CN105300030A - Device and method for producing LNG (liquefied natural gas) through pressure energy of natural gas pipeline network - Google Patents
Device and method for producing LNG (liquefied natural gas) through pressure energy of natural gas pipeline network Download PDFInfo
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Abstract
The invention relates to the field of recycling of pressure energy in natural gas transportation and discloses a device and a method for producing LNG (liquefied natural gas) through pressure energy of a natural gas pipeline network. The device comprises a natural gas liquefaction system, an expansion machine system and a cryogen circulating system, wherein a compressor, a cooler and a second separator of the cryogen circulating system are sequentially connected, a pipeline at the heavy-phase outlet end of the second separator is subjected to heat exchange of a first heat exchanger and then is connected with the inlet end of a first control valve, and a pipeline at the outlet end of the first control valve passes through the first heat exchanger and then is connected with an inlet of the compressor; a pipeline at the light-phase outlet end of the second separator sequentially passes through the first heat exchanger and a second heat exchanger and then is connected with the inlet end of a second control valve, and a pipeline at the outlet end of the second control valve sequentially passes through the second heat exchanger and the first heat exchanger and then is connected with the inlet end of the compressor. The indexes such as natural gas liquefaction efficiency, unit consumption, operation adaptability, stability and the like of the device are higher than those of conventional equipment.
Description
Technical field
The present invention relates to the recycling field of pressure energy in natural gas transport, particularly relate to a kind of device and method utilizing natural gas pipe network pressure energy to produce liquefied natural gas.
Background technology
Liquefied natural gas (LiquefiedNaturalGas, be called for short LNG), natural gas via compression, be cooled to its boiling point (-161.5 DEG C) after the liquid that becomes, its main component is methane, colourless, tasteless, nontoxic and non-corrosiveness, combusted air pollutes little, and thermal discharge is large, and being recognized is the energy the cleanest on the earth.Liquefied natural gas volume is about with amount gaseous natural gas volume 1/625, and weight is only about 45% of consubstantiality ponding.
At present, the extensive land transportation of domestic and international natural gas mainly adopts the mode of pipeline transportation.Long distance pipeline employing high-pressure transport is the development trend of countries in the world, and the discharge pressure of external many natural gas lines is all at more than 10MPa.The current defeated natural gas of length of China has also stepped into advanced international standard, and lineman's journey pipeline pressure of transferring natural gas from the west to the east reaches 10MPa, the 12MPa that the pipeline pressure of the second west to east gas pipeline project then reaches.High-pressure natural gas cannot directly use, and needs to enter downstream tube net after pressure regulation to mesolow.Traditional voltage regulating station carries out throttling expansion step-down by choke valve, has not only wasted a large amount of pressure energies, and due to natural gas temperature decline after step-down, also needs to adopt heat exchanger by the natural gas re-heat after step-down to normal temperature.Because the mistake tolerance of voltage regulating station every day is considerable, recycle this part energy, both met national energy-saving and reduced discharging policy, there is again good economic benefit.
At present, some schemes utilizing the pressure energy preparing liquefied natural gas of voltage regulating station are there is, but because the condensing temperature of natural gas is lower, often need the low-temperature receiver by partial high pressure natural gas depressurization to very low pressure makes it become temperature lower to remove liquefied natural gas, also need to pass through compressor boost after this portion gas re-heat.Therefore, these schemes in various degree there is liquefied fraction low (being all no more than 17%), the problems such as unit consumption of product is high, and equipment investment is high; When demand simultaneously in downstream produces fluctuation in a big way, the operation of device, output, energy consumption all can be greatly affected, and run extremely unstable.
Summary of the invention
The present invention is directed in prior art the unit efficiency recycling pressure energy low, unit consumption is high, the shortcomings such as fluctuation of service, provide the natural gas pipe network pressure energy that utilizes that a kind of efficiency is high, unit consumption is low, operation adaptability, stability are all good and produce the device and method of liquefied natural gas.
