Combustion system

Abstract

To provide a combustion system capable of suppressing emission of greenhouse effect gas caused by mixed combustion of combustion supporting fuel with mixed gas containing inert gas and hydrocarbon gas while suppressing atmospheric emission of hydrocarbon gas.SOLUTION: A combustion system 1 includes: a membrane separation device 3 that generates process gas Gp obtained by separating at least part of nitrogen gas Gn from mixed gas Gm by using a separation membrane; a boiler 19 capable of burning at least any of methane gas Gh, the mixed gas Gm and the process gas Gp; and a mixed gas control section 6 that controls supply of the mixed gas Gm to the membrane separation device 3. When inert gas ratio determination means 9 determines a ratio is larger than a first threshold value, the mixed gas control section 6 supplies the mixed gas Gm from a mixed gas line 2 to the membrane separation device 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a combustion system for combusting hydrocarbon gases, including inert gases. [Background technology]

[0002] When transporting natural gas by ship, it is transported in a liquefied state (liquefied gas) by cooling it to approximately -160°C under atmospheric pressure. Ships transporting such liquefied gas store the liquefied gas in liquefied gas tanks equipped with thermal insulation and heat-insulating functions capable of maintaining an extremely low temperature inside the tank. In the liquefied gas tank, boil-off gas (BOG) is generated when the liquefied gas vaporizes due to heat entering the liquefied gas tank. When the BOG generation causes the tank pressure to increase, the liquefied gas tank must discharge the BOG to the outside of the liquefied gas tank once the tank pressure reaches the allowable tank pressure. Meanwhile, due to increasing societal demands for the SDGs and other initiatives in recent years, there is a need to suppress the atmospheric release of BOG, which has a high global warming potential. Patent Document 1 describes a boiler system that continuously burns the BOG generated in the liquefied gas tank.

[0003] When a ship equipped with liquefied gas tanks enters dock, dunk maintenance work involves gas-freeing and gassing up of the liquefied gas tanks. This process requires the disposal of a mixed gas discharged from the liquefied gas tank, which is a mixture of hydrocarbon gas, such as natural gas, and inert gas (such as nitrogen). In gas-freeing, inert gas is gradually supplied into a liquefied gas tank filled with hydrocarbon gas, and the hydrocarbon gas is discharged from the liquefied gas tank. The proportion of natural gas in the liquefied gas tank gradually decreases, and the natural gas in the liquefied gas tank is eventually replaced with inert gas. In gassing up, hydrocarbon gas is gradually supplied into a liquefied gas tank filled with inert gas, and the inert gas is discharged from the liquefied gas tank. The proportion of inert gas in the liquefied gas tank gradually decreases, and the inert gas in the liquefied gas tank is eventually replaced with hydrocarbon gas. During the replacement of hydrocarbon gas with inert gas and the replacement of inert gas with hydrocarbon gas, a mixed gas of hydrocarbon gas and inert gas is discharged.

[0004] The boiler system described in Patent Document 1 controls the supply of fuel to the boiler in accordance with the mixture ratio of inert gas contained in the BOG discharged from the liquefied gas tank. When the mixture ratio of inert gas in the supplied BOG is greater than a reference value, the boiler supplies and combusts the BOG containing the inert gas and liquid fuel, etc., to the boiler in order to stabilize combustion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-2780 Summary of the Invention [Problem to be solved by the invention]

[0006] The boiler system described in Patent Document 1 co-combustes a mixed gas that is difficult to combust by itself due to a high proportion of inert gas, with the mixed gas and a supporting fuel. In other words, the boiler system suppresses the atmospheric release of the mixed gas that is difficult to combust by itself, while releasing greenhouse gases (such as carbon dioxide) generated by the combustion of the supporting fuel into the atmosphere. Therefore, the boiler system has a problem in that if the proportion of inert gas in the supplied BOG is higher than the standard value, the combustion of the supporting fuel increases greenhouse gas emissions.

[0007] The object of the present invention is to realize a combustion system that, in suppressing atmospheric release of a mixed gas containing an inert gas and a hydrocarbon gas, can expand the range of inert gas proportions in a mixed gas that can be combusted without co-combustion of a combustion supporting fuel, even when the mixing ratio of the inert gas in the mixed gas increases to the point where combustion of a combustion supporting fuel is required, and can suppress the generation of carbon dioxide due to combustion while suppressing the emission of greenhouse gases. [Means for solving the problem]

[0008] A combustion system according to one embodiment of the present invention includes a membrane separation device that generates a process gas by separating at least a portion of the inert gas from a mixed gas of a hydrocarbon gas and an inert gas using a separation membrane, a mixed gas line that supplies the mixed gas to the membrane separation device, a combustion device capable of combusting at least one of the hydrocarbon gas, the mixed gas, and the process gas, a fuel gas line that supplies at least one of the hydrocarbon gas, the mixed gas, and the process gas to the combustion device, and a mixed gas control unit that controls the supply of the mixed gas to the membrane separation device. The mixed gas control unit includes an inert gas proportion determination unit that determines the proportion of the inert gas contained in the mixed gas. When the inert gas proportion determination unit determines that the proportion is greater than a first threshold, the mixed gas control unit supplies the mixed gas from the mixed gas line to the membrane separation device.

[0009] The combustion system described above separates at least a portion of the inert gas from the mixed gas using a membrane separation device to maintain an appropriate combustion state in the combustion device when the proportion of the inert gas contained in the mixed gas is greater than a first threshold. The proportion of hydrocarbon gas in the treated gas from which at least a portion of the inert gas has been separated is greater than the proportion of hydrocarbon gas in the mixed gas before separation. Therefore, when the proportion of the inert gas contained in the mixed gas is greater than the first threshold, the combustion system increases the proportion of hydrocarbon gas using the membrane separation device, thereby continuously combusting the treated gas in the combustion device without supplying a combustion support fuel. This expands the range of inert gas proportions in the mixed gas that can be combusted without co-combustion of a combustion support fuel, even when inert gas and hydrocarbon gas are mixed, making it possible to reduce greenhouse gas emissions while suppressing carbon dioxide generation due to combustion.

