CN117029377A

CN117029377A - Cascaded refrigeration cycle LNG liquefaction system and method

Info

Publication number: CN117029377A
Application number: CN202310935526.8A
Authority: CN
Inventors: 张惊涛
Original assignee: Chengdu Sepmem Sci & Tech Co ltd
Current assignee: Chengdu Sepmem Sci & Tech Co ltd
Priority date: 2023-07-27
Filing date: 2023-07-27
Publication date: 2023-11-10

Abstract

The embodiment of the invention provides a cascade refrigeration cycle LNG liquefaction system and a method, and relates to the field of refrigeration cycle, wherein the cascade refrigeration cycle LNG liquefaction system comprises a first refrigeration component, a second refrigeration component and a third refrigeration component, and the first refrigeration component, the second refrigeration component and the third refrigeration component comprise a compressor, a heat exchanger, an evaporator and a separation tank; refrigerant discharged by the compressor is subjected to heat exchange separation; the separated gas phase is returned to the compressor after sensible heat is recovered by the heat exchanger; according to the invention, the heat exchanger is newly added, the connection modes of the compressors, the heat exchangers, the evaporators and the separating tanks in the cascade refrigeration cycle LNG liquefying system are adjusted, so that on one hand, the cold energy of the gas-phase refrigerant is recovered, on the other hand, the temperature of the gas-phase refrigerant returning to the compressor unit is ensured to be normal temperature, the compressor can be a normal temperature compressor, and the cost investment of the compressor is reduced.

Description

Cascaded refrigeration cycle LNG liquefaction system and method

Technical Field

The invention relates to the field of refrigeration cycle, in particular to a cascade refrigeration cycle LNG liquefaction system and method.

Background

The cascade refrigeration cycle is a more classical refrigeration cycle, also called "cascade", "cascade" or "cascade", and consists of a plurality of refrigeration cycles operating at different low temperatures. The cascade refrigeration cycle was first applied to lng products in 1939 using NH ₃ 、C ₂ H ₄ Is the first and second stage refrigerant. But classical cascade refrigeration cycle consists of C ₃ H ₈ 、C ₂ H ₄ And CH (CH) ₄ Three stage refrigeration as refrigerantThe circulation process adopts a three-stage throttling and low-temperature compressor to provide the required cold energy for purifying the natural gas liquefaction.

However, after the gas phase and the liquid phase are separated by the separating tank, the gas phase is directly returned to the low-temperature compressor by the existing cascade refrigeration cycle, so that the cost investment of the compressor is high.

In view of this, the present application has been made.

Disclosure of Invention

Objects of the present application include, for example, providing a cascade refrigeration cycle LNG liquefaction system and method.

Embodiments of the application may be implemented as follows:

in a first aspect, the application provides a cascaded refrigeration cycle LNG liquefaction system, which comprises a first refrigeration assembly, a second refrigeration assembly and a third refrigeration assembly;

the first refrigeration assembly comprises a normal-temperature first refrigerant compressor, a first refrigerant heat exchanger and a first refrigerant evaporator, the second refrigeration assembly comprises a normal-temperature second refrigerant compressor, a second refrigerant heat exchanger and a second refrigerant evaporator, and the third refrigeration assembly comprises a normal-temperature third refrigerant compressor, a third refrigerant heat exchanger and a third refrigerant evaporator;

The refrigerants discharged from the normal-temperature first refrigerant compressor, the normal-temperature second refrigerant compressor and the normal-temperature third refrigerant compressor are respectively subjected to evaporation separation through the first refrigerant evaporator, the second refrigerant evaporator and the third refrigerant evaporator;

the sensible heat of the first refrigerant gas phase separated by the first refrigerant evaporator is recovered by the first refrigerant heat exchanger and then returned to the normal-temperature first refrigerant compressor;

the second refrigerant gas phase separated by the second refrigerant evaporator is returned to the normal-temperature second refrigerant compressor after sensible heat is recovered by the second refrigerant heat exchanger;

and the sensible heat of the third refrigerant gas phase separated by the third refrigerant evaporator is recovered by the third refrigerant heat exchanger and then returned to the normal-temperature first refrigerant compressor.

In an alternative embodiment, the first refrigeration assembly further comprises a first refrigerant separator tank, the second refrigeration assembly further comprises a second refrigerant separator tank, and the third refrigeration assembly further comprises a third refrigerant separator tank; the refrigerant discharged from the normal-temperature first refrigerant compressor, the normal-temperature second refrigerant compressor and the normal-temperature third refrigerant compressor is firstly evaporated through the first refrigerant evaporator, the second refrigerant evaporator and the third refrigerant evaporator respectively, and then enters the first refrigerant separation tank, the second refrigerant separation tank and the third refrigerant separation tank for separation; or the refrigerant is separated through the first refrigerant separating tank, the second refrigerant separating tank and the third refrigerant separating tank, and then enters the first refrigerant evaporator for evaporation and the second refrigerant evaporator and the third refrigerant evaporator for evaporation.

In an alternative embodiment, the second refrigerant gas phase passes through the second refrigerant heat exchanger and then enters the first refrigerant heat exchanger to continue heat exchange; the third refrigerant gas phase passes through the third refrigerant heat exchanger and then passes through at least one of the second refrigerant heat exchanger and the first refrigerant heat exchanger to perform continuous heat exchange.

In an alternative embodiment, the first refrigerant discharged from the normal temperature first refrigerant compressor is introduced into the first refrigerant heat exchanger for heat exchange before entering the first refrigerant evaporator;

before the first refrigerant discharged by the normal-temperature second refrigerant compressor enters the second refrigerant evaporator, the method further comprises the steps of introducing the second refrigerant into the first refrigerant heat exchanger and the first refrigerant evaporator for heat exchange;

before entering the third refrigerant evaporator, the third refrigerant discharged by the normal-temperature third refrigerant compressor is led into the first refrigerant heat exchanger, the first refrigerant evaporator, the second refrigerant heat exchanger and the second refrigerant evaporator to exchange heat.

In an alternative embodiment, the first refrigerant heat exchanger and the first refrigerant evaporator are integrally provided, the second refrigerant heat exchanger and the second refrigerant evaporator are integrally provided, and the third refrigerant heat exchanger and the third refrigerant evaporator are integrally provided.

In an alternative embodiment, the first refrigerant heat exchanger and the first refrigerant evaporator are separately arranged and have N-stage heat exchange and N-stage evaporation, the second refrigerant heat exchanger and the second refrigerant evaporator are separately arranged and have N-stage heat exchange and N-stage evaporation, and the third refrigerant heat exchanger and the third refrigerant evaporator are separately arranged and have N-stage heat exchange and N-stage evaporation.

In an alternative embodiment, N in the N-stage heat exchange and N-stage evaporation is greater than or equal to 2, and the number of the first refrigerant separation tank, the second refrigerant separation tank and the third refrigerant separation tank is N-1.

In an alternative embodiment, a first liquid phase throttle valve is arranged on a first refrigerant inlet pipeline of the first refrigerant evaporator of each stage, a second liquid phase throttle valve is arranged on a second refrigerant inlet pipeline of the second refrigerant evaporator of each stage, and a third liquid phase throttle valve is arranged on a third refrigerant inlet pipeline of the third refrigerant evaporator of each stage.

In a second aspect, the present invention provides a cascade refrigeration cycle LNG liquefaction method using the cascade refrigeration cycle LNG liquefaction system according to any of the foregoing embodiments, comprising the steps of:

evaporating and separating gas-liquid two phases of a first refrigerant discharged from a normal-temperature first refrigerant compressor through a first refrigerant evaporator, wherein gas phase is subjected to gas-phase sensible heat recovery through the first refrigerant heat exchanger and then enters an inlet of the first refrigerant compressor, and liquid phase is subjected to liquid-phase latent heat recovery through the first refrigerant evaporator and then enters the first refrigerant heat exchanger and then enters an inlet of the first refrigerant compressor;

evaporating and separating gas-liquid two phases of a second refrigerant discharged from a normal-temperature second refrigerant compressor through a second refrigerant evaporator, wherein gas phase sequentially recovers gas phase sensible heat through the second refrigerant heat exchanger and then enters an inlet of the second refrigerant compressor, and liquid phase sequentially enters the second refrigerant heat exchanger and the first refrigerant heat exchanger after recovering liquid phase latent heat through the second refrigerant evaporator and then enters an inlet of the second refrigerant compressor;

Evaporating and separating gas-liquid two phases of a third refrigerant discharged from a normal-temperature third refrigerant compressor through a third refrigerant evaporator, wherein the gas phase sequentially recovers gas phase sensible heat through the third refrigerant heat exchanger and then enters an inlet of the third refrigerant compressor, and the liquid phase sequentially enters the third refrigerant heat exchanger, the second refrigerant heat exchanger and the first refrigerant heat exchanger after recovering liquid phase latent heat through the third refrigerant evaporator and then enters an inlet of the third refrigerant compressor.

In an alternative embodiment, the first refrigerant, the second refrigerant, and the third refrigerant are different from each other and are each selected from nitrogen, methane, ethane, ethylene, propane, propylene; any of butane, butene, pentane and pentene.

In an alternative embodiment, when the first refrigerant is propane, the second refrigerant is ethylene, and the third refrigerant is methane, the pressure of the first refrigerant discharged through the normal-temperature first refrigerant compressor is greater than or equal to 0.47mpa, the pressure of the first refrigerant entering the first refrigerant evaporator is 0.1-0.47 mpa, and the temperature is-43-0 ℃;

The pressure of the second refrigerant discharged by the normal-temperature second refrigerant compressor is more than or equal to 1.38MPaA, the pressure of the second refrigerant entering the second refrigerant evaporator is 0.1-1.38 MPaA, and the temperature is-104 to-42 ℃;

the pressure of the third refrigerant discharged by the normal-temperature third refrigerant compressor is more than or equal to 2.44MPaA, the pressure of the third refrigerant entering the third refrigerant evaporator is 0.1-2.44 MPaA, and the temperature is-161.8 to-102 ℃.

