JP7028600B2 - Methane production system and methane production method - Google Patents

Description

The present invention relates to a methane production system and a methane production method that consume less energy.

Carbon dioxide CO ₂ emissions, which cause global energy consumption and global warming, continue to increase, and there are concerns about climate change and its serious impact on human living environments and ecosystems. Energy conversion sectors such as power generation account for about 40% of the world's energy-derived CO ₂ emissions, and CO ₂ reduction is a major issue for the electric power industry. In particular, coal-fueled thermal power generation emits a large amount of CO ₂ , and research is being conducted on technological development to separate and recover the generated CO ₂ and return it to the ground for storage. If the generated CO ₂ can be chemically converted into fuel and reused, the overall CO ₂ emissions can be suppressed. Therefore, the technology of reacting CO ₂ with hydrogen H ₂ to convert it into methane is drawing attention.

As a CO ₂ methanation reaction, the reaction formula shown in (Equation 1) is known.
(Number 1) CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O

CO ₂ can be separated and recovered from combustion exhaust gas, and hydrogen can be produced by electrolysis of water such as alkaline water electrolysis and solid polymer water electrolysis using electric power. In recent years, renewable energy has been developed and promoted in each country, and power generation using renewable energy such as wind power generation and solar power generation is increasing in Europe. The problem with wind power generation and solar power generation is that the output fluctuates greatly, sometimes more power is generated than required, and surplus power that cannot be used is generated. The technology that uses electric power to electrolyze water to produce hydrogen and react it with carbon dioxide to convert it into methane fuel is called Power to Gas. If surplus electricity can be used as electricity, both CO ₂ emission reduction and effective use of surplus electricity can be expected. Is being promoted. The generated methane will be supplied to existing infrastructure equipment (pipelines, natural gas storage) as synthetic natural gas.

As a system combining a power plant and equipment for separating and recovering carbon dioxide from exhaust gas and converting it into methane, for example, Japanese Patent Application Laid-Open No. 2015-109767 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2016-531973 (Patent Document 2). It is described in.

JP-A-2015-109767 Special Table 2016-53 1973 Gazette

The chemical reaction of synthesizing methane from carbon dioxide and hydrogen (Equation 1) is an exothermic reaction, but in order for the reaction to start, it is necessary to preheat the raw material gas to the methane production reaction start temperature of about 300 ° C and supply it. be. Further, in order to separate and recover carbon dioxide from the exhaust gas using the solid adsorbent, a thermal operation for heating or cooling the solid adsorbent is required. When these thermal operations are performed individually, the purpose can be achieved by using an external heat source or a cold heat source, but the use of an external heat source causes an increase in energy consumption and a decrease in efficiency of the entire system. ..

Patent Document 1 describes a system that combines a power plant and equipment that separates and recovers carbon dioxide from exhaust gas and converts it into methane, but does not clearly indicate how to recover and use the heat of methane generation reaction. .. Further, Patent Document 2 describes a system that combines a power plant and a facility that separates and recovers carbon dioxide from exhaust gas and converts it into methane, and recovers the heat of methane generation reaction, but its utilization method is not clear. .. An object of the present invention is to provide a methane production system and a methane production method with low energy consumption as a whole system in a power plant having a facility for separating and recovering carbon dioxide from combustion exhaust gas to produce methane.

In order to achieve the above object, the methane production system according to the present invention includes a boiler for generating steam, a steam turbine driven by the steam, and a water supply heater for heating and supplying water to the boiler. The facility, a carbon dioxide recovery device that recovers and desorbs carbon dioxide contained in the exhaust gas of the power generation facility, and the desorbed carbon dioxide react with hydrogen supplied from the outside to convert it into methane. In a methane production system having a methaneization reactor , the steam discharged from the steam turbine is heated by the reaction heat at the time of methane conversion of the methaneization reactor, and the temperature is raised. After supplying hydrogen, the desorbed carbon dioxide and the carbon dioxide recovery device, it is supplied to the water supply heater.

