Natural gas liquefaction and supercooling unit for launch system of methane-powered launch vehicle

Abstract

FIELD: cryogenic technology.SUBSTANCE: invention relates to the technology of liquefying natural gas. This is achieved by the fact that in the natural gas liquefaction and supercooling unit for the launch system for refueling a launch vehicle with a methane engine, in the liquefaction and supercooling unit between the second recuperative heat exchanger and the nitrogen bath with the heat exchanger-subcooler, the first separator for removing high-boiling components from the natural gas, a throttle valve, a third recuperative heat exchanger, a second separator for removing high-boiling components from the natural gas and a fourth recuperative heat exchanger are installed in series, and after the nitrogen bath, two tanks are installed, which are connected in parallel to the LNG supply pipeline to the liquid natural gas storage facility, and, in addition, after the liquid nitrogen evaporator, an electric heater of gaseous nitrogen is installed.EFFECT: production of liquefied natural gas for a launch vehicle with a methane mole fraction of at least 99%, as well as the operation of the installation in a mode that ensures long-term drainage-free storage of liquefied natural gas in a storage facility.1 cl, 1 dwg

Description

[0001] The invention relates to cryogenic technology - in particular to the technology of liquefying natural gas.

[0002] A liquefied natural gas (LNG) system, particularly methane, is known, primarily for vehicle gas filling stations. It comprises a supply and return line, a compressor that pressurizes the natural gas to 250 atm, first and second methane heat exchangers, separators, an expansion device in the form of an ejector, and a freon refrigeration unit (see patent 2180081). The technical advantage of this system is that it uses natural gas itself as the working fluid, and the system is also distinguished by the cost-effectiveness of the liquefaction process.

[0003] At the same time, the main disadvantage of the installation is that the efficiency of the liquefaction process is achieved through the use of a booster compressor and a freon refrigeration machine, which increases the risk of failure during long-term operation.

[0004] A natural gas liquefier based on a nitrogen expander cycle is known, including two nitrogen turbocompressors, three turboexpanders operating at different temperature levels, a nitrogen three-flow heat exchanger, a liquefier heat exchanger, and a subcooler heat exchanger for the entire natural gas flow. (See Energy-Efficient Natural Gas Liquefaction Cycles. Scientific Journal of NRU ITMO, Refrigeration Engineering Series. No. 1, 2016, pp. 7-8, Fig. 3)

[0005] Although the liquefier with high thermodynamic efficiency supercools the entire natural gas flow, its main drawback is that the liquefier uses a complex refrigeration cycle, which requires the use of difficult-to-operate, expensive compressor and expander equipment, as well as highly qualified specialists.

[0006] The closest in technical essence to the claimed installation is an installation for liquefying and supercooling natural gas primarily for the launch complex for refueling a launch vehicle with a methane engine, including a section of the main pipeline, a pre-cooling unit in the form of a first recuperative heat exchanger and a unit for purifying the flow of natural gas from H2O and CO2, a liquefaction and supercooling unit made in the form of a second recuperative heat exchanger, a throttle valve and a nitrogen bath with a heat exchanger-subcooler, connected by an LNG supply pipeline to a liquid natural gas storage facility, a liquid nitrogen storage facility connected to the nitrogen bath, and a liquid nitrogen evaporator (see patent 2849122).The main disadvantages of the known installation are: - the absence in the installation of technology and equipment for the removal of high-boiling components such as propane (C3H8) and ethane (C3H6) and other hydrocarbons included in the composition of natural gas, which can lead to the production of liquefied natural gas of grade A GOST 34894-2022, required for a launch vehicle with a methane engine, with a molar fraction of methane less than 99%.

[0007] - the unit operates only in the natural gas liquefaction mode.

[0008] The problem to be solved is to obtain liquefied natural gas for a launch vehicle with a molar fraction of methane of at least 99%, as well as the operation of the installation in a mode that ensures long-term drainage-free storage of liquefied natural gas in a storage facility.

