CN115164461B - Mixed refrigerant recovery system and method of liquefied natural gas device - Google Patents
Mixed refrigerant recovery system and method of liquefied natural gas device Download PDFInfo
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- CN115164461B CN115164461B CN202210736317.6A CN202210736317A CN115164461B CN 115164461 B CN115164461 B CN 115164461B CN 202210736317 A CN202210736317 A CN 202210736317A CN 115164461 B CN115164461 B CN 115164461B
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- 239000003507 refrigerant Substances 0.000 title claims abstract description 507
- 238000011084 recovery Methods 0.000 title claims abstract description 319
- 239000003949 liquefied natural gas Substances 0.000 title claims abstract description 42
- 238000000034 method Methods 0.000 title claims abstract description 21
- QWTDNUCVQCZILF-UHFFFAOYSA-N isopentane Chemical compound CCC(C)C QWTDNUCVQCZILF-UHFFFAOYSA-N 0.000 claims abstract description 116
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims abstract description 110
- AFABGHUZZDYHJO-UHFFFAOYSA-N dimethyl butane Natural products CCCC(C)C AFABGHUZZDYHJO-UHFFFAOYSA-N 0.000 claims abstract description 58
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000005977 Ethylene Substances 0.000 claims abstract description 57
- 239000001294 propane Substances 0.000 claims abstract description 55
- 238000010438 heat treatment Methods 0.000 claims abstract description 29
- 238000007599 discharging Methods 0.000 claims abstract description 10
- 238000000926 separation method Methods 0.000 claims abstract description 9
- 238000003860 storage Methods 0.000 claims description 55
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 44
- 239000007788 liquid Substances 0.000 claims description 35
- 230000001276 controlling effect Effects 0.000 claims description 34
- 239000007789 gas Substances 0.000 claims description 33
- 238000010992 reflux Methods 0.000 claims description 18
- 239000003345 natural gas Substances 0.000 claims description 16
- 238000001816 cooling Methods 0.000 claims description 8
- 230000001105 regulatory effect Effects 0.000 claims description 8
- 238000009833 condensation Methods 0.000 claims description 7
- 230000005494 condensation Effects 0.000 claims description 7
- 238000004064 recycling Methods 0.000 claims description 5
- 238000007906 compression Methods 0.000 claims description 4
- 230000006835 compression Effects 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 4
- 230000009467 reduction Effects 0.000 abstract description 3
- 238000004134 energy conservation Methods 0.000 abstract description 2
- 238000005516 engineering process Methods 0.000 abstract 1
- 238000005057 refrigeration Methods 0.000 description 14
- 238000005259 measurement Methods 0.000 description 13
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 238000009529 body temperature measurement Methods 0.000 description 10
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical compound CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 6
- 238000009530 blood pressure measurement Methods 0.000 description 6
- 239000003795 chemical substances by application Substances 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 6
- 239000007791 liquid phase Substances 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 239000000203 mixture Substances 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 239000012808 vapor phase Substances 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000009835 boiling Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
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- 239000000126 substance Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
Classifications
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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
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B45/00—Arrangements for charging or discharging refrigerant
-
- 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
- F25J1/0055—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 originating from an incorporated cascade
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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
- F25J1/02—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
- F25J1/0212—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 a single flow MCR cycle
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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
- F25J1/02—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
- F25J1/0244—Operation; Control and regulation; Instrumentation
- F25J1/0245—Different modes, i.e. 'runs', of operation; Process control
- F25J1/0248—Stopping of the process, e.g. defrosting or deriming, maintenance; Back-up mode or systems
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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
- F25J1/02—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
- F25J1/0244—Operation; Control and regulation; Instrumentation
- F25J1/0245—Different modes, i.e. 'runs', of operation; Process control
- F25J1/0249—Controlling refrigerant inventory, i.e. composition or quantity
- F25J1/025—Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself
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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
- F25J1/02—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.
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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
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2345/00—Details for charging or discharging refrigerants; Service stations therefor
- F25B2345/002—Collecting refrigerant from a cycle
Landscapes
- 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 mixed refrigerant recovery system and a method of a liquefied natural gas device, wherein the mixed refrigerant recovery system comprises a refrigerant recovery tower, a refrigerant feeding pipeline is arranged in the middle of the refrigerant recovery tower, a refrigerant discharging pipeline is arranged at the top of the refrigerant recovery tower, a refrigerant recovery pipeline is arranged at the bottom of the refrigerant recovery tower, the final classifier is communicated with the inside of the refrigerant recovery tower through the refrigerant feeding pipeline, the refrigerant discharging pipeline is communicated with a refrigerant supply pipeline, a condensing loop is arranged on the refrigerant discharging pipeline, and a heating loop is arranged at the bottom of the refrigerant recovery tower. Compared with the prior art, the technology of the invention not only does not influence the safe operation of the original equipment, but also greatly improves the operation safety of the device, realizes independent separation and recovery of isopentane, propane and ethylene in the mixed refrigerant, reduces the emptying of the refrigerant and the burning of the torch, and has good effects of energy conservation and emission reduction. And the new equipment is less, so that isopentane, propane and ethylene which are expensive can be completely recovered, and the economic value is higher.
Description
Technical Field
The invention relates to the field of liquefied natural gas preparation, in particular to a mixed refrigerant recovery system and method of a liquefied natural gas device.
