Patent Application
20240053095
The present invention relates to a natural gas processing plant that produces liquefied natural gas and does not discharge a carbon dioxide gas.
A natural gas processing plant (hereinafter, also referred to as “LNG plant”) producing liquefied natural gas (LNG) cools natural gas (NG) using a refrigerant to produce liquefied and subcooled LNG, as disclosed in Patent Literature 1, for example.
This LNG plant is provided with a large number of energy consumption devices including a compressor that compresses a refrigerant vaporized by heat exchange with NG, and a power machine such as a pump that transports LNG.
For example, some compressors are configured to drive a gas turbine using NG as fuel or a steam turbine driven by steam obtained by combusting fuel to compress a refrigerant. In these cases, fuel is combusted in the LNG plant to discharge carbon dioxide (CO2).
Alternatively, even in a case where a compressor or another power machine is driven using a motor, electric power for driving the power machine may also be supplied from a stand-alone electric power generation facility provided in the LNG plant. The stand-alone electric power generation facility generally adopts a method of driving a generator using a fuel gas or steam, and CO2 is discharged from the LNG plant even in such a case.
In addition, NG contains CO2 as acid gases in some cases, and some LNG plants include an acid gas removal unit (AGRU) that removes these acid gases from NG.
Conventionally, an acid gas separated from NG has been released to the atmosphere after combustion and removal of environmental pollutants. In this case, CO2 separated from NG is also discharged to the atmosphere together with other CO2 generated by the combustion.
As described above, the LNG plant has a plurality of CO2 emission sources. Meanwhile, there is a demand for LNG plants with CO2 emissions reduced as much as possible from the viewpoint of reducing greenhouse gas emissions.
Here, the above-described Patent Literature 1 describes that light ends flushed from LNG by a device (end flash vessel) provided in an NG liquefaction apparatus is used as a fuel gas in a factory (paragraph 0023). On the other hand, Patent Literature 1 has no description regarding the handling of CO2 generated by combusting this fuel gas, and thus, it is considered that such CO2 is also discharged to the atmosphere.
Meanwhile, Patent Literature 2 describes a power generation system in which a hydrocarbon gas and oxygen are combusted under supply of boiler water in a gas generator, and a steam turbine is rotated by a combusted gas containing CO2 and steam to obtain mechanical energy and electrical energy (paragraphs 0032 to 0033 and
Here, each plant described in Patent Literatures 2 and 3 is installed for the purpose of obtaining energy for power generation and compressor driving, and thus, it is necessary to control stable properties and a fuel flow rate in accordance with required energy. In this regard, the power generation system described in Patent Literature 2 is configured such that LNG is supplied from a storage tank or a vessel to the above-described gas generator (paragraph 0029,
It is clearly described in Patent Literatures 2 and 3 that it is common technical knowledge that such an external fuel receiving type energy supply plant is operated using fuel having stable properties and supply amount, such as LNG which is a product produced by the NG liquefaction apparatus of Patent Literature 1. Therefore, the NG liquefaction apparatus of Patent Literature 1 merely has a role of supplying LNG as the product in relation to the various plants described in Patent Literatures 2 and 3. Thus, when the NG liquefaction apparatus described in Patent Literature 1 and the plants described in Patent Literatures 2 and 3 are combined, it is the fact that the entire CO2 contained in an exhaust gas after the combustion is released to the atmosphere regarding light hydrocarbon components by-produced in the NG liquefaction apparatus and are used as the fuel gas in the plants.
The present technology provides a combined cycle natural gas processing system that combusts a light hydrocarbon gas, by-produced in a natural gas processing plant, with high-purity oxygen and does not discharge generated carbon dioxide to the atmosphere.
A first combined cycle natural gas processing system includes: a natural gas processing plant that produces liquefied natural gas from natural gas; and a carbon dioxide cycle power plant that includes a power generation turbine using a carbon dioxide fluid as a driving fluid, and performs power generation using a carbon dioxide cycle that pressurizes and heats the carbon dioxide fluid discharged from the power generation turbine and supplies the carbon dioxide fluid again to the power generation turbine. The natural gas processing plant includes an acid gas removal unit (AGRU) that separates carbon dioxide contained in the natural gas. The carbon dioxide cycle power plant includes: a combustor that is provided on an inlet side of the power generation turbine, mixes the pressurized and heated carbon dioxide fluid with a light hydrocarbon gas containing methane as a main component and a high-purity oxygen gas and combusts the carbon dioxide fluid mixed with the light hydrocarbon gas and the high-purity oxygen gas to generate the carbon dioxide fluid containing high-temperature and high-pressure steam, the light hydrocarbon gas being by-produced when the liquefied natural gas is produced in the natural gas processing plant; a separator that cools the carbon dioxide fluid containing the steam, discharged from the power generation turbine and decompressed, to condense and separate the steam; and an extraction facility that extracts a carbon dioxide fluid exceeding a required circulation amount, determined according to electric power that needs to be obtained by the power generation, out of the carbon dioxide fluid from which moisture has been separated by the separator. Electric power obtained by driving a generator using the power generation turbine is supplied to a power consumption device provided in the natural gas processing plant, the carbon dioxide fluid extracted from the extraction facility and a carbon dioxide separation stream separated by the acid gas removal unit are supplied to a carbon dioxide reception facility capable of receiving carbon dioxide, and the carbon dioxide generated with production of the liquefied natural gas is not released to atmosphere.
