Steam generation system for cogeneration, cogeneration system, and steam generation method for cogeneration

Abstract

Provided is a steam generation system for cogeneration which can be used as a cogeneration system even when hot water is lower than 100°C. A steam generation system (9) includes: a steam generator (27) that generates negative pressure steam by heating negative pressure water with hot water of less than 100°C obtained from cooling water for cooling a gas engine (3); a steam supply path (31) that supplies the negative pressure steam generated by the steam generator (27) to a demand destination; a water supply path (29) that supplies water to the steam generator (27); and a pressure reduction valve (35) that is provided in the water supply path (29) and reduces the pressure of the water to atmospheric pressure or lower.

Description

Steam generation system for combined heat and power supply, combined heat and power supply system, and method for generating steam for combined heat and power supply

[0001] The present disclosure relates to a combined heat and power steam generation system and method.

[0002] Patent Document 1 discloses a cogeneration system (combined heat and power supply system) that generates steam using engine cooling water that cools the engine jacket of a power generation engine.

[0003] Patent No. 6463181

[0004] However, the cogeneration system described in Patent Document 1 requires engine coolant at 100°C or higher to generate steam. Therefore, if the engine coolant is below 100°C, a heating means is required to raise the temperature to 100°C or higher.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a steam generation system for combined heat and power supply, a combined heat and power supply system, and a method for generating steam for combined heat and power supply, which can be used as a combined heat and power supply system even with hot water of less than 100°C.

[0006] A steam generation system for combined heat and power supply according to one aspect of the present disclosure includes a steam generator that generates steam by heating negative pressure water with hot water obtained from cooling water that cools a power generation engine, a steam supply unit that supplies the steam generated by the steam generator to a demand destination, a water supply unit that supplies water to the steam generator, a pressure reducing valve that is provided in the water supply unit and reduces the pressure of the water to below atmospheric pressure, a steam compressor that is provided in the steam supply unit and increases the pressure of steam to above atmospheric pressure, and a control unit that adjusts the operation of the steam compressor to control the pressure reduction in a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve.

[0007] A cogeneration system according to one aspect of the present disclosure includes the above-described cogeneration steam generation system, a power generation engine, and a generator that generates electricity using the power generation engine.

[0008] A method for generating steam for combined heat and power supply according to one aspect of the present disclosure includes a steam generation process for generating steam by heating negative pressure water with hot water obtained from cooling water for cooling a power generation engine; a steam supply process for supplying the steam generated in the steam generation process to a demand destination; a water supply process for supplying water to the steam generator; a pressure reduction process for reducing the pressure of the water supplied to the steam generator to below atmospheric pressure using a pressure reducing valve; and a steam compression process for increasing the pressure of the steam generated in the steam supply process to above atmospheric pressure using a steam compressor, wherein the pressure reduction in a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve is controlled by operating the steam compressor.

[0009] Even hot water below 100°C can be used as a cogeneration system.

[0010] 1 is a schematic diagram illustrating a combined heat and power system according to an embodiment of the present disclosure.

[0011] An embodiment according to the present disclosure will be described below with reference to Fig. 1. Fig. 1 shows a combined heat and power supply system 1 according to this embodiment. The combined heat and power supply system 1 includes a gas engine (power generation engine) 3, an exhaust gas boiler 5, a CO2 recovery device 7, and a steam generator (combined heat and power steam generation system) 9.

[0012] The gas engine 3 is operated using gas fuel such as city gas as fuel. A generator (not shown) is driven by the gas engine 3 to generate electric power. The electric power generated by the generator is supplied to a consumer. Note that instead of the gas engine 3, other power generation engines such as a gas turbine engine or a diesel engine using oil fuel may be used. Also, multiple gas engines 3 may be used.

[0013] The exhaust gas boiler 5 generates steam from the exhaust gas discharged from the gas engine 3. The exhaust gas that has completed heat exchange in the exhaust gas boiler 5 is guided to the CO2 recovery device through an exhaust gas flow path 11. The steam generated in the exhaust gas boiler 5 is guided to a boiler steam supply path 13 and supplied to an external demand destination.

