A method and system for producing LNG using natural gas station field off-gas pressure energy

Abstract

The application discloses a method for preparing LNG by using the residual pressure energy of a natural gas station, and belongs to the technical field of oil and gas preparation. After high-pressure natural gas of a long-distance pipeline is preliminarily purified, the high-pressure natural gas is divided into two streams. One stream is subjected to deep decarburization and purification, and the other stream is subjected to pressurization and cooling in a high-temperature pressurization turbine expander. The pressurized stream is cooled in a precooling heat exchanger and then enters an expansion end of the high-temperature pressurization turbine expander. After being expanded, depressurized and cooled, the stream sequentially passes through a multistage separator, a deep cooling heat exchanger, a precooling heat exchanger, a pressurization end of a low-temperature pressurization turbine expander and then goes to a city natural gas pipeline network. The natural gas, which is subjected to deep decarburization and purification, is sequentially cooled in the precooling heat exchanger and the deep cooling heat exchanger and then divided into two streams. One part of the stream is stored as liquefied natural gas product, and the other part of the stream is pressurized and then goes to the city natural gas pipeline network. The method solves the technical problem of waste of residual pressure energy between low-pressure natural gas stations, cancels heating and heat tracing facilities of low-pressure natural gas, and realizes the effect of peak regulation and reserve capacity of the natural gas station.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas production, and particularly relates to a method and system for preparing LNG by using residual pressure energy of a natural gas station. BACKGROUND

[0002] The natural gas station is a terminal gas distribution station of long-distance natural gas pipeline and a receiving station of city natural gas, and has functions of detection, filtration, metering, pressure regulation, heat tracing, odorization, distribution and remote control. The working pressure of long-distance pipeline is generally 9.0-10.0 MPa, and the working pressure of city natural gas primary station is generally 3.0-4.0 MPa. In the natural gas station, the natural gas from the long-distance pipeline enters the city pipeline, and is generally depressurized by a regulating valve. In order to avoid the temperature of the depressurized natural gas being lower than the dew point temperature of the pipeline natural gas, hydrates are formed and the carbon steel pipeline of the natural gas is frozen, which affects the service life of the pipeline. Generally, the depressurized natural gas needs to be heated and the pipeline needs to be heat traced, which not only causes consumption of heating and heat tracing load and increases operation cost, but also causes waste of residual pressure energy between low pressures of the natural gas station.

[0003] Therefore, in the prior art, there is the technical problem of consumption of heating and heat tracing load, increase of operation cost and waste of residual pressure energy between low pressures of the natural gas station when the natural gas from the long-distance pipeline enters the city pipeline. SUMMARY

[0004] The present application provides a method and system for preparing LNG by using residual pressure energy of a natural gas station, which solves the technical problem of consumption of heating and heat tracing load, increase of operation cost and waste of residual pressure energy between low pressures of the natural gas station when the natural gas from the long-distance pipeline enters the city pipeline in the prior art.

[0005] The present application provides a method and system for preparing LNG by using residual pressure energy of a natural gas station.

[0006] In a first aspect, the present application provides a method for preparing LNG by using residual pressure energy of a natural gas station, which comprises the following steps.

[0007] Step S2: the high-pressure natural gas after the preliminary purification is divided into two streams, wherein the first stream of high-pressure natural gas is sequentially subjected to deep decarburization purification by a decarburization adsorption tower and a dust filter, and the second stream of high-pressure natural gas is subjected to pressure boosting and cooling in a high-temperature pressure boosting turboexpander.

[0008] Step S3: the second stream of high-pressure natural gas after the pressure boosting is cooled by a precooling heat exchanger and then enters an expansion end of the high-temperature pressure boosting turboexpander, and the medium-pressure natural gas after the expansion, pressure reduction and temperature reduction enters a primary separator.

[0009] Step S4: The gas from the top of the first-stage separator is cooled by the cryogenic heat exchanger, and the cooled natural gas enters the second-stage separator, and the gas from the top of the second-stage separator enters the expansion end of the low-temperature booster turboexpander, and the expanded, cooled and decompressed natural gas enters the third-stage separator;

[0010] Step S5: The medium-pressure natural gas from the top of the third-stage separator is pressurized by the cryogenic heat exchanger, the precooling heat exchanger and the low-temperature booster turboexpander, and then is sent to the city natural gas pipeline network.

[0011] Step S6: The first high-pressure natural gas after deep decarburization purification is sequentially cooled by the precooling heat exchanger and the cryogenic heat exchanger, and the liquefied natural gas after cooling is divided into two parts, one part is stored as a liquefied natural gas product after treatment, and the other part is sent to the city natural gas pipeline network after pressurization treatment.

[0012] In a second aspect, the present application provides a system for producing LNG by using the residual pressure energy of a natural gas station, which comprises: a preliminary purification unit for sequentially purifying the high-pressure natural gas from a long-distance pipeline by a dehydration adsorption tower, a mercury removal tower and a dust filter arranged in parallel; a branch execution unit for dividing the high-pressure natural gas after preliminary purification into two parts, wherein the first high-pressure natural gas is sequentially purified by a decarburization adsorption tower and a dust filter arranged in parallel to complete deep decarburization purification, and the second high-pressure natural gas enters the high-temperature booster turboexpander to be pressurized and cooled; a one-branch cooling and decompression treatment unit for cooling the second high-pressure natural gas after pressurization by a precooling heat exchanger, and then the cooled natural gas enters the expansion end of the high-temperature booster turboexpander, and the medium-pressure natural gas after expansion, decompression and cooling enters the first-stage separator; a one-branch separation control unit for cooling the gas from the top of the first-stage separator by a cryogenic heat exchanger, and then the cooled natural gas enters the second-stage separator, and the gas from the top of the second-stage separator enters the expansion end of the low-temperature booster turboexpander, and the expanded, cooled and decompressed natural gas enters the third-stage separator; a one-branch heat exchange and pressurization treatment unit for pressurizing the medium-pressure natural gas from the top of the third-stage separator by the cryogenic heat exchanger, the precooling heat exchanger and the low-temperature booster turboexpander, and then the pressurized natural gas is sent to the city natural gas pipeline network; and two-branch treatment units for sequentially cooling the first high-pressure natural gas after deep decarburization purification by the precooling heat exchanger and the cryogenic heat exchanger, and then dividing the liquefied natural gas after cooling into two parts, one part is stored as a liquefied natural gas product after treatment, and the other part is sent to the city natural gas pipeline network after pressurization treatment.

