CN102230570A - System and method for recovering vapour of liquefied natural gas transfer station - Google Patents
System and method for recovering vapour of liquefied natural gas transfer station Download PDFInfo
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- CN102230570A CN102230570A CN2011101799183A CN201110179918A CN102230570A CN 102230570 A CN102230570 A CN 102230570A CN 2011101799183 A CN2011101799183 A CN 2011101799183A CN 201110179918 A CN201110179918 A CN 201110179918A CN 102230570 A CN102230570 A CN 102230570A
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- 239000003949 liquefied natural gas Substances 0.000 title claims abstract description 100
- 238000000034 method Methods 0.000 title claims abstract description 23
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 216
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 87
- 239000007788 liquid Substances 0.000 claims abstract description 76
- 239000007789 gas Substances 0.000 claims abstract description 32
- 229910001873 dinitrogen Inorganic materials 0.000 claims description 42
- 238000009413 insulation Methods 0.000 claims description 26
- 238000011084 recovery Methods 0.000 claims description 18
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 14
- 239000003345 natural gas Substances 0.000 claims description 7
- 238000002309 gasification Methods 0.000 claims description 5
- 239000011810 insulating material Substances 0.000 claims 1
- 238000009834 vaporization Methods 0.000 claims 1
- 230000008016 vaporization Effects 0.000 claims 1
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- 239000002699 waste material Substances 0.000 abstract description 5
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
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- 238000006243 chemical reaction Methods 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000004880 explosion Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
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- 230000009286 beneficial effect Effects 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000004078 cryogenic material Substances 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
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Abstract
The invention relates to a system and a method for recovering the vapour of a liquefied natural gas transfer station. The system comprises a storage tank for storing LNG (Liquefied Natural Gas), a BOG (Boil Off Gas) compressor, a liquefier, a liquid nitrogen storage tank and a liquid nitrogen output pump, wherein the BOG compressor is communicated with the gaseous phase space of the storage tank and used for compressing normal-pressure BOG output by the gaseous phase space; the liquefier is connected with the BOG compressor and used for liquefying the compressed BOG output by the BOG compressor; the liquid nitrogen storage tank stores liquid nitrogen; the liquid nitrogen output pump is connected with the liquid nitrogen storage tank and used for providing power to the liquid nitrogen so as to output the liquid nitrogen to the liquefier; and the liquefier takes the cold amount of the liquid nitrogen as a cold amount source for liquefying the compressed BOG, and is connected with the storage tank so as to output the LNG obtained by liquefaction to the storage tank for storage. On the premise of avoiding environmental pollution and energy waste, the system and the method can be used for fully recycling the BOG, weakening the requirements on the building position of the LNG transfer station and lowering the operation cost.
Description
Technical Field
The invention relates to the field of liquefied natural gas storage and transportation, in particular to a system and a method for recovering boil-off gas of a liquefied natural gas transfer station.
Background
Liquefied Natural Gas (LNG) is a high-quality energy source with high heat value and low combustion pollution. The LNG terminal is a terminal between an LNG receiving station and an LNG consumer, and has a main function of receiving LNG transferred from a small LNG ship in the LNG receiving station or a large natural gas liquefaction plant, temporarily storing the LNG, and transferring the LNG to the LNG consumer through an LNG tanker.
In the production process of the LNG transfer station, due to various factors such as leakage of environmental heat, volume replacement during ship unloading and loading, flash evaporation, and rapid reduction of atmospheric environmental pressure, a certain amount of Boil-Off Gas (BOG) under normal pressure is released in the LNG storage tank, other LNG facilities and LNG pipelines, and the BOG is a combustible Gas and is likely to cause air pollution and may cause accidents such as explosion and fire, so how to safely and effectively process BOG generated under various operating conditions is a very important subject that the LNG transfer station must face.
