CN107560321A - BOG is reclaimed and nitrogen gas liquefaction system and process - Google Patents

Abstract

The invention discloses a kind of BOG recovery and nitrogen gas liquefaction system and process, the nitrogen prepared by LNG cold energy to PSA nitrogen-making devices is carried out two level cooling by the system makes it liquefy and store；In BOG liquefaction systems, BOG pressurizes through compressor and exchanged heat again with liquid nitrogen, makes its liquefaction, and liquid nitrogen absorbs heat gasification and is stored in nitrogen storage tank, purged available for yard；The BOG being liquefied enters defeated outside high-pressure pump or through expenditure and pressure, and into separator, the bottom storage of liquid phase injection LNG storage tank, gas phase enters BOG compression circulations.The inventive method solves the problems, such as that BOG recovery is difficult under the low outer throughput rate of LNG receiving stations, and meet the needs of yard low temperature purging process, it make use of LNG cold energy to improve efficiency of energy utilization, used the existing PSA equipments of making nitrogen in LNG station field to reduce equipment investment.

Description

BOG is reclaimed and nitrogen gas liquefaction system and process

Technical field

The present invention relates to LNG storages and the technical field of transport field, and in particular to a kind of BOG recovery and liquefaction of nitrogen system System and process.

Background technology

As atmosphere polluting problem increasingly highlights, China is more urgent to the demand of clean energy resource.LNG (liquefied natural gas) As a kind of accumulating form of this clean energy resource of natural gas, coastal cities combustion gas guarantee and peak regulation are widely used in.China LNG connects Receive station and be distributed widely in each coastal cities, caused a large amount of BOG (flash steam) produce to the safety of receiving station in its running It is raw to threaten.BOG is gases of the LNG by thermal evaporation formation, because insulation material is limited, unavoidably penetrates into heat from the external world, causes LNG is by thermal evaporation.As heat is constantly attacked, the increase of gas phase quality, pressure vessel pressure-bearing increase, if can not hold reaching container Release BOG will produce high risks to equipment before carrying pressure, and superpressure damage tank body occurs.Touched when gas-phase space reaches certain pressure Relief valve is sent out, unnecessary flashed vapour in tank is immediately discharged to torch emptying burning.Large LNG yard BOG total amounts are larger, directly Discharge causes the waste of the energy and the pollution of environment.

The BOG processing methods for having realized application in LNG receiving stations of China at present mainly have：

(1) direct compression process, i.e., BOG gases are carried out by high pressure compressed unit direct weighting to Trunk-line pressure Outer defeated, the few flow of process equipment is simple, but process energy consumption is high, and security is poor.

(2) recondensation process, i.e. BOG gases are first pressurizeed by compressor, then the LNG with being pumped out in tank is mixed, by LNG liquefaction BOG are subcooled, and through high-pressure pump two-stage pressurizing, are most sent into pipe network through gasifier gasification afterwards.The process energy consumption is far below straight Compression method is connect, but outer defeated LNG stream amount limits BOG yield, for the uneven urban pipe network of downstream gas, when in use LNG can not all condense BOG during gas low ebb, have to discharge.General BOG compressors not use by equipment, occurs needing under fortuitous event Prolonged maintenance, a large amount of BOG will be wasted.

Novel B OG handling process based on Condensation Theory again has：

(1) mix refrigerant BOG recondensation process, i.e., will using kind of refrigeration cycle by the use of multicomponent lighter hydrocarbons as refrigerant BOG condensation recovery, but the technique heat transmission equipment is more, and flow is complicated, and refrigerant proportioning needs extras.

(2) multistage compression BOG recondensation process, i.e., compression power consumption is reduced using multi-stage compression technology, and improves operation bullet Property, but the technique can not handle the BOG recovery under stopping transportation operating mode, still have in the case where BOG largely produces the operating mode that for example unloads There is limitation.

(3) the BOG recondensation process with expanding machine, expanding machine output shaft work is driven to supply using the high-pressure natural gas after gasification To high-pressure pump, reach LNG superchargings while hardly consume the purpose of additional energy source, but this technique is because of its higher pressure limit pair Process pipelines and supercharging equipment propose higher requirement, and the feasibility in the case where fluctuating operating mode needs further to be verified.

In view of the above state of the art, it is necessary to propose a kind of low energy consumption, in high yield, equipment investment is moderate, adapts to fluctuate Operating mode simultaneously disclosure satisfy that the BOG auxiliary recovery methods of other demands of Large LNG yard realize energy-saving and emission-reduction, carry technological operation bullet Property, high-energy source utilization ratio.

The content of the invention

It is an object of the invention to overcome the shortcomings of above-mentioned background technology, and provide a kind of energy-saving and emission-reduction, using energy source effect The high BOG recovery of rate and nitrogen gas liquefaction system, present invention also offers a kind of BOG recovery and the process of liquefaction of nitrogen.