[0013] In a third aspect, the present application provides an electronic device, which comprises:

[0014] a memory configured to store executable instructions; and

[0015] The processor is used for implementing a method for producing LNG by using the residual pressure energy of a natural gas station provided by the embodiments of the present application when executing the executable instructions stored in the memory.

[0016] The present application has at least the following technical effects:

[0017] The method for producing LNG by using the residual pressure energy of a natural gas station provided by the present application is used to sequentially purify high-pressure natural gas of a long-distance pipeline through a dehydration adsorption tower, a mercury removal tower and a dust filter arranged in parallel; the high-pressure natural gas after the preliminary purification is divided into two streams, wherein the first stream of high-pressure natural gas is sequentially purified through a decarburization adsorption tower and a dust filter arranged in parallel to complete deep decarburization purification, and the second stream of high-pressure natural gas is pressurized and cooled in a high-temperature pressurizing turbine expander; the second stream of high-pressure natural gas after the pressurization is cooled through a pre-cooling heat exchanger and then enters an expansion end of the high-temperature pressurizing turbine expander; the medium-pressure natural gas after the expansion, pressure reduction and temperature reduction enters a primary separator; the gas from the top of the primary separator is cooled through a cryogenic heat exchanger, and the natural gas after the cooling enters a secondary separator; the gas from the top of the secondary separator enters an expansion end of a low-temperature pressurizing turbine expander, and after the expansion, temperature reduction and pressure reduction, enters a tertiary separator; the medium-pressure natural gas from the top of the tertiary separator passes through a cryogenic heat exchanger, a pre-cooling heat exchanger and a pressurizing end of the low-temperature pressurizing turbine expander and then goes to a city natural gas pipeline network; the first stream of high-pressure natural gas after the deep decarburization purification is sequentially cooled through a pre-cooling heat exchanger and a cryogenic heat exchanger, and the liquefied natural gas after the low-temperature cooling is divided into two streams, one part of which is stored as a liquefied natural gas product after the treatment, and the other part of which goes to the city natural gas pipeline network after the treatment and pressurization. The method achieves the effects of not only canceling the low-pressure natural gas heating equipment and the pipeline heat tracing facilities, but also producing liquefied natural gas products and realizing the peak shaving and reserve capacity of the natural gas station, thereby solving the technical problems of the consumption of heating and heat tracing load, the increase of operation cost and the waste of residual pressure energy between low-pressure natural gas in the prior art.

[0018] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following will specifically describe the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments of the present disclosure will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present disclosure, but not limit the present disclosure.

[0020] Figure 1 It is a flowchart of the method for producing LNG by using the residual pressure energy of a natural gas station.

[0021] Figure 2 A preliminary purification process schematic diagram for a method for preparing LNG by using the natural gas station field residual pressure energy according to the present application;

[0022] Figure 3 A first high-pressure natural gas treatment process schematic diagram after deep decarburization purification for a method for preparing LNG by using the natural gas station field residual pressure energy according to the present application;

[0023] Figure 4 A second high-pressure natural gas treatment process schematic diagram for a method for preparing LNG by using the natural gas station field residual pressure energy according to the present application;

[0024] Figure 5 A structure schematic diagram of a system for preparing LNG by using the natural gas station field residual pressure energy according to the present application;

[0025] Figure 6 A structure schematic diagram of an electronic device of a system for preparing LNG by using the natural gas station field residual pressure energy according to the present application.

[0026] Legend: Dehydration adsorption column 1, 2, Regeneration gas dehydration column 3, Regeneration gas heater 4, Regeneration gas cooler 5, Regeneration gas heat exchanger 6, Cold gas unit 7, Regeneration gas separator 8, Mercury removal column 9, Powder layer filter 10, Pre-cooling heat exchanger 11, Cryogenic heat exchanger 12, High temperature turbo-expander 13, First stage separator 14, Second stage separator 15, Low temperature turbo-expander 16, Third stage separator 17, Fourth stage separator 18, BOG compressor 19, Decarbonization adsorption column 21-23, Decarbonization column regeneration gas heater 24, Decarbonization column regeneration gas cooler 25, Powder layer filter 26, Regulating valve 30, Dehydration adsorption column program-controlled valve 31A / B-36A / B, Regulating valve 37-42, Decarbonization adsorption column program-controlled valve 43A / B / C-48A / B / C, Raw material high pressure natural gas 51, High pressure raw material gas natural gas 52, Purified natural gas out of adsorption column 53, Purified natural gas after mercury removal 54, High pressure natural gas after preliminary purification 55, Regeneration gas 56, Dehydrated regeneration gas 58, Heated regeneration gas 59, Regeneration completed regeneration gas 60, Cooled regeneration gas 63, Pre-cooled regeneration gas 64, Super-cooled regeneration gas 65, Regeneration gas out of dehydration separator bottom end 66, Regeneration gas out of dehydration separator top end 67, Regeneration gas after re-warming 68, Second high pressure natural gas 69, Pressurized high pressure natural gas 70, Cooled pressurized high pressure natural gas 71, Medium pressure natural gas 72, Liquid out of first stage separator bottom 73, Gas out of first stage separator top 74, Cooled natural gas 75, Liquid out of second stage separator bottom 76, Gas out of second stage separator top 77, Expanded cooled and depressurized gas 78, Mixed gas liquid 79, Liquid out of third stage separator bottom 80, Medium pressure natural gas out of third stage separator top 82, Medium pressure gas after re-heating of cryogenic heat exchanger 83, Mixed gas 84, Medium pressure natural gas out of pre-cooling heat exchanger 85, Pressurized and cooled natural gas 86, City natural gas pipe network 87, First high pressure natural gas 88, Purified high pressure natural gas 94, Pre-cooling heat exchanger natural gas 95, Cooled liquefied natural gas 96, Second liquefied natural gas 97, Liquid out of fourth stage separator bottom 98, Gas out of fourth stage separator top 99, First liquefied natural gas 100, Mixed low pressure fluid 101, Low pressure gas out of cryogenic heat exchanger 102, Low pressure gas out of low pressure heat exchanger 103, Pressurized medium pressure natural gas 104, Preliminary purification unit 211, Sub- execution unit 212, Sub-cooling and depressurizing processing unit 213, Sub-separation control unit 214, Sub-heat exchange and pressurizing processing unit 215, Second sub-processing unit 216, Processor 310, Memory 320, Input device 330, Output device 340. DETAILED DESCRIPTION

