CN113701446A - Natural gas liquefaction system with supersonic two-phase expansion refrigeration cycle - Google Patents
Natural gas liquefaction system with supersonic two-phase expansion refrigeration cycle Download PDFInfo
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- CN113701446A CN113701446A CN202110371894.5A CN202110371894A CN113701446A CN 113701446 A CN113701446 A CN 113701446A CN 202110371894 A CN202110371894 A CN 202110371894A CN 113701446 A CN113701446 A CN 113701446A
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 152
- 238000005057 refrigeration Methods 0.000 title claims abstract description 104
- 239000003345 natural gas Substances 0.000 title claims abstract description 61
- 239000007789 gas Substances 0.000 claims description 64
- 239000007788 liquid Substances 0.000 claims description 45
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 36
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 28
- 230000007246 mechanism Effects 0.000 claims description 25
- 229910052757 nitrogen Inorganic materials 0.000 claims description 18
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 claims description 16
- 239000005977 Ethylene Substances 0.000 claims description 14
- 239000001294 propane Substances 0.000 claims description 14
- 239000001273 butane Substances 0.000 claims description 13
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims description 13
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 claims description 13
- 238000000926 separation method Methods 0.000 claims description 10
- 239000003507 refrigerant Substances 0.000 claims description 9
- 239000007921 spray Substances 0.000 claims description 7
- 230000000694 effects Effects 0.000 claims description 5
- 239000012530 fluid Substances 0.000 claims description 4
- 230000007423 decrease Effects 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims description 2
- 238000001816 cooling Methods 0.000 abstract description 4
- 238000005265 energy consumption Methods 0.000 abstract description 3
- 239000012071 phase Substances 0.000 description 67
- 238000000034 method Methods 0.000 description 16
- 230000008569 process Effects 0.000 description 14
- 230000009467 reduction Effects 0.000 description 7
- 239000007791 liquid phase Substances 0.000 description 5
- 238000009835 boiling Methods 0.000 description 3
- 238000004134 energy conservation Methods 0.000 description 3
- 230000002277 temperature effect Effects 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000003949 liquefied natural gas Substances 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002343 natural gas well Substances 0.000 description 1
- 238000005191 phase separation Methods 0.000 description 1
- 238000005381 potential energy Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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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
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
- F25J1/0022—Hydrocarbons, e.g. natural gas
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/003—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
- F25J2205/00—Processes or apparatus using other separation and/or other processing means
- F25J2205/10—Processes or apparatus using other separation and/or other processing means using combined expansion and separation, e.g. in a vortex tube, "Ranque tube" or a "cyclonic fluid separator", i.e. combination of an isentropic nozzle and a cyclonic separator; Centrifugal separation
Abstract
The invention provides a natural gas liquefaction system with supersonic two-phase expansion refrigeration cycle, which comprises a plurality of counter-flow heat exchangers and a plurality of supersonic two-phase expanders, wherein natural gas sequentially flows through the plurality of counter-flow heat exchangers to form a first flow pipeline, and each supersonic two-phase expander is arranged between the adjacent counter-flow heat exchangers to form a plurality of refrigeration units; and the refrigeration working medium sequentially passes through the plurality of refrigeration units so as to liquefy the gaseous natural gas introduced into the first circulation pipeline. By adopting the mode, the supersonic speed two-phase expander is used as the expansion cooling device, and the expansion cooling device has the advantages of high expansion refrigeration efficiency, small pressure drop, low energy consumption, simple and compact structure, no moving part, safety, reliability and low processing difficulty, greatly reduces the number of equipment, simplifies the system flow and improves the system efficiency.
Description
Technical Field
The invention relates to the technical field of liquefaction systems, in particular to a natural gas liquefaction system adopting supersonic two-phase expansion refrigeration cycle.
Background
Natural gas is widely applied to the world in recent years as a clean and environment-friendly energy source. The natural gas resources in the world are abundant, but some large natural gas wells are mostly located in desert regions and far away from densely populated and industrially developed regions, large-area oceans and complex landforms are often used for blocking, pipelines are laid for a long distance, and even natural gas is transported in a transoceanic gaseous state, which is often limited by cost and technical problems, so that the long-distance transportation of natural gas is mostly carried out in a Liquefied Natural Gas (LNG) mode, and the discussion of a natural gas liquefaction process has important significance.
