixed valve 252, and a trimming valve 256. That is, unlike the air supply unit 230 described above, the air supply unit 330 according to this embodiment does not include the first shutoff valve 250 and the second shutoff valve 254.

[0055] In this embodiment, the second flow path 236 has a smaller flow path cross-sectional area than the first flow path 234. For example, if the sum of the flow path cross-sectional areas of the first flow path 234 and the second flow path 236 is 100%, the flow path cross-sectional area of ​​the first flow path 234 is about 80%, and the flow path cross-sectional area of ​​the second flow path 236 is about 20%.

[0056] [Control by opening adjustment unit 142] Next, the control of the trimming valve 256 by the opening adjustment unit 142 according to the second embodiment will be described.

[0057] FIG. 6 is a flowchart illustrating the control by the opening degree adjusting unit 142 according to the second embodiment.

[0058] 6, the opening adjustment unit 142 determines whether or not an operation input to the effect that O2 trimming is not to be performed has been received (step S210). As a result, when it is determined that an operation input to the effect that O2 trimming is not to be performed has been received (YES in step S210), the opening adjustment unit 142 sets the opening of the trimming valve 256 to the opening (set value) that was set when the combustion system 100 started operating (step S212), and proceeds to the process of step S210.

[0059] On the other hand, if it is determined that an operation input to not perform O2 trimming has been received (NO in step S210), the opening adjustment unit 142 determines whether O2 trimming is being performed (step S214). As a result, if it is determined that O2 trimming is being performed (YES in step S214), the opening adjustment unit 142 proceeds to step S220.

[0060] On the other hand, if it is determined that O2 trimming is not being performed (NO in step S214), the opening adjustment unit 142 determines whether or not an operation input to perform O2 trimming has been received (step S216). As a result, if it is determined that an operation input to perform O2 trimming has not been received (NO in step S216), the opening adjustment unit 142 proceeds to step S210. On the other hand, if it is determined that an operation input to perform O2 trimming has been received (YES in step S216), the opening adjustment unit 142 proceeds to step S220.

[0061] The opening adjustment unit 142 determines whether the measurement value (oxygen concentration in the exhaust gas) of the oxygen sensor 130 exceeds the upper limit of the target oxygen range (step S220). If it is determined that the measurement value of the oxygen sensor 130 exceeds the upper limit (YES in step S220), the opening adjustment unit 142 reduces the opening of the trimming valve 256 (step S222) and proceeds to step S210.

[0062] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not above the upper limit value (NO in step S220), the opening adjustment unit 142 determines whether the measurement value of the oxygen sensor 130 is below the lower limit value of the target oxygen range (step S224). As a result, if it is determined that the measurement value of the oxygen sensor 130 is below the lower limit value (YES in step S224), the opening adjustment unit 142 increases the opening of the trimming valve 256 (step S226) and proceeds to step S210.

[0063] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not below the lower limit (NO in step S224), that is, if it is determined that the measurement value of the oxygen sensor 130 is within the target oxygen range, the opening degree adjustment unit 142 proceeds to step S210.

[0064] As described above, the air supply unit 330 according to this embodiment includes the second flow path 236 and the trimming valve 256. This allows the air supply unit 330 to easily perform O2 trimming. Therefore, the air supply unit 330 can prevent misfire or incomplete combustion in the burner 112, and can improve combustion efficiency.

[0065] Moreover, the air supply unit 330 can easily perform O2 trimming by simply adding the second flow path 236 and the trimming valve 256 to a conventional air supply mechanism that does not have an O2 trimming function.

[0066] As described above, the second flow path 236 of the present embodiment has a smaller flow path cross-sectional area than the first flow path 234. This allows the air supply unit 330 to be more space-saving than the air supply unit 230 according to the first embodiment.

[0067] [Modification: Fuel Supply Unit 420] 7 is a diagram for explaining a fuel supply unit 420 according to a modified example. Note that components substantially the same as those of the fuel supply unit 120 are given the same reference numerals and will not be described. In addition, in the modified example, the configurations other than the air supply unit 430, such as the combustion appliance 110, the fuel gas supply source 122, the main cutoff valve 124, the oxygen sensor 130, the central control unit 140, and the gas supply unit 210, are substantially the same as those in the first embodiment.

[0068] 7, the fuel supply unit 420 includes an air supply unit 430 and a gas supply unit 210. The air supply unit 430 includes an air supply passage 432, a blower 240, a flow rate adjustment valve 242, and a trimming valve 256.

[0069] Unlike the air supply passage 232 of the first and second embodiments, the air supply passage 432 does not include the second flow passage 236. The air supply passage 432 is a flow passage that connects the blower 240 and the burner 112.

[0070] The trimming valve 256 is provided in the air supply passage 432 between the flow rate adjustment valve 242 and the burner 112. In other words, the air supply unit 430 according to the modified example is provided with the trimming valve 256 instead of the fixed valve 252 constituting the conventional air supply mechanism not provided with an O2 trimming function.

[0071] [Control by opening adjustment unit 142] Next, the control of the trimming valve 256 by the degree of opening adjustment unit 142 according to the modified example will be described.

[0072] FIG. 8 is a flowchart illustrating the control by the opening degree adjusting unit 142 according to the modified example.

