Engine system, cogeneration equipment, and control method thereof

Abstract

When using raw fuels such as ammonia and reformed gas obtained by reforming said ammonia as fuel, the aim is to reduce the CO2 concentration in the exhaust gas while suppressing a decrease in efficiency and stably enabling various operational switching modes. [Solution] The device includes a temperature control unit for adjusting the temperature of the reformer RF. The control device R switches between raw fuel operation, which is an operation in which only raw fuel is burned in the combustion chamber, and reformed gas operation, which is an operation in which at least reformed gas K is included as fuel. Furthermore, the device performs temperature control by activating the temperature control unit from a predetermined preheating set time before the switching point from raw fuel operation to reformed gas operation to adjust the temperature of the reformer RF, and then performs reformed gas operation.

Description

Technical Field

[0001] The present invention relates to an engine system, a cogeneration facility, and a control method thereof, the engine system including a control device that controls operation, and a reformer that reforms part of ammonia to generate reformed gas containing a combustion-promoting gas with a high combustion rate, and combusting raw fuel that is at least one of hydrocarbon gas and ammonia together with the reformed gas generated by the reformer as fuel in a combustion chamber along with combustion air.

Background Art

[0002] Conventionally, various engine systems using ammonia as a main component have been proposed. In view of the fact that ammonia is flame-retardant, an engine system is known in which part of ammonia is reformed into highly ignitable hydrogen, and the reformed hydrogen is used as fuel together with ammonia. As an example of such an engine system, as shown in Patent Document 1, an engine system is known that includes a reformer for reforming ammonia, and an engine that uses, as fuel, ammonia and hydrogen reformed by the reformer in addition to ammonia. In the engine system disclosed in Patent Document 1, since the reforming reaction of ammonia is an endothermic reaction, the reforming in the reformer proceeds in a mode in which the reformer is heated by various methods to supply heat related to the reforming reaction in the reformer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the engine system disclosed in Patent Document 1, at least when operating with reformed gas, it is necessary to heat the reformer to promote the reforming reaction in the reformer. However, the timing and extent of this heating have not been considered, and there was room for improvement from the perspective of improving the overall thermal efficiency of the system.

[0005] The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an engine system, cogeneration equipment, and control method thereof that can reduce CO2 concentration in exhaust gas while suppressing efficiency degradation and stably switch between various operating modes when using raw fuel such as ammonia and reformed gas obtained by reforming said ammonia as fuel. [Means for solving the problem]

[0006] The engine system for achieving the above objective is: A control device that controls the operation, The system includes a reformer that modifies a portion of ammonia to produce a reformed gas containing a combustion-promoting gas with a high combustion rate, An engine system that burns a raw fuel, which is at least one of hydrocarbon gas and ammonia, and the reformed gas produced in the reformer, together with combustion air in a combustion chamber, wherein its characteristic configuration is: The reformer is equipped with a temperature control unit for adjusting the temperature of the reformer, The control device switches between raw fuel operation, which is an operation in which only the raw fuel is burned in the combustion chamber as the fuel, and reformed gas operation, which is an operation in which the fuel includes at least the reformed gas, The key feature is that the temperature control unit is activated from a predetermined preheating time before the switching point from raw fuel operation to reformed gas operation to perform temperature control to adjust the temperature of the reformer, and then the reformed gas operation is performed.

[0007] A control method for an engine system to achieve the above objective is: A control method for an engine system comprising a reformer that modifies a portion of ammonia to produce a reformed gas containing a combustion-promoting gas with a high combustion rate, and burning the raw fuel, which is at least one of hydrocarbon gas and ammonia, and the reformed gas produced in the reformer, together with combustion air in a combustion chamber, wherein the characteristic configuration is as follows: The system controls switching between raw fuel operation, which is an operation in which only the raw fuel is burned in the combustion chamber as the fuel, and reformed gas operation, which is an operation in which at least the reformed gas is included as the fuel, The key feature is that temperature control is performed to adjust the temperature of the reformer from a predetermined preheating time before the switching point from the raw fuel operation to the reformed gas operation.