In addition, a second combined cycle natural gas processing system includes: a natural gas processing plant that produces liquefied natural gas from natural gas; and a carbon dioxide cycle power plant that includes a power generation turbine using a carbon dioxide fluid as a driving fluid, and performs power generation using a carbon dioxide cycle that pressurizes and heats the carbon dioxide fluid discharged from the power generation turbine and supplies the carbon dioxide fluid again to the power generation turbine. The natural gas processing plant includes: an acid gas removal unit (AGRU) that separates carbon dioxide contained in the natural gas; a pressurizing unit that pressurizes a carbon dioxide separation stream separated by the acid gas removal unit; and a carbon dioxide supply line that causes the carbon dioxide separation stream pressurized in the pressurizing unit to join the carbon dioxide fluid flowing in the carbon dioxide cycle. The carbon dioxide cycle power plant includes: a combustor that is provided on an inlet side of the power generation turbine, mixes the pressurized and heated carbon dioxide fluid with a light hydrocarbon gas containing methane as a main component and a high-purity oxygen gas and combusts the carbon dioxide fluid mixed with the light hydrocarbon gas and the high-purity oxygen gas to generate the carbon dioxide fluid containing high-temperature and high-pressure steam, the light hydrocarbon gas being by-produced when the liquefied natural gas is produced in the natural gas processing plant; a separator that cools the carbon dioxide fluid containing the steam, discharged from the power generation turbine and decompressed, to condense and separate the steam; and an extraction facility that extracts a carbon dioxide fluid exceeding a required circulation amount, determined according to electric power that needs to be obtained by the power generation, out of the carbon dioxide fluid from which moisture has been separated by the separator. Electric power obtained by driving a generator using the power generation turbine is supplied to a power consumption device provided in the natural gas processing plant, the carbon dioxide fluid extracted from the extraction facility is supplied to a carbon dioxide reception facility capable of receiving carbon dioxide, and the carbon dioxide generated with production of the liquefied natural gas is not released to atmosphere.
Further, a third combined cycle natural gas processing system includes: a natural gas processing plant that produces liquefied natural gas from natural gas; and a carbon dioxide cycle plant that includes an energy conversion turbine configured to convert energy held by a driving fluid into mechanical energy using a carbon dioxide fluid as the driving fluid, and obtains the mechanical energy using a carbon dioxide cycle that pressurizes and heats the carbon dioxide fluid discharged from the energy conversion turbine and supplies the carbon dioxide fluid again to the energy conversion turbine. The natural gas processing plant includes an acid gas removal unit (AGRU) that separates carbon dioxide contained in the natural gas. The carbon dioxide cycle plant includes: a combustor that is provided on an inlet side of the energy conversion turbine, mixes the pressurized and heated carbon dioxide fluid with a light hydrocarbon gas containing methane as a main component and a high-purity oxygen gas and combusts the carbon dioxide fluid mixed with the light hydrocarbon gas and the high-purity oxygen gas to generate the carbon dioxide fluid containing high-temperature and high-pressure steam, the light hydrocarbon gas being by-produced when the liquefied natural gas is produced in the natural gas processing plant; a separator that cools the carbon dioxide fluid containing the steam, discharged from the energy conversion turbine and decompressed, to condense and separate the steam; and an extraction facility that extracts a carbon dioxide fluid exceeding a required circulation amount, determined according to the mechanical energy that needs to be obtained by the energy conversion, out of the carbon dioxide fluid from which moisture has been separated by the separator. The mechanical energy obtained by driving the energy conversion turbine is supplied to a mechanical energy consumption device provided in the natural gas processing plant, the carbon dioxide fluid extracted from the extraction facility and a carbon dioxide separation stream separated by the acid gas removal unit are supplied to a carbon dioxide reception facility capable of receiving carbon dioxide, and the carbon dioxide generated with production of the liquefied natural gas is not released to atmosphere.
Then, a fourth combined cycle natural gas processing system includes: a natural gas processing plant that produces liquefied natural gas from natural gas; and a carbon dioxide cycle plant that includes an energy conversion turbine configured to convert energy held by a driving fluid into mechanical energy using a carbon dioxide fluid as the driving fluid, and recovers energy using a carbon dioxide cycle that pressurizes and heats the carbon dioxide fluid discharged from the energy conversion turbine and supplies the carbon dioxide fluid again to the energy conversion turbine. The natural gas processing plant includes: an acid gas removal unit (AGRU) that separates carbon dioxide contained in the natural gas; a pressurizing unit that pressurizes a carbon dioxide separation stream separated by the acid gas removal unit; and a carbon dioxide supply line that causes the carbon dioxide separation stream pressurized in the pressurizing unit to join the carbon dioxide fluid flowing in the carbon dioxide cycle. The carbon dioxide cycle plant includes: a combustor that is provided on an inlet side of the energy conversion turbine, mixes the pressurized and heated carbon dioxide fluid with a light hydrocarbon gas containing methane as a main component and a high-purity oxygen gas and combusts the carbon dioxide fluid mixed with the light hydrocarbon gas and the high-purity oxygen gas to generate the carbon dioxide fluid containing high-temperature and high-pressure steam, the light hydrocarbon gas being by-produced when the liquefied natural gas is produced in the natural gas processing plant; a separator that cools the carbon dioxide fluid containing the steam, discharged from the energy conversion turbine and decompressed, to condense and separate the steam; and an extraction facility that extracts a carbon dioxide fluid exceeding a required circulation amount, determined according to the mechanical energy that needs to be obtained by the energy conversion, out of the carbon dioxide fluid from which moisture has been separated by the separator. The mechanical energy obtained by driving the energy conversion turbine is supplied to a mechanical energy consumption device provided in the natural gas processing plant, the carbon dioxide fluid extracted from the extraction facility is supplied to a carbon dioxide reception facility capable of receiving carbon dioxide, and the carbon dioxide generated with production of the liquefied natural gas is not released to atmosphere.
In the third and fourth combined cycle natural gas processing systems, the mechanical energy consumption device may be a rotary device provided in the natural gas processing plant, and the energy conversion turbine may be a drive turbine configured to drive the rotary device. The carbon dioxide cycle plant may further include a power generation turbine that converts the energy held by the driving fluid into electrical energy, and electric power obtained by driving a generator using the power generation turbine may be supplied to a power consumption device provided in the natural gas processing plant.
The first to fourth combined cycle natural gas processing systems may have the following features.
