CN106595220B - Liquefaction system for liquefying natural gas and liquefaction method thereof - Google Patents

Liquefaction system for liquefying natural gas and liquefaction method thereof Download PDF

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CN106595220B
CN106595220B CN201611269938.9A CN201611269938A CN106595220B CN 106595220 B CN106595220 B CN 106595220B CN 201611269938 A CN201611269938 A CN 201611269938A CN 106595220 B CN106595220 B CN 106595220B
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heat exchanger
temperature
medium
natural gas
stage
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CN106595220A (en
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白爽
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Shanghai Juchen New Energy Technology Co ltd
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Shanghai Juchen New Energy Technology Co ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0211—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle
    • F25J1/0217—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a multi-component refrigerant [MCR] fluid in a closed vapor compression cycle as at least a three level refrigeration cascade with at least one MCR cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0032—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration"
    • F25J1/0045—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using the feed stream itself or separated fractions from it, i.e. "internal refrigeration" by vaporising a liquid return stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0203—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle
    • F25J1/0208—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop
    • F25J1/0209—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using a single-component refrigerant [SCR] fluid in a closed vapor compression cycle in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop as at least a three level refrigeration cascade
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0269—Arrangement of liquefaction units or equipments fulfilling the same process step, e.g. multiple "trains" concept
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0279—Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
    • F25J1/0294—Multiple compressor casings/strings in parallel, e.g. split arrangement
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/60—Natural gas or synthetic natural gas [SNG]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2220/00—Processes or apparatus involving steps for the removal of impurities
    • F25J2220/60—Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
    • F25J2220/62—Separating low boiling components, e.g. He, H2, N2, Air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/66—Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

The invention discloses a liquefaction system and a liquefaction method for liquefied natural gas. The refrigeration compressor in this patent application can follow the direct purchase of the refrigeration compressor in the cold field of ordinary and use, and the heat exchanger adopts the plate heat exchanger that ordinary cold field is commonly used, need not special customization, has practiced thrift the investment cost of refrigeration compressor and heat exchanger greatly. In addition, the refrigerant is pure substance in this patent application, and it is convenient to add, and only high temperature level and two kinds of refrigerants of moderate temperature level have reduced and have revealed the hidden danger moreover. The traditional three-stage LNG special refrigeration process is changed into a traditional process of two-stage natural gas compression, so that special equipment is changed into general equipment, and special customization is not needed, so that the investment cost is reduced, and the control program is simplified.

Description

Liquefaction system for liquefying natural gas and liquefaction method thereof
Technical Field
The invention relates to the technical field of liquefied natural gas, in particular to a liquefaction system for liquefying natural gas and a liquefaction method thereof.
Background
The conventional liquefied natural gas technology usually adopts an MRC (Mixed Refrigeratant Cycle) process, but has the following defects: the manufacturing technology and patents of the MRC compressor, the MRC heat exchanger and the like are controlled by foreign manufacturers or a few domestic manufacturers, the price is high, the matching is slow, and the non-standard design is basically carried out according to the working conditions of users. The equipment adopting the MRC process has high requirement on operators because the refrigerant is a non-azeotropic mixture and components need to be detected frequently by a chromatograph mass spectrometer and the like after the refrigerant leaks and are reasonably proportioned.
The traditional cascade type liquefied natural gas process has low energy consumption, the refrigerant is pure substance, and the problem of proportioning is avoided, but the system is more complicated than the MRC process, the one-time investment is higher than the MRC process, and the occupied area is larger. Due to its complexity, its stability etc. may also be affected.
In addition, almost all LNG (Liquefied Natural Gas) plant manufacturers consider the liquefaction rate of the plant during design, and seek a greater liquefaction rate of the Gas entering the plant as their starting point, while neglecting the overall rational utilization of the Natural Gas.
The invention aims to solve the following problems:
1. almost all the existing standardized materials in the common cold field, such as a refrigeration compressor, a traditional plate heat exchanger, an expansion valve and the like, can be utilized, and the one-time investment cost is greatly reduced;
2. the existing unitized and modularized equipment is utilized, the operation is simple and convenient, the skid-mounted degree is high, the automation degree is high, and the dependence on operators is less;
3. the refrigerant is pure substance, has no proportioning problem, and reduces the dependence on operators;
the rational utilization of natural gas is emphasized, rather than the liquefaction rate of natural gas entering the plant alone. For example, the pressure energy and the cold energy of the natural gas can be utilized first, and then a part of the natural gas is used for generating electricity.
The traditional cascade liquefied natural gas technology can be seen in an attached figure 1, the liquefaction of natural gas is realized by using 9 main heat exchangers in the process, and the refrigeration capacity is provided by a closed propane refrigeration system through the first main heat exchanger to the third main heat exchanger, so that propane is evaporated under three pressures of high pressure, medium pressure and low pressure to obtain three different refrigeration temperatures, namely three suction pressures of the propane refrigeration system. However, the propane compressor is not specially customized, and three compressors with different inlet and outlet pressures are needed for realization.
For the second refrigerant cycle (corresponding to four, five and six main heat exchangers), ethylene refrigerant is adopted to form a closed loop, and a refrigeration compression system of the closed loop is realized by three ethylene compressors with different inlet and outlet pressure if the refrigeration compression system is not specially customized.
Similarly, for the third refrigerant cycle (corresponding to the seventh, eighth and ninth main heat exchangers), methane is used as the refrigerant to form a closed loop, and the refrigeration compression system is realized by three methane compressors with different intake and exhaust pressures if the refrigeration compression system is not specially customized.
On the other hand, for the first heat exchanger, the second heat exchanger and the third heat exchanger, 4 media with different pressures or types are adopted in each heat exchanger for heat exchange, and a special multi-stream heat exchanger special for LNG is required to be adopted; moreover, for the four to nine main heat exchangers, although the heat exchangers are 3 medium streams, at least the cold side adopts the design that the low-temperature gas and the liquid to be evaporated enter the heat exchangers at the same time, and the special heat exchanger for LNG is not a plate heat exchanger adopted in the common cold field.
The scheme of the invention is to improve the existing liquefied natural gas liquefaction system aiming at the problems.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides the liquefaction system for liquefying the natural gas and the liquefaction method thereof, which have the characteristics of no need of special customization of a refrigeration compressor and a heat exchanger, low investment cost, good stability, good heat exchange effect and the like.
