Combustion System

Abstract

To prevent backfire at low cost.SOLUTION: A combustion system includes: a burner 112; a fuel gas supply passage 232 connecting a fuel gas supply source 122 and the burner 112; an oxidant gas supply passage 212 connecting an air blower 214 and the burner 112; an inert gas supply passage 254 connecting an inert gas supply source 252 and the fuel gas supply passage 232; and a flow rate control section. The flow rate control section performs: control during operation for supplying inert gas to the fuel gas supply passage through the inert gas supply passage at least for a predetermined time during an operation of the burner; operation stop control for stopping the operation of the burner by stopping supply of fuel gas to the burner while maintaining supply of inert gas to the fuel gas supply passage through the inert gas supply passage; and post-purge control for supplying inert gas to the fuel gas supply passage through the inert gas supply passage for a predetermined time after performing the operation stop control.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to combustion systems such as industrial heating furnaces, boilers, and hot and cold water generators. [Background technology]

[0002] In recent years, there has been a demand to reduce CO2 (carbon dioxide) emissions in order to prevent global warming. For this reason, technology for burning hydrogen in addition to or instead of fossil fuels has been attracting attention.

[0003] In a burner that uses hydrogen as fuel, a combustible mixture containing hydrogen and air may be generated in the fuel pipe before operation starts and after operation stops, which may cause flashback.

[0004] Therefore, a technique of installing a flame arrester in the fuel pipe has been developed (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-200166 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the technology of Patent Document 1 has a problem in that the flame arrester is costly.

[0007] In view of the above problems, the present invention has an object to provide a combustion system that can prevent flashback at low cost. [Means for solving the problem]

[0008] In order to solve the above problems, the combustion system of the present invention comprises a burner, a fuel gas supply passage connecting a fuel gas supply source and the burner, an oxidant gas supply passage connecting a blower and the burner, an inert gas supply passage connecting an inert gas supply source and the fuel gas supply passage, and a flow rate control unit that controls one or more of the flow rate of the fuel gas supplied to the burner through the fuel gas supply passage, the flow rate of the oxidant gas supplied to the burner through the oxidant gas supply passage, and the flow rate of the inert gas supplied to the fuel gas supply passage through the inert gas supply passage, wherein the flow rate control unit: a pre-purge control for supplying an inert gas to a fuel gas supply path through an inert gas supply path; an operation start control that is a control performed after the pre-purge control and that starts supplying fuel gas to a burner to start operation of the burner; and a control that is performed after the operation start control, At least for a given period of time Supplying fuel gas to the burner In-driving control, A control performed after a driving control, Operation stop control to stop the operation of the burner by stopping the supply of fuel gas to the burner; A control performed after and post-purge control, in which an inert gas is supplied to the fuel gas supply line through the inert gas supply line for a predetermined period of time. During the period from the pre-purge control to the post-purge control, the supply of the inert gas to the fuel gas supply line through the inert gas supply line is maintained. .

[0009] In addition, during operation control, the flow rate control unit may control the flow rate of fuel gas supplied to the burner in accordance with the required heat quantity, and control the flow rate of oxidant gas supplied to the burner so as to maintain the air ratio within a predetermined range.

[0011] Furthermore, the flow rate control unit may control the flow rate of the inert gas based on the concentration of NOx contained in the exhaust gas generated by burning the fuel gas during the in-operation control.

[0012] Furthermore, when the flow rate control unit reduces the flow rate of the fuel gas supplied to the burner during the in-operation control, the flow rate control unit may increase the flow rate of the inert gas supplied to the fuel gas supply passage.

[0013] Furthermore, the flow rate control unit may maintain the supply of inert gas to the fuel gas supply path even when the flow rate of the fuel gas supplied to the burner is set to zero during the in-operation control. [Effects of the Invention]

[0014] According to the present invention, flashback can be prevented at low cost. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating a combustion system according to a first embodiment. [Figure 2] FIG. 2 is a functional block diagram of a control device according to the first embodiment. [Figure 3] FIG. 2 is a diagram illustrating a gas supply unit according to the first embodiment. [Figure 4] 5A and 5B are diagrams illustrating control by a flow rate control unit according to the first embodiment. [Figure 5] FIG. 3 is a diagram illustrating the relationship between the flow rate of hydrogen and the concentration of NOx contained in exhaust gas. [Figure 6] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a first modified example. [Figure 7] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a second modified example. [Figure 8] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a third modified example. [Figure 9] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a fourth modified example. [Figure 10] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a fifth modified example. [Figure 11] FIG. 10 is a diagram illustrating control by a flow rate control unit according to a sixth modified example. [Figure 12] FIG. 13 is a diagram illustrating control by a flow rate control unit according to a seventh modified example. [Figure 13] FIG. 4 is a diagram illustrating a combustion system according to a second embodiment. [Figure 14] FIG. 10 is a functional block diagram of a control device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Dimensions, materials, and other specific values ​​shown in the embodiments are merely examples for facilitating understanding of the invention and, unless otherwise specified, do not limit the present invention. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0017] [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 facility 110, a gas supply unit 120, and a control device 130.

[0018] The combustion equipment 110 is a furnace that burns fuel gas. The combustion equipment 110 is, for example, an industrial heating furnace, a furnace that constitutes a boiler or a hot / cold water heater. The combustion equipment 110 includes one or more burners 112.