[0008] According to the above-described configuration, firstly, it is configured to allow switching between raw fuel operation, which is operation in which only raw fuel, which is at least one of hydrocarbon gas or ammonia, is burned in the combustion chamber, and reformed gas operation, which is operation in which at least reformed gas is included as fuel. Therefore, in both raw fuel operation and reformed gas operation, when operating with a carbon-free gas such as ammonia or hydrogen as fuel, it is possible to reduce the CO2 concentration in the exhaust gas. Furthermore, in the above engine system, when performing reformed gas operation, it is necessary to supply heat to the reformer to generate a reforming reaction that produces reformed gas from ammonia. However, if the reformer is constantly heated, the overall efficiency of the system will deteriorate. Therefore, in the engine system according to the present invention, by performing temperature control control to adjust the temperature of the reformer by activating the temperature control unit from a predetermined preheating setting time before switching from raw fuel operation to reformed gas operation, unnecessary heating of the reformer can be suppressed and efficiency can be improved. Furthermore, by heating the reformer from a preheating setting time before the start of reformed gas operation, heat supply to the reforming reaction in the reformer can be appropriately performed when reformed gas operation starts, thereby enabling appropriate execution of subsequent reformed gas operation. Based on the above, when using raw fuel such as ammonia and reformed gas obtained by reforming said ammonia as fuel, it is possible to realize an engine system and its control method that can reduce CO2 concentration in the exhaust gas while suppressing efficiency degradation and stably switching between various operating modes.

[0009] Further characteristic features of the engine system are: The control device is The key feature is that the preheating time is set to be longer than the time it takes for the temperature of the reformer to rise from room temperature to the temperature at which the combustion-promoting gas is generated from ammonia by the reforming reaction.

[0010] According to the above-described configuration, the preheating time is set to be longer than the time it takes for the reformer temperature to rise from room temperature to the temperature at which a combustion-promoting gas is generated from ammonia by the reforming reaction. This allows the amount of reformed gas supplied from the reformer to the engine's combustion chamber at the start of reformed gas operation to be set to the desired amount. This enables the control of the equivalent ratio in the combustion chamber and the ratio of raw fuel to reformed gas at the time of switching from raw fuel operation to reformed gas operation to desired values, thereby achieving stable engine operation.

[0011] Further characteristic features of the engine system are: The reformer or the ammonia led to the reformer is provided with a heating exhaust gas flow path that is configured to heat the ammonia, The control device, in its temperature control function, adjusts the temperature of the reformer by adjusting at least one of the temperature and flow rate of the combustion exhaust gas flowing through the heating exhaust gas passage.

[0012] According to the above-described configuration, the control device adjusts the temperature of the reformer by adjusting at least one of the temperature and flow rate of the combustion exhaust gas flowing through the heating exhaust gas passage. Therefore, there is no need to separately install heaters or the like for heating the reformer, and the configuration can be simplified. Furthermore, for example, the amount of heat remaining from the amount of heat contained in the combustion exhaust gas that is required for the reforming reaction in the reformer can be supplied to a separately installed heat demand facility, thus further improving overall efficiency.

[0013] A further characteristic configuration of the engine system is that an inlet on-off valve that opens and closes the gas inlet to the reformer, and an outlet on-off valve that closes the gas outlet from the reformer are provided, in the temperature adjustment control, the control device adjusts the temperature of the reformer in a mode that closes both the inlet on-off valve and the outlet on-off valve and retains heated gas at a temperature higher than normal temperature in the reformer.

[0014] As in the above characteristic configuration, in the temperature adjustment control, a configuration may be adopted in which the temperature of the reformer is adjusted in a mode that closes both the inlet on-off valve and the outlet on-off valve and retains heated gas at a temperature higher than normal temperature in the reformer. Here, for example, by using non-flammable nitrogen as the heated gas, safe heating control can be performed.

[0015] A further characteristic configuration of the engine system is that the control device performs temperature adjustment stop control that stops the temperature adjustment of the reformer by the temperature adjustment unit during execution of the raw fuel operation and in a period other than the period from before the preheating set time to the switching time point.

[0016] As in the above characteristic configuration, the control device performs the temperature adjustment stop control that stops the temperature adjustment of the reformer by the temperature adjustment unit during execution of the raw fuel operation and in a period other than the period from before the preheating set time to the switching time point, whereby unnecessary energy supply to the reformer can be suppressed when it is not necessary to execute the reforming reaction in the reformer, and the efficiency of the entire system can be improved.