In the prior art, an LNG transfer station has two modes (as shown in fig. 1) for processing atmospheric BOG, the first mode is direct export through a pipeline, that is, after the atmospheric BOG is compressed to export pressure (usually 0.5MPa to 1.0MPa) by a BOG compressor, the atmospheric BOG is exported to a BOG user through the pipeline; the second is to discharge it directly into the air, or to burn it off via a flare system. Therefore, the BOG export pipeline needs to be laid around the LNG transfer station in the first mode, the LNG transfer station needs to be built near the BOG user, the operation cost of the LNG transfer station is greatly improved, and when the BOG user does not need to export BOG, the BOG can be processed only in the second mode, so that the waste of energy and the pollution to the environment are caused.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a boil-off gas recovery system and method for a liquefied natural gas transfer station, which can fully recycle BOG, reduce the requirement on the construction position of the LNG transfer station and reduce the operation cost of the LNG transfer station on the premise of not polluting the environment and wasting energy.
The technical scheme for solving the technical problems is as follows: a boil-off gas (BOG) recovery system of a Liquefied Natural Gas (LNG) transfer station, the system comprising: a storage tank for storing LNG; the BOG compressor is communicated with the gas phase space of the storage tank to compress the normal-pressure BOG output by the storage tank; a liquefier coupled to the BOG compressor to liquefy compressed BOG output therefrom to LNG; a liquid nitrogen storage tank for storing liquid nitrogen; the liquid nitrogen output pump is connected with the liquid nitrogen storage tank to provide power for the liquid nitrogen in the liquid nitrogen storage tank to output the power to the liquefier; wherein,
the liquefier takes the cold energy of the liquid nitrogen as a cold energy source for liquefying the compressed BOG, and is connected with the storage tank so as to output the liquefied LNG to the storage tank for storage.
On the basis of the technical scheme, the invention can be further improved as follows:
furthermore, the liquefier still has the nitrogen gas output tube for the nitrogen gas output that the liquid nitrogen gasification that will lose cold volume formed is for the inside use of LNG transfer station, thereby avoids the equipment investment of building liquid nitrogen carburetor.
Further, the BOG compressor is also provided with an output pipe which is used for outputting the compressed BOG to BOG users.
Further, still include: a Compressed Natural Gas (CNG) compressor and a CNG storage tank; wherein,
the CNG compressor is connected with the BOG compressor and is used for further compressing the compressed BOG output by the CNG compressor into CNG;
the CNG compressor is also connected with the CNG storage tank and used for conveying the compressed CNG into the CNG storage tank for storage.
Further, a CNG filling apparatus is included, coupled to the CNG tank, for filling the CNG stored in the CNG tank to an external apparatus.
Further, the liquid nitrogen output pump is a centrifugal output pump driven by a motor.
Further, the device also comprises a cold insulation box; the cold box is wrapped outside the liquefier to reduce heat transfer between the liquefier and the external atmospheric environment, maintaining the liquefier in a cryogenic operating state.
Further, a space inside the cold insulation box and outside the liquefier is filled with a cold insulation material.
Further, the space inside the cold insulation box and outside the liquefier is filled with nitrogen gas having a pressure greater than atmospheric pressure.
Further, be equipped with on the cold insulation box: a breather valve for keeping the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier to be more than the atmospheric pressure; and/or a nitrogen gas discharge port which is automatically opened to discharge excess nitrogen gas when the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier exceeds a first preset value; and/or an overpressure safety valve which automatically jumps when the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier exceeds a second preset value.
In addition, the invention also provides a boil-off gas BOG recovery method of the LNG transfer station, which comprises the following steps:
step 1: the BOG compressor receives the atmospheric BOG in the gas phase space in the storage tank, compresses the atmospheric BOG into compressed BOG and outputs the compressed BOG to the liquefier; the liquid nitrogen output pump provides power for liquid nitrogen stored in the liquid nitrogen storage tank to output the liquid nitrogen to the liquefier;
step 2: and the liquefier liquefies the received compressed BOG into LNG to be output to the storage tank for storage by taking the received cold energy of the liquid nitrogen as a cold energy source.
Further, the step 1 further comprises: and when the BOG output requirement exists, the BOG compressor transmits the compressed BOG to a BOG user through an output pipe of the BOG compressor.
