CN115164461A - Mixed refrigerant recovery system and method for liquefied natural gas device - Google Patents
Mixed refrigerant recovery system and method for liquefied natural gas device Download PDFInfo
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- CN115164461A CN115164461A CN202210736317.6A CN202210736317A CN115164461A CN 115164461 A CN115164461 A CN 115164461A CN 202210736317 A CN202210736317 A CN 202210736317A CN 115164461 A CN115164461 A CN 115164461A
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- 238000011084 recovery Methods 0.000 title claims abstract description 319
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- 238000000034 method Methods 0.000 title claims abstract description 20
- QWTDNUCVQCZILF-UHFFFAOYSA-N isopentane Chemical compound CCC(C)C QWTDNUCVQCZILF-UHFFFAOYSA-N 0.000 claims abstract description 113
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims abstract description 110
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims abstract description 60
- 239000005977 Ethylene Substances 0.000 claims abstract description 60
- AFABGHUZZDYHJO-UHFFFAOYSA-N dimethyl butane Natural products CCCC(C)C AFABGHUZZDYHJO-UHFFFAOYSA-N 0.000 claims abstract description 56
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- 239000007789 gas Substances 0.000 claims description 37
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- 238000004064 recycling Methods 0.000 claims description 15
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- 230000006872 improvement Effects 0.000 description 3
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Images
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
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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
- F25J1/003—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
Abstract
The invention discloses a mixed refrigerant recovery system and a mixed refrigerant recovery method of a liquefied natural gas device, and the mixed refrigerant recovery system comprises a refrigerant recovery tower, wherein 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, a final-stage classifier is communicated with the inside of the refrigerant recovery tower through the refrigerant feeding pipeline, the refrigerant discharging pipeline is communicated with the refrigerant feeding 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 does not influence the safe operation of the original equipment, greatly improves the operation safety of the device, realizes the independent separation and recovery of isopentane, propane and ethylene in the mixed refrigerant, reduces the emptying of the refrigerant and torch combustion, and has good energy-saving and emission-reducing effects. And the newly added equipment is few, isopentane, propane and ethylene with higher prices 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 for a liquefied natural gas device.
Background
The liquefied natural gas device is used for liquefying produced natural gas so as to be convenient for transportation and storage, the liquefied natural gas device adopts more processes at home and abroad as MRC (total mixed cycle) processes or C3+ MRC processes, the refrigerant generally adopts isoisopentane, propane, ethylene, methane and nitrogen as the refrigerant, the supply of the natural gas is directly cut off when the device is stopped every time, but the refrigerant in the liquefied natural gas device is kept in the device and continuously gasified, so that the pressure in the device is overlarge, the refrigerant can be discharged or recovered, the currently adopted refrigerant recovery scheme basically adopts a refrigerant recovery pump or a refrigerant recovery compressor, but only part of the refrigerant can be recovered, and the discharge can still be carried out. The existing device adopts a direct shutdown mode, the pressure in the equipment is too high after the natural gas supply is directly shut down, safety accidents are easy to occur, and therefore, the natural gas can only be discharged in an air mode and combusted through a torch, energy waste is caused, and the environment is influenced. 2. At present, a refrigerant recovery pump or a refrigerant recovery compressor is adopted for recovery, and incomplete refrigerant recovery exists, such as emptying of outsourcing refrigerant ethylene. 3. The refrigerant recovery pump or the refrigerant recovery compressor belongs to power equipment with large investment, but the use frequency is low, so that the economy is poor. 4. The liquefied natural gas device has requirements on the use ratio of the refrigerant, and the recovered refrigerant is mixed refrigerant, so that the refrigerant cannot be directly used in a secondary proportioning manner. 5. The recovered refrigerants isopentane, propane and 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 the separate separation, recovery and storage of isopentane, propane and ethylene.
In order to achieve the purpose, the invention adopts the technical scheme that: the utility model provides a liquefied natural gas device's mixed cryogen recovery system, includes refrigerant supply line, last stage classifier, natural gas pipeline and cold box, refrigerant supply line carries the mixed refrigerant to the refrigerant heat transfer pipeline in the cold box through last stage classifier after the second grade compression, still includes the cryogen recovery tower, cryogen recovery tower middle part is equipped with cryogen feed line, and cryogen recovery tower top is equipped with cryogen ejection of compact pipeline, and cryogen recovery tower bottom is equipped with cryogen recovery pipeline, last stage classifier passes through inside intercommunication of cryogen feed line and cryogen recovery tower, cryogen ejection of compact pipeline and refrigerant supply line's intercommunication, be equipped with condensation loop on the cryogen ejection of compact pipeline, be equipped with heating circuit at the bottom of the cryogen recovery tower, the cryogen recovery pipeline has the multichannel, and every way cryogen recovery pipeline is connected to corresponding refrigerant storage tank respectively.