At present, a plurality of natural gas liquefaction processes are available, wherein a cascade refrigeration cycle liquefaction process, a mixed refrigerant refrigeration cycle liquefaction process, an expander refrigeration cycle liquefaction process and the like are common, but corresponding problems exist. The step refrigeration cycle natural gas liquefaction process flow is complex, the number of units is large, the system is huge, and the maintenance and management investment is large; the mixed refrigerant refrigeration cycle natural gas liquefaction process has a plurality of gas-liquid separators and throttle valves, so that the equipment is complex, the control and management difficulty is high, the throttle valve loss is high, and the system efficiency is low; the expander in the natural gas liquefaction process of the refrigerating cycle of the expander has the hidden trouble that mechanical moving parts are unsafe and unstable in operation, and has large power consumption and low system efficiency.
Disclosure of Invention
The embodiment of the invention provides a natural gas liquefaction system adopting supersonic two-phase expansion refrigeration cycle, which is used for solving the technical problems of complex flow and low system efficiency of the natural gas liquefaction system in the prior art.
The embodiment of the invention provides a natural gas liquefaction system with supersonic two-phase expansion refrigeration cycle, which comprises: the natural gas sequentially flows through the plurality of counter-flow heat exchangers and forms a first circulation pipeline;
each supersonic two-phase expander is arranged between the adjacent counter-flow heat exchangers and forms a plurality of refrigeration units; wherein the content of the first and second substances,
the refrigeration working medium sequentially passes through the plurality of refrigeration units so as to liquefy the gaseous natural gas introduced into the first circulation pipeline.
According to an embodiment of the present invention, each of said refrigeration units comprises one of said counter-flow heat exchanger and one of said supersonic two-phase expander;
at least one group of gaseous heat exchange tubes and low-temperature heat exchange tubes are arranged in the countercurrent heat exchanger, the gaseous heat exchange tubes are used for transmitting gaseous working media towards the supersonic speed two-phase expander, and the low-temperature heat exchange tubes are used for receiving liquid working media formed by the supersonic speed two-phase expander.
According to the natural gas liquefaction system adopting supersonic two-phase expansion refrigeration cycle, the gaseous working medium flows through the plurality of refrigeration units to form a gas circulation pipeline, and the liquid working medium flows out of the refrigeration units to form a low-temperature return pipeline;
the gas circulation pipeline and the low-temperature return pipeline are connected end to end.
According to the natural gas liquefaction system of supersonic speed two-phase expansion refrigeration cycle of an embodiment of the invention, the supersonic speed two-phase expander comprises an air inlet, an air outlet and a liquid outlet;
the gas inlet and the gas outlet are communicated with the gas circulation pipeline, and the liquid outlet is communicated with the low-temperature return pipeline.
According to the natural gas liquefaction system of the supersonic speed two-phase expansion refrigeration cycle, the supersonic speed two-phase expander comprises a cyclone mechanism, a spray pipe, a cyclone separation pipe, a liquid discharge mechanism and a diffuser which are sequentially connected;
the gas inlet is communicated with the cyclone mechanism, the cyclone mechanism generates centrifugal force to enable the gaseous working medium entering through the gas inlet to form a low-temperature effect in the spray pipe, and the liquid working medium generated in the cyclone separating pipe flows to the low-temperature return pipeline through the liquid discharge mechanism and flows to the gas circulation pipeline through the diffuser.
According to the natural gas liquefaction system of the supersonic speed two-phase expansion refrigeration cycle, a compressor and a cooler are arranged on the low-temperature return pipeline flowing to the gas circulation pipeline;
the inlet side of the compressor is communicated with the low-temperature return pipeline, the outlet side of the compressor is communicated with the inlet side of the cooler, and the outlet side of the cooler is communicated with the gas circulation pipeline.
