Process system and method for recovering light hydrocarbon in LNG and re-liquefying BOG
By designing a process system that reliques light hydrocarbons and BOG in LNG, distillation and relique are achieved by countercurrent heat transfer and mass transfer, the problem of high energy consumption and lack of diversified products in the existing technology is solved, and the efficient recovery of light hydrocarbons and BOG is achieved. The energy consumption during reliquefaction is low, which improves the utilization efficiency of LNG.
Patent Information
- Application Number
- CN202311585216.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-24
- Publication Date
- 2025-05-27
AI Technical Summary
The prior art is difficult to effectively recover light hydrocarbons and BOG in LNG, and the energy consumption is high during reliquefaction, and there is a lack of diversified product production methods.
A process system that combines the recycling of light hydrocarbons and BOG reliquefaction in LNG is designed, including an LNG-rich booster pump, a tower gas cooler, a demethane tower and a DHX tower. It can achieve distillation and reliquefaction through countercurrent heat transfer and mass transfer, and reheating and reliquefaction using LNG cooling energy.
It has achieved efficient recycling of 95.7% of the light hydrocarbons in LNG, and the energy consumption per unit of light hydrocarbon recovery is only 688MJ/t. It has the characteristics of low energy consumption, high recovery rate, diversified products, and LNG cold energy recycling. It has improved the utilization efficiency of LNG and provided high-quality raw materials for the production of ethylene.
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Figure CN120043320A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the fields of light hydrocarbon recovery, BOG recovery, and cold energy utilization, and particularly to a process system and method for both recovering light hydrocarbons in LNG and re-liquefying BOG. Background Art
[0002] The statements in this section only provide background information related to the present disclosure and may not constitute prior art.
[0003] At present, China's LNG imports have exceeded 50% of the total domestic imported natural gas usage. The components of LNG may vary due to different origins and processes. International LNG trade calculates prices based on the calorific value of LNG, while domestic prices are calculated by volume. If the imported rich LNG is directly supplied to users, the enterprise's revenue will be affected. Separating and selling the light hydrocarbons in rich LNG can protect the enterprise's interests. At the same time, ethane in the C2+ components can replace naphtha to produce ethylene, which is an important chemical raw material. Compared with naphtha, diesel, and kerosene, producing ethylene from ethane has the advantages of low cost, low energy consumption, and small investment, which is conducive to promoting the development of China's ethylene industry, making up for the shortage of raw materials in ethylene production, and increasing the self-sufficiency rate of ethylene in China's chemical production. Summary of the Invention
[0004] The purpose of the present invention is to provide a process system and method for both recovering light hydrocarbons in LNG and re-liquefying BOG in view of the problems existing in the prior art. It has the dual functions of recovering light hydrocarbons in LNG and re-liquefying BOG, and has characteristics such as low energy consumption, high light hydrocarbon recovery rate, diversified products, LNG cold energy recovery and utilization, flexible operation, and simple process, which can improve the utilization efficiency of LNG and provide high-quality raw materials for ethylene production.
[0005] The technical solution of the present invention is as follows:
[0006] A process system for both recovering light hydrocarbons in LNG and re-liquefying BOG, comprising: a rich LNG booster pump, a top gas cooler, a lean gas liquefier, and a demethanizer connected in sequence along the flow direction of rich LNG; the top gas outlet of the demethanizer is connected to the middle inlet of the DHX tower through the top gas cooler in sequence;
[0007] It further comprises: a BOG condenser and a DHX tower connected in sequence along the flow direction of BOG. The top gas outlet of the DHX tower is connected to the lean gas compressor, the lean gas liquefier, the lean LNG booster pump, and the BOG condenser in sequence. The liquid phase outlet of the DHX tower is connected to the reflux pump and the upper reflux inlet of the demethanizer in sequence.
[0008] Further, a reboiler is provided at the bottom of the demethanizer.
[0009] Further, the demethanizer is a plate column or a packed column.
[0010] Further, the DHX column is a plate column or a packed column.
[0011] Further, the heat source of the reboiler is natural gas, steam, heat transfer oil or seawater.
[0012] Further, a deethanizer and an LPG fractionator may be provided downstream of the liquid phase of the demethanizer.
[0013] A process method for both recovering light hydrocarbons in LNG and re-liquefying BOG, based on the above process system, includes:
[0014] The rich LNG from the battery limit is pressurized by a rich LNG booster pump and then exchanges heat with the top gas cooler and the lean gas liquefier in sequence; the rich LNG is heated to -100 °C and then enters the middle of the demethanizer, and countercurrently transfers heat and mass with the reflux liquid at the top of the tower in the demethanizer to achieve rectification. The product at the bottom of the demethanizer is the light hydrocarbon product.