Preferably, the condensing 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 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, a reflux pipeline is arranged on the refrigerant recovery tower reflux tank, and the reflux pipeline is communicated with the inside of the top of the refrigerant recovery tower.
Preferably, a reboiler of the refrigerant recovery tower is arranged on the heating loop at the bottom of the refrigerant recovery tower, a heat conduction 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 conduction oil pipeline.
Preferably, a refrigerant feeding pipeline is provided with a refrigerant recovery tower feeding valve; a refrigerant recovery tower emptying valve and a refrigerant recovery tower emptying air reheater are arranged on the refrigerant discharge pipeline; and a refrigerant recovery tower liquid level control valve is arranged on the refrigerant recovery pipeline.
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 refrigerant coolers; and the ethylene recovery pipeline enters a corresponding refrigerant storage tank after being cooled by the cold box.
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 an outlet of the refrigerant heat exchange pipeline of the cold box, the circulation pipeline is communicated with a refrigerant supply pipeline, a switch valve is arranged on the circulation pipeline, and a gas chromatograph is arranged on the refrigerant supply pipeline.
Preferably, the refrigerant recovery tower is internally provided with tower plates at intervals from top to bottom.
A method for recovering mixed refrigerant of liquefied natural gas device comprises the following steps,
a. when the liquefied natural gas device needs to be shut down, starting the refrigerant recovery tower, and opening a refrigerant feeding pipeline and a refrigerant discharging pipeline to be communicated with a refrigerant supply pipeline to form a recovery cycle;
b. controlling the flow rate of a refrigerant entering a refrigerant recovery tower through a refrigerant feeding pipeline, controlling the temperature at the bottom of the refrigerant recovery tower through a heating loop at the bottom of the tower, and controlling the condensation temperature at an outlet at the top of the tower through a condensation loop at the top of the tower, so that a rectification section and a stripping section are formed in the refrigerant recovery tower, the rectification section and the stripping section enable single components in a liquid mixed refrigerant to be separated relatively completely, and a single refrigerant with required purity is extracted from the mixed refrigerant;
c. according to different physical properties of different refrigerants, multi-stage recovery is adopted to realize separation and recovery of a single refrigerant and slow stop of a liquefied natural gas device;
d. the recovered single refrigerant is respectively stored in the corresponding refrigerant storage tanks through the refrigerant recovery pipelines so as to be used for the allocation of the refrigerant next time.
Preferably, in step c, three refrigerants, i-pentane, propane and ethylene, are recovered in a three-stage manner by the following method,
first stage, recovering isopentane
Adjusting a refrigerant feeding pipeline to control the flow of refrigerant entering a refrigerant recovery tower, controlling the temperature of the bottom of the refrigerant recovery tower to be 120-140 ℃ through a heating loop, controlling the temperature of an outlet at the top of the tower to be 5-20 ℃ through a condensing loop at the top of the tower, 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 ℃, returning the uncondensed refrigerant gas to a refrigerant supply pipeline for recycling again, maintaining the device to operate until an online gas chromatograph detects that the content of isopentane in the circulating refrigerant is less than 0.5%, recycling qualified isopentane, cooling the isopentane in the refrigerant recovery pipeline to 30-40 ℃, and then entering an isopentane storage tank for storage;
second stage, recovering propane
Adjusting a refrigerant feeding pipeline to control the flow of 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 at the top of the tower to be-45-70 ℃ through a condensing loop at the top of the tower, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying propane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning to a refrigerant supply pipeline for recycling, maintaining the operation of a device until an online gas chromatograph detects that the content of propane in the circulating refrigerant is less than 0.5 percent, recovering qualified propane, cooling the propane in the refrigerant recovery pipeline to 30-40 ℃, and then entering a propane storage tank for storage;
in the third stage, ethylene is recovered
Adjusting a refrigerant feeding pipeline to control the flow of refrigerant entering a refrigerant recovery tower, controlling the temperature of the bottom of the refrigerant recovery tower to be-70 to-30 ℃ through a heating loop, controlling the temperature of an outlet at the top of the tower to be-110 to-140 ℃ through a condensing loop at the top of the tower, controlling the pressure of the refrigerant recovery tower to be 0.8 to 1.4MPa, purifying ethylene condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning to a refrigerant supply pipeline for recycling again, maintaining the operation of a device until an online gas chromatograph detects that the ethylene content in the circulating refrigerant is less than 0.5 percent, recycling qualified ethylene, and after the ethylene is cooled to-120 ℃ in the refrigerant recovery pipeline, feeding the ethylene into an ethylene storage tank for storage.