[0017] Further, the cogeneration facility including the engine system described so far functions favorably as a cogeneration facility that exhibits the operational effects described so far. [Brief Description of the Drawings]

[0018] [Figure 1]This is a schematic configuration diagram of an engine system according to an embodiment. [Figure 2] This is a control flow diagram of the engine system according to the embodiment. [Figure 3] This is a schematic configuration diagram of an engine system according to another embodiment. [Modes for Carrying Out the Invention]

[0019] The engine system 100, the cogeneration facility 200, and the control method thereof according to the embodiment of the present invention relate to a technology that, when using a raw fuel such as ammonia and a reformed gas obtained by reforming the raw fuel as fuels, can suppress efficiency reduction while reducing the CO₂ concentration in exhaust gas, and stably realize switching of various operations. Hereinafter, the engine system 100, the cogeneration facility 200, and the control method thereof according to the present embodiment will be described based on the drawings.

[0020] [Engine System] As shown in FIG. 1, the engine system 100 includes a control device R that controls operation, and a reformer RF that reforms part of ammonia to generate a reformed gas K containing a combustion promoting gas (for example, hydrogen) with a high combustion speed. The raw fuel which is at least one of hydrocarbon gas and ammonia, and the reformed gas K generated by the reformer RF are used as fuels and burned together with combustion air A2 in a combustion chamber (not shown) of the engine main body 40. The shaft output of the engine main body 40 is used as a power source for rotationally driving a generator (not shown) or the like.

[0021] The engine system 100 is provided with a combustion air flow passage L2 that supplies combustion air A2 to the engine main body 40, a reforming air flow passage L1 that supplies reforming air A1 to the reformer RF, a fuel flow passage L3 that guides ammonia as a raw fuel to the reformer RF and the engine main body 40, an exhaust gas flow passage L4 through which exhaust gas E from the engine main body 40 flows, and a reformed gas flow passage L5 that guides the reformed gas K generated by the reformer RF to the combustion air flow passage L2 at the inlet of the engine main body 40.

[0022] Incidentally, the RF reformer is an autothermal reformer that uses the heat generated by burning vaporized ammonia to reform the ammonia, thereby producing a hydrogen-containing reformed gas K. The RF reformer has a reforming catalyst (not shown) placed inside its casing (not shown).

[0023] The reforming catalyst (not shown) has, for example, a honeycomb structure and is a catalyst that burns vaporized ammonia and decomposes ammonia into hydrogen. Examples of reforming catalysts used include cobalt-based catalysts, rhodium-based catalysts, ruthenium-based catalysts, or palladium-based catalysts.

[0024] The fuel passage L3 consists of a first fuel passage L3b equipped with a reforming injector IJ1, which is an electromagnetic fuel injection valve that injects ammonia vaporized in a vaporizer 31 (not shown) that vaporizes ammonia stored in a cylinder (not shown) into a reformer RF, and a second fuel passage L3a equipped with a first engine injector IJ2, which is an electromagnetic fuel injection valve that injects ammonia vaporized in the vaporizer 31 into the combustion chamber of the engine body 40.

[0025] The reforming air passage L1 includes a first air cleaner 11 for purifying the reforming air A1 and an electromagnetic reforming throttle valve 12 for controlling the flow rate of the reforming air A1 supplied to the reformer RF. The reforming air A1 flowing through the reforming air passage L1 and the ammonia injected from the reforming injector IJ1 are supplied to the reformer RF.

[0026] In the reformer RF, when the temperature is raised to the catalytic activity temperature of the internal reforming catalyst (not shown) by heating with the heater L4b described later, the following exothermic reaction [Equation 1] occurs in the reforming catalyst, and the temperature of the reforming catalyst rises further due to its own heat.

[0027] NH3+3 / 4O2→1 / 2N2+3 / 2H2O... [Formula 1]

[0028] Furthermore, when the temperature of the reforming catalyst reaches the reaction temperature (as described above), the ammonia is reformed by the reforming catalyst. Specifically, as shown in [Equation 2] below, a decomposition reaction of ammonia occurs (endothermic reaction), and a reformed gas K containing hydrogen is produced.