According to the natural gas liquefaction system with the supersonic speed two-phase expansion refrigeration cycle, the temperature of the refrigeration working medium in the low-temperature return pipeline in the plurality of countercurrent heat exchangers is decreased progressively along the direction of the first circulation pipeline so as to reduce the temperature of the natural gas in the first circulation pipeline.
According to the natural gas liquefaction system with supersonic speed two-phase expansion refrigeration cycle, a throttle valve is further arranged at the connection position of the gas circulation pipeline and the low-temperature return pipeline after passing through the plurality of refrigeration units;
the inlet side of the throttling valve is communicated with the air outlet of the supersonic two-phase expander, and the outlet side of the throttling valve is communicated with the low-temperature return pipeline.
According to the natural gas liquefaction system of supersonic two-phase expansion refrigeration cycle, the number of the refrigeration units is three.
In a supersonic two-phase expansion refrigeration cycle natural gas liquefaction train according to one embodiment of the present invention, the refrigeration medium comprises nitrogen and one or more of butane, propane, ethylene, methane in combination with the nitrogen.
The natural gas liquefaction system with supersonic two-phase expansion refrigeration cycle provided by the embodiment of the invention comprises a plurality of counter-flow heat exchangers and a plurality of supersonic two-phase expanders, wherein the counter-flow heat exchangers and the supersonic two-phase expanders are matched to form a plurality of refrigeration units, so that gaseous natural gas flowing through a first flow pipeline exchanges heat with the refrigeration units to refrigerate, and a liquefaction effect is further generated to realize liquefaction of the natural gas. The supersonic speed two-phase expander is used as an expansion cooling device, and the supersonic speed two-phase expander has the advantages of high expansion refrigeration efficiency, small pressure drop, low energy consumption, simple and compact structure, no moving part, safety, reliability and low processing difficulty, greatly reduces the number of devices, simplifies the system flow and improves the system efficiency.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a supersonic two-phase expansion refrigeration cycle natural gas liquefaction system configuration according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the supersonic two-phase expander of FIG. 1;
FIG. 3 is a schematic illustration of a component configuration of another embodiment of a natural gas liquefaction train of the supersonic two-phase expansion refrigeration cycle shown in FIG. 1;
reference numerals:
10. a counter-flow heat exchanger; 110. A first flow line; 120. A gaseous heat exchange tube;
130. a low-temperature heat exchange pipe; 20. A supersonic two-phase expander; 210. A refrigeration unit;
220. an air inlet; 230. An air outlet; 240. A liquid outlet;
250. a swirling mechanism; 260. A nozzle; 270. A cyclone separation tube;
280. a liquid discharge mechanism; 290. A diffuser; 310. A gas circulation line;
320. a low temperature return line; 40. A compressor; 50. A cooler;
60. a throttle valve.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that all the directional indicators (such as upper, lower, left, right, front and rear … …) in the embodiment of the present invention are only used to explain the relative position relationship between the components, the movement situation, etc. in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indicator is changed accordingly.
Referring now to fig. 1, the present invention provides a supersonic two-phase expansion refrigeration cycle natural gas liquefaction system, comprising a plurality of counter-flow heat exchangers 10 and a plurality of supersonic two-phase expanders 20, wherein natural gas flows through the plurality of counter-flow heat exchangers 10 in sequence and forms a first flow line 110. Each supersonic two-phase expander 20 is disposed between adjacent counter-flow heat exchangers 10 and forms a plurality of refrigeration units 210. Wherein the refrigerant passes through the plurality of refrigeration units 210 in sequence to liquefy the gaseous natural gas introduced into the first flow line 110.
In an embodiment of the present invention, each refrigeration unit 210 includes a counter-flow heat exchanger 10 and a supersonic two-phase expander 20, at least one set of gaseous heat exchange tubes 120 and low-temperature heat exchange tubes 130 is disposed in the counter-flow heat exchanger 10, the gaseous heat exchange tubes 120 are used for transmitting a gaseous working medium toward the supersonic two-phase expander 20, and the low-temperature heat exchange tubes 130 are used for receiving a liquid working medium formed by passing through the supersonic two-phase expander 20. The gaseous heat exchange tube 120 is used for conveying the refrigeration working medium, that is, the gaseous refrigeration working medium is conveyed to the supersonic two-phase expander 20, the liquid working medium is generated by the supersonic two-phase expander 20 and flows through the low-temperature heat exchange tube 130, the low-temperature liquid in the low-temperature heat exchange tube 130 exchanges heat with the natural gas in the first flow pipeline 110 to cool and liquefy the gaseous natural gas, and the phase state of the low-temperature liquid is changed and changed into gaseous state to flow out due to the fact that the cold energy is transferred to the gaseous natural gas.