To achieve the above object, designed by the present invention in a kind of BOG recovery and nitrogen gas liquefaction system, including LNG storage tank, tank Pump, the first LNG dispenser, after-condenser, the first LNG blenders, high-pressure pump, the second LNG dispenser, First Heat Exchanger, second LNG blenders, LNG gasification device, PSA nitrogen-making devices, the first valve, nitrogen blender, nitrogen compressor, the second heat exchanger, nitrogen Gas separating device, liquid nitrogen container, the second valve, BOG- liquid nitrogen heat exchanger, nitrogen pot, the 3rd valve, liquid nitrogen converter, BOG compressors, BOG distributors, the 4th valve, the 5th valve, gas-liquid separator, the 6th valve；

Pump is arranged in LNG storage tank in the tank, the B of the first LNG dispenser of A outlets connection of pump in the tank₃Import, The B of first LNG dispenser₁The D of the first LNG blenders of outlet connection₁Import, the B of first LNG dispenser₂Outlet connects Meet the C of after-condenser₁Import, the C of the after-condenser₃The D of the first LNG blenders of outlet connection₂Import, the first LNG are mixed The outlet of clutch connects the E of the second LNG dispenser by high-pressure pump₃Import, the E of second LNG dispenser₁Outlet connection the The F of one heat exchanger₁Import, the F of the First Heat Exchanger₂The G of the 2nd LNG blenders of outlet connection₁Import；

The E of second LNG dispenser₂The L of the second heat exchanger of outlet connection₁Import, the L of second heat exchanger₂Outlet Connect the G of the 2nd LNG blenders₂Import, the outlet of the 2nd LNG blenders are connected to the H of LNG gasification device₁Import, it is described The H of LNG gasification device₂The extraneous gas line network of outlet connection；

The I of the PSA nitrogen-making devices₁It is divided into two branch roads behind outlet, connects First Heat Exchanger by the first valve all the way F₃Import, another way is by the extraneous scavenging pipeline of the 6th valve connection；The F of the First Heat Exchanger₄Outlet connection nitrogen mixes The J of clutch₁Import, the J of the nitrogen blender₃The K of outlet connection nitrogen compressor₁Import, the K of the nitrogen compressor₂Go out The L of mouth the second heat exchanger of connection₃Import, the L of second heat exchanger₄The M of outlet connection nitrogen separation device₃Import, the nitrogen The M of separator₂Gaseous phase outlet connects the J of nitrogen blender₂Import, the M of the nitrogen separation device₁Liquid-phase outlet connects liquid nitrogen container N₁Import, the N of the liquid nitrogen container₂It is divided into two branch roads behind outlet, connects BOG- liquid nitrogen heat exchangers by the second valve all the way O₃Import, another way connect the P of liquid nitrogen converter by the 3rd valve₁Import；The O of the BOG- liquid nitrogen heat exchanger₄Outlet connection The Q of nitrogen pot₁Import；

The R of the LNG storage tank₁The import of outlet connection BOG compressors, the outlet connection BOG distribution of the BOG compressors The T of device₃Import, the T of the BOG distributors₁The C of outlet connection after-condenser₂Import；The T of the BOG distributors₂Outlet connection The O of BOG- liquid nitrogen heat exchangers₁Import, the O of the BOG- liquid nitrogen heat exchanger₂It is divided into two branch roads behind outlet, all the way by the 5th valve The D of door the first LNG blenders of connection₃Import, another way connect the V of gas-liquid separator by the 4th valve₃Import, the gas-liquid The V of separator₁Gaseous phase outlet connects the import of BOG compressors, the V of the gas-liquid separator₂Liquid-phase outlet connection LNG storage tank R₂Import.

In above-mentioned technical proposal, it also includes the first sea water pump, the second sea water pump, the H of the LNG gasification device₃Import is led to Cross the first sea water pump to be connected with seawater, the LNG gasification device is additionally provided with the H for discharging seawater₄Outlet；The liquid nitrogen gasification The P of device₃Import is connected by the second sea water pump with seawater, and the liquid nitrogen converter is additionally provided with the P for discharging seawater₄Import.

In above-mentioned technical proposal, the Q of the nitrogen pot₂Outlet, the P of liquid nitrogen converter₂Connect after outlet converges with scavenging pipeline Connect.

In above-mentioned technical proposal, it also includes torch, and the air inlet of the torch passes through branch road and the R of LNG storage tank₁Outlet Connection.

In above-mentioned technical proposal, the L of second heat exchanger₄Outlet and the M of nitrogen separation device₃On pipeline between import It is provided with first throttle valve.

In above-mentioned technical proposal, the V of the gas-liquid separator₃Import and the O of BOG- liquid nitrogen heat exchangers₂Pipe between outlet Second throttle is provided with road.

Present invention also offers a kind of BOG recovery and the process of liquefaction of nitrogen, it comprises the following steps：

Step 1：The normal outer defeated flows of LNG：- 150~-100 DEG C in LNG storage tank, 115kPa BOG is through BOG compressors 0.5~0.9MPa is pressurized to, then is divided into two-way through BOG distributors, now the only T of BOG distributors₁Outlet, BOG enter The C of after-condenser₂Import, while it is pressurized to the B that 0.5~0.9MPa supercooling LNG passes through the first LNG dispenser through pump in tank₂Go out Mouth enters the C of after-condenser₁Import, BOG are contacted, mixed and are condensed into liquid with supercooling LNG in after-condenser, and lime set is led to Cross the C of after-condenser₃D of the outlet into the first LNG blenders₂Import and the B by the first LNG dispenser₁Outlet outflow LNG converges, and is sent into the import of high-pressure pump, through high-pressure pump be pressurized to 9MPa, -153 DEG C, be divided into two-way through the second LNG dispenser, one Road will be nitrogen precooled through First Heat Exchanger, and LNG temperature rises to -149.5 DEG C, and another way is through the second heat exchanger by liquefaction of nitrogen, LNG Temperature rises to -30.6 DEG C, and it is natural that two-way LNG is sent into LNG gasification device with seawater to make heat exchange gasification after the mixing of the 2nd LNG blenders Gas enters gas line network；H of the seawater through the supercharging of the first sea water pump into LNG gasification device₃Import, through LNG gasification after being exchanged heat with LNG The H of device₄Outlet discharge；