In order to achieve the above purpose, the technical solution adopted to solve the technical problems is as follows:
the invention discloses a liquefaction system for liquefying natural gas, which comprises a mixer, a first heat exchanger, a second heat exchanger, a third heat exchanger, a high-temperature-stage refrigeration compressor unit, a medium-temperature-stage refrigeration compressor unit, a low-temperature-stage throttle valve group, an LNG storage tank, a flow divider and a natural gas compressor unit, wherein:
three runners are arranged in the first heat exchanger, the second heat exchanger and the third heat exchanger respectively, and the first runner, the second runner and the third runner are arranged from top to bottom;
the output end of the mixer is connected with a second flow channel of the first heat exchanger, the second flow channel of the first heat exchanger is connected with a second flow channel of the second heat exchanger, and the second flow channel of the second heat exchanger is divided into two paths from the first flow channel to the second flow channel:
one path of the LNG throttling valve group is sequentially connected with a second flow channel of the third heat exchanger, and the second flow channel of the third heat exchanger is connected with the LNG storage tank after being connected with the LNG throttling valve group;
the other path of the gas flow is connected with a third flow channel of a third heat exchanger after passing through the low-temperature-stage throttling valve group, and is connected to the splitter after sequentially passing through a first flow channel of the third heat exchanger, a first flow channel of the second heat exchanger and a first flow channel of the first heat exchanger in a reverse direction, the splitter is divided into two paths to be output, one path of the gas flow is used for directly generating power or generating power after being used as purge gas of a purification part, and the other path of the gas flow is connected with the natural gas compressor unit and then is connected to the input end of the mixer;
the high-temperature stage refrigeration compressor set is connected to two ends of a third flow channel of the first heat exchanger and used for cooling natural gas;
and the middle-temperature stage refrigeration compressor set is connected to two ends of a third flow channel of the second heat exchanger and used for further cooling the natural gas.
Further, the high-temperature stage refrigeration compressor group includes a high-temperature stage refrigeration compressor, a high-temperature stage air condenser, a first high-temperature stage throttle valve group, a first inter-cooling heat exchanger and a first inter-cooling throttle valve group, wherein:
two flow passages are arranged in the first inter-cooling heat exchanger;
the high-temperature stage refrigeration compressor, the high-temperature stage air condenser, the first inter-cooling throttling valve group and a flow channel in the first inter-cooling heat exchanger are sequentially connected in a closed mode to form a first high-temperature stage circulation loop;
and the high-temperature-stage refrigeration compressor, the high-temperature-stage air condenser, the other flow channel in the first inter-cooling heat exchanger, the first high-temperature-stage throttling valve group and the third flow channel of the first heat exchanger are sequentially connected in a closed manner to form a second high-temperature-stage circulation loop.
Further, still include fourth heat exchanger and first precooling throttle valves, wherein:
the fourth heat exchanger is provided with three runners, namely a first runner, a second runner and a third runner from top to bottom;
the fourth heat exchanger is arranged between the mixer and the first heat exchanger, the output end of the mixer is positively connected to the second flow channel of the first heat exchanger through the second flow channel of the fourth heat exchanger, and the first flow channel of the first heat exchanger is reversely connected to the flow divider through the first flow channel of the fourth heat exchanger;
and the high-temperature stage refrigeration compressor, the high-temperature stage air condenser, the first precooling throttle valve group and a third flow channel of the fourth heat exchanger are sequentially connected in a closed manner to form a third high-temperature stage circulation loop.
Further, the high-temperature stage refrigeration compressor unit further comprises a second high-temperature stage throttling valve group and a medium-temperature stage evaporative condenser, wherein:
and the high-temperature-stage refrigeration compressor, the high-temperature-stage air condenser, the other flow channel in the first inter-cooling heat exchanger, the second high-temperature-stage throttling valve group and the intermediate-temperature-stage evaporative condenser are sequentially connected in a closed manner to form a fourth high-temperature-stage circulation loop.
Further, the medium-temperature-stage refrigeration compressor group comprises a medium-temperature-stage refrigeration compressor, a medium-temperature-stage air condenser, a medium-temperature-stage throttle valve group, a second intercooling heat exchanger and a second intercooling throttle valve group, wherein:
two flow passages are arranged in the second intercooling heat exchanger;
the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, the second inter-cooling throttling valve group and a flow channel in the second inter-cooling heat exchanger are sequentially connected in a closed mode to form a first medium-temperature stage circulation loop;
the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, another flow channel in the second inter-cooling heat exchanger, the medium-temperature stage throttling valve group and a third flow channel of the second heat exchanger are sequentially connected in a closed mode to form a second medium-temperature stage circulation loop.
Further, still include fifth heat exchanger and second precooling throttle valves, wherein:
the fifth heat exchanger is provided with three runners, namely a first runner, a second runner and a third runner from top to bottom;
the fifth heat exchanger is arranged between the first heat exchanger and the second heat exchanger, a second flow channel of the first heat exchanger is positively connected to a second flow channel of the second heat exchanger through a second flow channel of the fifth heat exchanger, and a first flow channel of the second heat exchanger is reversely connected to the second flow channel of the first heat exchanger through a first flow channel of the fifth heat exchanger;
and the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, the second precooling throttle valve group and a third flow channel of the fifth heat exchanger are sequentially connected in a closed manner to form a third medium-temperature stage circulation loop.
Preferably, the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger and/or the fifth heat exchanger are brazed plate heat exchangers.
The invention also discloses a liquefaction method for liquefying natural gas, which comprises the following steps:
step 1: mixing the natural gas with the pressure of 2.5-6.0 MPa, which is subjected to desulfurization, decarburization and dehydration purification with the gas exhausted from the natural gas compressor unit in a mixer, then feeding the mixed gas into a fourth heat exchanger, cooling the mixed gas to 10-15 ℃ after passing through the fourth heat exchanger, feeding the cooled natural gas into a first heat exchanger, and cooling the cooled natural gas to-15-35 ℃ after passing through the first heat exchanger;
and 2, step: the cooled natural gas enters a fifth heat exchanger and is cooled to minus 35 to minus 55 ℃ after passing through the fifth heat exchanger; the cooled natural gas enters a second heat exchanger and is cooled to minus 55 to minus 110 ℃ after passing through the second heat exchanger;
and step 3: the natural gas which is condensed to minus 55 to minus 110 ℃ from the second heat exchanger is divided into two parts, one part of the natural gas enters a third heat exchanger, and the temperature of the natural gas is further reduced to minus 110 to minus 140 ℃ in the third heat exchanger; the other part of the natural gas is throttled by the low-temperature stage throttle valve group and then is changed into low-temperature and low-pressure natural gas liquid serving as a refrigerant, and the heat of the natural gas is absorbed in a third heat exchanger, so that the natural gas of the main flow is further subcooled;
and 4, step 4: the natural gas of the main flow from the third heat exchanger is depressurized by the LNG throttling valve group and flows into the LNG storage tank for storage, and the flash steam discharged from the LNG storage tank is recycled by cold energy and then is used for power generation or enters the natural gas compressor unit to participate in recycling;
and 5: the natural gas which is taken as the refrigerant and is discharged from the third heat exchanger is evaporated into gas after absorbing heat, then the natural gas gradually passes through the third heat exchanger, the second heat exchanger, the fifth heat exchanger, the first heat exchanger and the fourth heat exchanger, the temperature basically returns to about 0 ℃ after all cold energy is recovered, and then the natural gas is divided into two strands, wherein one strand is taken as the blowing gas of the purification system or the energy of the gas generator; and the other strand of the natural gas enters the natural gas compressor set directly, is boosted to the inlet pressure of the purified natural gas in the natural gas compressor set, is mixed with the purified natural gas and then enters the circulation again.