[0027] Example One

[0028] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings, and the described embodiments should not be regarded as limitations to the present application. All other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0029] In the following description, "some embodiments" are referred to, which describe a subset of all possible embodiments, but it can be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments, and can be combined with each other without conflict.

[0030] In the following description, the terms "first\second\third" are only distinguished from similar objects, and do not represent a specific order of the objects. It can be understood that "first\second\third" can be interchanged in a specific order or sequence as allowed, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application.

[0032] Although the present application makes various references to certain modules in the system according to the embodiments of the present application, however, any number of different modules can be used and run on the user terminal and / or server, the modules are only illustrative, and different aspects of the system and method can use different modules.

[0033] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in sequence. On the contrary, various steps can be processed in reverse order or simultaneously as needed. Meanwhile, other operations can be added to these processes, or one or more steps of operations can be removed from these processes.

[0034] As Figure 1 shown, the embodiments of the present application provide a method for producing LNG by using the excess pressure energy of a natural gas station, the method comprising:

[0035] Step S1: sequentially passing the high-pressure natural gas of the long-distance pipeline through the dehydration adsorption tower, the mercury removal tower and the dust filter arranged in parallel to complete preliminary purification;

[0036] Further, the step S1: sequentially passing the high-pressure natural gas of the long-distance pipeline through the dehydration adsorption tower arranged in parallel, previously comprises:

[0037] A portion of the high-pressure natural gas is separated as a regeneration gas to regenerate the adsorbent in the adsorption tower, including the following specific steps:

[0038] Step S11: The regeneration gas 56 enters the regeneration gas adsorption tower 3 through the process control valve 33A for adsorption dehydration;

[0039] Step S12: The dehydrated regeneration gas 58 enters the regeneration gas heater 4 for heating;

[0040] S13: The heated regeneration gas 59 enters the adsorption tower that needs to be heated for regeneration through the process control valve 34B / 34A to heat and regenerate the adsorbent;

[0041] S14: The regenerated regeneration gas 60 enters the regeneration gas cooler 5 through the process control valve 36A for cooling;

[0042] S15: The cooled regeneration gas 63 is pre-cooled through the regeneration gas heat exchanger 6;

[0043] S16: The pre-cooled regeneration gas 64 is super-cooled through the cold gas unit 7;

[0044] S17: The super-cooled regeneration gas 65 enters the dehydration separator 8 to separate free water;

[0045] S18: The regeneration gas 67 from the dehydration separator 8 is warmed up through the regeneration gas heat exchanger 6 and then mixed with the high-pressure raw material gas natural gas 52 to enter the adsorption towers 1 and 2.

[0046] Specifically, please refer to Figure 2 , the raw high-pressure natural gas 51 is sequentially purified through the parallelly arranged dehydration adsorption towers 1 and 2, the regeneration gas adsorption tower 3, the demercuration tower 9, and the dust filter 10. A portion of the high-pressure natural gas 51 of the long-distance pipeline is separated as a regeneration gas 56 to regenerate the adsorbent in the adsorption tower before entering the parallelly arranged dehydration adsorption towers.

[0047] The treatment process of the regeneration gas 56 is as follows: the regeneration gas enters the regeneration gas adsorption tower 3 through the process control valve 33A for dehydration adsorption, the dehydrated regeneration gas 58 enters the regeneration gas heater 4 for heating, the heated regeneration gas 59 enters the adsorption tower that needs to be heated and regenerated through the process control valve 34B / 34A to heat and regenerate the adsorbent, the regenerated regeneration gas 60 enters the regeneration gas cooler 5 through the process control valve 36A for cooling, the cooled regeneration gas 63 is pre-cooled through the regeneration gas heat exchanger 6, the pre-cooled regeneration gas 64 is super-cooled through the cold gas unit 7, the super-cooled regeneration gas 65 enters the dehydration separator 8, the regeneration gas 66 from the bottom of the dehydration separator 8 enters the regulating valve 37 to separate the free water, the regeneration gas 67 from the top of the dehydration separator 8 is warmed up through the regeneration gas heat exchanger 6, the warmed-up regeneration gas 68 is mixed with the high-pressure raw gas natural gas 52 to enter the adsorption towers 1 and 2, and the natural gas 53 from the adsorption towers is subjected to demercuration through the demercuration tower 9 to obtain the demercurated purified natural gas 54, and then the demercurated purified natural gas is filtered through the powder layer filter 10 to obtain the high-pressure natural gas 55 that has been subjected to preliminary purification.

[0048] Step S2: The high-pressure natural gas 55 that has been subjected to preliminary purification is divided into two streams, wherein the first stream of high-pressure natural gas 88 is sequentially subjected to deep decarburization purification through the decarburization adsorption tower and the dust filter arranged in parallel, and the second stream of high-pressure natural gas 69 enters the high-temperature pressurized turboexpander 13 to be pressurized and cooled at the pressurized end.

[0049] Further, the first stream of high-pressure natural gas 88 in step S2 is subjected to decarburization through the decarburization adsorption tower to remove the carbon dioxide impurities in the natural gas, and the purified high-pressure natural gas becomes the high-pressure natural gas 89. The purified high-pressure natural gas is divided into a stream of natural gas 90 as the regeneration gas of the decarburization adsorption tower.