Further, the gaseous working medium flows through the plurality of refrigeration units 210 to form a gas circulation pipeline 310, the liquid working medium flows out of the refrigeration units 210 to form a low-temperature return pipeline 320, and the gas circulation pipeline 310 and the low-temperature return pipeline 320 are connected end to end. The refrigeration working medium completes the circulation so as to realize the recycling of the refrigeration working medium.
Supersonic two-phase expander 20 comprises a gas inlet 220, a gas outlet 230, and a liquid outlet 240. The gas inlet 220 and the gas outlet 230 are communicated with a gas circulation pipeline 310, and the liquid outlet 240 is communicated with a low-temperature return pipeline 320. That is, the refrigerant will flow in two directions when passing through the supersonic two-phase expander 20, wherein the gaseous refrigerant flows to the downstream counter-flow heat exchanger 10 and is communicated with the gas flow pipeline 310 to participate in the circulation. The formed liquid working medium flows to the low-temperature return pipeline 320, and exchanges heat with the natural gas flowing through the first circulation pipeline 110 of the counter-flow heat exchanger 10 when flowing to the low-temperature heat exchange pipe 130 in the counter-flow heat exchanger 10, so as to cool the natural gas.
Referring to fig. 2, specifically, the supersonic two-phase expander 20 includes a cyclone mechanism 250, a nozzle 260, a cyclone separating tube 270, a drainage mechanism 280 and a diffuser 290, which are connected in sequence; the air inlet 220 is communicated with the cyclone mechanism 250, the cyclone mechanism 250 generates centrifugal force to enable the gaseous working medium entering through the air inlet 220 to form a low-temperature effect in the spray pipe 260, and the generated liquid working medium flows to the low-temperature return pipeline 320 through the liquid discharge mechanism 280 in the cyclone separation pipe 270 and flows to the gas circulation pipeline 310 through the diffuser 290. The drainage mechanism 280 may be a pipe formed by the outer periphery of the diffuser 290 and the cyclone separator 270, or a separately provided drainage pipe, which is not limited herein.
The low-temperature return line 320 is provided with a compressor 40 and a cooler 50 in a gas flow line 310. The inlet side of the compressor 40 communicates with a low temperature return line 320, the outlet side of the compressor 40 communicates with the inlet side of the cooler 50, and the outlet side of the cooler 50 communicates with a gas circulation line 310. Compressor 40 is used to pressurize the gaseous working fluid and raise the temperature, and cooler 50 is used to lower the temperature of the gaseous working fluid delivered by compressor 40 to participate in the cycle.
A throttle valve 60 is further arranged at the connection part of the gas circulation pipeline 310 and the low-temperature return pipeline 320 after passing through the plurality of refrigeration units 210; the inlet side of the throttle valve 60 is communicated with the gas outlet 230 of the supersonic two-phase expander 20, and the outlet side of the throttle valve 60 is communicated with the low-temperature return line 320. The throttle valve 60 is provided for throttling cooling.
Along the direction of the first circulation pipeline 110, the temperature of the refrigerant in the low-temperature return pipeline 320 in the plurality of counterflow heat exchangers 10 decreases progressively to lower the temperature of the natural gas in the first circulation pipeline 110. In an embodiment of the present invention, the number of the refrigeration units 210 is three, and three counter-flow heat exchangers 10 and three supersonic two-phase expanders 20 are correspondingly disposed to cool the natural gas in the first flow pipeline 110.
It is noted that each of the refrigeration units 210 forms a first-stage refrigeration cycle, while three refrigeration units 210 form a third-stage refrigeration cycle, and the throttle valve 60 is provided as a fourth-stage refrigeration cycle.