Further, step 1 further comprises the following steps:
step 11: the high-temperature stage refrigeration compressor sucks medium-pressure and low-pressure refrigerant, and the discharged high-temperature and high-pressure gas is condensed in the high-temperature stage air condenser and is divided into three parts;
step 12: throttling and reducing a part of refrigerant into medium-temperature and medium-pressure liquid through a first precooling throttle valve, evaporating the liquid in a fourth heat exchanger, exchanging heat with natural gas, and cooling the liquid to 10 to-15 ℃ through the fourth heat exchanger;
step 13: the other part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a first intercooling throttle valve group, and the heat of a third part of high-pressure refrigerant is absorbed in a first intercooling heat exchanger to further supercool the high-pressure refrigerant;
step 14: the medium-pressure refrigerant coming out of the fourth heat exchanger and the medium-pressure refrigerant coming out of the first inter-cooling heat exchanger are mixed and then return to a medium-pressure air return channel of the high-temperature stage refrigeration compressor, and medium-pressure refrigeration circulation is completed;
step 15: a third part of high-pressure refrigerant from the high-temperature grade air condenser is further subcooled by a first intercooling heat exchanger and then is divided into two parts;
step 16: one part of the refrigerant is throttled by a first high-temperature-level throttle valve group to change the refrigerant into low-temperature low-pressure liquid, then the liquid enters a first heat exchanger to absorb the heat of natural gas, and the temperature of the liquid is reduced to-15 to-35 ℃ after the liquid passes through the first heat exchanger, and then the liquid is changed into low-pressure gas;
and step 17: the other part of the refrigerant after being subcooled by the first intercooling heat exchanger is throttled by the second high-temperature-level throttle valve group and then is changed into low-temperature and low-pressure liquid, and then the low-temperature and low-pressure liquid enters a medium-temperature-level evaporation condenser in the medium-temperature-level refrigeration compressor unit to absorb the heat of the medium-temperature-level refrigerant and then is changed into low-pressure gas;
step 18: and (4) after the two groups of low-pressure gases in the step (16) and the step (17) are mixed, returning to a low-pressure gas return channel of the high-temperature stage refrigeration compressor to complete the circulation of the low-pressure stage refrigerant.
Further, the step 2 further comprises the following steps:
step 21: the method comprises the following steps that a medium-temperature-stage refrigeration compressor sucks medium-pressure and low-pressure medium-temperature-stage refrigerants, discharged high-temperature and high-pressure gases are precooled to 30-60 ℃ in a medium-temperature-stage air cooler, condensed in a medium-temperature-stage evaporation condenser and then divided into three parts;
step 22: throttling and reducing a part of refrigerant into medium-temperature and medium-pressure liquid through a second precooling throttle valve, evaporating the liquid in a fifth heat exchanger, exchanging heat with natural gas, and cooling the liquid to-35 to-55 ℃ through the fifth heat exchanger;
step 23: the other part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a second intercooling throttle valve group, and the heat of the third part of high-pressure refrigerant is absorbed in a second intercooling heat exchanger to further supercool the high-pressure refrigerant;
step 24: the medium-pressure refrigerant coming out of the fifth heat exchanger and the medium-pressure refrigerant coming out of the second intercooling heat exchanger are mixed and then return to a medium-pressure air return channel of the medium-temperature stage refrigeration compressor, and medium-pressure refrigeration circulation is completed;
step 25: and a third part of high-pressure refrigerant from the intermediate-temperature stage evaporative condenser passes through a second inter-cooling heat exchanger and is throttled by an intermediate-temperature stage throttle valve group to be changed into low-temperature and low-pressure liquid, then enters the second heat exchanger to absorb the heat of natural gas, is cooled to minus 55 to minus 110 ℃ after passing through the second heat exchanger, is changed into low-pressure gas, returns to a low-pressure gas return channel of the intermediate-temperature stage refrigeration compressor, and completes the low-pressure stage refrigerant circulation of the intermediate-temperature stage compressor.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
(1) the refrigeration compressor in the ordinary cold field basically has an intercooler (or an economizer), and the refrigeration compressor is designed in a standardized way to provide cold energy at two evaporation temperatures, namely, each compressor is fixed with two suction pressures (medium pressure and low pressure), so that the refrigeration compressor in the patent application can be directly purchased and used from the refrigeration compressor in the ordinary cold field, a refrigerator which is specially designed like a traditional process is not needed, or 3 refrigerators are adopted in each cycle, and the investment cost of the refrigerator is greatly saved.
(2) Plate heat exchangers commonly used in the ordinary cooling field can be generally designed into three flow channels, and due to the progress of the plate heat exchanger manufacturing technology, the universal pressure bearing of the plate heat exchanger can be accepted by 6.4MPa, so that the plate heat exchanger completely meets the pressure requirement in the LNG liquefaction process, and does not need to adopt a specially designed LNG heat exchanger like the traditional process, thereby greatly saving the investment cost of the heat exchanger.
(3) The traditional three-stage LNG special refrigeration process is changed into a traditional process of two-stage natural gas compression, so that special equipment is changed into common equipment, the traditional methane refrigeration cycle which is difficult to realize is replaced by a natural gas compressor unit with mature technology, the stability is improved, the natural gas compressor unit can be completely customized in a modularization mode, and the methane refrigeration cycle system is not like a methane refrigeration cycle system, and the natural gas compressor unit or other auxiliary components of the refrigeration system need to be customized specially, so that the investment is reduced, the control is simplified, and the operation is simplified.
(4) The refrigerant in this patent application is pure material, and it is convenient to add, only has two kinds of refrigerants of high temperature level and middle temperature level moreover, has reduced and has revealed the hidden danger. The traditional MRC process is a mixed working medium, the ratio is complex after leakage, three refrigerants are needed in the traditional cascade refrigeration, and the number of refrigeration compressors is large and the leakage point is large.
(5) The traditional MRC process is customized according to the components and pressure of the raw material gas, when the components and pressure of the raw material gas are changed, the mixed working medium and the special LNG heat exchanger are difficult to match the original design, so the yield is reduced sharply, and the process adopts a cascade process in the common cooling field, and the refrigeration interval can keep good energy efficiency ratio in a large range. The heat exchanger also adopts the plate heat exchanger in the traditional common cold field, and the heat exchange effect is verified on a large scale, so that better adaptability can be kept.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:
FIG. 1 is a block diagram of a prior art cascading liquefaction system for liquefying natural gas;
fig. 2 is a schematic view showing the overall construction of a liquefaction system for liquefying natural gas according to the present invention;
FIG. 3 is a schematic flow diagram of an overall process for liquefying natural gas according to the present invention;
FIG. 4 is a schematic diagram showing the steps of step 1 of a liquefaction process for liquefying natural gas according to the present invention;
fig. 5 is a schematic view showing the detailed steps of step 2 in a liquefaction method for liquefying natural gas according to the present invention.