[0010] From another perspective, the combustion system of the present invention preferably includes the following configuration: The combustion device includes a burner capable of combusting at least one of the hydrocarbon gas, the mixed gas, and the process gas, which are fuel gases, and a combustion supporting fuel for combusting the mixed gas or the process gas, and a combustion control unit that controls combustion in the combustion device. The combustion control unit includes a combustion heat quantity determination unit that determines the amount of heat generated by combustion of the fuel gas supplied to the burner, and when the combustion heat quantity determination unit determines that the amount of heat generated by combustion of at least one of the mixed gas and the process gas supplied to the burner is less than a second threshold, the combustion control unit controls the combustion of at least one of the mixed gas and the process gas and the combustion supporting fuel.

[0011] In the above configuration, when the combustion control unit of the combustion device determines that the proportion of hydrocarbon gas in the fuel is low and the amount of heat generated in the burner is less than a second threshold, it supplies auxiliary fuel to the burner to maintain an appropriate combustion state in the burner. In other words, the combustion system uses a membrane separation device to increase the proportion of hydrocarbons in the mixed gas that is difficult to combust alone in the combustion device, thereby maintaining combustion in the combustion device without supplying the auxiliary fuel until the amount of heat generated in the burner becomes less than the second threshold. This expands the range of inert gas proportions in the mixed gas that can be combusted without co-combustion of auxiliary fuel, even when inert gas and hydrocarbon gas are mixed, making it possible to suppress carbon dioxide generation during combustion and reduce greenhouse gas emissions.

[0012] From another perspective, the combustion system of the present invention preferably includes the following configuration: The combustion device includes a burner capable of combusting the hydrocarbon gas, which is a fuel gas, a combustion supporting fuel for combusting the mixed gas, or the process gas, and at least one of the mixed gas and the process gas, and a combustion control unit that controls combustion in the combustion device. The combustion control unit includes a combustion heat quantity determination unit that determines the magnitude of the amount of heat generated by combustion of the fuel gas supplied to the burner. When the combustion heat quantity determination unit determines that the amount of heat generated by combustion of at least one of the mixed gas and the process gas supplied to the burner is less than a second threshold, the combustion control unit controls the mixed gas control unit to combust at least one of the mixed gas and the process gas with the combustion supporting fuel after a predetermined time has elapsed since the mixed gas was supplied to the membrane separation device.

[0013] In the above configuration, when the combustion control unit determines that the amount of heat generated by the burner is less than the second threshold, the combustion control unit can adjust the flow rate of combustion air so that the process gas and the auxiliary fuel are stably combusted while combusting the process gas that has passed through the membrane separation device. Therefore, combustion oxygen is supplied to the combustion device based on the type and amount of fuel. This expands the range of inert gas ratio in the mixed gas that can be combusted without co-combustion of the auxiliary fuel, even when an inert gas and a hydrocarbon gas are mixed. This makes it possible to suppress the generation of carbon dioxide due to combustion and reduce greenhouse gas emissions.

[0014] From another perspective, the combustion system of the present invention preferably includes the following configuration: the combustion device includes a fuel gas flow rate adjuster provided in the fuel gas line and adjusting the flow rate of the fuel gas, an air supply line to which combustion air is supplied, an air flow rate adjuster provided in the air supply line and adjusting the flow rate of the combustion air, and an exhaust gas oxygen concentration detector that detects the oxygen concentration in the exhaust gas. The combustion heat quantity determiner calculates the quantity of heat generated by combustion of the fuel gas supplied to the burner based on a gas fuel flow rate adjustment value of the gas fuel flow rate adjuster, an air flow rate adjustment value of the air flow rate adjuster, and a detection value of the exhaust gas oxygen concentration detector.

[0015] In the above-described configuration, the amount of fuel contained in the mixed gas, which is the fuel gas supplied to the combustion device, and the process gas varies depending on the flow rate of the fuel gas, the hydrocarbon gas concentration in the fuel gas, the density of the fuel gas, the pressure of the fuel gas, etc. Meanwhile, the calorific value of the fuel gas combusted in the burner is correlated with the amount of fuel contained in the fuel gas. Therefore, the amount of fuel contained in the fuel gas can be calculated from the flow rate of the fuel gas, the oxygen concentration in the exhaust gas, and the flow rate of the combustion air. As a result, since the combustion support fuel is supplied to the burner at an appropriate timing, even when an inert gas and a hydrocarbon gas are mixed, the range of the inert gas ratio in the mixed gas that can be combusted and processed without co-combustion of the combustion support fuel can be expanded, thereby suppressing the generation of carbon dioxide due to combustion and reducing greenhouse gas emissions. [Effects of the Invention]

[0016] Even when an inert gas and a hydrocarbon gas are mixed, the range of the inert gas ratio in the mixed gas that can be combusted without mixing in a combustion support fuel can be expanded, and greenhouse gas emissions can be reduced while suppressing the generation of carbon dioxide due to combustion. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a BOG treatment system including a combustion system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the path of fuel supplied to the combustion device when the proportion of inert gas in the supplied gas is equal to or less than a first threshold value, and the path of fuel supplied to the combustion device when the proportion of inert gas in the supplied gas is greater than the first threshold value, in a combustion system according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing a path of fuel supplied to the combustion device when the amount of heat generated per unit time in the combustion device is less than a second threshold value in the combustion system according to the second embodiment of the present invention. [Figure 4] FIG. 4 is a table showing the control of the shutoff valve when gas is released from the liquefied gas tank in the combustion system according to the second embodiment of the present invention. [Figure 5] FIG. 5 is a table showing the control of the shutoff valve when gassing up the liquefied gas tank in the combustion system according to the second embodiment of the present invention.

[0018] Each embodiment of the combustion system according to the present invention will be described with reference to the drawings. In each drawing, the same parts are designated by the same reference numerals, and the description of the same parts will not be repeated. Note that the dimensions of the components in each drawing do not faithfully represent the actual dimensions of the components and the dimensional ratios of the components.

[0019] In the following description, hydrocarbon gas refers to a hydrocarbon compound gas such as natural gas, methane gas, ethane gas, or propane gas. Inert gas refers to a low-reactivity gas such as helium gas or nitrogen gas. Mixed gas refers to a mixture of the hydrocarbon gas and the inert gas discharged from a liquefied gas tank. Examples of mixed gases include a mixture of natural gas and nitrogen gas, and a mixture of methane gas and nitrogen gas. Treated gas refers to a gas from which at least a portion of the inert gas contained in the mixed gas has been separated by the membrane separation device 3. Fuel gas refers to hydrocarbon gas, mixed gas, or treated gas supplied to the boiler 19 as fuel (see FIG. 1).