Step 2：Liquefaction of nitrogen stores flow：20~25 DEG C made from PSA nitrogen-making devices, 0.6~0.7MPa nitrogen enters Enter First Heat Exchanger to exchange heat with -153 DEG C, 9MPa LNG, precooling is cooled to -150 DEG C, then with the M of nitrogen separation device₂Gas phase Outlet outflow -175 DEG C, 0.69MPa low temperature nitrogen mixing temperature be down to -160 DEG C, be pressurized to through nitrogen compressor 2.95MPa, -85 DEG C, exchanged heat into the second heat exchanger and -153 DEG C, 9MPa LNG, be cooled to -150 DEG C, then through first throttle Valve be decompressed to 0.69MPa, -175 DEG C, flow into nitrogen separation device separate liquid phase, through nitrogen separation device separation after liquid nitrogen enter Liquid nitrogen container stores, and the low temperature nitrogen after the separation of nitrogen separation device converges with the nitrogen after First Heat Exchanger precooling in nitrogen blender Conjunction enters nitrogen compressor and carries out nitrogen compression circulation, continuously utilizes LNG cold liquefaction nitrogen；

Step 3：BOG liquefaction is outer defeated and returns tank flow：- 150~-100 DEG C in LNG storage tank, 115kPa BOG is through BOG Compressor boost is divided into two-way to 0.5~0.9MPa, then through BOG distributors, is carried out all the way into after-condenser described in step 1 The normal outer defeated flows of LNG；Another way enters BOG- liquid nitrogen heat exchangers, -175 DEG C with liquid nitrogen container outflow, 0.69MPa liquid nitrogen changes Heat is cooled to -148 DEG C of BOG lime sets, and -40 DEG C of nitrogen temperature, 0.68MPa enter nitrogen pot after liquid nitrogen gasification, and BOG lime sets are passed through The O of BOG- liquid nitrogen heat exchangers₂Outlet is divided into two-way, and the LNG being sent into all the way through the 5th valve described in high-pressure pump progress step 1 is normal Outer defeated flow, another way enter gas-liquid separator through second throttle decompression, and the liquid phase after gas-liquid separator separates flows into LNG In storage tank, the gas phase after gas-liquid separator separates enters the import of BOG compressors, continuously outside progress BOG liquefaction Defeated and time tank.

In above-mentioned technical proposal, in the step 1, the distribution of the second LNG dispenser enters First Heat Exchanger, the second heat exchanger LNG mass ratioes be 1:70~72.

In above-mentioned technical proposal, nitrogen sweeping process is also included in the step 2, the nitrogen of the nitrogen sweeping process comes Source is three parts, and Part I is that nitrogen caused by PSA nitrogen-making devices enters scavenging pipeline through the 6th valve；Part II is liquid Liquid nitrogen in nitrogen tank passes through the 3rd valve, then enters scavenging pipeline after liquid nitrogen converter gasification is nitrogen；Part III is nitrogen Nitrogen in gas tank is directly entered scavenging pipeline.

In above-mentioned technical proposal, if the step 1 and step 2 can not be realized, the R of LNG storage tank₁Outlet will be with torch Air inlet connect, BOG will be fed into torch emptying burning.

Compared with prior art, the invention has the advantages that：

First, the present invention utilizes " cold energy " that LNG more than needed is carried by PSA (pressure-variable adsorption separation) nitrogen caused by nitrogen-making device Gas liquefaction condenses, and is stored in standby in liquid nitrogen container, and nitrogen exchanges heat by one-level precooling and LNG, is pressurized through nitrogen compressor, then with LNG carries out heat exchange and realizes that two level cools down, and produces temperature drop by throttling, and separate low temperature liquid nitrogen through separator stores into storage tank； Separator nitrogen and the nitrogen of one-level precooling, which converge to compress into nitrogen, to be circulated, and when the outer throughput rates of LNG are low or BOG yields are big, is adjusted Take the low temperature liquid nitrogen in liquid nitrogen container to be used for BOG liquefaction condensations, and the gas nitrogen after heat exchange is stored in nitrogen storage tank；Condense BOG It is outer defeated through high-pressure pump supercharging again, or LNG pressure stores are decompressed to through choke valve, separate lime set by separator notes from tank bottom Enter storage, gas phase BOG returns to gas phase house steward and enters BOG compression circulations, takes full advantage of the PSA that domestic LNG station field generally possesses Swing adsorption nitrogen producing apparatus, this causes the equipment investment needed for yard process modification to be reduced.

Second, the nitrogen prepared by LNG cold energy to PSA nitrogen-making devices is carried out two level cooling by the present invention makes its liquefaction simultaneously Store；In BOG liquefaction systems, BOG pressurizes through compressor and exchanged heat again with liquid nitrogen, makes its liquefaction, and liquid nitrogen absorbs heat gas Change is stored in nitrogen storage tank, is purged available for yard；The BOG being liquefied enters defeated or through expenditure and pressure outside high-pressure pump, enters Enter separator, the bottom storage of liquid phase injection LNG storage tank, gas phase enters BOG compression circulations.The inventive method solves LNG receiving stations The problem of BOG recovery is difficult under low outer throughput rate, and the needs of yard low temperature purging process are met, it make use of LNG cold energy to improve Efficiency of energy utilization, has used the existing PSA equipments of making nitrogen in LNG station field to reduce equipment investment.

