Patent Application
20240093937
The present invention relates to a technology for producing liquid hydrogen through liquefaction of gaseous hydrogen.
In recent years, there is a demand for reduction of an amount of greenhouse gas emission, and attention is being attracted to a fuel cell and a zero-emission fuel that is a carbon-neutral fuel represented by hydrogen and a biofuel that serve as an energy source of thermal power generation in the future.
Hydrogen is purified by steam reforming of hydrocarbon as described in, for example, Patent Literature 1 and Patent Literature 2. Hydrogen produced in the described manner is liquefied in order to facilitate transportation and storage thereof. However, due to an extremely low liquefaction temperature of hydrogen, much energy is required during a process of producing liquid hydrogen. Obtaining such energy for liquefaction of hydrogen may consequently cause emission of a large amount of carbon dioxide. Thus, also in a process of producing liquid hydrogen, a technology for reducing emission of carbon dioxide to the atmosphere is required.
The present technology provides a technology for producing liquid hydrogen while reducing emission of carbon dioxide to the atmosphere.
According to the present invention, there is provided a liquid hydrogen production device including:
The liquid hydrogen production device may have the following features.
According to the liquid hydrogen production device, the liquefaction plant configured to liquefy gaseous hydrogen is attached with the carbon dioxide cycle plant that obtains motive power with use of a carbon dioxide cycle, and hydrogen is liquefied by the motive power.
With this configuration, motive power for liquefaction of hydrogen that requires much energy can be obtained with use of a carbon dioxide cycle that can recover carbon dioxide at a high concentration, which enables reduction of emission of carbon dioxide to the atmosphere.
The hydrogen production plant 3 generates synthesis gas composed mainly of H2 gas from hydrocarbon (HC) gas (HC gas). The hydrogen production plant 3 uses natural gas (NG) composed mainly of methane as, for example, HC gas, and includes a reforming reactor 31 that is a reforming unit configured to reform HC gas. Alternatively, the hydrogen production plant 3 may produce H2 with use of HC gas obtained by, for example, gasification of coal.
For example, in the hydrogen production plant 3, steam supplied from a boiler 33 and HC gas that are mixed with each other (mixed gas) are supplied to the reforming reactor 31. Then, the hydrogen production plant 3 heats the mixed gas to a temperature of, for example, from 300° C. to 450° C., in the presence of a catalyst, to cause a steam reforming reaction to proceed, thereby generating reformed gas including H2 and CO. The reformed gas is gas in which H2, CO2, CO, and H2O are mixed with each other. Note that the reformed gas additionally includes a small amount of hydrogen sulfide (H2S) gas and the like.
The reformed gas generated in the reforming reactor 31 is supplied to a shift reactor 32 that is a shift reaction unit filled with a catalyst. In the shift reactor 32, when the reformed gas is supplied, a shift reaction in which H2 and CO2 are generated from CO and H2O proceeds. As a result, reformed gas with reduced CO (hereinafter referred to as “synthesis gas”) is generated.
The synthesis gas obtained in the hydrogen production plant 3 is supplied to the liquefaction plant 4. The liquefaction plant 4 is a plant configured to cool H2 gas included in the synthesis gas to produce liquid hydrogen. The liquefaction plant 4 includes a pretreatment unit 49 configured to remove acid gas and moisture mixed into the synthesis gas, and cools the synthesis gas having been subjected to pretreatment to produce liquid hydrogen.
The pretreatment unit 49 includes an acid gas removal unit (AGRU) 47 and a dehydration unit 48. The acid gas removal unit (AGRU) 47 is configured to separate acid gas included in the synthesis gas, such as CO2 and H2S. The dehydration unit 48 is configured to remove moisture included in the synthesis gas.
The AGRU 47 removes acid gas that may possibly be solidified during cooling of the synthesis gas, such as CO2 and H2S. Examples of a method of removing acid gas include a method that uses a gas absorption liquid including an amine compound in an absorption column and a method that uses a gas separation membrane which allows acid gas in the synthesis gas to permeate.
The dehydration unit 48 removes a small amount of moisture included in the synthesis gas. For example, the dehydration unit 48 includes an adsorption column filled with an adsorbent such as a molecular sieve and silica gel for removing moisture. There are provided a plurality of adsorption columns, and a process of removing moisture in the synthesis gas and a process of regenerating an adsorbent having adsorbed moisture are performed alternately. Further, the dehydration unit 48 includes a device that heats regeneration gas for an adsorbent (for example, synthesis gas provided after removal of moisture), such as a heater.