Further, a power generation facility including a boiler that generates steam, a steam turbine driven by the steam, and a water supply heater that heats and supplies water to the boiler, and carbon dioxide contained in the exhaust gas of the power generation facility. It is carried out in a methane production system having a carbon dioxide recovery device that recovers and desorbs the methane, and a methaneization reactor that reacts the desorbed carbon dioxide with hydrogen supplied from the outside to convert it into methane. In the methane production method, the steam discharged from the steam turbine is heated by the reaction heat at the time of methane conversion of the methaneization reactor, and the heated steam is the hydrogen and the desorbed dioxide. A methane production method in which carbon and the methane are supplied to the carbon dioxide recovery device and then supplied to the water supply heater.

According to the present invention, it is possible to provide a methane production system and a methane production method that consume less energy as a whole system.

It is an example of the system configuration diagram of the present invention shown in Example 1. It is an example of the system configuration diagram of the present invention shown in Example 2. It is a figure which showed the example of the carbon dioxide solid adsorbent adsorption property. It is a conceptual diagram of the operation method of the carbon dioxide capture device of two steps. It is an example of the system configuration diagram of the present invention shown in Example 3. It is an example of the system configuration diagram of the present invention shown in Example 4.

Hereinafter, embodiments of the present invention will be described with reference to examples, but the present invention is not limited to the following embodiments.

FIG. 1 shows an embodiment of a coal-fired thermal power generation system according to the present invention. The steam generated in the boiler 101 is guided to the steam turbine 102, drives the generator 103, returns to water by the condenser 104, is pressurized by the feed water pump 105, is heated by the feed water heater 106, and then the boiler. Supplied to 101. The exhaust gas generated in the boiler is discharged to the atmosphere from the exhaust tower 130 via the denitration device 110, the heat recovery device 111, the electrostatic precipitator 113, the wet desulfurization device 114, and the exhaust gas reheater 112. FIG. 1 shows a device 200 for recovering carbon dioxide in exhaust gas and a device 300 for converting the recovered carbon dioxide into methane. In the device 200 for recovering carbon dioxide, a part of the boiler exhaust gas emitted from the wet desulfurization device 114 is branched by the branching device 120 and guided to the CO ₂ adsorption desorption tower 201a filled with the CO ₂ adsorbent. Figure 3 shows an example of the adsorption characteristics of the carbon dioxide solid adsorbent CeO ₂ , and the vertical axis shows the relative value with the adsorption rate at 50 ° C as 100%. As shown in Fig. 3, this solid adsorbent has a high CO ₂ adsorption rate in the low temperature range of about 50 ° C, releases most of the CO ₂ adsorbed at 150 ° C or higher, and has a low adsorption rate at high temperature. It is a value. Therefore, CO ₂ can be separated and recovered from the exhaust gas by using a plurality of these solid adsorbents and repeating heating and cooling in a temperature range of about 50 ° C to 150 ° C at different times.

Returning to FIG. 1, the CO ₂ adsorption / desorption tower 201a corresponds to the cooling process by the low temperature exhaust gas, and the CO ₂ adsorption / desorption tower 201b corresponds to the heating process by the extracted steam. In the coal-fired power generation plant 100 having a wet desulfurization apparatus, the outlet exhaust gas temperature of the wet desulfurization apparatus 114 is close to the saturated water vapor temperature of the desulfurization liquid, for example, a low temperature of about 40 ° C. If low-temperature exhaust gas at this temperature is released into the atmosphere as it is, depending on the weather conditions, the water vapor in the exhaust gas may condense to generate white smoke and generate sulfuric acid mist, or the exhaust gas rising capacity due to buoyancy is weak, so sufficient diffusion can be achieved. However, since the exhaust gas may stay near the ground surface, the exhaust gas temperature is usually raised to about 90 ° C. or higher by the exhaust gas reheater 112 and then discharged from the exhaust tower. However, since the carbon dioxide recovery device this time is intended for cooling, a part of this low-temperature exhaust gas is branched at the exhaust gas supply pipe 141 and used for cooling. The low-temperature exhaust gas after being used for cooling is mixed with the high-temperature exhaust gas heated by the exhaust gas reheater 112 by the merging device 121, and then discharged from the exhaust tower 130.