Third, the cool storage medium that uses of the present invention is inert nitrogen gas, compared to the refrigerant of light hydrocarbon mixture class, Compression in heat-exchanging process with hardly bringing danger；And using nitrogen-liquid nitrogen as cool storage medium rather than simple nitrogen, Cool storage medium total amount can be reduced using its latent heat rather than sensible heat.

Fourth, the storage and discharge of liquid nitrogen of the present invention, nitrogen will not cause greenhouse effects and environmental pollution, compare alkane Class has the characteristic of clean environment firendly with fluorochlorohydrocarbon class refrigerating medium；

Fifth, the BOG and liquefaction of nitrogen technique in the present invention are simple, cost is cheap, easy to operate, and combines yard nitrogen The demand of gas purging process, without outer enough liquid nitrogen again so that yard technical process has obtained integrated.

Sixth, the present invention adapts to fluctuate operating mode, cold more than needed is being stored with gas peak, released cold with gas low ebb Put, realize the condensation recovery under BOG high load capacities, reduce energy waste and environmental pollution.

Brief description of the drawings

Fig. 1 is a kind of BOG recovery and the structural representation of nitrogen gas liquefaction system；

Embodiment

Describe the performance of the present invention in detail with reference to case study on implementation, but they do not form the limit to the present invention It is fixed, it is only for example.Simultaneously by illustrating that advantages of the present invention will become clearer and be readily appreciated that.

Pump 2, first in a kind of BOG recovery of the present invention as shown in Figure 1 and nitrogen gas liquefaction system, including LNG storage tank 1, tank LNG dispenser 3, after-condenser 4, the first LNG blenders 5, high-pressure pump 6, the second LNG dispenser 7, First Heat Exchanger 8, second LNG blenders 9, LNG gasification device 10, PSA nitrogen-making devices 11, the first valve 12, nitrogen blender 13, nitrogen compressor 14, Two heat exchangers 15, nitrogen separation device 17, liquid nitrogen container 18, the second valve 19, BOG- liquid nitrogen heat exchanger 20, nitrogen pot 21, the 3rd valve Door 22, liquid nitrogen converter 23, BOG compressors 24, BOG distributors 25, the 4th valve 26, the 5th valve 27, gas-liquid separator 29, 6th valve 33, torch 30；

Pump 2 is arranged in LNG storage tank 1 in the tank, the first LNG dispenser 3 of connection of A outlets 2.1 of pump 2 in the tank B₃Import 3.3, the B of first LNG dispenser 3₁The D of the first LNG blenders 5 of the connection of outlet 3.1₁Import 5.1, described first The B of LNG dispenser 3₂The C of the connection of outlet 3.2 after-condenser 4₁Import 4.1, the C of the after-condenser 4₃The connection of outlet 4.3 first The D of LNG blenders 5₂Import 5.2, the outlet of the first LNG blenders 5 connect the second LNG dispenser 7 by high-pressure pump 6 E₃Import 7.3, the E of second LNG dispenser 7₁The F of the connection of outlet 7.1 First Heat Exchanger 8₁Import 8.1, first heat exchange The F of device 8₂The G of the 2nd LNG blenders 9 of the connection of outlet 8.2₁Import 9.1；

The E of second LNG dispenser 7₂The L of second heat exchanger 15 of the connection of outlet 7.2₁Import 15.1, second heat exchange The L of device 15₂The G of the 2nd LNG blenders 9 of the connection of outlet 15.2₂Import 9.2, the outlet of the 2nd LNG blenders 9 are connected to The H of LNG gasification device 10₁Import 10.1, the H of the LNG gasification device 10₂The extraneous gas line network 35 of the connection of outlet 10.2；

The I of the PSA nitrogen-making devices 11₁It is divided into two branch roads behind outlet 11.1, all the way by the first valve 12 connection the The F of one heat exchanger 8₃Import 8.3, another way connect the scavenging pipeline 34 in the external world by the 6th valve 33；The First Heat Exchanger 8 F₄The J of the connection nitrogen blender of outlet 8.4 13₁Import 13.1, the J of the nitrogen blender 13₃The connection of outlet 13.3 nitrogen pressure The K of contracting machine 14₁Import 14.1, the K of the nitrogen compressor 14₂The L of second heat exchanger 15 of the connection of outlet 14.2₃Import 15.3, institute State the L of the second heat exchanger 15₄The M of the connection nitrogen separation device of outlet 15.4 17₃Import 17.3, the L of second heat exchanger 15₄Go out The M of mouth 15.4 and nitrogen separation device 17₃First throttle valve 16, the nitrogen separation device are provided with pipeline between import 17.3 17 M₂Gaseous phase outlet 17.2 connects the J of nitrogen blender 13₂Import 13.2, the M of the nitrogen separation device 17₁Liquid-phase outlet The N of 17.1 connection liquid nitrogen containers 18₁Import 18.1, the N of the liquid nitrogen container 18₂It is divided into two branch roads behind outlet 18.2, all the way by the The O of two valves 19 connection BOG- liquid nitrogen heat exchanger 20₃Import 20.3, another way is by the 3rd valve 22 connection liquid nitrogen converter 23 P₁The O of BOG- liquid nitrogen heat exchanger 20 described in import 23.1₄The Q of the connection of outlet 20.4 nitrogen pot 21₁Import 21.1, the nitrogen The Q of tank 21₂Outlet 21.2, the P of liquid nitrogen converter 23₂Outlet 23.2 is connected after converging with scavenging pipeline 34, the liquid nitrogen storage tank 18 Outlet streams need to flow to distinct device according to yard, when needing the liquefaction for BOG to supplement cold, open the second valve 19 and flow To BOG- liquid nitrogen heat exchangers, stored for future use after gasification into nitrogen storage tank 21；When needing a large amount of nitrogen to be used for yard purging, open Open the liquid nitrogen of the 3rd valve 22 and flow to liquid nitrogen converter 23, realize that Quick-gasifying supplements Nitrogen source gases, flow to blow line.The liquid Nitrogen storage tank 18, the tank of nitrogen storage tank 21 hold need according to scale of station and BOG yields, purging with nitrogen amount be designed calculating with Meet different scales LNG process requirements.