The liquefaction plant 4 cools H2 gas by heat exchange between H2 gas provided after removal of acid gas and moisture from the synthesis gas, and a refrigerant, to obtain liquid hydrogen. In the liquefaction plant 4 of this embodiment, H2 is used as a refrigerant that cools H2 gas. More specifically, a case in which boil-off gas generated by vaporization of a part of liquid hydrogen in a liquid hydrogen storage tank 46 is used can be exemplified.
The liquefaction plant 4 includes a heat exchanger 43 that performs heat exchange between H2 gas and a refrigerant.
On the inlet side of the heat exchanger 43, a hydrogen compressor 42 that is a compressor configured to increase the pressure of H2 gas is provided. H2 gas having been subjected to removal of acid gas and dehydration in the pretreatment unit 49 is supplied to the hydrogen compressor 42. Then, after the pressure of the H2 gas is increased by the hydrogen compressor 42, the H2 gas is cooled in a cooler 421 and supplied to the heat exchanger 43.
Further, the liquefaction plant 4 includes a refrigerant compressor 41 that is a compressor configured to increase the pressure of H2 gas for a refrigerant. After the pressure of the H2 gas for a refrigerant is increased by the refrigerant compressor 41, the H2 gas is cooled in a cooler 411 and is introduced into the heat exchanger 43.
In the heat exchanger 43, the H2 gas for a refrigerant is pre-cooled by a nitrogen refrigerant. Subsequently, the H2 gas for a refrigerant is adiabatically expanded in an expansion turbine 44, and hence the temperature thereof is further reduced. After that, the H2 gas is returned back to the heat exchanger 43. Note that a pressure reducing valve may be used in place of the expansion turbine 44. In this manner, there is formed a refrigeration cycle 400 in which the H2 gas for a refrigerant having a reduced temperature is subjected to heat exchange with H2 gas in the heat exchanger 43, and then is returned back to the refrigerant compressor 41.
Note that the refrigeration cycle 400 of the liquefaction plant 4 is not limited to the refrigeration cycle 400 that uses a dual system of a cooling refrigerant and a pre-cooling refrigerant as described above. For example, a refrigeration cycle in which a single system of only H2 gas for a refrigerant is used without pre-cooling by a nitrogen refrigerant may be formed. Further, the refrigeration cycle may have a plurality of systems of pre-cooling refrigerants. Further, a cooling refrigerant and a pre-cooling refrigerant are not limited to H2 gas and nitrogen. For example, helium and neon may be used for a cooling refrigerant, and light hydrocarbon such as methane, ethane, and propane may be used as a pre-cooling refrigerant.
By the heat exchange between the H2 gas for a refrigerant and the compressed H2 gas as described above, the compressed H2 gas is cooled. The pressure of the further cooled H2 gas is reduced by an expansion valve 45, and the H2 gas is liquefied and stored in the liquid hydrogen storage tank 46.
Note that, the reference symbol 401 of
In the liquid hydrogen production system 1 of this embodiment, motive power for driving the compressor forming the refrigerant compressor 41 of the liquefaction plant 4 is generated in the SC-CO2 cycle plant 2. The SC-CO2 cycle plant 2 is a plant that drives a turbine 23 to generate motive power with use of CO2 in a supercritical state as a driving fluid. As illustrated in
In the following, a configuration example of the CO2 cycle 200 is described with reference to
The CO2 cycle 200 is provided with a combustor 22 configured to combust HC gas and supply CO2. The combustor 22 mixes oxygen (O2) gas and HC gas and combusts the mixed gas in a flow of SC-CO2, to replenish the CO2 cycle 200 with CO2. Further, in the combustor 22, steam is also generated by combustion of HC gas.
In the liquid hydrogen production system 1 of this embodiment, HC gas combusted in the combustor 22 is NG. On the inlet side of the combustor 22, a HC-gas pressure increasing unit 211 configured to increase the pressure of HC gas is provided. HC gas is introduced into the combustor 22 after the pressure thereof is increased to a supply pressure for the CO2 cycle 200.
Further, in the combustor 22, HC gas is combusted with use of high-purity O2 gas having a concentration of, for example, 99.8% or more. The high-purity O2 gas is produced by separation of air into O2 gas and N2 gas by, for example, an air separation unit (ASU) (not shown).
On the inlet side of the combustor 22, an oxygen-gas pressure increasing unit 212 configured to increase the pressure of O2 gas is provided. O2 gas produced in the ASU is introduced into the combustor 22 after the pressure thereof is increased to a supply pressure for the CO2 cycle.
