CN113446514B - Flash evaporation gas liquefaction recovery system and method - Google Patents
Flash evaporation gas liquefaction recovery system and method Download PDFInfo
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- CN113446514B CN113446514B CN202110716337.2A CN202110716337A CN113446514B CN 113446514 B CN113446514 B CN 113446514B CN 202110716337 A CN202110716337 A CN 202110716337A CN 113446514 B CN113446514 B CN 113446514B
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 492
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- 229910001873 dinitrogen Inorganic materials 0.000 claims description 14
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- 239000007791 liquid phase Substances 0.000 claims description 6
- 239000012071 phase Substances 0.000 claims description 6
- 238000007664 blowing Methods 0.000 claims description 5
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- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
- F25J1/0022—Hydrocarbons, e.g. natural gas
- F25J1/0025—Boil-off gases "BOG" from storages
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C9/00—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure
- F17C9/02—Methods or apparatus for discharging liquefied or solidified gases from vessels not under pressure with change of state, e.g. vaporisation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
- F17C6/00—Methods and apparatus for filling vessels not under pressure with liquefied or solidified gases
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
- F25J1/007—Primary atmospheric gases, mixtures thereof
- F25J1/0072—Nitrogen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0221—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using the cold stored in an external cryogenic component in an open refrigeration loop
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
- F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
- F25J1/0277—Offshore use, e.g. during shipping
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/42—Nitrogen
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Abstract
The invention provides a flash evaporation gas liquefaction recovery system, wherein a natural gas condenser is vertically arranged, and the lower end of the natural gas condenser is provided with a liquefied natural gas liquid storage cavity communicated with the natural gas condenser; the liquid nitrogen storage tank is connected with an evaporator valve, the evaporator valve is connected with an inlet of the evaporator, the evaporator is connected with the liquid nitrogen storage tank, the liquid nitrogen storage tank is connected with a liquid discharge valve of the liquid nitrogen storage tank, and the liquid discharge valve of the liquid nitrogen storage tank is connected with the natural gas condenser; the liquefied natural gas storage cavity is connected with a liquefied natural gas tank through a drainage device, the liquefied natural gas tank is connected with a natural gas condenser, and control valves are arranged at an outlet and an inlet of the liquefied natural gas tank; the natural gas condenser is connected with the nitrogen heater, the nitrogen heater is connected with the nitrogen storage tank, a temperature display instrument is arranged between the natural gas condenser and the nitrogen heater, and a nitrogen storage tank pressure regulating valve is arranged at an outlet of the nitrogen storage tank. The invention also provides a method for liquefying and recovering the flash evaporation gas. The invention has good recovery effect and is simple and easy to operate.
Description
Technical Field
The invention relates to the technical field of gas recovery, in particular to a flash evaporation gas liquefaction recovery system and a flash evaporation gas liquefaction recovery method.
Background
With the global emphasis on environmental protection, the world is spreading liquefied natural gas in advanced countries. Liquefied natural gas is generally recognized as the cleanest energy source on earth, is colorless, tasteless, nontoxic and noncorrosive, has very little pollution to air after being combusted, and emits large heat. The liquefied natural gas manufacturing process is that natural gas produced in a gas field is purified and is liquefied at a series of ultralow temperatures, and then is transported by using transportation tools such as liquefied natural gas ships or liquefied natural gas tank cars, and generally the liquefied natural gas is stored in a vacuum pressure container, but because of the absence of absolute vacuum, part of liquefied natural gas in a low-temperature state can be changed into flash gas, and because heat exchange can be inevitably carried out between the liquefied natural gas and the outside in the processes of storage, transportation and the like, the temperature of the liquefied natural gas in the container is increased, part of the liquefied natural gas can be evaporated to generate the flash gas, the pressure of the container can be increased after the flash gas is formed, if the liquefied natural gas is directly emptied, resource waste can be caused, the flash gas can cause a greenhouse effect, and low-temperature burn can be caused to human bodies.
At present, a plurality of enterprises design systems for recovering flash steam, the flash steam can be changed into natural gas at normal temperature, and the natural gas is generally condensed to be changed into liquefied natural gas and then recovered. The prior art scheme includes a multiple liquefaction system composed of a plurality of heat exchange systems, recovery systems such as a condensation system using a compressor principle, for example, a recovery system in a recovery system for reliquefying and recovering boil-off gas (CN2019104031707) of polar shipping company in norway, a multi-stage cooling device is adopted, a propane cooler needs to be additionally arranged, the structure is complex, the safety is poor, a condensation separation tank and a condensation heat exchanger are separately arranged, unnecessary loss can be caused in actual operation, loss of recovery amount of flash evaporation gas is caused, or for example, a recovery device in a recovery device for reliquefaction and liquefaction of boil-off gas (CN2011204942916) of the general oil company in china, a compressor is adopted for compression, a large amount of electric energy is consumed, and the purpose of saving energy can not be achieved. The recovery effect of current many schemes is also not ideal, some schemes are separately condenser and condensate recovery unit, condensate in the condenser gets into condensate recovery unit's in-process can form more loss, some schemes are directly continuous condenser and liquefied natural gas jar for avoiding the loss, the condensate in the condenser is not concentrated and is collected, the flow is little, the recovery effect is not good, and present most condenser is horizontal state, and the recovery efficiency of condensate is not considered, consequently, need a new flash distillation gas liquefaction recovery system and method to solve above problem urgently.
Disclosure of Invention
The invention aims to provide a flash evaporation gas liquefaction recovery system which can realize recovery of flash evaporation gas without a compressor and has the advantages of energy conservation, good condensation effect, good recovery effect and good safety performance.