The R of the LNG storage tank 1₁The import of the connection BOG compressors of outlet 1.1 24, the outlet of the BOG compressors 24 connect Meet the T of BOG distributors 25₃Import 25.3, the T of the BOG distributors 25₁The C of the connection of outlet 25.1 after-condenser 4₂Import 4.2； The T of the BOG distributors 25₂The O of the connection BOG- liquid nitrogen heat exchanger of outlet 25.2 20₁Import 20.1, the BOG- liquid nitrogen heat exchanger 20 O₂It is divided into two branch roads behind outlet 20.2, connects the D of the first LNG blenders 5 by the 5th valve 27 all the way₃Import 5.3, Another way connects the V of gas-liquid separator 29 by the 4th valve 26₃Import 29.3, the V of the gas-liquid separator 29₃Import 29.3 With the O of BOG- liquid nitrogen heat exchanger 20₂Second throttle 28, the gas-liquid separator 29 are provided with pipeline between outlet 20.2 V₁Gaseous phase outlet 29.1 connects the import of BOG compressors 24, the V of the gas-liquid separator 29₂Liquid-phase outlet 29.2 connects LNG The R of storage tank 1₂Import 1.2, the air inlet of the torch 30 pass through branch road and the R of LNG storage tank 1₁The connection of outlet 1.1.

In above-mentioned technical proposal, in addition to the first sea water pump 31, the second sea water pump 32, the H of the LNG gasification device 10₃Enter Mouth 10.3 is connected by the first sea water pump 31 with seawater, and the LNG gasification device 10 is additionally provided with the H for discharging seawater₄Outlet 10.4；The P of the liquid nitrogen converter 23₃Import 23.3 is connected by the second sea water pump 32 with seawater, the liquid nitrogen converter 23 It is additionally provided with the P for discharging seawater₄Import 23.4.

BOG recovery of the present invention and the process of liquefaction of nitrogen, it comprises the following steps：

Step 1：The normal outer defeated flows of LNG：- 150~-100 DEG C in LNG storage tank 1,115kPa BOG is through BOG compressors 24 are pressurized to 0.5~0.9MPa, then divide through BOG distributors 25 for two-way, now the only T of BOG distributors 25₁Outlet 25.1 connects Logical, BOG enters the C of after-condenser 4₂Import 4.2, while 0.5~0.9MPa supercooling LNG is pressurized to by through pump in tank 2 The B of one LNG dispenser 3₂Outlet 3.2 enters the C of after-condenser 4₁Import 4.1, BOG are carried out with supercooling LNG in after-condenser 4 Contact, mix and be condensed into liquid (its saturated vapour pressure need to meet the necessary NPSH requirement of high pressure pump inlet), lime set passes through The C of after-condenser 4₃Outlet 4.3 enters the D of the first LNG blenders 5₂The import 5.2 and B by the first LNG dispenser 3₁Outlet 3.1 outflow LNG converge, be sent into high-pressure pump 6 import, through high-pressure pump 6 be pressurized to 9MPa, -153 DEG C, through the second LNG dispenser 7 points are two-way, all the way will be nitrogen precooled through First Heat Exchanger 8, and LNG temperature rises to -149.5 DEG C, and another way is through the second heat exchanger Liquefaction of nitrogen, LNG temperature are risen to -30.6 DEG C by 15, and (distribution of the second LNG dispenser 7 enters First Heat Exchanger 8, the second heat exchanger 15 LNG mass ratioes are 1:70~72, first order cooling institute chilling requirement is smaller, and second level cooling nitrogen undergoes phase transition latent heat consumption Cold is more), two-way LNG is sent into LNG gasification device 10 after the mixing of the 2nd LNG blenders 9 and gasifies to enter for natural gas with seawater to make heat exchange Enter gas line network 35；H of the seawater through the supercharging of the first sea water pump 31 into LNG gasification device 10₃Import 10.3, passed through after being exchanged heat with LNG The H of LNG gasification device 10₄The discharge of outlet 10.4；

Step 2：Liquefaction of nitrogen stores flow：20~25 DEG C, 0.6~0.7MPa nitrogen made from PSA nitrogen-making devices 11 The LNG that (oxygen content is less than 1%) enters First Heat Exchanger 8 and -153 DEG C, 9MPa exchanges heat, and precooling is cooled to -150 DEG C, then With the M of nitrogen separation device 17₂Gaseous phase outlet 17.2 flow out -175 DEG C, 0.69MPa low temperature nitrogen mixing temperature be down to -160 DEG C, through nitrogen compressor 14 be pressurized to 2.95MPa, -85 DEG C, the LNG into the second heat exchanger 15 and -153 DEG C, 9MPa exchanges heat, Be cooled to -150 DEG C, then through first throttle valve 16 be decompressed to 0.69MPa, -175 DEG C, flow into nitrogen separation device 17 and separate liquid phase, Liquid nitrogen after the separation of nitrogen separation device 17 stores into liquid nitrogen container 18, nitrogen separation device 17 separate after low temperature nitrogen and through the Nitrogen after the precooling of one heat exchanger 8 converges into nitrogen compressor 14 in nitrogen blender 13 carries out nitrogen compression circulation, continuously Constantly utilize LNG cold liquefaction nitrogen；