In order to solve the problems of the technologies described above, the present invention is solved by following technical proposals:
Utilize natural gas pipe network pressure energy to produce the device of liquefied natural gas, comprise natural gas liquefaction system, expander system, and refrigerant cycle system,
Natural gas liquefaction system comprises First Heat Exchanger, second heat exchanger, first separator, 3rd separator and the 3rd control valve, the pipeline be connected with natural gas to be liquefied is after First Heat Exchanger heat exchange, be connected with the 3rd separator entrance point, 3rd separator light phase export end is connected with the first separator entrance point after First Heat Exchanger, the light phase export end pipeline of the first separator is connected with downstream pipe network after First Heat Exchanger heat exchange, the heavy out end pipeline of the first separator is connected with warehousing and transportation facilities after the 3rd control valve through the second heat exchanger heat exchange, the heavy out end pipeline of the 3rd separator connects heavy hydrocarbon and discharges system,
Expander system comprises expanding end and the pressurized end of expansion unit, pipe network gas phase after the import of expanding end and the upstream after First Heat Exchanger precooling purify connects, the export pipeline of expanding end is after First Heat Exchanger heat exchange, be connected with the import of pressurized end, the outlet of pressurized end is connected with downstream pipe network;
Also comprise refrigerant cycle system, comprise compressor, cooler, the second separator, First Heat Exchanger, the second heat exchanger, the first control valve and the second control valve, compressor, cooler are connected successively with the second separator, the heavy out end pipeline of the second separator is connected with the first control valve entrance point after First Heat Exchanger heat exchange, and the pipeline of the first control valve port of export is connected with compressor inlet after First Heat Exchanger heat exchange again; The light phase export end pipeline of the second separator is connected with the second control valve entrance point after the second heat exchanger heat exchange through First Heat Exchanger successively, and the second control valve port of export pipeline is being connected with compressor inlet after First Heat Exchanger heat exchange through the second heat exchanger successively.
Routine high-pressure natural gas expand provide on the basis of cold, add independent refrigerant cycle system, refrigerant cycle system for cooling and liquefaction operation cold is provided, liquefied fraction is higher, and under same output, the unit consumption of product is lower; Because liquefaction operation provides cold primarily of azeotrope, therefore when voltage regulating station working conditions change, have better adaptability and stability, wherein, natural gas to be liquefied is through two-stage separating treatment, not easily blocking pipe, and purity is high.
As preferably, First Heat Exchanger and the second heat exchanger are plate-fin heat exchanger.Plate-fin heat exchanger is high because specific area has greatly heat exchange efficiency, and facility compact is light and handy, and cold scatters and disappears little advantage, simultaneously plate-fin heat exchanger strong adaptability, can be adapted to the heat-exchanging state of multithread stock by the layout of runner and combination.Freezing mixture is after the second separator is separated, and be gently pre-chilled to-140 DEG C ~-160 DEG C through twice heat exchange, in the throttling through the second control valve, temperature and pressure declines further, for heat exchanger provides sufficient cold, ensures the operation of liquefaction system; The heavy phase of freezing mixture is after First Heat Exchanger cooling, temperature is reduced to-65 DEG C ~-80 DEG C, and after the first control valve throttling, temperature and pressure declines further, and return First Heat Exchanger by reflux passage, for natural gas to be liquefied provides the cold needed for precooling.
As preferably, compressor is refrigerant compressor.Because natural gas enters the necessary no liquid of expanding end entrance requirement, otherwise expansion impeller can be damaged, therefore temperature technological design entering expanding end entrance can not be very low, and the sink temperature of namely expanding end outlet is relatively high, can't meet the requirement of liquefied natural gas.Therefore the project of conventional pressure differential preparing liquefied natural gas, also needing one natural gas to drop to very low pressure provides lower temperature as the low-temperature receiver of liquefied natural gas, also needs compressor boost before this strand of natural gas enters downstream pipe network.During voltage regulating station actual operation, the mistake tolerance of every day all can changing by gas situation because of downstream, as use gas in winter peak, factory's maintenance that downstream gas consumption is large, downstream gas scale also do not reach planning degree.Like this, cross tolerance actual day and can be less than design and day cross tolerance, this operational efficiency reclaiming compressor for expansion unit and low pressure gas has considerable influence, directly affects energy consumption and the output of factory.Select refrigerant compressor, on the one hand can by regulating the ratio optimization liquefaction of various cryogen, improve heat exchange efficiency, reduce energy consumption, relative to conventional pressure differential preparing liquefied natural gas factory, operability adds; On the other hand when actual tolerance of crossing was lower than when designing tolerance, suitably can reduce output, increase the acting ratio of refrigerant compressor, although unit consumption can increase to some extent, change of production amplitude is less, little to factory economy Efficiency.