In order to achieve the technical purpose and achieve the technical requirements, the invention adopts the technical scheme that: a flash evaporation gas liquefaction recovery system comprises a liquid nitrogen storage tank, a liquid discharge valve of the liquid nitrogen storage tank, a liquefied natural gas tank, a natural gas condenser, an evaporator connected with an evaporator valve, a nitrogen storage tank and a nitrogen heater connected with the nitrogen storage tank, wherein the natural gas condenser is vertically arranged, and the lower end of the natural gas condenser is provided with a liquefied natural gas storage cavity communicated with the natural gas condenser;
the first outlet of the liquid nitrogen storage tank is connected with the inlet of an evaporator valve through a pipeline, the outlet of the evaporator valve is connected with the inlet of an evaporator through a pipeline, the outlet of the evaporator is connected with the inlet of a liquid nitrogen storage tank through a pipeline, the second outlet of the liquid nitrogen storage tank is connected with the inlet of a liquid discharge valve of the liquid nitrogen storage tank through a pipeline, and the outlet of the liquid discharge valve of the liquid nitrogen storage tank is connected with the first inlet of a natural gas condenser through a pipeline;
the outlet of the liquefied natural gas storage cavity is connected with the inlet of the liquefied natural gas tank through a drainage device with opening and closing functions, the drainage device drains the liquefied natural gas condensate in the liquefied natural gas storage cavity into the liquefied natural gas tank, the outlet of the liquefied natural gas tank is connected with the second inlet of the natural gas condenser through a pipeline, and control valves are arranged on the outlet pipeline and the inlet pipeline of the liquefied natural gas tank;
the outlet of the natural gas condenser is connected with the inlet of the nitrogen heater through a pipeline, the outlet of the nitrogen heater is connected with the inlet of the nitrogen storage tank through a pipeline, a temperature display instrument is arranged between the outlet of the natural gas condenser and the inlet of the nitrogen heater, and a nitrogen storage tank pressure regulating valve is arranged at the outlet of the nitrogen storage tank.
As a preferred technical scheme: and a liquid nitrogen storage tank pressure regulating valve is connected between the outlet of the evaporator and the inlet of the liquid nitrogen storage tank.
As a preferred technical scheme: the natural gas condenser is arranged above the liquefied natural gas tank, the drainage device comprises a condensate discharge valve and a pipeline, an outlet of the liquefied natural gas liquid storage cavity is connected with an inlet of the condensate discharge valve through the pipeline, an outlet of the condensate discharge valve is connected with an inlet of the liquefied natural gas tank through the pipeline, and liquefied natural gas liquid in the liquefied natural gas liquid storage cavity enters the liquefied natural gas tank through the condensate discharge valve and the pipeline by utilizing self weight.
As a preferred technical scheme: the drainage device comprises a liquefied natural gas pump, a condensate discharging valve and a pipeline, wherein the outlet of the liquefied natural gas liquid storage cavity is connected with the inlet of the condensate discharging valve through the pipeline, the outlet of the condensate discharging valve is connected with the inlet of the liquefied natural gas pump through the pipeline, the outlet of the liquefied natural gas pump is connected with the inlet of the liquefied natural gas tank, and the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity is pumped to the liquefied natural gas tank by the liquefied natural gas pump.
As a preferred technical scheme: the nitrogen storage tank is provided with a purging port, the purging port is connected with an inlet of a purging valve, and an outlet of the purging valve is connected with a pipeline which is connected with an outlet of the liquefied natural gas tank and a second inlet of the natural gas condenser.
As a preferred technical scheme: the nitrogen heater is a finned heater.
As a preferred technical scheme: the nitrogen heater is an ethylene glycol heating system.
As a preferred technical scheme: the pipeline of the export of liquefied natural gas stock solution chamber links to each other with the import of liquefied natural gas level gauge, the export of liquefied natural gas level gauge links to each other with the pipeline of the second import of natural gas condenser, liquefied natural gas level gauge parallel connection has the balanced valve, the feed liquor and the play liquid of liquefied natural gas level gauge pass through control flap control.
The invention also provides a flash evaporation gas liquefaction recovery method, which comprises the following steps:
step 1: when the pressure in the liquefied natural gas tank reaches the allowable upper limit value, a control valve at the outlet of the liquefied natural gas tank is opened, the flash gas in the liquefied natural gas tank enters the tube side of a natural gas condenser, the flash gas is converted into natural gas, an evaporator valve in a liquid nitrogen storage tank is opened to increase the pressure in the liquid nitrogen storage tank to a set working pressure, then a liquid discharge valve of the liquid nitrogen storage tank is opened, the liquid nitrogen enters the shell side of the natural gas condenser to condense and liquefy the natural gas in the tube side, and the flow of the liquid nitrogen is controlled by the temperature of nitrogen at the outlet of the natural gas condenser;
step 2: the gasified nitrogen is heated to be above 0 ℃ by a nitrogen heater, enters a nitrogen storage tank, can be discharged to the air or used for blowing, the pressure setting value of the pressure regulating valve of the nitrogen storage tank is lower than the working pressure of the liquid nitrogen storage tank minus the pressure drop of the nitrogen flow route, when the pressure in the nitrogen storage tank reaches the specified upper limit value, the pressure regulating valve of the nitrogen storage tank is automatically opened, and the gas in the nitrogen storage tank is discharged to reduce the pressure to the specified value;
and step 3: the condensed liquefied natural gas condensate flows into the liquefied natural gas liquid storage cavity along the pipe wall of the heat exchange pipe in the natural gas condenser, and when the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity is gathered to a certain liquid level height, the drainage device is opened to drain the liquefied natural gas condensate to the liquefied natural gas tank;
and 4, step 4: after the natural gas on the upper part of the natural gas condenser is condensed, the pressure on the upper part of the natural gas condenser is lower than that of the liquefied natural gas tank, then a certain pressure difference is formed between the upper part of the natural gas condenser and the liquefied natural gas tank, the gas in the liquefied natural gas tank is conveyed to the natural gas condenser for liquefaction, the pressure in the liquefied natural gas tank is gradually reduced, an evaporator valve in a liquid nitrogen storage tank and a liquid discharge valve of the liquid nitrogen storage tank are closed after the pressure in the liquefied natural gas tank is reduced to a specified value, and a condensation liquefaction working cycle is finished.
As a preferred technical scheme: the temperature of nitrogen at the outlet of the natural gas condenser in the step 1 is 60-80 ℃.