The beneficial effects of the embodiment of the invention include, for example:

the embodiment of the invention provides a cascading refrigeration cycle LNG liquefaction system, which is characterized in that a first refrigerant heat exchanger, a second refrigerant heat exchanger and a third refrigerant heat exchanger are additionally arranged, and the connection modes of a plurality of compressors, heat exchangers, evaporators and separation tanks in the cascading refrigeration cycle LNG liquefaction system 100 are adjusted, so that a novel cascading refrigeration cycle LNG liquefaction process is formed. The unit energy index of the cascaded refrigeration cycle LNG liquefaction system 100 is 0.25kW/Nm ³ Purifying natural gas, compared with a conventional cascade refrigeration cycle system (0.30 kW/Nm) ³ Purified natural gas) by about 15% less than the MRC mixed refrigerant refrigeration cycle system (0.33 kW/Nm) ³ Purified natural gas) by about 25%.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a process flow diagram of a cascaded refrigeration cycle LNG liquefaction system provided in embodiment 1 of the present application;

fig. 2 is a flow chart in a process flow chart of the cascaded refrigeration cycle LNG liquefaction system provided in embodiment 1 of the present application;

fig. 3 is a process flow diagram of a cascaded refrigeration cycle LNG liquefaction system provided in embodiment 2 of the present application;

fig. 4 is a process flow diagram of a cascaded refrigeration cycle LNG liquefaction system provided in embodiment 3 of the present application;

fig. 5 is a process flow diagram of a cascaded refrigeration cycle LNG liquefaction system provided in embodiment 4 of the present application;

Fig. 6 is a schematic diagram of a integrated process flow of the cascaded refrigeration cycle LNG liquefaction system according to embodiment 4 of the present application;

fig. 7 is a process flow diagram of a conventional cascade refrigeration cycle LNG liquefaction system provided in comparative example 1 of the present application.

Icon: a 100-cascade refrigeration cycle LNG liquefaction system;

110-a first refrigeration assembly; 111-a normal temperature first refrigerant compressor; 112-a first buffer tank; 113-a first refrigerant heat exchanger; 1131-a first stage first refrigerant heat exchanger; 1132-a second stage first refrigerant heat exchanger; 1133-three stage first refrigerant heat exchanger; 114-a first refrigerant evaporator; 1141-a first stage first refrigerant evaporator; 1142-a second stage first refrigerant evaporator; 1143-a three stage first refrigerant evaporator; 115-a first refrigerant separator tank; 1151-a first stage first refrigerant separator tank; 1152-a second stage first refrigerant separator tank; 116-a first refrigerant throttle valve; 117-a first liquid phase throttle valve; 118-a first refrigerant heat exchange evaporation integrator; 119-a first refrigerant cooler;

120-a second refrigeration assembly; 121-a normal temperature second refrigerant compressor; 122-a second buffer tank; 123-a second refrigerant heat exchanger; 1231-a primary second refrigerant heat exchanger; 1232-second stage second refrigerant heat exchanger; 1233-three stage second refrigerant heat exchanger; 124-a second refrigerant evaporator; 1241-a first stage second refrigerant evaporator; 1242-a second stage second refrigerant evaporator; 1243-three stage second refrigerant evaporator; 125-a second refrigerant separator tank; 1251-a first stage second refrigerant separator tank; 1252-a second refrigerant separator tank; 126-a second refrigerant throttle valve; 127-a second liquid phase throttle valve; 128-a second refrigerant heat exchange evaporation integrator; 129-a second refrigerant cooler;

130-a third refrigeration assembly; 131-a normal temperature third refrigerant compressor; 132-a third buffer tank; 133-a third refrigerant heat exchanger; 1331-a primary third refrigerant heat exchanger; 1332-a second stage third refrigerant heat exchanger; 134-a third refrigerant evaporator; 1341-a first stage third refrigerant evaporator; 1342-second stage third refrigerant evaporator; 1343-three stage third refrigerant evaporator; 135-a third refrigerant separator tank; 1351-a first stage third refrigerant separator tank; 1352-a second-stage third refrigerant separator tank; 136-a third refrigerant throttle valve; 137-a third liquid phase throttle valve; 1371-a first-stage third liquid-phase throttle valve; 1372-a second-stage third liquid-phase throttle valve; 138-a third refrigerant heat exchange evaporation integrator; 139-a third refrigerant cooler;

201-a first high pressure flow path; 202-a second high pressure flow path; 203-a third high pressure flow path; 204—a feed gas flow path; 205-a first vapor phase sensible heat recovery runner; 206-a first liquid-to-gas phase sensible heat recovery runner; 207-a primary first liquid phase recovery latent heat flow path; 208-a secondary first liquid phase recovery latent heat flow channel; 209-a second vapor phase sensible heat recovery runner; 210-a second liquid-to-gas phase sensible heat recovery runner; 211-a primary second liquid phase recovery latent heat flow channel; 212-a secondary second liquid phase recovery latent heat flow path; 213-third gas phase sensible heat recovery flow path; 214-a third liquid-to-gas phase sensible heat recovery runner; 215-a primary third liquid phase recovery latent heat flow channel; 216-a secondary third liquid phase recovery latent heat flow channel;

300-a conventional cascade refrigeration cycle LNG liquefaction system; 301-low temperature propylene compressor train; 302-a low temperature ethylene compressor train; 303-a low temperature methane compressor train; 304-propylene first-stage separation tank; 305-propylene secondary separation tank; 306-ethylene first-stage separation tank; 307-ethylene secondary separation tank; 308-methane separation tank; 309-propylene first-stage evaporator; 310-propylene secondary evaporator; 311-propylene three-stage evaporator; 312-ethylene first-stage evaporator; 313-ethylene secondary evaporator; 314-ethylene three-stage evaporator; 315-methane heat exchanger; 316-high pressure propylene cooler; 317-high pressure ethylene chiller; 318-high pressure methane cooler; 319-high pressure propylene buffer tank; 320-high pressure ethylene buffer tank; 321-a high-pressure methane buffer tank;

a-refrigerant compressor unit; b-vehicle LNG liquefaction case.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.

In the description of the present invention, it should be noted that, if the terms "upper", "lower", "inner", "outer", and the like indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, or the azimuth or the positional relationship in which the inventive product is conventionally put in use, it is merely for convenience of describing the present invention and simplifying the description, and it is not indicated or implied that the apparatus or element referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus it should not be construed as limiting the present invention.

Furthermore, the terms "first," "second," and the like, if any, are used merely for distinguishing between descriptions and not for indicating or implying a relative importance.

It should be noted that the features of the embodiments of the present invention may be combined with each other without conflict.

Referring to fig. 1-5, the present embodiment provides a cascaded refrigeration cycle LNG liquefaction system 100, which includes a first refrigeration assembly 110, a second refrigeration assembly 120, and a third refrigeration assembly 130;

the first refrigeration assembly 110 includes a normal temperature first refrigerant compressor 111, a first buffer tank 112, a first refrigerant heat exchanger 113, a first refrigerant evaporator 114, a first refrigerant separation tank 115, and a first refrigerant cooler 119;

the second refrigeration assembly 120 includes a normal temperature second refrigerant compressor 121, a second buffer tank 122, a second refrigerant heat exchanger 123, a second refrigerant evaporator 124, a second refrigerant separation tank 125, and a second refrigerant cooler 129;

the third refrigeration assembly 130 includes a normal temperature third refrigerant compressor 131, a third buffer tank 132, a third refrigerant heat exchanger 133, a third refrigerant evaporator 134, a third refrigerant separation tank 135, and a third refrigerant cooler 139.

The refrigerants discharged from the normal temperature first refrigerant compressor 111, the normal temperature second refrigerant compressor 121, and the normal temperature third refrigerant compressor 131 are subjected to evaporation separation by the first refrigerant evaporator, the second refrigerant evaporator, and the third refrigerant evaporator;

The first refrigerant gas phase separated by the first refrigerant evaporator recovers sensible heat by the first refrigerant heat exchanger 113 and returns to the normal temperature first refrigerant compressor 111; the second refrigerant gas phase separated by the second refrigerant evaporator recovers sensible heat by the second refrigerant heat exchanger 123 and returns to the normal temperature second refrigerant compressor 121; the third refrigerant gas phase separated by the third refrigerant evaporator sequentially recovers sensible heat by the third refrigerant heat exchanger 133 and returns to the normal temperature first refrigerant compressor 111.

In the present application, the first refrigeration assembly 110 further includes a first refrigerant separation tank 115, the first refrigeration assembly 110 further includes a second refrigerant separation tank 125, and the first refrigeration assembly 110 further includes a third refrigerant separation tank 135;

the refrigerant discharged from the normal temperature first refrigerant compressor 111, the normal temperature second refrigerant compressor 121, and the normal temperature third refrigerant compressor 131 may be evaporated and gas-liquid separated, or may be evaporated and gas-liquid separated. Specifically, the refrigerant may be first evaporated by the first, second and third refrigerant evaporators 114, 124 and 134, respectively, and then separated by the first, second and third refrigerant separation tanks 115, 125 and 135; alternatively, the refrigerant is first separated by the first, second and third refrigerant separation tanks 115, 125 and 135, respectively, and then evaporated by the first, second and third refrigerant evaporators 124 and 134. In the application, by adding the first refrigerant heat exchanger 113, the second refrigerant heat exchanger 123 and the third refrigerant heat exchanger 133, on one hand, the cold energy of the gas-phase first refrigerant, the gas-phase second refrigerant and the gas-phase third refrigerant is recovered, and on the other hand, the temperature of the gas-phase refrigerant of the back-compression unit is ensured to be normal temperature, and the compressor can be a normal temperature compressor, so that the cost investment of the compressor is reduced.