[0073] 8, the opening adjustment unit 142 determines whether or not an operation input to the effect that O2 trimming is not to be performed has been received (step S310). As a result, when it is determined that an operation input to the effect that O2 trimming is not to be performed has been received (YES in step S310), the opening adjustment unit 142 fully opens the trimming valve 256 (step S312) and proceeds to step S310.

[0074] On the other hand, if it is determined that an operation input to not perform O2 trimming has been received (NO in step S310), the opening adjustment unit 142 determines whether O2 trimming is being performed (step S314). As a result, if it is determined that O2 trimming is being performed (YES in step S314), the opening adjustment unit 142 proceeds to step S320.

[0075] On the other hand, if it is determined that O2 trimming is not being performed (NO in step S314), the opening adjustment unit 142 determines whether or not an operation input to perform O2 trimming has been received (step S316). As a result, if it is determined that an operation input to perform O2 trimming has not been received (NO in step S316), the opening adjustment unit 142 proceeds to step S310. On the other hand, if it is determined that an operation input to perform O2 trimming has been received (YES in step S316), the opening adjustment unit 142 proceeds to step S320.

[0076] The opening adjustment unit 142 determines whether the measurement value (oxygen concentration in the exhaust gas) of the oxygen sensor 130 exceeds the upper limit of the target oxygen range (step S320). If it is determined that the measurement value of the oxygen sensor 130 exceeds the upper limit (YES in step S320), the opening adjustment unit 142 reduces the opening of the trimming valve 256 (step S322) and proceeds to step S310.

[0077] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not above the upper limit value (NO in step S320), the opening adjustment unit 142 determines whether the measurement value of the oxygen sensor 130 is below the lower limit value of the target oxygen range (step S324). As a result, if it is determined that the measurement value of the oxygen sensor 130 is below the lower limit value (YES in step S324), the opening adjustment unit 142 increases the opening of the trimming valve 256 (step S326) and proceeds to step S310.

[0078] On the other hand, if it is determined that the measurement value of the oxygen sensor 130 is not below the lower limit (NO in step S324), that is, if it is determined that the measurement value of the oxygen sensor 130 is within the target oxygen range, the opening degree adjustment unit 142 proceeds to step S310.

[0079] As described above, the air supply unit 430 according to the modified example includes the trimming valve 256. This allows the air supply unit 430 to easily perform O2 trimming. Therefore, the air supply unit 430 can prevent misfire or incomplete combustion in the burner 112, and can improve combustion efficiency.

[0080] Furthermore, the air supply unit 430 can easily perform O2 trimming by a simple operation of replacing the fixed valve 252 constituting a conventional air supply mechanism not equipped with an O2 trimming function with the trimming valve 256.

[0081] Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention.

[0082] For example, in the above-described second embodiment, the air supply unit 330 does not include the first shutoff valve 250 and the second shutoff valve 254. However, the air supply unit 330 may include the second shutoff valve 254.

[0083] Furthermore, the flow path cross-sectional areas and dimensional relationships of the gas supply path 212, the first flow path 234, the second flow path 236, and the air supply path 432 are not limited to those exemplified in the first and second embodiments and the modified examples. Therefore, the flow path cross-sectional areas of the gas supply path 212, the first flow path 234, the second flow path 236, and the air supply path 432 may be approximately equal, or the size relationships may be reversed from those exemplified in the first and second embodiments and the modified examples.

[0084] In addition, in the fuel supply units 120, 320, 420, the pressure regulator 214 may be omitted. [Explanation of symbols]

[0085] 100 Combustion System 110 Combustion appliances 212 Gas supply line 218 Pressure equalization valve 232 Air supply line 234 First Channel 236 Second Channel 250 First shutoff valve 252 Fixed valve 254 Second shutoff valve 256 Trimming valve 432 Air supply line

Claims

1. Combustion appliances, An air supply passage connected to the combustion appliance; A gas supply passage connected to the combustion appliance; A flow rate regulating valve provided in the air supply passage; a trimming valve provided in the air supply passage between the flow rate control valve and the combustion appliance; a pressure equalizing valve for equalizing the pressure of the air supply path and the gas supply path; an oxygen sensor for measuring an oxygen concentration in exhaust gas generated by the combustion appliance; an opening adjustment unit that adjusts the opening of the trimming valve based on a measurement value of the oxygen sensor and adjusts the opening of the flow rate adjustment valve based on an in-furnace temperature of the combustion appliance; Equipped with The flow rate regulating valve is provided upstream of the pressure equalizing valve, The trimming valve is provided downstream of the pressure equalizing valve, The air supply passage is a first flow path provided with a fixed valve; a second flow passage connected to the first flow passage, bypassing the fixed valve, and in which the trimming valve is provided; A combustion system having

2. a first shutoff valve provided in the first flow path upstream of the fixed valve; a second shutoff valve provided in the second flow path upstream of the trimming valve; Equipped with The combustion system according to claim 1 , wherein the first flow passage has a cross-sectional area substantially equal to that of the second flow passage.

3. The combustion system according to claim 1 , wherein the second flow passage has a smaller flow passage cross-sectional area than the first flow passage.

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