As preferably, the cryogen in refrigerant cycle system comprises nitrogen, methane, ethene, propane and isopentane.Adopt azeotrope in refrigerant cycle system, azeotrope has the large advantage of specific refrigerating effect, can reduce plant energy consumption, reduces compressor apparatus cost.
As preferably, the pipeline that the pipe network gas phase after purifying with upstream in expander system connects first is connected with the import of expanding end after First Heat Exchanger cools.Natural gas is first pre-chilled to an optimum temperature through First Heat Exchanger before entering expanding end and enters decompressor, under this precooling temperature, the energy consumption of liquefying plant and output optimum.
Utilize natural gas pipe network pressure energy to produce the method for liquefied natural gas, comprise the steps:
(1) pretreated raw natural gas is after First Heat Exchanger cooling, enters the 3rd separator, and the 3rd separator is separated the light stock that flows mutually obtained and enters the first separator, and the 3rd separator is separated the heavy phase stream stock obtained and discharges; First separator is separated light the stream mutually after stock returns First Heat Exchanger re-heat obtained and flows into downstream pipe network, and the first separator is separated the heavy phase stream stock obtained and enters after the second heat exchanger cools further, obtains liquefied natural gas product;
(2) after the high-pressure natural gas in the pipe network of upstream cools in First Heat Exchanger, enter the expanding end step-down cooling of expansion unit, then enter after First Heat Exchanger is heated to 15 ~ 40 DEG C, enter the pressurized end of expansion unit, after supercharging, flow into downstream pipe network;
(3) cryogen in refrigerant cycle system is successively after compressor pressurization, cooler cooling, enter the second separator, be separated the light stock that flows mutually obtained and flow through First Heat Exchanger and the cooling of the second heat exchanger successively, flowing through the second heat exchanger successively and First Heat Exchanger provides cold after the second control valve reducing pressure by regulating flow cooling, then return compressor; Be separated the heavy phase stream stock obtained and enter into First Heat Exchanger cooling, after lowering the temperature through the first control valve reducing pressure by regulating flow, flow into First Heat Exchanger cold is provided, then return compressor.
As preferably, in step (1), fluid temperature after First Heat Exchanger cooling is-2 DEG C ~ 2 DEG C.
As preferably, in step (2), the temperature after First Heat Exchanger cooling of the high-pressure natural gas in the pipe network of upstream be-80 DEG C ~-60 DEG C, and fluid temperature after the second heat exchanger cools is-160 DEG C ~-150 DEG C.
As preferably, in step (3), the cryogen in refrigerant cycle system is the mixture of 8 ~ 17% nitrogen, 37 ~ 42% methane, 29 ~ 38% ethene, 1 ~ 10% propane and surplus isopentane.
As preferably, in step (3), the cryogen in refrigerant cycle system is forced into 3.0 ~ 4.0MPa through compressor, and cryogen is cooled to-80 DEG C ~-40 DEG C through cooler, be cooled to-80 DEG C ~-65 DEG C through First Heat Exchanger, be cooled to-160 DEG C ~-140 DEG C through the second heat exchanger.
The present invention, owing to have employed above technical scheme, has significant technique effect:
1. save energy consumption, adopt the present invention to replace original natural gas pressure regulating technique, reclaimed pressure energy, saved in original pressure regulation technique and needed heat supply to promote energy after pressure regulation spent by natural gas temperature and equipment.
2. stable, present invention optimizes technological process, utilize refrigerant compressor to replace conventional booster compressor, upstream ductwork pressure, with when crossing tolerance change, can be guaranteed the liquefied fraction of device, realize steady production and device benefit.
3. the present invention adopts conventional natural gas production equipment, although equipment investment slightly increases, because output increases, and actual production was subject to the impact of tolerance little, and thus real economy benefit is better.
4. technological process is simply controlled, and equipment of the present invention is this area conventional equipment, and application is ripe, and type selecting is convenient, and flow process is simple, and maintenance cost is low, system cloud gray model safety and stability.
Accompanying drawing explanation
Fig. 1 is structural representation of the present invention.