[0014] The CO2 recovery device 7 recovers CO2 (carbon dioxide) from the exhaust gas guided from the gas engine 3. The CO2 recovery device 7 employs a chemical absorption method using an absorbing solution such as an amine absorbing solution that chemically absorbs CO2.

[0015] The CO2 recovery system 7 includes an absorption tower 15 and a regeneration tower 16. In the absorption tower 15, an amine absorbing solution is brought into contact with the flue gas to absorb CO2 in the flue gas. A lean solution supply unit 15a is connected to the absorption tower 15, which supplies a lean solution from which CO2 has been desorbed and whose CO2 concentration has been made lean. The amine absorbing solution (lean solution) supplied from the lean solution supply unit 15a absorbs CO2 in the flue gas while flowing through the absorption tower 15. The rich solution, which has absorbed CO2 in the absorption tower 15 and whose CO2 concentration has been made rich, is sent to the rich solution supply unit 16a via a heat exchanger 20 by an absorption tower pump 22.

[0016] The heat exchanger 20 is a non-contact heat exchanger, and exchanges heat between the lean solution supplied from the regeneration tower pump 18 and the rich solution supplied from the absorption tower pump 22 .

[0017] The exhaust gas from which CO2 has been removed by the amine absorbent is discharged to the outside from the absorption tower 15.

[0018] In the regeneration tower 16, CO2 is desorbed from the rich solution that has absorbed CO2. The amine absorbing solution (rich solution) supplied from the rich solution supply unit 16a into the regeneration tower 16 is heated by the heat exchanger 20, thereby providing the amount of heat required for the endothermic reaction of desorbing CO2. CO2 is desorbed from the rich solution while the amine absorbing solution (rich solution) supplied from the rich solution supply unit 16a flows through the regeneration tower 16. The CO2 desorbed from the rich solution is discharged from the regeneration tower 16 and led to a CO2 storage unit (not shown).

[0019] A reboiler 17 that heats the amine absorption solution is connected to the regeneration tower 16. The reboiler 17 heats the amine absorption solution extracted from the regeneration tower 16 via an absorption solution recovery line 16b. Steam introduced from a boiler steam branch line (steam supply section) 13a branched from the boiler steam supply line 13 is used as a heat source for the reboiler 17. The amine absorption solution heated by the reboiler 17 is returned to the regeneration tower 16 via an absorption solution return line 16c. The heated amine absorption solution (lean solution) is extracted from the bottom of the regeneration tower 16 and sent to a heat exchanger 20 by a regeneration tower pump 18.

[0020] The steam generating system 9 is connected to the gas engine 3. The steam generating system 9 includes a hot water circuit 25 through which hot water circulates between the gas engine 3 and the steam generating system 9, and a steam generator 27 to which the hot water circuit 25 is connected.

[0021] The hot water circuit 25 is a closed-loop flow path for circulating hot water guided from the gas engine 3. The hot water is heated by heat exchange with the cooling water that cools the gas engine 3, and the temperature is reduced to less than 100°C. The hot water circuit 25 is provided with a hot water pump 33. The operation of the hot water pump 33 is controlled by a control unit (not shown). The cooling water that cooled the gas engine 3 may be directly supplied to the hot water circuit 25, or the hot water circuit 25 may be formed by the cooling water circulation path itself. Alternatively, the cooling water that cools the gas engine 3 may be drawn to the outside of the gas engine 3 through a water supply pipe, and the hot water in the hot water circuit 25 may be heated by a heat exchanger provided outside the gas engine 3. Here, the cooling water that cools the gas engine 3 also includes the cooling water that cools the oil circulating or passing through the gas engine 3. The power generation engine is not limited to a gas engine, and a gas turbine engine may also be used.

[0022] The steam generator 27 is a non-contact heat exchanger in which hot water and feed water exchange heat without contact, and a partition-type heat exchanger such as a plate-type heat exchanger, a shell-and-plate heat exchanger, or a shell-and-tube heat exchanger can be used.