[ description of main symbols ]
1-a mixer;
2-a first heat exchanger;
3-a second heat exchanger;
4-a third heat exchanger;
5-high temperature stage refrigeration compressor set;
51-high temperature stage refrigeration compressor;
52-high temperature grade air condenser;
53-first high temperature stage throttle valve group;
54-a first intercooled heat exchanger;
55-a first inter-cooling throttle valve set;
56-first pre-cooling throttle valve set;
57-a second high temperature stage throttle valve set;
6-middle temperature stage refrigeration compressor group;
61-medium temperature stage evaporative condenser;
62-a medium temperature stage refrigeration compressor;
63-medium temperature grade air condenser;
64-medium temperature stage throttle valve group;
65-a second intercooled heat exchanger;
66-a second inter-cooling throttle valve set;
67-a second pre-cooling throttle valve set;
7-a low-temperature-level throttling valve group;
8-LNG throttle valves;
9-an LNG storage tank;
10-a flow divider;
11-natural gas compressor train;
12-a fourth heat exchanger;
13-fifth heat exchanger.
Detailed Description
While the embodiments of the present invention will be described and illustrated in detail with reference to the accompanying drawings, it is to be understood that the invention is not limited to the specific embodiments disclosed, but is intended to cover various modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
Example one
As shown in fig. 2, the present invention discloses a liquefaction system for liquefying natural gas, comprising a mixer 1, a first heat exchanger 2, a second heat exchanger 3, a third heat exchanger 4, a high-temperature stage refrigeration compressor unit 5, a medium-temperature stage refrigeration compressor unit 6, a low-temperature stage throttle valve group 7, an LNG throttle valve group 8, an LNG storage tank 9, a flow divider 10, and a natural gas compressor unit 11, wherein:
three runners are respectively arranged in the first heat exchanger 2, the second heat exchanger 3 and the third heat exchanger 4 and respectively form a first runner, a second runner and a third runner from top to bottom;
the output end of the mixer 1 is connected with a second flow channel of the first heat exchanger 2, the second flow channel of the first heat exchanger 2 is connected with a second flow channel of the second heat exchanger 3, and the second flow channel of the second heat exchanger 3 is divided into two paths:
one path of the second flow path is sequentially connected with a second flow path of the third heat exchanger 4, and the second flow path of the third heat exchanger 4 is connected with the LNG throttle valve group 8 and then is connected to the LNG storage tank 9;
the other path of the flow is connected with a third flow channel of a third heat exchanger 4 through the low-temperature-level throttle valve group 7, and is sequentially connected to the flow divider 10 after reversely passing through a first flow channel of the third heat exchanger 4, a first flow channel of the second heat exchanger 3 and a first flow channel of the first heat exchanger 2, the flow divider 10 is divided into two paths to be output, one path of the flow is used for directly generating power or generating power after being used as purge gas of a purification part, and the other path of the flow is connected with the natural gas compressor unit 11 and then is connected to the input end of the mixer 1;
the high-temperature stage refrigeration compressor unit 5 is connected to two ends of the third flow channel of the first heat exchanger 2 and used for cooling natural gas;
and the middle-temperature stage refrigeration compressor unit 6 is connected to two ends of a third flow channel of the second heat exchanger 3 and used for further cooling the natural gas.
In a specific embodiment, the high-temperature-stage refrigeration compressor set 5 includes a high-temperature-stage refrigeration compressor 51, a high-temperature-stage air condenser 52, a first high-temperature-stage throttle valve set 53, a first inter-cooler heat exchanger 54, and a first inter-cooler throttle valve set 55, where:
two flow passages are arranged inside the first inter-cooling heat exchanger 54;
a flow passage in the high-temperature-stage refrigeration compressor 51, the high-temperature-stage air condenser 52, the first inter-cooling throttle valve set 55 and the first inter-cooling heat exchanger 54 are sequentially connected in a closed manner to form a first high-temperature-stage circulation loop;
the high-temperature-stage refrigeration compressor 51, the high-temperature-stage air condenser 52, the other flow channel in the first inter-cooler heat exchanger 54, the first high-temperature-stage throttling valve group 53 and the third flow channel of the first heat exchanger 2 are sequentially connected in a closed manner to form a second high-temperature-stage circulation loop.
In a preferred embodiment, the liquefaction system further comprises a fourth heat exchanger 12 and a first pre-cooling throttle set 56, wherein:
the fourth heat exchanger 12 is provided with three flow channels, namely a first flow channel, a second flow channel and a third flow channel from top to bottom;
the fourth heat exchanger 12 is arranged between the mixer 1 and the first heat exchanger 2, the output end of the mixer 1 is forward connected to the second flow channel of the first heat exchanger 2 through the second flow channel of the fourth heat exchanger 12, and the first flow channel of the first heat exchanger 2 is backward connected to the flow divider 10 through the first flow channel of the fourth heat exchanger 12;
and the high-temperature-stage refrigeration compressor 51, the high-temperature-stage air condenser 52, the first precooling throttle valve set 56 and a third flow channel of the fourth heat exchanger 12 are sequentially connected in a closed manner to form a third high-temperature-stage circulation loop.
Further, the high-temperature stage refrigeration compressor group 5 further includes a second high-temperature stage throttle valve group 57 and a medium-temperature stage evaporative condenser 61, wherein:
the high-temperature stage refrigeration compressor 51, the high-temperature stage air condenser 52, the other flow channel in the first inter-cooler heat exchanger 54, the second high-temperature stage throttle valve group 57 and the medium-temperature stage evaporative condenser 61 are sequentially connected in a closed manner to form a fourth high-temperature stage circulation loop.
In a specific embodiment, the medium-temperature-stage refrigeration compressor unit 6 includes a medium-temperature-stage refrigeration compressor 62, a medium-temperature-stage air condenser 63, a medium-temperature-stage throttle valve group 64, a second inter-cooling heat exchanger 65, and a second inter-cooling throttle valve group 66, where:
two flow passages are arranged inside the second inter-cooling heat exchanger 65;
a flow passage in the middle-temperature stage refrigeration compressor 62, the middle-temperature stage air condenser 63, the middle-temperature stage evaporative condenser 61, the second inter-cooling throttle valve group 66 and the second inter-cooling heat exchanger 65 are sequentially connected in a closed manner to form a first middle-temperature stage circulation loop;
and the medium-temperature-stage refrigeration compressor 62, the medium-temperature-stage air condenser 63, the medium-temperature-stage evaporative condenser 61, another flow channel in the second inter-cooling heat exchanger 65, the medium-temperature-stage throttling valve group 64 and a third flow channel of the second heat exchanger 3 are sequentially connected in a closed manner to form a second medium-temperature-stage circulation loop.