Compared with the prior art, the invention has the advantages that: the invention, through the technical innovation and improvement aiming at the original liquefied natural gas device, not only does not influence the safe operation of the original equipment, but also greatly improves the safety of the operation of the device, realizes the independent separation and recovery of isopentane, propane and ethylene in the mixed refrigerant, reduces the emptying of the refrigerant and the combustion of a torch, and has good effects of energy conservation and emission reduction. And the newly-added equipment is few, the installation and the transformation are easy, and the device investment is low. Can completely recover isopentane, propane and ethylene with higher prices, and has higher economic value. Is suitable for large-scale popularization and use.
A new liquefied natural gas device production system is designed, and the system can realize separate separation and recycling of three refrigerants with higher values, namely mixed isopentane, propane and ethylene, and realize great improvement of economy. And the mode that the former device is directly shut down is changed, the slow stop of the liquefied natural gas device is realized, and the problems of equipment overpressure damage and the like caused by sudden stop of the device are solved. The invention adopts a circulating recovery mode to recover the high purity of the refrigerant one by one, and the supply amount and the refrigerating capacity of the natural gas are gradually reduced along with the recovery of the refrigerant, thereby realizing the slow stop of the device. Because the device realizes the slow stop, the refrigerant is gradually recovered in stages, and the refrigerant does not need to be discharged to the outside again to cause resource waste. Because the device realizes the slow stop, 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 also greatly improved.
Drawings
FIG. 1 is an overall system schematic of the present invention;
FIG. 2 is a system schematic of a refrigerant recovery column of the present invention;
FIG. 3 is the liquid phase composition parameters of each tray when the refrigerant of the present invention is returned to isopentane;
FIG. 4 is the gas phase composition parameters of each tray when the refrigerant of the present invention is returned to isopentane;
FIG. 5 is a graph showing the temperature parameters of each tray when the refrigerant of the present invention is returned to isopentane.
In fig. 1, a refrigerant supply line; 2. a gas chromatograph; 3. an inlet balancing tank; 4. a refrigerant compressor; 5. an interstage cooler; 6. an interstage surge tank; 7. a final refrigerant compressor; 8. a final stage cooler; 9. a final classifier; 10. a cold box; 11. a refrigerant heat exchange line; 12. a circulation line; 13. a natural gas pipeline; 14. a cryogen feed pipe; 15. a refrigerant recovery tower; 16. a refrigerant discharge line; 17. a refrigerant recovery tower condenser; 18. a refrigerant recovery tower reflux drum; 19. a refrigeration circuit; 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 tower reboiler; 25. a heat conductive oil pipeline; 26. a temperature control valve at the bottom of the refrigerant recovery tower; 27. a refrigerant recovery line; 28. a refrigerant recovery tower liquid level control valve; 29. an isopentane recovery pipeline; 30. a propane recovery line; 31. an ethylene recovery line; 32. an isopentane storage tank; 33. a propane tank; 34. an ethylene storage tank; 35. a refrigerant cooler; 36. a refrigerant recovery column feed valve; 37. a FIA flow measurement and control instrument; 38. TIC temperature instrumentation; 39. an LIC liquid level measurement and control instrument; 40. an emptying valve of the refrigerant recovery tower; 41. a PIA pressure measurement and control instrument; 42. the refrigerant recovery tower is used for emptying the air reheater.
Detailed Description
The present invention will be further explained below.
The conventional 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 two-stage compression on a 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 subjected to circulating refrigeration. The method comprises the following steps of firstly, respectively conveying required refrigerants into a refrigerant supply pipeline 1 in proportion, sequentially arranging 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 on the refrigerant supply pipeline 1 from front to back, enabling mixed refrigerants to 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 refrigerant pipelines to be secondarily compressed into low-temperature refrigerant liquid, enabling the low-temperature refrigerant liquid to enter a refrigerant heat exchange pipeline 11 of a cold box 10 through a final-stage classifier 9 in two pipelines to be refrigerated, enabling produced gaseous natural gas to enter the cold box 10 through a natural gas pipeline 13, carrying out heat exchange with the mixed refrigerants in the refrigerant heat exchange pipeline 11 and then liquefying the natural gas to be output, enabling the two refrigerants entering the cold box 10 to enter a circulating pipeline 12 after completing heat exchange in the refrigerant heat exchange pipeline 11 and converging into one pipeline, outputting the cold box 10 from the LNG, enabling the circulating pipeline 12 to be communicated with the refrigerant pipelines, enabling the returned mixed refrigerants to flow back into the inlet balance tank 1, and compressing the natural gas for refrigeration again.
Example (b): the mixed refrigerant recovery system of the liquefied natural gas device disclosed by the invention is additionally provided with a refrigerant recovery tower 15, 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 on the basis of the existing refrigerant supply pipeline 1, a final classifier 9, a natural gas pipeline 13 and a cold box 10, and a novel liquefied natural gas device production system is additionally arranged and designed, so that the system can be used for realizing the independent separation, recovery and reutilization of three refrigerants with higher values, namely mixed isopentane, propane and ethylene, and realizing the huge improvement of the economy. And the mode that the former device is directly shut down is changed, the slow stop of the liquefied natural gas device is realized, and the problems of equipment overpressure damage and the like caused by sudden stop of the device are solved. The invention adopts a circulating recovery mode to recover the high purity of the refrigerant one by one, and the supply amount and the refrigerating capacity of the natural gas are gradually reduced along with the recovery of the refrigerant, thereby realizing the slow stop of the device. Because the device realizes the slow stop, the refrigerant is gradually recovered in stages, and the refrigerant does not need to be discharged to the outside again to cause waste. Because the device realizes the slow stop, 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.