The toponym that in accompanying drawing, each number designation refers to is as follows: 1-expansion unit, 2-First Heat Exchanger, 3-the second heat exchanger, 4-the first separator, 5-the second separator, 6-the three separator, 7-the first control valve, 8-the second control valve, 9-compressor, 10-cooler, 11-expanding end, 12-pressurized end, 13-valve, 14-the three control valve, 15-valve, 21-pipeline, 22-pipeline, 23-pipeline, 24-pipeline, 25-pipeline, 26-pipeline, 27-pipeline, 28-pipeline, 29-pipeline, 30-pipeline, 31-pipeline, 32-pipeline, 33-pipeline, 34-pipeline, 35-pipeline, 36-pipeline, 37-pipeline, 38-pipeline, 39-pipeline, 40-pipeline, 41-pipeline, 42-pipeline, 43-pipeline, 44-pipeline, 45-pipeline, 46-pipeline, 47-pipeline.
Detailed description of the invention
Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail.
Embodiment 1
Utilize natural gas pipe network pressure energy to produce the device of liquefied natural gas, as shown in Figure 1, comprise expander system, natural gas liquefaction system and refrigerant cycle system.
Natural gas liquefaction system comprises First Heat Exchanger 2, second heat exchanger 3, first separator 4, 3rd separator 4 and the 3rd control valve 14, the pipeline be connected with natural gas to be liquefied is after First Heat Exchanger 2 heat exchange, be connected with the 3rd separator 6 entrance point, 3rd separator 6 light phase export end is connected with the first separator 4 entrance point, the light phase export end pipeline of the first separator 4 is connected with downstream pipe network after First Heat Exchanger 2, the heavy out end pipeline of the first separator 4 is connected with warehousing and transportation facilities after the 3rd control valve 14 through the second heat exchanger 3, the heavy out end pipeline of the 3rd separator 6 connects heavy hydrocarbon pipeline and discharges system.
Natural gas tube way outlet to be liquefied is connected with pipeline 26, pipeline 26 other end connects the fluid passage of First Heat Exchanger 2, this outlet flow channels is connected with pipeline 27, pipeline 27 is connected with the 3rd separator 6 import again, the light phase export end of the 3rd separator 6 is connected with pipeline 28, valve 13 and pipeline 29 successively, pipeline 29 is connected with the second separator 4 import, second separator 4 light phase export end connecting line 30, pipeline 30 is connected with the reflux passage of First Heat Exchanger 2 again, and this reflux channel outlet is connected with downstream pipe network by pipeline 31; The heavy out end of the second separator 4 is connected with pipeline 32, pipeline 32 is connected with the fluid passage of the second heat exchanger 3, this outlet flow channels connecting line 33, pipeline 33 is connected with pipeline 34 successively with the 3rd control valve 14, and pipeline 34 connects liquefied natural gas warehousing and transportation facilities; The heavy out of the 3rd separator 6 is connected with pipeline 35 successively, valve 15 and pipeline 36, and pipeline 36 connects heavy hydrocarbon pipeline and discharges system.
Expander system comprises expansion unit 1 and First Heat Exchanger 2, decompressor 1 group comprises expanding end 11 and pressurized end 12, pipe network gas phase after the entrance point of expanding end 11 and the upstream after First Heat Exchanger 2 precooling purify connects, the export pipeline of expanding end 11 is after First Heat Exchanger 2 heat exchange, be connected with the entrance point of pressurized end 12, the port of export of pressurized end 12 is connected with downstream pipe network.
The fluid passage of First Heat Exchanger 2 is connected with pipeline 21 and pipeline 22, pipeline 21 is connected with upstream pipe network, pipeline 22 is connected with the import of the expanding end 11 of expansion unit 1, expanding end 11 is also connected with outlet line 23, outlet line 23 is connected with the reflux passage of First Heat Exchanger 2, and this reflux channel outlet goes out to be connected with pipeline 24, and pipeline 24 is connected with the import of the pressurized end 12 of expansion unit 1, the outlet of pressurized end 12 goes out to be connected with pipeline 25, and pipeline 25 is connected with downstream pipe network.
Refrigerant cycle system comprises compressor 9, cooler 10, second separator 5, First Heat Exchanger 2, second heat exchanger 3, first control valve 7 and the second control valve 8, compressor 9, cooler 10 are connected successively with the second separator 5, second separator 5 heavy out end pipeline is connected with the first control valve 7 entrance point after First Heat Exchanger 2 heat exchange, and the pipeline of first control valve 7 port of export is connected with compressor 9 import after First Heat Exchanger 2 heat exchange again; Second separator 5 light phase export end pipeline is connected with the second control valve 8 entrance point after the second heat exchanger 3 heat exchange through First Heat Exchanger 2 successively, and the second control valve 8 port of export pipeline is being connected with compressor 9 entrance point after First Heat Exchanger 2 heat exchange through the second heat exchanger 3 successively.