[0019] The gas supply unit 120 supplies one or more of a fuel gas, an oxidant gas, and an inert gas to the burner 112. In this embodiment, a gas supply unit 120 is provided for each burner 112. A fuel gas supply source 122 is connected to the gas supply unit 120. A main shutoff valve 124 is provided between the fuel gas supply source 122 and the gas supply unit 120. The main shutoff valve 124 opens and closes a flow path formed between the fuel gas supply source 122 and the gas supply unit 120. During operation of the combustion system 100, the main shutoff valve 124 is maintained in an open state. Details of the gas supply unit 120 will be described later.

[0020] The fuel gas is either or both of a gas with a high combustion rate and a gas with a high adiabatic flame temperature. The fuel gas contains, for example, at least one of hydrogen and acetylene. The combustion rate of hydrogen is about seven times that of hydrocarbon fuel gas (for example, city gas 13A). The adiabatic flame temperature of hydrogen is about 200°C higher than that of methane or city gas 13A. In this embodiment, hydrogen is used as an example of the fuel gas.

[0021] The oxidant gas includes one or more of air, oxygen, and oxygen-enriched gas. In this embodiment, air is used as the oxidant gas.

[0022] The inert gas includes one or more of nitrogen, carbon dioxide, helium, argon, and combustion exhaust gas. In this embodiment, nitrogen is taken as an example of the inert gas.

[0023] 2 is a functional block diagram of the control device 130 according to the first embodiment. As shown in FIG. 2, the control device 130 includes a central control unit 132 and a memory 134.

[0024] The central control unit 132 is configured with a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 132 reads programs, parameters, etc. for operating the CPU from the ROM. The central control unit 132 manages and controls the entire combustion system 100 in cooperation with RAM as a work area and other electronic circuits.

[0025] In this embodiment, the central control unit 132 functions as a flow rate control unit 140. The flow rate control unit 140 controls the gas supply unit 120. The flow rate control unit 140 will be described in detail later.

[0026] The memory 134 is composed of a ROM, a RAM, a flash memory, a HDD, etc. The memory 134 stores programs and various data used by the central control unit 132. For example, the memory 134 holds NOx information, etc. The NOx information is information that associates the flow rate of hydrogen being combusted with the flow rate of nitrogen at which the concentration of NOx (nitrogen oxides) contained in exhaust gas produced by the combustion of the hydrogen becomes a predetermined value. The NOx information is created in advance by experiments, simulations, etc., and is held in the memory 134.

[0027] [Gas supply unit 120] 3 is a diagram illustrating the gas supply unit 120 according to the first embodiment. As shown in FIG. 3, the gas supply unit 120 includes an oxidizing agent supply unit 210, a fuel supply unit 230, and an inert gas supply unit 250.

[0028] [Oxidizing agent supply unit 210] The oxidant supply unit 210 supplies air to the burner 112. In this embodiment, the oxidant supply unit 210 includes an oxidant gas supply passage 212, a blower 214, a flow control valve 216, and a flow adjustment valve 218.

[0029] The oxidizing gas supply channel 212 is a flow path that connects the blower 214 and the burner 112. The intake side of the blower 214 is open to the atmosphere. The discharge side of the blower 214 is connected to the oxidizing gas supply channel 212. The blower 214 supplies air to the burner 112 through the oxidizing gas supply channel 212.

[0030] The flow control valve 216 is provided in the oxidizing gas supply channel 212. The opening degree of the flow control valve 216 is adjusted by the flow control unit 140. The flow control valve 216 is, for example, a butterfly valve with a control motor.

[0031] The flow rate adjustment valve 218 is provided in the oxidant gas supply passage 212 between the flow rate control valve 216 and the burner 112. The flow rate adjustment valve 218 is, for example, a butterfly valve.

[0032] [Fuel supply section 230] The fuel supply unit 230 supplies hydrogen to the burner 112. In this embodiment, the fuel supply unit 230 includes a fuel gas supply passage 232, a pressure regulating valve 234, shutoff valves 236a and 236b, a pressure equalizing valve 238, and a flow rate regulating valve 240.

[0033] The fuel gas supply path 232 is a flow path that connects the fuel gas (hydrogen) supply source 122 (main shutoff valve 124) and the burner 112.

[0034] The pressure regulating valve 234 is provided in the fuel gas supply passage 232. The pressure regulating valve 234 regulates the pressure of hydrogen supplied downstream to a preset pressure.

[0035] The shutoff valves 236a and 236b are provided in the fuel gas supply channel 232 downstream of the pressure regulating valve 234. The shutoff valves 236a and 236b open and close the fuel gas supply channel 232.

[0036] The pressure equalizing valve 238 is provided downstream of the shutoff valve 236b in the fuel gas supply channel 232. The pressure equalizing valve 238 equalizes the pressure between the oxidant gas supply channel 212 and the fuel gas supply channel 232. By providing the pressure equalizing valve 238, the pressure downstream of the flow rate control valve 216 in the oxidant gas supply channel 212 (between the flow rate control valve 216 and the burner 112) and the pressure downstream of the pressure equalizing valve 238 in the fuel gas supply channel 232 (between the pressure equalizing valve 238 and the burner 112) can be made substantially equal (for example, 2 kPaG). Furthermore, by the action of the pressure equalizing valve 238, the flow rate of air is controlled by the flow rate control valve 216, so that the flow rate of hydrogen can be controlled while maintaining a constant ratio of the flow rates of air and hydrogen (air ratio).

[0037] The flow rate adjustment valve 240 is provided in the fuel gas supply passage 232 between the pressure equalizing valve 238 and the burner 112. The flow rate adjustment valve 240 is, for example, a butterfly valve.