Step 3：BOG liquefaction is outer defeated and returns tank flow：- 150~-100 DEG C in LNG storage tank 1,115kPa BOG is through BOG Compressor 24 is pressurized to 0.5~0.9MPa, then divides through BOG distributors 25 for two-way, carries out step 1 into after-condenser 4 all the way The normal outer defeated flows of described LNG；Another way enters BOG- liquid nitrogen heat exchanger 20, with liquid nitrogen container 18 flow out -175 DEG C, 0.69MPa liquid nitrogen heat exchange is cooled to -148 DEG C of BOG lime sets, while pressure need to meet NPSH (the required vapour of high pressure pump inlet Lose surplus) (NPSH is 0.1MPa in this example) is required, -40 DEG C of nitrogen temperature, 0.68MPa enter nitrogen pot after liquid nitrogen gasification 21, BOG lime sets pass through the O of BOG- liquid nitrogen heat exchanger 20₂20.2 points of outlet is two-way, is sent into high-pressure pump through the 5th valve 27 all the way 6 carry out the normal outer defeated flows of LNG described in step 1, and another way enters gas-liquid separator 29 through the decompression of second throttle 28, through gas Liquid phase after liquid/gas separator 29 separates is flowed into LNG storage tank 1, and the gas phase after the separation of gas-liquid separator 29 enters BOG compressors 24 import, continuously carry out defeated outside BOG liquefaction and return tank, wherein consumption liquid nitrogen is with the mass ratio for condensing BOG 2.2~2.3 (outer defeated after BOG condensations)：2.6~2.7 (depressurizing back tank after BOG condensations).

In above-mentioned technical proposal, nitrogen sweeping process is also included in the step 2, the nitrogen of the nitrogen sweeping process comes Source is three parts, and Part I is that nitrogen caused by PSA nitrogen-making devices 11 enters scavenging pipeline 34 through the 6th valve 33；Second It is divided into the liquid nitrogen in liquid nitrogen container 18 and passes through the 3rd valve 22, then enters scavenging pipeline after the gasification of liquid nitrogen converter 23 is nitrogen 34；Part III is that the nitrogen in nitrogen pot 21 is directly entered scavenging pipeline 34.Three of the above nitrogen gas source complements one another, no elder generation Order afterwards.If the step 1 and step 2 can not be realized, the R of LNG storage tank 1₁Outlet 1.1 connects the air inlet with torch 30 Logical, BOG will be fed into torch emptying burning.

The present invention utilizes " cold energy " that LNG more than needed is carried by PSA (pressure-variable adsorption separation) Nitrogen Headspace caused by nitrogen-making device Change condensation, be stored in standby in liquid nitrogen container, nitrogen exchanges heat by one-level precooling and LNG, is pressurized through nitrogen compressor, then with LNG Carry out heat exchange and realize that two level cools down, and temperature drop is produced by throttling, separate low temperature liquid nitrogen through separator stores into storage tank；Separation Device nitrogen and the nitrogen of one-level precooling, which converge to compress into nitrogen, to be circulated, and when the outer throughput rates of LNG are low or BOG yields are big, transfers liquid Low temperature liquid nitrogen in nitrogen tank is used for BOG liquefaction condensations, and the gas nitrogen after heat exchange is stored in nitrogen storage tank；Condensation BOG is passed through again High-pressure pump supercharging is outer defeated, or is decompressed to LNG pressure stores through choke valve, and separate lime set by separator injects storage from tank bottom Deposit, gas phase BOG returns to gas phase house steward and enters BOG compression circulations, takes full advantage of the PSA transformations that domestic LNG station field generally possesses Adsorption nitrogen making device, this causes the equipment investment needed for yard process modification to be reduced.

More than, it is only embodiment of the invention, it is noted that any those skilled in the art are in this hair In bright disclosed technical scope, the change or replacement that can readily occur in should be all included within the scope of the present invention.

Claims (10)

1. pump (2) in a kind of BOG recovery and nitrogen gas liquefaction system, including LNG storage tank (1), tank, the first LNG dispenser (3), again Condenser (4), the first LNG blenders (5), high-pressure pump (6), the second LNG dispenser (7), First Heat Exchanger (8), the 2nd LNG are mixed Clutch (9), LNG gasification device (10), PSA nitrogen-making devices (11), the first valve (12), nitrogen blender (13), nitrogen compressor (14), the second heat exchanger (15), nitrogen separation device (17), liquid nitrogen container (18), the second valve (19), BOG- liquid nitrogen heat exchangers (20), nitrogen pot (21), the 3rd valve (22), liquid nitrogen converter (23), BOG compressors (24), BOG distributors (25), the 4th Valve (26), the 5th valve (27), gas-liquid separator (29), the 6th valve (33)；