Specifically, the refrigerant comprises nitrogen and one or more of butane, propane, ethylene and methane, so that the system can reach the liquefaction temperature zone of the nitrogen. Wherein the liquefaction temperature of butane, propane, ethylene, methane and nitrogen is decreased progressively. In an embodiment of the present invention, it is described by taking an example that butane, propane, ethylene, methane, and nitrogen all participate in the refrigeration cycle, and the lowest temperature finally reached corresponds to the liquefaction temperature region of nitrogen, that is, the temperature region lower than the liquefaction temperature region of natural gas. It will be appreciated that the number of refrigerant media corresponds to the number of refrigeration units 210. That is, on the basis of the nitrogen, one of butane, propane, ethylene and methane is added to correspond to one refrigeration unit 210.
Butane, propane, ethylene, methane and nitrogen are multi-component mixed working media, and when the multi-component mixed working media participate in the primary refrigeration cycle, the multi-component mixed working media correspondingly participate in the first refrigeration unit 210. The multi-element mixed working medium enters the first-stage supersonic two-phase expander 20, centrifugal force is generated through the cyclone mechanism 250, the medium entropy expansion, temperature reduction and pressure reduction are performed in the spray pipe 260 to generate low temperature effect, high boiling point gas such as butane can be condensed and nucleated to generate liquid drops to further grow after the temperature is reduced, liquid phase butane is continuously condensed and liquefied in the cyclone separation pipe 270 due to the tangential speed and the centrifugal action generated by rotation and is discharged through the liquid discharge mechanism 280 to realize gas-liquid separation, and residual gas phases such as propane, ethylene, methane and nitrogen are discharged after being decelerated, heated and pressurized through the diffuser 290, so that most of pressure energy can be recovered, and the pressure loss of an inlet and an outlet is greatly reduced. The liquid butane flows to the low-temperature return pipeline 320, is subjected to heat exchange through the first-stage counter-flow heat exchanger 10, is subjected to adiabatic compression through the compressor 40 to increase the pressure value to be the same as the gas pressure when entering the first-stage supersonic two-phase expander 20, further enters the first-stage counter-flow heat exchanger 10 through the cooler 50 to exchange heat, and enters the first-stage supersonic two-phase expander 20 again to complete first-stage circulation.
When participating in the secondary refrigeration cycle, the multi-element mixed working medium correspondingly participates in a second refrigeration unit 210 arranged at the downstream of the first refrigeration unit 210, the residual gas phase after the primary refrigeration cycle comprises propane, ethylene, methane and nitrogen, the residual mixed gas phase flows to the secondary supersonic speed two-phase expander 20, centrifugal force is generated through the cyclone mechanism 250, the medium entropy expansion, temperature reduction and pressure reduction in the spray pipe 260 generate low temperature effect, high boiling point gas propane can be condensed and nucleated after the temperature is reduced, liquid drops are generated and further grow, liquid phase propane continues to be condensed and liquefied in the cyclone separation pipe 270 due to tangential speed generated by rotation and centrifugal action and is discharged through the liquid discharge mechanism 280, gas-liquid separation is achieved, residual gas phases, namely ethylene, methane and nitrogen, are discharged after being decelerated, heated and pressurized through the diffuser 290, therefore, most of pressure energy can be recovered, and pressure loss of an inlet and an outlet is greatly reduced. The liquid propane flows to the low-temperature return pipeline 320, enters the secondary countercurrent heat exchanger 10 for heat exchange, then is converged with the low-temperature liquid-phase propane discharged by the primary supersonic two-phase expander 20, participates in the primary circulation, and completes the secondary circulation.