In a preferred embodiment, the liquefaction system further comprises a fifth heat exchanger 13 and a second pre-cooling throttle valve set 67, wherein:
the fifth heat exchanger 13 is provided with three flow channels, namely a first flow channel, a second flow channel and a third flow channel from top to bottom;
the fifth heat exchanger 13 is arranged between the first heat exchanger 2 and the second heat exchanger 3, a second flow channel of the first heat exchanger 2 is connected to a second flow channel of the second heat exchanger 3 in a forward direction through a second flow channel of the fifth heat exchanger 13, and a first flow channel of the second heat exchanger 3 is connected to a second flow channel of the first heat exchanger 2 in a reverse direction through a first flow channel of the fifth heat exchanger 13;
and the medium-temperature stage refrigeration compressor 62, the medium-temperature stage air condenser 63, the medium-temperature stage evaporative condenser 61, the second precooling throttle valve set 67 and the third flow channel of the fifth heat exchanger 13 are sequentially connected in a closed manner to form a third medium-temperature stage circulation loop.
Preferably, the first heat exchanger 2, the second heat exchanger 3, the third heat exchanger 4, the fourth heat exchanger 12 and/or the fifth heat exchanger 13 are brazed plate heat exchangers.
In this embodiment, the high-temperature stage refrigeration compressor group uses R404A, R290, R507A, R744 or R22 refrigerant. Preferably, the high-temperature stage refrigeration compressor group adopts R404A and R507A refrigerants.
In this embodiment, the middle-temperature-stage refrigeration compressor group uses R23, R508B, or R1150 refrigerant. Preferably, the medium-temperature stage refrigeration compressor group adopts R23 refrigerant.
Example two
As shown in fig. 3, the present invention also discloses a liquefaction method for liquefying natural gas, comprising the steps of:
step 1: mixing the natural gas with the pressure of 2.5-6.0 MPa, which is subjected to desulfurization, decarburization and dehydration purification with the gas discharged from the natural gas compressor unit 11 in the mixer 1, then feeding the mixed gas into the fourth heat exchanger 12, cooling the mixed gas to 10-15 ℃ after passing through the fourth heat exchanger 12, feeding the cooled natural gas into the first heat exchanger 2, and cooling the cooled natural gas to-15-35 ℃ after passing through the first heat exchanger 2;
and 2, step: the cooled natural gas enters the fifth heat exchanger 13 and is cooled to minus 35 to minus 55 ℃ after passing through the fifth heat exchanger 13; the cooled natural gas enters a second heat exchanger 3 and is cooled to-55 to-110 ℃ after passing through the second heat exchanger 3;
and 3, step 3: the natural gas which is condensed to minus 55 to minus 110 ℃ from the second heat exchanger 3 is divided into two parts, one part of the natural gas enters the third heat exchanger 4, and the temperature of the natural gas is further reduced to minus 110 to minus 140 ℃ in the third heat exchanger 4; the other part of the natural gas is throttled by the low-temperature throttling valve group 7 and then changed into low-temperature and low-pressure natural gas liquid serving as a refrigerant, and the heat of the natural gas is absorbed in the third heat exchanger 4, so that the natural gas of the main flow is further subcooled;
and 4, step 4: the natural gas of the main flow from the third heat exchanger 4 is depressurized by the LNG throttling valve group 8 and flows into the LNG storage tank 9 for storage, and the flash steam discharged from the LNG storage tank 9 is recycled by cold energy and then used for power generation or enters the natural gas compressor unit 11 to participate in recycling;
and 5: the natural gas which is taken as the refrigerant and is discharged from the third heat exchanger 4 is evaporated into gas after absorbing heat, then the natural gas gradually passes through the third heat exchanger 4, the second heat exchanger 3, the fifth heat exchanger 13, the first heat exchanger 2 and the fourth heat exchanger 12, the temperature basically returns to about 0 ℃ after all cold energy is recovered, and then the natural gas is divided into two strands, one strand is taken as the energy of the scavenging gas of the purification system or the energy of the gas generator; the other stream directly enters the natural gas compressor set 11, is boosted to the inlet pressure of the purified natural gas in the natural gas compressor set 11, and is mixed with the purified natural gas to enter the circulation again.
Further, as shown in fig. 4, step 1 further includes the following steps:
step 11: the high-temperature stage refrigeration compressor 51 sucks in medium-pressure and low-pressure refrigerant, and the discharged high-temperature and high-pressure gas is condensed in the high-temperature stage air condenser 52 and is divided into three parts;
step 12: a part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a first precooling throttle valve 56, then is evaporated in a fourth heat exchanger 12, exchanges heat with natural gas, and is cooled to 10 to minus 15 ℃ after passing through the fourth heat exchanger 12;
step 13: another part of the refrigerant is throttled and decompressed into liquid with medium temperature and medium pressure by the first intercooling throttle valve bank 55, and absorbs the heat of the third part of the high-pressure refrigerant in the first intercooling heat exchanger 54 to further supercool the high-pressure refrigerant;
step 14: the medium-pressure refrigerant from the fourth heat exchanger 12 and the medium-pressure refrigerant from the first inter-cooling heat exchanger 54 are mixed and then return to the medium-pressure air return channel of the high-temperature stage refrigeration compressor 51, and the medium-pressure refrigeration cycle is completed;
step 15: the third part of high-pressure refrigerant from the high-temperature grade air condenser 52 is further subcooled by a first intercooler heat exchanger 54 and then is divided into two parts;
step 16: one part of the refrigerant is throttled by a first high-temperature-level throttle valve group 53 to be changed into low-temperature low-pressure liquid, then enters a first heat exchanger 2 to absorb the heat of natural gas, is cooled to-15 to-35 ℃ after passing through the first heat exchanger 2, and then is changed into low-pressure gas;
and step 17: the other part of the refrigerant supercooled by the first intercooling heat exchanger 54 is throttled by the second high-temperature stage throttling valve group 57 to become low-temperature and low-pressure liquid, and then enters the medium-temperature stage evaporative condenser 61 in the medium-temperature stage refrigeration compressor unit to become low-pressure gas after absorbing the heat of the medium-temperature stage refrigerant;
step 18: and (4) after the two groups of low-pressure gases in the step (16) and the step (17) are mixed, returning the mixed gases to a low-pressure gas return channel of the high-temperature stage refrigeration compressor (51) to complete the circulation of the low-pressure stage refrigerant.