The invention has the beneficial effects that: compared with the traditional scheme, the flash evaporation gas liquefaction recovery system and the method thereof are as follows:
1) the natural gas condenser is vertically arranged, the lower end of the natural gas condenser is provided with an liquefied natural gas liquid storage cavity for storing liquefied natural gas condensate, when the natural gas condenser is vertically arranged, the liquefied natural gas condensate flows to the liquefied natural gas liquid storage cavity by utilizing self weight, and after a certain amount of liquefied natural gas condensate is collected in the liquefied natural gas liquid storage cavity, the drainage device is opened to drain the liquefied natural gas condensate to the liquefied natural gas tank, so that the recovery efficiency is high, the recovery effect is good, and unnecessary waste can not be caused; the liquid nitrogen is used for condensing the flash evaporation gas in the liquefied natural gas pipe, and the recovery of the flash evaporation gas can be realized without a compressor; the method comprises the following steps that self pressurization is realized by an evaporator on a liquid nitrogen storage tank, so that the liquid nitrogen storage tank has enough working pressure, and the recovery efficiency is improved; the liquid nitrogen enters the natural gas condenser to be changed into nitrogen, and the nitrogen is heated by the nitrogen heater and then enters the nitrogen storage tank to be stored, so that the resource waste can be reduced, and the stored nitrogen can be recycled; the temperature display instrument can display the temperature of the nitrogen and control the flow of the liquid nitrogen according to the temperature of the nitrogen so as to achieve the best condensation effect; the whole system has simple structure, good condensation and recovery effects, reasonable spatial arrangement and resource saving;
2) preferably, the natural gas condenser is arranged above the liquefied natural gas tank, the drainage device comprises a condensate discharge valve and a pipeline, when the drainage device is arranged above the liquefied natural gas tank, the liquefied natural gas condensate in the liquefied natural gas condensation cavity enters the liquefied natural gas tank by virtue of dead weight, the liquefied natural gas condensate can be recovered without a liquefied natural gas pump, and the recovery effect is good;
3) preferably, the drainage device comprises an liquefied natural gas pump, a condensate discharge valve and a pipeline, the liquefied natural gas pump pumps the liquefied natural gas condensate in the liquefied natural gas storage cavity into the liquefied natural gas tank, the recovery efficiency can be further improved by the aid of the liquefied natural gas pump, and whether the liquefied natural gas pump is used or not can be selected according to different working conditions;
4) preferably, the nitrogen storage tank is provided with a purging port, and the nitrogen recovered from the nitrogen storage tank can purge the pipeline;
5) preferably, the nitrogen heater is a fin heater or an ethylene glycol heating system, and is heated by adopting an air fin tube mode, so that the nitrogen heater has larger occupied volume and is easily influenced by the ambient temperature, and the nitrogen heater is extremely convenient and simple to operate; the heating of the ethylene glycol system has the advantages of small volume, no influence of ambient temperature and capability of being set according to different working conditions;
6) preferably, the liquefied natural gas liquid level meter and the balance valve connected in parallel with the liquefied natural gas liquid level meter can indicate the liquid level height in the liquefied natural gas liquid storage cavity, the balance valve can balance the pressure difference between a liquid phase and a gas phase in the natural gas condenser pipe, and the indicating precision of the liquefied natural gas liquid level meter is improved;
7) the recovery method has the advantages of simple flow, easy operation, concise and understandable recovery principle, clear and reasonable layout, low cost and excellent recovery effect, and the volume ratio of the condensed liquid nitrogen to the recovered flash evaporation gas is close to 1: 1;
8) preferably, the condensation effect is best when the temperature of the nitrogen at the outlet of the natural gas condenser is 60-80 ℃, and the temperature range of the nitrogen which is changed into the nitrogen after the liquid nitrogen passes through the natural gas condenser is 60-80 ℃.
Drawings
FIG. 1 is a block diagram of the present invention;
FIG. 2 is a structural view of embodiment 1 of the present invention;
fig. 3 is a structural view of embodiment 2 of the present invention.
In the figures 1-3, 1, a liquid nitrogen storage tank, 2, a liquefied natural gas tank, 3, a natural gas condenser, 301, a liquefied natural gas storage cavity, 4, an evaporator, 5, an evaporator valve, 6, a drainage device, 601, a condensate discharge valve, 602, a liquefied natural gas pump, 7, a liquid nitrogen storage tank discharge valve, 8, a nitrogen heater, 9, a nitrogen storage tank, 901, a purge port, 10, a nitrogen storage tank pressure regulating valve, 11, a temperature display instrument, 12, a control valve, 13, a purge valve, 14, a liquefied natural gas level meter, 15, a balance valve, 16, a liquid nitrogen storage tank pressure regulating valve, 17, a standby nitrogen discharge valve, 18 and a pressure release valve.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if the terms "top", "bottom", "left", "right", "front", "back", "inner", "outer", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, it is only for convenience of description of the present invention, but does not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and are not to be construed as limiting the present patent, and the specific meaning of the terms described above will be understood by those of ordinary skill in the art according to the specific circumstances.