[0038] [Inert gas supply unit 250] The inert gas supply unit 250 supplies nitrogen to the fuel gas supply path 232. In this embodiment, the inert gas supply unit 250 includes an inert gas (nitrogen) supply source 252, an inert gas supply path 254, a pressure regulating valve 256, a pressure switch 258, a shutoff valve 260, a flow rate regulating valve 262, and a check valve 264.

[0039] The nitrogen supply source 252 is, for example, a nitrogen cylinder that stores nitrogen, or a nitrogen production device. The nitrogen production device is equipped with, for example, a nitrogen separation membrane and separates nitrogen from compressed air. By employing a nitrogen production device as the nitrogen supply source 252, the cost required for nitrogen can be reduced.

[0040] The inert gas supply channel 254 is a flow channel that connects the nitrogen supply source 252 and the fuel gas supply channel 232. In this embodiment, the inert gas supply channel 254 connects the nitrogen supply source 252 with the shutoff valve 236b and the pressure equalizing valve 238 in the fuel gas supply channel 232.

[0041] The pressure regulating valve 256 is provided in the inert gas supply path 254. The pressure regulating valve 256 regulates the pressure of the nitrogen supplied downstream to a preset pressure.

[0042] Pressure switch 258 is provided downstream of pressure adjustment valve 256 in inert gas supply path 254. Pressure switch 258 detects when the pressure of nitrogen supply source 252 falls below a predetermined value. For example, if nitrogen supply source 252 is a nitrogen cylinder, pressure switch 258 detects when the pressure of the nitrogen cylinder falls below a predetermined value. Providing pressure switch 258 makes it possible to know when to replace the nitrogen cylinder.

[0043] The shutoff valve 260 is provided in the inert gas supply path 254 downstream of the pressure switch 258. The shutoff valve 260 opens and closes the inert gas supply path 254.

[0044] The flow rate adjustment valve 262 is provided downstream of the shutoff valve 260 in the inert gas supply path 254. The opening degree of the flow rate adjustment valve 262 is adjusted by the flow rate control unit 140. The flow rate adjustment valve 262 is, for example, a butterfly valve.

[0045] The check valve 264 is provided downstream of the flow rate adjustment valve 262 in the inert gas supply channel 254. The check valve 264 prevents hydrogen from entering the inert gas supply channel 254 from the fuel gas supply channel 232.

[0046] [Control by flow rate control unit 140] Next, the control of the gas supply unit 120 by the flow rate control unit 140 will be described.

[0047] The flow rate control unit 140 controls one or more of the flow rate of hydrogen supplied to the burner 112 through the fuel gas supply path 232, the flow rate of nitrogen supplied to the fuel gas supply path 232 through the inert gas supply path 254, and the flow rate of air supplied to the burner 112 through the oxidant gas supply path 212, thereby performing pre-purge control, operation start control, operation control, operation stop control, and post-purge control.

[0048] The operation start control is a control that starts the supply of hydrogen to the burner 112 and starts the operation of the burner 112 (combustion equipment 110). The operation control is performed while the burner 112 (combustion equipment 110) is in operation. The operation control is a control that is performed to operate the burner 112 (combustion equipment 110) efficiently. The operation stop control is a control that stops the supply of hydrogen to the burner 112 and stops the operation of the burner 112 (combustion equipment 110). The pre-purge control is a control that is performed before the operation start control. The post-purge control is a control that is performed after the operation stop control.

[0049] In this embodiment, the flow rate control unit 140 controls the shutoff valves 236a, 236b and the flow rate control valve 216 to control the flow rates of air and hydrogen supplied to the burner 112. The flow rate control unit 140 also controls the shutoff valve 260 and the flow rate adjustment valve 262 to control the flow rate of nitrogen supplied to the fuel gas supply path 232.

[0050] 4 is a diagram illustrating the control of the flow rate control unit 140 according to the first embodiment. In FIG. 4, the vertical axis represents flow rate. In FIG. 4, the horizontal axis represents time. At time T0, the blower 214 is stopped, the main shutoff valve 124 is open, and the shutoff valves 236a, 236b, and 260 are closed.

[0051] As shown in Fig. 4, the flow rate control unit 140 performs pre-purge control from time T1 to time T2. The flow rate control unit 140 also performs operation start control at time T2. The flow rate control unit 140 then performs operation stop control at time T7. Therefore, the flow rate control unit 140 performs operation control after time T2 until just before time T7. The flow rate control unit 140 also performs post-purge control from time T7 to time T8. Each control will be described in detail below.

[0052] [Pre-purge control, operation start control] At time T1, the flow rate control unit 140 starts pre-purge control by opening the shutoff valve 260 and starting the supply of nitrogen to the fuel gas supply path 232 through the inert gas supply path 254. The flow rate control unit 140 adjusts the opening of the flow rate adjustment valve 262 to control the nitrogen supplied to the fuel gas supply path 232 to a flow rate Fa.

[0053] Furthermore, at time T1, the flow rate control unit 140 starts the operation of the blower 214 to purge the inside of the combustion equipment 110 with air.

[0054] Then, at time T2, a predetermined time after time T1, the flow rate control unit 140 performs operation start control, which opens the shutoff valves 236a and 236b, starts supplying hydrogen to the burner 112 through the fuel gas supply path 232, ignites the gas, and starts operation of the burner 112. As shown in FIG. 4 , the flow rate control unit 140 performs operation start control while maintaining the supply of nitrogen to the fuel gas supply path 232 through the inert gas supply path 254. In the operation start control, the flow rate control unit 140 adjusts the aperture of the flow rate control valve 216 to control the air flow rate to a required flow rate and controls the hydrogen supplied to the burner 112 to a flow rate F1. The flow rate F1 is the minimum flow rate required for ignition.