The specific scheme is that a refrigerant recovery tower 15 is additionally arranged, a refrigerant feeding pipe 14 is arranged in the middle of the refrigerant recovery tower 15, a refrigerant discharging 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, a last-stage classifier 9 is communicated with the inside of the refrigerant recovery tower 15 through the refrigerant feeding pipe 14, the refrigerant discharging pipeline 16 is communicated with a refrigerant supply pipeline 1, a condensation loop is arranged on the refrigerant discharging pipeline 16, a heating loop 23 is arranged at the bottom of the refrigerant recovery tower 15, tower plates are arranged in the refrigerant recovery tower 15 at intervals from top to bottom, in the embodiment, 16 layers of tower plates are adopted, when a liquefied natural gas device is ready to stop, the refrigerant feeding pipe 14 is used for recovering mixed refrigerants in the device, the mixed refrigerants are quantitatively led into the recovery tower 15, the heating loop 23 of the refrigerant at the bottom of the tower is used for controlling the temperature of the refrigerant recovery tower 15 from top of the tower, liquid refrigerants are heated, the temperature of the refrigerant recovery tower 15 is controlled through the condensation loop at the gas outlet of the refrigerant recovery tower top, gaseous refrigerants are condensed, the uncondensed gaseous refrigerants are circulated to the inlet balance tank 1 through the refrigerant discharging pipeline 16 to be compressed and circulated to be recycled to the refrigerant recovery tank, the single refrigerant recovery tank 15 is used for recovering refrigerant recovery, the single refrigerant recovery of the single refrigerant recovery refrigerant, the single refrigerant, and the single refrigerant recovery tank, the single refrigerant recovery tank is achieved after the single refrigerant recovery, and the single refrigerant recovery tank. The problem of liquefied natural gas device shut down the back internal mixed refrigerant of being difficult to match again and use is solved.
The working principle of the refrigerant recovery tower 15 is illustrated (taking the recovery of isopentane as an example):
a refrigerant recovery tower reboiler 24 positioned at the tower bottom is heated to 128 ℃ by adopting heat conducting oil, so that the liquid part at the bottom of the refrigerant recovery tower 15 is vaporized, the vapor rises along the tower, and the rest isopentane is taken as a tower bottom product. And a refrigerant recovery tower condenser 17 positioned at the top of the tower is cooled to 15 ℃ by refrigerant throttling refrigeration, so that the gas at the top of the tower is partially condensed and liquefied, the condensed liquid flows back along the tower, and the rest components (nitrogen, methane, ethylene and propane) return to the inlet balance tank 1 from the top of the tower to continue circulation.
The mixed refrigerant material of nitrogen, methane, ethylene, propane and isopentane enters the middle part of the tower, the liquid in the feed and the liquid from the upper tower section descend along the tower, and the vapor in the feed and the vapor from the lower tower section ascend along the tower. In the whole rectifying tower, gas-liquid two phases are in countercurrent contact to carry out interphase mass transfer, volatile components (nitrogen, methane, ethylene and propane) in the liquid phase enter a gas phase, nonvolatile components in the gas phase are transferred into a liquid phase (isopentane) to form a system of an azeotrope, the volatile components (nitrogen, methane, ethylene and propane) are arranged at the top of the tower, and the high-purity nonvolatile components (isopentane) are arranged at the bottom of the tower. The tower section above the feed inlet is used for further concentrating volatile components in the ascending vapor and is called as a rectifying section; the section of the column below the feed opening, which extracts the volatile components from the descending liquid, is referred to as the stripping section. The combination of the two stages of operation allows for more complete separation of the isopentane component of the liquid mixture to produce a product of desired purity.
And (3) related data: the liquid phase composition of each tray is shown in FIG. 3, the gas phase composition of each tray is shown in FIG. 4, and the temperature of each tray is shown in FIG. 5. As can be seen from fig. 3 and 4, the recovery purity of isopentane in the refrigerant recovery tower 15 reaches 99% under the process parameters of fig. 5, and the recovery standard is completely reached.