Pump (2) is arranged in LNG storage tank (1) in the tank, A outlets (2.1) connection the first LNG distribution of pump (2) in the tank The B of device (3)₃Import (3.3), the B of first LNG dispenser (3)₁Export the D that (3.1) connect the first LNG blenders (5)₁Enter Mouth (5.1), the B of first LNG dispenser (3)₂Export the C of (3.2) connection after-condenser (4)₁Import (4.1), it is described cold again The C of condenser (4)₃Export the D that (4.3) connect the first LNG blenders (5)₂Import (5.2), the first LNG blenders (5) go out Mouth connects the E of the second LNG dispenser (7) by high-pressure pump (6)₃Import (7.3), the E of second LNG dispenser (7)₁Outlet (7.1) F of First Heat Exchanger (8) is connected₁Import (8.1), the F of the First Heat Exchanger (8)₂Export (8.2) and connect the 2nd LNG The G of blender (9)₁Import (9.1)；

The E of second LNG dispenser (7)₂Export the L that (7.2) connect the second heat exchanger (15)₁Import (15.1), described second The L of heat exchanger (15)₂Export the G that (15.2) connect the 2nd LNG blenders (9)₂Import (9.2), the 2nd LNG blenders (9) Outlet be connected to the H of LNG gasification device (10)₁Import (10.1), the H of the LNG gasification device (10)₂It is outer to export (10.2) connection The gas line network (35) on boundary；

The I of the PSA nitrogen-making devices (11)₁It is divided into two branch roads behind outlet (11.1), all the way by the first valve (12) connection the The F of one heat exchanger (8)₃Import (8.3), another way is by the extraneous scavenging pipeline (34) of the 6th valve (33) connection；Described The F of one heat exchanger (8)₄Export the J of (8.4) connection nitrogen blender (13)₁Import (13.1), the nitrogen blender (13) J₃Export the K of (13.3) connection nitrogen compressor (14)₁Import (14.1), the K of the nitrogen compressor (14)₂Export (14.2) Connect the L of the second heat exchanger (15)₃Import (15.3), the L of second heat exchanger (15)₄Export (15.4) connection nitrogen separation The M of device (17)₃Import (17.3), the M of the nitrogen separation device (17)₂Gaseous phase outlet (17.2) connection nitrogen blender (13) J₂Import (13.2), the M of the nitrogen separation device (17)₁The N of liquid-phase outlet (17.1) connection liquid nitrogen container (18)₁Import (18.1), The N of the liquid nitrogen container (18)₂It is divided into two branch roads behind outlet (18.2), is changed all the way by the second valve (19) connection BOG- liquid nitrogen The O of hot device (20)₃Import (20.3), another way connect the P of liquid nitrogen converter (23) by the 3rd valve (22)₁Import (23.1)； The O of the BOG- liquid nitrogen heat exchanger (20)₄Export the Q of (20.4) connection nitrogen pot (21)₁Import (21.1)；

The R of the LNG storage tank (1)₁Export the import of (1.1) connection BOG compressors (24), the outlet of the BOG compressors (24) Connect the T of BOG distributors (25)₃Import (25.3), the T of the BOG distributors (25)₁Export (25.1) connection after-condenser (4) C₂Import (4.2)；The T of the BOG distributors (25)₂Export the O of (25.2) connection BOG- liquid nitrogen heat exchanger (20)₁Import (20.1), the O of the BOG- liquid nitrogen heat exchanger (20)₂It is divided into two branch roads behind outlet (20.2), all the way by the 5th valve (27) D of the first LNG blenders (5) is connected₃Import (5.3), another way is by the 4th valve (26) connection gas-liquid separator (29) V₃Import (29.3), the V of the gas-liquid separator (29)₁Gaseous phase outlet (29.1) connection BOG compressor (24) is entered Mouthful, the V of the gas-liquid separator (29)₂The R of liquid-phase outlet (29.2) connection LNG storage tank (1)₂Import (1.2).

2. BOG recovery according to claim 1 and nitrogen gas liquefaction system, it is characterised in that：Also include the first sea water pump (31), the second sea water pump (32), the H of the LNG gasification device (10)₃Import (10.3) is connected by the first sea water pump (31) and seawater Connect, the LNG gasification device (10) is additionally provided with the H for discharging seawater₄Export (10.4)；The P of the liquid nitrogen converter (23)₃ Import (23.3) is connected by the second sea water pump (32) with seawater, and the liquid nitrogen converter (23) is additionally provided with for discharging seawater P₄Import (23.4).

3. BOG recovery according to claim 2 and nitrogen gas liquefaction system, it is characterised in that：The Q of the nitrogen pot (21)₂Go out Mouth (21.2), the P of liquid nitrogen converter (23)₂Outlet (23.2) is connected after converging with scavenging pipeline (34).

4. BOG recovery according to claim 3 and nitrogen gas liquefaction system, it is characterised in that：It also includes torch (30), institute The air inlet for stating torch (30) passes through branch road and the R of LNG storage tank (1)₁Export (1.1) connection.

5. BOG recovery according to claim 4 and nitrogen gas liquefaction system, it is characterised in that：Second heat exchanger (15) L₄Export (15.4) and the M of nitrogen separation device (17)₃First throttle valve (16) is provided with pipeline between import (17.3).