Background
The liquefied natural gas device is used for liquefying the produced natural gas so as to carry out transportation and storage, more processes are adopted at home and abroad by the liquefied natural gas device, namely an MRC process or a C3+MRC process, the refrigerant is usually isopentane, propane, ethylene, methane and nitrogen, the supply of the natural gas is directly cut off when the device is stopped, but the refrigerant in the liquefied natural gas device is left in the device to be gasified continuously, so that the pressure in the device is overlarge, and therefore the refrigerant can be emptied or recovered, and the refrigerant recovery scheme adopted at present basically adopts a refrigerant recovery pump or a refrigerant recovery compressor, but only part of the refrigerant can be recovered, and still the emptying can be carried out. The device mainly has the problems that 1. The prior device adopts a direct shut-down mode, and the natural gas supply can cause excessive pressure in the device after the direct shut-down, and safety accidents are easy to generate, so that the device can only be used for emptying and burning through a torch, thereby not only causing energy waste, but also affecting the environment. 2. At present, a refrigerant recovery pump or a refrigerant recovery compressor is adopted for recovery, and the refrigerant recovery is incomplete, such as the emptying of outsourced refrigerant ethylene. 3. The refrigerant recovery pump or the refrigerant recovery compressor belongs to the power equipment with large investment, but has low use frequency, so that the economy is poor. 4. Because the liquefied natural gas device has a requirement on the usage proportion of the refrigerant, the recycled refrigerant is mixed refrigerant, and the secondary proportioning can not be directly carried out. 5. The recovered refrigerants isopentane, propane, ethylene cannot be separated and stored separately.
Disclosure of Invention
The invention aims to provide a mixed refrigerant recovery system and a mixed refrigerant recovery method for a liquefied natural gas device, which solve the problem of direct shutdown of the liquefied natural gas device and realize independent separation, recovery and storage of isopentane, propane and ethylene.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: the utility model provides a mixed refrigerant recovery system of liquefied natural gas device, includes refrigerant feed line, last stage classifier, natural gas line and cold box, after refrigerant feed line carries out the second grade compression with mixed refrigerant, carries the refrigerant heat transfer pipeline to the cold box in through last stage classifier, still includes the refrigerant recovery tower, refrigerant recovery tower middle part is equipped with the refrigerant feed line, and refrigerant recovery tower top is equipped with the refrigerant ejection of compact pipeline, and refrigerant recovery tower bottom is equipped with the refrigerant recovery pipeline, last stage classifier passes through refrigerant feed line and the inside intercommunication of refrigerant recovery tower, refrigerant ejection of compact pipeline and refrigerant feed line's intercommunication, be equipped with the condensation circuit on the refrigerant ejection of compact pipeline, be equipped with the heating circuit at the bottom of the refrigerant recovery tower, the refrigerant recovery pipeline has the multichannel, and every way refrigerant recovery pipeline is connected to the refrigerant storage tank that corresponds respectively.
Preferably, the condensation loop comprises a refrigerant recovery tower condenser and a refrigerant recovery tower reflux tank, the refrigerant recovery tower condenser and the refrigerant recovery tower reflux tank are arranged on a refrigerant discharging pipeline, a refrigeration pipeline is arranged on the refrigerant recovery tower condenser and is communicated with a refrigerant heat exchange pipeline of the cold box, a refrigerant recovery tower top temperature control valve is arranged on the refrigeration pipeline, a switching valve is arranged between the refrigeration pipeline and the refrigerant heat exchange pipeline, and a reflux pipeline is arranged on the refrigerant recovery tower reflux tank and is communicated with the inside of the top of the refrigerant recovery tower.
Preferably, a refrigerant recovery tower reboiler is arranged on the heating loop at the bottom of the refrigerant recovery tower, a heat conduction oil pipeline is arranged on the refrigerant recovery tower reboiler, and a temperature control valve at the bottom of the refrigerant recovery tower is arranged on the heat conduction oil pipeline.
Preferably, a refrigerant recovery tower feed valve is arranged on the refrigerant feed pipeline; the refrigerant discharge pipeline is provided with a refrigerant recovery tower emptying valve and a refrigerant recovery tower emptying air reheater; the refrigerant recovery pipeline is provided with a refrigerant recovery tower liquid level control valve.
Preferably, the refrigerant recovery pipeline is divided into an isopentane recovery pipeline, a propane recovery pipeline and an ethylene recovery pipeline, the corresponding refrigerant storage tanks are an isopentane storage tank, a propane storage tank and an ethylene storage tank, and the isopentane recovery pipeline, the propane recovery pipeline and the ethylene recovery pipeline are respectively connected to the corresponding refrigerant storage tanks.
Preferably, the isopentane recovery pipeline and the propane recovery pipeline are provided with a refrigerant cooler; the ethylene recovery pipeline is cooled by the cold box and then enters the corresponding refrigerant storage tank.
Preferably, the isopentane recovery pipeline, the propane recovery pipeline and the ethylene recovery pipeline are respectively provided with a refrigerant storage tank feeding valve, the refrigerant storage tanks are respectively communicated with a refrigerant supply pipeline through supply pipelines, and the supply pipelines are respectively provided with a control valve.
Preferably, a circulation pipeline is connected to the outlet of the refrigerant heat exchange pipeline of the cold box, the circulation pipeline is communicated with a refrigerant supply pipeline, the circulation pipeline is provided with a switch valve, and the refrigerant supply pipeline is provided with a gas chromatograph.
Preferably, trays are arranged in the refrigerant recovery tower at intervals from top to bottom.
A mixed refrigerant recovery method of a liquefied natural gas device comprises the following steps,
a. when the liquefied natural gas device needs to be stopped, a refrigerant recovery tower is started, and a refrigerant feeding pipeline and a refrigerant discharging pipeline are started to be communicated with a refrigerant supply pipeline to form recovery circulation;
b. controlling the flow of the refrigerant entering the refrigerant recovery tower through a refrigerant feeding pipeline, controlling the temperature of the bottom of the refrigerant recovery tower through a heating loop at the bottom of the tower, controlling the condensing temperature of an outlet at the top of the tower through a condensing loop at the top of the tower, so that a rectifying section and a stripping section are formed in the refrigerant recovery tower, and the rectifying section and the stripping section enable single components in the liquid mixed refrigerant to be completely separated, and extracting the single refrigerant with the required purity from the mixed refrigerant;
c. according to the physical differences of different refrigerants, the separation and recovery of a single refrigerant and the slow stop of the liquefied natural gas device are realized by adopting multi-stage recovery;
d. the recovered single refrigerants are respectively stored into corresponding refrigerant storage tanks through refrigerant recovery pipelines so as to be used for the next blending of the refrigerants.