[0009] The stated objective is achieved in that in a natural gas liquefaction and subcooling unit for a launch vehicle refueling complex with a methane engine, including a section of the main pipeline, a pre-cooling unit in the form of a first recuperative heat exchanger and a unit for purifying the natural gas flow from H2O and CO2, a liquefaction and subcooling unit made in the form of a second recuperative heat exchanger, a throttle valve and a nitrogen bath with a subcooler heat exchanger connected by an LNG supply pipeline to a liquid natural gas storage facility, a liquid nitrogen storage facility connected to the nitrogen bath, and a liquid nitrogen evaporator, in the liquefaction and subcooling unit between the second recuperative heat exchanger and the nitrogen bath with the subcooler heat exchanger, the first separator for removing high-boiling components from natural gas, a throttle valve, a third recuperative heat exchanger are installed in series,a second separator for removing high-boiling components from natural gas and a fourth recuperative heat exchanger, and after the nitrogen bath, two tanks are installed that are connected in parallel to the LNG supply pipeline to the liquid natural gas storage facility, and in addition, after the liquid nitrogen evaporator, an electric heater for gaseous nitrogen is installed.

[0010] The conducted analysis of the state of the art allowed us to establish that the applicant has not found an analogue characterized by the aggregate features identical to all the essential features of the claimed invention, therefore, it meets the criterion of NOVELTY.

[0011] The installation for liquefying and supercooling natural gas for the launch complex for refueling a launch vehicle with a methane engine, shown in Fig. 1 on two sheets, includes:

[0012] - section 1 of the natural gas main pipeline;

[0013] - pre-cooling unit 2, made in the form of the first recuperative heat exchanger 3, unit 4 for cleaning the natural gas flow from H2O and CO2, and valve 5;

[0014] - a natural gas liquefaction and subcooling unit 6, made in the form of a second recuperative heat exchanger 7, a first separator 8 for removing high-boiling components from natural gas, a throttle valve 9, a third recuperative heat exchanger 10, a second separator 11 for removing high-boiling components from natural gas and a fourth recuperative heat exchanger 12, a nitrogen bath 13 with a subcooler heat exchanger 14, connected through a control valve 15 to a pipeline 16 for feeding liquefied natural gas into storage 17 through a lower filling valve 18 and through a valve 19 with a collector 20 for top filling of storage 17, equipped with a valve 21 for discharging vapors from storage 17, made, for example, in the form of a spherical tank with a volume of 1400 m 3 working pressure 1.0 MPa;

[0015] - first container 22, connected in parallel to pipeline 16 for supplying liquefied natural gas to storage 17 using valves 23 and 24, including vapor relief valve 25 and pressurization evaporator 26 with control valve 27;

[0016] - a second container 28, connected in parallel to the pipeline 16 for supplying liquefied natural gas to the storage facility 17 using valves 29 and 30, including a vapor discharge valve 31 and a pressurization evaporator 32 with a control valve 33;

[0017] - pipeline 34 with control valve 35, connecting nitrogen bath 13 to liquid nitrogen storage 36.

[0018] The pre-cooling unit 2 is connected to the liquefaction and subcooling unit 6 by a natural gas pipeline 37 and a gaseous nitrogen pipeline 38, and is also connected by a pipeline 39 to section 1 of the main pipeline. In addition, the natural gas liquefaction and subcooling unit includes a pipeline 40 equipped with a control valve 41, a liquid nitrogen evaporator 42 and an electric heater 43, while the pipeline 40 is connected to a pipeline 35 for feeding liquid nitrogen to a nitrogen bath 13 from a storage 36 and a gaseous nitrogen pipeline 38 connecting the pre-cooling unit 2 and the liquefaction and subcooling unit 6.