Compressor is connected with cooler 10 by pipeline 38, cooler 10 is connected with the second separator 5 import by pipeline 39, second separator 5 light phase export end is connected with pipeline 40, pipeline 40 is connected with the fluid passage of First Heat Exchanger 2, this outlet flow channels is connected with pipeline 41, pipeline 41 is connected with the fluid passage of the second heat exchanger 3 again, this outlet flow channels is connected with pipeline 42, pipeline 42 end is connected with the second control valve 8, second control valve 8 outlet is connected with pipeline 43, pipeline 43 connects the reflux passage of the second heat exchanger 3, the outlet corresponding with this reflux passage goes out to be connected with pipeline 44, the other end of pipeline 44 connects the reflux passage of First Heat Exchanger 2, this reflux channel exit is connected with pipeline 37, pipeline 37 end is connected with the import of compressor 9, second separator 5 heavy out end is connected with pipeline 45, pipeline 45 is connected with the fluid passage of First Heat Exchanger 2, this outlet flow channels place is connected with pipeline 46 and the first control valve 7 successively, the exit of the first control valve 7 is connected with pipeline 47, enter the reflux passage of First Heat Exchanger 2 together with after pipeline 47 confluxes with pipeline 44, and flow into compressor 9 by the pipeline 37 be connected with this reflux channel outlet.
Embodiment 2
Utilize natural gas pipe network pressure energy to produce the method for liquefied natural gas, as shown in Figure 1, comprise the steps:
(1) pretreated raw natural gas enters First Heat Exchanger 2 through pipeline 26, after cooling, the 3rd separator 6 is entered through pipeline 27,3rd separator 6 is separated obtain light and flows stock-traders' know-how pipeline 28 mutually and enter the first separator the 4, three separator 6 and be separated the heavy phase stream stock-traders' know-how pipeline 35, valve 15 and the pipeline 36 that obtain and discharge; First separator 4 is separated obtain light and flows the reflux pipeline that stock-traders' know-how pipeline 30 returns First Heat Exchanger 2 mutually, cold is provided, downstream pipe network is flowed into through pipeline 31 after re-heat, after the heavy phase stream stock-traders' know-how pipeline 32 that first separator 4 separation obtains enters the further cooling of the second heat exchanger 3, entered after the 3rd control valve 14 reduces pressure by pipeline 33 and obtain liquefied natural gas product, flowing into storing and transporting system by pipeline 34;
(2) high-pressure natural gas in the pipe network of upstream enters First Heat Exchanger 2 through pipeline 21, after cooling, expanding end 11 step-down being entered expansion unit 1 by pipeline 22 is lowered the temperature, the reflux passage of First Heat Exchanger 2 is being entered by pipeline 23, release cold, entered the pressurized end 12 of expansion unit 1 by pipeline 24, after supercharging, flow into downstream pipe network by pipeline 25;
(3) cryogen flows into cooler 10 by pipeline 38 after compressor 9 pressurizes, in cooler 10 after cooling, the second separator 5 is entered by pipeline 39, second separator 5 is separated obtain light and flows the fluid passage that stock-traders' know-how pipeline 40 enters First Heat Exchanger 2 mutually, enter pipeline 41 after cooling to enter the second heat exchanger 3 cool further along fluid passage, then pipeline 42 is flowed out to, the second heat exchanger 3 reflux passage is being entered by pipeline 43 after the second control valve 8 reducing pressure by regulating flow cooling, released cold quantity, thereafter, after reflux passage flow to pipeline 44, the reflux passage entering First Heat Exchanger 2 continues released cold quantity, compressor 9 is being returned by pipeline 37 outflow, second separator 5 is separated the heavy phase stream stock obtained and enters into the cooling of First Heat Exchanger 2 fluid passage from pipeline 45, then the first control valve 7 is flowed out to by the pipeline 46 be connected with this fluid passage, after the first control valve 7 reducing pressure by regulating flow cooling, there are pipeline 47 and pipeline 44 to conflux, the reflux passage flowing into First Heat Exchanger 2 after confluxing provides cold, then returns compressor 9 through pipeline 37.