Referring to fig. 1-3, a flash gas liquefaction recovery system comprises a liquid nitrogen storage tank 1, a liquid discharge valve 7 of the liquid nitrogen storage tank, a liquefied natural gas tank 2, a natural gas condenser 3, an evaporator 4 connected with an evaporator valve 5, a nitrogen storage tank 9, a nitrogen heater 8 connected with the nitrogen storage tank 9, the natural gas condenser 3 is vertically arranged, and the lower end is provided with an liquefied natural gas liquid storage cavity 301 communicated with the natural gas condenser 3, the liquefied natural gas liquid storage cavity 301 is directly arranged at the lower end of the natural gas condenser 3 and can collect the liquefied natural gas condensate to the maximum extent, the natural gas condenser 3 vertically arranged enables the liquefied natural gas condensate to flow to the liquefied natural gas liquid storage cavity 301 by utilizing the dead weight, the liquefied natural gas condensate is firstly collected in a centralized way, and further, on the basis of the original natural gas condenser 3, the lower part of the natural gas condenser is properly lengthened and is provided with a cavity to form a liquefied natural gas liquid storage cavity 301;
a first outlet of the liquid nitrogen storage tank 1 is connected with an inlet of an evaporator valve 5 through a pipeline, an outlet of the evaporator valve 5 is connected with an inlet of an evaporator 4 through a pipeline, an outlet of the evaporator 4 is connected with an inlet of the liquid nitrogen storage tank 1 through a pipeline, a second outlet of the liquid nitrogen storage tank 1 is connected with an inlet of a liquid nitrogen storage tank drain valve 7 through a pipeline, an outlet of the liquid nitrogen storage tank drain valve 7 is connected with a first inlet of a natural gas condenser 3 through a pipeline, the evaporator 4 can pressurize the liquid nitrogen storage tank 1, when the liquid nitrogen storage tank 1 reaches the working pressure, the liquid nitrogen enters the natural gas condenser 3 through the liquid nitrogen storage tank drain valve 7, furthermore, a liquid nitrogen storage tank pressure regulating valve 16 is connected between the outlet of the evaporator 4 and the inlet of the liquid nitrogen storage tank 1, and the liquid nitrogen storage tank 16 can control the pressure of the liquid nitrogen storage tank 1 according to the set working pressure value;
the outlet of the liquefied natural gas liquid storage cavity 301 is connected with the inlet of the liquefied natural gas tank 2 through the drainage device 6 with opening and closing functions, when the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity 301 reaches a certain height, the drainage device 6 is opened and drains the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity 301 into the liquefied natural gas tank 2, the liquefied natural gas condensate is collected in a concentrated mode and then drained to be recycled as clean as possible, unnecessary waste is avoided, the outlet of the liquefied natural gas tank 2 is connected with the second inlet of the natural gas condenser 3 through a pipeline, control valves 12 are arranged at the outlet and the inlet of the liquefied natural gas tank 2, the flash evaporation gas in the liquefied natural gas tank 2 is controlled through the control valve 12 at the outlet of the liquefied natural gas tank 2, and the backflow of the liquefied natural gas condensate in the liquefied natural gas tank 2 is controlled through the control valve 12 at the inlet of the liquefied natural gas tank 2, the control valve 12 can be an electromagnetic valve, and the automatic control can be realized by combining the electromagnetic valve with a control system;
the outlet of the natural gas condenser 3 is connected with the inlet of a nitrogen heater 8 through a pipeline, the outlet of the nitrogen heater 8 is connected with the inlet of a nitrogen storage tank 9 through a pipeline, a temperature display instrument 11 is arranged between the outlet of the natural gas condenser 3 and the inlet of the nitrogen heater 8, the temperature display instrument 11 is used for displaying the temperature of nitrogen at the outlet of the natural gas condenser 3, the flow of liquid nitrogen is adjusted according to the temperature of the temperature display instrument 11, a nitrogen storage tank pressure regulating valve 10 is arranged at the outlet of the nitrogen storage tank 9, and when the pressure in the nitrogen storage tank 9 exceeds a set upper pressure limit value, the nitrogen storage tank pressure regulating valve 10 opens and discharges the gas in the nitrogen storage tank 9 to reduce the pressure to a specified value; the whole system is compact and reasonable in equipment layout, does not waste space resources, is good in recovery effect, can recover flash steam to the maximum extent, saves resources, avoids unnecessary waste, can recycle nitrogen, is environment-friendly and efficient, and is good in safety.
As shown in fig. 1-3, the natural gas condenser 3 is arranged above the liquefied natural gas tank 2, the drainage device 6 comprises a condensate drain valve 601 and a pipeline, the outlet of the liquefied natural gas storage cavity 301 is connected with the inlet of the condensate drain valve 601 through the pipeline, the outlet of the condensate drain valve 601 is connected with the inlet of the liquefied natural gas tank 2 through the pipeline, when the natural gas condenser 3 is arranged above the liquefied natural gas tank 2, the liquefied natural gas condensate in the liquefied natural gas storage cavity 301 enters the liquefied natural gas tank 2 by self weight, the liquefied natural gas condensate can be recycled without the liquefied natural gas pump 602, the cost is reduced, the space is released, and the recycling effect is good.
As shown in fig. 1-3, the drainage device 6 includes an lng pump 602, a condensate drain valve 601 and a pipeline, the outlet of the lng liquid storage chamber 301 is connected to the inlet of the condensate drain valve 601 through a pipeline, the outlet of the condensate drain valve 601 is connected to the inlet of the lng pump 602 through a pipeline, the outlet of the lng pump 602 is connected to the inlet of the lng tank 2, no matter whether the natural gas condenser 3 is disposed above the lng tank 2 or disposed at other positions of the lng tank 2, the lng condensate in the lng liquid storage chamber 301 can be pumped to the lng tank 2 by the lng pump 602, the recovery efficiency is high, and the recovery effect is good.
As shown in fig. 1 to 3, the nitrogen storage tank 9 is provided with a purge port 901, the purge port 901 is connected to an inlet of the purge valve 13, an outlet of the purge valve 13 is connected to a pipeline connecting an outlet of the lng tank 2 and a second inlet of the natural gas condenser 3, and the nitrogen storage tank 9 provided with the purge port 901 has two functions: firstly, residual liquefied natural gas condensate possibly exists in the pipeline, and the residual liquefied natural gas condensate can be completely blown by nitrogen blowing; and secondly, the gas phase and the liquid phase in the pipeline are mixed to cause pressure imbalance, and the nitrogen purging is utilized to balance the pressure of the gas phase and the liquid phase in the pipeline and reduce the pressure build-up phenomenon.
As shown in fig. 1-3, the nitrogen heater 8 is a fin heater or a glycol heating system, and is heated by an air fin tube, so that the nitrogen heater occupies a large volume and is easily influenced by the ambient temperature, but the nitrogen heater is extremely convenient and simple to operate; the advantage of ethylene glycol system heating is small, does not receive ambient temperature's influence, and the operation is more complicated than the finned heater, can set up according to the operating mode of difference.