In (f) and (e), the natural gas processing plant includes: a main cryogenic heat exchanger that liquefies and subcools the natural gas to obtain the LNG; an end flash unit that decompresses the LNG sent from the main cryogenic heat exchanger to a pressure of the storage tank and separates an end flash gas generated by the decompressing from the liquefied natural gas; an auxiliary supply line that causes a light hydrocarbon gas obtained by vaporizing the LNG in the end flash unit to join the light hydrocarbon gas supply line; and a control unit that executes control to increase a temperature of the LNG at an outlet of the main cryogenic heat exchanger in order to increase an evaporation amount of the LNG in the end flash unit in a case where a supply flow rate of the light hydrocarbon gas supplied from the light hydrocarbon gas supply line to the combustor is less than a target supply flow rate necessary for maintaining the required circulation amount of the carbon dioxide fluid even when an entire amount of the boil-off gas that is suppliable from the storage tank is supplied to the light hydrocarbon gas supply line.
In (g) and (e), the natural gas processing LNG plant includes: a main cryogenic heat exchanger that liquefies and subcools the natural gas to obtain the LNG; an auxiliary supply line that extracts a part of the natural gas before being liquefied, which is supplied to the main cryogenic heat exchanger, from an inlet side of the main cryogenic heat exchanger to join the light hydrocarbon gas supply line as the light hydrocarbon gas; and a control unit that executes control to increase an extraction amount of the natural gas from the inlet side of the main cryogenic heat exchanger in a case where a supply flow rate of the light hydrocarbon gas supplied from the light hydrocarbon gas supply line to the combustor is less than a target supply flow rate necessary for maintaining the required circulation amount of the carbon dioxide fluid even if an entire amount of the boil-off gas that is suppliable from the storage tank is supplied to the light hydrocarbon gas supply line.
According to the present combined cycle natural gas processing system, the carbon dioxide cycle is also installed in the natural gas processing plant for producing the liquefied natural gas, and the light hydrocarbon gas mainly containing methane, which is by-produced in the natural gas processing plant, is combusted with high-purity oxygen to supply combustion energy to the carbon dioxide cycle. Then, in the carbon dioxide cycle, the energy of the carbon dioxide fluid is converted into electrical energy or mechanical energy. As a result, it is possible to effectively utilize the thermal energy generated by the combustion of the light hydrocarbon gas by-produced in the natural gas processing plant, and the carbon dioxide in the carbon dioxide cycle is supplied to various carbon dioxide reception facilities in the high purity and high pressure state, and thus, the release to the atmospheric associated with the combustion of the light hydrocarbon gas is not performed.
In addition, the carbon dioxide separated from the natural gas in the acid gas removal unit of the natural gas processing plant is also supplied to the carbon dioxide reception facilities together with the above-described carbon dioxide fluid directly or after being once merged with the carbon dioxide fluid circulating in the carbon dioxide cycle, and thus, is not discharged to the outside.
In the example illustrated in
As the facilities for the pretreatment system, an acid gas removal unit (AGRU) 31 that separates acid gases such as CO2 and hydrogen sulfide (H2S) contained in NG, a dehydration unit 32 that removes moisture contained in NG, and a heavy component separation unit 33 that removes heavy hydrocarbons heavier than methane contained in NG are provided
The AGRU 31 removes the acid gases, such as CO2 and H2S, which are likely to solidify in LNG during liquefaction. As a method for removing the acid gases, it is possible to apply a method using a gas absorbing liquid containing an amine compound or a method using a gas separation membrane that allows permeation of the acid gases in NG.
The acid gases separated from NG by the AGRU 31 are separated into CO2 containing a trace of light hydrocarbons and the other acid gases containing a sulfur compound such as H2S by an extraction operation or the like using a gas absorbing liquid of an amine compound in a separation unit 311. The acid gases from which CO2 containing a trace of light hydrocarbons has been separated is combusted in an acid gas combustion facility 37 to be detoxified, subjected to a treatment for removing air pollutants as necessary, and then, released to the atmosphere. When a sulfur concentration in the acid gases is high, sulfur is recovered and then combusted in the combustion facility 37.
In addition, a CO2 gas separated from the other acid gases in the separation unit 311 is sent to a CCS facility 4, which will be described later, as a CO2 separation stream (carbon dioxide separation stream).
The dehydration unit 32 removes a trace of moisture contained in the NG. For example, the dehydration unit 32 is filled with an adsorbent such as a molecular sieve or a silica gel, and includes: a plurality of adsorption columns in which an NG moisture removal operation and a regeneration operation of the adsorbent having adsorbed moisture are alternately switched; and a device such as a heater that heats a regeneration gas (for example, NG after moisture removal) of the adsorbent supplied to the adsorption columns where the regeneration operation is being performed.
NG containing moisture after being used for regeneration of the adsorbent is pressurized using a regeneration gas compressor 321 and returned to an inlet side of the AGRU 31, or is used as a fuel gas for a heater and the like provided in the combined cycle natural gas processing system 1.
The NG from which impurities such as the acid gases and moisture have been removed is subjected to a treatment of removing a heavy component heavier than methane in the heavy component separation unit 33. The heavy component separation unit 33 includes a cooler that cools the NG to liquefy the heavy component, a distillation column (demethanizer) that performs distillation and separation between a light gas (methane gas) containing methane as a main component and the liquefied heavy component, and the like. In addition, the heavy component separated from the methane gas by the demethanizer is distilled and separated into ethane, propane, butane, and a heavy condensate using a plurality of rectification columns.
The cooler that liquefies the heavy component may use the methane gas sent from the demethanizer as a self-refrigerant or may use a pre-cooling medium such as propane (
The methane gas from which the heavy component has been separated is pressurized by the separation unit 311 including a compressor as necessary, and then, cooled by a liquefying unit 341 to be liquefied, thereby producing LNG. The liquefying unit 341 includes, for example, a main cryogenic heat exchanger (MCHE) that cools, liquefies, and subcools NG with a liquefaction refrigerant that is a mixed refrigerant containing a plurality of types of refrigerant raw materials such as nitrogen, methane, ethane, and propane.