[0050] Further, please refer to Figure 3 The regeneration of the decarburization adsorption tower includes the following steps:

[0051] Step S211: The regeneration gas 90 is adjusted to the pressure level of the city natural gas pipeline network through the regulating valve 49;

[0052] Step S212: The medium-pressure regeneration gas 90 enters the adsorption towers 22, 23 and 21 that need to be cooled and purged through the process control valve 45B / C / A to be cooled and purged;

[0053] Step S213: The cooled and purged regeneration gas enters the regeneration gas heater 24 for heating;

[0054] Step S214: The heated regeneration gas enters the decarburization adsorption tower 23 / 21 / 22 that needs to be heated and regenerated through the process control valve 47C / A / B to heat and regenerate the adsorbent;

[0055] Step S215: The heated regenerated gas enters the regenerated gas cooler 25 through the process control valve 48C / A / B for cooling;

[0056] Step S216: The cooled regenerated gas is the regenerated gas 92 entering the city natural gas pipeline network 87.

[0057] Step S3: Please refer to Figure 4 The second high-pressure natural gas after pressurization enters the high-temperature pressurized turbo expander expansion end after cooling through the pre-cooling heat exchanger 11, and the medium-pressure natural gas after expansion, pressure reduction and temperature reduction enters the primary separator 14.

[0058] Specifically, the second high-pressure natural gas 69 after pressurization is the pressurized high-pressure natural gas 70, which after cooling through the pre-cooling heat exchanger 11, wherein the pre-cooling heat exchanger 11 is an aluminum plate-fin heat exchanger, enters the high-temperature pressurized turbo expander 13 expansion end after cooling, and becomes the medium-pressure natural gas 72 after expansion, pressure reduction and temperature reduction, which enters the primary separator 14. The gas from the top of the primary separator 14 and the liquid from the bottom of the primary separator 14 enter different pipelines to provide energy for the deep cooling heat exchanger 12, and are respectively prepared as natural gas and liquefied natural gas.

[0059] Step S4: The gas 74 from the top of the primary separator 14 is cooled through the deep cooling heat exchanger 12, and the cooled natural gas 75 enters the secondary separator 15. The gas 77 from the top of the secondary separator 15 enters the low-temperature pressurized turbo expander 16 expansion end, and after expansion, temperature reduction and pressure reduction, enters the tertiary separator 17.

[0060] Step S5: The medium-pressure natural gas 82 from the top of the tertiary separator 17 passes through the deep cooling heat exchanger 12, the pre-cooling heat exchanger 11 and the low-temperature pressurized turbo expander 16 pressurization end, and then goes to the city natural gas pipeline network 87.

[0061] Further, the step S5 includes:

[0062] Step S51: The medium-pressure natural gas 82 from the top of the tertiary separator 17 returns to the deep cooling heat exchanger 12 return flow channel to provide a cold source for the deep cooling heat exchanger 12;

[0063] Step S52: The medium-pressure natural gas 83 from the deep cooling heat exchanger 12 returns to the pre-cooling heat exchanger 11 return flow channel to provide a cold source for the pre-cooling heat exchanger 11;

[0064] Step S53: The medium-pressure natural gas 85 from the pre-cooling heat exchanger 11 passes through the low-temperature pressurized turbo expander 16 pressurization end, and after pressurization and cooling, goes to the city natural gas pipeline network 87.

[0065] Further, after the step S5, the method further includes:

[0066] The liquid 73 from the bottom of the first separator 14 is depressurized by the regulating valve 38 and mixed with the return gas 83 from the cryogenic heat exchanger to provide cold energy for the pre-cooling heat exchanger 11. The liquid 76 from the bottom of the second separator 15 is depressurized by the regulating valve 39 and enters the third separator 17. The liquid 80 from the bottom of the third separator 17 returns to the cryogenic heat exchanger 12 to provide cold energy for the cryogenic heat exchanger 12, and then is mixed with the liquid 73 from the bottom of the first separator 14 and the medium-pressure gas 83 after being reheated by the cryogenic heat exchanger to obtain the mixed gas 84, which provides cold energy for the pre-cooling heat exchanger 11.

[0067] Specifically, the gas 74 from the top of the first separator 14 is cooled by the cryogenic heat exchanger 12, which is an aluminum plate-fin heat exchanger. The cooled natural gas 75 enters the second separator 15. The gas 77 from the top of the second separator 15 enters the expansion end of the low-temperature booster turbo-expander 16, and the gas 78 after being cooled and depressurized by expansion enters the third separator 17 after being mixed with the liquid 76 from the bottom of the second separator 15. The medium-pressure natural gas 82 from the top of the third separator 17 is heated by the cryogenic heat exchanger 12 to obtain the medium-pressure gas 83 after being reheated by the cryogenic heat exchanger, and then enters the pre-cooling heat exchanger 11 and the booster end of the low-temperature booster turbo-expander 16 before going to the city natural gas pipeline network 87.

[0068] The liquid 73 from the bottom of the first separator 14 is depressurized by the regulating valve 38 and mixed with the return gas 83 from the cryogenic heat exchanger to provide cold energy for the pre-cooling heat exchanger 11. The liquid 76 from the bottom of the second separator 15 is depressurized by the regulating valve 39 and enters the third separator 17. The liquid 80 from the bottom of the third separator 17 returns to the cryogenic heat exchanger 12 to provide cold energy for the cryogenic heat exchanger 12, and then is mixed with the liquid 73 from the bottom of the first separator 14 and the medium-pressure gas 83 after being reheated by the cryogenic heat exchanger to provide cold energy for the pre-cooling heat exchanger 11.

[0069] The medium-pressure natural gas 82 from the top of the third separator 17 returns to the return flow channel of the cryogenic heat exchanger 12 to provide cold energy for the cryogenic heat exchanger 12. The medium-pressure natural gas 83 from the cryogenic heat exchanger 12 returns to the return flow channel of the pre-cooling heat exchanger 11 to provide cold energy for the pre-cooling heat exchanger 11. The medium-pressure natural gas 85 from the pre-cooling heat exchanger 11 is pressurized by the booster end of the low-temperature booster turbo-expander 16, and the cooled and pressurized natural gas 86 enters the city natural gas pipeline network 87 through the pipeline.