Further, in order to improve the heat exchange efficiency, in the present application, the second refrigerant gas phase may further enter the first refrigerant heat exchanger 113 to continue heat exchange after passing through the second refrigerant heat exchanger 123, and then enter the normal temperature second refrigerant compressor 121 after passing through the first refrigerant heat exchanger 113 to exchange heat; the third refrigerant gas phase may further pass through at least one of the second refrigerant heat exchanger 123 and the first refrigerant heat exchanger 113 to perform heat exchange after passing through the third refrigerant heat exchanger 133, and then is introduced into the normal temperature third refrigerant compressor 131 after heat exchange is completed. The heat exchange route can be adjusted or selected according to actual conditions, so that a better heat exchange effect is achieved, the temperature of the gas-phase refrigerant after heat exchange is ensured to be normal temperature, the compressor can be a normal temperature compressor, and the cost investment of the compressor is reduced.

In addition, in order to avoid that the temperature difference is large because the refrigerant discharged from the compressor directly enters the evaporator or the separation tank, the first refrigerant discharged from the normal-temperature first refrigerant compressor 111 in the present application is introduced into the first refrigerant heat exchanger 113 to perform heat exchange before entering the first refrigerant evaporator; the first refrigerant discharged from the normal temperature second refrigerant compressor 121 is introduced into the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 to exchange heat before entering the second refrigerant evaporator; the third refrigerant discharged from the normal temperature third refrigerant compressor 131 is introduced into the first refrigerant heat exchanger 113, the first refrigerant evaporator 114, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124 before entering the third refrigerant evaporator, thereby performing heat exchange. By arranging the first refrigerant heat exchanger 113, the second refrigerant heat exchanger 123 and the third refrigerant heat exchanger 133, the temperature difference from the compressor to the evaporator or the separation tank can be reduced, so that the temperature gradient is more, the product temperature is lower, and the device is more energy-saving.

In the application, a plurality of flow passages are arranged in each heat exchanger and evaporator, so that different materials can conveniently enter and exit, one passage of the same substance is named as one flow passage in the application, specifically, the first refrigerant heat exchanger 113 is provided with a first high-pressure flow passage 201 for high-pressure first refrigerant to enter and exit, the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 are provided with a second high-pressure flow passage 202 for high-pressure second refrigerant to enter and exit in sequence, and the first refrigerant heat exchanger 113, the first refrigerant evaporator 114, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124 are provided with a third high-pressure flow passage 203 for high-pressure third refrigerant to enter and exit in sequence; the first refrigerant heat exchanger 113, the first refrigerant evaporator 114, the second refrigerant heat exchanger 123, the second refrigerant evaporator 124, the third refrigerant heat exchanger 133 and the third refrigerant evaporator 134 are each provided with a feed gas flow passage 204 through which feed gas sequentially passes in and out.

The first refrigerant heat exchanger 113 is provided with a first gas-phase sensible heat recovery flow passage 205 and a first liquid-to-gas-phase sensible heat recovery flow passage 206, and the first refrigerant evaporator 114 is provided with a first-stage first-liquid-phase latent heat recovery flow passage 207 and a second-stage first-liquid-phase latent heat recovery flow passage 208; the first refrigerant heat exchanger 113 and the second refrigerant heat exchanger 123 are respectively provided with a second gas-phase sensible heat recovery flow channel 209 and a second liquid-to-gas-phase sensible heat recovery flow channel 210, and the second refrigerant evaporator 124 is provided with a first-stage second liquid-phase recovery latent heat flow channel 211 and a second-stage second liquid-phase recovery latent heat flow channel 212; the first refrigerant heat exchanger 113, the second refrigerant heat exchanger 123 and the third refrigerant heat exchanger 133 are each provided with a third vapor-phase sensible heat recovery flow passage 213 and a third liquid-to-vapor-phase sensible heat recovery flow passage 214, and the second refrigerant evaporator 124 is provided with a first-stage third liquid-phase latent heat recovery flow passage 215 and a second-stage third liquid-phase latent heat recovery flow passage 216.

Referring to fig. 2, an outlet of a normal temperature first refrigerant compressor 111 is communicated with a first high pressure runner 201, the first high pressure runner 201 is communicated with a first liquid-phase recovery latent heat runner 207, a first refrigerant throttle valve 116 is arranged on a pipeline between the first high pressure runner 201 and the first liquid-phase recovery latent heat runner 207, the first liquid-phase recovery latent heat runner 207 is communicated with a first refrigerant separation tank 115, a gas phase outlet of the first refrigerant separation tank 115 is communicated with a first gas-phase sensible heat recovery runner 205, a liquid phase outlet of the first refrigerant separation tank 115 is communicated with a second first liquid-phase recovery latent heat runner 208, the second first liquid-phase recovery latent heat runner 208 is communicated with a first liquid-to-gas-phase sensible heat recovery runner 206, and both the first gas-phase sensible heat recovery runner 205 and the first liquid-to-gas-phase sensible heat recovery runner 206 are communicated with an inlet of the normal temperature first refrigerant compressor 111;

the outlet of the normal temperature second refrigerant compressor 121 is communicated with a second high-pressure runner 202, the second high-pressure runner 202 is communicated with a first-stage second liquid-phase recovery latent heat runner 211, a second refrigerant throttle valve 126 is arranged on a pipeline between the second high-pressure runner 202 and the first-stage second liquid-phase recovery latent heat runner 211, the first-stage second liquid-phase recovery latent heat runner 211 is communicated with a second refrigerant separation tank 125, the gas-phase outlet of the second refrigerant separation tank 125 is communicated with a second gas-phase sensible heat recovery runner 209, the liquid-phase outlet of the second refrigerant separation tank 125 is communicated with a second-stage second liquid-phase recovery latent heat runner 212, the second-stage second liquid-phase recovery latent heat runner 212 is communicated with a second liquid-to-gas-phase sensible heat recovery runner 210, and both the second gas-phase sensible heat recovery runner 209 and the second liquid-to-gas-phase sensible heat recovery runner 210 are communicated with the inlet of the normal temperature second refrigerant compressor 121;

The outlet of the normal temperature third refrigerant compressor 131 is communicated with the third high pressure runner 203, the third high pressure runner 203 is communicated with the first-stage third liquid-phase recovery latent heat runner 215, a third refrigerant throttle valve 136 is arranged on a pipeline between the third high pressure runner 203 and the first-stage third liquid-phase recovery latent heat runner 215, the first-stage third liquid-phase recovery latent heat runner 215 is communicated with the third refrigerant separation tank 135, the gas-phase outlet of the third refrigerant separation tank 135 is communicated with the third gas-phase sensible heat recovery runner 213, and the liquid-phase outlet of the third refrigerant separation tank 135 is communicated with the second-stage third liquid-phase recovery latent heat runner 216. The second-stage third liquid-phase recovery latent heat flow passage 216 is communicated with the third liquid-to-gas-phase sensible heat recovery flow passage 214, and both the third gas-phase sensible heat recovery flow passage 213 and the third liquid-to-gas-phase sensible heat recovery flow passage 214 are communicated with the inlet of the normal-temperature third refrigerant compressor 131.

It should be understood that fig. 2 in the present application shows only a typical but non-limiting example, for example, "the primary second liquid-phase recovery latent heat flow channel 211 communicates with the second refrigerant separation tank 125" in other embodiments, it may be replaced by "the primary second liquid-phase recovery latent heat flow channel 211 communicates with the first refrigerant evaporator 114", and thus, the connection manner of the present application may have various alternatives, and some structures thereof may be omitted.

In the present application, the pressurization operation is performed by passing the first refrigerant, the second refrigerant and the third refrigerant into the normal temperature first refrigerant compressor 111, the normal temperature second refrigerant compressor 121 and the normal temperature third refrigerant compressor 131, respectively, and then the throttling is performed through the throttle valve, wherein the design of the first liquid-phase throttle valve 117, the second liquid-phase throttle valve 127 and the third liquid-phase throttle valve 137 facilitates the depressurization of the liquid phase of the gas-liquid separation. Heat exchange with the purified natural gas is performed in subsequent heat exchangers (the first refrigerant heat exchanger 113, the second refrigerant heat exchanger 123 and the third refrigerant heat exchanger 133) and evaporators (the first refrigerant evaporator 114, the second refrigerant evaporator 124 and the third refrigerant evaporator 134) step by step, thereby providing cold for the liquefaction of the purified natural gas.

The first buffer tank 112 is disposed between the normal temperature first refrigerant compressor 111 and the first high pressure flow path 201, the second buffer tank 122 is disposed between the second high pressure flow path 202 and the first-stage second liquid-phase latent heat recovery flow path 211, and the third buffer tank 132 is disposed between the third high pressure flow path 203 and the first-stage third liquid-phase latent heat recovery flow path 215. According to the application, the first buffer tank 112, the second buffer tank 122 and the third buffer tank 132 can buffer the refrigerant added by the compressor to a certain extent, so that the stability of the subsequent flow passage is protected.

In the application, the number and the setting method of the heat exchangers and the evaporators can be adjusted according to actual conditions, for example, different heat exchangers and evaporators can be set according to different scale natural gas liquefaction treatment capacity or application scenes.

For example, when applied to a small-scale device, the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 are integrally provided, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124 are integrally provided, and the third refrigerant heat exchanger 133 and the third refrigerant evaporator 134 are integrally provided. At this time, the device integration level is high, and the occupied area is smaller.