[0055] In this way, the flow rate control unit 140 performs pre-purge control to supply nitrogen to the fuel gas supply channel 232 through the inert gas supply channel 254 from time T1 to time T2. The time from time T1 to time T2 is set to the longer of the time during which the inside of the combustion equipment 110 is purged with air and the time during which the inside of the fuel gas supply channel 232 is purged with nitrogen. The time during which the inside of the combustion equipment 110 is purged with air is the time from the start of air supply until air is supplied in an amount approximately five times the volume of the inside of the combustion equipment 110. The time during which the inside of the fuel gas supply channel 232 is purged with nitrogen is, for example, the time from the start of nitrogen supply until nitrogen is supplied in an amount approximately five times the volume of the fuel gas supply channel 232. Generally, the time during which the inside of the combustion equipment 110 is purged with air is longer than the time during which the inside of the fuel gas supply channel 232 is purged with nitrogen.

[0056] [Control during operation] Then, after time T2, the flow rate control unit 140 performs in-operation control to control the flow rates of air and hydrogen supplied to the burner 112 in accordance with the required heat quantity (required temperature) of the combustion equipment 110, while maintaining the supply of nitrogen to the fuel gas supply path 232 through the inert gas supply path 254.

[0057] For example, once ignition is complete (time T3), the flow rate control unit 140 increases the opening of the flow rate control valve 216 to increase the air flow rate, and controls the hydrogen supplied to the burner 112 to a flow rate F2. The flow rate F2 is a flow rate greater than the flow rate F1. The flow rate F2 is a flow rate required for rated combustion.

[0058] Then, when the flow rate reaches F2 (time T4), the flow rate control unit 140 maintains the flow rate at F2 and performs rated combustion until time T5.

[0059] After rated combustion, that is, from time T5 to time T6, the flow rate control unit 140 adjusts the aperture of the flow rate control valve 216 based on the heat quantity required by the combustion equipment 110, and controls the flow rate of air supplied to the burner 112, thereby controlling the hydrogen to a range of not less than flow rate F1 and not more than flow rate F2 while keeping the air ratio constant. Also, from time T5 to time T6, the flow rate control unit 140 references the NOx information stored in the memory 134, and controls the aperture of the flow rate adjustment valve 262 so that the concentration of NOx contained in the exhaust gas is not more than a predetermined value, thereby controlling the nitrogen supplied to the fuel gas supply path 232 to a range of not less than flow rate Fa and not more than flow rate Fb.

[0060] Fig. 5 is a diagram illustrating the relationship between the volume fraction of nitrogen in the mixed gas and the concentration of NOx contained in the exhaust gas. In Fig. 5, the vertical axis represents the concentration of NOx contained in the exhaust gas, and the horizontal axis represents the volume percentage (vol%) of nitrogen contained in the mixed gas (hydrogen and nitrogen) supplied from the fuel gas supply path 232 to the burner 112. In Fig. 5, circles represent a case where the flow rate of the mixed gas supplied from the fuel gas supply path 232 to the burner 112 is relatively low (low flow rate). In Fig. 5, triangles represent a case where the flow rate of the mixed gas supplied from the fuel gas supply path 232 to the burner 112 is relatively high (high flow rate). In Fig. 5, the NOx concentration at a low flow rate is set to 100 when the mixed gas supplied from the fuel gas supply path 232 to the burner 112 contains 0% nitrogen (i.e., only hydrogen is supplied).

[0061] As shown in FIG. 5, regardless of the flow rate of the mixed gas, as the nitrogen concentration in the mixed gas increases, the concentration of NOx contained in the exhaust gas decreases.

[0062] 5, the NOx concentration in the exhaust gas tends to be lower when the flow rate of the mixed gas is high than when the flow rate is low. This is because the flow velocity of the mixed gas and air ejected from the burner 112 is higher when the flow rate of the mixed gas is high than when the flow rate is low. Therefore, the amount of exhaust gas in the combustion chamber that is entrained by the jet of mixed gas and air increases near the burner 112 in the combustion equipment 110. As a result, the oxygen concentration in the combustion area decreases, which lowers the flame temperature and suppresses the amount of NOx generated (low NOx effect due to self-exhaust gas recirculation).

[0063] 4, when the flow rate control unit 140 reduces the flow rate of hydrogen supplied to the burner 112 in accordance with the required heat quantity between time T5 and time T6, it increases the flow rate of nitrogen supplied to the fuel gas supply path 232. This allows the flow rate control unit 140 to reduce the concentration of NOx contained in the exhaust gas.

[0064] The nitrogen flow rate Fa is the larger of the flow rate at which the NOx concentration becomes a predetermined value when the hydrogen flow rate is F2, and the flow rate at which the fuel gas supply channel 232 can be replaced with nitrogen in a time equal to or shorter than the time it takes for the combustion equipment 110 to be replaced with air during pre-purge control. The nitrogen flow rate Fb is a flow rate that exceeds the flow rate Fa, and is the flow rate at which the NOx concentration becomes a predetermined value when the hydrogen flow rate is F1.

[0065] Then, at time T6, the flow rate control unit 140 adjusts the aperture of the flow rate control valve 216 to control the air flow rate, setting the hydrogen flow rate to flow rate F2, and maintaining the flow rate F2 to perform rated combustion. During rated combustion, the flow rate control unit 140 adjusts the aperture of the flow rate adjustment valve 262 to maintain the nitrogen supplied to the fuel gas supply path 232 at flow rate Fa.