[0070] By using high-temperature booster turboexpander 13 to expand and cool the high-pressure natural gas, the expanded low-temperature liquid is returned to the pre-cooling heat exchanger to provide a cold source for the pre-cooling heat exchanger. The low-temperature booster turboexpander 16 is used to expand the medium-pressure natural gas, which is separated into low-temperature gas and low-temperature liquid by the three-stage separator 17, and is distributed into the deep cooling heat exchanger 12 to provide a cold source for the deep cooling heat exchanger 12, so as to realize the peak shaving and storage capacity of the natural gas station and reasonably recycle the pressure difference in the pipeline.

[0071] Step S6: The first high-pressure natural gas after deep decarburization purification is sequentially cooled by the pre-cooling heat exchanger 11 and the deep cooling heat exchanger 12, and the low-temperature liquefied natural gas 96 is divided into two parts, one part is treated and stored as liquefied natural gas product, and the other part is treated and pressurized and sent to the city natural gas pipeline network.

[0072] Further, the step S6: the first high-pressure natural gas after deep decarburization purification is sequentially cooled by the pre-cooling heat exchanger 11 and the deep cooling heat exchanger 12, and the low-temperature liquefied natural gas is divided into two parts, one part is treated and stored as liquefied natural gas product, and the other part is treated and pressurized and sent to the city natural gas pipeline network, comprising:

[0073] Step S61: The low-temperature liquefied natural gas is divided into two parts, which are the first liquefied natural gas and the second liquefied natural gas, wherein the first liquefied natural gas is returned to the deep cooling heat exchanger low-pressure channel after being depressurized by the regulating valve;

[0074] Step S62: The second liquefied natural gas is depressurized by the regulating valve and then enters the four-stage separator 18, and the liquid from the bottom of the four-stage separator 18 is output as liquefied natural gas product for storage;

[0075] Step S63: The gas from the top of the four-stage separator is returned to the deep cooling heat exchanger low-pressure return channel and mixed with the low-pressure fluid of the first liquefied natural gas to provide a cold source for the deep cooling heat exchanger;

[0076] Step S64: The low-pressure gas from the deep cooling heat exchanger enters the pre-cooling heat exchanger low-pressure return channel to provide a cold source for the pre-cooling heat exchanger;

[0077] Step S65: The low-pressure gas from the low-pressure heat exchanger enters the BOG compressor, is pressurized and then sent to the city natural gas pipeline network 87.

[0078] Specifically, as shown in Figure 3 The high-pressure natural gas after deep decarburization purification is obtained after the powder layer filter 26, and the purified high-pressure natural gas 94 is connected to Figure 4 The pre-cooling heat exchanger 11, as shown in Figure 4As shown, the pre-cooling heat-exchanged natural gas 95 obtained after the pre-cooling heat exchanger 11 is cooled by the cryogenic heat exchanger 12, and the liquefied natural gas 96 after cooling is divided into two streams, one of which is the first stream of liquefied natural gas 100, and the other is the second stream of liquefied natural gas 97. The first stream of liquefied natural gas 100 is depressurized by the regulating valve 41 and returned to the low-pressure passage of the cryogenic heat exchanger 12. The second stream of liquefied natural gas 97 is depressurized by the regulating valve 40 and enters the four-stage separator 18. The liquid 98 from the bottom of the four-stage separator 18 is used as the liquefied natural gas product and is stored as the LNG product after being regulated by the regulating valve 42. The gas 99 from the top of the four-stage separator 18 is returned to the low-pressure return passage of the cryogenic heat exchanger 12 and mixed with the first stream of low-pressure fluid, the first stream of liquefied natural gas 100. The mixed low-pressure fluid 101 enters the cryogenic heat exchanger 12 to provide a cold source for the cryogenic heat exchanger 12. The low-pressure gas 102 from the cryogenic heat exchanger 12 enters the low-pressure return passage of the pre-cooling heat exchanger 11 to provide a cold source for the pre-cooling heat exchanger 11. The low-pressure gas 103 from the low-pressure heat exchanger enters the BOG compressor 19, is pressurized to the pressure level required by the city gas pipeline network by the BOG compressor 19, and obtains the pressurized medium-pressure natural gas 104, which is mixed with other medium-pressure natural gas entering the city gas pipeline network and is sent to the city gas pipeline network 87. The effect of not only canceling the low-pressure natural gas heating equipment and the pipe heat tracing facility, but also using the high-low temperature dual-stage pressurizing turbo-expander to provide cold energy for part of the natural gas liquefaction, producing liquefied natural gas products, realizing the peak shaving and storage capacity of the natural gas station and the liquefied natural gas products, using the differential pressure of the site to be consumed, converting it into energy in the pipeline process, realizing the recovery and utilization of differential pressure energy, thereby solving the technical problems of heating and heat tracing load consumption, increasing the operation cost, and causing the waste of residual pressure energy between the low-pressure natural gas station in the prior art.

[0079] The present application is suitable for the long-distance pipeline natural gas before the city natural gas pipeline network in the natural gas station, realizes the recovery and utilization of differential pressure energy, produces part of the LNG product, meets the demand of the surrounding market, realizes the dual peak shaving function of the natural gas station and the liquefied natural gas product, and has good market use value.

[0080] In summary, the method for producing LNG by using the residual pressure energy of the natural gas station has at least the following technical effects:

[0081] 1. The three-tower high-pressure closed-circuit dehydration process is adopted to solve the problem of regenerative gas recycling;

[0082] 2. The three-tower medium-pressure open-decarbonization process is adopted, and the analyzed carbon dioxide is sent to the city natural gas pipeline network;

[0083] 3. The high-pressure natural gas is expanded and cooled by a high-temperature turbo-expander, and the low-temperature liquid after expansion is returned to the pre-cooling heat exchanger to provide a cold source for the pre-cooling heat exchanger;

[0084] 4. The medium-pressure natural gas is expanded by a low-temperature turbo-expander, and is separated into low-temperature gas and low-temperature liquid by a three-stage separator, and is distributed into the cryogenic heat exchanger to provide a cold source for the cryogenic heat exchanger.