Preferably, in the step c, three refrigerants of isopentane, propane and ethylene are recovered in three stages, the method is as follows,
in the first stage, isopentane is recovered
Regulating a refrigerant feeding pipeline to control the flow of the refrigerant entering a refrigerant recovery tower, controlling the temperature at the bottom of the refrigerant recovery tower to be 120-140 ℃ through a heating loop, controlling the temperature at the outlet of the tower top to be 5-20 ℃ through a condensing loop at the tower top, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying isopentane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning the uncondensed refrigerant gas to the refrigerant feeding pipeline for recycling, maintaining the device to operate until the online gas chromatograph detects that the isopentane content in the circulating refrigerant is less than 0.5%, recovering qualified isopentane, and cooling isopentane to 30-40 ℃ in the refrigerant recovery pipeline and then entering an isopentane storage tank for storage;
second stage, recovery of propane
Regulating a refrigerant feeding pipeline to control the flow of the refrigerant entering a refrigerant recovery tower, controlling the temperature at the bottom of the refrigerant recovery tower to be 20-60 ℃ through a heating loop, controlling the temperature at an outlet of the tower top to be-45-70 ℃ through a condensing loop at the tower top, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying the propane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ to return to the refrigerant feeding pipeline for recirculation, maintaining the device to operate until the online gas chromatograph detects that the propane content in the circulating refrigerant is less than 0.5%, recovering qualified propane, and cooling the propane to 30-40 ℃ in the refrigerant recovery pipeline and then entering a propane storage tank for storage;
third stage, ethylene is recovered
The refrigerant feeding pipeline is regulated to control the flow rate of the refrigerant entering the refrigerant recovery tower, the temperature at the bottom of the refrigerant recovery tower is controlled to be between 70 ℃ below zero and 30 ℃ below zero through the heating loop, the temperature at the outlet of the tower top is controlled to be between 110 ℃ below zero and 140 ℃ below zero through the condensing loop at the tower top, the pressure of the refrigerant recovery tower is controlled to be between 0.8 MPa and 1.4MPa, the ethylene condensed into liquid is purified at the bottom of the refrigerant recovery tower, the uncondensed refrigerant gas is heated to 5 ℃ and returns to the refrigerant feeding pipeline for recirculation, the maintaining device operates until the online gas chromatograph detects that the ethylene content in the circulating refrigerant is less than 0.5%, and the ethylene which is recovered to be qualified is cooled to 120 ℃ in the refrigerant recovery pipeline and enters the ethylene storage tank for storage.
Compared with the prior art, the invention has the advantages that: according to the invention, through the innovation and innovation of the original liquefied natural gas device, the safe operation of the original equipment is not influenced, the operation safety of the device is greatly improved, the independent separation and recovery of isopentane, propane and ethylene in the mixed refrigerant are realized, the emptying and torch burning of the refrigerant are reduced, and the effects of energy conservation and emission reduction are good. And the new equipment is less, the installation and the transformation are easy, and the device investment is low. Can completely recycle isopentane, propane and ethylene which are expensive, and has higher economic value. Is suitable for being popularized and used in a large range.
A new liquefied natural gas device production system is designed, and the system can realize independent separation, recovery and reutilization of three refrigerants with higher values, namely mixed isopentane, propane and ethylene, and realize great improvement of economy. And the method of directly shutting down the prior device is changed, so that the slow stopping of the liquefied natural gas device is realized, and the problems of overvoltage damage of equipment and the like caused by sudden stopping of the device are solved. The invention adopts a circulating recovery mode to recover the refrigerants one by one, and gradually reduces the supply quantity and the refrigerating capacity of the natural gas along with the recovery of the refrigerants, thereby realizing the slow stop of the device. Because the device realizes slow stopping, the refrigerant is recycled in a stepwise manner, and the refrigerant does not need to be emptied to cause resource waste. As the device realizes slow stopping, the load of the device is gradually reduced, the influence on other production system equipment is small, and the operation safety of the device equipment is greatly improved.
Drawings
FIG. 1 is a schematic diagram of the overall system of the present invention;
FIG. 2 is a schematic system diagram of a refrigerant recovery column of the present invention;
FIG. 3 is a graph showing the parameters of the liquid phase components of each layer of trays when the refrigerant of the present invention returns isopentane;
FIG. 4 is a graph showing the gas phase composition parameters of each layer of trays for the refrigerant isopentane return of the present invention;
FIG. 5 is a graph showing the temperature parameters of each tray layer for the recovery of isopentane from the refrigerant according to the present invention.
In the figure 1, a refrigerant supply line; 2. a gas chromatograph; 3. an inlet balancing tank; 4. a refrigerant compressor; 5. an inter-stage cooler; 6. an inter-stage balancing tank; 7. a final stage refrigerant compressor; 8. a final stage cooler; 9. a final stage classifier; 10. a cold box; 11. a refrigerant heat exchange pipeline; 12. a circulation line; 13. a natural gas pipeline; 14. a coolant feed pipe; 15. a refrigerant recovery tower; 16. a refrigerant discharge line; 17. a refrigerant recovery column condenser; 18. a refrigerant recovery tower reflux drum; 19. a refrigeration pipeline; 20. a return line; 21. a temperature control valve at the top of the refrigerant recovery tower; 22. a switching valve; 23. a heating circuit; 24. a refrigerant recovery column reboiler; 25. a heat conduction oil pipeline; 26. a temperature control valve at the bottom of the refrigerant recovery tower; 27. a refrigerant recovery line; 28. a refrigerant recovery column liquid level control valve; 29. isopentane recovery pipelines; 30. a propane recovery line; 31. an ethylene recovery line; 32. isopentane storage tank; 33. a propane storage tank; 34. an ethylene storage tank; 35. a cryogen cooler; 36. a refrigerant recovery column feed valve; 37. a FIA flow measurement and control instrument; 38. a TIC temperature measurement and control instrument; 39. an LIC liquid level measurement and control instrument; 40. a refrigerant recovery column vent valve; 41. PIA pressure measurement and control instrument; 42. the refrigerant recovery tower empties the air reheater.