In addition, the liquefying unit 341 is provided together with a liquefaction refrigerant cycle 342 for compressing, cooling, and re-liquefying a gas of the liquefaction refrigerant vaporized by heat exchange with the methane gas, and supplying the resultant to the MCHE.
The LNG produced in the liquefying unit 341 is decompressed to a pressure equal to or lower than a reception pressure on an LNG tank (storage tank) 36 side in an end flash unit 35, and then, sent to the LNG tank 36 by an LNG pump 351. From the LNG tank 36, LNG is shipped to the LNG carrier 5 using a shipping pump 362, and the LNG loaded on the LNG carrier 5 is transported to a demand site.
The LNG plant 3 having the schematic configuration described above includes dynamic devices such as a compressor that compresses the above-described various refrigerants, a compressor (for example, a compressor of the regeneration gas compressor 321 or an NG pressurizing unit 331, a compressor 361 of a BOG to be described later, or a compressor 352 of an end flash gas) that pressurizes NG or the like, and pumps (for example, the LNG pump 351 and the shipping pump 362) for transfer of LNG. These dynamic devices consume energy to pressurize and transport various fluids, and the combined cycle natural gas processing system 1 of the present example is configured to operate these dynamic devices (power consumption devices) using a drive motor driven by electric power generated in the SC-CO2 cycle power plant 2.
The SC-CO2 cycle power plant 2 is a known power plant that generates power by driving a power generation turbine 23 using CO2 in the supercritical state as a driving fluid. In the example illustrated in
Hereinafter, a configuration example of the CO2 cycle will be described with reference to
The power generation turbine 23 of the CO2 cycle is provided with a combustor 22, which combusts a light hydrocarbon gas to supply CO2, on an inlet side. The combustor 22 replenishes CO2 to the CO2 cycle by mixing and combusting an oxygen (O2) gas and light hydrocarbon gas in a flow of SC-CO2. In addition, steam is also generated by the combustion of the light hydrocarbon gas in the combustor 22.
In the combined cycle natural gas processing system 1 of the present example, a light hydrocarbon gas mainly containing a methane gas generated (by-produced) in the process of producing and storing LNG in the LNG plant 3 is used as the light hydrocarbon gas to be combusted in the combustor 22. In the following description, the light hydrocarbon (HC) gas containing methane as the main component is also simply referred to as an “HC gas”.
More specifically, the boil-off gas (BOG) generated by vaporization of a part of LNG in the LNG tank 36, the end flash gas generated when the pressure of LNG is adjusted in the end flash unit 35, and the like are used. These HC gases are separated from a nitrogen (N2) gas by a nitrogen gas separation unit 39, then pressurized by an HC gas supply unit 391 including a compressor, and supplied to the SC-CO2 cycle power plant 2 through an HC gas supply line 301. Note that reference signs 352 and 361 denote the compressors that supply the end flash gas and the BOG to the nitrogen gas separation unit 39, respectively. As described above, both the BOG and the end flash gas are supplied to the SC-CO2 cycle power plant 2 as the HC gas that is the methane gas with high purity from which the N2 gas has been removed.
An HC gas pressurizing unit 211 that pressurizes the HC gas is provided on the inlet side of the combustor 22, and the HC gas supplied through the HC gas supply line 301 is pressurized to a supply pressure for the CO2 cycle, and then, introduced into the combustor 22.
Note that a configuration example of a supply control mechanism configured to supply a required amount of the HC gas for the CO2 cycle will be described in detail with reference to
In addition, the HC gas is combusted in the combustor 22 using, for example, a high-purity O2 gas having a concentration equal to or higher than 99.8%. Thus, the LNG plant 3 is provided with an air separation unit (ASU) 38 configured to separate air into an O2 gas and a N2 gas to produce the oxygen gas to be supplied to the combustor 22.
The O2 gas produced in the ASU 38 is supplied to the SC-CO2 cycle power plant 2 through an O2 gas supply line 302. An oxygen gas pressurizing unit 212 that pressurizes the O2 gas is provided on the inlet side of the combustor 22, and the O2 gas supplied through the O2 gas supply line 302 is pressurized to the supply pressure for the CO2 cycle, and then, introduced into the combustor 22.
Note that a part of the O2 gas produced by the ASU 38 is supplied to the above-described acid gas combustion facility 37 and used for the combustion of the acid gas.
In the ASU 38 described above, the N2 gas is produced together with the O2 gas. This N2 gas is supplied to at least one N2 gas use facility selected from a utility facility that supplies the N2 gas as necessary in the combined cycle natural gas processing system 1, a facility that supplies a purge gas into a seal drum of a flare stack for combusting a surplus gas, a facility that supplies a blanket gas to a gas phase side in the LNG tank 36 to prevent formation of a flammable air-fuel mixture, and a facility that is used an oil-water separation unit, which performs oil-water separation of oil-containing wastewater discharged from a device in the combined cycle natural gas processing system 1, and supplies a microbubble gas into the wastewater to promote the oil-water separation function. The N2 gas is supplied to these N2 gas use facilities through a N2 gas supply line 305. In addition, the N2 gas may be used as a part of the refrigerant for liquefying and subcooling the methane gas.
In addition, the BOG and the end flash gas supplied to the combustor 22 as the HC gases are subjected to the N2 gas separation in the nitrogen gas separation unit 39 as described above. The N2 gas separated from the HC gases by the nitrogen gas separation unit 39 also merges with the nitrogen of the above-described N2 gas supply line 305 and is used in each of the N2 gas use facilities or is used as a part of the refrigerant for liquefying and subcooling the methane gas.
Returning to the description of the configuration of the CO2 cycle, the SC-CO2 replenished with CO2 in the combustor 22 is supplied to the power generation turbine 23, and power generation is performed by driving the power generation turbine 23 to which a generator 231 is connected. Electric power obtained by the power generation is supplied to each power consumption device in the LNG plant 3 and the SC-CO2 cycle power plant 2 including the compressor that compresses the refrigerant to be used for the production of LNG.