[0085] 5. The high-low temperature two-stage turbo-expander is used to provide cold energy for part of the natural gas liquefaction, and has the advantages of simple system, low energy consumption, small investment, etc.

[0086] Example Two

[0087] Based on the same inventive concept as the method for preparing LNG by using the residual pressure energy of a natural gas station in the foregoing embodiments, the application further provides a system for preparing LNG by using the residual pressure energy of a natural gas station. The system can be realized in the form of hardware and / or software, and can be integrated in an electronic device to execute the method provided in any of the embodiments of the application. As shown in FIG. 2, the system comprises: Figure 5

[0088] A preliminary purification unit 211 is configured to sequentially purify the high-pressure natural gas of the long-distance pipeline by means of a dehydration adsorption tower, a mercury removal tower and a dust filter arranged in parallel;

[0089] A branch execution unit 212 is configured to divide the high-pressure natural gas after preliminary purification into two branches, wherein the first branch of high-pressure natural gas is sequentially purified by means of a decarburization adsorption tower and a dust filter arranged in parallel to complete deep decarburization purification, and the second branch of high-pressure natural gas is pressurized and cooled by a high-temperature turbo-expander pressurization end;

[0090] A branch cooling and pressure reduction processing unit 213 is configured to cool the second branch of high-pressure natural gas after pressurization by means of a pre-cooling heat exchanger, and then the cooled high-pressure natural gas enters an expansion end of a high-temperature turbo-expander, and the medium-pressure natural gas after expansion, pressure reduction and cooling enters a primary separator;

[0091] A branch separation control unit 214 is configured to cool the gas from the top of the primary separator by means of a cryogenic heat exchanger, and then the cooled natural gas enters a secondary separator, and the gas from the top of the secondary separator enters an expansion end of a low-temperature turbo-expander, and then the natural gas after expansion, pressure reduction and cooling enters a tertiary separator;

[0092] A branch heat exchange and pressurization processing unit 215 is configured to pass the medium-pressure natural gas from the top of the tertiary separator through a cryogenic heat exchanger, a pre-cooling heat exchanger and a pressurization end of a low-temperature turbo-expander, and then the natural gas enters a city natural gas pipeline network;

[0093] ​The two-stream processing unit 216 is used for sequentially cooling the first high-pressure natural gas purified through deep decarburization by the pre-cooling heat exchanger and the cryogenic heat exchanger, and the liquefied natural gas after low-temperature cooling is divided into two streams, one part is stored as liquefied natural gas product after processing, and the other part is sent to the city natural gas pipe network after pressure increasing processing.

[0094] Further, the system further comprises:

[0095] The heat exchange and energy storage execution unit is used for mixing the liquid from the bottom of the first separator with the return gas of the cryogenic heat exchanger after pressure reduction by the regulating valve, to provide cold energy for the pre-cooling heat exchanger; the liquid from the bottom of the second separator enters the third separator after pressure reduction by the regulating valve, and the liquid from the bottom of the third separator returns to the cryogenic heat exchanger to provide a cold source for the cryogenic heat exchanger, and then mixes with the liquid from the bottom of the first separator and the medium-pressure gas after re-heating of the cryogenic heat exchanger to provide a cold source for the pre-cooling heat exchanger.

[0096] Further, the one-stream heat exchange and pressure increasing processing unit 215 is further used for executing:

[0097] Step S51: the medium-pressure natural gas from the top of the third separator returns to the return flow channel of the cryogenic heat exchanger to provide a cold source for the cryogenic heat exchanger;

[0098] Step S52: the medium-pressure natural gas from the cryogenic heat exchanger returns to the return flow channel of the pre-cooling heat exchanger to provide a cold source for the pre-cooling heat exchanger;

[0099] Step S53: the medium-pressure natural gas from the pre-cooling heat exchanger passes through the pressure increasing end of the low-temperature pressure increasing turbo-expander, and is sent to the city natural gas pipe network after pressure increasing cooling.

[0100] Further, the two-stream processing unit 216 is further used for executing:

[0101] Step S61: the liquefied natural gas after low-temperature cooling is divided into two streams, which are a first stream of liquefied natural gas and a second stream of liquefied natural gas, wherein the first stream of liquefied natural gas returns to the low-pressure channel of the cryogenic heat exchanger after pressure reduction by the regulating valve;

[0102] Step S62: the second stream of liquefied natural gas enters the fourth separator after pressure reduction by the regulating valve, and the liquid from the bottom of the fourth separator is stored as a liquefied natural gas product;

[0103] Step S63: the gas from the top of the fourth separator returns to the low-pressure return flow channel of the cryogenic heat exchanger, and mixes with the low-pressure fluid of the first stream of liquefied natural gas to provide a cold source for the cryogenic heat exchanger;

[0104] Step S64: the low-pressure gas from the cryogenic heat exchanger enters the low-pressure return flow channel of the pre-cooling heat exchanger to provide a cold source for the pre-cooling heat exchanger;

[0105] Step S65: The low-pressure gas from the low-pressure heat exchanger enters the BOG compressor, and after being pressurized, goes to the city natural gas pipeline network.

[0106] Further, the system further comprises:

[0107] An adsorption tower regeneration unit for separating a portion of the high-pressure natural gas as a regeneration gas to regenerate the adsorbent in the adsorption tower.

[0108] Further, the adsorption tower regeneration unit is further configured to perform:

[0109] Step S11. The regeneration gas enters the regeneration gas adsorption tower through the process control valve for adsorption dehydration;

[0110] Step S12. The dehydrated regeneration gas enters the regeneration gas heater for heating;

[0111] Step S13. The heated regeneration gas enters the adsorption tower that needs to be heated for regeneration through the process control valve to heat and regenerate the adsorbent;

[0112] Step S14. The regenerated regeneration gas enters the regeneration gas cooler through the process control valve for cooling;

[0113] Step S15. The cooled regeneration gas is pre-cooled through the regeneration gas heat exchanger;

[0114] Step S16. The pre-cooled regeneration gas is supercooled through the cold gas unit;

[0115] Step S17. The supercooled regeneration gas enters the dehydration separator to separate free water;

[0116] Step S18. The regeneration gas from the dehydration separator is reheated through the regeneration gas heat exchanger and mixed with the high-pressure raw gas natural gas to enter the adsorption tower.