Detailed Description
The present invention will be further described below.
The prior liquefied natural gas device comprises a refrigerant supply pipeline 1, a final-stage classifier 9, a natural gas pipeline 13 and a cold box 10, wherein the refrigerant supply pipeline 1 carries out secondary compression on mixed refrigerant and then conveys the mixed refrigerant to a refrigerant heat exchange pipeline 11 in the cold box 10 through the final-stage classifier 9, so that the natural gas in the natural gas pipeline 13 is circularly refrigerated. The specific process is that firstly, required refrigerants are respectively conveyed into a refrigerant supply pipeline 1 in proportion, an inlet balance tank 1, a refrigerant compressor 4, an interstage cooler 5, an interstage balance tank 6, a final stage refrigerant compressor 7 and a final stage cooler 8 are sequentially arranged on the refrigerant supply pipeline 1 from front to back, mixed refrigerants enter the refrigerant compressor 4, the interstage cooler 5, the interstage balance tank 6, the final stage refrigerant compressor 7 and the final stage cooler 8 through the refrigerant pipelines to be compressed into low-temperature refrigerant liquid for the second time, then the mixed refrigerants enter a refrigerant heat exchange pipeline 11 of a cold box 10 through a final stage classifier 9 in two pipelines to be refrigerated, the produced gaseous natural gas enters the cold box 10 through a natural gas pipeline 13 to be liquefied into LNG natural gas after heat exchange with the mixed refrigerants in the refrigerant heat exchange pipeline 11, the two paths of the cold box 10 are subjected to heat exchange, and then enter a circulation pipeline 12 after being converged into one pipeline, the circulation pipeline 12 is communicated with the refrigerant pipeline, and the mixed refrigerants which are returned back flow into the inlet balance tank 1 to be compressed into the natural gas for refrigerating again.
Examples: referring to fig. 1 and 2, the mixed refrigerant recovery system of the liquefied natural gas device is characterized in that a refrigerant recovery tower 15 is additionally arranged on the basis of an existing refrigerant supply pipeline 1, a final-stage classifier 9, a natural gas pipeline 13 and a cold box 10, a refrigerant recovery tower reboiler 24, a refrigerant cooler, a refrigerant recovery tower emptying air reheater 42, a refrigerant recovery tower condenser 17 and a refrigerant recovery tower reflux tank 18 are additionally arranged, and a new liquefied natural gas device production system is additionally arranged, so that the system not only can separate, recover and recycle three refrigerants with higher values, namely mixed isopentane, propane and ethylene, but also can realize great improvement of economy. And the method of directly shutting down the prior device is changed, so that the slow stopping of the liquefied natural gas device is realized, and the problems of overvoltage damage of equipment and the like caused by sudden stopping of the device are solved. The invention adopts a circulating recovery mode to recover the refrigerants one by one, and gradually reduces the supply quantity and the refrigerating capacity of the natural gas along with the recovery of the refrigerants, thereby realizing the slow stop of the device. Because the device realizes slow stopping, the refrigerant is recycled in a stepwise manner, and the refrigerant does not need to be wasted by emptying. As the device realizes slow stopping, the load is gradually reduced, the influence on other production system equipment is small, and the operation safety of the device equipment is greatly improved.
The concrete scheme is that a refrigerant recovery tower 15 is additionally arranged, a refrigerant feed pipe 14 way is arranged in the middle of the refrigerant recovery tower 15, a refrigerant discharge pipeline 16 is arranged at the top of the refrigerant recovery tower 15, a refrigerant recovery pipeline 27 is arranged at the bottom of the refrigerant recovery tower 15, the final classifier 9 is communicated with the inside of the refrigerant recovery tower 15 through the refrigerant feed pipe 14 way, the refrigerant discharge pipeline 16 is communicated with the refrigerant supply pipeline 1, a condensing loop is arranged on the refrigerant discharge pipeline 16, a heating loop 23 is arranged at the bottom of the refrigerant recovery tower 15, trays are arranged in the refrigerant recovery tower 15 from top to bottom at intervals, the embodiment adopts 16 layers of trays, wherein the refrigerant feed pipe 14 way is used for quantitatively introducing mixed refrigerant in a recovery device into the refrigerant recovery tower 15 when a liquefied natural gas device is ready to stop, the heating loop 23 at the bottom of the tower is used for controlling the temperature at the bottom of the refrigerant recovery tower 15, heating liquid refrigerant, controlling the temperature at the gas outlet of the refrigerant recovery tower 15 through the condensing loop at the top of the tower, condensing gaseous refrigerant, circulating uncondensed gaseous refrigerant into the inlet balance tank 1 through the refrigerant discharging pipeline 16 for re-compression and circulation into the refrigerant recovery tower 15, and refluxing the condensed liquid to the bottom of the tower for re-heating and vaporization, wherein the refrigerant recovery tower 15 is internally provided with reciprocating evaporation and condensation circulation, so that single refrigerant in the mixture refrigeration is completely separated, and a single refrigerant product with required purity is obtained, the refrigerant recovery pipelines 27 are provided with multiple paths, each path of refrigerant recovery pipeline 27 is respectively connected to a corresponding refrigerant storage tank, single refrigerant storage is realized, and other refrigerants can be directly proportioned for use in the next production. The problem that the mixed refrigerant in the liquefied natural gas device is difficult to proportioning again for use after the liquefied natural gas device is stopped is solved.
Description of the working principle of the refrigerant recovery column 15 (taking isopentane recovery as an example):
the refrigerant recovery column reboiler 24 at the bottom of the column was heated to 128 c using heat transfer oil to partially vaporize the liquid at the bottom of the refrigerant recovery column 15, with the vapor rising up the column and the remaining isopentane as the bottom product. The refrigerant recovery column condenser 17 at the top of the column is cooled to 15 ℃ by refrigerant throttling refrigeration to partially condense and liquefy the gas at the top of the column, the condensed liquid flows back along the column, and the remaining components (nitrogen, methane, ethylene and propane) are returned from the top of the column to the inlet balance tank 1 for continuous circulation.