Wherein: First Heat Exchanger 2 and the second heat exchanger 3 are plate-fin heat exchanger, and compressor 9 is refrigerant compressor;
In step (1), the fluid of pipeline 21 is cooled to 0 DEG C through First Heat Exchanger 2;
In step (2), the fluid of pipeline 26 is cooled to-60 DEG C through First Heat Exchanger 2, and the fluid in pipeline 32 is cooled to-150 DEG C through the second heat exchanger 3;
In step (3), the mixture of to be mass fraction be 10% nitrogen, 37% methane, 29% ethene, 10% propane and 14% isopentane of the cryogen in refrigerant cycle system; In pipeline 38, fluid is forced into 3.3MPa through compressor 9, and the fluid in pipeline 38 is cooled to-40 DEG C through cooler 10, and the fluid in pipeline 45 is cooled to-66 DEG C through First Heat Exchanger 2, and the fluid in pipeline 41 is cooled to-150 DEG C through the second heat exchanger 3.
Embodiment 3
Embodiment 3 is identical with embodiment 2, and difference is:
In step (1), the fluid of pipeline 21 is cooled to 2 DEG C through First Heat Exchanger 2;
In step (2), the fluid of pipeline 26 is cooled to-75 DEG C through First Heat Exchanger 2, and the fluid in pipeline 32 is cooled to-160 DEG C through the second heat exchanger 3;
In step (3), the mixture of to be mass fraction be 17% nitrogen, 40% methane, 38% ethene, 5% propane and 0% isopentane of the cryogen in refrigerant cycle system; In pipeline 37, fluid is forced into 3.0MPa through compressor 9, and the fluid in pipeline 38 is cooled to-80 DEG C through cooler 10, and the fluid in pipeline 45 is cooled to-80 DEG C through First Heat Exchanger 2, and the fluid in pipeline 41 is cooled to-160 DEG C through the second heat exchanger 3.
Embodiment 4
Embodiment 4 is identical with embodiment 2, and difference is:
In step (1), the fluid of pipeline 21 is cooled to-2 DEG C through First Heat Exchanger 2;
In step (2), the fluid of pipeline 26 is cooled to-80 DEG C through First Heat Exchanger 2, and the fluid in pipeline 32 is cooled to-155 DEG C through the second heat exchanger 3;
In step (3), the mixture of to be mass fraction be 8% nitrogen, 42% methane, 37% ethene, 1% propane and 12% isopentane of the cryogen in refrigerant cycle system; In pipeline 37, fluid is forced into 4.0MPa through compressor 9, and the fluid in pipeline 38 is cooled to-60 DEG C through cooler 10, and the fluid in pipeline 45 is cooled to-65 DEG C through First Heat Exchanger 2, and the fluid in pipeline 41 is cooled to-140 DEG C through the second heat exchanger 3.
In a word, the foregoing is only preferred embodiment of the present invention, all equalizations done according to the present patent application the scope of the claims change and modify, and all should belong to the covering scope of patent of the present invention.
Claims (10)
1. utilize natural gas pipe network pressure energy to produce the device of liquefied natural gas, comprise natural gas liquefaction system and expander system, wherein:
Natural gas liquefaction system comprises First Heat Exchanger (2), second heat exchanger (3), first separator (4), 3rd separator (4) and the 3rd control valve (14), the pipeline be connected with natural gas to be liquefied is after First Heat Exchanger (2) heat exchange, be connected with the 3rd separator (6) entrance point, 3rd separator (6) light phase export end is connected with the first separator (4) entrance point, the light phase export end pipeline of the first separator (4) is connected with downstream pipe network after First Heat Exchanger (2), the heavy out end pipeline of the first separator (4) is connected with warehousing and transportation facilities after the 3rd control valve (14) through the second heat exchanger (3), the heavy out end pipeline of the 3rd separator (6) connects heavy hydrocarbon pipeline and discharges system,
Expander system comprises expansion unit (1) and First Heat Exchanger (2), expansion unit (1) comprises expanding end (11) and pressurized end (12), the import of expanding end (11) is connected with upstream pipe network, the export pipeline of expanding end (11) is after First Heat Exchanger (2) heat exchange, be connected with the import of pressurized end (12), the outlet of pressurized end (12) is connected with downstream pipe network;
It is characterized in that, also comprise refrigerant cycle system,
Refrigerant cycle system comprises compressor (9), cooler (10), second separator (5), First Heat Exchanger (2), second heat exchanger (3), first control valve (7) and the second control valve (8), compressor (9), cooler (10) is connected successively with the second separator (5), the heavy out end pipeline of the second separator (5) is connected with the first control valve (7) entrance point after First Heat Exchanger (2) heat exchange, the pipeline of the first control valve (7) port of export is connected with compressor (9) import after First Heat Exchanger (2) heat exchange again, the light phase export end pipeline of the second separator (5) is connected with the second control valve (14) entrance point after the second heat exchanger (3) heat exchange through First Heat Exchanger (2) successively, and the second control valve (14) port of export pipeline is being connected with compressor (9) entrance point after First Heat Exchanger (2) heat exchange through the second heat exchanger (3) successively.