[0023] The steam generating system 9 may also have a bypass means for adjusting the amount of heat supplied to the heat exchanger that heats the steam generator 27 or the hot water in the hot water circuit 25. Specifically, the hot water circuit 25 may have a hot water bypass flow path 25a for circulating hot water guided from the gas engine 3 without passing through the steam generator 27. The hot water circuit 25 has a hot water bypass control valve 25b for adjusting the amount of hot water that passes through the hot water bypass flow path 25a. The amount of heat input to the steam generator 27 can be controlled by opening the hot water bypass control valve 25b as desired. When the hot water is returned to the gas engine without passing through the steam generator 27, a heat dissipation means such as a cooling tower may be provided on the hot water circuit to maintain the heat balance.

[0024] Furthermore, when the cooling water for cooling the gas engine 3 and the hot water in the hot water circuit 25 exchange heat in a heat exchanger, a bypass flow path may be provided to bypass the cooling water so that the cooling water does not pass through the heat exchanger. In this case, a bypass adjustment valve having the same function as the hot water bypass adjustment valve 25b on the hot water circuit 25 can also be provided.

[0025] A water supply line (water supply unit) 29 that supplies water to be heated is connected to the steam generator 27. A pressure reducing valve 35 is provided in the water supply line 29. The pressure reducing valve 35 reduces the pressure of the water supply, which is at atmospheric pressure at room temperature (e.g., 20°C), to produce negative pressure water. The opening of the pressure reducing valve 35 is controlled by a control unit (not shown). The pressure reducing valve 35 is controlled as necessary in coordination with the operation of each steam compressor 37 so that the interior of the steam generator 27 is at a desired pressure.

[0026] A steam supply path (steam supply unit) 31 through which negative pressure steam generated by the steam generator 27 flows out is connected to the steam generator 27. The negative pressure steam generated by the steam generator 27 is generated by hot water of less than 100°C supplied from the hot water circuit 25. For example, when the pressure of the feed water is −0.054 MPaG, saturated steam is at 80°C, so negative pressure steam can be generated with hot water of about 85°C.

[0027] The steam supply line 31 is provided with multiple steam compressors 37 and supply rate adjusters 39. Each steam compressor 37 compresses the negative pressure steam to above atmospheric pressure. The steam compressors 37 may be, for example, positive displacement compressors such as screw compressors or claw compressors, or turbo compressors. Operation of the steam compressors 37 reduces the pressure in the flow path from their upstream side to the downstream side of the pressure reducing valve 35. The steam compressors 37 are driven by, for example, an electric motor, and their rotation speed is controlled by a control unit (not shown). The capacity of the steam compressors 37 may be increased or decreased by increasing or decreasing the rotation speed of the electric motor. Alternatively, the rotation speed may be fixed and a bypass line from the discharge side to the suction side of the compressor may be provided, and a control valve may be provided in the line to change the pressure loss in the bypass line. Although the present embodiment shown in FIG. 1 has four steam compressors 37 arranged in series, the number is not limited to one, two, three, five, or more.

[0028] The supply amount adjusting unit 39 separates the pressurized steam into gas and liquid and adjusts the flow rate of the steam to be discharged. The flow rate of the steam discharged from the supply amount adjusting unit 39 is controlled by a control unit (not shown).

[0029] Furthermore, the steam flow rate can be adjusted by coordinating the control of the capacity of the steam compressor 37 with the control of the opening degree of the pressure reducing valve 35. For example, the amount of steam can be increased by increasing the capacity of the steam compressor 37 and increasing the opening degree of the pressure reducing valve 35. This makes it possible to increase the steam flow rate while keeping the circulation flow rate of the hot water circuit 25 and the amount of heat input to the steam generator 27 constant. Furthermore, increasing the capacity of the steam compressor 37 also increases the total amount of heat energy input per hour by steam compression.

[0030] At this time, the valve opening degree of the hot water bypass means may be adjusted. For example, the opening degree of the hot water bypass control valve 25b provided in the hot water circuit 25 may be further linked to the capacity control of the steam compressor 37 or the opening degree control of the pressure reducing valve 35 by a command from the control unit. For example, when the capacity of the steam compressor 37 is increased and the opening degree of the pressure reducing valve 35 is increased, the opening degree of the hot water bypass control valve 25b is increased to increase the amount of heat input to the steam generator 27, thereby increasing the steam flow rate and maintaining or increasing the thermal energy supplied per unit time.