[0020] In the following description, in the free flow line L1 through which at least one of hydrocarbon gas and mixed gas flows from the liquefied gas tank T1, the liquefied gas tank T1 side is defined as the upstream side, and the boiler 19 side is defined as the downstream side. In the liquid fuel line 14 that supplies combustion supporting fuel such as heavy oil from the liquid fuel tank 15 to the boiler 19, the liquid fuel tank 15 side is defined as the upstream side, and the boiler 19 side is defined as the downstream side (see FIG. 1).

[0021] Furthermore, in the following description, the expressions "fix," "connect," and "attach" (hereinafter referred to as "fixing") include not only cases where members are directly fixed to each other, but also cases where members are fixed via other members. In other words, in the following description, the expression "fixing" includes both direct and indirect fixing of members to each other.

[0022] (Embodiment 1) Using Fig. 1, a combustion system 1 according to a first embodiment of the present invention will be described taking as an example a case in which methane, a main component of natural gas, is stored in a liquefied gas storage tank. Fig. 1 is a schematic configuration diagram of a liquefied gas fuel system S including the combustion system 1 according to the first embodiment of the present invention. In this embodiment, the liquefied gas fuel system S is installed on a ship that transports liquefied gas. The liquefied gas fuel system S processes a mixed gas generated in a liquefied gas tank T1.

[0023] (Liquefied gas fuel system) 1, the liquefied gas tank T1 is configured to be capable of gas free (nitrogen gas purging) in which nitrogen gas is supplied into the liquefied gas tank T1 through a nitrogen gas line L2 in order to discharge methane gas and the like from the liquefied gas tank T1 to the outside. Also, the liquefied gas tank T1 is configured to be capable of gassing up (methane gas purging) in which methane gas is supplied into the liquefied gas tank T1 through a methane gas line L3 in order to discharge the nitrogen gas from the liquefied gas tank T1 to the outside.

[0024] The liquefied gas fuel system S includes a free flow line L1, a compressor C, a generator Ge, a pump P, a vaporizer H, a main engine Eg, and a combustion system 1.

[0025] The free flow line L1 is a pipe that discharges methane gas Gh (hereinafter simply referred to as "methane gas Gh") containing BOG formed when liquefied methane gas in the liquefied gas tank T1 is evaporated by heat, a mixed gas Gm of nitrogen gas and methane gas (hereinafter simply referred to as "mixed gas Gm") supplied to the liquefied gas tank T1, and nitrogen gas Gn to the outside of the liquefied gas tank T1. The free flow line L1 is connected to the liquefied gas tank T1.

[0026] The compressor C pressurizes the methane gas Gh. The compressor C is connected to the free flow line L1. The generator Ge generates electricity by burning the methane gas Gh. The generator Ge is connected downstream of the compressor C. The generator Ge is supplied with the methane gas Gh that has been pressurized by the compressor C.

[0027] The pump P supplies liquefied methane in the liquefied gas tank T1 to the vaporizer H. The pump P is connected to the liquefied gas tank T1. The vaporizer H vaporizes the liquefied methane. The vaporizer H is connected downstream of the pump P. The main engine Eg generates power by burning methane gas Gh. The main engine Eg is connected downstream of the vaporizer H. The main engine Eg is supplied with methane gas Gh vaporized by the vaporizer H.

[0028] (Combustion System) The combustion system 1 combusts the methane gas Gh and the mixed gas Gm flowing through the free flow line L1. The combustion system 1 includes a mixed gas line 2, a membrane separation device 3, a fuel gas line 4, a bypass line 5, a mixed gas control unit 6, a fuel gas flow rate adjustment unit 10, a liquid fuel line 14, a liquid fuel tank 15, a liquid fuel flow rate adjustment unit 16, a boiler 19, an air flow rate adjustment unit 22, an exhaust gas oxygen concentration detection unit 23, and a combustion control unit 30.

[0029] The mixed gas line 2 is a pipe that supplies the methane gas Gh and mixed gas Gm flowing in the free flow line L1 to the mixed gas control unit 6. The upstream side of the mixed gas line 2 is connected to the free flow line L1. The downstream side of the mixed gas line 2 is connected to the mixed gas control unit 6. The methane gas Gh (BOG) in the free flow line L1 flows into the mixed gas line 2 due to the pressure in the liquefied gas tank T1. In addition, either the methane gas Gh, mixed gas Gm, or nitrogen gas Gn in the free flow line L1 flows into the mixed gas line 2 due to the pressure of the nitrogen gas Gn supplied to the liquefied gas tank T1 through the nitrogen gas line L2, or the pressure of the methane gas Gh supplied to the liquefied gas tank T1 through the methane gas line L3.

[0030] The mixed gas control unit 6 switches between supplying the methane gas Gh or the mixed gas Gm flowing in the mixed gas line 2 to the membrane separation device 3 and supplying it to the bypass line 5. The mixed gas control unit 6 has a shutoff valve 7 for the membrane separation device and a shutoff valve 8 for the bypass line.

[0031] The membrane separation apparatus shutoff valve 7 is configured as an air-driven valve, an electric valve, etc. The membrane separation apparatus shutoff valve 7 can block the flow of the mixed gas Gm in the mixed gas line 2, and is switched between an open state in which the mixed gas Gm is supplied from the free flow line L1 to the membrane separation apparatus 3, and a closed state in which the mixed gas Gm is not supplied to the membrane separation apparatus 3.

[0032] The membrane separation device 3 separates at least a portion of the nitrogen gas Gn contained in the mixed gas Gm. The membrane separation device 3 has a separation membrane that separates methane gas Gh and nitrogen gas Gn, for example, based on differences in molecular size. By separating at least a portion of the nitrogen gas Gn contained in the mixed gas Gm, the nitrogen gas proportion (nitrogen gas concentration) Cn, which is the proportion of nitrogen gas in the mixed gas Gm, decreases (the methane gas proportion (methane gas concentration) Ch, which is the proportion of methane gas in the mixed gas Gm, increases). In other words, the membrane separation device 3 generates a treated gas Gp from the mixed gas Gm with an increased methane gas proportion Ch, thereby expanding the range of the nitrogen gas proportion Cn of the mixed gas Gm that can be combusted and treated in the boiler 19 without co-firing heavy oil (heavy oil A) Fo, which is a combustion supporting fuel.