2. the device utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 1, is characterized in that: First Heat Exchanger (2) and the second heat exchanger (3) are plate-fin heat exchanger.
3. the device utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 1, is characterized in that: compressor (9) is refrigerant compressor.
4. the device utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 1, is characterized in that: the cryogen in refrigerant cycle system comprises nitrogen, methane, ethene, propane and isopentane.
5. the device utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 1, is characterized in that: the pipeline that the pipe network gas phase after purifying with upstream in the expansion unit of expander system connects first is connected with the import of expanding end (11) after First Heat Exchanger (2) cools.
6. application rights requirement 1 or 2 or 3 or the device described in 4 or 5 utilize natural gas pipe network pressure energy to produce the method for liquefied natural gas, it is characterized in that: comprise the steps:
(1) pretreated raw natural gas is after First Heat Exchanger (2) cooling, enter the 3rd separator (6), 3rd separator (6) is separated the light stock that flows mutually obtained and enters the first separator (4), and the 3rd separator (6) is separated the heavy phase stream stock obtained and discharges; First separator (4) is separated light the stream mutually after stock returns First Heat Exchanger (2) re-heat obtained and flows into downstream pipe network, the heavy phase stream stock that first separator (4) separation obtains obtains liquefied natural gas product after entering the further cooling of the second heat exchanger (3);
(2) after the high-pressure natural gas in the pipe network of upstream cools in First Heat Exchanger (2), enter expanding end (11) the step-down cooling of expansion unit (1), then enter after First Heat Exchanger (2) is heated to 15 ~ 40 DEG C, enter the pressurized end (12) of expansion unit (1), after supercharging, flow into downstream pipe network;
(3) cryogen in refrigerant cycle system is successively after compressor (9) pressurization, cooler (10) cooling, enter the second separator (5), be separated the light stock that flows mutually obtained and flow through First Heat Exchanger (2) and the second heat exchanger (3) cooling successively, flowing through the second heat exchanger (3) successively and First Heat Exchanger (2) provides cold after the cooling of the second control valve (8) reducing pressure by regulating flow, then return compressor (9); Be separated the heavy phase stream stock obtained and enter into First Heat Exchanger (2) cooling, after lowering the temperature through the first control valve (7) reducing pressure by regulating flow, flow into First Heat Exchanger (2) cold is provided, then return compressor (9).
7. the method utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 6, is characterized in that: in step (1), and fluid temperature after First Heat Exchanger (2) cooling is-2 DEG C ~ 2 DEG C.
8. the method utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 6, it is characterized in that: in step (2), high-pressure natural gas in the pipe network of upstream temperature after First Heat Exchanger (2) cooling is-80 DEG C ~-60 DEG C, and fluid temperature after the second heat exchanger (3) cooling is-160 DEG C ~-150 DEG C.
9. the method utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 6, it is characterized in that: in step (3), the cryogen in refrigerant cycle system is the mixture of 8 ~ 17% nitrogen, 37 ~ 42% methane, 29 ~ 38% ethene, 1 ~ 10% propane and surplus isopentane.
10. the method utilizing natural gas pipe network pressure energy to produce liquefied natural gas according to claim 6, it is characterized in that: in step (3), cryogen in refrigerant cycle system is forced into 3.0 ~ 4.0MPa through compressor (9), cryogen is cooled to-80 DEG C ~-40 DEG C through cooler (10), be cooled to-80 DEG C ~-65 DEG C through First Heat Exchanger (2), be cooled to-160 DEG C ~-140 DEG C through the second heat exchanger (3).
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