Further, as shown in fig. 5, step 2 further includes the following steps:
step 21: the medium-temperature stage refrigeration compressor 62 sucks medium-pressure and low-pressure medium-temperature stage refrigerant, and discharged high-temperature and high-pressure gas is pre-cooled to 30-60 ℃ in the medium-temperature stage air cooler 63, condensed in the medium-temperature stage evaporation condenser 61 and then divided into three parts;
step 22: a part of refrigerant is throttled and decompressed into medium-temperature and medium-pressure liquid through a second precooling throttle valve 67, then is evaporated in a fifth heat exchanger 13, exchanges heat with natural gas, and is cooled to-35 to-55 ℃ after passing through the fifth heat exchanger 13;
step 23: another part of refrigerant is throttled and decompressed into liquid with medium temperature and medium pressure through a second intercooling throttle valve group 66, and absorbs the heat of a third part of high-pressure refrigerant in a second intercooling heat exchanger 65 to further supercool the high-pressure refrigerant;
and step 24: the medium-pressure refrigerant from the fifth heat exchanger 13 and the medium-pressure refrigerant from the second inter-cooling heat exchanger 65 are mixed and then return to the medium-pressure gas return channel of the medium-temperature stage refrigeration compressor 62, so that medium-pressure refrigeration cycle is completed;
step 25: the third part of high-pressure refrigerant from the medium-temperature-stage evaporative condenser 61 passes through the second inter-cooling heat exchanger 65 and is throttled by the medium-temperature-stage throttle valve group 64, so that the refrigerant is changed into low-temperature and low-pressure liquid, then enters the second heat exchanger 3 to absorb the heat of natural gas, is cooled to-55 to-110 ℃ after passing through the second heat exchanger 3, then is changed into low-pressure gas, and returns to a low-pressure gas return channel of the medium-temperature-stage refrigeration compressor 62 to complete the low-pressure-stage refrigerant circulation of the medium-temperature-stage compressor.
The specific process flow is as follows:
firstly, mixing natural gas with the pressure of 2.5-6.0 MPa and purified through desulfurization, decarburization, dehydration and the like with gas exhausted by a natural gas compressor unit 11 in a mixer 1, then feeding the mixed gas into a fourth heat exchanger 12, wherein the fourth heat exchanger 12 supplies cold energy through a third high-temperature stage circulation loop in a high-temperature stage refrigeration compressor unit 51, cooling the mixed gas to 10-15 ℃ through the fourth heat exchanger 12, then feeding the cooled gas into a first heat exchanger 2, the first heat exchanger 2 supplies cold energy through a second high-temperature stage circulation loop in the high-temperature stage refrigeration compressor unit, and cooling the cooled gas to-15-35 ℃ through the first heat exchanger 2; the fourth circulation loop in the high-temperature-stage refrigeration compressor unit is used for condensing high-pressure medium-temperature-stage refrigerant through the medium-temperature-stage evaporative condenser 61, and forms a cascade refrigeration system with the medium-temperature stage.
Next, the high-temperature stage refrigeration compressor 51 sucks in medium-pressure and low-pressure refrigerant, and the discharged high-temperature and high-pressure gas is condensed in the high-temperature stage air condenser 52 and divided into three parts:
a part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a first precooling throttle valve 56, then is evaporated in a fourth heat exchanger 12, exchanges heat with natural gas, and is cooled to 10 to minus 15 ℃ after passing through the fourth heat exchanger 12;
another part of the refrigerant is throttled and decompressed into liquid with medium temperature and medium pressure through the first intercooling throttling valve group 55, and absorbs the heat of the third part of high-pressure refrigerant in the first intercooling heat exchanger 54 to further supercool the high-pressure refrigerant;
the medium-pressure refrigerant from the fourth heat exchanger 12 and the medium-pressure refrigerant from the first inter-cooler heat exchanger 54 are mixed and then return to the medium-pressure return air channel of the high-temperature stage refrigeration compressor 51, and thus the medium-pressure refrigeration cycle is completed.
A third part of high-pressure refrigerant from the high-temperature grade air condenser 52 is further subcooled by a first inter-cooling heat exchanger 54 and then divided into two parts, one part of the refrigerant is throttled by a first high-temperature grade throttle valve group 53 to change the refrigerant into low-temperature and low-pressure liquid, then the low-temperature and low-pressure liquid enters a first heat exchanger 2 to absorb the heat of natural gas, and the low-temperature and low-pressure liquid is cooled to-15 to-35 ℃ after passing through the first heat exchanger 2 and then is changed into low-pressure gas;
the other part of the refrigerant supercooled by the first intercooling heat exchanger 54 is throttled by the second high-temperature stage throttling valve group 57 to become low-temperature and low-pressure liquid, and then enters the medium-temperature stage evaporative condenser 61 in the medium-temperature stage refrigeration compressor group 6 to become low-pressure gas after absorbing the heat of the medium-temperature stage refrigerant;
the two groups of low-pressure gas are mixed and then return to the low-pressure gas return passage of the high-temperature stage refrigeration compressor 51, and the circulation of the low-pressure stage refrigerant is completed.
Similarly, the medium-temperature stage refrigeration compressor 62 sucks medium-pressure and low-pressure medium-temperature stage refrigerant, and the discharged high-temperature and high-pressure gas is pre-cooled to 30-60 ℃ in the medium-temperature stage air cooler 63, condensed in the medium-temperature stage evaporative condenser 61, and then divided into three parts:
a part of refrigerant is throttled and decompressed into medium-temperature and medium-pressure liquid through a second precooling throttle valve 67, then is evaporated in a fifth heat exchanger 13, exchanges heat with natural gas, and is cooled to-35 to-55 ℃ after passing through the fifth heat exchanger 13;
another part of refrigerant is throttled and decompressed into liquid with medium temperature and medium pressure through a second intercooling throttle valve group 66, and absorbs the heat of a third part of high-pressure refrigerant in a second intercooling heat exchanger 65 to further supercool the high-pressure refrigerant;
the medium-pressure refrigerant coming out of the fifth heat exchanger 13 and the medium-pressure refrigerant coming out of the second inter-cooling heat exchanger 65 are mixed and then return to the medium-pressure return air channel of the medium-temperature stage refrigeration compressor 62, and the medium-pressure refrigeration cycle is completed.
The third part of high-pressure refrigerant from the intermediate-temperature stage evaporative condenser 61 passes through the second intermediate-cooling heat exchanger 65, is throttled by the intermediate-temperature stage throttle valve group 64, is changed into low-temperature and low-pressure liquid, then enters the second heat exchanger 3 to absorb the heat of natural gas, is cooled to-55 to-110 ℃ after passing through the second heat exchanger 3, is changed into low-pressure gas, and returns to the low-pressure gas return channel of the intermediate-temperature stage refrigeration compressor 62 to complete the low-pressure stage refrigerant circulation of the intermediate-temperature stage compressor.