[0033] A mixed gas line 2 is connected to the inlet of the membrane separation device 3. A fuel gas line 4 is connected to the outlet of the membrane separation device 3. A mixed gas Gm is supplied to the inlet of the membrane separation device 3. A treated gas Gp is ​​discharged from the outlet of the membrane separation device 3. Separated nitrogen gas Gn is discharged from the outlet of the membrane separation device 3. A nitrogen discharge valve 3a is provided at the outlet. A pressure booster may be provided on the inlet side of the membrane separation device 3 as needed to ensure the pressure required for membrane separation of the nitrogen gas Gn in the mixed gas Gm.

[0034] The bypass line 5 is a pipe that supplies the methane gas Gh and the mixed gas Gm flowing in the mixed gas line 2 to the fuel gas line 4. The upstream side of the bypass line 5 is connected to the mixed gas line 2. The downstream side of the bypass line 5 is connected to the fuel gas line 4. The bypass line 5 circulates either the methane gas Gh or the mixed gas Gm in the free flow line L1. Either the methane gas Gh or the mixed gas Gm in the free flow line L1 flows into the bypass line 5 due to the pressure of the nitrogen gas Gn supplied to the liquefied gas tank T1 through the nitrogen gas line L2 or the pressure of the methane gas Gh supplied to the liquefied gas tank T1 through the methane gas line L3.

[0035] The fuel gas line 4 is a pipe that supplies the treated gas Gp to the boiler 19. The upstream side of the fuel gas line 4 is connected to the membrane separation device 3 and the bypass line 5. The downstream side of the fuel gas line 4 is connected to the boiler 19 via a fuel gas flow rate adjuster 10. The fuel gas line 4 circulates the treated gas Gp discharged from the membrane separation device 3. The fuel gas line 4 also circulates at least one of methane gas Gh, mixed gas Gm, and nitrogen gas Gn in the free flow line L1 via the bypass line 5. In the following embodiments, the fuel gas is at least one of methane gas Gh, mixed gas Gm, and treated gas Gp.

[0036] The bypass line shutoff valve 8 is configured as an air-driven valve, an electric valve, etc. The bypass line shutoff valve 8 can block the flow of the mixed gas in the bypass line 5, and is switched between an open state in which the mixed gas Gm is supplied to the bypass line 5 from the free flow line L1 via the mixed gas line 2, and a closed state in which the mixed gas Gm is not supplied to the bypass line 5.

[0037] The fuel gas flow rate adjustment unit 10 is a valve unit that adjusts the flow rates of the methane gas Gh, the mixed gas Gm, and the treated gas Gp. The fuel gas flow rate adjustment unit 10 is connected to the fuel gas line 4 downstream of the junction with the bypass line 5 and upstream of the boiler 19. The fuel gas flow rate adjustment unit 10 has a fuel gas pressure reducing valve 11, a fuel gas shutoff valve 12, and a fuel gas flow rate adjustment valve 13. The fuel gas pressure reducing valve 11, the fuel gas shutoff valve 12, and the fuel gas flow rate adjustment valve 13 are each configured by a direct-acting diaphragm-type pressure reducing valve, an air-driven direct-acting pressure reducing valve, a pilot-operated pressure reducing valve, an electric valve, or the like.

[0038] The fuel gas pressure reducing valve 11 adjusts the pressure of the fuel gas so that the pressure of the fuel gas downstream of the fuel gas pressure reducing valve 11 is below a certain pressure. The fuel gas shutoff valve 12 shuts off the flow of fuel gas. The fuel gas flow rate adjusting valve 13 adjusts the flow rate of the fuel gas.

[0039] The liquid fuel line 14 is a pipe that supplies heavy oil F0, which is a supporting fuel, to the boiler 19. The liquid fuel line 14 is connected to a liquid fuel tank 15 that stores heavy oil Lp, and is configured to allow the heavy oil Lp from the liquid fuel tank 15 to flow into the liquid fuel line 14. The liquid fuel line 14 may also be connected to the generator Ge and the main engine Eg, and configured to allow the generator Ge and the main engine Eg to use the heavy oil Lp.

[0040] The liquid fuel flow rate adjustment unit 16 is a valve unit that adjusts the flow rate of the heavy oil Lp. The liquid fuel flow rate adjustment unit 16 is provided on the boiler inlet side of the liquid fuel line 14, and has a liquid fuel shutoff valve 17 and a liquid fuel flow rate adjustment valve 18. The liquid fuel shutoff valve 17 and the liquid fuel flow rate adjustment valve 18 are configured as air-driven valves, electric valves, or the like. The liquid fuel shutoff valve 17 shuts off the flow of the heavy oil Lp. The liquid fuel flow rate adjustment valve 18 adjusts the flow rate of the heavy oil Lp.

[0041] The boiler 19, which is a combustion device, heats water using heat from the combustion of fuel to generate hot water or steam. The boiler 19 has a dual fuel burner capable of burning at least one of fuel gas containing at least one of methane gas Gh, mixed gas Gm, and treated gas Gp, and heavy oil Lp. The boiler 19 supplies hot water or steam to the inside of the ship through a heat medium line 19a. The boiler 19 takes in combustion air through an air supply line 20 and discharges exhaust gas overboard through an exhaust line 21.

[0042] The boiler 19 is an auxiliary boiler that is not used to supply power to the main engine Eg of the ship. The steam generated by the boiler 19 is supplied to steam-using equipment of the ship (heating liquid fuel and cargo, supplying hot water for cleaning, etc., a heat source for a binary power generation system, and supplying steam to a steam turbine generator) through a heat medium line 19a, and is then condensed by a condenser or the like.

[0043] Air flow rate adjustment unit 22 is an air damper, combustion air blower, or the like that adjusts the flow rate of combustion air supplied to boiler 19. Air flow rate adjustment unit 22 is located in air supply line 20 that supplies combustion air to boiler 19. The flow rate of combustion air may be adjusted by adjusting the motor rotation speed of the combustion air blower with an inverter (not shown), or by combining adjustment of the damper opening of the air damper with adjustment of the motor rotation speed of the combustion air blower.

[0044] The exhaust gas oxygen concentration detection unit 23 is a sensor that detects the oxygen concentration Co contained in the exhaust gas of the boiler 19. The exhaust gas oxygen concentration detection unit 23 is located in the exhaust line 21 through which the exhaust gas of the boiler 19 is discharged.