The CO2 gas discharged from the power generation turbine 23 and decompressed is subjected to heat exchange with CO2 before being supplied to the combustor 22 in a heat exchanger 241, and then, further cooled in a cooler 242. Through these cooling operations, the steam generated by combustion of the HC gas is condensed, and moisture is separated in a gas-liquid separator 243.
The CO2 gas from which the moisture has been separated is compressed by a compressor 251 and further cooled by a cooler 252 to become liquid CO2 and flow into a drum 261.
The liquid CO2 in the drum 261 is pressurized by a pressurizing pump 262, further heated to be in a state of SC-CO2, and supplied again to combustor 22. In the CO2 cycle of the present example, as means for heating CO2, a CO2 fluid heating unit 27 that uses exhaust heat obtained by combusting the acid gas in the above-described acid gas combustion facility 37 provided on the SC-CO2 cycle power plant 2 side, the heat exchanger 241 that performs heat exchange with the CO2 gas discharged from the power generation turbine 23, and the above-described combustor 22 that uses the combustion heat of the HC gas are provided.
Although simplified in
In
Returning to the description of the CO2 cycle, the power generation is performed in the SC-CO2 cycle power plant 2 by circulating a CO2 fluid (CO2 gas, liquid CO2, or SC-CO2) in the CO2 cycle to drive the power generation turbine 23. Thus, the combustion gas containing CO2 is not released to the atmosphere as compared with a power plant using a gas turbine generator that drives a turbine by combusting a fuel gas or a steam turbine generator that drives a turbine by steam generated by combusting fuel. In addition, a high-purity and high-pressure CO2 fluid can be obtained from the CO2 cycle.
In this regard, the SC-CO2 cycle power plant 2 of the present example is configured to be capable of extracting a part of the CO2 fluid circulating in the CO2 cycle toward a CO2 reception facility configured for storage, fixation, utilization, and the like of CO2. In the present example, a liquid CO2 extraction line 201 for extracting the liquid CO2 before being heated by the CO2 fluid heating unit 27 from a position on an outlet side of the pressurizing pump 262 provided in the CO2 cycle is provided. The liquid CO2 extraction line 201 corresponds to a CO2 fluid extraction facility in the present example.
The pressure of the liquid CO2 extracted through the liquid CO2 extraction line 201 can be exemplified by a value within a range of 8 to 30 MPa. In addition, a flow rate of the liquid CO2 extracted through the liquid CO2 extraction line 201 is adjusted so as to maintain a state in which a circulation amount (required circulation amount) of the CO2 fluid, required for the generator 231 to generate power, circulates through the CO2 cycle with a preset output. That is, the CO2 fluid exceeding the required circulation amount is extracted through the liquid CO2 extraction line 201.
The liquid CO2 extracted by the liquid CO2 extraction line 201 is supplied to at least one carbon dioxide reception facility (CO2 reception facility) selected from a facility group including a carbon dioxide capture and storage (CCS) facility that stores CO2 in an underground aquifer 6, an enhanced oil recovery facility (EOR) facility that increases oil production by injecting CO2 into an oil field by pressure, a urea synthesis facility that causes CO2 to react with ammonia (NH 3) to synthesize urea, a carbon dioxide mineralization facility that causes CO2 to react with calcium or magnesium to be fixed, a methanation facility in which methane (CH 4) is produced using CO2 as a raw material, and a carbon dioxide supply facility for photosynthesis promotion configured to increase a crop production amount.
Here, the CCS facility may be configured to store CO2 in a deep salt water layer of the sea floor. In addition, in a case where CO2 is supplied to the EOR and the CCS in parallel, components of the EOR facility and the CCS facility may be shared.
Note that the extraction of CO2 in a liquid state is not an essential requirement, and the CO2 gas may be supplied according to the CO2 reception specification on the CO2 reception facility side. For example, a CO2 gas extraction line as an extraction facility may be connected to a position on an outlet side of the gas-liquid separator 243 provided in the CO2 cycle. Since the pressure of CO2 in the CO2 cycle is higher than the atmospheric pressure, high-purity and high-pressure CO2 can be supplied even when the CO2 gas before being compressed by the compressor 251 is extracted.
Further, in the combined cycle natural gas processing system 1, the CO2 gas separated from the NG in the AGRU 31 of the LNG plant 3 may also be supplied to at least one CO2 reception facility selected from the above-described facility group together with the liquid CO2 extracted from the CO2 cycle.
For example, an example in which the CO2 gas sent from the separation unit 311 at the subsequent stage of the AGRU 31 is pressurized by the CO2 gas pressurizing unit 312 and sent to the CCS facility 4 through the CO2 gas extraction line 303 is illustrated in the combined cycle natural gas processing system 1 illustrated in
In the CCS facility 4, the received CO2 gas is compressed by a CO2 compressor 41 (in this case, the compressor 41 may be shared with the CO2 gas pressurizing unit 312 or omitted), and condensed moisture is separated by the CO2 dehydration unit 42. Subsequently, the CO2 gas is compressed again by a CO2 compressor 43 and then cooled by a cooler 44, thereby obtaining high purity and high pressure liquid CO2. The CO2 liquefied in the CCS facility 4 is separated into gas and liquid by a gas-liquid separator 45, and is sent to the underground aquifer 6 by a CO2 pump 46.
On the other hand, the liquid CO2 extracted from the SC-CO2 cycle power plant 2 through the liquid CO2 extraction line 201 described above is separated from moisture, and has a sufficiently high pressure. Thus, this liquid CO2 joins the liquid CO2 discharged from the SC-CO2 cycle power plant 2 side on the outlet side of the CO2 pump 46 in the CCS facility 4 and can be directly stored in the underground aquifer 6 as in the example illustrated in
Even when being supplied to another CO2 reception facility other than the CCS facility 4, the CO2 gas discharged from the LNG plant 3 (AGRU 31) is subjected to pressurization, moisture removal, and liquefaction according to the reception specification of each CO2 reception facility. Then, this CO2 gas is supplied to each CO2 reception facility together with the CO2 fluid (CO2 gas or liquid CO2) extracted from the SC-CO2 cycle power plant 2.