As shown in fig. 1 to 3, a pipeline of an outlet of the lng liquid storage cavity 301 is connected to an inlet of the lng liquid level meter 14, an outlet of the lng liquid level meter 14 is connected to a pipeline of a second inlet of the natural gas condenser 3, the lng liquid level meter 14 is connected in parallel to a balance valve 15, liquid inlet and outlet of the lng liquid level meter 14 are controlled by a control valve 12, the lng liquid level meter 14 can indicate a liquid level height in the lng liquid storage cavity 301, the balance valve 15 connected in parallel to the lng liquid level meter can balance a pressure difference between a liquid phase and a gas phase in the natural gas condenser pipe 3, and indication accuracy of the lng liquid level meter 14 is improved.
As shown in fig. 1-3, further, a spare nitrogen gas discharge valve 17 is connected to a pipeline connected to an inlet of the control valve 12 at an inlet of the lng tank 2, an outlet of the spare nitrogen gas discharge valve 17 is connected to a pipeline as a spare nitrogen gas discharge port, when the nitrogen gas in the pipeline is excessive, the nitrogen gas in the pipeline is completely discharged, a spring-type pressure release valve 18 is further provided on the nitrogen gas storage tank 9, and the instantaneous high pressure in the nitrogen gas storage tank 9 can be discharged and reduced through the pressure release valve 18.
Referring to fig. 1-3, a method for recovering flash gas by liquefaction includes the following steps:
step 1: when the pressure in the liquefied natural gas tank 2 reaches the allowable upper limit value, a control valve 12 at the outlet of the liquefied natural gas tank 2 is opened, the flash gas in the liquefied natural gas tank 2 enters the tube side of the natural gas condenser 3, the flash gas is changed into natural gas, an evaporator valve 5 in the liquid nitrogen storage tank 1 is opened, the pressure in the liquid nitrogen storage tank 1 is increased to a set working pressure, the set value range of the working pressure is 0.1 MPa-0.8 MPa, the recovery effect is best in the range, the whole loop is stable in circulation, a liquid discharge valve 7 of the liquid nitrogen storage tank is opened, liquid nitrogen at the temperature of-196 ℃ enters the shell side of the natural gas condenser 3 to condense and liquefy the natural gas in the tube side, and the flow rate of the liquid nitrogen is controlled by the temperature of the nitrogen at the outlet of the natural gas condenser 3;
step 2: the gasified nitrogen is heated to be higher than 0 ℃ by a nitrogen heater 8, enters a nitrogen storage tank 9, can be discharged to the air or used for purging, and is recycled, the pressure setting value of a nitrogen storage tank pressure regulating valve 10 is lower than the working pressure of a liquid nitrogen storage tank 1 minus the pressure drop of a nitrogen flow route, when the pressure in the nitrogen storage tank 9 reaches a specified upper limit value, the nitrogen storage tank pressure regulating valve 10 is automatically opened, and the gas in the nitrogen storage tank 9 is discharged to enable the pressure to be reduced to a specified value, so that the safety performance is improved;
and step 3: the condensed liquefied natural gas condensate flows into the liquefied natural gas liquid storage cavity 301 along the pipe wall of the heat exchange pipe in the natural gas condenser 3, and when the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity 301 is gathered to a certain liquid level height, the drainage device 6 is opened to drain the liquefied natural gas condensate to the liquefied natural gas tank 2;
and 4, step 4: after the natural gas condensation of the upper portion of natural gas condenser 3, the pressure on its upper portion is less than liquefied natural gas tank 2, and then the upper portion of natural gas condenser 3 will form certain pressure differential with liquefied natural gas tank 2, the gas in liquefied natural gas tank 2 will be carried natural gas condenser 3 constantly and liquefy, pressure in the liquefied natural gas tank 2 will also descend gradually, when descending to the specified value after closing evaporimeter valve 5 and liquid nitrogen storage tank flowing back valve 7 in the liquid nitrogen storage tank 1, a condensation liquefaction duty cycle finishes, the proportion that is used for the liquid nitrogen of condensation and the flash distillation gas of retrieving in the actual operation is close 1:1, the loss amount is very small, and the recovery effect is very good.
As shown in fig. 1-3, the temperature of the nitrogen gas at the outlet of the natural gas condenser 3 is 60 ℃ to 80 ℃, further, the temperature of the nitrogen gas at the outlet of the natural gas condenser 3 is-80 ℃, the liquid nitrogen passes through the natural gas condenser 3 and becomes nitrogen gas, the temperature of the nitrogen gas at the outlet of the natural gas condenser 3 is-80 ℃, the condensing effect is best, when the temperature of the nitrogen gas is lower than-80 ℃, the flow rate of the liquid nitrogen is properly reduced, and when the temperature of the nitrogen gas is higher than-80 ℃, the flow rate of the liquid nitrogen is properly increased.