[0031] The steam flow rate or temperature can also be adjusted using a steam bypass flow path 31a equipped with a steam bypass valve 31b that bypasses a specific stage among the multiple steam compressors 37. For example, to reduce the steam temperature, the control unit can open the steam bypass valve 31b to bypass the lower-stage steam compressor 37 and utilize the compression capacity of the steam compressor 37 at a later stage, thereby reducing the temperature rise. In this case, the operation of the lower-stage steam compressor 37 can be stopped. This reduces the temperature rise by reducing the number of operating compressors without controlling the hot water bypass control valve 25b of the hot water circuit 25 (i.e., without discarding heat in a cooling tower), leading to improved efficiency of the entire system. Furthermore, even when retrofitting the steam generation system 9 to an existing engine heat utilization system and it is difficult to precisely control the existing hot water circuit 25 according to the operating conditions of the steam generation system 9, it is relatively easy to achieve the desired steam volume or temperature by simply operating or controlling the steam generation system 9.

[0032] A portion of the feed water is guided from the water supply passage 29 to the downstream side of each steam compressor 37 and the supply amount adjustment unit 39 via a water injection pipe 41. The feed water guided from the water injection pipe 41 is injected to cool the pressurized steam and the steam guided to the supply amount adjustment unit 39. The water injection pipe 41 may be provided with a pressure boosting means (such as a pump) to obtain the pressure required for injection.

[0033] The pressurized steam flowing out from the supply amount adjustment unit 39 passes through the steam supply path 31 and merges with the boiler steam branch path 13a. In this way, the steam guided from the supply amount adjustment unit 39 merges with the boiler steam branch path 13a and is guided to the reboiler 17 of the CO2 recovery device 7.

[0034] A turbine 14 is provided in the boiler steam branch passage 13a upstream of a junction position P1 where the boiler steam branch passage 13a joins the steam supply passage 31. The turbine 14 reduces the pressure of the steam and recovers pressure energy. Note that an expansion valve may be provided instead of the turbine 14.

[0035] The control unit is composed of, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium, for example, in the form of a program. The CPU reads this program into RAM and executes information processing and arithmetic operations to realize various functions. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0036] The above-described cogeneration system 1 operates as follows. Electricity is generated by operating the gas engine 3, and exhaust gas discharged from the gas engine 3 is passed through the exhaust gas boiler 5 and guided to the CO2 recovery unit 7. Steam generated in the exhaust gas boiler 5 passes through the boiler steam supply path 13 and is supplied to a demand destination. A portion of the steam generated in the exhaust gas boiler 5 is branched off at the boiler steam branch path 13a, depressurized by the turbine 14, and then guided to the reboiler 17 of the CO2 recovery unit 7. Steam generated in the steam generator 27 and pressurized by each steam compressor 37 also flows into the boiler steam branch path 13a.

[0037] Hot water below 100°C, heated by the cooling water that cooled the gas engine 3, circulates through the hot water circuit 25. The hot water below 100°C is reduced in pressure by a pressure reducing valve 35 to a negative pressure, and is then heated in a steam generator 27 to generate negative pressure steam. The negative pressure steam generated by the steam generator 27 passes through a steam supply path 31, is pressurized to atmospheric pressure or higher by a plurality of steam compressors 37, and is then guided to a supply amount adjustment unit 39. The steam, the flow rate of which is adjusted by the supply amount adjustment unit 39, passes through the steam supply path 31 and merges with the boiler steam branch path 13a. The steam that has merged at the boiler steam branch path 13a is guided to the reboiler 17 and used as a heat source.

[0038] In the CO2 recovery unit 7, CO2 is recovered from the exhaust gas guided from the gas engine 3 in an absorption tower 15, and the exhaust gas after CO2 absorption is released to the outside. In the regeneration tower 16, the amine absorption solution is heated by a reboiler 17. CO2 desorbed from the amine absorption solution is discharged from the regeneration tower 16 and sent to a CO2 storage section.