[0066] [Shutdown control, post-purge control] Then, at time T7, the flow control unit 140 performs operation shutdown control to stop the operation of the burner 112 by stopping the supply of hydrogen to the burner 112 while maintaining the supply of nitrogen to the fuel gas supply line 232 through the inert gas supply line 254.

[0067] Specifically, at time T7, the flow control unit 140 closes the shut-off valves 236a and 236b to stop the supply of hydrogen to the burner 112 through the fuel gas supply path 232, thereby performing shutdown control to stop the operation of the burner 112.

[0068] Then, at time T8, a predetermined time after time T7 when the operation shutdown control was performed, the flow rate control unit 140 closes the shutoff valve 260 and performs post-purge control by stopping the supply of nitrogen to the fuel gas supply path 232 through the inert gas supply path 254. In addition, the flow rate control unit 140 stops the operation of the blower 214 at time T8.

[0069] In this way, the flow rate control unit 140 performs post-purge control to supply nitrogen to the fuel gas supply channel 232 through the inert gas supply channel 254 from time T7 to time T8. The time from time T7 to time T8 is set to the time during which the inside of the fuel gas supply channel 232 is replaced with nitrogen. Note that the time from time T7 to time T8 may be the same as the time from time T1 to time T2.

[0070] As described above, the combustion system 100 according to this embodiment performs pre-purge control and post-purge control. Therefore, the combustion system 100 can prevent a combustible mixture of hydrogen and air from being formed in the fuel gas supply passage 232. In particular, fuel gases such as hydrogen, which have a high combustion speed, have a high incidence of flashback, but by performing pre-purge control and post-purge control, the combustion system 100 can prevent the occurrence of flashback.

[0071] Furthermore, the combustion system 100 has a simple configuration in which nitrogen is supplied to the fuel gas supply line 232, and can minimize the risk of equipment damage due to flashback without installing a flashback prevention device such as a flame arrester in the fuel gas supply line 232. This makes it possible for the combustion system 100 to prevent flashback at low cost.

[0072] Furthermore, in addition to the pre-purge control and post-purge control, the combustion system 100 supplies nitrogen to the fuel gas supply passage 232 during operation control. This allows the combustion system 100 to dilute hydrogen with nitrogen, thereby lowering the flame temperature. As a result, the combustion system 100 can reduce the NOx concentration in the exhaust gas of fuel gases with high flame temperatures, such as hydrogen.

[0073] Furthermore, the combustion system 100 can increase the flow rate of the mixed gas (hydrogen and nitrogen) injected from the fuel injection port of the burner 112, thereby promoting self-exhaust gas recirculation, which allows the combustion system 100 to lower the flame temperature and further reduce the NOx concentration in the exhaust gas.

[0074] Furthermore, the combustion system 100 controls the flow rate of nitrogen during the in-operation control so that the concentration of NOx is equal to or less than a predetermined value, thereby making it possible to reduce the concentration of NOx in the exhaust gas to equal to or less than the predetermined value.

[0075] Furthermore, since the combustion system 100 supplies nitrogen to the fuel gas supply passage 232 during control during operation, the nozzle of the burner 112 and the like can be cooled, and the durability of the burner 112 can be improved.

[0076] Furthermore, as described above, during the control during operation, the flow rate control unit 140 controls the flow rate of hydrogen supplied to the burner 112 in accordance with the required heat quantity while keeping the air ratio constant. As a result, during the control during operation, the flow rate control unit 140 can improve the thermal efficiency of the heating operation by burning hydrogen.

[0077] [First Modification] In the first embodiment described above, the flow rate control unit 140 refers to the NOx information stored in the memory 134 and controls the opening degree of the flow rate adjustment valve 262 so that the concentration of NOx contained in the exhaust gas becomes equal to or less than a predetermined value during the in-operation control from time T5 to time T6. However, the flow rate control unit 140 may supply nitrogen to the fuel gas supply path 232 through the inert gas supply path 254 during the in-operation control.

[0078] 6 is a diagram illustrating the control of the flow rate control unit 140 according to the first modified example. In FIG. 6, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0079] As shown in FIG. 6, the flow rate control unit 140 of the first modified example adjusts the opening degree of the flow rate adjustment valve 262 during the in-operation control period from time T5 to time T6, and maintains the flow rate of nitrogen supplied to the fuel gas supply path 232 at Fa.

[0080] That is, the flow rate control unit 140 of the first modified example maintains the opening degree of the flow rate adjustment valve 262 so that the nitrogen supplied to the fuel gas supply channel 232 is at a flow rate Fa from time T1 to time T8.

[0081] As described above, during the in-operation control, the flow rate control unit 140 of the first modified example supplies nitrogen to the fuel gas supply path 232. This allows the flow rate control unit 140 of the first modified example to lower the flame temperature, thereby making it possible to reduce the concentration of NOx in the exhaust gas.

[0082] Furthermore, the flow control unit 140 of the first modified example supplies nitrogen to the fuel gas supply path 232 during operation control, thereby making it possible to cool the nozzle of the burner 112 and the like, thereby improving the durability of the burner 112.

[0083] [Second Modification] 7 is a diagram illustrating the control of the flow rate control unit 140 according to the second modified example. In FIG. 7, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0084] As shown in FIG. 7, the flow rate control unit 140 of the second modified example controls the flow rate adjustment valve 262 during the control during operation so that nitrogen is supplied at a constant rate relative to the flow rate of hydrogen supplied to the burner 112.