For example, when applied to the LNG on board, the normal temperature first refrigerant compressor 111, the normal temperature second refrigerant compressor 121, and the normal temperature third refrigerant compressor 131 are highly integrated as a refrigerant compressor group; the first refrigerant heat exchanger 113, the first refrigerant evaporator 114, the second refrigerant heat exchanger 123, the second refrigerant evaporator 124, the third refrigerant heat exchanger 133 and the third refrigerant evaporator 134 are highly integrated into a vehicle-mounted LNG liquefaction tank, so that the application of the vehicle-mounted LNG is realized. At this time, the device integration level is high, and the occupied area is smaller.

For example, when applied to a large-scale apparatus, the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 are separately provided and have N-stage heat exchange and N-stage evaporation, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124 are separately provided and have N-stage heat exchange and N-stage evaporation, and the third refrigerant heat exchanger 133 and the third refrigerant evaporator 134 are separately provided and have N-stage heat exchange and N-stage evaporation. N is greater than or equal to 2 in the N-stage heat exchange and N-stage evaporation, and the number of the first refrigerant separation tank 115, the second refrigerant separation tank 125 and the third refrigerant separation tank 135 is N-1.

A first liquid-phase throttle valve 117 is disposed on a first refrigerant inlet line of the first refrigerant evaporator 114 of each stage, a second liquid-phase throttle valve 127 is disposed on a second refrigerant inlet line of the second refrigerant evaporator 124 of each stage, and a third liquid-phase throttle valve 137 is disposed on a third refrigerant inlet line of the third refrigerant evaporator 134 of each stage.

In addition, the present application also provides a cascade refrigeration cycle LNG liquefaction method using the cascade refrigeration cycle LNG liquefaction system 100 according to any one of the foregoing embodiments, comprising the steps of:

The first refrigerant discharged from the normal temperature first refrigerant compressor 111 is subjected to heat exchange through the first refrigerant heat exchanger 113, is introduced into the first refrigerant evaporator to recover latent heat, and is separated into gas phase and liquid phase through the first refrigerant separation tank 115, wherein the gas phase is subjected to gas phase sensible heat recovery through the first refrigerant heat exchanger 113 and then enters an inlet of the first refrigerant compressor, and the liquid phase is subjected to liquid phase latent heat recovery through the first refrigerant evaporator 114 and then enters the first refrigerant heat exchanger 113 to recover gas phase sensible heat and enters an inlet of the first refrigerant compressor;

the second refrigerant discharged from the normal temperature second refrigerant compressor 121 is precooled through the first refrigerant heat exchanger and the first refrigerant evaporator 114, latent heat is recovered through the second refrigerant evaporator 124, and then gas-liquid two phases are separated through the second refrigerant separation tank 125, wherein gas phase sequentially recovers gas phase sensible heat through the second refrigerant heat exchanger 123 and the first refrigerant heat exchanger 113 and then enters an inlet of the second refrigerant compressor, and liquid phase sequentially enters the second refrigerant heat exchanger 123 and the first refrigerant heat exchanger 113 to recover gas phase sensible heat and then enters an inlet of the second refrigerant compressor after liquid phase recovers liquid phase latent heat through the second refrigerant evaporator 124;

The third refrigerant discharged from the normal temperature third refrigerant compressor 131 is precooled through the first refrigerant heat exchanger 113, the first refrigerant evaporator 114, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124, then latent heat is recovered through the third refrigerant evaporator 134, and then two phases of gas and liquid are separated through the third refrigerant separation tank 135, wherein a gas phase sequentially recovers sensible heat of the gas phase through the third refrigerant heat exchanger 133, the second refrigerant heat exchanger 123 and the first refrigerant heat exchanger 113, then enters an inlet of the normal temperature third refrigerant compressor 131, a liquid phase sequentially enters the third refrigerant heat exchanger 133, the second refrigerant heat exchanger 123 and the first refrigerant heat exchanger 113 after recovering latent heat of the liquid phase through the third refrigerant evaporator 134, and then enters an inlet of the normal temperature third refrigerant compressor 131.

The first refrigerant, the second refrigerant, and the third refrigerant are different from each other and are each selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene; any of butane, butene, pentane and pentene.

When the first refrigerant is propane, the second refrigerant is ethylene, and the third refrigerant is methane, the pressure of the first refrigerant discharged from the normal-temperature first refrigerant compressor 111 is more than or equal to 0.47Mpa, the pressure of the first refrigerant entering the first refrigerant evaporator 114 is 0.1-0.47 MPaA, and the temperature is-43-0 ℃;

The pressure of the second refrigerant discharged through the normal temperature second refrigerant compressor 121 is more than or equal to 1.38MPaA, the pressure of the second refrigerant entering the second refrigerant evaporator 124 is 0.1-1.38 MPaA, and the temperature is-104 to-42 ℃;

the pressure of the third refrigerant discharged through the normal temperature third refrigerant compressor 131 is equal to or more than 2.44mpa, the pressure of the third refrigerant entering the third refrigerant evaporator 134 is 0.1 to 2.44mpa, and the temperature is-161.8 to-102 ℃.

The technical scheme of the application is explained below in connection with specific embodiments.

Example 1

Taking fig. 1 as an example, the process is a two-stage throttling cascade refrigeration cycle LNG liquefaction process, and a normal temperature compressor is adopted. Wherein the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 are two stages.

The high-pressure liquid-phase propane (the pressure is more than or equal to the saturation pressure and is 10-50 ℃) from the normal-temperature first refrigerant compressor 111 is cooled by the first refrigerant cooler 119 and then enters the first buffer tank 112 for buffering, then is introduced into the first-stage first refrigerant heat exchanger 1131, the high-pressure propane is precooled to about 10 ℃, and is reduced in pressure to about 0.298MPaA through the first refrigerant throttle valve 116. The medium pressure propane (0.298 MPaA, -15 ℃) enters a first-stage first refrigerant evaporator 1141, after recovering part of latent heat of liquid phase propane, gas-liquid two phases are separated through a first refrigerant separating tank 115, after recovering sensible heat of gas phase propane through a first-stage first refrigerant heat exchanger 1131 (37 ℃,0.295 MPaA), the gas phase propane enters a second-stage inlet of a normal-temperature first refrigerant compressor 111, and the liquid phase propane is depressurized to about 0.124MPaA through a first liquid phase throttle valve 117. The low-pressure propane (0.124 MPaA, -37.36 ℃) enters a second-stage first refrigerant evaporator 1142, after the whole latent heat of the liquid-phase propane is recovered, the sensible heat of the gas-phase propane is recovered through a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131 (37 ℃,0.12 MPaA) and then enters a first-stage inlet of a normal-temperature first refrigerant compressor 111.

The high-pressure ethylene (1.85 mpa, 10 to 40 ℃) from the normal-temperature second refrigerant compressor 121 is cooled by the second refrigerant cooler 129, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, and the second-stage first refrigerant evaporator 1142, precooled to-35 ℃ and then introduced into the second buffer tank 122 to be buffered, and then reduced in pressure to about 0.325mpa by the second refrigerant throttle valve 126. The medium-pressure ethylene (0.325 MPaA, -81 ℃) enters a first-stage second refrigerant evaporator 1241, after recovering part of latent heat of liquid-phase ethylene, two phases of gas and liquid are separated through a second refrigerant separating tank 125, the gas-phase ethylene is recovered by a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, after recovering the sensible heat of the gas-phase ethylene (37 ℃,0.316 MPaA) enters a second-stage inlet of a normal-temperature second refrigerant compressor 121, and the liquid-phase ethylene is reduced to about 0.127MPaA through a second liquid-phase throttle valve 127. The low-pressure ethylene (0.127 MPaA, -99 ℃) enters a second-stage second refrigerant evaporator 1242, after the whole latent heat of the liquid-phase ethylene is recovered, the liquid-phase ethylene sensible heat is recovered through a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, and then the liquid-phase ethylene sensible heat (37 ℃,0.12 MPaA) enters a first-stage inlet of a normal-temperature second refrigerant compressor 121.

The high-pressure methane (3.2 mpa, 10 to 40 ℃) from the normal-temperature third refrigerant compressor 131 is cooled 139 by the third refrigerant cooler 139, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, the second-stage first refrigerant evaporator 1142, the first-stage second refrigerant heat exchanger 1231, the first-stage second refrigerant evaporator 1241, the second-stage second refrigerant heat exchanger 1232, and the second-stage second refrigerant evaporator 1242, and then introduced into the third buffer tank 132 to be buffered, and reduced in pressure to about 1.091mpa by the third refrigerant throttle 136. Medium-pressure methane (1.091 MPaA, -122 ℃) enters a first-stage third refrigerant evaporator 1341, partial latent heat of liquid-phase methane is recovered, gas-liquid two phases are separated through a first-stage third refrigerant separation tank 1351, gas-phase methane is recovered through a third refrigerant heat exchanger 133, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, sensible heat of the gas-phase methane is recovered (37 ℃,0.108 MPaA) and then enters a third-stage inlet of a normal-temperature third refrigerant compressor 131, and the liquid-phase methane is reduced to about 0.388MPaA through a first-stage third liquid-phase throttle valve 1371. The low-pressure methane (0.388 MPaA, -142 ℃) enters a second-stage third refrigerant evaporator 1342, partial latent heat of liquid-phase methane is recovered, gas-liquid two phases are separated through a second-stage third refrigerant separating tank 1352, the gas-phase methane is recovered through a third refrigerant heat exchanger 133, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, the sensible heat of the gas-phase methane (37 ℃ and 0.108 MPaA) enters a second-stage inlet of a normal-temperature third refrigerant compressor 131, and the liquid-phase methane is depressurized to about 0.128MPaA through a second-stage third liquid-phase throttle valve 1372. The low-pressure methane (0.128 MPaA, -158.7 ℃) enters a three-stage third refrigerant evaporator 1343, after the total latent heat of the liquid-phase methane is recovered, the liquid-phase methane is recovered through a third refrigerant heat exchanger 133, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, and then the liquid-phase methane sensible heat (37 ℃ and 0.12 MPaA) enters a first-stage inlet of a normal-temperature third refrigerant compressor 131.