[0117] Further, the sub-stream execution unit 12 further comprises:

[0118] A decarburization adsorption tower regeneration unit for removing carbon dioxide impurities in the first portion of high-pressure natural gas through the decarburization adsorption tower, and the purified high-pressure natural gas is separated into a portion as a regeneration gas for the decarburization adsorption tower.

[0119] Further, the decarburization adsorption tower regeneration unit is further configured to perform:

[0120] Step S211: The regeneration gas is adjusted to the pressure level of the city natural gas pipeline network through the regulating valve;

[0121] Step S212: The medium-pressure regeneration gas enters the adsorption tower that needs to be cooled and purged through the process control valve for cooling and purging;

[0122] Step S213: The cooled and purged regenerated gas enters a regenerated gas heater for heating;

[0123] Step S214: The heated regenerated gas enters a desorption tower adsorption for heating and regeneration of the adsorbent through a process control valve;

[0124] Step S215: The heated regenerated gas enters a regenerated gas cooler for cooling through a process control valve;

[0125] Step S216: The cooled regenerated gas enters a city natural gas pipeline network.

[0126] The various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be implemented; in addition, the specific names of the functional units are only for easy differentiation, and do not limit the protection scope of the present application.

[0127] Example Three

[0128] Figure 6 The structural schematic diagram of the electronic device provided for the third embodiment of the present application shows a block diagram of an exemplary electronic device suitable for implementing the embodiments of the present application. Figure 6 The electronic device shown is only an example and should not impose any limitation on the functions and use range of the embodiments of the present application. For example, Figure 6 As shown, the electronic device includes a processor 310, a memory 320, an input device 330 and an output device 340; the number of processors 310 in the electronic device can be one or more, Figure 6 For example, the processor 310, the memory 320, the input device 330 and the output device 340 in the electronic device can be connected through a bus or other means, Figure 6 For example, by way of connection through a bus.

[0129] The memory 320, as a kind of computer readable storage medium, can be used to store software programs, computer executable programs and modules, such as the program instructions / modules of the method for producing LNG by using the residual pressure energy of a natural gas station in the embodiments of the present application. The processor 310 executes various functional applications and data processing of the computer device by running the software programs, instructions and modules stored in the memory 320, that is, implements the above-mentioned method for producing LNG by using the residual pressure energy of a natural gas station.

[0130] Note that the above merely describes preferred embodiments of the present application and the principles of the technology applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the claims.

Claims

1. A method for producing LNG using the excess pressure energy of a natural gas station, characterized by, The method comprises: Step S1: high-pressure natural gas of a long-distance pipeline is sequentially purified by a dehydration adsorption tower, a mercury removal tower and a dust filter arranged in parallel; Step S2: the high-pressure natural gas purified in step S1 is divided into two streams, wherein the first stream of high-pressure natural gas is sequentially purified by a decarburization adsorption tower and a dust filter to complete deep decarburization purification, and the second stream of high-pressure natural gas is pressurized and cooled in a high-temperature pressurized turboexpander; Step S3: the second stream of high-pressure natural gas pressurized in step S2 is cooled by a precooling heat exchanger and then enters an expansion end of the high-temperature pressurized turboexpander, and the medium-pressure natural gas after expansion, pressure reduction and temperature reduction enters a primary separator; Step S4: the gas from the top of the primary separator is cooled by a cryogenic heat exchanger, and the cooled natural gas enters a secondary separator, and the gas from the top of the secondary separator enters an expansion end of a low-temperature pressurized turboexpander, and the medium-pressure natural gas after expansion, pressure reduction and temperature reduction enters a tertiary separator; Step S5: the medium-pressure natural gas from the top of the tertiary separator is pressurized by the cryogenic heat exchanger, the precooling heat exchanger and the low-temperature pressurized turboexpander and then enters a city natural gas pipeline network; Step S6: the first stream of high-pressure natural gas after deep decarburization purification is sequentially cooled by the precooling heat exchanger and the cryogenic heat exchanger, and the liquefied natural gas after low-temperature cooling is divided into two streams, one of which is stored as a liquefied natural gas product after treatment, and the other of which is pressurized and then enters the city natural gas pipeline network; After step S5, the method further comprises: The liquid from the bottom of the primary separator is mixed with the return gas of the cryogenic heat exchanger after pressure reduction by an adjusting valve to provide cold energy for the precooling heat exchanger, the liquid from the bottom of the secondary separator enters the tertiary separator after pressure reduction by an adjusting valve, the liquid from the bottom of the tertiary separator returns to the cryogenic heat exchanger to provide a cold source for the cryogenic heat exchanger, and then is mixed with the liquid from the bottom of the primary separator and the medium-pressure gas after reheat of the cryogenic heat exchanger to provide a cold source for the precooling heat exchanger; Step S5: the medium-pressure natural gas from the top of the tertiary separator is pressurized by the cryogenic heat exchanger, the precooling heat exchanger and the low-temperature pressurized turboexpander and then enters the city natural gas pipeline network, comprising: Step S51: the medium-pressure natural gas from the top of the tertiary separator returns to a return flow channel of the cryogenic heat exchanger to provide a cold source for the cryogenic heat exchanger; Step S52: the medium-pressure natural gas from the cryogenic heat exchanger returns to a return flow channel of the precooling heat exchanger to provide a cold source for the precooling heat exchanger; Step S53: the medium-pressure natural gas from the precooling heat exchanger passes through the low-temperature pressurized turboexpander, is pressurized and cooled, and then enters the city natural gas pipeline network.