[0019] The process parameters in the installation are controlled using pressure sensors 44-49, temperature sensors 50-56, liquid nitrogen level sensors 57-59 and flow sensors 60-62, and in the liquefied natural gas storage 17 - using pressure sensor 63 and liquid nitrogen level sensor 64.

[0020] The operation of the natural gas liquefaction and supercooling unit for the launch vehicle refueling complex with a methane engine is as follows.

[0021] Initial natural gas with the composition, mol.%: methane (CH4) - 0.93, CO2 + H2O vapor - 0.01, high-boiling components - ethane (C2H6) - 0.03, propane (C3H8) - 0.02, low-boiling components nitrogen, hydrogen, helium - 0.01, with a pressure of 5.0 MPa, controlled by sensor 44, a temperature of 290K - 300K, controlled by sensor 50, and a flow rate of 1600 kg / h (2050 nm 3 / h), controlled by sensor 60, comes from section 1 of the main pipeline through pipeline 39 to pre-cooling unit 2, wherein the partial pressure of each component in natural gas in accordance with the Boyle and Dalton law will be equal to: methane - 4.65 MPa, ethane - 0.15 MPa, propane - 0.1 MPa, CO2 + vapor H2O - 0.05 MPa, low-boiling components nitrogen, hydrogen, helium - 0.05 MPa, and the mass composition of each component will be equal to: methane - 1495 kg, ethane - 45 kg, propane - 30 kg, CO2 + vapor H2O - 15 kg, low-boiling components nitrogen, hydrogen, helium - 15 kg. In block 2 for preliminary cooling, natural gas with the above parameters sequentially passes through valve 5, the first recuperative heat exchanger 3 and block 4 for cleaning the natural gas flow from H2O and CO2.In the recuperative heat exchanger 3, the natural gas flow is cooled by gaseous nitrogen supplied through the gaseous nitrogen pipeline 37 from the liquefaction and supercooling unit 6, to a temperature of 275K - 280K, controlled by the sensor 51, and in unit 4, the removal of H2O and CO2 vapors occurs, which leads to an increase in the partial pressure and molar fraction of methane due to the effective adsorption process. The dried and purified natural gas flow enters the liquefaction and subcooling unit 6 via pipeline 37 at the inlet of the second recuperative heat exchanger 7, where it is cooled by gaseous nitrogen coming from the third recuperative heat exchanger 10 to a temperature of 192K-195K, controlled by sensor 52, and enters the separator 8, where it is separated from the natural gas at a pressure of 5.0 MPa, controlled by sensor 45. In the separator 8, at this temperature of 192K-195K, the ethane condensation process will only begin and propane will condense, the partial pressure of which at a temperature of 192K-195K is equal to 1.2⋅10.-2MPa (see Thermodynamic Properties of Propane. Moscow, Standards Publishing House, 1989), which will result in the precipitation of 26.4 kg of propane as a liquid phase from 30 kg of gaseous propane. As a result of the isobaric process of propane removal, the partial pressure and molar fraction of methane will increase again. After separator 8, the pressure of natural gas is reduced by throttle valve 9 to a pressure of 0.3 MPa - 0.25 MPa, controlled by sensor 46 and maintained by control valve 15. Then, natural gas enters third recuperative heat exchanger 10, where its temperature, controlled by sensor 53, is reduced to 132K-135K both due to throttling of natural gas and heat exchange with gaseous nitrogen coming from fourth recuperative heat exchanger 12. After third recuperative heat exchanger 10, natural gas enters separator 11.In separator 11, at a given temperature of 132K-135K, the process of condensation of the remaining propane will end and ethane will condense, the partial pressure of which at a temperature of 132K-135K will be 0.13⋅10. -2MPa (see Thermodynamic Properties of Ethane. Moscow, Standards Publishing House, 1982), which will result in the precipitation of 44.6 kg of ethane as a liquid phase from 45 kg of gaseous ethane. As a result of the isobaric process of propane and ethane removal, the partial pressure of methane will increase from 4.65 MPa to 4.95 MPa, and the molar fraction of methane will increase from 0.93% to 0.99%, taking into account that low-boiling components nitrogen, hydrogen, and helium remain in the natural gas. After separator 11, the natural gas flow with a mass flow rate of 1510 kg / h (1495 kg / h methane plus 15 kg / h low-boiling components dissolved in methane) passes through the fourth recuperative heat exchanger 12, where the process of condensation of natural gas begins due to gaseous nitrogen coming from nitrogen bath 13, and enters the heat exchanger - supercooler 14, located in nitrogen bath 13 with liquid nitrogen.As a result of heat exchange, the flow of liquefied natural gas after the heat exchanger-subcooler 14 with a temperature of 95K - 98K, controlled by the sensor 54, is diverted by the control valve 15 through the pipeline 16 through the valve 18 of the lower filling into the storage 17 with the open valve 21 for discharging vapors from the storage 17, while the pressure is controlled by the sensor 47, the temperature by the sensor 55, and the flow rate of liquefied natural gas supplied to the storage 17 by the sensor 61, and in the storage 17 itself - the pressure by the sensor 63, and the level of liquefied natural gas by the sensor 64. When storage 17 is filled to 65% - 70%, filling continues through the top filling valve 19 and the manifold 20 located in the gas cushion of storage 17. Nitrogen vapors formed as a result of the evaporation of liquid nitrogen in the nitrogen bath 13 sequentially pass through recuperative heat exchangers 12, 10, 7.3 and are discharged into the atmosphere.Compensation for the flow of liquid nitrogen in the nitrogen bath 13, the level of which is controlled by the sensor 51, is carried out from the liquid nitrogen storage 36 through the pipeline 34 by the control valve 35.