[0085] For example, when hydrogen is supplied to the burner 112 at a flow rate F1, the flow rate control unit 140 of the second modified example controls the flow rate adjustment valve 262 so that nitrogen has a flow rate Fc. The nitrogen flow rate Fc is equal to or greater than the flow rate Fa, for example, 20% by volume of the hydrogen flow rate F1. Furthermore, when hydrogen is supplied to the burner 112 at a flow rate F2, the flow rate control unit 140 of the second modified example controls the flow rate adjustment valve 262 so that nitrogen has a flow rate Fd. The nitrogen flow rate Fd is, for example, 20% by volume of the hydrogen flow rate F2.

[0086] As described above, the flow rate control unit 140 of the second modified example sets the flow rate of nitrogen to a predetermined volume ratio (for example, 20% by volume) relative to the flow rate of hydrogen. As a result, in the second modified example, the concentration of NOx in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see FIG. 5). Therefore, in the second modified example, the concentration of NOx in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned (combustion conditions).

[0087] Furthermore, during the in-operation control, the flow rate control unit 140 of the second modified example supplies nitrogen to the fuel gas supply path 232. This allows the flow rate control unit 140 of the second modified example to lower the flame temperature, thereby making it possible to reduce the concentration of NOx in the exhaust gas.

[0088] Furthermore, the flow control unit 140 of the second modified example supplies nitrogen to the fuel gas supply path 232 during operation control, thereby making it possible to cool the nozzle of the burner 112 and the like, thereby improving the durability of the burner 112.

[0089] [Third Modification] 8 is a diagram illustrating the control of the flow rate control unit 140 according to the third modified example. In FIG. 8, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0090] 8, there is a period during the in-operation control from time T5 to time T6 during which the flow rate control unit 140 of the third modified example closes the shutoff valves 236a, 236b (the flow rate of hydrogen is zero) based on the required heat quantity of the combustion equipment 110. The flow rate control unit 140 of the third modified example maintains the supply of nitrogen to the fuel gas supply path 232 even during this period during which the flow rate of hydrogen is zero during the in-operation control.

[0091] A comparative example can be considered in which the supply of nitrogen to the fuel gas supply channel 232 is stopped when the supply of hydrogen is stopped during in-operation control. In such a comparative example, flashback may occur unless the fuel gas supply channel 232 is purged with nitrogen before the supply of hydrogen is resumed. In other words, in the comparative example, it is necessary to purge the fuel gas supply channel 232 with nitrogen before resuming the supply of hydrogen. Therefore, in the comparative example, the responsiveness of stopping and resuming the supply of hydrogen during in-operation control is reduced, which is a problem in that the accuracy of temperature control of the combustion equipment 110 is reduced.

[0092] On the other hand, the flow rate control unit 140 of the third modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the third modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, thereby improving the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the third modified example can control the temperature of the combustion equipment 110 with high precision.

[0093] Furthermore, the flow rate control unit 140 of the third modified example sets the flow rate of nitrogen to a predetermined volume ratio (for example, 20% by volume) relative to the flow rate of hydrogen. As a result, in the third modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see FIG. 5). Therefore, in the third modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

[0094] [Fourth Variation] 9 is a diagram illustrating the control of the flow rate control unit 140 according to the fourth modification. In FIG. 9, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0095] 9, the flow rate control unit 140 of the fourth modified example opens and closes the shutoff valves 236a and 236b so that the flow rate of hydrogen supplied to the burner 112 is zero or a flow rate F2. For example, the flow rate control unit 140 of the fourth modified example opens the shutoff valves 236a and 236b from time T2 to time T5 to supply hydrogen to the burner 112 at a constant flow rate of F2.

[0096] In addition, the flow control unit 140 of the fourth modified example opens and closes the shut-off valves 236a, 236b so that the flow rate of hydrogen supplied to the burner 112 is zero (supply stopped) or flow rate F2 (supply resumed) based on the required heat quantity of the combustion equipment 110 between time T5 and time T6.

[0097] Then, from time T6 to time T7, the flow rate control unit 140 of the fourth modified example maintains the shutoff valves 236a and 236b in an open state so that the hydrogen supplied to the burner 112 is at a flow rate F2.

[0098] Furthermore, similar to the first modified example, the flow control unit 140 of the fourth modified example maintains the opening degree of the flow control valve 262 so that the nitrogen supplied to the fuel gas supply path 232 is at a flow rate Fa from time T1 to time T8.

[0099] As described above, the flow rate control unit 140 of the fourth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the fourth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, thereby improving the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the fourth modified example can control the temperature of the combustion equipment 110 with high precision.

[0100] [Fifth Variation] 10 is a diagram illustrating the control of the flow rate control unit 140 according to the fifth modified example. In FIG. 10, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0101] As shown in FIG. 10, the flow rate control of hydrogen by the flow rate control unit 140 of the fifth modified example (opening and closing control of the shutoff valves 236a, 236b) is the same as that of the fourth modified example.

[0102] On the other hand, the flow rate control unit 140 of the fifth modified example controls the flow rate adjustment valve 262 during the control during operation so that nitrogen is supplied at a constant rate relative to the flow rate of hydrogen supplied to the burner 112.

[0103] For example, when the flow rate of hydrogen supplied to the burner 112 is F2, the flow rate control unit 140 of the fifth modified example controls the flow rate adjustment valve 262 so that the flow rate of nitrogen is Fe. The flow rate of nitrogen Fe is, for example, 20% by volume of the flow rate F2 of hydrogen. Furthermore, when the flow rate of hydrogen supplied to the burner 112 is zero, the flow rate control unit 140 of the fifth modified example controls the flow rate adjustment valve 262 so that the flow rate of nitrogen is Fa.