Thirdly, the natural gas which is condensed to-55 to-110 ℃ from the second heat exchanger 3 is divided into two parts, one part of the two parts enters the third heat exchanger 4, and the temperature is further reduced to-110 to-140 ℃ in the third heat exchanger 4; and one part of the natural gas is throttled by the low-temperature throttling valve group 7 to become low-temperature and low-pressure natural gas liquid serving as a refrigerant, and the heat of the natural gas is absorbed in the third heat exchanger 4, so that the natural gas of the main flow is further subcooled.
And then, the natural gas of the main flow from the third heat exchanger 4 is depressurized by the LNG throttling valve group 8 and flows into the LNG storage tank 9 for storage, and the flash steam (BOG) discharged from the LNG storage tank 9 is used for power generation after being recovered by cold energy or enters the natural gas compressor unit 11 to participate in recycling.
The natural gas which is taken as the refrigerant and is discharged from the third heat exchanger 4 is evaporated into gas after absorbing heat, then the natural gas gradually passes through the third heat exchanger 4, the second heat exchanger 3, the fifth heat exchanger 13, the first heat exchanger 2 and the fourth heat exchanger 12, the temperature basically returns to about 0 ℃ after all cold energy is recovered, and then the natural gas is divided into two strands, one strand is taken as the energy of the scavenging gas of the purification system or the energy of the gas generator; the other stream directly enters the natural gas compressor set 11, is boosted to the inlet pressure of the purified natural gas in the natural gas compressor set 11, and is mixed with the purified natural gas to enter the circulation again.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. The utility model provides a liquefaction system for liquefied natural gas, its characterized in that includes blender, first heat exchanger, second heat exchanger, third heat exchanger, high temperature level refrigeration compressor group, medium temperature level refrigeration compressor group, low temperature level throttle valves, LNG storage tank, shunt and natural gas compressor group, wherein:
three runners are arranged in the first heat exchanger, the second heat exchanger and the third heat exchanger respectively, and the first runner, the second runner and the third runner are arranged from top to bottom;
the output end of the mixer is connected with a second flow channel of the first heat exchanger, the second flow channel of the first heat exchanger is connected with a second flow channel of the second heat exchanger, and the second flow channel of the second heat exchanger is divided into two paths from the first flow channel to the second flow channel:
one path of the LNG throttling valve group is connected with a second flow channel of the third heat exchanger in sequence, and the second flow channel of the third heat exchanger is connected with the LNG storage tank after being connected with the LNG throttling valve group;
the other path of the gas flow is connected with a third flow channel of a third heat exchanger after passing through the low-temperature-stage throttling valve group, and is connected to the splitter after sequentially passing through a first flow channel of the third heat exchanger, a first flow channel of the second heat exchanger and a first flow channel of the first heat exchanger in a reverse direction, the splitter is divided into two paths to be output, one path of the gas flow is used for directly generating power or generating power after being used as purge gas of a purification part, and the other path of the gas flow is connected with the natural gas compressor unit and then is connected to the input end of the mixer;
the high-temperature stage refrigeration compressor set is connected to two ends of a third flow channel of the first heat exchanger and used for cooling natural gas;
the high-temperature stage refrigeration compressor set comprises a high-temperature stage refrigeration compressor, a high-temperature stage air condenser, a first high-temperature stage throttle valve set, a first inter-cooling heat exchanger and a first inter-cooling throttle valve set, wherein:
two flow passages are arranged in the first inter-cooling heat exchanger;
the high-temperature stage refrigeration compressor, the high-temperature stage air condenser, the first inter-cooling throttling valve group and a flow channel in the first inter-cooling heat exchanger are sequentially connected in a closed mode to form a first high-temperature stage circulation loop;
the high-temperature-stage refrigeration compressor, the high-temperature-stage air condenser, the other flow channel in the first inter-cooling heat exchanger, the first high-temperature-stage throttling valve group and the third flow channel of the first heat exchanger are sequentially connected in a closed manner to form a second high-temperature-stage circulation loop;
and the middle-temperature stage refrigeration compressor set is connected to two ends of a third flow channel of the second heat exchanger and used for further cooling the natural gas.
2. The liquefaction system for liquefying natural gas according to claim 1, further comprising a fourth heat exchanger and a first pre-cooling throttle set, wherein:
the fourth heat exchanger is provided with three runners, namely a first runner, a second runner and a third runner from top to bottom;
the fourth heat exchanger is arranged between the mixer and the first heat exchanger, the output end of the mixer is positively connected to the second flow channel of the first heat exchanger through the second flow channel of the fourth heat exchanger, and the first flow channel of the first heat exchanger is reversely connected to the flow divider through the first flow channel of the fourth heat exchanger;
and the high-temperature stage refrigeration compressor, the high-temperature stage air condenser, the first precooling throttle valve group and a third flow channel of the fourth heat exchanger are sequentially connected in a closed manner to form a third high-temperature stage circulation loop.
3. The liquefaction system for liquefying natural gas according to claim 1 or 2, wherein the high-temperature stage refrigeration compressor train further comprises a second high-temperature stage throttle valve bank and a medium-temperature stage evaporative condenser, wherein:
and the high-temperature-stage refrigeration compressor, the high-temperature-stage air condenser, the other flow channel in the first inter-cooler heat exchanger, the second high-temperature-stage throttling valve group and the intermediate-temperature-stage evaporative condenser are sequentially connected in a closed manner to form a fourth high-temperature-stage circulation loop.
4. The liquefaction system for liquefying natural gas according to claim 3, wherein the medium-temperature-stage refrigeration compressor unit comprises a medium-temperature-stage refrigeration compressor, a medium-temperature-stage air condenser, a medium-temperature-stage throttle valve group, a second inter-cooling heat exchanger and a second inter-cooling throttle valve group, wherein:
two flow passages are arranged in the second intercooling heat exchanger;
the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, the second inter-cooling throttling valve group and a flow channel in the second inter-cooling heat exchanger are sequentially connected in a closed mode to form a first medium-temperature stage circulation loop;
the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, another flow channel in the second inter-cooling heat exchanger, the medium-temperature stage throttling valve group and a third flow channel of the second heat exchanger are sequentially connected in a closed mode to form a second medium-temperature stage circulation loop.
5. The liquefaction system for liquefying natural gas according to claim 4, further comprising a fifth heat exchanger and a second pre-cooling throttle set, wherein:
the fifth heat exchanger is provided with three runners, namely a first runner, a second runner and a third runner from top to bottom;
the fifth heat exchanger is arranged between the first heat exchanger and the second heat exchanger, a second flow channel of the first heat exchanger is positively connected to a second flow channel of the second heat exchanger through a second flow channel of the fifth heat exchanger, and a first flow channel of the second heat exchanger is reversely connected to the second flow channel of the first heat exchanger through a first flow channel of the fifth heat exchanger;
and the medium-temperature stage refrigeration compressor, the medium-temperature stage air condenser, the medium-temperature stage evaporative condenser, the second precooling throttle valve group and a third flow channel of the fifth heat exchanger are sequentially connected in a closed manner to form a third medium-temperature stage circulation loop.