The mixed refrigerant material of nitrogen, methane, ethylene, propane and isopentane enters the middle part of the tower, liquid in the feed and liquid from the upper tower section descend along the tower, and vapor in the feed and vapor from the lower tower section ascend along the tower. In the whole rectifying tower, the vapor phase and the liquid phase are in countercurrent contact for carrying out phase mass transfer, volatile components (nitrogen, methane, ethylene and propane) in the liquid phase enter a vapor phase, the difficult volatile components in the vapor phase enter a liquid phase (isopentane) to form a constant boiling substance system, the volatile components (nitrogen, methane, ethylene and propane) at the top of the tower are volatile components, and a tower bottom product is the difficult volatile components (isopentane) with high purity. The tower section above the feed inlet is used for further concentrating volatile components in the rising vapor and is called a rectifying section; and a tower section below the feed inlet is used for extracting volatile components from the descending liquid and is called stripping section. The combination of the two operations allows for more complete separation of the isopentane component of the liquid mixture to produce the desired purity product.
Related data: the liquid phase components of each layer of tower plates are shown in fig. 3, the gas phase components of each layer of tower plates are shown in fig. 4, and the temperature of each layer of tower plates is shown in fig. 5. As can be seen from fig. 3 and 4, the recovery purity of isopentane reaches 99% and reaches the recovery standard completely in the refrigerant recovery column 15 under the process parameters of fig. 5.
In order to solve the problem of condensation reflux of the mixed refrigerant at the top of the tower and realize the temperature control of the air outlet at the top of the tower, the condensation loop comprises a refrigerant recovery tower condenser 17 and a refrigerant recovery tower reflux tank 18, the refrigerant recovery tower condenser 17 and the refrigerant recovery tower reflux tank 18 are arranged on a refrigerant discharge pipeline 16, the gas mixed refrigerant in the refrigerant discharge pipeline 16 and the refrigerant recovery tower condenser 17 exchange heat and condense and then enter the refrigerant recovery tower reflux tank 18, a reflux pipeline 20 is arranged on the refrigerant recovery tower reflux tank 18 and returns to the tower through the reflux pipeline 20 for re-gasification purification, a refrigeration pipeline 19 arranged on the refrigerant recovery tower condenser 17 is communicated with a refrigerant heat exchange pipeline 11 of a cold box 10, the refrigerant recovery tower condenser 17 directly references the refrigerant in the cold box 10 through the refrigeration pipeline 19 and can perform refrigeration without external energy, a refrigerant quantity control valve 21 is arranged on the refrigeration pipeline 19, the control of the temperature of the refrigerant recovery tower can be realized, the temperature of the air outlet is realized, a switching valve 22 is arranged between the refrigeration pipeline 19 and the refrigerant heat exchange pipeline 11, and the switching valve 19 is realized between the refrigeration pipeline 11 and the refrigeration pipeline 11.
In order to solve the problem of controlling the heating temperature of the mixed refrigerant at the bottom of the tower, a heating loop 23 at the bottom of the refrigerant recovery tower 15 is provided with a refrigerant recovery tower reboiler 24, the refrigerant at the bottom of the tower is heated and controlled by the refrigerant recovery tower reboiler 24, so that the temperature at the bottom of the tower is regulated and controlled, the refrigerant recovery tower reboiler 24 is provided with a heat-conducting oil pipeline 25, the heat-conducting oil pipeline 25 is provided with a refrigerant recovery tower bottom temperature control valve 26, and the heating temperature entering the refrigerant recovery tower reboiler 24 can be controlled by the refrigerant recovery tower bottom temperature control valve 26.
In order to ensure accurate temperature control of the top and the bottom of the refrigerant recovery tower 15, TIC temperature measurement and control instruments 38 are respectively arranged at the top and the bottom of the refrigerant recovery tower, and the TIC temperature measurement and control instruments 38 are respectively connected with the refrigerant recovery tower top temperature control valve 21 and the refrigerant recovery tower bottom temperature control valve 26 in an electric signal manner. The temperature of the top and the bottom of the tower can be precisely controlled by the TIC temperature measurement and control instrument 38, so that the temperatures of the top and the bottom of the tower are ensured to be within a specified temperature range, when the temperature of the bottom of the tower is too high, the feeding flow of the refrigerant feeding pipe 14 path can be increased, the refrigerating capacity of the refrigerating pipeline 19 of the top of the tower can be increased, the temperature of the bottom of the tower can be reduced, when the temperature of the bottom of the tower is too low, the feeding flow of the refrigerant feeding pipe 14 path can be reduced, the temperature control valve 26 of the bottom of the refrigerant recovery tower on the heat conducting oil pipeline 25 can be increased, and the heating temperature of the reboiler 24 of the refrigerant recovery tower can be increased.
The cold agent feeding pipe 14 is provided with a cold agent recovery tower feeding valve 36, the cold agent feeding pipe 14 is provided with a FIA flow measurement and control instrument 37, the FIA flow measurement and control instrument 37 is in electrical signal connection with the cold agent recovery tower feeding valve 36, and the feeding amount entering the cold agent recovery tower 15 can be accurately regulated and controlled through the FIA flow measurement and control instrument 37 and the cold agent recovery tower feeding valve 36; the refrigerant discharging pipeline 16 is provided with a refrigerant recovery tower vent valve 40 and a refrigerant recovery tower vent air reheater 42, the refrigerant discharging pipeline 16 is also provided with a PIA pressure measurement and control instrument 41, the PIA pressure measurement and control instrument 41 is electrically connected with the refrigerant recovery tower vent valve 40, and the pressure of the refrigerant recovery tower vent valve 40 is controlled within 0.8-1.4 MPa, so that the product purity of each recovered refrigerant can be ensured within a set temperature range within 0.8-1.4 MPa to meet the requirements due to insufficient refrigeration capacity caused by too high tower pressure which is unfavorable for refrigerant separation. The refrigerant recovery tower vent air reheater 42 can heat uncondensed gas to 5 ℃, and the refrigerant recovery tower vent air reheater 42 is additionally arranged to meet the operating temperature requirement of the refrigerant compressor 4, so that the recovered refrigerant can be put into circulation again. The refrigerant recovery pipeline 27 is provided with a liquid level control valve of the refrigerant recovery tower 15, the refrigerant recovery tower 15 is provided with an LIC liquid level measurement and control instrument 39, the LIC liquid level measurement and control instrument 39 is electrically connected with the liquid level control valve of the refrigerant recovery tower 15, and purified refrigerant is recovered through the LIC liquid level measurement and control instrument 39 and the liquid level control valve of the refrigerant recovery tower 15.