[0045] The combustion control unit 30 is a control device that controls the mixed gas control unit 6, the fuel gas flow rate adjusting unit 10, the liquid fuel flow rate adjusting unit 16, the boiler 19, the air flow rate adjusting unit 22, etc. The combustion control unit 30 has an inert gas proportion determining unit 9 and a memory unit 33.

[0046] The inert gas proportion determination unit 9 switches between the open / closed state of the membrane separation apparatus shutoff valve 7 and the open / closed state of the bypass line shutoff valve 8 based on the detection result of the nitrogen gas proportion detection unit 9a, which detects the nitrogen gas proportion Cn contained in the mixed gas Gm. When the inert gas proportion determination unit 9 determines that the nitrogen gas proportion Cn in the mixed gas Gm is greater than the first threshold, it opens the membrane separation apparatus shutoff valve 7 and closes the bypass line shutoff valve 8. On the other hand, when it determines that the nitrogen gas proportion Cn in the mixed gas Gm is equal to or less than the first threshold, it closes the membrane separation apparatus shutoff valve 7 and opens the bypass line shutoff valve 8. Note that the inert gas proportion determination unit 9 does not necessarily have the nitrogen gas proportion detection unit 9a. The inert gas proportion determination unit 9 may be configured to acquire the nitrogen gas proportion Cn from a nitrogen gas proportion detection unit 9a included in a system other than the combustion system 1 (for example, a ship). The inert gas proportion determination unit 9 may be included in the mixed gas control unit 6.

[0047] The memory unit 33 stores various programs and data for controlling the operations of the mixed gas control unit 6, fuel gas flow rate adjusting unit 10, liquid fuel flow rate adjusting unit 16, boiler 19, and air flow rate adjusting unit 22, and for acquiring detection data from the nitrogen gas proportion detecting unit 9a and exhaust gas oxygen concentration detecting unit 23. The memory unit 33 also stores a first threshold value that serves as a reference for controlling the mixed gas control unit 6.

[0048] The combustion control unit 30 can acquire the adjustment amount of the fuel gas flow rate adjustment unit 10, the adjustment amount of the liquid fuel flow rate adjustment unit 16, the adjustment amount of the air flow rate adjustment unit 22, the nitrogen gas ratio Cn contained in the mixed gas Gm detected by the nitrogen gas ratio detection unit 9a, and the oxygen concentration Co contained in the exhaust gas of the boiler 19 detected by the exhaust gas oxygen concentration detection unit 23 every unit time.

[0049] The combustion control unit 30 can transmit control signals that switch between an open state and a closed state of the membrane separation device shutoff valve 7, the bypass line shutoff valve 8, the fuel gas shutoff valve 12, and the liquid fuel shutoff valve 17. The combustion control unit 30 can transmit control signals to the fuel gas pressure reducing valve 11, the fuel gas flow rate adjustment valve 13, and the liquid fuel flow rate adjustment valve 18 to adjust the valve opening.

[0050] The combustion control unit 30 detects the operating state of the boiler 19 and is capable of transmitting and receiving various measurement data and control signals to the boiler 19. Based on the oxygen concentration Co contained in the exhaust gas of the boiler 19 acquired per unit time from the exhaust gas oxygen concentration detection unit 23, the combustion control unit 30 is capable of transmitting a control signal to the air flow rate adjustment unit 22 to adjust the damper opening of the air damper so that the oxygen concentration Co becomes a predetermined oxygen concentration.

[0051] Next, the combustion support fuel suppression control of the boiler 19 in the combustion system 1 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing, in the combustion system 1, the route of fuel supplied to the boiler 19 when the nitrogen gas ratio Cn of the supplied mixed gas Gm is equal to or less than a first threshold value, indicated by an outlined arrow, and the route of fuel supplied to the boiler 19 when the nitrogen gas ratio Cn of the supplied mixed gas Gm is greater than the first threshold value, indicated by a filled arrow.

[0052] 2, the combustion system 1 uses a nitrogen gas ratio detection unit 9a to detect the nitrogen gas ratio Cn contained in the gas flowing into the mixed gas line 2 every unit time. If the inert gas ratio determination unit 9 determines that the nitrogen gas ratio Cn of the gas is equal to or less than the first threshold value, that is, if the inert gas ratio determination unit 9 determines that the gas is a mixed gas Gm or methane gas Gh with a nitrogen gas ratio Cn that can be burned alone in the boiler 19 without co-firing heavy oil Lp, the inert gas ratio determination unit 9 closes the membrane separation device shutoff valve 7 and opens the bypass line shutoff valve 8. As shown by the white arrow in FIG. 2, the methane gas Gh or mixed gas Gm in the mixed gas line 2 flows into the fuel gas line 4 via the bypass line 5.

[0053] The combustion control unit 30 adjusts the fuel gas flow rate adjusting unit 10 so that methane gas Gh or mixed gas Gm is supplied as fuel gas to the boiler 19. Furthermore, the combustion control unit 30 adjusts the liquid fuel flow rate adjusting unit 16 so that heavy oil Lp in the liquid fuel tank 15 is not supplied to the boiler 19. The combustion system 1 continues to combust the mixed gas Gm as fuel gas in the boiler 19 without burning the heavy oil Lp.

[0054] If the inert gas ratio determination unit 9 determines that the nitrogen gas ratio Cn of the gas flowing into the mixed gas line 2 is greater than the first threshold value, that is, if it determines that the gas is a mixed gas Gm with a nitrogen gas ratio Cn that cannot be burned alone in the boiler 19, it opens the shut-off valve 7 for the membrane separation device and closes the shut-off valve 8 for the bypass line.

[0055] When the mixed gas Gm is supplied from the inlet, the membrane separation device 3 separates at least a portion of the nitrogen gas Gn contained in the mixed gas Gm using a separation membrane. The membrane separation device 3 generates a treated gas Gp from the mixed gas Gm, having a methane gas ratio Ch that allows combustion to continue in the boiler 19 without co-firing heavy oil Lp. The membrane separation device 3 discharges the treated gas Gp from the outlet to the fuel gas line 4. As shown by the black arrow in Figure 2, the mixed gas Gm in the mixed gas line 2 flows into the fuel gas line 4 via the membrane separation device 3.