6. The liquefaction system for liquefying natural gas according to claim 5, wherein the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger and/or the fifth heat exchanger are brazed plate heat exchangers.
7. A liquefaction process for liquefying natural gas, characterized by comprising the steps of:
step 1: mixing the natural gas with the pressure of 2.5-6.0 MPa, which is subjected to desulfurization, decarburization and dehydration purification with the gas exhausted from the natural gas compressor unit in a mixer, then feeding the mixed gas into a fourth heat exchanger, cooling the mixed gas to 10-15 ℃ after passing through the fourth heat exchanger, feeding the cooled natural gas into a first heat exchanger, and cooling the cooled natural gas to-15-35 ℃ after passing through the first heat exchanger;
the step 1 further comprises the following steps:
step 11: the high-temperature stage refrigeration compressor sucks medium-pressure and low-pressure refrigerant, and the discharged high-temperature and high-pressure gas is condensed in the high-temperature stage air condenser and is divided into three parts;
step 12: throttling and reducing a part of refrigerant into medium-temperature and medium-pressure liquid through a first precooling throttle valve, evaporating the liquid in a fourth heat exchanger, exchanging heat with natural gas, and cooling the liquid to 10 to-15 ℃ through the fourth heat exchanger;
step 13: the other part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a first intercooling throttle valve group, and the heat of a third part of high-pressure refrigerant is absorbed in a first intercooling heat exchanger to further supercool the high-pressure refrigerant;
step 14: the medium-pressure refrigerant coming out of the fourth heat exchanger and the medium-pressure refrigerant coming out of the first inter-cooling heat exchanger are mixed and then return to a medium-pressure air return channel of the high-temperature stage refrigeration compressor, and medium-pressure refrigeration circulation is completed;
step 15: a third part of high-pressure refrigerant from the high-temperature grade air condenser is further subcooled by a first intercooling heat exchanger and then is divided into two parts;
step 16: one part of the refrigerant is throttled by a first high-temperature-level throttle valve group to change the refrigerant into low-temperature low-pressure liquid, then the liquid enters a first heat exchanger to absorb the heat of natural gas, and the temperature of the liquid is reduced to minus 15 to minus 35 ℃ after the liquid passes through the first heat exchanger, and then the liquid is changed into low-pressure gas;
and step 17: the other part of the refrigerant after being subcooled by the first intercooling heat exchanger is throttled by the second high-temperature-level throttle valve group and then is changed into low-temperature and low-pressure liquid, and then the low-temperature and low-pressure liquid enters a medium-temperature-level evaporation condenser in the medium-temperature-level refrigeration compressor unit to absorb the heat of the medium-temperature-level refrigerant and then is changed into low-pressure gas;
step 18: after the two groups of low-pressure gas in the step 16 and the step 17 are mixed, returning to a low-pressure gas return channel of the high-temperature stage refrigeration compressor to complete the circulation of the low-pressure stage refrigerant;
step 2: the cooled natural gas enters a fifth heat exchanger and is cooled to minus 35 to minus 55 ℃ after passing through the fifth heat exchanger; the cooled natural gas enters a second heat exchanger and is cooled to minus 55 to minus 110 ℃ after passing through the second heat exchanger;
and step 3: the natural gas which is condensed to minus 55 to minus 110 ℃ from the second heat exchanger is divided into two parts, one part of the natural gas enters a third heat exchanger, and the temperature of the natural gas is further reduced to minus 110 to minus 140 ℃ in the third heat exchanger; the other part of the natural gas is throttled by the low-temperature throttling valve group and then is changed into low-temperature and low-pressure natural gas liquid serving as a refrigerant, and the heat of the natural gas is absorbed in a third heat exchanger, so that the natural gas of a main flow is further subcooled;
and 4, step 4: the natural gas of the main flow from the third heat exchanger is depressurized by the LNG throttling valve group and flows into the LNG storage tank for storage, and the flash steam discharged from the LNG storage tank is recycled by cold energy and then is used for power generation or enters the natural gas compressor unit to participate in recycling;
and 5: the natural gas which is taken as the refrigerant and is discharged from the third heat exchanger is evaporated into gas after absorbing heat, then the natural gas gradually passes through the third heat exchanger, the second heat exchanger, the fifth heat exchanger, the first heat exchanger and the fourth heat exchanger, the temperature basically returns to about 0 ℃ after all cold energy is recovered, and then the natural gas is divided into two strands, wherein one strand is taken as the blowing gas of the purification system or the energy of the gas generator; and the other strand of the natural gas enters the natural gas compressor set directly, is boosted to the inlet pressure of the purified natural gas in the natural gas compressor set, is mixed with the purified natural gas and then enters the circulation again.
8. The liquefaction method for liquefying natural gas according to claim 7, wherein the step 2 further comprises the steps of:
step 21: the medium-temperature stage refrigeration compressor sucks medium-pressure and low-pressure medium-temperature stage refrigerant, and discharged high-temperature and high-pressure gas is pre-cooled to 30-60 ℃ in a medium-temperature stage air cooler, condensed in a medium-temperature stage evaporation condenser and then divided into three parts;
step 22: throttling and reducing a part of refrigerant into medium-temperature and medium-pressure liquid through a second precooling throttle valve, evaporating the liquid in a fifth heat exchanger, exchanging heat with natural gas, and cooling the liquid to-35 to-55 ℃ through the fifth heat exchanger;
step 23: the other part of refrigerant is throttled and reduced into medium-temperature and medium-pressure liquid through a second intercooling throttle valve group, and the heat of the third part of high-pressure refrigerant is absorbed in a second intercooling heat exchanger to further supercool the high-pressure refrigerant;
step 24: the medium-pressure refrigerant coming out of the fifth heat exchanger and the medium-pressure refrigerant coming out of the second intercooling heat exchanger are mixed and then return to a medium-pressure air return channel of the medium-temperature stage refrigeration compressor, and medium-pressure refrigeration circulation is completed;
step 25: and a third part of high-pressure refrigerant from the medium-temperature-stage evaporative condenser passes through a second intercooling heat exchanger, is throttled by a medium-temperature-stage throttle valve group to be changed into low-temperature and low-pressure liquid, then enters the second heat exchanger to absorb the heat of natural gas, is cooled to minus 55 ℃ to minus 110 ℃ after passing through the second heat exchanger, is changed into low-pressure gas, returns to a low-pressure gas return channel of the medium-temperature-stage refrigeration compressor, and completes the low-pressure-stage refrigerant circulation of the medium-temperature-stage compressor.
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