The natural gas (40 ℃) purified at normal temperature is cooled to-158 ℃ step by step after passing through a first-stage first refrigerant heat exchanger 1131, a first-stage first refrigerant evaporator 1141, a second-stage first refrigerant heat exchanger 1132, a second-stage first refrigerant evaporator 1142, a first-stage second refrigerant heat exchanger 1231, a first-stage second refrigerant evaporator 1241, a second-stage second refrigerant heat exchanger 1232, a second-stage second refrigerant evaporator 1242, a third refrigerant heat exchanger 133, a first-stage third refrigerant evaporator 1341, a second-stage third refrigerant evaporator 1342 and a third-stage third refrigerant evaporator 1343, is reduced to 0.11-0.15 mpa (product pressure is adjustable) by a product J-T valve, and is sent to an LNG tank or LNG tank car.

Example 2

Taking fig. 3 as an example, the process is a three-stage throttling cascade refrigeration cycle LNG liquefaction process, and is improved on the basis of the embodiment 1 by adopting a normal-temperature compressor, so that the temperature gradient is more, the product temperature is lower, and the device is more energy-saving.

The high-pressure liquid-phase propane (the pressure is more than or equal to the saturation pressure and is 10-50 ℃) from the normal-temperature first refrigerant compressor 111 is cooled by the first refrigerant cooler 119 and then enters the first buffer tank 112 to be buffered, then is introduced into the first-stage first refrigerant heat exchanger 1131, the high-pressure propane is precooled to about 10 ℃, and is reduced in pressure to about 0.6MPaA through the first refrigerant throttle valve 116. The medium pressure propane (0.6 MPaA,7.8 ℃) enters a first-stage first refrigerant evaporator 1141, after recovering part of latent heat of liquid phase propane, gas-liquid two phases are separated by a first-stage first refrigerant separating tank 1151, after recovering sensible heat of gas phase propane by a first-stage first refrigerant heat exchanger 1131 (35 ℃,0.6 MPaA) enters a third-stage inlet of a normal-temperature first refrigerant compressor 111, and the liquid phase propane is depressurized to about 0.24MPaA by a first liquid phase throttle valve 117 (one stage). The low pressure propane (0.24 MPaA, -20 ℃) enters a second-stage first refrigerant evaporator 1142, after recovering part of latent heat of liquid phase propane, gas-liquid two phases are separated by a second-stage first refrigerant separating tank 1152, gas phase propane is recovered by a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131 (10), after recovering gas phase propane sensible heat (35 ℃,0.24 MPaA) enters a second-stage inlet of a normal-temperature first refrigerant compressor 111, and liquid phase propane is reduced to about 0.1MPaA by a first liquid phase throttle valve 117 (second stage). The low-pressure propane (0.1 MPaA, -42 ℃) enters the primary inlet of the normal-temperature first refrigerant compressor 111 after the whole latent heat and sensible heat of the propane are recovered by the three-stage first refrigerant evaporator 1143, the three-stage first refrigerant heat exchanger 1133, the two-stage first refrigerant heat exchanger 1132 and the primary first refrigerant heat exchanger 1131 (0.1 MPaA, 35C).

The high-pressure ethylene (1.5 mpa, 40 ℃) from the normal-temperature second refrigerant compressor 121 is cooled 129 by the second refrigerant cooler 129, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, the second-stage first refrigerant evaporator 1142, the third-stage first refrigerant heat exchanger 1133 and the third-stage first refrigerant evaporator 1143, precooled to-40 ℃ and then introduced into the second buffer tank 122 to be buffered, and then reduced in pressure to about 0.6mpa by the second refrigerant throttle valve 126. The medium-pressure ethylene (0.6 MPaA, -66 ℃) enters a first-stage second refrigerant evaporator 1241, after recovering part of latent heat of liquid-phase ethylene, two phases of gas and liquid are separated through a first-stage second refrigerant separating tank 1251, the gas-phase ethylene is recovered by a first-stage second refrigerant heat exchanger 1231, a third-stage first refrigerant heat exchanger 1133, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, after recovering the sensible heat of the gas-phase ethylene (35 ℃,0.6 MPaA) enters a three-stage inlet of a normal-temperature second refrigerant compressor 121, and the liquid-phase ethylene is reduced in pressure to about 0.25MPaA through a second liquid-phase throttle valve 127. The low-pressure ethylene (0.25 MPaA, -87 ℃) enters a second-stage second refrigerant evaporator 1242, after partial latent heat of liquid-phase ethylene is recovered, gas-liquid two phases are separated through a second-stage second refrigerant separating tank 1252 (7), gas-phase ethylene is recovered through a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a third-stage first refrigerant heat exchanger 1133 (14), a second-stage first refrigerant heat exchanger 1132 (12) and a first-stage first refrigerant heat exchanger 1131, after the gas-phase ethylene sensible heat (35 ℃,0.24 MPaA) is recovered, the gas-phase ethylene enters a second-stage inlet of a normal-temperature second refrigerant compressor 121, and the liquid-phase ethylene is reduced to about 0.1MPaA through an ethylene three-stage J-T valve. Low-pressure ethylene (0.1 mpa, -104 ℃) enters a primary inlet of the normal-temperature second refrigerant compressor 121 through a three-stage second refrigerant evaporator 1243 (21), a three-stage second refrigerant heat exchanger 1233 (20), a two-stage second refrigerant heat exchanger 1232 (18), a primary second refrigerant heat exchanger 1231 (16), a three-stage first refrigerant heat exchanger 1133 (14), a two-stage first refrigerant heat exchanger 1132 (12) and a primary first refrigerant heat exchanger 1131 (10) after recovering all latent heat and sensible heat of the ethylene (0.1 mpa, 35 c).

The high-pressure methane (2.55 mpa, 40 ℃) from the normal-temperature third refrigerant compressor 131 is cooled 129 by the second refrigerant cooler 129, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, the second-stage first refrigerant evaporator 1142, the third-stage first refrigerant heat exchanger 1133, the third-stage first refrigerant evaporator 1143, the first-stage second refrigerant heat exchanger 1231, the first-stage second refrigerant evaporator 1241 (17), the second-stage second refrigerant heat exchanger 1232, the second-stage second refrigerant evaporator 1242 (19), the third-stage second refrigerant heat exchanger 1233, and the third-stage second refrigerant evaporator 1243, after being precooled to-102 ℃, introduced into the third buffer tank 132, buffered, and reduced in pressure to about 0.86mpa by the third refrigerant throttle 136. Medium-pressure methane (0.86 mpa, -127 ℃) enters a first-stage third refrigerant evaporator 1341, partial latent heat of liquid-phase methane is recovered, two phases of gas and liquid are separated through a first-stage third refrigerant separation tank 1351, the gas-phase methane is subjected to three-stage inlet of a normal-temperature third refrigerant compressor 131 after being recovered by a third refrigerant heat exchanger 133, a third-stage second refrigerant heat exchanger 1233, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a third-stage first refrigerant heat exchanger 1133, a second-stage first refrigerant heat exchanger 1132 (12) and a first-stage first refrigerant heat exchanger 1131 (10), and the liquid-phase methane is subjected to pressure reduction to about 0.3mpa through a first-stage third liquid-phase throttle valve 1371. The low-pressure methane (0.3 MPaA, -147 ℃) enters a second-stage third refrigerant evaporator 1342, partial latent heat of liquid-phase methane is recovered, gas-liquid two phases are separated through a second-stage third refrigerant separation tank 1352, the gas-phase methane enters a second-stage inlet of a normal-temperature third refrigerant compressor 131 after being recovered by a third refrigerant heat exchanger 133 (22), a third-stage second refrigerant heat exchanger 1233 (20), a second-stage second refrigerant heat exchanger 1232 (18), a first-stage second refrigerant heat exchanger 1231 (16), a third-stage first refrigerant heat exchanger 1133 (14), a second-stage first refrigerant heat exchanger 1132 (12) and a first-stage first refrigerant heat exchanger 1131 (10), and the liquid-phase methane is depressurized to about 0.1MPaA through a second-stage third liquid-phase throttle valve 1372. The low-pressure methane (0.1 MPaA, -162 ℃) enters a three-stage third refrigerant evaporator 1343 (25), after the whole latent heat of the liquid-phase methane is recovered, the liquid-phase methane enters a first-stage inlet of the normal-temperature third refrigerant compressor 131 through a third refrigerant heat exchanger 133 (22), a three-stage second refrigerant heat exchanger 1233 (20), a second-stage second refrigerant heat exchanger 1232 (18), a first-stage second refrigerant heat exchanger 1231 (16), a three-stage first refrigerant heat exchanger 1133 (14), a second-stage first refrigerant heat exchanger 1132 (12) and a first-stage first refrigerant heat exchanger 1131 (10), and after the sensible heat of the liquid-phase methane is recovered (35 ℃,0.1 MPaA).