[0056] The combustion control unit 30 adjusts the fuel gas flow rate adjusting unit 10 so that the process gas Gp is ​​supplied as fuel gas to the boiler 19. In addition, the combustion control unit 30 adjusts the liquid fuel flow rate adjusting unit 16 so that the heavy oil Lp in the liquid fuel tank 15 is not supplied to the boiler 19. As a result, the combustion system 1 continues to combust the process gas Gp as fuel gas in the boiler 19 without burning the heavy oil Lp.

[0057] The combustion system 1 configured as described above generates a treated gas Gp using the membrane separation device 3 to maintain an appropriate combustion state in the boiler 19. The methane gas proportion Ch in the treated gas Gp is ​​greater than the methane gas proportion Ch in the mixed gas Gm before separation. Therefore, the combustion system 1 expands the range of the nitrogen gas proportion Cn in the mixed gas Gm that can be combusted without co-combusting heavy oil Lp. This increases the nitrogen gas proportion Cn in the mixed gas Gm that can be combusted without co-combusting heavy oil Lp, while suppressing atmospheric release of the mixed gas Gm, thereby suppressing greenhouse gas emissions.

[0058] (Embodiment 2) Next, a combustion system 1A according to a second embodiment of the present invention will be described using Fig. 3 as an example in which methane, a main component of natural gas, is stored in a liquefied gas storage tank. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof will be omitted, and only the parts that differ from the first embodiment will be described. Fig. 3 is a schematic diagram showing the path of fuel supplied to the boiler 19 in the combustion system 1A when the amount of heat generated per unit time in the boiler 19 is less than a second threshold value.

[0059] 3, the combustion control unit 30 further includes a combustion heat quantity determination unit 32. A method for calculating the amount of heat generated when fuel is combusted in the burner of the boiler 19 by the combustion heat quantity determination unit 32 will be described later. The combustion heat quantity determination unit 32 determines whether the amount of combustion heat generated per unit time by the combustion of the methane gas Gh, mixed gas Gm, process gas Gp, and heavy oil Lp supplied to the dual fuel burner of the boiler 19 is less than a second threshold value. The second threshold value is set, for example, based on the opening degree of the air damper indicating the flow rate of combustion air, the pressure loss value of the air supply line 20, etc.

[0060] The storage unit 33 stores a first threshold value and a second threshold value that serve as standards for controlling the mixed gas control unit 6.

[0061] Next, the control of suppressing combustion support fuel for the boiler 19 in the combustion system 1A will be described. In this embodiment, the combustion system 1A supplies the boiler 19 with a treated gas Gp obtained by separating at least a portion of the nitrogen gas Gn contained in the mixed gas Gm using the membrane separation device 3 (see the black arrow in FIG. 2).

[0062] The combustion heat quantity determination unit 32 calculates the combustion heat quantity per unit time of the fuel gas supplied to the dual fuel burner of the boiler 19. For example, when the combustion heat quantity determination unit 32 determines that the combustion heat quantity per unit time of the process gas Gp combusted in the dual fuel burner is less than a second threshold value, that is, when the combustion heat quantity determination unit 32 determines that the process gas Gp is ​​a fuel gas that can continue to burn if heavy oil Lp is mixed with the process gas Gp in the boiler 19, the combustion heat quantity determination unit 32 adjusts the liquid fuel flow rate adjustment unit 16 so that a certain amount of heavy oil Lp is supplied to the boiler 19 from the liquid fuel tank 15. As shown in FIG. 3 , in addition to the process gas Gp, the heavy oil Lp is supplied to the boiler 19 via the liquid fuel line 14. The combustion system 1 continuously combusts the process gas Gp in the boiler 19 by mixing the process gas Gp with heavy oil Lp.

[0063] The combustion system 1A configured as described above supplies the mixed gas Gm to the membrane separation device 3 when the nitrogen gas ratio Cn becomes greater than the first threshold, and continues to burn the treated gas Gp, which has a reduced nitrogen gas ratio Cn (and an increased methane gas ratio Ch), as fuel gas without burning the heavy oil Lp. Furthermore, the system does not supply the heavy oil Lp to the dual fuel burner until the methane gas ratio Ch in the fuel gas becomes low and it is determined that the amount of heat generated in the burner is less than the second threshold. This makes it possible to suppress the generation of carbon dioxide due to the combustion of the heavy oil Lp while suppressing the release of methane gas Gh into the atmosphere.

[0064] Next, a method for calculating the amount of heat generated when fuel is combusted in the burner of the boiler 19 will be described. In this embodiment, the combustion heat amount determination unit 32 has in advance information for calculating the amount of combustion air A1 supplied to the boiler 19 based on the air flow rate adjustment value of the air flow rate adjustment unit 22 (for example, the opening degree of the air damper or the pressure loss value of the air supply line 20). Also, in this embodiment, the combustion control unit 30 adjusts the air flow rate adjustment unit 22 so that the oxygen concentration Co contained in the exhaust gas becomes a predetermined value.

[0065] The amount of combustion air A1 required for burning the fuel gas is calculated from the fuel consumption Fc, which is the amount of fuel gas supplied to the boiler 19, and the oxygen concentration Co contained in the exhaust gas from the boiler 19, using the following formula (1).

number

[0066] The combustion heat quantity determination unit 32 calculates the combustion air volume A1 based on the air flow rate adjustment value of the air flow rate adjustment unit 22. Furthermore, the combustion heat quantity determination unit 32 acquires the air temperature t1 supplied to the boiler 19 from a temperature sensor (not shown). The combustion heat quantity determination unit 32 calculates the fuel consumption Fc from the theoretical air volume A0, the combustion air volume A1, and the air temperature t1 based on equation (1). Based on the fuel consumption Fc, the combustion heat quantity determination unit 32 calculates the amount of heat generated by the combustion of the fuel gas supplied to the burner of the boiler 19.

[0067] In calculating the amount of heat generated when fuel is combusted in the burner of the boiler 19, the methane gas proportion Ch of the fuel gas can be calculated from the ratio to the fuel consumption amount Fc at the rated output of the boiler 19 (calculated by subtracting the heat amount of the co-combustion supporting fuel if co-combustion of a supporting fuel is used). Therefore, the nitrogen gas proportion detection unit 9a may use this calculation of the methane gas proportion Ch to determine the nitrogen gas proportion Cn. Furthermore, the first threshold value serving as the threshold for the nitrogen gas proportion Cn may be the opening degree of the air damper, the pressure loss value of the air supply line 20, or the like.