[0039] The effects of the present embodiment described above are as follows: In the steam generator 27, negative pressure steam is generated by heating negative pressure water from hot water of less than 100°C obtained from the cooling water that cools the gas engine 3. The generated negative pressure steam is supplied to a demand destination via the steam supply path 31. As a result, even if the hot water obtained from the engine cooling water is less than 100°C, steam can be generated and cogeneration of heat and electricity becomes possible.

[0040] A pressure reducing valve 35 is provided in the water supply line 29 that supplies water to the steam generator 27, and the water is made to be negative pressure water below atmospheric pressure. This allows negative pressure water to be supplied to the steam generator 27 even if the pressure of the water is above atmospheric pressure.

[0041] The negative pressure steam is boosted to atmospheric pressure or higher by the steam compressor 37 and supplied to the demand destination, thereby enabling flexible response to the pressure required by the demand destination.

[0042] The CO2 recovery unit 7 recovers CO2 from exhaust gas using a chemical absorption method in which CO2 is chemically absorbed and recovered using an amine absorption solution, and heating (heat of absorption) is required to desorb CO2 from the absorption solution that has absorbed CO2 and regenerate the absorption solution. By supplying steam generated by the steam generator 27 to the reboiler 17 of the CO2 recovery unit 7, it can be used as a heat source for regenerating the amine absorption solution.

[0043] The cogeneration steam generating system, the cogeneration system, and the cogeneration steam generating method described in the above-described embodiments can be understood, for example, as follows.

[0044] A steam generation system (9) for combined heat and power supply according to a first aspect of the present disclosure includes a steam generator (27) that generates steam by heating negative pressure water with hot water obtained from cooling water that cools a power generation engine (3), a steam supply unit (31) that supplies the steam generated by the steam generator to a demand destination, a water supply unit (29) that supplies water to the steam generator, a pressure reducing valve (35) that is provided in the water supply unit and reduces the pressure of the water to below atmospheric pressure, a steam compressor (37) that is provided in the steam supply unit and increases the pressure of steam to above atmospheric pressure, and a control unit that adjusts the operation of the steam compressor to control the pressure reduction of a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve.

[0045] The steam generator generates negative pressure steam by heating negative pressure water from hot water obtained from the cooling water used to cool the power generation engine. The generated negative pressure steam is supplied to the demand destination by the steam supply unit. This makes it possible to generate steam and provide cogeneration even if the hot water obtained from the engine cooling water is below 100°C.

[0046] A pressure reducing valve is installed in the water supply section that supplies water to the steam generator, and the water is kept at a negative pressure below atmospheric pressure. This allows negative pressure water to be supplied to the steam generator even when the pressure is above atmospheric pressure.

[0047] The steam compressor boosts the negative pressure steam above atmospheric pressure before supplying it to the consumer, allowing for flexible response to the pressure demanded by the consumer.

[0048] By adjusting the operation of the steam compressor, the pressure reduction in the flow path from the upstream side of the steam compressor to the downstream side of the pressure reducing valve is controlled, thereby making it possible to adjust the pressure of the steam generator to a desired value.

[0049] In a steam generation system for combined heat and power supply (9) according to a second aspect of the present disclosure, in the first aspect, the control unit controls the steam flow rate by adjusting the operation of the steam compressor and the opening degree of the pressure reducing valve.

[0050] A steam generation system (9) for combined heat and power supply according to a third aspect of the present disclosure is the first or second aspect, and includes a hot water circuit (25) that supplies hot water to the steam generator, and a bypass flow path (25a) that is provided in the hot water circuit and bypasses the hot water that is supplied to the steam generator.

[0051] A fourth aspect of the present disclosure relates to a steam generation system for combined heat and power supply according to the first aspect, wherein the demand destination is a CO2 recovery device that recovers carbon dioxide from exhaust gas discharged from the power generation engine.

[0052] In a CO2 capture system that captures carbon dioxide (CO2) from exhaust gas, for example, in the case of a chemical absorption method in which CO2 is chemically absorbed and captured using an absorption solution (e.g., an amine absorption solution), heating is required to desorb the CO2 from the absorption solution and regenerate the absorption solution. By targeting the CO2 capture system as the demand destination, the negative pressure steam generated by the steam generator can be used as a heat source for regenerating the absorption solution. It is preferable that the negative pressure steam be compressed to the desired pressure by a steam compressor.