Further, the step 2 further comprises: the liquefier exports the nitrogen gas that the liquid nitrogen gasification that loses cold volume forms through self nitrogen gas output tube for inside the use of LNG transfer station.
Further, the step 1 further comprises:
step 1-1: the BOG compressor outputting the compressed BOG into a Compressed Natural Gas (CNG) compressor;
step 1-2: the CNG compressor compresses the compressed BOG into CNG and outputs it to the CNG storage tank for storage.
Further, after the step 1-2, the method also comprises the step 1-3: a CNG filling apparatus fills the CNG stored in the CNG storage tank to an external apparatus.
The invention has the beneficial effects that: in the invention, the BOG compressor compresses the normal-pressure BOG volatilized by the LNG transfer station into compressed BOG, and then outputs the compressed BOG to the liquefier for liquefaction, and the liquefier utilizes the cold energy of liquid nitrogen to convey the LNG liquefied by the compressed BOG to the storage tank for storage, so the storage tank, the BOG compressor and the liquefier form a BOG gas-liquid conversion circulation circuit, the BOG volatilized by the LNG transfer station is fully recycled, the BOG does not need to be discharged into the air, the energy waste and the environmental pollution are avoided, the LNG transfer station does not need to be built near a BOG user, the requirement on the construction position of the LNG transfer station is weakened, in addition, the building of a BOG external transportation pipeline is not necessary for the invention, and the operation cost of the LNG transfer station can be reduced.
Drawings
FIG. 1 is a block diagram of a prior art system for processing atmospheric BOG generated at an LNG terminal;
FIG. 2 is a block diagram of a BOG recovery system of an LNG terminal provided by the present invention;
fig. 3 is a flowchart of a BOG recovery method for an LNG terminal according to the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
Fig. 2 is a structural diagram of a BOG recovery system of an LNG terminal according to the present invention. As shown in fig. 2, the system includes: a storage tank 201 for storing LNG; a BOG compressor 202 communicated with the gas phase space of the storage tank 201 to compress the normal pressure BOG output by the storage tank; a liquefier 203 coupled to BOG compressor 202 to liquefy compressed BOG output therefrom to LNG; a liquid nitrogen storage tank 204 for storing liquid nitrogen; a liquid nitrogen output pump 205 connected with the liquid nitrogen storage tank 204 to provide power output for the liquid nitrogen therein to the liquefier 203; wherein,
the liquefier 203 uses the cold energy of the liquid nitrogen as a cold energy source for liquefying the compressed BOG, and is connected to the storage tank 201 to output the liquefied LNG to the storage tank 201 for storage.
Here, the storage tank 201 is a facility for storing LNG, which is a liquid substance and is located in a lower space inside the storage tank 201, and BOG in a gaseous state volatilized from each part of the LNG terminal is concentrated in an upper space inside the storage tank 201, which is a gas phase space of the storage tank 201.
The gas phase space of the storage tank 201 is usually at normal pressure, and if the gas pressure is too high (i.e. too much BOG is inside), the pressure needs to be released in time to prevent the storage tank 201 from being damaged. Therefore, the BOG compressor 202 needs to receive the BOG (atmospheric pressure) output from the gas phase space of the storage tank 201 in real time so that the gas pressure in the gas phase space is maintained at the atmospheric pressure (slightly higher than the atmospheric pressure).
In the present invention, the BOG compressor 202 is a device for compressing atmospheric BOG into compressed BOG having an output pressure (typically 0.5MPa to 1.0MPa), and has a main structure of a cylinder, and cyclically compresses atmospheric BOG in the cylinder into compressed BOG output by reciprocating a piston. Certainly, if one BOG compressor is not enough to meet the power requirement, the BOG compressor 202 in the present invention may be a parallel connection of multiple BOG compressors, and in addition, in order to prevent the BOG compressor 202 shown in fig. 2 from malfunctioning, thereby causing the complete stop of the BOG recovery system provided by the present invention, a spare BOG compressor may also be provided, and when the BOG main compressor malfunctions, the spare BOG compressor is immediately started, and the BOG generated by the LNG transfer station is timely processed, thereby preventing the storage tank from being damaged, and causing environmental pollution.