The normal temperature purified natural gas (40 ℃) is cooled to below-158 ℃ step by step through a first-stage first refrigerant heat exchanger 1131 (10), a first-stage first refrigerant evaporator 1141 (11), a second-stage first refrigerant heat exchanger 1132 (12), a second-stage first refrigerant evaporator 1142 (13), a third-stage first refrigerant heat exchanger 1133 (14), a third-stage first refrigerant evaporator 1143 (15), a first-stage second refrigerant heat exchanger 1231 (16), a first-stage second refrigerant evaporator 1241 (17), a second-stage second refrigerant heat exchanger 1232 (18), a second-stage second refrigerant evaporator 1242 (19), a third-stage second refrigerant heat exchanger 1233 (20), a third-stage second refrigerant evaporator 1243 (21), a third-stage refrigerant heat exchanger 133 (22), a first-stage third refrigerant evaporator 1341 (23), a second-stage third refrigerant evaporator 1342 (24) and a third-stage third refrigerant evaporator 1343 (25), is depressurized to 0.11-0.15 mpa (mpa) pressure is regulated through a product J-T valve and then sent to an LNG tank or LNG storage tank.

Example 3

Taking fig. 4 as an example, the process is a three-stage throttling cascade refrigeration cycle LNG liquefaction process, and is modified based on embodiment 1 by adopting a normal temperature compressor, wherein the first refrigerant heat exchanger 113 and the first refrigerant evaporator 114 in embodiment 1 are integrated into a first refrigerant heat exchange evaporation integrator 118, the second refrigerant heat exchanger 123 and the second refrigerant evaporator 124 are integrated into a second refrigerant heat exchange evaporation integrator 128, and the third refrigerant heat exchanger 133 and the third refrigerant evaporator 134 are integrated into a third refrigerant heat exchange evaporation integrator 138.

The high-pressure liquid-phase propane (the pressure is more than or equal to the saturation pressure and is 10-50 ℃) from the normal-temperature first refrigerant compressor 111 is cooled by a first refrigerant cooler 119 and then enters a first buffer tank 112 for buffering, then is introduced into a first refrigerant heat exchange evaporation integrator 118, the high-pressure propane is precooled to about 11 ℃, and is reduced in pressure to about 0.6MPaA through a first refrigerant throttle valve 116. The medium pressure propane (0.6 MPaA,7.8 ℃) enters the first refrigerant heat exchange evaporation integrator 118, after recovering part of latent heat of liquid phase propane, gas-liquid two phases are separated through the first stage first refrigerant separation tank 1151, after recovering sensible heat of gas phase propane through the first refrigerant heat exchange evaporation integrator 118 (35 ℃,0.6 MPaA) enters the third-stage inlet of the normal temperature first refrigerant compressor 111, and the liquid phase propane is depressurized to about 0.24MPaA through the first liquid phase throttle valve 117. The low pressure propane (0.24 MPaA, -20 ℃) enters the first refrigerant heat exchange evaporation integrator 118, after recovering part of the latent heat of the liquid phase propane, the gas phase and the liquid phase are separated by the second-stage first refrigerant separation tank 1152, the gas phase propane recovers the sensible heat of the gas phase propane by the first refrigerant heat exchange evaporation integrator 118 (35 ℃,0.24 MPaA) and enters the second-stage inlet of the normal temperature first refrigerant compressor 111, and the liquid phase propane is depressurized to about 0.1MPaA by the first liquid phase throttle valve 117. The low pressure propane (0.1 MPaA, -42 ℃) passes through the first refrigerant heat exchange and evaporation integrator 118, and after the whole latent heat and sensible heat of the propane are recovered (0.1 MPaA,35 ℃) enters the first-stage inlet of the normal temperature first refrigerant compressor 111.

The high-pressure ethylene (1.5 mpa, 40 ℃) from the normal-temperature second refrigerant compressor 121 is cooled by the first refrigerant cooler 119, then enters the first buffer tank 112 to be buffered, then enters the first refrigerant heat exchange and evaporation integrator 118, is precooled to about-40 ℃ to enter the second buffer tank 122 to be buffered, and is reduced in pressure to about 0.6mpa by the second refrigerant throttle valve 126. The medium-pressure ethylene (0.6 MPaA, -66 ℃) enters the second refrigerant heat exchange evaporation integrator 128, after recovering part of latent heat of the liquid-phase ethylene, two phases of gas and liquid are separated through the first-stage second refrigerant separation tank 1251 (6), the gas-phase ethylene is recovered by the second refrigerant heat exchange evaporation integrator 128 and the first refrigerant heat exchange evaporation integrator 118, sensible heat of the gas-phase ethylene (35 ℃,0.6 MPaA) enters the three-stage inlet of the normal-temperature second refrigerant compressor 121, and the liquid-phase ethylene is depressurized to about 0.25MPaA through the second liquid-phase throttle valve 127. The low-pressure ethylene (0.25 MPaA, -87 ℃) enters the second refrigerant heat exchange evaporation integrator 128, after recovering part of latent heat of the liquid-phase ethylene, two phases of gas and liquid are separated through the second-stage second refrigerant separation tank 1252 (7), the gas-phase ethylene is recovered by the second refrigerant heat exchange evaporation integrator 128 and the first refrigerant heat exchange evaporation integrator 118, sensible heat of the gas-phase ethylene (35 ℃,0.24 MPaA) enters the second-stage inlet of the normal-temperature second refrigerant compressor 121, and the liquid-phase ethylene is reduced to about 0.1MPaA through the ethylene three-stage J-T valve. The low-pressure ethylene (0.1 MPaA, -104 ℃) passes through the second refrigerant heat exchange evaporation integrator 128 and the first refrigerant heat exchange evaporation integrator 118, and enters the first-stage inlet of the normal-temperature second refrigerant compressor 121 after the whole latent heat and sensible heat of the ethylene are recovered (0.1 MPaA,35 ℃).

The high-pressure methane (2.55 mpa, 40 ℃) from the normal-temperature third refrigerant compressor 131 is cooled by the third refrigerant cooler 139, then introduced into the first refrigerant heat-exchanging evaporation integrator 118 and the second refrigerant heat-exchanging evaporation integrator 128, precooled to about-102 ℃ and introduced into the third buffer tank 132 to be buffered, and then reduced in pressure to about 0.86mpa by the third refrigerant throttle valve 136. Medium-pressure methane (0.86 MPaA, -127 ℃) enters a third refrigerant heat exchanger 133 (12), partial latent heat of liquid-phase methane is recovered, gas-liquid two phases are separated through a first-stage third refrigerant separating tank 1351 (8), gas-phase methane is recovered through a third refrigerant heat exchange evaporation integrator 138 (12), a second refrigerant heat exchange evaporation integrator 128 and a first refrigerant heat exchange evaporation integrator 118, the sensible heat of gas-phase methane (35 ℃ and 0.85 MPaA) enters a three-stage inlet of a normal-temperature third refrigerant compressor 131, and the liquid-phase methane is reduced in pressure to about 0.3MPaA through a first-stage third liquid-phase throttle valve 1371. The low-pressure methane (0.3 MPaA, -147 ℃) enters a third refrigerant heat exchange evaporation integrator 138 (12), after partial latent heat of liquid-phase methane is recovered, two phases of gas and liquid are separated through a second-stage third refrigerant separation tank 1352 (9), the gas-phase methane is recovered by the third refrigerant heat exchange evaporation integrator 138 (12), a second refrigerant heat exchange evaporation integrator 128 and a first refrigerant heat exchange evaporation integrator 118, after the sensible heat of the gas-phase methane is recovered (35 ℃,0.28 MPaA) enters a second-stage inlet of a normal-temperature third refrigerant compressor 131, and the liquid-phase methane is reduced to about 0.1MPaA through a second-stage third liquid-phase throttle valve 1372. The low-pressure methane (0.1 MPaA, -162 ℃) passes through the third refrigerant heat exchanger 133 (12), the second refrigerant heat exchange evaporation integrator 128 and the first refrigerant heat exchange evaporation integrator 118, and enters the first-stage inlet of the normal-temperature third refrigerant compressor 131 after the total latent heat and sensible heat of ethylene are recovered (0.1 MPaA,35 ℃). The normal temperature purified natural gas (40 ℃) is cooled to below minus 158 ℃ step by step after passing through the first refrigerant heat exchange evaporation integrator 118, the second refrigerant heat exchange evaporation integrator 128 and the third refrigerant heat exchanger 133 (12), is depressurized to 0.11-0.15 MPaA (product pressure is adjustable) by a product J-T valve and is then sent to an LNG storage tank or an LNG tank car.

Example 4

Taking fig. 5 as an example, the improvement is performed on the basis of the embodiment 1 and the embodiment 2, and compared with the embodiment 1 and the embodiment 2, the way ensures that the refrigerant entering the evaporator is in full liquid phase, and reduces the operation difficulty. The process is a two-stage throttling and three-stage throttling combined cascading refrigeration cycle LNG liquefaction process, and compared with the embodiment 1 and the embodiment 2, the throttling process route is different, and a normal-temperature compressor is adopted.

The high-pressure liquid-phase propane (the pressure is more than or equal to the saturation pressure and is 10-50 ℃) from the normal-temperature first refrigerant compressor 111 is cooled by the first refrigerant cooler 119 and then enters the first buffer tank 112 for buffering, then is introduced into the first-stage first refrigerant heat exchanger 1131, the high-pressure propane is precooled to about 10 ℃, and is reduced in pressure to about 0.298MPaA through the first refrigerant throttle valve 116. The medium pressure propane (0.298 MPaA, -15 ℃) enters the first refrigerant separating tank 115, the gas phase and the liquid phase are separated, part of the liquid phase propane enters the first-stage first refrigerant evaporator 1141, after the liquid phase latent heat is recovered, the liquid phase propane and the medium pressure gas phase propane are summarized, after the gas phase propane sensible heat is recovered through the first-stage first refrigerant heat exchanger 1131 (37 ℃,0.295 MPaA) enters the second-stage inlet of the normal temperature first refrigerant compressor 111. Part of medium-pressure liquid-phase propane is depressurized to about 0.124MPaA through a first liquid-phase throttle valve 117, low-pressure propane (0.124 MPaA, -37.36 ℃) enters a second-stage first refrigerant evaporator 1142, all latent heat of the liquid-phase propane is recovered, gas-phase propane sensible heat is recovered through a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, and then (37 ℃,0.12 MPaA) enters a first-stage inlet of a normal-temperature first refrigerant compressor 111.