In order to solve the problem of condensation reflux of mixed refrigerant at the top of the tower and realize temperature control of an 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 enters the refrigerant recovery tower reflux tank 18 after heat exchange and condensation with the refrigerant recovery tower condenser 17, 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 and purification, a refrigeration pipeline 19 is arranged on the refrigerant recovery tower condenser 17, the refrigeration pipeline 19 is communicated with a refrigerant heat exchange pipeline 11 of the cold box 10, the refrigerant recovery tower condenser 17 directly uses the refrigerant in the cold box 10 for refrigeration through the refrigeration pipeline 19 without additional energy, a refrigerant recovery tower top temperature control valve 21 is arranged on the refrigeration pipeline 19 and can control the refrigerating capacity to realize temperature control of the outlet at the top of the tower, and a switching valve 22 is arranged between the refrigeration pipeline 19 and the refrigerant heat exchange pipeline 11.
In order to solve the problem of controlling the heating temperature of the mixed refrigerant at the bottom of the tower, a reboiler 24 of the refrigerant recovery tower is arranged on a heating loop 23 at the bottom of the refrigerant recovery tower 15, the refrigerant at the bottom of the tower is heated and controlled by the reboiler 24 of the refrigerant recovery tower to realize the temperature control at the bottom of the tower, a heat conduction oil pipeline 25 is arranged on the reboiler 24 of the refrigerant recovery tower, a temperature control valve 26 at the bottom of the refrigerant recovery tower is arranged on the heat conduction oil pipeline 25, and the heating temperature entering the reboiler 24 of the refrigerant recovery tower can be controlled by the temperature control valve 26 at the bottom of the refrigerant recovery tower.
In order to ensure accurate temperature control of the top and the bottom of the tower, TIC temperature measuring and controlling instruments 38 are respectively arranged at the top and the bottom of the refrigerant recovery tower 15, and the TIC temperature measuring and controlling instruments 38 are respectively in electric signal connection with the top temperature control valve 21 of the refrigerant recovery tower and the bottom temperature control valve 26 of the refrigerant recovery tower. The temperature of the tower top and the tower bottom can be accurately controlled through the TIC temperature measuring and controlling instrument 38, so that the temperature of the tower top and the tower bottom is ensured to be in a specified temperature interval, when the temperature of the tower bottom is overhigh, the feeding flow of a refrigerant feeding pipe 14 path can be increased, the refrigerating capacity of a refrigerating pipeline 19 at the tower top is increased, the temperature of the tower bottom is reduced, when the temperature of the tower bottom is overlow, the feeding flow of the refrigerant feeding pipe 14 path can be reduced, a refrigerant recovery tower bottom temperature control valve 26 on a heat conducting oil pipeline 25 can be increased, and the heating temperature of a refrigerant recovery tower reboiler 24 is increased.
A refrigerant recovery tower feed valve 36 is arranged on the refrigerant feed pipe 14, an FIA flow measurement and control instrument 37 is arranged on the refrigerant feed pipe 14, the FIA flow measurement and control instrument 37 is in electrical signal connection with the refrigerant recovery tower feed valve 36, and the feed quantity entering the refrigerant recovery tower 15 can be accurately regulated and controlled through the FIA flow measurement and control instrument 37 and the refrigerant recovery tower feed valve 36; the device is characterized in that a refrigerant recovery tower emptying valve 40 and a refrigerant recovery tower emptying air reheater 42 are arranged on the refrigerant discharging pipeline 16, a PIA pressure measurement and control instrument 41 is further arranged on the refrigerant discharging pipeline 16, the PIA pressure measurement and control instrument 41 is in electrical signal connection with the refrigerant recovery tower emptying valve 40, refrigeration capacity is insufficient due to too high tower pressure and too low tower pressure, pressure in the refrigerant recovery tower 15 can be accurately controlled within 0.8-1.4 MPa through the PIA pressure measurement and control instrument 41 and the refrigerant recovery tower emptying valve 40, and product purity of each recovered refrigerant can be guaranteed within a set temperature range within 0.8-1.4 MPa. The refrigerant recovery tower vent air recuperator 42 can heat the uncondensed gas to 5 ℃, and the refrigerant recovery tower vent air recuperator 42 is added to meet the operating temperature requirement of the refrigerant compressor 4, so that the recovered refrigerant can be put into circulation again. The liquid level control valve of the refrigerant recovery tower 15 is arranged on the refrigerant recovery pipeline 27, the LIC liquid level measuring and controlling instrument 39 is arranged on the refrigerant recovery tower 15, the LIC liquid level measuring and controlling instrument 39 is in electrical signal connection with the liquid level control valve of the refrigerant recovery tower 15, and purified refrigerant is recovered through the LIC liquid level measuring and controlling 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 the independent storage of isopentane, propane and ethylene is realized.
The isopentane recovery pipeline 29 and the propane recovery pipeline 30 are provided with refrigerant coolers 35; the ethylene recovery pipeline 31 enters the corresponding refrigerant storage tank after being cooled by the cold box 10, and because the temperature of ethylene to be cooled is lower and the conventional refrigerant cooler 35 cannot be cooled to minus 128 ℃, the ethylene recovery pipeline is designed to be introduced into the cold box 10 in the scheme, and the temperature of the cold box 10 is fully utilized, so that the cooling requirement of ethylene is met.