Next, a configuration example of a combined cycle natural gas processing system 1a according to a second embodiment will be described with reference to
The combined cycle natural gas processing system 1a of
In the example illustrated in
The joined CO2 gas is subjected to moisture separation, pressurization, liquefaction, and heating together with the other CO2 fluid, and forms SC-CO2 to drive the generator 231.
Here, as compared with a case where CO2 is supplied using only the combustor 22 capable of supplying high-temperature CO2 by combustion of an HC gas, the supply of a relatively low-temperature CO2 gas from another position as described above also becomes a factor of lowering the thermal efficiency of the CO2 cycle. On the other hand, it is not necessary to provide the CCS facility 4 described with reference to
The combined cycle natural gas processing systems 1 and 1a according to the respective embodiments described above have the following effects. The LNG plant 3 that produces LNG is provided together with the SC-CO2 cycle power plant 2 that performs power generation using the CO2 cycle. This LNG plant 3 combusts the HC gas (light hydrocarbon gas containing methane as the main component), by-produced in the LNG plant 3, with the high-purity O2 gas (of which the concentration is equal to or higher than 99.8%) obtained by the air separation using the ASU 38, and supplies the obtained CO2 having high energy to the CO2 cycle. Then, the power generation is performed in the CO2 cycle. As a result, the high energy at high pressure and high temperature obtained by combusting the HC gas by-produced in the LNG plant 3 can be effectively utilized. In addition, the low-energy CO2 consumed in the CO2 cycle is still supplied to various CO2 reception facilities in the high-purity state, and thus, the release of CO2 to the atmosphere accompanying the combustion of the HC gas is not performed.
In addition, CO2 separated from NG in the AGRU 31 of the LNG plant 3 is not released to the atmosphere either by being supplied to the CO2 reception facilities directly with the above-described CO2 fluid or after once joining the CO2 fluid circulating in the CO2 cycle.
Next, a configuration example of a control system that supplies the HC gas to the CO2 cycle 20 will be described with reference to
In
A generation amount of a BOG supplied to the SC-CO2 cycle power plant 2 as an HC gas greatly increases or decreases depending on the outside temperature, the presence or absence of shipment to the LNG carrier 5, and the like. In addition, the end flash unit 35 is the device provided for pressure adjustment of LNG as described above, and is not normally configured to prioritize securing of a supply amount of the HC gas with respect to the CO2 cycle 20.
In this regard, a combined cycle natural gas processing system 1b illustrated in
In the example illustrated in
On the other hand, a flowmeter 106 is provided in the HC gas supply line 301 that supplies the HC gas toward the CO2 cycle 20, and an extraction amount of NG is controlled such that a flow rate of the HC gas detected by the flowmeter 106 approaches a target value. In the present example, the target value of the flow rate of the HC gas is set by the combustor supply gas control unit 101. In addition, the extraction amount of NG is controlled by adjusting an opening degree of an extraction control valve 104, provided in an auxiliary supply line 304a, by an HC gas supply control unit 103a. The auxiliary supply line 304a is connected to an inlet side of the MCHE in order to extract a part of NG before being liquefied that is supplied to the MCHE provided in the liquefying unit 341.
With this configuration, when the generation amount of the BOG and the extraction amount of the end flash gas are small and the flow rate of the flowmeter 106 is insufficient with respect to the target value, control is performed to increase the opening degree of the extraction control valve 104 to increase the extraction amount of NG. On the other hand, when the generation amount of the BOG and the extraction amount of the end flash gas are sufficient and the flow rate of the flowmeter 106 exceeds the target value, control is performed to reduce the opening degree of the extraction control valve 104 to decrease the extraction amount of NG.
Next, as another embodiment of the supply control mechanism of the HC gas, a combined cycle natural gas processing system 1c illustrated in
Note that a plurality of the CO2 gas pressurizing units 312 may be arranged in parallel on an outlet side of the end flash unit 35 as illustrated in
A control operation of the configuration illustrated in
On the other hand, when the generation amount of the BOG is sufficient and the flow rate of the flowmeter 106 exceeds the target value, the temperature of LNG at the outlet of the liquefying unit 341 is lowered to decrease the generation amount of the end flash gas.
Here, a type of energy, which is supplied to an energy consumption device provided in the LNG plant 3 using the CO2 cycle, is not limited to the electrical energy generated by the generator 231. The high energy (high-temperature and high-pressure combustion energy) of CO2 flowing in the CO2 cycle may be converted into mechanical energy and supplied.
The SC-CO2 cycle power plant 2 illustrated in
Further, the SC-CO2 cycle power plant 2 illustrated in
In addition, SC-CO2 extracted from the SC-CO2 cycle power plant 2 may be supplied to a turbine that drives a pump pressurizing a liquid. As the process fluid in this case, boiler water or the like can be exemplified.
The compressor 712 and the pump described above correspond to rotary devices of the present example, and the compressor 711 for driving these rotary devices corresponds to an energy conversion turbine of the SC-CO2 cycle power plant (carbon dioxide cycle plant) 2.
As described above, the SC-CO2 cycle power plant 2 illustrated in
A single (external fuel receiving type) power plant that combusts fuel having stable properties to obtain CO2 circulating in the CO2 cycle is normally intended to convert energy of high-temperature and high-pressure SC-CO2 into electrical energy. Thus, the power generation turbine 23 have a large size is provided, and the entire amount of high-temperature and high-pressure SC-CO2 obtained in the combustor 22 is supplied to the power generation turbine 23 to generate power. On the other hand, when a part of the high-temperature and high-pressure fluid of SC-CO2 is directly extracted and used for driving the turbine 711 as in the SC-CO2 cycle power plant 2 of the present example, the amount of electric power generated by the power generation turbine 23 decreases by such a usage.