When participating in the three-stage refrigeration cycle, the multi-element mixed working medium correspondingly participates in a third refrigeration unit 210 arranged at the downstream of the second refrigeration unit 210, the residual gas phase after the two-stage refrigeration cycle comprises ethylene, methane and nitrogen, the residual mixed gas phase flows to the three-stage supersonic speed two-phase expander 20, centrifugal force is generated through the cyclone mechanism 250, the medium entropy expansion, temperature reduction and pressure reduction in the spray pipe 260 generate low temperature effect, after the temperature is reduced, high boiling point ethylene can be condensed and nucleated, liquid drops are generated and further grow, liquid phase ethylene continues to be condensed and liquefied in the cyclone separation pipe 270 due to the tangential speed generated by rotation and the centrifugal effect and is discharged through the liquid discharge mechanism 280, gas-liquid separation is achieved, residual gas phases, namely methane and nitrogen, are discharged after being subjected to speed reduction, temperature rise and pressure rise through the diffuser 290, therefore, most of pressure energy can be recovered, and pressure loss of an inlet and an outlet is greatly reduced. The liquid ethylene flows to the low-temperature return pipeline 320, enters the secondary countercurrent heat exchanger 10 for heat exchange, then is converged with the low-temperature liquid butane discharged by the secondary supersonic two-phase expander 20, participates in the secondary circulation and the primary circulation, and completes the three-stage circulation.
The residual gas phase after the three-stage refrigeration cycle includes methane and nitrogen, the residual gas phase discharged from the diffuser 290 of the three-stage supersonic two-phase expander 20 is throttled and cooled by the throttle valve 60, the gas-phase methane is liquefied, part of the nitrogen is liquefied and flows to the low-temperature return pipeline 320 together, joins with the liquid-phase ethylene generated by the three-stage refrigeration cycle, and participates in the three-stage refrigeration cycle, the two-stage refrigeration cycle and the one-stage refrigeration cycle, thereby completing the four-stage refrigeration cycle.
The first circulation line 110 exchanges heat and continuously cools through the counter-flow heat exchanger 10 in the primary refrigeration cycle, the secondary refrigeration cycle and the tertiary refrigeration cycle in sequence, so that the gaseous natural gas in the first circulation line 110 is liquefied.
Referring to fig. 3, it should be noted that a plurality of compressors 40 and coolers 50 may also be provided, for example, the supersonic two-phase expander 20 in the second-stage circulation refrigeration system compresses liquid butane to raise the temperature and lower the temperature through one compressor 40 and one cooler 50 after the low-temperature return line 320 flows through the second-stage counter-flow heat exchanger 10 and the first-stage heat exchanger, and then merges with the gaseous butane flowing out from the counter-flow heat exchanger 10 in the first-stage circulation refrigeration system, so as to further lower the temperature through gasification. Similarly, the compressor 40 and the cooler 50 are arranged in the three-stage circulation and the four-stage circulation, so that the liquid propane, the liquid ethylene and the liquid methane can be rapidly gasified to participate in the refrigeration circulation, and the circulation refrigeration efficiency of the multi-component mixed working medium can be improved.
Further, the energy conservation analysis within the supersonic two-phase expander 20 is as follows: from the steady flow energy equation:
the potential energy change is not considered and the external work is not done, namely, the whole process only has the conversion between the enthalpy and the kinetic energy, and the energy equation can be simplified as follows:
the process of the gaseous working medium from the gas outlet 230 to the liquid outlet 240 of the supersonic two-phase expander 20 is obtained by energy conservation:
wherein m is1Mass flow of gas, m, into supersonic two-phase expander 202gIs the mass flow rate of gas to the diffuser 290, m2lIs the mass flow rate of liquid through the drain 280. u. of2gIs the flow rate of gas, u, to the diffuser 2902lIs the flow rate of the liquid through the drain 280. u. of1Is the flow velocity of the gaseous working medium before entering the supersonic two-phase expander 20. h is2gIs the specific enthalpy, h, of the gas flowing to the diffuser 2902lIs the specific enthalpy of the liquid flowing through the drainage mechanism 280.
The change process of the gaseous working medium from the diffuser 290 to the air outlet 230 is obtained by energy conservation:
from the isentropic equation2g＝s3. Wherein h is2gIs the specific enthalpy, h, of the gas flowing to the diffuser 2903Is the specific enthalpy of the gas exiting the gas outlet 230. u. of2gIs the flow rate of gas, u, to the diffuser 2903To flow outThe flow rate of the gas at the gas outlet 230. s2gIs the specific entropy, s, of the gas after two-phase separation3Is the specific entropy of the gas exiting the gas outlet 230.