The refrigerant recovery pipeline 27 is divided into an isopentane recovery pipeline 29, a propane recovery pipeline 30 and an ethylene recovery pipeline 31, the corresponding refrigerant storage tanks are an isopentane storage tank 32, a propane storage tank 33 and an ethylene storage tank 34, and the isopentane recovery pipeline 29, the propane recovery pipeline 30 and the ethylene recovery pipeline 31 are respectively connected to the corresponding refrigerant storage tanks, so that independent storage of isopentane, propane and ethylene is realized.
The isopentane recovery pipeline 29 and the propane recovery pipeline 30 are provided with a refrigerant cooler 35; the ethylene recovery pipeline 31 enters the corresponding refrigerant storage tank after being cooled by the cold box 10, and the conventional refrigerant cooler 35 cannot be cooled to-128 ℃ because the temperature of ethylene to be cooled is low, so that the ethylene recovery pipeline is designed to be led into the cold box 10, and the temperature of the cold box 10 is fully utilized, so that the cooling requirement of ethylene is met.
The isopentane recovery pipeline 29, the propane recovery pipeline 30 and the ethylene recovery pipeline 31 are respectively provided with a refrigerant storage tank feeding valve, and the refrigerant storage tank feeding valves are used for controlling feeding in the storage tanks; the refrigerant storage tanks are provided with LIC liquid level measurement and control instruments 39, and the LIC liquid level measurement and control instruments 39 perform liquid level detection and warning; the refrigerant storage tanks are respectively communicated with the refrigerant supply pipeline 1 through supply pipelines, and the supply pipelines are respectively provided with control valves for controlling the supply of the refrigerant. The isopentane recovery line 29, the propane recovery line 30 and the ethylene recovery line 31 may be partially shared, as in fig. 1, and although a small amount of other refrigerant remains in part of the lines during recovery, the remaining ratio is small for the entire recovery amount and the effect is not great. Or three completely independent pipelines can be used for independent conveying, so that other refrigerants are not remained in the recovery process, but the cost of the valves and the pipelines is correspondingly increased.
The outlet of the refrigerant heat exchange pipeline 11 of the cold box 10 is connected with a circulation pipeline 12, the circulation pipeline 12 is communicated with the refrigerant supply pipeline 1, the refrigerant after heat exchange returns to the inlet balance tank 1 through the circulation pipeline 12 and the refrigerant supply pipeline 1, the circulation pipeline 12 is provided with a switch valve, the switch valve is used for switching control of the circulation pipeline 12, the refrigerant supply pipeline 1 is provided with a gas chromatograph 2AIA, and the gas chromatograph 2 is used for detecting the refrigerant content in the circulating refrigerant.
A mixed refrigerant recovery method of a liquefied natural gas device comprises the following steps,
a. when the liquefied natural gas device needs to be stopped, a refrigerant recovery tower 15 is started, a refrigerant feeding pipe 14 and a refrigerant discharging pipeline 16 are opened, and the refrigerant recovery tower 15 is communicated with a refrigerant supply pipeline 1 to form recovery circulation;
b. the flow rate of the refrigerant entering the refrigerant recovery tower 15 is controlled through a refrigerant feeding pipe 14, the temperature of the bottom of the refrigerant recovery tower 15 is controlled through a heating loop 23 at the bottom of the tower, the condensing temperature of an outlet at the top of the tower is controlled through a condensing loop at the top of the tower, so that a tower section above a feed port of the refrigerant recovery tower 15 forms a rectifying section, the volatile components in rising vapor can be further concentrated, a tower section below the feed port of the refrigerant recovery tower 15 forms a stripping section, the volatile components can be extracted from descending liquid, and the single components in liquid mixed refrigerant are completely separated by combining the two sections of operations, so that the single refrigerant with the required purity is extracted from the mixed refrigerant;
c. according to the physical differences of different refrigerants, the separation and recovery of a single refrigerant and the slow stop of the liquefied natural gas device are realized by adopting multi-stage recovery;
three-stage recovery of three refrigerants of isopentane, propane and ethylene is adopted, and the method is as follows
In the first stage, isopentane is recovered:
180 ℃ heat conduction oil enters a reboiler 24 of the refrigerant recovery tower through a heat conduction oil pipeline 25, and the temperature of the bottom of the refrigerant recovery tower 15 is controlled to be 120-140 ℃ by controlling the amount of the supplied hot oil through a TIC temperature measurement and control instrument 38 at the bottom of the tower and a temperature control valve 26 at the bottom of the refrigerant recovery tower. Controlling the flow entering the refrigerant recovery tower 15 through a FIA flow measurement and control instrument 37 and a refrigerant recovery tower feeding valve 36, controlling the tower top temperature of the refrigerant recovery tower 15 to be 5-20 ℃ through a TIC temperature measurement and control instrument 38 at the tower top and a temperature control valve 21 at the tower top of the refrigerant recovery tower, controlling the pressure of the refrigerant recovery tower 15 to be 0.8-1.4 MPa through a PIA pressure measurement and control instrument 41 and a refrigerant recovery tower emptying valve 40, purifying isopentane condensed into liquid at the bottom of the refrigerant recovery tower 15, heating uncondensed refrigerant gas to 5 ℃ through a refrigerant recovery tower emptying air reheater 42, returning to an inlet balance tank 1 of a refrigerant compressor 4 for recycling, maintaining the device to operate until the isopentane content in circulating refrigerant is detected to be less than 0.5% by an online gas chromatograph 2, cooling the isopentane qualified in recovery to 30-40 ℃ through a cooler, and entering an isopentane refrigerant storage tank through a valve;
and in the second stage, recovering propane:
180 ℃ heat conduction oil enters a reboiler 24 of the refrigerant recovery tower through a heat conduction oil pipeline 25, and the amount of the supplied hot oil is controlled through a TIC temperature measurement and control instrument 38 at the bottom of the tower and a temperature control valve 26 at the bottom of the refrigerant recovery tower, so that the bottom temperature of the refrigerant recovery tower 15 is controlled to be 20-60 ℃. Controlling the flow entering the refrigerant recovery tower 15 through a FIA flow measurement and control instrument 37 and a refrigerant recovery tower feeding valve 36, controlling the tower top temperature of the refrigerant recovery tower 15 to be-45 to-70 ℃ through a TIC temperature measurement and control instrument 38 and a refrigerant recovery tower top temperature control valve 21, controlling the pressure of the refrigerant recovery tower 15 to be 0.8-1.4 MPa through a PIA pressure measurement and control instrument 41 and a refrigerant recovery tower emptying valve 40, purifying the propane condensed into liquid at the bottom of the refrigerant recovery tower 15, heating the uncondensed refrigerant gas to 5 ℃ through a refrigerant recovery tower emptying air reheater 42, returning the refrigerant gas to the inlet balance tank 1 of the refrigerant compressor 4 for recirculation, maintaining the device to operate until the online gas chromatograph 2 detects that the propane content in the circulating refrigerant is less than 0.5%, cooling the recovered qualified propane to 30-40 ℃ through a cooler, and entering a propane refrigerant storage tank through a valve;
and in the third stage, recovering ethylene:
180 ℃ heat conduction oil enters a reboiler 24 of the refrigerant recovery tower through a heat conduction oil pipeline 25, and the temperature of the bottom of the refrigerant recovery tower 15 is controlled to be-70 to-30 ℃ by controlling the amount of the supplied hot oil through a TIC temperature measurement and control instrument 38 at the bottom of the tower and a temperature control valve 26 at the bottom of the refrigerant recovery tower. Controlling the flow entering the refrigerant recovery tower 15 through a FIA flow measurement and control instrument 37 and a refrigerant recovery tower feeding valve 36, controlling the tower top temperature of the refrigerant recovery tower 15 to be minus 110 ℃ to minus 140 ℃ through a TIC temperature measurement and control instrument 38 and a refrigerant recovery tower top temperature control valve 21, controlling the pressure of the refrigerant recovery tower 15 to be 0.8 MPa to 1.4MPa through a PIA pressure measurement and control instrument 41 and a refrigerant recovery tower emptying valve 40, purifying ethylene condensed into liquid at the bottom of the refrigerant recovery tower 15, heating uncondensed refrigerant gas to 5 ℃ through a refrigerant recovery tower emptying air reheater 42, returning the refrigerant gas to an inlet balance tank 1 of a refrigerant compressor 4 for recycling, maintaining the device to operate until the online gas chromatograph 2 detects that the ethylene content in circulating refrigerant is less than 0.5%, cooling the ethylene qualified in recovery to minus 120 ℃ through a cooler, and entering an ethylene refrigerant storage tank through a valve;
d. the recovered single refrigerants are respectively stored into corresponding refrigerant storage tanks through refrigerant recovery pipelines 27 for the next refrigerant allocation.
The invention mainly utilizes the original equipment system, and the newly added equipment has less investment and less device investment. Pentane, propane and ethylene can be recovered independently. The waste of torch burning is reduced, and the energy saving and emission reduction effects are good. The economic index is greatly improved, for example: 50X 104Nm 3 The total amount of refrigerant in each device of the liquefied natural gas device of/d is nitrogen: 1.25t, methane: 1.4t, ethylene: 4.9t, propane: 4.3t, pentane: 12t. The total price of the refrigerant recovered by each stopping of the device (the current market price is that ethylene unit price is 1.55 ten thousand yuan/ton, propane is 1.45 ten thousand yuan/ton, pentane is 1.6 ten thousand yuan/ton), the total price of the recovered refrigerant is about 32.89 ten thousand yuan, the recycling is realized, the combustion emission is reduced, and the economic benefit is extremely huge.
The above describes the mixed refrigerant recovery system of the lng plant in detail, and specific examples are applied to illustrate the principles and embodiments of the present invention, and the above examples are only used to help understand the method and core ideas of the present invention; also, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The utility model provides a mixed refrigerant recovery system of liquefied natural gas device, includes refrigerant supply line, final stage classifier, natural gas line and cold box, after the refrigerant supply line carries out the second grade compression with mixed refrigerant, carries to the refrigerant heat exchange pipeline in the cold box through final stage classifier, its characterized in that: still include the refrigerant recovery tower, refrigerant recovery tower middle part is equipped with the refrigerant feed line, and refrigerant recovery tower top is equipped with the refrigerant ejection of compact pipeline, and refrigerant recovery tower bottom is equipped with the refrigerant recovery pipeline, last classifier passes through refrigerant feed line and the inside intercommunication of refrigerant recovery tower, refrigerant ejection of compact pipeline and refrigerant feed line's intercommunication, be equipped with the condensation circuit on the refrigerant ejection of compact pipeline, the refrigerant recovery tower bottom is equipped with the heating circuit, the refrigerant recovery pipeline has the multichannel, and every way refrigerant recovery pipeline is connected to the refrigerant storage tank that corresponds respectively, the condensation circuit includes refrigerant recovery tower condenser and refrigerant recovery tower reflux drum, refrigerant recovery tower reflux drum sets up on refrigerant ejection of compact pipeline, the refrigerant pipeline that is equipped with on the refrigerant recovery tower condenser, refrigerant pipeline and the refrigerant heat exchange pipeline intercommunication of cold box, be equipped with refrigerant recovery tower top temperature control valve on the refrigerant pipeline, be equipped with the switching valve between refrigerant pipeline and the refrigerant heat exchange pipeline, be equipped with the reboiler on the reflux drum, the refrigerant recovery tower bottom is equipped with the inside with the refrigerant recovery tower reflux drum.