[0053] A cogeneration system according to a first aspect of the present disclosure includes any of the above-described steam generation systems for cogeneration, a power generation engine, and a generator that generates electricity using the power generation engine.

[0054] A method for generating steam for combined heat and power supply according to a first aspect of the present disclosure includes a steam generation process for generating steam by heating negative pressure water with hot water obtained from cooling water for cooling a power generation engine; a steam supply process for supplying the steam generated in the steam generation process to a demand destination; a water supply process for supplying water to the steam generator; a pressure reduction process for reducing the pressure of the water supplied to the steam generator to below atmospheric pressure using a pressure reducing valve; and a steam compression process for increasing the pressure of the steam generated in the steam supply process to above atmospheric pressure using a steam compressor, wherein the pressure reduction in a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve is controlled by operation of the steam compressor.

[0055] DESCRIPTION OF SYMBOLS 1 Combined heat and power supply system 3 Gas engine (power generation engine) 5 Exhaust gas boiler 7 CO2 recovery device 9 Steam generation system (combined heat and power supply steam generation system) 11 Exhaust gas flow path 13 Boiler steam supply path 13a Boiler steam branch path (steam supply section) 14 Turbine 15 Absorber 15a Lean solution supply section 16 Regenerator 16a Rich solution supply section 16b Absorbent liquid recovery path 16c Absorbent liquid return path 17 Reboiler 18 Regenerator pump 20 Heat exchanger 22 Absorber pump 25 Hot water circuit 25a Hot water bypass flow path 25b Hot water bypass control valve 27 Steam generator 29 Water supply path (water supply section) 31 Steam supply path (steam supply section) 31a Steam bypass flow path 31b Steam bypass valve 33 Hot water pump 35 Pressure reducing valve 37 Steam compressor 39 Supply amount adjusting section 41 Water injection pipe

Claims

1. A steam generation system for combined heat and power supply comprising: a steam generator that generates steam by heating negative pressure water with hot water obtained from cooling water that cools a power generation engine; a steam supply unit that supplies steam generated by the steam generator to a demand destination; a water supply unit that supplies water to the steam generator; a pressure reducing valve that is provided in the water supply unit and reduces the pressure of water to below atmospheric pressure; a steam compressor that is provided in the steam supply unit and increases the pressure of steam to above atmospheric pressure; and a control unit that controls the pressure reduction in a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve by adjusting the operation of the steam compressor.

2. A steam generating system for combined heat and power supply according to claim 1, wherein the control unit controls the steam flow rate by adjusting the operation of the steam compressor and the opening of the pressure reducing valve.

3. The steam generating system for combined heat and power supply according to claim 1, comprising: a hot water circuit that supplies hot water to the steam generator; and a bypass flow path that is provided in the hot water circuit and that bypasses the hot water supplied to the steam generator.

4. A steam generation system for combined heat and power generation as described in claim 1, wherein the demand destination is a CO2 recovery device that recovers carbon dioxide from exhaust gas emitted from the power generation engine.

5. A combined heat and power system comprising: a steam generating system for combined heat and power generation according to any one of claims 1 to 4; a power generation engine; and a generator that generates electricity using the power generation engine.

6. A method for generating steam for combined heat and power supply, comprising: a steam generation process for generating steam in a steam generator by heating negative pressure water with hot water obtained from cooling water for cooling a power generation engine; a steam supply process for supplying the steam generated in the steam generation process to a demand destination; a water supply process for supplying water to the steam generator; a pressure reduction process for reducing the pressure of the water supplied to the steam generator to below atmospheric pressure using a pressure reducing valve; and a steam compression process for increasing the pressure of the negative pressure steam obtained in the steam supply process to above atmospheric pressure using a steam compressor, wherein the pressure reduction in a flow path ranging from the upstream side of the steam compressor to the downstream side of the pressure reducing valve is controlled by operation of the steam compressor.

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