[0029] NH3→3 / 2H2+1 / 2N2... [Formula 2]

[0030] The reformed gas passage L5 through which the reformed gas K generated in the reformer RF flows includes a hydrogen sensor S1 for measuring the hydrogen concentration contained in the reformed gas K generated in the reformer RF, an intercooler 13 for cooling the flowing reformed gas K by heat exchange with cooling water, and an electromagnetic flow control valve V1 for controlling the flow rate of the flowing reformed gas K.

[0031] Furthermore, the engine system 100 according to this embodiment has at least the following configuration in order to use hydrocarbon gas (for example, methane alone or city gas 13A) as the raw fuel. The engine system 100 includes a hydrocarbon gas passage L6 through which hydrocarbon gas is passed and guided to the combustion chamber of the engine body 40, and a second engine injector IJ3 which is an electromagnetic fuel injection valve that injects hydrocarbon gas into the combustion chamber of the engine body 40.

[0032] The combustion air passage L2 includes a second air cleaner 21 for purifying the combustion air A2 and an electromagnetic main throttle valve 22 for controlling the flow rate of the combustion air A2 supplied to the engine body 40. In addition, the combustion air passage L2 is provided with an inlet L5a for reformed gas K from the reformed gas passage L5. Furthermore, at the connection point of the combustion air passage L2 to the combustion chamber (not shown) of the engine body 40, ammonia as raw fuel is injected from the first engine injector IJ2, and hydrocarbon gas as raw fuel is injected from the second engine injector IJ3.

[0033] The exhaust gas passage L4 through which exhaust gas E from the engine body 40 flows includes a heater L4b (an example of an exhaust gas passage for heating) located inside the housing of the reformer RF, which surrounds the reforming catalyst along the inner surface of the substantially cylindrical housing. The heater L4b is configured to adjust the temperature of the reforming catalyst by the temperature or flow rate of the exhaust gas E flowing through it. In other words, the heater L4b and the three-way valve V2 function as a temperature control unit.

[0034] Furthermore, the exhaust gas passage L4 is equipped with a three-way catalyst CT1 downstream of the heater L4b, which purifies carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust gas E, and an SCR catalyst CT2 which removes nitrogen oxides (NOx) contained in the exhaust gas E. Thus, when a three-way catalytic converter CT1 is provided, and the purpose is to remove nitrogen oxides contained in the exhaust gas E mainly with the three-way catalytic converter CT1, it is preferable that the control device R causes the engine body 40 to burn stoichiometrically, in other words, causes the mixture of fuel and combustion air to burn stoichiometrically in the combustion chamber (not shown) of the engine body 40.

[0035] Furthermore, within the exhaust gas passage L4, an exhaust gas branch passage L4a is connected between the engine body 40 and the heater L4b to branch off and pass a portion of the exhaust gas E through it. A three-way valve V2 is provided at the connection point between the exhaust gas passage L4 and the exhaust gas branch passage L4a to adjust the distribution ratio between the flow rate of exhaust gas E passing through the exhaust gas passage L4 and the flow rate of exhaust gas E passing through the exhaust gas branch passage L4a. Furthermore, the exhaust gas branch passage L4a is provided with a heat exchange section HE that exchanges heat between the exhaust gas E flowing through the exhaust gas branch passage L4a and an external fluid (not shown), and is configured to supply the waste heat from the exhaust gas E to an external heat utilization section via the external fluid. In other words, the engine system 100 of the present invention is configured as a cogeneration facility 200 that can supply both shaft output and heat output from the engine body 40.

[0036] Incidentally, the rotating shaft (not shown) of the engine body 40 is equipped with a rotation speed sensor, which measures the rotation speed of the rotating shaft (not shown), as an operating state detection unit 41. Furthermore, a torque measuring sensor is provided on the rotating shaft (not shown) of the engine body 40 as an operating state detection unit 41 to measure the torque of the rotating shaft. The control device R controls, for example, the opening degree of the reforming injector IJ1, the first engine injector IJ2, the second engine injector IJ3, the reforming throttle valve 12, the main throttle valve 22, the flow control valve V1, and the distribution ratio in the three-way valve V2 so that the engine shaft output calculated based on the engine rotation speed measured by the rotation speed sensor and the torque measured by the torque measuring sensor becomes the target shaft output.