2. The lng plant mixed refrigerant recovery system of claim 1, wherein: and a heat-conducting oil pipeline is arranged on the reboiler of the refrigerant recovery tower, and a temperature control valve at the bottom of the refrigerant recovery tower is arranged on the heat-conducting oil pipeline.
3. The lng plant mixed refrigerant recovery system of claim 1, wherein: a refrigerant recovery tower feeding valve is arranged on the refrigerant feeding pipeline; the refrigerant discharge pipeline is provided with a refrigerant recovery tower emptying valve and a refrigerant recovery tower emptying air reheater; the refrigerant recovery pipeline is provided with a refrigerant recovery tower liquid level control valve.
4. The lng plant mixed refrigerant recovery system of claim 1, wherein: the refrigerant recovery pipeline is divided into an isopentane recovery pipeline, a propane recovery pipeline and an ethylene recovery pipeline, the corresponding refrigerant storage tanks are an isopentane storage tank, a propane storage tank and an ethylene storage tank, and the isopentane recovery pipeline, the propane recovery pipeline and the ethylene recovery pipeline are respectively connected to the corresponding refrigerant storage tanks.
5. The lng plant mixed refrigerant recovery system of claim 4, wherein: the isopentane recovery pipeline and the propane recovery pipeline are provided with a refrigerant cooler; the ethylene recovery pipeline is cooled by the cold box and then enters the corresponding refrigerant storage tank.
6. The lng plant mixed refrigerant recovery system of claim 5, wherein: the isopentane recovery pipeline, the propane recovery pipeline and the ethylene recovery pipeline are respectively provided with a refrigerant storage tank feeding valve, the refrigerant storage tanks are respectively communicated with a refrigerant supply pipeline through supply pipelines, and the supply pipelines are respectively provided with a control valve.
7. The lng plant mixed refrigerant recovery system of claim 1, wherein: the outlet of the refrigerant heat exchange pipeline of the cold box is connected with a circulating pipeline which is communicated with a refrigerant supply pipeline, and the circulating pipeline is provided with a switch valve and a gas chromatograph.
8. The refrigerant recovery method of a mixed refrigerant recovery system of a lng plant according to claim 1, wherein: the method comprises the steps of,
a. when the liquefied natural gas device needs to be stopped, a refrigerant recovery tower is started, and a refrigerant feeding pipeline and a refrigerant discharging pipeline are started to be communicated with a refrigerant supply pipeline to form recovery circulation;
b. controlling the flow of the refrigerant entering the refrigerant recovery tower through a refrigerant feeding pipeline, controlling the temperature of the bottom of the refrigerant recovery tower through a heating loop at the bottom of the tower, controlling the condensing temperature of an outlet at the top of the tower through a condensing loop at the top of the tower, so that a rectifying section and a stripping section are formed in the refrigerant recovery tower, and the rectifying section and the stripping section enable single components in the liquid mixed refrigerant to be completely separated, and extracting the single refrigerant with the required purity from the mixed refrigerant;
c. according to the physical differences of different refrigerants, the separation and recovery of a single refrigerant and the slow stop of the liquefied natural gas device are realized by adopting multi-stage recovery;
d. the recovered single refrigerants are respectively stored into corresponding refrigerant storage tanks through refrigerant recovery pipelines so as to be used for the next blending of the refrigerants.
9. The refrigerant recovery method of a mixed refrigerant recovery system of a lng plant according to claim 8, wherein: in the step c, three refrigerants of isopentane, propane and ethylene are recovered in three stages, the method is as follows,
in the first stage, isopentane is recovered
Regulating a refrigerant feeding pipeline to control the flow of the refrigerant entering a refrigerant recovery tower, controlling the temperature at the bottom of the refrigerant recovery tower to be 120-140 ℃ through a heating loop, controlling the temperature at the outlet of the tower top to be 5-20 ℃ through a condensing loop at the tower top, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying isopentane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning the uncondensed refrigerant gas to the refrigerant feeding pipeline for recycling, maintaining the device to operate until the online gas chromatograph detects that the isopentane content in the circulating refrigerant is less than 0.5%, recovering qualified isopentane, and cooling isopentane to 30-40 ℃ in the refrigerant recovery pipeline and then entering an isopentane storage tank for storage;
and in the second stage, recovering propane:
regulating a refrigerant feeding pipeline to control the flow of the refrigerant entering a refrigerant recovery tower, controlling the temperature at the bottom of the refrigerant recovery tower to be 20-60 ℃ through a heating loop, controlling the temperature at an outlet of the tower top to be-45-70 ℃ through a condensing loop at the tower top, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying the propane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ to return to the refrigerant feeding pipeline for recirculation, maintaining the device to operate until the online gas chromatograph detects that the propane content in the circulating refrigerant is less than 0.5%, recovering qualified propane, and cooling the propane to 30-40 ℃ in the refrigerant recovery pipeline and then entering a propane storage tank for storage;
third stage, ethylene is recovered
The refrigerant feeding pipeline is regulated to control the flow rate of the refrigerant entering the refrigerant recovery tower, the temperature at the bottom of the refrigerant recovery tower is controlled to be between 70 ℃ below zero and 30 ℃ below zero through the heating loop, the temperature at the outlet of the tower top is controlled to be between 110 ℃ below zero and 140 ℃ below zero through the condensing loop at the tower top, the pressure of the refrigerant recovery tower is controlled to be between 0.8 MPa and 1.4MPa, the ethylene condensed into liquid is purified at the bottom of the refrigerant recovery tower, the uncondensed refrigerant gas is heated to 5 ℃ and returns to the refrigerant feeding pipeline for recirculation, the maintaining device operates until the online gas chromatograph detects that the ethylene content in the circulating refrigerant is less than 0.5%, and the ethylene which is recovered to be qualified is cooled to 120 ℃ in the refrigerant recovery pipeline and enters the ethylene storage tank for storage.
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