On the other hand, as the heating heat source of the CO ₂ adsorption / desorption tower 201b, a method of indirect heating via a heat exchanger using the bleed steam of the steam turbine as a heat medium is adopted. The low-pressure steam (0.4 MPa, 150 ° C.) extracted from the steam turbine passes through the extracted steam supply pipe 151, and the reaction heat of the methane conversion reaction is recovered by the methaneization reactor 301 to raise the temperature. The bleed steam flow rate is controlled by the methanation reaction temperature detector 350 using the steam flow rate controller 150 so that the methanation reaction temperature can be maintained at an appropriate value (for example, 400 to 450 ° C.). The extracted steam from which the heat of the methane conversion reaction has been recovered is used in the CO2 preheater 303 and the H2 preheater 304 to preheat the raw material gas for methane conversion (about 280 ° C) and in the CO2 adsorption / desorption step 304 to regenerate the carbon dioxide recovery device (150 to). After being used at 200 ° C.), it is returned to the water supply preheater 106 and condensed to give excess heat of the methane conversion reaction heat to the boiler water supply. Specifically, in (Equation 1), heat of -165 kJ / mol is generated as the heat of reaction. At that time, the heat of reaction for methanation and the heat of recovery from cooling are 3600 kW, the amount of hydrogen and CO2 preheat is 500 kW, and the amount of heat during regeneration of the solid adsorbent is 1600 kW. Therefore, 1500 kW will be recovered to the feed water heater of the condensate system as process surplus heat. This is equivalent to 0.2% in terms of fuel reduction. Since the calorific value of methane per weight is about twice that of coal, if 1% of coal-fired CO2 is methaneized and reused, the amount of coal used will be reduced by 2%.

FIG. 4 is a conceptual diagram showing a simplified carbon dioxide recovery device from exhaust gas. FIG. 4 shows an example in which the simplest two-step carbon capture system can be constructed by sequentially switching the valve 203 to the valve 207 between the regeneration process by steam heating and the cooling / adsorption process by low-temperature exhaust gas. The graph in FIG. 4 is a diagram conceptually showing the change in the adsorbent temperature of the CO ₂ adsorption desorption tower 201a. When the adsorbent 202a is heated by the extracted steam and the temperature rises, the adsorbed carbon dioxide is desorbed and released (regeneration step). When the valve is switched and the low temperature exhaust gas is supplied, the temperature of the adsorbent 202a begins to drop, and carbon dioxide is adsorbed at an adsorption rate according to the temperature of the adsorbent (cooling / adsorption step). Combining the CO ₂ adsorption and desorption tower 201a and the CO ₂ adsorption and desorption tower 201b creates a carbon dioxide recovery system. Although not shown here, the carbon dioxide recovery system is divided into a regeneration process, a cooling process, and an adsorption process according to the required purity of carbon dioxide, and a purging process that discharges all the gas in the adsorption device is added. It may be expanded to a 4-tower system.

As described above, as seen in FIG. 1, in a power generation facility equipped with a boiler and a steam turbine having a device for converting carbon dioxide contained in combustion exhaust gas into methane, a methaneization reaction is carried out using the low-pressure extracted steam of the steam turbine. After recovering the reaction heat of the system and using the heat as a heat source for various heating processes, the energy consumption of the entire system is consumed by using it for heating the water supply and by using low-temperature exhaust gas to cool the solid adsorbent of carbon dioxide. It is possible to build a power plant with reduced energy consumption.

FIG. 2 shows another embodiment of the power generation system according to the present invention.