[0068] Next, a description will be given of a modified example of the combustion system 1A according to the first embodiment of the present invention. In the modified example of the combustion system 1A, the timing at which the heavy oil Lp is supplied to the boiler 19 is different.

[0069] When the combustion heat quantity determination unit 32 determines that the combustion heat quantity per unit time of the fuel gas burned in the burner of the boiler 19 is less than the second threshold value, the combustion control unit 30 adjusts the liquid fuel flow rate adjustment unit 16 so that a certain amount of heavy oil Lp is supplied to the boiler 19 after a predetermined time has elapsed since the mixed gas control unit 6 supplied the mixed gas Gm to the membrane separation device 3.

[0070] When the process gas Gp is ​​being combusted in the boiler 19, the combustion control unit 30 adjusts the damper opening of the air flow rate adjustment unit 22 in advance so that the air flow rate required for the mixed combustion of the process gas Gp and the process gas Gp in the boiler 19 is supplied, and then adjusts the liquid fuel flow rate adjustment unit 16 so that the process gas Lp is supplied to the boiler 19. In this way, the combustion system 1A can suppress incomplete combustion of the process gas Lp when the process gas Gp transitions from combustion of only the process gas Gp to mixed combustion of the process gas Gp and the process gas Gp in the boiler 19.

[0071] Next, using Figures 4 and 5, the combustion supporting fuel suppression control when a gas free (nitrogen gas purging) is performed on a liquefied gas tank T1 storing methane gas Gh and when a gassing up (methane gas purging) is performed will be described. In this embodiment, the first threshold value is set to a nitrogen gas ratio of 50% in the mixed gas Gm. In this embodiment, the second threshold value is set to the amount of heat generated when treated gas Gp obtained by separating nitrogen gas Gn from mixed gas Gm having a methane gas ratio Ch of less than 20% by a membrane separation device 3 is supplied to the boiler 19.

[0072] When gas freeing is performed, nitrogen gas Gn is supplied into the liquefied gas tank T1, and any one of methane gas Gh, mixed gas Gm, and nitrogen gas Gn is discharged from the free flow line L1. The combustion control unit 30 switches the control modes of the membrane separation device shutoff valve 7, the bypass line shutoff valve 8, the liquid fuel shutoff valve 17, and the liquid fuel flow rate adjustment valve 18 based on the methane gas proportion Ch and the nitrogen gas proportion Cn of the gas flowing from the free flow line L1 to the mixed gas line 2 (see FIG. 1).

[0073] As shown in Fig. 4, while the methane gas proportion Ch in the gas flowing from the free flow line L1 to the mixed gas line 2 decreases from 100 percent to 50 percent and the nitrogen gas proportion Cn increases from 0 percent to 50 percent, the combustion control unit 30 closes the membrane separation device shutoff valve 7 and opens the bypass line shutoff valve 8 in a gas-only combustion mode M1 in which the membrane separation device 3 is not used. At this time, heavy oil Lp is not supplied to the boiler 19 (see the gas-only combustion mode M1 column in Fig. 4). At this time, the boiler 19 burns mixed gas Gm with a nitrogen gas proportion Cn of 50 percent or less (methane gas proportion Ch of 50 percent or more) as fuel gas.

[0074] The combustion control unit 30 opens the membrane separation device shutoff valve 7 and closes the bypass line shutoff valve 8 in a gas-only combustion mode M2 ​​in which the membrane separation device 3 is used while the methane gas ratio Ch in the gas flowing from the free flow line L1 to the mixed gas line 2 decreases from 50 percent to 20 percent and the nitrogen gas ratio Cn increases from 50 percent (first threshold) to 80 percent. During this period, heavy oil Lp is not supplied to the boiler 19 (see the gas-only combustion mode M2 ​​column in FIG. 4). When the closed membrane separation device shutoff valve 7 is opened and the open bypass line shutoff valve 8 is closed, the bypass line shutoff valve 8 is closed a predetermined time after the membrane separation device shutoff valve 7 is opened so that the fuel supply to the boiler 19 is not interrupted. During this period, the boiler 19 burns the treated gas Gp from the membrane separation device 3 as fuel gas. Furthermore, it is preferable to set the methane gas ratio of the treatment gas Gp to more than 50 percent, which is the same range as the methane gas ratio Ch in the fuel gas in the gas-only combustion mode M1, in order to improve the efficiency of the membrane treatment and stabilize combustion.

[0075] The combustion control unit 30 sets the mixed combustion mode M3 by opening the membrane separation unit shutoff valve 7 and closing the bypass line shutoff valve 8 while the methane gas ratio Ch in the gas flowing from the free flow line L1 to the mixed gas line 2 becomes smaller than 20 percent (second threshold) and decreases to 0 percent, and the nitrogen gas ratio Cn becomes larger than 80 percent and increases to 100 percent. Furthermore, the combustion control unit 30 opens the liquid fuel shutoff valve 17 and adjusts the liquid fuel flow control valve 18 so that the required amount of heavy oil Lp is supplied to the boiler 19 at the minimum load factor (see the mixed combustion mode M3 column in Figure 4).

[0076] As shown in FIG. 5, gassing-up supplies methane gas Gh into the liquefied gas tank T1 and discharges any of methane gas Gh, mixed gas Gm, and nitrogen gas Gn from the free flow line L1. The combustion control unit 30 switches from dual-fuel combustion mode M3 to exclusive gas combustion mode M2 ​​when the methane gas ratio Ch of the gas flowing into the mixed gas line 2 becomes equal to or greater than a second threshold (20 percent). The combustion control unit 30 switches from exclusive gas combustion mode M2 ​​to exclusive gas combustion mode M1 when the nitrogen gas ratio Cn of the gas flowing into the mixed gas line 2 becomes equal to or less than a first threshold (50 percent) (methane gas ratio Ch 50 percent or greater). When the open membrane separation unit shutoff valve 7 is closed and the closed bypass line shutoff valve 8 is opened, the membrane separation unit shutoff valve 7 is closed a predetermined time after the bypass line shutoff valve 8 is opened.

[0077] (Other embodiments) Although the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and it is possible to appropriately modify the above-described embodiments within the scope of the spirit of the present invention.

[0078] In each of the above-described embodiments, the combustion system 1 burns heavy oil Lp as a combustion supporting fuel that assists the combustion of the mixed gas Gm and the treated gas Gp in the boiler 19. However, the combustion system may also use, for example, kerosene, naphtha, or the like as the combustion supporting fuel.