Refrigerant storage tank feeding valves are arranged on the isopentane recovery pipeline 29, the propane recovery pipeline 30 and the ethylene recovery pipeline 31, and the refrigerant storage tank feeding valves are used for controlling feeding in the storage tanks; the refrigerant storage tanks are all provided with an LIC liquid level measuring and controlling instrument 39, and the LIC liquid level measuring and controlling instrument 39 is used for carrying out liquid level detection warning; the refrigerant storage tanks are respectively communicated with the refrigerant supply lines 1 through supply pipes, and the supply pipes are respectively provided with control valves for controlling the supply of the refrigerant. The isopentane recycle line 29, the propane recycle line 30 and the ethylene recycle line 31 may be partially shared, as shown in fig. 1, although a small amount of other refrigerants may remain in some lines during the recycle process, the remaining ratio is small for the whole recycle amount, and the influence is not great. Or three completely independent pipelines can be used for independent conveying, so that other refrigerants cannot remain in the recovery process, but the cost of the valves and the pipelines is correspondingly increased.
The outlet of a refrigerant heat exchange pipeline 11 of the cold box 10 is connected with a circulating pipeline 12, the circulating pipeline 12 is communicated with a refrigerant supply pipeline 1, the refrigerant after heat exchange returns to an inlet balance tank 1 through the circulating pipeline 12 and the refrigerant supply pipeline 1, the circulating pipeline 12 is provided with a switch valve, the switch valve is used for controlling the on-off of the circulating pipeline 12, the refrigerant supply pipeline 1 is provided with a gas chromatograph 2AIA, and the gas chromatograph 2 is used for detecting the content of the refrigerant in the circulating refrigerant.
A method for recovering mixed refrigerant of liquefied natural gas device comprises the following steps,
a. when the liquefied natural gas device needs to be shut down, the refrigerant recovery tower 15 is started, the refrigerant feeding pipe 14 and the refrigerant discharging pipe 16 are opened, and the refrigerant recovery tower 15 is communicated with the refrigerant supply pipe 1 to form a recovery cycle;
b. the flow rate of refrigerant entering a refrigerant recovery tower 15 is controlled through a refrigerant feeding pipe 14, the temperature at the bottom of the refrigerant recovery tower 15 is controlled through a heating loop 23 at the bottom of the tower, the condensing temperature at an outlet at the top of the tower is controlled through a condensing loop at the top of the tower, so that a rectifying section is formed at a tower section above a feed inlet of the refrigerant recovery tower 15, volatile components in ascending vapor can be further concentrated, a stripping section is formed at a tower section below the feed inlet of the refrigerant recovery tower 15, the volatile components can be extracted from descending liquid, and the single component in the liquid mixed refrigerant is completely separated through the combination of two sections of operation, so that the single refrigerant with the required purity is extracted from the mixed refrigerant;
c. according to different physical properties of different refrigerants, multi-stage recovery is adopted to realize separation and recovery of a single refrigerant and slow stop of a liquefied natural gas device;
three refrigerants of isopentane, propane and ethylene are recovered by adopting a three-stage mode, and the method is as follows
First stage, recovery of isopentane:
the heat conducting oil with the temperature of 180 ℃ enters a reboiler 24 of the refrigerant recovery tower through a heat conducting oil pipeline 25, and the temperature of the bottom of the refrigerant recovery tower 15 is controlled to be 120-140 ℃ by controlling the supplied hot oil through a TIC temperature measuring and controlling 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 an FIA flow measuring and controlling instrument 37 and a refrigerant recovery tower feed valve 36, controlling the tower top temperature of the refrigerant recovery tower 15 to be 5-20 ℃ through a TIC temperature measuring and controlling instrument 38 and a refrigerant recovery tower top temperature control valve 21 on the tower top, controlling the pressure of the refrigerant recovery tower 15 to be 0.8-1.4 MPa through a PIA pressure measuring and controlling instrument 41 and a refrigerant recovery tower emptying valve 40, purifying the condensed isopentane 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 regenerator 42, returning the refrigerant gas to an inlet balance tank 1 of a refrigerant compressor 4 for recycling again, maintaining the operation of the device until an online gas chromatograph 2 detects that the content of isopentane in the circulating refrigerant is less than 0.5%, cooling the recycled qualified isopentane to 30-40 ℃ through a cooler, and feeding the isopentane refrigerant storage tank through a valve;
second stage, recovery of propane:
the heat conducting oil with the temperature of 180 ℃ enters a reboiler 24 of the refrigerant recovery tower through a heat conducting oil pipeline 25, and the supplied heat oil is controlled through a TIC temperature measuring and controlling 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 temperature of the bottom of the refrigerant recovery tower 15 is controlled to be 20-60 ℃. Controlling the flow entering the refrigerant recovery tower 15 through an FIA flow measuring and controlling 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 measuring and controlling instrument 38 and a refrigerant recovery tower top temperature control valve 21 on the tower top, controlling the pressure of the refrigerant recovery tower 15 to be 0.8 to 1.4MPa through a PIA pressure measuring and controlling instrument 41 and a refrigerant recovery tower emptying valve 40, purifying the condensed liquid propane at the bottom of the refrigerant recovery tower 15, heating the uncondensed refrigerant gas to 5 ℃ through a refrigerant recovery tower emptying air regenerator 42, returning the refrigerant gas to an inlet balance tank 1 of a refrigerant compressor 4 for recycling, maintaining the operation of a device until the online gas chromatograph 2 detects that the content of propane in the circulating refrigerant is less than 0.5%, cooling the recycled qualified propane to 30 to 40 ℃ through a cooler, and feeding the propane into a propane refrigerant storage tank through a valve;
in the third stage, ethylene recovery:
the heat conducting oil with the temperature of 180 ℃ enters a reboiler 24 of the refrigerant recovery tower through a heat conducting 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 supplied heat oil through a TIC temperature measuring and controlling 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 an FIA flow measuring and controlling instrument 37 and a refrigerant recovery tower feeding valve 36, controlling the tower top temperature of the refrigerant recovery tower 15 to be-110 to-140 ℃ through a TIC temperature measuring and controlling instrument 38 and a refrigerant recovery tower top temperature control valve 21 on the tower top, controlling the pressure of the refrigerant recovery tower 15 to be 0.8 to 1.4MPa through a PIA pressure measuring and controlling 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 recuperator 42, returning the refrigerant gas to an inlet balance tank 1 of a refrigerant compressor 4 for recycling, maintaining the operation of a device until the content of ethylene in the circulating refrigerant is detected to be less than 0.5% by an online gas chromatograph 2, cooling the recycled qualified ethylene to-120 ℃ through a cooler, and feeding the ethylene refrigerant into an ethylene storage tank through a valve;
d. the single recovered refrigerant is stored in the corresponding refrigerant storage tanks through the refrigerant recovery pipelines 27 for the next refrigerant allocation.
The invention mainly utilizes the original equipment system, has less newly added equipment and less equipment investment. Can independently recover pentane, propane and ethylene. The waste of torch combustion is reduced, and the energy-saving and emission-reducing effects are good. Economic indexes are greatly improved, such as: one 50X 104Nm 3 The total amount of coolant in each liquefied natural gas device of the/d is as follows: 1.25t, methane: 1.4t, ethylene: 4.9t, propane: 4.3t, pentane: 12t. The total price of the recovered refrigerants is about 32.89 ten thousand yuan, thereby realizing the recycling, reducing the combustion emission and having extremely great economic benefit.
The mixed refrigerant recovery system of the lng plant according to the present invention is described in detail, and the principle and the embodiment of the present invention are explained herein by using specific examples, and the description of the above examples is only used to help understanding the method and the core concept of the present invention; while the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The utility model provides a mixed refrigerant recovery system of liquefied natural gas device, includes refrigerant supply line, last stage classifier, natural gas pipeline and cold box, the refrigerant supply line carries mixed refrigerant to the refrigerant heat transfer pipeline in the cold box through last stage classifier after carrying out the second grade compression, its characterized in that: the multi-stage separator is characterized by further comprising 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 last stage 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 condensation loop is arranged on the refrigerant discharging pipeline, a heating loop is arranged at the bottom of the refrigerant recovery tower, multiple paths of refrigerant recovery pipelines are arranged, and each path of refrigerant recovery pipeline is connected to a corresponding refrigerant storage tank respectively.
2. The mixed refrigerant recovery system of a liquefied natural gas device according to claim 1, wherein: the condensing 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 pipe, a refrigerating pipeline is arranged on the refrigerant recovery tower condenser and communicated with a refrigerant heat exchange pipeline of a cold box, a refrigerant recovery tower top temperature control valve is arranged on the refrigerating pipeline, a switching valve is arranged between the refrigerating pipeline and the refrigerant heat exchange pipeline, a reflux pipeline is arranged on the refrigerant recovery tower reflux tank, and the reflux pipeline is communicated with the inside of the top of the refrigerant recovery tower.
3. The mixed refrigerant recovery system of a liquefied natural gas device according to claim 1, wherein: and a heating loop at the bottom of the refrigerant recovery tower is provided with a refrigerant recovery tower reboiler, the refrigerant recovery tower reboiler is provided with a heat conduction oil pipeline, and the heat conduction oil pipeline is provided with a temperature control valve at the bottom of the refrigerant recovery tower.