In a power plant using coal as fuel, it is mainstream to install a wet desulfurization device as shown in Example 1, but in a power plant using natural gas or low sulfur fuel, a wet desulfurization device is not installed. Therefore, the combustion exhaust gas temperature is often 100 ° C or higher. In such a situation, the exhaust gas cannot be expected to cool the carbon dioxide solid adsorbent. Therefore, a part of the exhaust gas is branched by the branching device 120, and the exhaust gas temperature is cooled to near the water vapor dew point temperature (for example, 40 ° C.) in the exhaust gas by the cooler 115, and then used for cooling the carbon dioxide adsorption tower 201a. The low-temperature exhaust gas after being used for cooling is mixed with the unbranched exhaust gas by the merging device 121 and then discharged from the exhaust tower 130. Further, FIG. 2 shows an example in which the steam condenser 305 is not installed. The raw material gases supplied to the methanation reactor 301 are carbon dioxide and hydrogen, but when carbon dioxide is separated and recovered from the exhaust gas using a solid adsorbent, some water vapor is also adsorbed on the adsorbent and supplied. It is possible that carbon contains water vapor. Therefore, in Example 1 of FIG. 1, an example in which the steam condenser 305 is installed for the purpose of condensing and removing the steam mixed with carbon dioxide is shown. On the other hand, depending on the type of solid adsorbent, it is possible that only carbon dioxide is selectively adsorbed and water vapor is not adsorbed. FIG. 2 assumes a case where the gas supplied from the carbon dioxide recovery device contains almost no steam, and in this case, the steam condenser 305 is not installed because the steam condenser 305 is unnecessary. Of course, also in the second embodiment, if the gas supplied from the carbon dioxide capture device contains water vapor and it is desired to remove the water vapor, the water vapor condenser 305 may be installed.

FIG. 5 shows yet another embodiment of the power generation system according to the present invention.

The difference from the first embodiment of FIG. 1 is that the bleed steam from the steam turbine is branched by the steam branching device 310 in the middle of the bleed steam supply pipe 151, and a bypass path directly to the carbon dioxide recovery device 201b is provided. be. If the heat capacity of the device is relatively large at the time of system startup, it is expected that it will take a long time to reach a stable state. In such a case, the bleed steam supply pipe 156 is provided so that the amount of steam supplied can be adjusted individually. As a result, the time required for the system to stabilize and settle can be shortened, and the overall system efficiency can be improved.

FIG. 6 shows yet another embodiment of the power generation system according to the present invention.

The difference from Example 3 of FIG. 5 is a steam branch pipe that recovers the heat of the methanation reactor cooler 302 that adjusts the temperature of the methanation reactor 301 in the middle of the return air extraction steam pipe 155 after heat exchange. 157 was set up. As shown in (Equation 1), the methaneation reactor 301 produces 1 mol of methane and 2 mol of steam from 1 mol of carbon dioxide. Since the generated gas is a mixed gas at about 400 ° C. containing a large amount of water vapor, the heat of this gas is recovered. A steam branch pipe 157 was provided for the purpose of supplying the recovered gas to the steam turbine water supply. As a result, the heat recovery efficiency of the entire system can be expected.

Based on the above, according to the invention described in the above Examples, according to the present invention, carbon dioxide and hydrogen are used as raw materials in a power generation facility equipped with a boiler and a steam turbine having a device for converting carbon dioxide contained in combustion exhaust gas into methane. The amount of heat required for methane production can be covered by the reaction heat of the methaneization reaction, and the excess heat can be recovered by heating the water supply of the steam turbine system, reducing the fuel consumption of the boiler and improving the efficiency of the power plant. be able to.