Example 1
A flash evaporation gas liquefaction recovery system comprises a liquid nitrogen storage tank 1, a liquid nitrogen storage tank drain valve 7, a liquefied natural gas tank 2, a vertically arranged natural gas condenser 3, an evaporator 4 connected with an evaporator valve 5, a nitrogen storage tank 9 and a nitrogen heater 8 connected with the nitrogen storage tank 9, wherein the lower end of the natural gas condenser 3 is provided with a liquefied natural gas storage cavity 301 communicated with the natural gas condenser 3, a first outlet of the liquid nitrogen storage tank 1 is connected with an inlet of the evaporator valve 5 through a pipeline, an outlet of the evaporator valve 5 is connected with an inlet of the evaporator 4 through a pipeline, an outlet of the evaporator 4 is connected with an inlet of the liquid nitrogen storage tank 1 through a pipeline, a second outlet of the liquid nitrogen storage tank 1 is connected with an inlet of the liquid nitrogen storage tank drain valve 7 through a pipeline, an outlet of the liquid nitrogen drain valve 7 is connected with a first inlet of the natural gas condenser 3 through a pipeline, a liquid nitrogen storage tank pressure regulating valve 16 is connected between the outlet of the evaporator 4 and the inlet of the liquid nitrogen storage tank 1, the natural gas condenser 3 is arranged above the liquefied natural gas tank 2, the outlet of the liquefied natural gas liquid storage cavity 301 is connected with the inlet of the condensate discharging valve 601 through a pipeline, the outlet of the condensate discharging valve 601 is connected with the inlet of the liquefied natural gas tank 2 through a pipeline, the nitrogen storage tank 9 is provided with a purging port 901, the purging port 901 is connected with the inlet of the purging valve 13, the outlet of the purging valve 13 is connected with a pipeline which is connected with the outlet of the liquefied natural gas tank 2 and the second inlet of the natural gas condenser 3, the nitrogen heater 8 is a fin heater, the pipeline of the outlet of the liquefied natural gas liquid storage cavity 301 is connected with the inlet of the liquefied natural gas liquid level meter 14, the outlet of the liquefied natural gas liquid level meter 14 is connected with the pipeline of the second inlet of the natural gas condenser 3, the liquefied natural gas liquid level meter 14 is connected with a balance valve 15 in parallel, the liquid inlet of the liquefied natural gas liquid level meter 14 is connected with a control valve 12, a liquid outlet of the liquefied natural gas liquid level meter 14 is connected with a control valve 12.
A flash gas liquefaction recovery method comprises the following steps:
step 1: when the pressure in the liquefied natural gas tank 2 reaches the allowable upper limit value, a control valve 12 at the outlet of the liquefied natural gas tank 2 is opened, flash gas in the liquefied natural gas tank 2 enters a tube pass of a natural gas condenser 3, the flash gas is changed into natural gas, an evaporator valve 5 in a liquid nitrogen storage tank 1 is opened to increase the pressure in the liquid nitrogen storage tank 1 to a set working pressure, the working pressure is set to be 0.8MPa, then a liquid discharge valve 7 of the liquid nitrogen storage tank is opened, liquid nitrogen at the temperature of-196 ℃ enters a shell pass of the natural gas condenser 3 to condense and liquefy the natural gas in the tube pass, the flow is controlled by the temperature of nitrogen at the outlet of the natural gas condenser 3, and the temperature of the nitrogen at the outlet of the natural gas condenser 3 is controlled to be-80 ℃;
step 2: the gasified nitrogen is heated to be above 0 ℃ by a finned heater and enters a nitrogen storage tank 9, when the nitrogen is required to be blown, a blowing valve 13 is opened, the pressure set value of a nitrogen storage tank pressure regulating valve 10 is lower than the working pressure of a liquid nitrogen storage tank 1 minus the pressure drop of a nitrogen flow route, when the pressure in the nitrogen storage tank 9 reaches a specified upper limit value, the nitrogen storage tank pressure regulating valve 10 is automatically opened, and the gas in the nitrogen storage tank 9 is discharged to reduce the pressure to a specified value;
and step 3: the condensed liquefied natural gas condensate flows into the liquefied natural gas liquid storage cavity 301 along the pipe wall of the heat exchange pipe in the natural gas condenser 3, and when the liquefied natural gas liquid level meter 14 displays that the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity 301 is gathered to a set liquid level height, the condensate discharge valve 601 is opened, and the liquefied natural gas condensate is drained to the liquefied natural gas tank 2;
and 4, step 4: after the natural gas at the upper part of the natural gas condenser 3 is condensed, the pressure at the upper part of the natural gas condenser is lower than that of the liquefied natural gas tank 2, then a certain pressure difference is formed between the upper part of the natural gas condenser 3 and the liquefied natural gas tank 2, the gas in the liquefied natural gas tank 2 is conveyed to the natural gas condenser 3 for liquefaction, the pressure in the liquefied natural gas tank 2 is gradually reduced, an evaporator valve 5 and a liquid nitrogen storage tank drain valve 7 in the liquid nitrogen storage tank 1 are closed after the pressure is reduced to a specified value, and a condensing and liquefying work cycle is finished.
Example 2
A flash evaporation gas liquefaction recovery system comprises a liquid nitrogen storage tank 1, a liquid nitrogen storage tank drain valve 7, a liquefied natural gas tank 2, a vertically arranged natural gas condenser 3, an evaporator 4 connected with an evaporator valve 5, a nitrogen storage tank 9 and a nitrogen heater 8 connected with the nitrogen storage tank 9, wherein the lower end of the natural gas condenser 3 is provided with a liquefied natural gas storage cavity 301 communicated with the natural gas condenser 3, a first outlet of the liquid nitrogen storage tank 1 is connected with an inlet of the evaporator valve 5 through a pipeline, an outlet of the evaporator valve 5 is connected with an inlet of the evaporator 4 through a pipeline, an outlet of the evaporator 4 is connected with an inlet of the liquid nitrogen storage tank 1 through a pipeline, a second outlet of the liquid nitrogen storage tank 1 is connected with an inlet of the liquid nitrogen storage tank drain valve 7 through a pipeline, an outlet of the liquid nitrogen drain valve 7 is connected with a first inlet of the natural gas condenser 3 through a pipeline, a liquid nitrogen storage tank pressure regulating valve 16 is connected between the outlet of the evaporator 4 and the inlet of the liquid nitrogen storage tank 1, the outlet of the liquefied natural gas liquid storage cavity 301 is connected with the inlet of the condensate discharge valve 601 through a pipeline, the outlet of the condensate discharge valve 601 is connected with the inlet of the liquefied natural gas pump 602 through a pipeline, the outlet of the liquefied natural gas pump 602 is connected with the inlet of the liquefied natural gas tank 2, the nitrogen storage tank 9 is provided with a purging port 901, the purging port 901 is connected with the inlet of the purging valve 13, the outlet of the purging valve 13 is connected with a pipeline connecting the outlet of the liquefied natural gas tank 2 and the second inlet of the natural gas condenser 3, the nitrogen heater 8 is an ethylene glycol heating system, the pipeline of the outlet of the liquefied natural gas liquid storage cavity 301 is connected with the inlet of the liquefied natural gas liquid level meter 14, the outlet of the liquefied natural gas liquid level meter 14 is connected with the pipeline connecting the second inlet of the natural gas condenser 3, the liquefied natural gas liquid level meter 14 is connected with a balance valve 15 in parallel, and the liquid inlet of the liquefied natural gas liquid level meter 14 is connected with a control valve 12, a liquid outlet of the liquefied natural gas liquid level meter 14 is connected with a control valve 12.