The high-pressure ethylene (3.3 mpa, 10 to 40 ℃) from the normal-temperature second refrigerant compressor 121 is cooled by the second refrigerant cooler 129, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, and the second-stage first refrigerant evaporator 1142, and after being precooled to about-35 ℃, the ethylene enters the second buffer tank 122 to be buffered, and is reduced in pressure to about 0.67mpa by the second refrigerant throttle valve 126. The medium-pressure ethylene (0.67 MPaA, -63 ℃) enters a first-stage second refrigerant separating tank 1251, gas-liquid two-phase separation is carried out, the pressure of the liquid-phase ethylene is directly reduced to about 0.3MPaA through an ethylene second-stage J-T valve, and the gas-phase ethylene returns to the third-stage inlet of the normal-temperature second refrigerant compressor 121 after sensible heat is recovered through a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131 (0.66 MPaA,30 ℃). The low-pressure ethylene (0.3 MPaA, -84 ℃) enters a second-stage second refrigerant separating tank 1252, two phases of gas and liquid are separated, part of liquid-phase ethylene enters a first-stage second refrigerant evaporator 1241, after the latent heat of the liquid-phase ethylene is recovered, the liquid-phase ethylene and the low-pressure gas-phase ethylene are gathered, and after the sensible heat of the gas-phase ethylene is recovered through a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131 (37 ℃,0.28 MPaA), the liquid-phase ethylene enters a second-stage inlet of a normal-temperature second refrigerant compressor 121. Part of the low pressure liquid phase ethylene is reduced in pressure to about 0.13MPaA by the second liquid phase throttle valve 127. The low-pressure ethylene (0.13 MPaA, -99 ℃) enters a second-stage second refrigerant evaporator 1242, after the whole latent heat of the liquid-phase ethylene is recovered, the liquid-phase ethylene sensible heat is recovered through a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, and then the liquid-phase ethylene sensible heat (37 ℃,0.12 MPaA) enters a first-stage inlet of a normal-temperature second refrigerant compressor 121.

The high-pressure methane (5.3 mpa, 10 to 40 ℃) from the normal-temperature third refrigerant compressor 131 is cooled by the third refrigerant cooler 139, then introduced into the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, the second-stage first refrigerant evaporator 1142, the first-stage second refrigerant heat exchanger 1231, the first-stage second refrigerant evaporator 1241, the second-stage second refrigerant heat exchanger 1232, and the second-stage second refrigerant evaporator 1242, and then introduced into the third buffer tank 132 to be buffered, and reduced in pressure to about 1.1mpa by the third refrigerant throttle 136. The medium-pressure methane (1.1 MPaA, -122 ℃) enters a first-stage third refrigerant separation tank 1351, after gas-liquid two phases are separated, part of liquid-phase methane passes through a first-stage third refrigerant evaporator 1341, after the latent heat of the liquid-phase methane is recovered, the methane is collected with the medium-pressure gas-phase methane, and then enters a third-stage inlet of a normal-temperature third refrigerant compressor 131 after the gas-phase methane is recovered through a first-stage third refrigerant heat exchanger 1331, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131 (37 ℃,1.08 MPaA). Part of the medium pressure liquid phase methane is depressurized to about 0.37mpa through a first stage third liquid phase throttle 1371. Part of the low-pressure methane (0.37 MPaA, -143 ℃) enters a second-stage third refrigerant evaporator 1342, after the latent heat of the liquid-phase methane is recovered, the liquid-phase methane is collected with the low-pressure gas-phase methane and enters a second-stage inlet of the normal-temperature third refrigerant compressor 131 through a second-stage third refrigerant heat exchanger 1332, a first-stage third refrigerant heat exchanger 1341, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131. Part of the low pressure liquid phase methane is depressurized to about 0.13mpa through a second stage third liquid phase throttle 1372. The low-pressure methane (0.13 MPaA, -159 ℃) enters a three-stage third refrigerant evaporator 1343, the whole latent heat of the liquid-phase methane is recovered, and then the liquid-phase methane enters a first-stage inlet of the normal-temperature third refrigerant compressor 131 through a second-stage third refrigerant heat exchanger 1332, a first-stage third refrigerant evaporator 1341, a first-stage third refrigerant heat exchanger 1331, a second-stage second refrigerant heat exchanger 1232, a first-stage second refrigerant heat exchanger 1231, a second-stage first refrigerant heat exchanger 1132 and a first-stage first refrigerant heat exchanger 1131, and the sensible heat of the gas-phase methane is recovered (37 ℃,0.12 MPaA).

The natural gas (40 ℃) purified at normal temperature is cooled to-158 ℃ step by a first-stage first refrigerant heat exchanger 1131, a first-stage first refrigerant evaporator 1141, a second-stage first refrigerant heat exchanger 1132, a second-stage first refrigerant evaporator 1142, a first-stage second refrigerant heat exchanger 1231, a first-stage second refrigerant evaporator 1241, a second-stage second refrigerant heat exchanger 1232, a second-stage second refrigerant evaporator 1242, a first-stage third refrigerant heat exchanger 1331, a first-stage third refrigerant evaporator 1341, a second-stage third refrigerant heat exchanger 1332, a second-stage third refrigerant evaporator 1342 and a third-stage third refrigerant evaporator 1343, and then reduced to 0.11-0.15 mpa (product pressure is adjustable) by a product J-T valve, and then sent to an LNG tank or LNG tank car.

According to the above application case, the cascade refrigeration cycle LNG liquefaction system 100 of the present embodiment may be applied to a vehicle-mounted natural gas liquefaction device, and the normal-temperature first refrigerant compressor 111, the normal-temperature second refrigerant compressor 121, and the normal-temperature third refrigerant compressor 131 are highly integrated into the refrigerant compressor group a, respectively; the first-stage first refrigerant heat exchanger 1131, the first-stage first refrigerant evaporator 1141, the second-stage first refrigerant heat exchanger 1132, the second-stage first refrigerant evaporator 1142, the first-stage second refrigerant heat exchanger 1231, the first-stage second refrigerant evaporator 1241, the second-stage second refrigerant heat exchanger 1232, the second-stage second refrigerant evaporator 1242, the first-stage third refrigerant heat exchanger 1331, the first-stage third refrigerant evaporator 1341, the second-stage third refrigerant heat exchanger 1332, the second-stage third refrigerant evaporator 1342, and the third-stage third refrigerant evaporator 1343 are highly integrated into the LNG liquefaction tank B, see fig. 6 for details.

Comparative example 1

Taking fig. 7 as an example, the conventional cascade refrigeration cycle LNG liquefaction system 300 employs a process of C ₃ H ₆ 、C ₂ H ₄ And CH (CH) ₄ As the refrigerant, three-stage throttling and low-temperature compressors are employed.

The high pressure liquid propylene (0.92 MPaA,16 ℃) from the low temperature propylene compressor train 301 is cooled by a high pressure propylene cooler 316 and then enters a high pressure propylene buffer tank 319 for buffering, and then is depressurized to about 0.52MPaA by a propylene primary J-T valve. The medium-pressure propylene (0.52 MPaA, -4 ℃) enters a propylene primary evaporator 309, after recovering part of latent heat of liquid-phase propylene, gas-liquid two-phase is separated through a propylene primary separation tank 304, the gas-phase propylene directly enters a three-stage inlet of a low-temperature propylene compressor unit 301, and the liquid-phase propylene is depressurized to about 0.3MPaA through a propylene secondary J-T valve. The low-pressure propylene (0.3 MPaA, -28 ℃) enters a propylene secondary evaporator 310, after recovering part of latent heat of liquid-phase propylene, two phases of gas and liquid are separated through a propylene secondary separation tank 305, the gas-phase propylene directly enters a secondary inlet of a low-temperature propylene compressor unit 301, and the liquid-phase propylene is depressurized to about 0.13MPaA through a propylene three-stage J-T valve. The low-pressure propylene (0.13 MPaA, -42 ℃) is fed into the primary inlet of the low-temperature propylene compressor unit 301 after the whole latent heat of the propylene is recovered by the propylene three-stage evaporator 311 (0.13 MPaA, -42 ℃).

The high-pressure ethylene (1.8 MPaA, -36 ℃) from the low-temperature ethylene compressor unit 302 is cooled by a high-pressure ethylene cooler 317, then is led into a high-pressure ethylene buffer tank 320 for buffering after being precooled to-36 ℃ by a propylene primary evaporator 309, a propylene secondary evaporator 310 and a propylene tertiary evaporator 311, and is reduced to about 0.4MPaA by an ethylene primary J-T valve. Medium-pressure ethylene (0.4 MPaA, -77 ℃) enters an ethylene primary evaporator 312, after partial latent heat of liquid-phase ethylene is recovered, gas-liquid two phases are separated through an ethylene primary separation tank 306, gas-phase ethylene directly enters a secondary inlet of a low-temperature ethylene compressor unit 302, and the liquid-phase ethylene is depressurized to about 0.25MPaA through an ethylene secondary J-T valve. The low-pressure ethylene (0.25 MPaA, -87 ℃) enters an ethylene secondary evaporator 313, after recovering partial latent heat of liquid-phase ethylene, two phases of gas and liquid are separated through an ethylene secondary separation tank 307, the gas-phase ethylene directly enters a secondary inlet of a low-temperature ethylene compressor unit 302, and the liquid-phase ethylene is depressurized to about 0.13MPaA through an ethylene three-stage J-T valve. The low pressure ethylene (0.13 MPaA, -104 ℃) is fed into the primary inlet of the low temperature ethylene compressor train 302 after the total latent heat of the ethylene is recovered by the ethylene tertiary evaporator 314 (0.13 MPaA, -104 ℃).