[0015] The gas phase at the top of the demethanizer enters the top gas cooler and is cooled to -108 °C by the rich LNG. The contained light hydrocarbons are liquefied to form a gas-liquid two-phase and enter the middle of the DHX column; the 1.6 MPa.g BOG from the battery limit enters the BOG condenser and is re-liquefied by the lean LNG and then enters the top of the DHX column; the two fluids contact and transfer heat and mass countercurrently in the DHX column. The rich light hydrocarbon liquid at the bottom of the DHX column is pressurized by a reflux pump and then enters the upper part of the demethanizer as the top reflux liquid of the demethanizer; the gas phase at the top of the DHX column is pressurized by a lean gas compressor and then enters the lean gas liquefier and is re-liquefied by the rich LNG to obtain the lean LNG product. According to the external transmission pressure requirement, it is pressurized by a lean LNG booster pump, recovers part of the cold energy after entering the BOG condenser, and then enters the downstream gasification facility to be gasified and then externally transmitted.
[0016] Further, the rich LNG is pressurized to 1.6 MPa.g by the rich LNG booster pump.
[0017] Further, the gas phase at the top of the DHX column is pressurized to 2.5 MPa.g by the lean gas compressor;
[0018] The lean LNG product is pressurized to 10 MPa.g by the lean LNG booster pump.
[0019] Further, the gas phase at the top of the demethanizer is -99.99 °C.
[0020] Compared with the existing technology, the beneficial effects of the present invention are:
[0021] 1. A process system and method for simultaneously recovering light hydrocarbons from LNG and re-liquefying BOG. By utilizing the cold energy of LNG, the pressurized LNG enters the demethanizer for rectification after being reheated by subsequent methane gas, thereby achieving the purpose of separating light hydrocarbon products from LNG; the cold energy of LNG is used to re-liquefy BOG, realizing the recovery of BOG; the secondary separated light hydrocarbon-rich liquid is used as the reflux liquid of the demethanizer, and at the same time, the operating pressure of the demethanizer is adjusted to match the temperature of the incoming LNG. The light hydrocarbon recovery rate is as high as 95.7%, and the energy consumption per unit of light hydrocarbon recovery is only 688 MJ / t. The bottom temperature of the demethanizer in the present invention is about 10 °C, and seawater can be used as the heat source, converting the heat energy demand into the electrical energy demand of the seawater pump, which can greatly reduce the energy consumption level of the system. This process system has the dual functions of recovering light hydrocarbons from LNG and re-liquefying BOG, and has characteristics such as low energy consumption, high light hydrocarbon recovery rate, diversified products, recovery and utilization of LNG cold energy, flexible operation, and simple process, which can improve the utilization efficiency of LNG and provide high-quality raw materials for ethylene production.
[0022] 2. A process method for simultaneously recovering light hydrocarbons from LNG and re-liquefying BOG, including the following 5 entry points: 1. The reheating method of rich LNG liquid; 2. The re-liquefying method of lean methane gas; 3. The supply method of the reflux liquid of the demethanizer; 4. The method of re-liquefying BOG; 5. The selection of the heat source for the reboiler. Through the above 5 entry points, low-energy consumption and high-recovery rate recovery of light hydrocarbons are achieved. The rich LNG liquid is supplied in a low-temperature form, which contains a large amount of cold energy. However, in order to separate light hydrocarbons, it must be heated to gasify nitrogen and methane. In order to reduce the external transportation energy consumption of lean methane gas, cold energy is required to liquefy the lean methane gas into a liquid and then pressurize it for external transportation. Therefore, the rich LNG liquid is exchanged heat with the lean methane gas, which not only meets the process requirements but also fully utilizes the cold energy contained in the rich LNG liquid to achieve the purpose of energy saving. In the demethanizer, in order to improve the recovery rate of light hydrocarbons, reflux liquid needs to be supplied to the top of the methane tower. If the temperature level of the reflux liquid is too low, it will cause a large increase in the load of the reboiler. Therefore, the liquid separated by the initial cooling of lean methane gas is selected as the reflux at the top of the demethanizer, and this liquid is rich in light hydrocarbons, which can achieve the purpose of secondary recovery of light hydrocarbons. While improving the light hydrocarbon recovery rate, it will not cause a large proportion increase in the reboiler load. After being pressurized, the lean LNG needs to be gasified for external transportation at normal temperature. The cold energy contained in the pressurized lean LNG is used to re-liquefy BOG, saving the energy consumption for BOG recovery. After the BOG is re-liquefied, it directly contacts and transfers heat and mass with the lean LNG in the DHX tower, improving the light hydrocarbon recovery rate in the bottom liquid of the tower. The bottom temperature of the demethanizer is about 10 °C. According to the ambient temperature, seawater can be selected as the heat source, converting the heat energy demand into the electrical energy demand of the seawater pump, which can greatly reduce the energy consumption level of the system. Description of the Drawings
[0023] Figure 1 It is the process system flow schematic diagram for simultaneously recovering light hydrocarbons from LNG and re-liquefying BOG.