[0104] As described above, the flow rate control unit 140 of the fifth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the fifth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, thereby improving the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the fifth modified example can control the temperature of the combustion equipment 110 with high precision.

[0105] Furthermore, the flow rate control unit 140 of the fifth modified example sets the flow rate of nitrogen to a predetermined volume ratio (for example, 20% by volume) relative to the flow rate of hydrogen. As a result, in the fifth modified example, the concentration of NOx in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see FIG. 5). Therefore, in the fifth modified example, the concentration of NOx in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

[0106] [Sixth Modification] 11 is a diagram illustrating the control of the flow rate control unit 140 according to the sixth modified example. In FIG. 11, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0107] As shown in FIG. 11, the flow rate control of nitrogen by the flow rate control unit 140 (control of the flow rate adjustment valve 262) in the sixth modified example is the same as in the first modified example.

[0108] On the other hand, the flow rate control unit 140 of the sixth modified example controls the flow rate of hydrogen supplied to the burner 112 to one of zero (supply stopped), flow rate F1 (supply resumed), and flow rate F2 (supply resumed) during in-operation control. As shown in Fig. 11, the flow rate control unit 140 of the sixth modified example adjusts the aperture of the flow rate control valve 216 so that the hydrogen flow rate becomes F1 during operation start control (time T2), and controls the flow rates of air and hydrogen. Furthermore, at time T3 during in-operation control, the flow rate control unit 140 of the sixth modified example increases the aperture of the flow rate control valve 216 to increase the flow rate of air and the flow rate of hydrogen so that the hydrogen flow rate becomes F2, thereby performing rated combustion.

[0109] Then, the flow control unit 140 of the sixth variant adjusts the opening of the flow control valve 216 and controls the air flow rate and the hydrogen flow rate so that the flow rate of hydrogen supplied to the burner 112 is either zero, a flow rate F1, or a flow rate F2 based on the required heat quantity of the combustion equipment 110 during the period from time T5 to time T6 of the in-operation control.

[0110] Furthermore, the flow rate control unit 140 of the sixth modified example performs rated combustion by adjusting the opening of the flow rate control valve 216 so that the hydrogen flows at a flow rate F2 during the in-operation control period from time T6 to time T7.

[0111] As described above, the flow rate control unit 140 of the sixth modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the sixth modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, thereby improving the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the sixth modified example can control the temperature of the combustion equipment 110 with high precision.

[0112] [Seventh Variation] 12 is a diagram illustrating the control of the flow rate control unit 140 according to the seventh modification. In FIG. 12, the vertical axis represents the flow rate, and the horizontal axis represents time.

[0113] As shown in FIG. 12, the flow rate control of hydrogen by the flow rate control unit 140 (control of the flow rate control valve 216) in the seventh modified example is the same as in the sixth modified example.

[0114] On the other hand, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 during the control during operation so that nitrogen is supplied at a constant rate relative to the flow rate of hydrogen supplied to the burner 112.

[0115] For example, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 so that when hydrogen supplied to the burner 112 is at a flow rate F1, nitrogen is at a flow rate Ff. The flow rate Ff of nitrogen is greater than the flow rate Fa, for example, 20% by volume of the hydrogen flow rate F1. Furthermore, when hydrogen supplied to the burner 112 is at a flow rate F2, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 so that nitrogen is at a flow rate Fg. The flow rate Fg of nitrogen is, for example, For example, the hydrogen flow rate is 20% by volume of F2.

[0116] Furthermore, the flow rate control unit 140 of the seventh modified example controls the flow rate adjustment valve 262 during the in-operation control so that the flow rate of nitrogen becomes Fa even when the flow rate of hydrogen supplied to the burner 112 is zero.

[0117] As described above, the flow rate control unit 140 of the seventh modified example constantly supplies nitrogen to the fuel gas supply path 232 during in-operation control. Therefore, the flow rate control unit 140 of the seventh modified example can instantly switch between stopping and restarting the supply of hydrogen during in-operation control, thereby improving the responsiveness of stopping and restarting the supply of hydrogen. Therefore, the flow rate control unit 140 of the seventh modified example can control the temperature of the combustion equipment 110 with high precision.

[0118] Furthermore, the flow rate control unit 140 of the seventh modified example sets the flow rate of nitrogen to a predetermined volume ratio (for example, 20% by volume) relative to the flow rate of hydrogen. As a result, in the seventh modified example, the NOx concentration in the exhaust gas can be reduced regardless of the amount of hydrogen burned (see FIG. 5). Therefore, in the seventh modified example, the NOx concentration in the exhaust gas can be kept below a predetermined value regardless of the amount of hydrogen burned.

[0119] [Second embodiment] Fig. 13 is a diagram illustrating a combustion system 300 according to the second embodiment. Fig. 14 is a functional block diagram of a control device 330 according to the second embodiment. In Fig. 13, dashed arrows indicate the flow of signals.

[0120] 13, the combustion system 300 includes a combustion facility 110, a gas supply unit 120, a concentration sensor 310, and a control device 330. Note that components that are substantially the same as those in the combustion system 100 described above are denoted by the same reference numerals and will not be described again.

[0121] The concentration sensor 310 detects the concentration of NOx contained in the exhaust gas generated by burning hydrogen in the combustion equipment 110.

[0122] As shown in FIG. 14, the control device 330 includes a central control unit 332 and a memory 334 .