[0022] During unit operation, the natural gas temperature, monitored by sensor 50, may vary widely depending on the season, from -40°C to +40°C, but the unit's operating mode must remain stable. A decrease in the natural gas temperature will also lead to a decrease in the inlet temperature to Unit 4, which purifies the natural gas stream from H2O and CO2, monitored by sensor 51, and the formation of ice crystals from water vapor. If the inlet temperature in Unit 4 drops by 2K - 3K below the lower limit of the set temperature range of 275K - 280K, the inlet temperature in Complex Purification Unit 4 is automatically restored.For this purpose, liquid nitrogen is supplied to evaporator 42 by means of control valve 41, where it is gasified and at a temperature of 90K-100K enters electric heater 43, is heated and is directed through pipeline 40 to natural gas liquefaction and supercooling unit 6, where it is mixed with gaseous nitrogen coming from recuperative heat exchanger 7, while the nitrogen flow rate, controlled by sensor 62, and the temperature, controlled by sensor 56, are set such as to maintain the optimal operating temperature range of unit 4 for purifying the natural gas flow from H2O and CO2.In the event that the temperature of natural gas before the unit 4 for cleaning the natural gas flow from H2O and CO2, controlled by the sensor 51, increases by 2K - 3K relative to the upper limit of the set temperature range of 280K - 275K, then the temperature is restored by taking liquid nitrogen using the control valve 41, gasifying it in the atmospheric evaporator 42 and supplying gaseous nitrogen with a temperature of 90K - 100K and is sent through the pipeline 40 to the unit 6 for liquefying and supercooling natural gas, where it is mixed with gaseous nitrogen coming from the recuperative heat exchanger 7, while the flow rate required to restore the optimal temperature range for the operation of the complex cleaning unit 4 will be automatically maintained using the control valve 41.

[0023] In addition to the mode of filling storage 17 with liquefied natural gas at a temperature of 95K - 98K, the installation provides a mode of long-term drainless storage of liquefied natural gas due to the condensation of vapors in storage 17, which is carried out as follows.