The description refers back to the explanation of the configuration of the CO2 cycle 200. The SC-CO2 replenished with CO2 in the combustor 22 is supplied to the turbine 23, and motive power is obtained when the turbine 23 is driven. The turbine 23 is connected to the compressor forming the refrigerant compressor 41 configured to compress the H2 gas for a refrigerant in the liquefaction plant 4 as described above. Specifically, a rotation shaft of the turbine 23 and a rotation shaft of the refrigerant compressor 41 are mechanically connected, and rotation of the turbine 23 drives the refrigerant compressor 41 to rotate. With this configuration, motive power generated by driving of the turbine 23 is mechanically transmitted, to cause the compressor of the refrigerant compressor 41 to operate, so that the pressure of the refrigerant can be increased.
The CO2 gas discharged from the turbine 23 and reduced in pressure is cooled by heat exchange with CO2 before supply to the combustor 22, in the heat exchanger 241, and then is further cooled in a cooler 242. By those cooling operations, the steam generated by combustion of HC gas condenses, and the resulting moisture is separated by a gas-liquid separator 243.
The CO2 gas from which the moisture has been separated is compressed by a compressor 251 and is further cooled in a cooler 252. Thus, the CO2 gas is converted into liquid CO2 and flows into a drum 261.
The liquid CO2 in the drum 261 is increased in pressure by a pressure increasing pump 262, and is further heated by the heat exchanger 241, to be placed in a SC-CO2 state. The SC-CO2 is supplied to the combustor 22 and is subsequently re-supplied to the turbine 23. In the CO2 cycle 200 of this embodiment, the heat exchanger 241 configured to perform heat exchange with CO2 gas discharged from the turbine 23, and the above-mentioned combustor 22 that uses combustion heat of HC gas, are provided as CO2 heating means.
Further, the SC-CO2 cycle power generation plant 2 of this embodiment has a configuration capable of extracting a part of a CO2 fluid circulating through the CO2 cycle, toward a CO2 receiving facility for, for example, storage, fixation, and use of CO2. In this embodiment, a liquid CO2 extraction line that extracts liquid CO2 before being heated by the heat exchanger 241 from a position on the outlet side of the pressure increasing pump 262 provided in the CO2 cycle, is provided.
For the pressure of the liquid CO2 extracted through the liquid CO2 extraction line, a value in a range of from 8 MPa to 30 MPa can be exemplified. For the flow rate, a value matching the flow rate of CO2 supplied to the CO2 cycle through the combustor 22 can be exemplified.
The liquid CO2 extracted through the above-mentioned liquid CO2 extraction line is supplied to at least one carbon dioxide receiving facility (CO2 receiving facility) selected from a facility group consisting of a carbon-dioxide capture and storage (CCS) facility that stores CO2 in an underground aquifer, an enhanced oil recovery (EOR) facility that injects CO2 into an oil field to boost the production of oil, a urea synthesis facility that causes CO2 to react with ammonia (NH3) to synthesize urea, a carbon dioxide mineralization facility that causes CO2 to react with calcium and magnesium to fix the CO2, a methanation facility that produces methane (CH4) with use of CO2 as a raw material, and a photosynthesis-promoting carbon-dioxide supply facility for boosting the production of crops.
Here, the CCS facility may store CO2 in a saline-water aquifer in the sea floor. Further, in a case in which CO2 is supplied to the EOR facility and the CCS facility in parallel, the EOR facility and the CCS facility may share the composing devices thereof.
Note that it is not essentially required that CO2 be extracted in a liquid state. The position where CO2 gas is extracted may be determined depending on the CO2 receiving specification of the CO2 receiving facility. For example, a CO2-gas extraction line serving as an extraction facility may be connected at a position on the outlet side of the gas-liquid separator 243 provided in the CO2 cycle. The pressure of CO2 in the CO2 cycle is higher than the atmospheric pressure, and hence high-purity and high-pressure CO2 can be supplied even in a case in which CO2 gas before being compressed by the compressor 251 is extracted.
As described above, in the SC-CO2 cycle plant 2, a CO2 fluid (CO2 gas, liquid CO2, SC-CO2) is caused to circulate in the CO2 cycle, and thus the turbine 23 is driven, to generate motive power. Further, in the SC-CO2 cycle plant 2, high-purity and high-pressure CO2 can be obtained, and hence CO2 can be captured by CO2 capture means such as the CCS. Thus, an amount of emission of CO2 to the atmosphere can be reduced. Thus, when comparing a plant using a gas turbine that combusts a fuel gas to drive a turbine and a steam turbine that drives a turbine with use of steam generated by combustion of a fuel, no combustion gas including CO2 is emitted to the atmosphere.
The liquid hydrogen production system 1 according to the embodiment described above produces the following effects. H2 gas, which is gaining attention as a zero-emission fuel, requires much energy for production and liquefaction thereof. Especially, much motive power is required in the refrigerant compressor 41 configured to compress a refrigerant used for liquefying H2 gas. As a result, this causes a concern that much CO2 gas may be emitted during a process of producing liquid hydrogen.