[0037] Now, in the engine system 100 described so far, the control device R is configured to switch between raw fuel operation, in which only raw fuel is burned in the combustion chamber, and reformed gas operation, in which at least reformed gas is included as fuel. In order to reduce the CO2 concentration in the exhaust gas while suppressing a decrease in efficiency and to stably switch between various operating modes, the following control can be performed.

[0038] In other words, the control device R performs temperature control by activating the aforementioned temperature control unit to adjust the temperature of the reformer RF from a predetermined preheating setting time before the switching point from raw fuel operation to reformed gas operation, and then performs reformed gas operation. Incidentally, the switching point from raw fuel operation to reformed gas operation is set in advance by a program or the like, and the control device R executes the switch from raw fuel operation to reformed gas operation based on the set switching point.

[0039] Here, the preheating time is set to be longer than the time it takes for the reformer RF temperature to rise from room temperature to the temperature at which combustion-promoting gas is generated from ammonia by the reforming reaction. Specifically, the temperature at which combustion-promoting gas is generated is the reaction temperature in the reformer RF, which is approximately 450°C to 525°C. This allows the amount of reformed gas supplied from the reformer RF to the engine's combustion chamber to be set to the desired amount at the start of reformed gas operation, and enables stable engine operation by controlling the equivalent ratio in the combustion chamber and the ratio of raw fuel to reformed gas to desired values ​​at the time of switching from raw fuel operation to reformed gas operation.

[0040] Incidentally, in the engine system 100 according to this embodiment, the control device R may perform control to maintain a constant ratio between the amount of ammonia supplied per unit time injected from the reforming injector IJ1 and the amount of ammonia supplied per unit time injected from the first engine injector IJ2 during reformed gas operation, after the switching point. Furthermore, the control device R may be operated in a manner that gradually increases the ratio of the amount of ammonia supplied per unit time from the reforming injector IJ1 to the amount of ammonia supplied per unit time from the first engine injector IJ2 during reformed gas operation. This makes it possible to reduce the amount of nitrogen oxides contained in the combustion exhaust gas.

[0041] Incidentally, in the engine system 100 according to this embodiment, from the viewpoint of improving efficiency, the control device R performs temperature control stop control, which stops the temperature control of the reformer FR by the temperature control unit described above, when raw fuel operation is being performed and during periods other than from before the preheating setting time to the switching point. The control flow of the engine system 100 according to this embodiment will be described below with reference to Figure 2.

[0042] <Control Flow> The control device R first starts the raw fuel operation (#01).

[0043] Next, if the current time is one preheating setting time before the switching point from raw fuel operation to reformed gas operation (a pre-set switching scheduled time) (Yes in #02), the control device R performs temperature adjustment control (#04) and then performs reformed gas operation (#05). Note that temperature adjustment control continues to be performed while reformed gas operation is in progress. On the other hand, if the current time is not the point in time when the switch from raw fuel operation to reformed gas operation is made (i.e., the preheating setting time is not earlier than the pre-set switching time (No in #02)), the control device R waits for a predetermined time (#03) and then repeatedly performs the judgment in #02. In other words, the raw fuel operation continues.

[0044] If the control device R determines that it should switch to raw fuel operation due to reasons such as engine instability (Yes in #06), it will execute raw fuel operation (#07), and will also execute temperature control stop control to stop the temperature control of the reformer FR by the temperature control unit for all periods except the period from before the preheating setting time to the time of switching (#08), and then repeat the control steps #02 to #06. On the other hand, if there is no need to switch to raw fuel operation for reasons such as engine instability (No in #06), the control device R terminates the control.

[0045] [Another embodiment] (1) The temperature control unit may have the following configuration: That is, as shown in Figure 3, the reformer RF is equipped with an inlet valve V3 that opens and closes the inlet for nitrogen gas flowing into the reformer RF, and an outlet valve V4 that opens and closes the outlet for nitrogen gas flowing out of the reformer RF. The control device R may be configured to adjust the temperature of the reformer RF by closing both the inlet valve V3 and the outlet valve V4 and allowing nitrogen gas at a temperature higher than room temperature (an example of heated gas) to remain in the reformer RF.