In this regard, the combined cycle natural gas processing system 1d of the present example is provided with the LNG plant 3 and the SC-CO2 cycle power plant 2 together, which is different from the single power plant intended for power generation. With this configuration, it is possible to more freely provide a supply form contributing to improvement of energy efficiency of the entire combined cycle natural gas processing system 1d to each device in the LNG plant 3 without being limited to only the supply of electrical energy.
In general, when the energy of high-temperature and high-pressure SC-CO2 is used, it is most efficient to use the energy in a state of thermal energy by heat exchange or the like (energy efficiency is about 98%). Then, the energy efficiency decreases in the order of the conversion into mechanical energy for driving the turbine (about 40%) and the conversion into electrical energy (about 30%).
In this regard, since the SC-CO2 cycle power plant 2 is provided together with the LNG plant 3 in the combined cycle natural gas processing system 1d of the present example, it is possible to select the energy supply form from SC-CO2 of the high-temperature and high-pressure fluid while considering the function and scale of each energy consumption device and to enhance the energy efficiency of the entire combined cycle natural gas processing system 1d. Thus, the energy efficiency of the entire combined cycle natural gas processing system 1d can be improved as compared with a case where the entire energy is supplied as electrical energy. As described above, it is difficult to derive the idea of selecting the supply/use form of energy in each device to improve the energy efficiency of the entire combined cycle natural gas processing system 1d from the external fuel receiving type power plant installed only for power generation.
In addition, in a case where the LNG plant 3 is not provided with the SC-CO2 cycle power plant 2, it is necessary to combust an HC fuel gas in a boiler for generating steam or a gas turbine if the compressor 712 is driven by a steam turbine or the gas turbine. At this time, if CO2 generated by combustion of the fuel gas is not recovered, the CO2 is released to the atmosphere.
In this regard, the SC-CO2 cycle power plant 2 illustrated in
As described above, it is difficult to drive the configuration of the combined cycle natural gas processing system 1d that avoids not only the comprehensive energy efficiency but also the release of CO2 to the atmosphere from the external fuel receiving type CO2 cycle power plant that does not include an energy utilization device other than the power generation facility.
Further, installing the turbine type compressor 71 that supplies high-temperature and high-pressure SC-CO2 to the turbine 711 to drive the compressor 712 also has an effect of reducing a footprint (occupied area) of a facility. For example, in the case of a gas turbine compressor that drives the compressor 712 using a gas turbine, it is necessary to provide an air compressor that compresses combustion air.
In general, the air compressor provided together with the gas turbine compressor is extremely large and has a large footprint. On the other hand, it is unnecessary to provide the air compressor together with the turbine type compressor 71 of the present example using high-temperature and high-pressure SC-CO2, and there is a possibility that the footprint can be reduced to about ⅓ as compared with the gas turbine compressor. As a result, it is possible to obtain a significant cost reduction effect in terms of both device cost and site cost.
Note that it is not essential to provide the power generation turbine 23 and the generator 231 together with the CO2 cycle plant that supplies SC-CO2 to the turbine 711 for driving the compressor 712. A carbon dioxide cycle plant including only an energy conversion turbine that supplies mechanical energy to a rotary device may be configured.
In addition, thermal energy may be supplied from the CO2 cycle to a “device requiring a heat source” provided in the LNG plant 3 through a heat exchange unit, in addition to the conversion into mechanical energy and electrical energy. A combined cycle natural gas processing system 1e of
The heating medium heated by the heat exchanger 241a is used for heating of a fluid to be heated by a reboiler 743 which is a heat exchange unit provided in the LNG plant 3, and then, is supplied again to the heat exchanger 241a.
In the above example, the gas absorbing liquid in the regeneration column 742 corresponds to the fluid to be heated, and the reboiler 743 corresponds to a heating unit for the fluid to be heated.
In addition, in the case of adopting a configuration for separating CO2 from another acid gas using a gas absorbing liquid as in the separation unit 311 described with reference to
Here, the fluid to be heated to which thermal energy is supplied from the CO2 cycle is not limited to the gas absorbing liquid for which regeneration is performed. For example, a heavy component which is subjected to distillation and separation in the distillation column and the rectification column of the heavy component separation unit 33 or a regeneration gas used for regeneration of the adsorbent in the dehydration unit 32 may be used as the fluid to be heated. As the heating medium for heating the fluid to be heated, the above-described hot oil, hot water, steam, or the like can be appropriately selected. In this case, various distillation column and rectification column provided in the LNG plant 3 correspond to the “device requiring the heat source” in the present example, and the reboiler and the heater provided in the distillation column and the rectification column correspond to the “heating unit” in the present example.
As described above, the combined cycle natural gas processing system 1e illustrated in
For example, a combined cycle natural gas processing system if illustrated in
In the combined cycle natural gas processing system if illustrated in
On the other hand, a part of the high-temperature heating medium heated by the oxygen combustion heater 81 is supplied to each user in the LNG plant 3. In addition, a part of the high-temperature heating medium is also supplied to the heat exchanger 241b provided in the CO2 cycle of the SC-CO2 cycle power plant 2 by a pump 82. The heat exchanger 241b of the present example heats CO2 before being supplied to the combustor 22 by heat exchange with the heating medium heated by the oxygen combustion heater 81 in addition to heat exchange with CO2 discharged from the power generation turbine 23 in the CO2 cycle.
The low-temperature heating medium after having been used to heat CO2 in the heat exchanger 241b is returned to the oxygen combustion heater 81 and heated. In addition, the low-temperature heating medium returned from each user in the LNG plant 3 joins a flow path for returning the heating medium from the heat exchanger 241b to the oxygen combustion heater 81, is returned to the oxygen combustion heater 81, and is heated.
As described above, when the high thermal energy obtained in a fuel combustion facility such as the oxygen combustion heater 81 is excessive on the LNG plant 3 side, the excessive thermal energy can be supplied to the SC-CO2 cycle power plant 2 side through the heat exchanger 241b. As a result, a combustion amount of an HC gas combusted in the combustor 22 can be reduced as compared with a case where the thermal energy is not supplied.