4. The mixed refrigerant recovery system of a liquefied natural gas plant according to claim 1, wherein: a refrigerant feeding pipeline is provided with a refrigerant recovery tower feeding valve; a refrigerant recovery tower emptying valve and a refrigerant recovery tower emptying air reheater are arranged on the refrigerant discharge pipeline; and a refrigerant recovery tower liquid level control valve is arranged on the refrigerant recovery pipeline.
5. The mixed refrigerant recovery system of a liquefied natural gas device according to 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.
6. The mixed refrigerant recovery system of a liquefied natural gas plant according to claim 5, wherein: refrigerant coolers are arranged on the isopentane recovery pipeline and the propane recovery pipeline; and the ethylene recovery pipeline enters a corresponding refrigerant storage tank after being cooled by the cold box.
7. The mixed refrigerant recovery system of a liquefied natural gas device according to claim 6, wherein: the system is characterized in that 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.
8. The mixed refrigerant recovery system of a liquefied natural gas device according to claim 1, wherein: and a circulating pipeline is connected to the outlet of the refrigerant heat exchange pipeline of the cold box, the circulating pipeline is communicated with a refrigerant supply pipeline, and a switch valve and a gas chromatograph are arranged on the circulating pipeline.
9. The method for recovering mixed refrigerant of a liquefied natural gas device according to claim 1, wherein: the method comprises the following steps of,
a. when the liquefied natural gas device needs to be shut down, starting the refrigerant recovery tower, and opening a refrigerant feeding pipeline and a refrigerant discharging pipeline to be communicated with a refrigerant supply pipeline to form a recovery cycle;
b. controlling the flow rate of a refrigerant entering a refrigerant recovery tower through a refrigerant feeding pipeline, controlling the temperature at the bottom of the refrigerant recovery tower through a heating loop at the bottom of the tower, and controlling the condensation temperature at an outlet at the top of the tower through a condensation loop at the top of the tower, so that a rectification section and a stripping section are formed in the refrigerant recovery tower, the rectification section and the stripping section enable single components in a liquid mixed refrigerant to be separated relatively completely, and a single refrigerant with required purity is extracted from the mixed refrigerant;
c. according to different physical properties of different refrigerants, multi-stage recovery is adopted to realize separation and recovery of a single refrigerant and slow stop of a liquefied natural gas device;
d. the recovered single refrigerant is respectively stored in the corresponding refrigerant storage tanks through the refrigerant recovery pipelines so as to be used for the allocation of the refrigerant next time.
10. The mixed refrigerant recovery method of a liquefied natural gas apparatus according to claim 9, wherein: in the step c, three refrigerants of isopentane, propane and ethylene are recovered in a three-stage mode, and the method comprises the following steps,
first stage, recovery of isopentane
Adjusting a refrigerant feeding pipeline to control the flow of refrigerant entering a refrigerant recovery tower, controlling the temperature of the bottom of the refrigerant recovery tower to be 120-140 ℃ through a heating loop, controlling the temperature of an outlet at the top of the tower to be 5-20 ℃ through a condensing loop at the top of the tower, 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 ℃, returning the uncondensed refrigerant gas to a refrigerant supply pipeline for recycling again, maintaining the device to operate until an online gas chromatograph detects that the content of isopentane in the circulating refrigerant is less than 0.5%, recycling qualified isopentane, cooling the isopentane in the refrigerant recovery pipeline to 30-40 ℃, and then entering an isopentane storage tank for storage;
second stage, recovery of propane:
adjusting a refrigerant feeding pipeline to control the flow of 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 at the top of the tower to be-45-70 ℃ through a condensing loop at the top of the tower, controlling the pressure of the refrigerant recovery tower to be 0.8-1.4 MPa, purifying propane condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning to a refrigerant supply pipeline for recycling, maintaining the operation of a device until an online gas chromatograph detects that the content of propane in the circulating refrigerant is less than 0.5 percent, recovering qualified propane, cooling the propane in the refrigerant recovery pipeline to 30-40 ℃, and then entering a propane storage tank for storage;
in the third stage, ethylene is recovered
Adjusting a refrigerant feeding pipeline to control the flow of refrigerant entering a refrigerant recovery tower, controlling the temperature at the bottom of the refrigerant recovery tower to be-70 to-30 ℃ through a heating circuit, controlling the temperature at an outlet at the top of the tower to be-110 to-140 ℃ through a condensing circuit at the top of the tower, controlling the pressure of the refrigerant recovery tower to be 0.8 to 1.4MPa, purifying ethylene condensed into liquid at the bottom of the refrigerant recovery tower, heating uncondensed refrigerant gas to 5 ℃ and returning the uncondensed refrigerant gas to a refrigerant supply pipeline for recycling, maintaining the operation of a device until an online gas chromatograph detects that the ethylene content in the circulating refrigerant is less than 0.5 percent, recycling qualified ethylene, cooling the ethylene in the refrigerant recovery pipeline to-120 ℃, and then entering an ethylene storage tank for storage.
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