A flash gas liquefaction recovery method comprises the following steps:
step 1: when the pressure in the liquefied natural gas tank 2 reaches the allowable upper limit value, a control valve 12 at the outlet of the liquefied natural gas tank 2 is opened, flash gas in the liquefied natural gas tank 2 enters a tube pass of a natural gas condenser 3, the flash gas is changed into natural gas, an evaporator valve 5 in a liquid nitrogen storage tank 1 is opened to increase the pressure in the liquid nitrogen storage tank 1 to a set working pressure, the working pressure is set to be 0.1MPa, then a liquid discharge valve 7 of the liquid nitrogen storage tank is opened, liquid nitrogen at the temperature of-196 ℃ enters a shell pass of the natural gas condenser 3 to condense and liquefy the natural gas in the tube pass, the flow is controlled by the temperature of nitrogen at the outlet of the natural gas condenser 3, and the temperature of the nitrogen at the outlet of the natural gas condenser 3 is controlled to be-65 ℃;
step 2: the gasified nitrogen is heated to be above 0 ℃ by an ethylene glycol heating system, enters a nitrogen storage tank 9 and can be emptied or used for purging, the pressure setting value of a nitrogen storage tank pressure regulating valve 10 is lower than the working pressure of a liquid nitrogen storage tank 1 minus the pressure drop of a nitrogen flow route, when the pressure in the nitrogen storage tank 9 reaches a specified upper limit value, the nitrogen storage tank pressure regulating valve 10 is automatically opened, and the gas in the nitrogen storage tank 9 is discharged to reduce the pressure to a specified value;
and step 3: the condensed liquefied natural gas condensate flows into the liquefied natural gas liquid storage cavity 301 along the pipe wall of the heat exchange pipe in the natural gas condenser 3, and when the liquefied natural gas liquid level meter 14 displays that the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity 301 is gathered to a set liquid level height, the condensate discharge valve 601 and the liquefied natural gas pump 602 are opened, and the liquefied natural gas condensate is pumped into the liquefied natural gas tank 2;
and 4, step 4: after the natural gas at the upper part of the natural gas condenser 3 is condensed, the pressure at the upper part of the natural gas condenser is lower than that of the liquefied natural gas tank 2, then a certain pressure difference is formed between the upper part of the natural gas condenser 3 and the liquefied natural gas tank 2, the gas in the liquefied natural gas tank 2 is conveyed to the natural gas condenser 3 for liquefaction, the pressure in the liquefied natural gas tank 2 is gradually reduced, an evaporator valve 5 and a liquid nitrogen storage tank drain valve 7 in the liquid nitrogen storage tank 1 are closed after the pressure is reduced to a specified value, and a condensing and liquefying work cycle is finished.
In view of the recovery system and method of example 2, the liquid nitrogen storage tank 1 was operated at 0.1MPa, inlet temperature-196 deg.C (liquid), outlet temperature-65 deg.C (gas), flash gas operation pressure 0kPa, inlet temperature-40 deg.C (gas), outlet temperature-161 deg.C (liquid), and 800kg (liquid volume 1 m), calculated by calculation3) 363.5kg of liquefiable liquid nitrogen (liquid volume 0.86 m)3) Considering the heat preservation effect and the operation control error, the actual flash evaporation gas liquefaction amount is 322kg, and the conversion coefficient is 0.7, namely 460Nm3The volume ratio of the amount of liquid nitrogen for condensation to the amount of flash gas vaporization recovered is close to 1: 1.
The foregoing examples are given solely for the purpose of illustrating the invention and are not to be construed as limiting the embodiments, and other variations and modifications in form thereof will be suggested to those skilled in the art upon reading the foregoing description, and it is not necessary or necessary to exhaustively enumerate all embodiments and all such obvious variations and modifications are deemed to be within the scope of the invention.