In the present invention, the liquefier 203 is a device for liquefying compressed BOG, and the source of cold energy used for liquefaction is liquid nitrogen. Thus, the liquefier 203 is a heat exchanger that transfers heat of the compressed BOG to the liquid nitrogen, so that the compressed BOG is liquefied into LNG due to the loss of heat, and the liquid nitrogen absorbing heat is gasified into nitrogen. The liquefier 203 transfers the liquefied LNG to the storage tank 201 for storage, i.e. the BOG processing is completed. In addition, because the liquefier generates nitrogen in the working process, the liquefier 203 can also be provided with a nitrogen output pipe for outputting nitrogen which is formed by gasifying the liquid nitrogen losing the cold energy to be used in the LNG transfer station, and because the LNG transfer station needs to use the nitrogen, the invention reduces the equipment (such as a gasifier) investment of the LNG transfer station in the aspect of liquid nitrogen gasification. Of course, the nitrogen gas can be filled into the nitrogen gas cylinder by using a nitrogen gas filling device, and the nitrogen gas can also be directly conveyed to a nitrogen gas user through a nitrogen gas output pipeline.
The liquid nitrogen output pump in the invention can adopt a centrifugal output pump driven by a motor.
Both LNG and liquid nitrogen are cryogenic substances, and therefore, the storage tank 201, the liquefier 203, the liquid nitrogen storage tank 204, the liquid nitrogen output pump 205, and the pipeline for transporting LNG and liquid nitrogen in the present invention are all made of cryogenic materials, such as 9 nickel steel and stainless steel, which are cryogenic resistant.
Therefore, in the invention, the BOG compressor compresses the normal-pressure BOG volatilized by the LNG transfer station into the compressed BOG, and then outputs the compressed BOG to the liquefier for liquefaction, and the liquefier utilizes the cold energy of liquid nitrogen to convey the LNG obtained by the liquefaction of the compressed BOG to the storage tank for storage, so that the storage tank, the BOG compressor and the liquefier form a BOG gas-liquid conversion circulation line, the BOG volatilized by the LNG transfer station is fully recycled, the BOG does not need to be discharged into the air, the energy waste and the environmental pollution are avoided, the LNG transfer station does not need to be built near a BOG user, the requirement on the construction position of the LNG transfer station is weakened, and in addition, the building of a BOG external transmission pipeline is not necessary for the invention, and therefore, the invention can reduce the operation cost of the LNG transfer station.
Of course, the present invention does not exclude the presence of a BOG export line, for example, the BOG compressor 202 of the present invention also has an export line for exporting compressed BOG to a BOG user.
In addition to processing the BOG generated by the LNG receiving station by using the above-mentioned liquefaction method, the BOG may be processed by using other methods, as shown in fig. 2, the BOG recovery system provided by the present invention may further include: a Compressed Natural Gas (CNG) compressor 206, a CNG storage tank 207; wherein,
the CNG compressor 206 is connected to the BOG compressor 202, and is configured to further compress the compressed BOG output by the CNG compressor into CNG;
the CNG compressor 206 is also connected to the CNG storage tank 207 for delivering compressed CNG to the CNG storage tank 207 for storage.
In addition, the BOG recovery system further includes a CNG filling apparatus 208 connected to the CNG tank 207 for filling CNG stored in the CNG tank 207 to an external apparatus.
The CNG compressor 206 here may further compress the compressed BOG output by the BOG compressor 202 into CNG of higher gas pressure, which is stored in a CNG storage tank to be filled by the CNG filling apparatus 208 for use by external equipment. For example, the external device may be a CNG-fueled vehicle, and thus, the CNG filling device 208 of fig. 2 may be a dispenser that fills the CNG-fueled vehicle with CNG fuel.
The invention processes BOG by three modes of liquefaction, recompression and outward transportation, can fully utilize BOG generated by the LNG receiving station, saves energy, protects environment, and simultaneously prevents accidents such as damage of the storage tank, combustion of BOG, explosion and the like.