In conclusion, the supersonic two-phase expander 20 has the characteristics of high expansion refrigeration efficiency, small pressure drop, low energy consumption, simple and compact structure, no moving parts, safety, reliability, low processing difficulty and capability of realizing expansion in a two-phase region, simplifies the refrigeration process, can be used for efficiently liquefying the gaseous natural gas by matching with the countercurrent heat exchanger 10, and solves the technical problem of low efficiency of a liquefaction system in the conventional natural gas liquefaction system.
It should be noted that the terms "comprises" and "comprising," and any variations thereof, in the embodiments of the present application, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or may alternatively include other components or elements inherent to such process, method, article, or apparatus.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A supersonic two-phase expansion refrigeration cycle natural gas liquefaction system, comprising:
the natural gas sequentially flows through the plurality of counter-flow heat exchangers and forms a first circulation pipeline;
each supersonic two-phase expander is arranged between the adjacent counter-flow heat exchangers and forms a plurality of refrigeration units; wherein the content of the first and second substances,
the refrigeration working medium sequentially passes through the plurality of refrigeration units so as to liquefy the gaseous natural gas introduced into the first circulation pipeline.
2. A supersonic two-phase expansion refrigeration cycle natural gas liquefaction system according to claim 1, wherein each of said refrigeration units comprises one of said counter-flow heat exchangers and one of said supersonic two-phase expanders;
at least one group of gaseous heat exchange tubes and low-temperature heat exchange tubes are arranged in the countercurrent heat exchanger, the gaseous heat exchange tubes are used for transmitting gaseous working media towards the supersonic speed two-phase expander, and the low-temperature heat exchange tubes are used for receiving liquid working media formed by the supersonic speed two-phase expander.
3. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 2, wherein said gaseous working fluid flows through a plurality of said refrigeration units forming a gas flow path and said liquid working fluid exits said refrigeration units forming a cryogenic return line;
the gas circulation pipeline and the low-temperature return pipeline are connected end to end.
4. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 3, wherein the supersonic two-phase expander comprises a gas inlet, a gas outlet, and a liquid outlet;
the gas inlet and the gas outlet are communicated with the gas circulation pipeline, and the liquid outlet is communicated with the low-temperature return pipeline.
5. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 4, wherein the supersonic two-phase expander comprises a swirl mechanism, a nozzle, a swirl separation tube, a drainage mechanism and a diffuser connected in sequence;
the gas inlet is communicated with the cyclone mechanism, the cyclone mechanism generates centrifugal force to enable the gaseous working medium entering through the gas inlet to form a low-temperature effect in the spray pipe, and the liquid working medium generated in the cyclone separating pipe flows to the low-temperature return pipeline through the liquid discharge mechanism and flows to the gas circulation pipeline through the diffuser.
6. A supersonic two-phase expansion refrigeration cycle natural gas liquefaction train as in claim 3, wherein a compressor and a cooler are provided in said cryogenic return line to said gas flow line;
the inlet side of the compressor is communicated with the low-temperature return pipeline, the outlet side of the compressor is communicated with the inlet side of the cooler, and the outlet side of the cooler is communicated with the gas circulation pipeline.
7. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 3, wherein the temperature of said refrigerant in said cryogenic return line in a plurality of counterflow heat exchangers decreases in the direction of said first flow path to reduce the temperature of the natural gas in said first flow path.
8. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 3, wherein a throttle valve is further provided at a connection of said gas flow line to said cryogenic return line after passing through a plurality of said refrigeration units;
the inlet side of the throttling valve is communicated with the air outlet of the supersonic two-phase expander, and the outlet side of the throttling valve is communicated with the low-temperature return pipeline.
9. The supersonic two-phase expansion refrigeration cycle natural gas liquefaction system of claim 8, wherein the number of refrigeration units is three.
10. A supersonic two-phase expansion refrigeration cycle natural gas liquefaction system according to claim 9, wherein said refrigeration medium comprises nitrogen and one or more of butane, propane, ethylene, methane in combination with said nitrogen.
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