In this regard, in the liquid hydrogen production system 1 of the present invention, motive power for the refrigerant compressor 41 is generated in the SC-CO2 cycle plant 2.
The SC-CO2 cycle plant 2 can recover CO2 generated at the time of generation of motive power efficiently and at a high concentration, and thus can significantly reduce emission of CO2 to the atmosphere. As a result, this enables reduction of generation of CO2 in liquefaction of H2 gas that requires much motive power in general. Further, the turbine 23 and the refrigerant compressor 41 are physically connected to drive the refrigerant compressor 41, which eliminates a need for establishment of facilities required for power supply, such as a power generator and a cable, thereby simplifying the configuration of the facility.
In the following, with reference to
The SC-CO2 cycle plant 2 may be configured so as to recover exhaust heat discharged from the turbine 23. For example,
In the example illustrated in
With the above-mentioned configuration, emission of CO2 can be reduced as compared to a case in which regeneration gas is heated by combustion of a fuel in a heating furnace.
Further, also in the AGRU 47 forming the pretreatment unit 49 together with the dehydration unit 48, heat recovered by the exhaust-heat recovery unit 27 can be used. For example, an absorption liquid in which acid gas has been removed by contact of synthesis gas with the absorption column is delivered to a regeneration column and then is heated by a reboiler, to emit acid gas and be regenerated. At that time, as a heat source of the reboiler, heat recovered by the exhaust-heat recovery unit 27 may be used.
With use of exhaust heat in the SC-CO2 cycle plant 2 as described above, liquid hydrogen with less energy can be produced while reducing emission of CO2 to the atmosphere.
Further, as illustrated in
In addition to the above-described examples, a boiler that uses, as a heat source thereof, exhaust heat of the turbine 23 that is recovered by the first exhaust-heat recovery unit 27, may be provided. Then, power generation may be performed by driving of a steam turbine with use of steam generated in the boiler. Further, exhaust heat recovered by the second exhaust-heat recovery unit 34 may also be used as a heat source for generating steam in the boiler.
Further, exhaust heat in combustion gas of the combustor 22 may be supplied to the boiler, to generate steam. Then, the steam turbine may be driven by the generated steam.
Further, CO2 gas separated from the synthesis gas in the above-mentioned AGRU 47 may be recovered, to be supplied to, for example, the inlet side of the compressor 251 of the SC-CO2 cycle plant 2.
Further, a second reforming reactor may be provided at a stage subsequent to the reforming reactor 31 in the hydrogen production plant 3. In the second reforming reactor, partial oxidation in which reformed gas generated in the reforming reactor 31 and O2 gas are caused to react with each other takes place. With the second reforming reactor being provided, hydrocarbon left unreformed by the reforming reactor 31 can be reformed. Then, a part of O2 gas produced in the ASU may be supplied to the second reforming reactor, in parallel with O2 gas supplied to the combustor 22. Moreover, at that time, exhaust heat of the second reforming reactor may be recovered, to be used for a reforming reaction in the reforming reactor 31.
Further, exhaust heat of the shift reactor 32 may be recovered, to be used as a heat source for generating steam in the boiler 33.
Still further, exhaust heat recovered in the hydrogen production plant 3 may be used for heating CO2 gas circulating through the CO2 cycle 200. With this configuration, the temperature of CO2 gas that is compressed by the compressor 251 and is returned back to the combustor 22 can be increased, and hence the thermal efficiency of the CO2 cycle can be improved.
Next,
Further, the power generated by the power generator 28 may be used for driving facilities placed in the liquefaction plant 4 and the hydrogen production plant 3, such as a heater and a blower. Moreover, in a case in which power generated in the SC-CO2 cycle plant 2 is superfluous with respect to power consumption of respective power-consuming devices in the liquid hydrogen production system 1, the power may be supplied to areas and facilities outside of the liquid hydrogen production system 1.
Still further, the hydrogen production plant 3 may be a plant that produces H2 gas by, for example, water electrolysis. For example, as illustrated in
Note that it is not essentially required that power generated by the power generator 28 be supplied to the water electrolysis unit 35. For example, regeneratable energy, power generated in another local power generation facility, or power purchased from outside may be supplied to the water electrolysis unit 35.
In this case, the motive power of the turbine 23 can be used for driving the compressor of the refrigerant compressor 41 in the same manner as in the example described with reference to
Further, the SC-CO2 cycle plant 2 is not limited to one having the configuration in which the turbine 23 is driven with use of SC-CO2 to obtain motive power. For example, a case in which the SC-CO2 cycle plant 2 configured so as to drive the turbine 23 with use of CO2 gas to obtain motive power is employed is not excluded.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/005352 | 2/12/2021 | WO |