The BOG recovery system provided by the present invention may further include a cold box wrapped outside the liquefier 203 to reduce heat transfer between the liquefier 203 and the external atmospheric environment, thereby maintaining the liquefier 203 in a low temperature operating state.
The cold insulation box is a heat insulation device, the shell can be made of carbon steel plates, and cold insulation materials (such as pearlife and the like) can be filled in the space inside the cold insulation box and outside the liquefier 203 so as to further improve the heat insulation capacity of the cold insulation box. In order to prevent the water vapor in the space where the cold insulation material is located from being condensed when the liquefier 203 works, so that the heat insulation performance of the cold insulation material is damaged, and simultaneously, the oxygen is prevented from being burnt and exploded when meeting the BOG which can be leaked out from the liquefier 203, the invention also fills the space inside the cold storage box and outside the liquefier with nitrogen with the pressure higher than the atmospheric pressure so as to completely replace the air in the space, and simultaneously prevents the external air (especially the oxygen and the water vapor in the space) from entering the space.
In addition, the cold insulation box can be further provided with one or more safety devices to ensure that the internal pressure (pressure of nitrogen) of the cold insulation box is stabilized in a state slightly larger than atmospheric pressure, for example, a breather valve can be arranged on the cold insulation box to keep the pressure of nitrogen in the space inside the cold insulation box and outside the liquefier larger than atmospheric pressure, and the working principle is as follows: when the nitrogen gas pressure is higher (higher than the upper limit of the opening pressure of the breather valve), the breather valve which is originally in the closed state is opened to discharge redundant nitrogen gas, so that the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier is reduced; when the nitrogen gas pressure is lower (lower than the lower limit of the opening pressure of the breather valve), the breather valve which is originally in the closed state is opened to suck partial air, so that the air pressure in the space inside the cold insulation box and outside the liquefier is improved, the purpose of sucking the air is to ensure the stability of the air pressure, and at the moment, the entered oxygen, water vapor and the like can be replaced by continuously inputting the nitrogen gas, so that the normal work of the cold insulation material and the liquefier is ensured; when the air pressure in the space inside the cold insulation box and outside the liquefier is proper (higher than the lower limit of the opening air pressure of the breather valve and lower than the upper limit of the opening air pressure of the breather valve), the breather valve is in a closed state, so that the inside and the outside of the cold insulation box are isolated.
The cold insulation box can also be provided with a nitrogen gas discharge port, and the nitrogen gas discharge port is automatically opened to discharge redundant nitrogen gas when the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier exceeds a first preset value.
The cold storage box can be further provided with an overpressure safety valve which automatically jumps when the nitrogen gas pressure in the space inside the cold storage box and outside the liquefier exceeds a second preset value (higher than the first preset value) so as to quickly discharge the redundant nitrogen gas.
In conclusion, the BOG recovery system provided by the invention is flexible to operate, simple and reliable, has a good use effect, and is low in investment and operation cost and good in economic benefit.
The invention also provides a BOG recovery method of the LNG transfer station, which is based on the BOG recovery system shown in the figure 2. As shown in fig. 3, the method includes:
step 301: the BOG compressor receives the atmospheric BOG in the gas phase space in the storage tank, compresses the atmospheric BOG into compressed BOG and outputs the compressed BOG to the liquefier; the liquid nitrogen output pump provides power to the liquid nitrogen stored in the liquid nitrogen storage tank to output the liquid nitrogen to the liquefier.
In the present invention, the storage tank is used for storing LNG, and the BOG generated by the LNG terminal is concentrated in a space above the LNG inside the storage tank, which is referred to as a gas phase space of the storage tank. If the gas pressure in the gas phase space is too high, the storage tank is easily damaged, and therefore, the BOG in the gas phase space of the storage tank must be outputted in time to maintain the gas pressure in the gas phase space in a state slightly higher than the atmospheric pressure.
The BOG compressor receives BOG output by the gas phase space of the storage tank in real time, and the BOG is in a normal pressure state because the gas pressure of the gas phase space is maintained at a state slightly higher than the atmospheric pressure. The BOG compressor is a device for compressing atmospheric BOG, and compresses the atmospheric BOG into compressed BOG having an export pressure (typically 0.5 to 1.0MPa), and then outputs the compressed BOG to the liquefier, so that the liquefier performs liquefaction of the compressed BOG in step 302.