In addition, the CO2 fluid heating unit 27 illustrated in
The combined cycle natural gas processing system 1e described with reference to
As described above, in the configuration in which the LNG plant 3 and the SC-CO2 cycle power plant 2 are provided together, the thermal energy can be supplied from one side of the LNG plant 3 and the SC-CO2 cycle power plant 2 to the other side according to the balance of the thermal energy. In addition, the SC-CO2 cycle power plant 2 can supply the thermal energy from the LNG plant 3 while supplying the thermal energy to the LNG plant 3. As described above, the heat exchange can be performed simultaneously and bidirectionally between the LNG plant 3 and the SC-CO2 cycle power plant 2 in the configuration in which the LNG plant 3 and the SC-CO2 cycle power plant 2 are provided together, so that a synergy effect can be obtained.
Here, examples of the combined cycle natural gas processing system 1 (
Among these, an application example of a technology for performing energy transfer between the SC-CO2 cycle power plant 2 and the LNG plant 3 with respect to the combined cycle natural gas processing system 1a of the type of
As described above, the combined cycle natural gas processing systems 1 and 1a to 1f of the present application include the SC-CO2 cycle power plant that supplies the high-temperature and high-pressure SC-CO2 to the power generation turbine 23 or the SC-CO2 cycle plant that drives the compressor 712 or the like using the high-temperature and high-pressure SC-CO2 to perform the conversion into mechanical energy (hereinafter, these are also collectively referred to as the “SC-CO2 plant 2”). In these combined cycle natural gas processing systems 1 and 1a to 1f, the electrical energy, mechanical energy and/or thermal energy generated by using the high-temperature and high-pressure SC-CO2 are used in the LNG plant 3. Then, CO2 discharged from the SC-CO2 plant 2 and the LNG plant 3 is supplied to the CO2 reception facility. As a result, zero emission is achieved in the entire facility required for the production of LNG.
Specifically, first, the HC gas containing methane as the main component, which is by-produced in the adjacent LNG plant 3, is supplied to the SC-CO2 plant 2. Then, the high energy of CO2 obtained by combusting the HC gas under the high temperature and high pressure together with the high-purity O2 gas (of which the concentration is equal to or higher than 99.8%) obtained by air separation by the ASU 38 is supplied as the electrical energy, mechanical energy, and/or thermal energy. As a result, the thermal energy obtained by the combustion of the HC gas by-produced in the LNG plant 3 is effectively utilized.
Second, the high energy generated in the SC-CO2 plant is converted into various energy forms as the electrical energy, mechanical energy, or thermal energy, and is used in the LNG plant 3 provided together with the SC-CO2 plant. This reduces CO2 generated when the hydrocarbon fuel is independently combusted in the LNG plant 3 in order to obtain required energy.
Third, the CO2 in the process removed from NG and the CO2 constantly extracted from the SC-CO2 plant 2 are isolated in the ground by the CO2 reception facility and are not released to the atmosphere. Through the above-described integration between facilities, a combined facility that does not discharge the CO2 in the LNG production process including not only the CO2 directly generated during the LNG production but also the CO2 generated as the by-product along with energy supply is constructed.
That is, the combined cycle natural gas processing systems 1 and 1a to 1f of the present examples can produce LNG without depending on renewable energy having unstable power supply capacity or external power that is likely to discharge CO2 during power generation, and thus, a zero-emission fuel can be achieved. In addition, in a case where carbon dioxide in an exhaust gas discharged from an air-combustion type combustion apparatus is absorbed using a chemical absorbing liquid (so-called Post Combustion), a recovery rate of carbon dioxide remains about 90%. However, the combined cycle natural gas processing systems 1 and 1a to 1f of the present examples can recover the carbon dioxide generated in the present system at a level close to 100%.
In this regard, external fuel receiving type power generation facilities in Patent Literatures 2 and 3 described above do not focus on CO2 generated in a facility to which energy is supplied and a facility which produces a fuel for power generation. Thus, even if an external fuel receiving type power plant itself includes the CO2 reception facility, when the facility to which the energy is supplied and the facility which produces the fuel for power generation includes hydrocarbon fuel combustion facilities, CO2 generated in these combustion facilities is released to the atmosphere. As described above, when the CO2 reception facility is provided for the external fuel receiving type power generation facility, it is difficult to achieve the zero emission in the entire facility including the facility to which the energy is supplied and the facility which produces the fuel for power generation. As described above, the combined cycle natural gas processing systems 1 and 1a to 1f of the present application do not perform simple and one-sided energy supply as in the conventional external fuel receiving type power generation facilities, but achieves the comprehensive zero emission in combination with the LNG plant 3.
In the combined cycle natural gas processing systems 1 and 1a to 1f according to the respective embodiments described above, the LNG plant 3 is not limited to one having a configuration provided on the ground. For example, the above-described embodiments can also be applied to a floating LNG (FLNG) plant in which the LNG plant 3 is disposed on a floating surface on the water. In this case, all the combined cycle natural gas processing systems 1 and 1a to 1f including the SC-CO2 cycle power plant 2 may be disposed on the floating surface.
In addition, the SC-CO2 cycle power plant 2 is not limited to the configuration in which the power generation turbine 23 is driven using SC-CO2 to generate power. For example, a case of adopting the SC-CO2 cycle power plant 2 configured to drive the power generation turbine 23 using a CO2 gas or a liquid CO2 to generate power is not excluded.
In addition, when excessive power is generated even if the power generated in the SC-CO2 cycle power plant 2 is supplied to the LNG plant 3 and the power consumption device in the SC-CO2 cycle power plant 2, the power may be supplied to a region outside the combined cycle natural gas processing systems 1 and 1a to 1f.
In addition, the term “by-produced” is a concept including both a case where the generation amount of the HC gas is not controlled in the process of producing and storing LNG and a case where the generation amount of the HC gas is controlled in consideration of excess or deficiency of fuel although not specifically described in the above embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/047748 | Dec 2020 | WO | international |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/047228 | 12/21/2021 | WO |