[0024] Reference numerals: 1 - rich LNG booster pump, 2 - top gas cooler, 3 - lean gas liquefier, 4 - demethanizer, 5 - DHX column, 6 - BOG condenser, 7 - lean gas compressor, 8 - lean LNG booster pump, 9 - reflux pump, 10 - reboiler. Detailed implementation manners
[0025] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.
[0026] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.
[0027] Embodiment 1
[0028] Please refer to Figure 1 , a process system that combines the recovery of light hydrocarbons in LNG and the re-liquefaction of BOG, including:
[0029] A rich LNG booster pump 1, a top gas cooler 2, a lean gas liquefier 3, and a demethanizer 4 connected in sequence along the flow direction of rich LNG; the top gas outlet of the demethanizer 4 is connected to the middle inlet of the top gas cooler 2 and the DHX column 5 in sequence;
[0030] It also includes: a BOG condenser 6 and a DHX column 5 connected in sequence along the flow direction of BOG, the top gas outlet of the DHX column 5 is connected to the lean gas compressor 7, the lean gas liquefier 3, the lean LNG booster pump 8, and the BOG condenser 6 in sequence, and the liquid phase outlet of the DHX column 5 is connected to the upper reflux inlet of the demethanizer 4 through a reflux pump 9.
[0031] In this embodiment, specifically, a reboiler 10 is provided at the bottom of the demethanizer 4.
[0032] In this embodiment, specifically, the demethanizer 4 is a plate column or a packed column.
[0033] In this embodiment, specifically, the DHX column 5 is a plate column or a packed column.
[0034] In this embodiment, specifically, the heat source of the reboiler 10 is natural gas, steam, heat-conducting oil or seawater.
[0035] In this embodiment, specifically, a deethanizer and an LPG fractionator may also be provided downstream of the liquid phase of the demethanizer 4.
[0036] Under ideal conditions, after the cold energy of the rich LNG recovery is reheated, the light components are heated into a gaseous state, and the light hydrocarbons are in a liquid state. The function of the rich LNG booster pump 1 is to boost the pressure of the rich LNG to match the temperature after reheating, providing the necessary pressure conditions for recovering the light hydrocarbons.
[0037] The reboiler 10 is a heat supply device for the system, providing heat for the system. Its heat source can be natural gas, steam, heat-conducting oil, seawater, etc., and needs to be selected according to the external environmental conditions.
[0038] The demethanizer 4 and the DHX tower 5 are the places for heat and mass transfer in the whole system, and the types are packed towers or plate towers.
[0039] The lean gas generated at the top of the DHX tower 5 needs to be liquefied to achieve low-energy-consuming pressurized export. However, the cold energy temperature level contained in the rich LNG is not low enough to fully liquefy the lean gas. Therefore, the lean gas compressor 7 is required to boost the pressure of the lean gas to increase the re-liquefaction temperature level of the lean gas.
[0040] Embodiment Two
[0041] Based on the process system proposed in Embodiment One, Embodiment Two proposes a process method that combines the recovery of light hydrocarbons in LNG and the re-liquefaction of BOG, including:
[0042] The rich LNG from the battery limit is boosted to 1.6 MPa.g by the rich LNG booster pump 1 and exchanges heat with the top gas cooler 2 and the lean gas liquefier 3 in sequence; after being heated, the rich LNG enters the middle part of the demethanizer 4 at -100 °C and transfers heat and mass countercurrently with the reflux liquid at the top of the tower in the demethanizer 4 to achieve rectification. The product at the bottom of the demethanizer 4 is the light hydrocarbon product;
[0043] The gas phase at the top of the demethanizer 4 is -99.99 °C and enters the top gas cooler 2, where it is cooled to -108 °C by the rich LNG. The contained light hydrocarbons are liquefied to form a gas-liquid two-phase and enter the middle part of the DHX tower 5; the 1.6 MPa.g BOG from the battery limit enters the BOG condenser 6 and is re-liquefied by the lean LNG and then enters the top of the DHX tower 5;
[0044] Two streams of fluid contact each other countercurrently in the DHX tower 5 for heat and mass transfer. The light hydrocarbon-rich liquid at the bottom of the DHX tower 5 enters the upper part of the demethanizer 4 as the top reflux liquid of the demethanizer 4 after being pressurized by the reflux pump 9. The gas phase at the top of the DHX tower 5 is pressurized to 2.5 MPa.g by the lean gas compressor 7 and then enters the lean gas liquefier 3 to be re-liquefied by the rich LNG, obtaining the lean LNG product. According to the export pressure requirement, it is pressurized to 10 MPa.g by the lean LNG booster pump 8, enters the BOG condenser 6 to recover part of the cold energy, and then enters the downstream gasification facility to be gasified and exported.