In addition, the liquefaction of the liquefier needs to use cold energy, and the cold energy source of the liquefier is liquid nitrogen which is stored in a liquid nitrogen storage tank and is provided with power by a liquid nitrogen output pump to be output to the liquefier as the cold energy source of the liquefaction.
Step 302: the liquefier liquefies the received compressed BOG into LNG to be output to the storage tank for storage by taking the cold energy of the received liquid nitrogen as a cold energy source.
The liquefier is a heat exchange device, and transfers the heat of the compressed BOG to liquid nitrogen, so that the compressed BOG is liquefied into LNG, and then is conveyed to the storage tank to be stored, and the BOG treatment process is completed. In addition, the liquid nitrogen absorbing heat (i.e. losing cold) is gasified into nitrogen as a resource, and if the nitrogen is directly discharged, the nitrogen is wasted, so the step can be further comprehensively utilized, namely the step can also comprise: the nitrogen gas that the liquefier will lose cold volume that liquid nitrogen gasification formed carries out the defeated outward through the nitrogen gas output tube of self, and the nitrogen gas output that the liquefier will gasify and form supplies the inside use of LNG transfer station promptly, also can carry out direct outward through nitrogen gas defeated pipeline, perhaps exports nitrogen gas through the nitrogen gas output tube and fills a bottle equipment to with nitrogen gas in the nitrogen gas steel bottle.
In step 301, if the user has a BOG export demand, the step may further include: the BOG compressor transmits the compressed BOG to BOG users through an external transmission pipe of the BOG compressor, so that the comprehensive utilization of the BOG is realized.
In addition to processing the BOG by liquefaction, export, and the like, the step 301 may further compress the compressed BOG into Compressed Natural Gas (CNG) by further compression, so as to further utilize the BOG, and thus may further include:
step 301-1: the BOG compressor outputs compressed BOG to the CNG compressor;
step 301-2: the CNG compressor compresses the compressed BOG into CNG and outputs it to a CNG tank for storage.
CNG, a useful fuel, can be stored in CNG tanks for a variety of uses, for example, after step 301-2, further comprising step 301-3: CNG filling equipment fills CNG stored in a CNG tank to an external device, i.e., CNG fuel is supplied to the external device (e.g., a CNG fuel car, etc.) by filling.
It can be seen that the present invention has the following advantages:
(1) in the invention, the BOG compressor compresses the normal-pressure BOG volatilized by the LNG transfer station into compressed BOG, and then outputs the compressed BOG to the liquefier for liquefaction, and the liquefier utilizes the cold energy of liquid nitrogen to convey the LNG liquefied by the compressed BOG to the storage tank for storage, so the storage tank, the BOG compressor and the liquefier form a BOG gas-liquid conversion circulation circuit, the BOG volatilized by the LNG transfer station is fully recycled, the BOG does not need to be discharged into the air, the energy waste and the environmental pollution are avoided, the LNG transfer station does not need to be built near a BOG user, the requirement on the construction position of the LNG transfer station is weakened, in addition, the building of a BOG external transportation pipeline is not necessary for the invention, and the operation cost of the LNG transfer station can be reduced.
(2) The invention processes BOG by three modes of liquefaction, recompression and outward transportation, can fully utilize BOG generated by the LNG receiving station, saves energy, protects environment, and simultaneously prevents accidents such as damage of the storage tank, combustion of BOG, explosion and the like.
(3) The BOG recovery system provided by the invention uses liquid nitrogen to provide cold energy for liquefying BOG, and the generated nitrogen is directly supplied to the interior of the LNG transfer station for use, so that the investment of the LNG transfer station on liquid nitrogen vaporizer equipment is saved, and the overall investment of the LNG transfer station is further reduced.