6. BOG recovery according to claim 5 and nitrogen gas liquefaction system, it is characterised in that：The gas-liquid separator (29) V₃Import (29.3) and the O of BOG- liquid nitrogen heat exchanger (20)₂Second throttle is provided with pipeline between outlet (20.2) (28)。

7. a kind of utilize BOG recovery described in claim 6 and the process of liquefaction of nitrogen, it is characterised in that it includes as follows Step：

Step 1：The normal outer defeated flows of LNG：- 150~-100 DEG C in LNG storage tank (1), 115kPa BOG is through BOG compressors (24) 0.5~0.9MPa is pressurized to, then is divided into two-way through BOG distributors (25), now the only T of BOG distributors (25)₁Outlet (25.1) connect, BOG enters the C of after-condenser (4)₂Import (4.2), while it is pressurized to 0.5~0.9MPa's through pump in tank (2) Bs of the LNG by the first LNG dispenser (3) is subcooled₂Export the C that (3.2) enter after-condenser (4)₁Import (4.1), BOG and supercooling LNG is contacted, mixed and is condensed into liquid, the C that lime set passes through after-condenser (4) in after-condenser (4)₃Outlet (4.3) is entered Enter the D of the first LNG blenders (5)₂Import (5.2) and the B by the first LNG dispenser (3)₁The LNG for exporting (3.1) outflow converges Close, be sent into high-pressure pump (6) import, through high-pressure pump (6) be pressurized to 9MPa, -153 DEG C, be divided into two through the second LNG dispenser (7) Road, all the way will be nitrogen precooled through First Heat Exchanger (8), and LNG temperature rises to -149.5 DEG C, and another way will through the second heat exchanger (15) Liquefaction of nitrogen, LNG temperature rise to -30.6 DEG C, and two-way LNG is sent into LNG gasification device (10) after the mixing of the 2nd LNG blenders (9) Enter gas line network (35) with seawater to make heat exchange gasification for natural gas；Seawater enters LNG gasification device through the first sea water pump (31) supercharging (10) H₃Import (10.3), the H through LNG gasification device (10) after being exchanged heat with LNG₄Export (10.4) discharge；

Step 2：Liquefaction of nitrogen stores flow：20~25 DEG C made from PSA nitrogen-making devices (11), 0.6~0.7MPa nitrogen enters Enter First Heat Exchanger (8) to exchange heat with -153 DEG C, 9MPa LNG, precooling is cooled to -150 DEG C, then with nitrogen separation device (17) M₂Gaseous phase outlet (17.2) outflow -175 DEG C, 0.69MPa low temperature nitrogen mixing temperature be down to -160 DEG C, through nitrogen compressor (14) be pressurized to 2.95MPa, -85 DEG C, exchanged heat into the second heat exchanger (15) and -153 DEG C, 9MPa LNG, be cooled to -150 DEG C, then through first throttle valve (16) be decompressed to 0.69MPa, -175 DEG C, flow into nitrogen separation device (17) separate liquid phase, through nitrogen Liquid nitrogen after separator (17) separation enters liquid nitrogen container (18) and stored, low temperature nitrogen after nitrogen separation device (17) separation and through the Nitrogen after one heat exchanger (8) precooling converges into nitrogen compressor (14) progress nitrogen compression in nitrogen blender (13) to follow Ring, continuously utilize LNG cold liquefaction nitrogen；

Step 3：BOG liquefaction is outer defeated and returns tank flow：- 150~-100 DEG C in LNG storage tank (1), 115kPa BOG presses through BOG Contracting machine (24) is pressurized to 0.5~0.9MPa, then is divided into two-way through BOG distributors (25), is walked all the way into after-condenser (4) It is rapid 1) described in the normal outer defeated flows of LNG；Another way enters BOG- liquid nitrogen heat exchanger (20), and -175 with liquid nitrogen container (18) outflow DEG C, the heat exchange of 0.69MPa liquid nitrogen be cooled to -148 DEG C of BOG lime sets, -40 DEG C of nitrogen temperature, 0.68MPa enter after liquid nitrogen gasification Nitrogen pot (21), BOG lime sets pass through the O of BOG- liquid nitrogen heat exchanger (20)₂Outlet (20.2) is divided into two-way, all the way through the 5th valve (27) be sent into high-pressure pump (6) and carry out normal outer defeated flows of LNG described in step 1, another way through second throttle (28) depressurize into Enter gas-liquid separator (29), the liquid phase after gas-liquid separator (29) separation is flowed into LNG storage tank (1), through gas-liquid separator (29) gas phase after separating enters the import of BOG compressors (24), continuously carries out defeated outside BOG liquefaction and returns tank.

8. BOG recovery according to claim 7 and the method for liquefaction of nitrogen, it is characterised in that also include in the step 2 Nitrogen sweeping process, the nitrogen gas source of the nitrogen sweeping process is three parts, and Part I produces for PSA nitrogen-making devices (11) Nitrogen enter scavenging pipeline (34) through the 6th valve (33)；Part II is that the liquid nitrogen in liquid nitrogen container (18) passes through the 3rd valve (22), then after liquid nitrogen converter (23) gasification is nitrogen scavenging pipeline (34) is entered；Part III is in nitrogen pot (21) Nitrogen is directly entered scavenging pipeline (34).

9. BOG recovery according to claim 7 and the method for liquefaction of nitrogen, it is characterised in that in the step 1, second LNG dispenser (7) distribution enters First Heat Exchanger (8), the LNG mass ratioes of the second heat exchanger (15) are 1:70~72.

10. BOG recovery according to claim 9 and the method for liquefaction of nitrogen, it is characterised in that if the step 1 and step Rapid 2 when can not realize, the R of LNG storage tank (1)₁Exporting (1.1) will be connected with the air inlet of torch (30), and BOG is put into torch Air-fuel is burnt.