[0045] The above-described embodiments only represent the specific implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application.
[0046] This background art section is provided to generally present the context of the present invention. The work of the currently named inventors, to the extent described in this background art section, and aspects of the work that are not prior art as of the time of filing this application are neither expressly nor impliedly admitted to be prior art to the present invention.
Claims
1. A process system that can recover light hydrocarbons from LNG and reliquefy BOG. It is characterized in that include: A rich LNG booster pump (1), a tower top gas cooler (2), a lean gas liquefier (3), and a demethanizer (4) are sequentially connected along the rich LNG flow direction; the tower top gas outlet of the demethanizer (4) is sequentially connected to the tower top gas cooler (2) and the middle inlet of the DHX tower (5); The invention also comprises: a BOG condenser (6) and a DHX tower (5) which are connected in sequence along the flow direction of BOG, wherein the top gas outlet of the DHX tower (5) is connected in sequence to a lean gas compressor (7), a lean gas liquefier (3), a lean LNG booster pump (8), and a BOG condenser (6), and the liquid phase outlet of the DHX tower (5) is connected in sequence to a reflux pump (9) and an upper reflux inlet of a demethanizer (4).
2. The process system for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 1, It is characterized in that A reboiler (10) is arranged at the bottom of the demethanizer (4).
3. The process system for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 1, It is characterized in that The demethanizer (4) is a plate tower or a packed tower.
4. The process system for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 1, It is characterized in that The DHX tower (5) is a plate tower or a packed tower.
5. The process system for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 2, It is characterized in that The heat source of the reboiler (10) is natural gas, steam, heat transfer oil or seawater.
6. The process system for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 1, It is characterized in that A deethanizer and an LPG fractionation tower may also be arranged downstream of the liquid phase of the demethanizer (4).
7. A process for recovering light hydrocarbons from LNG and reliquefying BOG. It is characterized in that The process system according to any one of claims 1 to 6 comprises: The rich LNG from the boundary area is pressurized by the rich LNG booster pump (1) and then heat-exchanged with the tower top gas cooler (2) and the lean gas liquefier (3) in sequence; the rich LNG is heated to -100°C and then enters the middle of the demethanizer (4), where it performs countercurrent heat and mass transfer with the reflux liquid at the top of the tower to achieve distillation, and the product exiting the bottom of the demethanizer (4) is the light hydrocarbon product; The gas phase at the top of the demethanizer (4) enters the top gas cooler (2) and is cooled to -108°C by the rich LNG. The light hydrocarbons contained in the gas are liquefied to form a gas-liquid two-phase system and enter the middle of the DHX tower (5). The BOG with a concentration of 1.6 MPa.g from the boundary zone enters the BOG condenser (6) and is reliquefied by the lean LNG. The BOG enters the top of the DHX tower (5). The two fluids are in countercurrent contact in the DHX tower (5) for heat and mass transfer. The rich light hydrocarbons exit the bottom of the DHX tower (5). The hydrocarbon liquid is pressurized by a reflux pump (9) and enters the upper part of the demethanizer (4) as the top reflux liquid of the demethanizer (4); the gas phase at the top of the DHX tower (5) is pressurized by a lean gas compressor (7) and enters the lean gas liquefier (3) to be reliquefied by rich LNG to obtain a lean LNG product. According to the external transmission pressure requirement, the lean LNG booster pump (8) is used to pressurize the product and then the lean LNG product enters the BOG condenser (6) to recover part of the cold energy and then enters the downstream gasification facility for gasification before external transmission.
8. The process for recovering light hydrocarbons from LNG and reliquefying BOG according to claim 7, It is characterized in that The rich LNG is pressurized to 1.6 MPa.g by a rich LNG boosting pump (1).
9. The process for recovering light hydrocarbons from LNG and reliquefying BOG according to claim 7, It is characterized in that The gas phase at the top of the DHX tower (5) is pressurized to 2.5 MPa.g by a lean gas compressor (7); The lean LNG product is pressurized to 10 MPa.g by a lean LNG boosting pump (8).
10. The process for recovering light hydrocarbons in LNG and reliquefying BOG according to claim 7, It is characterized in that The temperature of the gas phase at the top of the demethanizer (4) is -99.99°C.