(4) The BOG recovery system provided by the invention is flexible to operate, simple and reliable, has a good use effect, and is low in investment and operation cost and good in economic benefit.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (15)
1. The utility model provides a boil off gas BOG recovery system of liquefied natural gas LNG terminal, its characterized in that, this system includes: a storage tank for storing LNG; the BOG compressor is communicated with the gas phase space of the storage tank to compress the normal-pressure BOG output by the storage tank; a liquefier coupled to the BOG compressor to liquefy compressed BOG output therefrom to LNG; a liquid nitrogen storage tank for storing liquid nitrogen; the liquid nitrogen output pump is connected with the liquid nitrogen storage tank to provide power for the liquid nitrogen in the liquid nitrogen storage tank to output the power to the liquefier; wherein,
the liquefier takes the cold energy of the liquid nitrogen as a cold energy source for liquefying the compressed BOG, and is connected with the storage tank so as to output the liquefied LNG to the storage tank for storage.
2. The system of claim 1, wherein the liquefier further comprises a nitrogen outlet line for outputting nitrogen from the vaporization of the cold depleted liquid nitrogen for use within the LNG terminal.
3. The system of claim 1, wherein the BOG compressor further has an export pipe for exporting the compressed BOG to a BOG user.
4. The system of claim 1, further comprising: a Compressed Natural Gas (CNG) compressor and a CNG storage tank; wherein,
the CNG compressor is connected with the BOG compressor and is used for further compressing the compressed BOG output by the CNG compressor into CNG;
the CNG compressor is also connected with the CNG storage tank and used for conveying the compressed CNG into the CNG storage tank for storage.
5. The system of claim 4, further comprising a CNG filling facility coupled to the CNG storage tank for filling the CNG stored in the CNG storage tank to an external facility.
6. The system of any one of claims 1-5, wherein the liquid nitrogen output pump is a centrifugal output pump driven by a motor.
7. The system of any one of claims 1-5, further comprising a cold box; the cold box is wrapped outside the liquefier to reduce heat transfer between the liquefier and the external atmospheric environment, maintaining the liquefier in a cryogenic operating state.
8. The system of claim 7, wherein a space inside the cold box and outside the liquefier is filled with cold-insulating material.
9. The system of claim 7, wherein a space inside the cold box and outside the liquefier is filled with nitrogen at a pressure greater than atmospheric pressure.
10. The system of claim 9, wherein the cold box is provided with: a breather valve for keeping the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier to be more than the atmospheric pressure; and/or a nitrogen gas discharge port which is automatically opened to discharge excess nitrogen gas when the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier exceeds a first preset value; and/or an overpressure safety valve which automatically jumps when the nitrogen gas pressure in the space inside the cold insulation box and outside the liquefier exceeds a second preset value.
11. A boil-off gas (BOG) recovery method for a Liquefied Natural Gas (LNG) transfer station is characterized by comprising the following steps:
step 1: the BOG compressor receives the atmospheric BOG in the gas phase space in the storage tank, compresses the atmospheric BOG into compressed BOG and outputs the compressed BOG to the liquefier; the liquid nitrogen output pump provides power for liquid nitrogen stored in the liquid nitrogen storage tank to output the liquid nitrogen to the liquefier;
step 2: and the liquefier liquefies the received compressed BOG into LNG to be output to the storage tank for storage by taking the received cold energy of the liquid nitrogen as a cold energy source.
12. The method of claim 11, wherein step 1 further comprises: and when the BOG output requirement exists, the BOG compressor transmits the compressed BOG to a BOG user through an output pipe of the BOG compressor.
13. The method of claim 11, wherein the step 2 further comprises: the liquefier exports the nitrogen gas that the liquid nitrogen gasification that loses cold volume forms through self nitrogen gas output tube for inside the use of LNG transfer station.
14. The method of claim 11, 12 or 13, wherein step 1 further comprises:
step 1-1: the BOG compressor outputting the compressed BOG into a Compressed Natural Gas (CNG) compressor;
step 1-2: the CNG compressor compresses the compressed BOG into CNG and outputs it to the CNG storage tank for storage.
15. The method according to claim 14, wherein after the step 1-2, further comprising the step 1-3: a CNG filling apparatus fills the CNG stored in the CNG storage tank to an external apparatus.
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