[0024] As is well known, during long-term drainless storage of liquefied natural gas, heat influx from the environment causes evaporation of a portion of the liquefied natural gas, accompanied by an isochoric process of pressure increase in storage 17, monitored by sensor 63. When the pressure in storage 17 increases above 0.5 MPa, the unit is started up in the normal mode described earlier, but with the accumulation of liquefied natural gas in the first tank 22, which is connected in parallel to the pipeline 16 for supplying liquefied natural gas to the liquid natural gas storage 17. The filling of the first tank 22 with liquefied natural gas at a temperature of 95K - 98K is carried out through the control valve 23 with the discharge of vapors through valve 25.When 85% - 90% of the volume of tank 22, controlled by sensor 58, is filled, the operation of the installation is switched to filling the second tank 28 through control valve 29 with the discharge of vapors through valve 31, and in tank 22, valve 25 is closed and the pressure in the gas cushion is increased to 0.9 MPa, controlled by sensor 48, and maintained with the help of control valve 27 due to the gasification of liquefied natural gas in supercharging evaporator 26.

[0025] Then valve 24 is opened and a flow of liquefied natural gas is directed from tank 22 and through cryogenic pipeline 16 to storage 17 and it is fed through valve 19 to manifold 20 located in the gas cushion of storage 17. In manifold 20, the flow of liquefied natural gas is sprayed over the volume of the gas cushion, which leads to condensation of vapors and a decrease in the pressure in storage 17, controlled by sensor 63. In the event that the level of liquefied natural gas in tank 22, controlled by sensor 58, reaches the minimum value, and the pressure in storage 17 is greater than 0.25 MPa, then the mode is continued by supplying liquefied natural gas from the second tank 28, for which, at the beginning, valve 25 is opened in tank 22 and the process of filling it with liquefied natural gas begins through valve 23, and valves 29, 31 are closed in tank 28 and the pressure is increased in gas cushion to 0.9 MPa, controlled by sensor 49, and maintained using control valve 33 due to gasification of liquefied natural gas in supercharging evaporator 32.

[0026] Next, valve 30 is opened and a flow of liquefied natural gas is directed from tank 28 and through cryogenic pipeline 16 to collector 20 of storage 17. When the pressure in storage 17 drops below 0.2 MPa, the operating mode of the unit is stopped until the next increase in pressure in storage 17 above 0.5 MPa.

[0027] Thus, the proposed natural gas liquefaction and supercooling plant allows not only to produce liquefied natural gas of the required composition with a temperature of 95K-98K for refueling and operating a launch vehicle with a methane engine, and not only to perform long-term drainless storage of liquefied natural gas in the storage facility, but also to replenish the storage facility with liquefied natural gas, partially compensating for the losses caused by the discharge of vapors into the atmosphere during the technological modes of refueling the launch vehicle tanks from storage facility 17, and in addition, to ensure the stability of the plant's operating mode from seasonal changes in ambient air temperature.

Claims

A natural gas liquefaction and subcooling unit for a launch vehicle fueling system with a methane engine, comprising a section of a main pipeline, a pre-cooling unit in the form of a first recuperative heat exchanger and a unit for purifying a natural gas flow from H2O and CO2, a liquefaction and subcooling unit made in the form of a second recuperative heat exchanger, a throttle valve and a nitrogen bath with a subcooler heat exchanger connected by an LNG supply pipeline to a liquid natural gas storage facility, a liquid nitrogen storage facility connected to the nitrogen bath, and a liquid nitrogen evaporator, characterized in that in the liquefaction and subcooling unit between the second recuperative heat exchanger and the nitrogen bath with the subcooler heat exchanger, a first separator for removing high-boiling components from the natural gas, a throttle valve, a third recuperative heat exchanger are installed in series,a second separator for removing high-boiling components from natural gas and a fourth recuperative heat exchanger, and after the nitrogen bath, two tanks are installed that are connected in parallel to the LNG supply pipeline to the liquid natural gas storage facility, and, in addition, after the liquid nitrogen evaporator, an electric heater for gaseous nitrogen is installed.

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