[0079] In each of the above-described embodiments, the membrane separation device 3 is connected to the mixed gas line 2, but this is not limiting, and the membrane separation device 3 may be connected to a line through which pressurized methane gas Gh flows downstream of the compressor C. This increases the mixed gas pressure, allowing the membrane separation device 3 to effectively separate the inert gas.

[0080] In each of the above-described embodiments, when the combustion system 1 determines that the amount of combustion heat per unit time of the treatment gas Gp in the boiler 19 is less than the second threshold value, it adjusts the liquid fuel flow rate adjuster 16 so that a certain amount of heavy oil Lp is supplied to the boiler 19. However, the combustion system may be configured to adjust the amount of heavy oil supplied based on the amount of combustion heat in the boiler.

[0081] In each of the above-described embodiments, the fuel gas flow rate adjustment valve 13 may be located upstream of the fuel gas cutoff valve 12 .

[0082] In each of the above-described embodiments, the liquid fuel flow rate adjustment valve 18 may be located upstream of the liquid fuel cutoff valve 17 .

[0083] In each of the above-described embodiments, the boiler 19 may be a boiler capable of burning fuel other than methane gas Gh and heavy oil Lp. For example, in a ship equipped with a vaporizer H (see FIG. 1) for liquefied gas for the main engine Eg, the boiler 19 may burn fuel gasified by the vaporizer H.

[0084] In each of the above-described embodiments, the combustion system 1, 1A may adjust the air flow rate adjuster based on the value of an inert gas detector that detects the proportion of an inert gas such as nitrogen or the flow rate of the inert gas.

[0085] In each of the above-described embodiments, the flow rate of the fuel gas supplied to the boiler 19 may be fixed or may be configured to be arbitrarily set.

[0086] In each of the above-described embodiments, the combustion system 1, 1A may be configured to adjust the supply amount of fuel gas based on the pressure of the free flow line L1. [Explanation of symbols]

[0087] 1. 1A Combustion System 2 Mixed gas line 3 Membrane separation equipment 3a Nitrogen exhaust valve 4 Fuel gas lines 5. Bypass Line 6 Mixed gas control section 7. Membrane separation device shutoff valve 8. Bypass line shutoff valve 9 Inert gas ratio determination section 10 Fuel gas flow rate adjusting section 11 Fuel gas pressure reducing valve 12 Fuel gas shutoff valve 13 Fuel gas flow control valve 14 Liquid fuel line 15 Liquid fuel tank 16 Liquid fuel flow rate adjustment section 17 Liquid fuel shutoff valve 18 Liquid fuel flow control valve 19 Boiler 19a Heat transfer medium line 20 Air supply line 21 Exhaust line 22 Air flow rate adjustment unit 23 Exhaust gas oxygen concentration detector 30 Combustion control unit 32 Combustion heat quantity determination unit 33 Storage section L1 Free Flow Line L2 Nitrogen gas line L3 methane gas line Gn Nitrogen gas Gm mixed gas Gh Methane gas Gp Process gas Lp heavy oil Co oxygen concentration Cn Nitrogen gas ratio Ch methane gas percentage BOG Boil-off gas P pump Eg main engine Ge generator C Compressor H vaporizer M1, M2 Gas only combustion mode M3 mixed firing mode

Claims

1. a membrane separation device that separates at least a portion of the inert gas from a mixed gas of a hydrocarbon gas and an inert gas using a separation membrane to generate a treated gas; a mixed gas line that supplies the mixed gas to the membrane separation device; a combustion device capable of combusting at least one of the hydrocarbon gas, the mixed gas, and the processing gas; a fuel gas line for supplying at least one of the hydrocarbon gas, the mixed gas, and the process gas to the combustion device; a mixed gas control unit that controls the supply of the mixed gas to the membrane separation device, The mixed gas control unit an inert gas ratio determination unit that determines the ratio of the inert gas contained in the mixed gas, When the inert gas ratio determination unit determines that the ratio is greater than a first threshold value, the mixed gas is supplied from the mixed gas line to the membrane separation device. Combustion system.

2. 10. The combustion system of claim 1, The combustion device is a burner capable of combusting at least one of the hydrocarbon gas, the mixed gas, and the processing gas, which are fuel gases, and a combustion supporting fuel for burning the mixed gas or the processing gas; a combustion control unit that controls combustion in the combustion device, The combustion control unit a combustion heat quantity determination unit that determines the quantity of heat generated by combustion of the fuel gas supplied to the burner, and when the combustion heat quantity determination unit determines that the quantity of heat generated by combustion of at least one of the mixed gas and the processing gas supplied to the burner is less than a second threshold value, control is performed to combust at least one of the mixed gas and the processing gas and the combustion supporting fuel. Combustion system.

3. 10. The combustion system of claim 1, The combustion device is a burner capable of combusting at least one of the hydrocarbon gas, the mixed gas, and the processing gas, which are fuel gases, and a combustion supporting fuel for burning the mixed gas or the processing gas; a combustion control unit that controls combustion in the combustion device, The combustion control unit a combustion heat quantity determination unit that determines the magnitude of the heat quantity generated by combustion of the fuel gas supplied to the burner, and when the combustion heat quantity determination unit determines that the heat quantity generated by combustion of at least one of the mixed gas and the treatment gas supplied to the burner is less than a second threshold value, the mixed gas control unit controls so that at least one of the mixed gas and the treatment gas and the combustion supporting fuel are combusted after a predetermined time has elapsed since the mixed gas was supplied to the membrane separation device. Combustion system.

4. 4. The combustion system according to claim 2 or 3, The combustion device is a fuel gas flow rate adjusting unit provided in the fuel gas line and adjusting the flow rate of the fuel gas; an air supply line through which combustion air is supplied; an air flow rate adjusting unit provided in the air supply line and adjusting the flow rate of the combustion air; an exhaust gas oxygen concentration detection unit that detects the oxygen concentration in the exhaust gas, The combustion heat amount determination unit calculating the amount of heat generated by combustion of the fuel gas supplied to the burner based on the gas fuel flow rate adjustment value of the fuel gas flow rate adjustment unit, the air flow rate adjustment value of the air flow rate adjustment unit, and the detection value of the exhaust gas oxygen concentration detection unit; Combustion system.

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