[0046] (2) In the above embodiment, the engine system 100 is shown as having a configuration that performs stoichiometric combustion, but in a configuration in which the SCR catalyst CT2 removes nitrogen oxides, lean combustion or rich combustion may be performed.

[0047] (3) In the above embodiment, an example configuration is shown in which a heater L4b is provided as a temperature control unit for adjusting the temperature of the reformer RF, which heats the reformer RF using the exhaust heat of the exhaust gas E. In the example shown, the heater L4b is installed inside the housing (not shown) of the reformer RF, but it may also be configured to heat the reforming air A1 flowing through the reforming air passage L1.

[0048] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, provided that no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0049] The engine system, cogeneration equipment, and control method of the present invention can be effectively used as an engine system, cogeneration equipment, and control method that can stably achieve various operation switching while suppressing efficiency degradation while reducing CO2 concentration in exhaust gas when using raw fuel such as ammonia and reformed gas obtained by reforming said ammonia as fuel. [Explanation of Symbols]

[0050] 100: Engine System 200: Cogeneration equipment E: Exhaust gas K: Reformed gas L4b: Heater R: Control device RF: Modifier V3: Inlet / Outlet Valve V4: Outlet / outlet valve

Claims

1. A control device that controls the operation, The system includes a reformer that modifies a portion of ammonia to produce a reformed gas containing a combustion-promoting gas with a high combustion rate, An engine system that burns a raw fuel, which is at least one of hydrocarbon gas and ammonia, and the reformed gas produced in the reformer, together with combustion air in a combustion chamber, The reformer is equipped with a temperature control unit for adjusting the temperature of the reformer, The control device switches between raw fuel operation, which is an operation in which only the raw fuel is burned in the combustion chamber as the fuel, and reformed gas operation, which is an operation in which the fuel includes at least the reformed gas, An engine system that performs temperature control to adjust the temperature of the reformer by activating the temperature control unit from a predetermined preheating setting time before switching from raw fuel operation to reformed gas operation, and then performs the reformed gas operation.

2. The control device is The engine system according to claim 1, wherein the preheating setting time is set to be longer than the time it takes for the temperature of the reformer to rise from room temperature to a temperature at which the combustion-promoting gas is produced from ammonia by the reforming reaction.

3. The reformer or the ammonia led to the reformer is provided with a heating exhaust gas flow path that is configured to heat the ammonia, The engine system according to claim 1 or 2, wherein the control device adjusts the temperature of the reformer in a manner that causes it to adjust at least one of the temperature and flow rate of the combustion exhaust gas flowing through the heating exhaust gas passage.

4. The reformer comprises an inlet valve for opening and closing the gas inlet to the reformer, and an outlet valve for closing the gas outlet from the reformer. The engine system according to claim 1 or 2, wherein the control device adjusts the temperature of the reformer in a manner in which, in the temperature adjustment control, both the inlet valve and the outlet valve are closed and heated gas at a temperature higher than ambient temperature is retained in the reformer.

5. The control device is The engine system according to claim 1 or 2, wherein, while the raw fuel operation is being performed, a temperature control stop control is executed to stop the temperature control of the reformer by the temperature control unit during a period other than from before the preheating setting time to the switching point.

6. A cogeneration system comprising the engine system described in claim 1 or 2.

7. A control method for an engine system comprising a reformer that modifies a portion of ammonia to produce a reformed gas containing a combustion-promoting gas with a high combustion rate, and a method for burning in a combustion chamber together with combustion air using raw fuel, which is at least one of hydrocarbon gas and ammonia, and the reformed gas produced in the reformer as fuel, The system controls switching between raw fuel operation, which is an operation in which only the raw fuel is burned in the combustion chamber as the fuel, and reformed gas operation, which is an operation in which at least the reformed gas is included as the fuel, A control method for an engine system, comprising: performing temperature control to adjust the temperature of the reformer, which is performed from a predetermined preheating time before the switching point from raw fuel operation to reformed gas operation; and then performing reformed gas operation.

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