The high-pressure methane (4.3 MPaA,40 ℃) from the low-temperature methane compressor group 303 is cooled by a high-pressure methane cooler 318 and then is introduced into a propylene primary evaporator 309, a propylene secondary evaporator 310, a propylene tertiary evaporator 311, an ethylene primary evaporator 312, an ethylene secondary evaporator 313 and an ethylene tertiary evaporator 314, and is precooled to-102 ℃ and then enters a high-pressure methane buffer tank 321 for buffering, and is reduced to about 0.24MPaA by a methane J-T valve. The low pressure methane (0.24 MPaA, -150 ℃) is separated into gas phase and liquid phase by a methane separation tank 308, and the gas phase methane and the liquid phase methane are directly fed into the inlet of a low temperature methane compressor unit 303 after the gas phase and the liquid phase coldness of the methane are recovered by a methane heat exchanger 315 ((0.24 MPaA, -105 ℃).

The normal temperature purified natural gas (40 ℃) is cooled to below-150 ℃ step by step through a propylene first-stage evaporator 309, a propylene second-stage evaporator 310, a propylene third-stage evaporator 311, an ethylene first-stage evaporator 312, an ethylene second-stage evaporator 313, an ethylene third-stage evaporator 314 and a methane heat exchanger 315, is depressurized to 0.11-0.15 MPaA (product pressure is adjustable) through a product J-T valve, and is then sent to an LNG storage tank or an LNG tank car.

In addition, the recovery of cold energy at the temperature of minus 30 ℃ is not necessarily energy-saving, so that methane and ethylene in the application can be selected whether to return to the first heat exchanger at the inlet according to specific conditions, the operation is more flexible, and the application can be suitable for various climatic conditions. The last heat exchanger of the application is considered to be on one hand and on the other hand, so that the problem of reduction of liquid phase increased evaporation refrigerant caused by the impurities of propane and ethane in methane is solved. The application has smaller equipment size and smaller occupied area, can be used in the fields of natural gas liquefaction factories, vehicle-mounted natural gas liquefaction and the like, and has wider application range.

Furthermore, the composition of the refrigerant is not limited to propane, ethylene and methane, and according to the temperature requirement of the product, any combination of nitrogen, methane, ethane, ethylene, propane, propylene, butane, butene, pentane and pentene can be adopted, the process flow is unchanged, and the product is cooled or condensed to the temperature value required by the process after the refrigerant is subjected to one-stage or multi-stage throttling. Each time the refrigerant passes through the throttling, the refrigerant corresponds to a gas-phase refrigerant heat exchanger and a liquid-phase refrigerant evaporator, the sensible heat and the latent heat of the liquid phase corresponding to the gas-phase are recovered, and the refrigerant also can correspond to the gas-phase refrigerant heat exchanger through multi-stage throttling, but one throttling is required to correspond to the liquid-phase refrigerant evaporator.

The cascade refrigeration cycle LNG liquefaction system 100 provided by the application is suitable for purifying natural gas liquefaction devices with different air inlet pressure working conditions (more than or equal to 2.0MPa.G and less than 2.0MPa.G and needing to be pressurized) and different treatment scales, the natural gas liquefaction device with larger treatment scale (more than or equal to 20 square meters per day) can be implemented by adopting the system with the secondary throttling provided by the embodiment 1, the system with the tertiary throttling provided by the embodiment 2, the natural gas liquefaction device with smaller treatment scale (less than or equal to 20 square meters per day) can be implemented by adopting the integrated system provided by the embodiment 3, and the cascade refrigeration cycle LNG liquefaction system 100 provided by the application can be applied to the vehicle-mounted natural gas liquefaction device through integration.

In summary, the embodiment of the application provides a cascaded refrigeration cycle LNG liquefaction system 100, which is formed by adding a first refrigerant heat exchanger 113, a second refrigerant heat exchanger 123 and a third refrigerant heat exchanger 133, and adjusting the connection modes of a plurality of compressors, heat exchangers, evaporators and separation tanks in the cascaded refrigeration cycle LNG liquefaction system 100, so as to form a new cascaded refrigeration cycle LNG liquefaction process. The unit energy index of the cascaded refrigeration cycle LNG liquefaction system 100 is 0.25kW/Nm ³ Purifying natural gas, compared with a conventional cascade refrigeration cycle system (0.30 kW/Nm) ³ Purified natural gas) by about 15% less than the MRC mixed refrigerant refrigeration cycle system (0.33 kW/Nm) ³ Purified natural gas) by about 25%.

The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A cascade refrigeration cycle LNG liquefaction system is characterized by comprising a first refrigeration component, a second refrigeration component and a third refrigeration component,

the refrigerants discharged from the normal-temperature first refrigerant compressor, the normal-temperature second refrigerant compressor and the normal-temperature third refrigerant compressor are respectively recovered by the first refrigerant evaporator, the second refrigerant evaporator and the third refrigerant evaporator to obtain liquid-phase latent heat;

The first refrigerant gas phase after recovering the liquid phase latent heat through the first refrigerant evaporator recovers the sensible heat through the first refrigerant heat exchanger and returns to the normal-temperature first refrigerant compressor;

the second refrigerant gas phase after the liquid phase latent heat is recovered through the second refrigerant evaporator recovers the sensible heat through the second refrigerant heat exchanger and returns to the normal-temperature second refrigerant compressor;

and the sensible heat of the third refrigerant gas phase after the liquid phase latent heat is recovered by the third refrigerant evaporator is recovered by the third refrigerant heat exchanger and then returned to the normal-temperature first refrigerant compressor.

2. The cascade refrigeration cycle LNG liquefaction system of claim 1, wherein the first refrigeration assembly further comprises a first refrigerant separator tank, the second refrigeration assembly further comprises a second refrigerant separator tank, and the third refrigeration assembly further comprises a third refrigerant separator tank;

the refrigerant discharged from the normal-temperature first refrigerant compressor, the normal-temperature second refrigerant compressor and the normal-temperature third refrigerant compressor is firstly evaporated through the first refrigerant evaporator, the second refrigerant evaporator and the third refrigerant evaporator respectively, and then enters the first refrigerant separation tank, the second refrigerant separation tank and the third refrigerant separation tank for separation; or the refrigerant is separated through the first refrigerant separating tank, the second refrigerant separating tank and the third refrigerant separating tank, and then enters the first refrigerant evaporator for evaporation and the second refrigerant evaporator and the third refrigerant evaporator for evaporation.

3. The cascade refrigeration cycle LNG liquefaction system of claim 2, wherein the second refrigerant gas phase passes through the second refrigerant heat exchanger and then enters the first refrigerant heat exchanger to continue heat exchange; the third refrigerant gas phase passes through the third refrigerant heat exchanger and then passes through at least one of the second refrigerant heat exchanger and the first refrigerant heat exchanger to perform continuous heat exchange.

4. The LNG liquefaction system according to claim 2, wherein the first refrigerant discharged from the normal temperature first refrigerant compressor is introduced into the first refrigerant heat exchanger before entering the first refrigerant evaporator, and further comprising heat exchanging the first refrigerant;

before the second refrigerant discharged by the normal-temperature second refrigerant compressor enters the second refrigerant evaporator, the method further comprises the steps of introducing the second refrigerant into the first refrigerant heat exchanger and the first refrigerant evaporator for heat exchange;

5. The cascade refrigeration cycle LNG liquefaction system of claim 2, wherein the first refrigerant heat exchanger and the first refrigerant evaporator are integrally provided, the second refrigerant heat exchanger and the second refrigerant evaporator are integrally provided, and the third refrigerant heat exchanger and the third refrigerant evaporator are integrally provided.

6. The cascade refrigeration cycle LNG liquefaction system of claim 2, wherein the first refrigerant heat exchanger and the first refrigerant evaporator are separately disposed and have N-stage heat exchange and N-stage evaporation, the second refrigerant heat exchanger and the second refrigerant evaporator are separately disposed and have N-stage heat exchange and N-stage evaporation, and the third refrigerant heat exchanger and the third refrigerant evaporator are separately disposed and have N-stage heat exchange and N-stage evaporation.

7. The cascade refrigeration cycle LNG liquefaction system of claim 6, wherein N is 2 or more in the N-stage heat exchange and N-stage evaporation, and the number of the first, second and third refrigerant separation tanks is N-1.

8. The cascade refrigeration cycle LNG liquefaction system of claim 6, wherein a first liquid phase throttling valve is disposed on a first refrigerant inlet line of each stage of the first refrigerant evaporator, a second liquid phase throttling valve is disposed on a second refrigerant inlet line of each stage of the second refrigerant evaporator, and a third liquid phase throttling valve is disposed on a third refrigerant inlet line of each stage of the third refrigerant evaporator.

9. A cascade refrigeration cycle LNG liquefaction method, characterized in that it is performed using the cascade refrigeration cycle LNG liquefaction system according to any one of claims 1 to 8, comprising the steps of:

10. The cascade refrigeration cycle LNG liquefaction process of claim 9, wherein the first refrigerant, the second refrigerant and the third refrigerant are different from each other and are each selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene; any of butane, butene, pentane, and pentene;

preferably, when the first refrigerant is propane, the second refrigerant is ethylene, and the third refrigerant is methane, the pressure of the first refrigerant discharged through the normal-temperature first refrigerant compressor is more than or equal to 0.47MpaA, the pressure of the first refrigerant entering the first refrigerant evaporator is 0.1-0.47 MPaA, and the temperature is-43-0 ℃;