100 ... power generation system, 101 ... boiler, 102 ... steam turbine, 103 ... generator, 104 ... water recovery device, 105 ... water supply pump, 106 ... water supply heater, 110 ... exhaust gas denitration device, 111 ... exhaust gas heat recovery device, 112 … Exhaust steam reheater, 113… Electric dust collector, 114… Wet desulfurizer, 115… Cooler, 120… Branching device, 121… Merger, 130… Exhaust tower, 141… Exhaust steam supply pipe, 142… Exhaust steam exhaust pipe , 150 ... Steam flow control device, 151 ... Extract steam supply pipe, 152 ... Extract steam supply pipe, 153 ... Extract steam supply pipe, 154 ... Extract steam return pipe, 155 ... Extract steam return pipe, 156 ... Steam branch pipe, 157 … Steam branch pipe, 200… CO2 adsorption / desorption system, 201… CO2 adsorption / desorption tower, 202… CO2 adsorbent, 203… exhaust gas inlet side valve, 204… exhaust gas outlet side valve, 205… CO2 outlet side valve, 206… Regenerated steam inlet side valve, 207 ... Regenerated steam outlet side valve, 212 ... CO2 discharge pipe, 300 ... Methanization system, 301 ... Methanization reactor, 302 ... Cooler, 303 ... CO2 preheater, 304 ... H2 preheater, 305 ... Steam condenser, 306 ... H2 supply device, 310 ... Steam branching device, 311 ... Steam merging device, 320 ... Steam branching device, 321 ... Steam merging device, 350 ... Methanization reaction temperature detector

Claims (9)

A boiler that generates steam and
The steam turbine driven by the steam and
A power generation facility including a feed water heater that heats and supplies water to the boiler, and
A carbon dioxide recovery device that recovers and desorbs carbon dioxide contained in the exhaust gas of the power generation facility, and
A methane production system having a methanation reactor that reacts the desorbed carbon dioxide with hydrogen supplied from the outside to convert it into methane, and the steam discharged from the steam turbine is converted into the methaneization. The temperature is raised by the reaction heat at the time of methane conversion of the reactor, and the heated steam is supplied to the hydrogen, the desorbed carbon dioxide and the carbon dioxide recovery device, and then the methane supplied to the water supply heater. Manufacturing system. The methane production system according to claim 1.
A methane production system comprising heating the hydrogen and the desorbed carbon dioxide with the heat of reaction to a temperature suitable for initiating the reaction of the methane conversion. The methane production system according to claim 1 or 2.
A methane production system comprising cooling the carbon dioxide recovery device with a gas obtained by lowering the temperature of the combustion exhaust gas of the boiler . The methane production system according to any one of claims 1 to 3.
A methane production system characterized in that the recovered material in the carbon dioxide recovery device and the steam do not come into contact with each other. The methane production system according to any one of claims 1 to 4.
A methane production system characterized in that the power generation facility is a coal-fired thermal power plant. The methane production system according to any one of claims 1 to 5.
A methane production system comprising a cooler that cools the desorbed carbon dioxide and condenses the water vapor mixed with the carbon dioxide. The methane production system according to any one of claims 1 to 6.
A methane production system characterized in that steam discharged from the steam turbine is supplied to the carbon dioxide recovery device. The methane production system according to any one of claims 1 to 7.
A methane production system including a methaneization reactor cooler that cools the temperature of the methaneization reactor, and supplying the reaction heat recovered by the methaneization reactor cooler to the water supply heater. A boiler that generates steam and
The steam turbine driven by the steam and
A power generation facility including a feed water heater that heats and supplies water to the boiler, and
A carbon dioxide recovery device that recovers and desorbs carbon dioxide contained in the exhaust gas of the power generation facility, and
A methane production method performed in a methane production system including a methanation reactor that reacts the desorbed carbon dioxide with hydrogen supplied from the outside to convert it into methane.
The steam discharged from the steam turbine is heated by the reaction heat at the time of methane conversion of the methaneization reactor, and the heated steam is the hydrogen, the desorbed carbon dioxide, and the carbon dioxide recovery device. A method for producing methane, which is supplied to the water supply heater after being supplied to the water supply heater.

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