Claims (7)
1. The utility model provides a flash distillation gas liquefaction recovery system, includes liquid nitrogen storage tank, liquid nitrogen storage tank flowing back valve, liquefied natural gas jar, natural gas condenser, its characterized in that: the natural gas condenser is vertically arranged, and the lower end of the natural gas condenser is lengthened to form a cavity so as to form a liquefied natural gas liquid storage cavity;
the first outlet of the liquid nitrogen storage tank is connected with the inlet of an evaporator valve through a pipeline, the outlet of the evaporator valve is connected with the inlet of an evaporator through a pipeline, the outlet of the evaporator is connected with the inlet of a liquid nitrogen storage tank through a pipeline, the second outlet of the liquid nitrogen storage tank is connected with the inlet of a liquid discharge valve of the liquid nitrogen storage tank through a pipeline, and the outlet of the liquid discharge valve of the liquid nitrogen storage tank is connected with the first inlet of a natural gas condenser through a pipeline;
the outlet of the liquefied natural gas storage cavity is connected with the inlet of the liquefied natural gas tank through a drainage device with opening and closing functions, the drainage device drains the liquefied natural gas condensate in the liquefied natural gas storage cavity into the liquefied natural gas tank, the outlet of the liquefied natural gas tank is connected with the second inlet of the natural gas condenser through a pipeline, and control valves are arranged on the outlet pipeline and the inlet pipeline of the liquefied natural gas tank;
the outlet of the natural gas condenser is connected with the inlet of the nitrogen heater through a pipeline, the outlet of the nitrogen heater is connected with the inlet of the nitrogen storage tank through a pipeline, a temperature display instrument is arranged between the outlet of the natural gas condenser and the inlet of the nitrogen heater, and a nitrogen storage tank pressure regulating valve is arranged at the outlet of the nitrogen storage tank;
be provided with on the nitrogen gas basin and sweep the mouth, it links to each other with the import of sweeping the valve to sweep the mouth, the export of sweeping the valve links to each other with the pipeline of the export of connecting liquefied natural gas jar and the second import of natural gas condenser, it has two effects to sweep the mouth: firstly, residual liquefied natural gas condensate possibly exists in the pipeline, and the residual liquefied natural gas condensate can be completely blown by nitrogen blowing; secondly, the gas phase and the liquid phase in the pipeline are mixed to cause pressure imbalance, and the gas phase and the liquid phase in the pipeline can be balanced by utilizing nitrogen purging, so that the pressure build-up phenomenon is reduced;
the pipeline of the outlet of the liquefied natural gas liquid storage cavity is connected with the inlet of the liquefied natural gas liquid level meter, the outlet of the liquefied natural gas liquid level meter is connected with the pipeline of the second inlet of the natural gas condenser, the liquefied natural gas liquid level meter is connected with a balance valve in parallel, and liquid inlet and liquid outlet of the liquefied natural gas liquid level meter are controlled by a control valve;
the recovery method of the flash evaporation gas liquefaction recovery system comprises the following steps:
step 1: when the pressure in the liquefied natural gas tank reaches the allowable upper limit value, a control valve at the outlet of the liquefied natural gas tank is opened, the flash gas in the liquefied natural gas tank enters the tube side of a natural gas condenser, the flash gas is converted into natural gas, an evaporator valve in a liquid nitrogen storage tank is opened to increase the pressure in the liquid nitrogen storage tank to a set working pressure, then a liquid discharge valve of the liquid nitrogen storage tank is opened, the liquid nitrogen enters the shell side of the natural gas condenser to condense and liquefy the natural gas in the tube side, and the flow of the liquid nitrogen is controlled by the temperature of nitrogen at the outlet of the natural gas condenser;
step 2: the gasified nitrogen is heated to be above 0 ℃ by a nitrogen heater, enters a nitrogen storage tank, can be discharged to the air or used for blowing, the pressure setting value of the pressure regulating valve of the nitrogen storage tank is lower than the working pressure of the liquid nitrogen storage tank minus the pressure drop of the nitrogen flow route, when the pressure in the nitrogen storage tank reaches the specified upper limit value, the pressure regulating valve of the nitrogen storage tank is automatically opened, and the gas in the nitrogen storage tank is discharged to reduce the pressure to the specified value;
and step 3: the condensed liquefied natural gas condensate flows into the liquefied natural gas liquid storage cavity along the pipe wall of the heat exchange pipe in the natural gas condenser, and when the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity is gathered to a certain liquid level height, the drainage device is opened to drain the liquefied natural gas condensate to the liquefied natural gas tank;
and 4, step 4: after the natural gas on the upper part of the natural gas condenser is condensed, the pressure on the upper part of the natural gas condenser is lower than that of the liquefied natural gas tank, then a certain pressure difference is formed between the upper part of the natural gas condenser and the liquefied natural gas tank, the gas in the liquefied natural gas tank is conveyed to the natural gas condenser for liquefaction, the pressure in the liquefied natural gas tank is gradually reduced, an evaporator valve in a liquid nitrogen storage tank and a liquid discharge valve of the liquid nitrogen storage tank are closed after the pressure in the liquefied natural gas tank is reduced to a specified value, and a condensation liquefaction working cycle is finished.
2. The flash gas liquefaction recovery system of claim 1, wherein: and a liquid nitrogen storage tank pressure regulating valve is connected between the outlet of the evaporator and the inlet of the liquid nitrogen storage tank.
3. The flash gas liquefaction recovery system of claim 1, wherein: the natural gas condenser is arranged above the liquefied natural gas tank, the drainage device comprises a condensate discharge valve and a pipeline, an outlet of the liquefied natural gas liquid storage cavity is connected with an inlet of the condensate discharge valve through the pipeline, an outlet of the condensate discharge valve is connected with an inlet of the liquefied natural gas tank through the pipeline, and liquefied natural gas liquid in the liquefied natural gas liquid storage cavity enters the liquefied natural gas tank through the condensate discharge valve and the pipeline by means of self weight.
4. The flash gas liquefaction recovery system of claim 1, wherein: the drainage device comprises a liquefied natural gas pump, a condensate discharging valve and a pipeline, wherein an outlet of the liquefied natural gas liquid storage cavity is connected with an inlet of the condensate discharging valve through the pipeline, an outlet of the condensate discharging valve is connected with an inlet of the liquefied natural gas pump through the pipeline, an outlet of the liquefied natural gas pump is connected with an inlet of the liquefied natural gas tank, and the liquefied natural gas condensate in the liquefied natural gas liquid storage cavity is pumped into the liquefied natural gas tank by the liquefied natural gas pump.
5. The flash gas liquefaction recovery system of claim 1, wherein: the nitrogen heater is a finned heater.
6. The flash gas liquefaction recovery system of claim 1, wherein: the nitrogen heater is an ethylene glycol heating system.
7. The flash gas liquefaction recovery system of claim 1, wherein: the temperature of nitrogen at the outlet of the natural gas condenser in the step 1 is 60-80 ℃.
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| CN106287219A (en) * | 2016-09-26 | 2017-01-04 | 湖北和远气体股份有限公司 | A kind of natural gas liquefaction plant BOG recycling system |
| CN207471122U (en) * | 2017-11-30 | 2018-06-08 | 湖北天圜工程有限公司 | A kind of LNG gas stations BOG gas recovery systems |
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| CN106287219A (en) * | 2016-09-26 | 2017-01-04 | 湖北和远气体股份有限公司 | A kind of natural gas liquefaction plant BOG recycling system |
| CN207471122U (en) * | 2017-11-30 | 2018-06-08 | 湖北天圜工程有限公司 | A kind of LNG gas stations BOG gas recovery systems |
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