[0123] The central control unit 332 is configured with a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 332 reads programs, parameters, etc. for operating the CPU from the ROM. The central control unit 332 manages and controls the entire combustion system 300 in cooperation with RAM as a work area and other electronic circuits.

[0124] The memory 334 is configured with a ROM, a RAM, a flash memory, a HDD, etc. The memory 334 stores programs and various data used by the central control unit 332.

[0125] In this embodiment, the central control unit 332 functions as a signal acquisition unit 340 and a flow rate control unit 342 .

[0126] The signal acquisition unit 340 acquires the detection result of the concentration sensor 310 .

[0127] As in the first embodiment described above, the flow rate control unit 342 controls one or more of the flow rate of hydrogen supplied to the burner 112 through the fuel gas supply path 232, the flow rate of nitrogen supplied to the fuel gas supply path 232 through the inert gas supply path 254, and the flow rate of air supplied to the burner 112 through the oxidant gas supply path 212, thereby performing pre-purge control, operation start control, operation stop control, and post-purge control.

[0128] In this embodiment, after rated combustion during in-operation control, that is, from time T5 to time T6, the flow rate control unit 342 adjusts the aperture of the flow rate control valve 216 to control the flow rate of air based on the required heat quantity of the combustion equipment 110, thereby controlling the hydrogen supplied to the burner 112 to a range of not less than flow rate F1 and not more than flow rate F2. Furthermore, from time T5 to time T6, based on the detection result of the concentration sensor 310 acquired by the signal acquisition unit 340, the flow rate control unit 140 controls the aperture of the flow rate adjustment valve 262 to control the nitrogen supplied to the fuel gas supply path 232 to a range of not less than flow rate Fa and not more than flow rate Fb.

[0129] As described above, the combustion system 300 according to this embodiment controls the flow rate of nitrogen during the in-operation control so that the NOx concentration is equal to or less than a predetermined value. This makes it possible to reduce the NOx concentration in the exhaust gas to equal to or less than the predetermined value.

[0130] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present invention.

[0131] For example, in the first embodiment described above, the fuel supply unit 230 is provided with the pressure equalizing valve 238. However, the fuel supply unit 230 may be provided with a flow control valve instead of the pressure equalizing valve 238. The flow control valve is, for example, a butterfly valve with a control motor.

[0132] In the first embodiment, the fuel supply unit 230 includes the shutoff valve 236a and the shutoff valve 236b. However, the fuel supply unit 230 may include either the shutoff valve 236a or the shutoff valve 236b.

[0133] In the first embodiment and the first to seventh modifications, the flow rate control unit 140 performs pre-purge control. However, it is sufficient that the flow rate control unit 140 performs at least operation start control, operation control, operation stop control, and post-purge control.

[0134] Furthermore, the combustion system 300 of the second embodiment may perform the controls of the first to seventh modified examples.

[0135] In the first and second embodiments, the gas supply unit 120 includes the pressure equalizing valve 238, and the air ratio is kept constant. However, the flow rate control unit may control the flow rate of the fuel gas supplied to the burner 112 in accordance with the required heat quantity, and may control the flow rate of the oxidizing gas supplied to the burner 112, so that the air ratio is maintained within a predetermined air ratio range, at least during control during operation. [Explanation of symbols]

[0136] 100 Combustion System 112 Burner 140 Flow control section 212 Oxidant gas supply line 232 Fuel gas supply line 254 Inert gas supply line 300 Combustion System 342 Flow control section

Claims

1. Burner and a fuel gas supply line connecting a fuel gas supply source and the burner; an oxidant gas supply passage connecting the blower and the burner; an inert gas supply channel connecting an inert gas supply source and the fuel gas supply channel; a flow rate control unit that controls one or more of the flow rate of the fuel gas supplied to the burner through the fuel gas supply path, the flow rate of the oxidant gas supplied to the burner through the oxidant gas supply path, and the flow rate of the inert gas supplied to the fuel gas supply path through the inert gas supply path; Equipped with The flow rate control unit pre-purge control for supplying the inert gas to the fuel gas supply line through the inert gas supply line; an operation start control that is performed after the pre-purge control and starts supplying the fuel gas to the burner to start operation of the burner; an in-operation control that is a control performed after the operation start control and that supplies the fuel gas to the burner for at least a predetermined period of time; an operation stop control that is a control performed after the operation control, and stops the supply of the fuel gas to the burner to stop the operation of the burner; a post-purge control that is a control that is performed after the operation shutdown control, and that supplies the inert gas to the fuel gas supply line through the inert gas supply line for a predetermined time; and The combustion system maintains the supply of the inert gas to the fuel gas supply passage through the inert gas supply passage during the period from the pre-purge control to the post-purge control.

2. 2. The combustion system according to claim 1, wherein the flow rate control unit controls the flow rate of the fuel gas supplied to the burner in accordance with the required heat quantity during the in-operation control, and controls the flow rate of the oxidizer gas supplied to the burner so as to maintain the air ratio within a predetermined range.

3. 3. The combustion system according to claim 1, wherein the flow rate control unit controls the flow rate of the inert gas based on a concentration of NOx contained in exhaust gas generated by burning the fuel gas during the in-operation control.

4. 3. The combustion system according to claim 1, wherein the flow rate control unit increases the flow rate of the inert gas supplied to the fuel gas supply path when the flow rate of the fuel gas supplied to the burner is reduced during the in-operation control.

5. 3. The combustion system according to claim 1, wherein the flow control unit maintains the supply of the inert gas to the fuel gas supply path even when the flow rate of the fuel gas supplied to the burner is set to zero during the in-operation control.

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