2. The method of claim 1, wherein, Step S6: the first stream of high-pressure natural gas after deep decarburization purification is sequentially cooled by the precooling heat exchanger and the cryogenic heat exchanger, and the liquefied natural gas after low-temperature cooling is divided into two streams, one of which is stored as a liquefied natural gas product after treatment, and the other of which is pressurized and then enters the city natural gas pipeline network, comprising: Step S61: the liquefied natural gas after low-temperature cooling is divided into two streams, namely a first stream of liquefied natural gas and a second stream of liquefied natural gas, wherein the first stream of liquefied natural gas returns to a low-pressure channel of the cryogenic heat exchanger after pressure reduction by an adjusting valve; Step S62: The second stream of liquefied natural gas is depressurized by the regulating valve and then enters the fourth-stage separator, and the liquid from the bottom of the fourth-stage separator is output as a liquefied natural gas product and stored; Step S63: The gas from the top of the fourth-stage separator is returned to the low-pressure reflux channel of the deep cooling heat exchanger, mixed with the low-pressure fluid of the first stream of liquefied natural gas, and provides a cold source for the deep cooling heat exchanger; Step S64: The low-pressure gas from the deep cooling heat exchanger enters the low-pressure reflux channel of the pre-cooling heat exchanger, and provides a cold source for the pre-cooling heat exchanger; Step S65: The low-pressure gas from the low-pressure heat exchanger enters the BOG compressor, is pressurized, and then goes to the city natural gas pipeline network.

3. The method of claim 1, wherein, The step S1: the high-pressure natural gas of the long-distance pipeline is sequentially passed through the parallelly arranged dehydration adsorption tower, and the previous step includes: A stream of high-pressure natural gas is branched off as regeneration gas to regenerate the adsorbent in the adsorption tower.

4. The method of claim 3, wherein, The step of branching off a stream of high-pressure natural gas as regeneration gas to regenerate the adsorbent in the adsorption tower includes: Step S11. The regeneration gas enters the regeneration gas adsorption tower through the process control valve to adsorb and dehydrate; Step S12. The dehydrated regeneration gas enters the regeneration gas heater to be heated; Step S13. The heated regeneration gas enters the adsorption tower that needs to be heated and regenerated through the process control valve to heat and regenerate the adsorbent; Step S14. The regenerated regeneration gas enters the regeneration gas cooler through the process control valve to be cooled; Step S15. The cooled regeneration gas is pre-cooled through the regeneration gas heat exchanger; Step S16. The pre-cooled regeneration gas is supercooled through the cold gas unit; Step S17. The supercooled regeneration gas enters the dehydration separator to separate free water; Step S18. The regeneration gas from the dehydration separator is warmed up through the regeneration gas heat exchanger and then mixed with the high-pressure raw gas natural gas to enter the adsorption tower.

5. The method of claim 1, wherein, The step S2: the high-pressure natural gas that has completed preliminary purification is divided into two streams, and the first stream of high-pressure natural gas sequentially passes through the parallelly arranged decarburization adsorption tower and dust filter to complete deep decarburization purification, and the step includes: Step S21: The first stream of high-pressure natural gas passes through the decarburization adsorption tower to remove carbon dioxide impurities in the natural gas, and a stream of purified high-pressure natural gas is branched off as regeneration gas of the decarburization adsorption tower.

6. The method of claim 5, wherein, The regeneration of the decarburization adsorption tower includes: Step S211: The regeneration gas adjusts the pressure of the regeneration gas to the pressure level of the city natural gas pipeline network through the regulating valve; Step S212: The medium-pressure regeneration gas enters the adsorption tower that needs to be cooled and purged through the process control valve to cool and purge; Step S213: The cooled and purged regeneration gas enters the regeneration gas heater to be heated; Step S214: The heated regeneration gas enters the decarburization adsorption tower that needs to be heated and regenerated through the process control valve to heat and regenerate the adsorbent; Step S215: The heated regeneration gas enters the regeneration gas cooler through the process control valve to be cooled; Step S216: The cooled regeneration gas enters the city natural gas pipeline network.

7. A system for producing LNG using the excess pressure energy of a natural gas station, characterized by, The system is used to execute the method of any one of claims 1-6, and the system includes: A preliminary purification unit for sequentially passing the high-pressure natural gas of the long-distance pipeline through the parallelly arranged dehydration adsorption tower, mercury removal tower and dust filter to complete preliminary purification; The split execution unit is used for splitting the high-pressure natural gas after primary purification into two streams, wherein the first stream of high-pressure natural gas is sequentially subjected to deep decarburization purification by the decarburization adsorption tower and the dust filter arranged in parallel, and the second stream of high-pressure natural gas enters the high-temperature pressurized turbine expander pressurization end for pressurization cooling; The one-stream cooling and pressure reduction processing unit is used for cooling the second stream of high-pressure natural gas after pressurization by the pre-cooling heat exchanger, and then the cooled natural gas enters the high-temperature pressurized turbine expander expansion end for expansion pressure reduction and temperature reduction, and the medium-pressure natural gas after the expansion pressure reduction and temperature reduction enters the primary separator; The one-stream separation control unit is used for cooling the gas from the top of the primary separator by the cryogenic heat exchanger, and then the cooled natural gas enters the secondary separator, and the gas from the top of the secondary separator enters the low-temperature pressurized turbine expander expansion end for expansion temperature reduction and pressure reduction, and then enters the tertiary separator; The one-stream heat exchange and pressurization processing unit is used for cooling the medium-pressure natural gas from the top of the tertiary separator by the cryogenic heat exchanger, the pre-cooling heat exchanger and the low-temperature pressurized turbine expander pressurization end, and then the cooled natural gas is sent to the city natural gas pipeline network; The two-stream processing unit is used for cooling the first stream of high-pressure natural gas after deep decarburization purification by the pre-cooling heat exchanger and the cryogenic heat exchanger, and then the liquefied natural gas after low-temperature cooling is split into two streams, one part of which is stored as liquefied natural gas product after processing, and the other part is sent to the city natural gas pipeline network after pressurization processing.

8. An electronic device, comprising: The electronic device comprises: a memory for storing executable instructions; a processor for executing the executable instructions stored in the memory to implement the method for producing LNG by using the waste pressure energy of a natural gas station according to any one of claims 1 to 6.

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