Membrane separation decarburization process for LNG (Liquefied Natural Gas) cold energy utilization

Abstract

The invention relates to a membrane separation decarburization process for LNG (Liquefied Natural Gas) cold energy utilization. The device comprises a pre-separation unit, a first-stage membrane separation unit, a heat exchange unit and a second-stage membrane separation unit. The pre-separation unit comprises a separator; the primary membrane separation unit comprises a membrane separator; the heat exchange unit comprises a compressor, a cooler, a heat exchanger and a low-temperature pump; and the secondary membrane separation unit comprises a membrane separator. According to the technology, the technical scheme of two-stage membrane separation and multi-stage heat exchange is adopted, meanwhile, cold energy of LNG can be fully utilized, excessive energy waste is avoided, and compared with other technologies, the technology is high in decarburization rate, low in energy consumption, relatively simple in technological process and low in equipment investment under the same condition.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation, relates to natural gas decarbonization, and specifically relates to a secondary membrane separation decarbonization process utilizing LNG cold energy. Background Art

[0002] Coal, oil and natural gas will release a large amount of CO2 when burned, which has a huge impact on the global ecological environment. my country is one of the countries with the largest CO2 emissions in the world. At present, my country's energy consumption structure is mainly based on coal, and oil and natural gas also account for a large proportion. One of the main sources of carbon emissions is the flue gas emitted after fuel combustion. Domestic and foreign research on carbon capture mainly focuses on capture and storage after fuel combustion. Therefore, in order to effectively reduce the emission of CO2 gas in flue gas and slow down the intensification of the greenhouse effect, it is necessary to develop the capture and storage technology of CO2 after flue gas emissions and realize mature process treatment as soon as possible.

[0003] Removing CO2 from natural gas is an important technology for post-combustion capture. Currently, the main post-combustion CO2 capture technologies include absorption, adsorption, membrane separation, low-temperature separation, bio-enzyme, hydrate, etc. Among them, chemical absorption is the most mature decarbonization technology, but its process is relatively complex, the equipment cost is high, and the energy consumption is relatively high. When decarbonizing natural gas with high CO2 content, it often increases the equipment load and cost. In contrast, the membrane separation method has the advantages of low energy consumption, easy operation, simple equipment, and good decarbonization effect on natural gas with high CO2 content. Therefore, the use of membrane separation to remove CO2 from natural gas can not only reduce energy consumption, but also significantly remove CO2.

[0004] When using only a secondary membrane for natural gas decarbonization, a large amount of cooling equipment is required. Therefore, it is planned to utilize the cold energy of LNG. The LNG at the LNG receiving station needs to be gasified before entering the pipeline network. The cold energy in it will be directly discharged and not utilized. Therefore, combining the cold energy of LNG with natural gas decarbonization can reduce energy consumption and make full use of energy. A membrane separation decarbonization process utilizing LNG cold energy has been established. Summary of the invention

[0005] The existing high-C02 natural gas decarbonization technology basically adopts the amine method for decarbonization, which has the problems of large equipment load, high operating cost, high energy consumption, etc. The purpose of the present invention is to provide a membrane separation decarbonization process for utilizing LNG cold energy. The process adopts a two-stage membrane separation and multi-stage heat exchange technical solution, and can fully utilize the cold energy of LNG without causing excessive waste of energy. Under the same conditions as other processes, the process has a high decarbonization rate, low energy consumption, a relatively simple process flow, and low equipment investment.

[0006] In order to achieve the above-mentioned object, the present invention provides a membrane separation decarbonization process for utilizing LNG cold energy, comprising a pre-separation unit, a primary membrane separation unit, a heat exchange unit, and a secondary membrane separation unit;

[0007] The pre-separation unit includes a separator S-1; the primary membrane separation unit includes a membrane separator OP-1; the heat exchange unit includes a compressor K-1, a cooler E-1, a cooler E-2, a heat exchanger HX-1, a heat exchanger HX-2, a heat exchanger HXX-3, and a cryogenic pump P-1; the secondary membrane separation unit includes a membrane separator OP-2;

[0008] In the pre-separation unit, the feed gas inlet pipeline is connected to the separator S-1 inlet, the top outlet of the separator S-1 is connected to the membrane separator OP-1 inlet, and a small amount of water is discharged from the bottom outlet of the separator S-1;

[0009] In the first-stage membrane separation unit, the top outlet of the separator S-1 is connected to the inlet of the membrane separator OP-1, the bottom outlet of the membrane separator OP-1 discharges the decarbonized retentate gas, and the right outlet of the membrane separator OP-1 is connected to the inlet of the compressor K-1;

[0010] In the heat exchange unit, the right outlet of the membrane separator OP-1 is connected to the inlet of the compressor K-1, the cooler E-1, the cooler E-2, the heat exchanger HX-1, the heat exchanger HX-2, and the heat exchanger HX-3 in sequence; the LNG inlet pipeline is connected to the inlet of the cryogenic pump P-1, the heat exchanger HX-3, the heat exchanger HX-2, and the heat exchanger HX-1 in sequence;

[0011] In the secondary membrane separation unit, the outlet of the heat exchanger HX-3 is connected to the inlet of the membrane separator OP-2, the right outlet of the membrane separator OP-2 discharges CO2 permeate gas, and the lower outlet of the membrane separator OP-2 is connected to the inlet of the separator S-1, and the cycle continues.

[0012] The above-mentioned membrane separation and decarbonization process for utilizing LNG cold energy uses room temperature, high-pressure natural gas with a high CO2 content as the raw material gas, and is suitable for natural gas with a high CO2 content in the raw material gas.

[0013] The above-mentioned membrane separation decarbonization process for utilizing cold energy of LNG includes heat exchangers HX-1, HX-2, and HX-3, which are mainly used to realize heat exchange and transfer in the production of the device and are conventional equipment in the field. In the present invention, the heat exchanger HX-1 is provided with a first heat exchange channel and a second heat exchange channel;

[0014] The head end of the second heat exchange channel is connected to the cooler E-2 through a pipeline, and the end of the second heat exchange channel is connected to the heat exchanger HX-2 through a pipeline; the head end of the first heat exchange channel produces NG through a pipeline, and the end of the first heat exchange channel is connected to the heat exchanger HX-2 through a pipeline.

[0015] In the present invention, the heat exchanger HX-2 is provided with a third heat exchange channel and a fourth heat exchange channel;

[0016] The first end of the third heat exchange channel is connected to the end of the first heat exchange channel of the heat exchanger HX-1 through a pipeline, and the end of the third heat exchange channel is connected to the heat exchanger HX-3 through a pipeline; the first end of the fourth heat exchange channel is connected to the end of the second heat exchange channel of the heat exchanger HX-1 through a pipeline, and the end of the fourth heat exchange channel is connected to the heat exchanger HX-3 through a pipeline.

[0017] In the present invention, the heat exchanger HX-3 is provided with a fifth heat exchange channel and a sixth heat exchange channel;

[0018] The first end of the fifth heat exchange channel is connected to the end of the third heat exchange channel of the heat exchanger HX-2 through a pipeline, and the end of the fifth heat exchange channel is connected to the low-temperature pump P-1 through a pipeline; the first end of the sixth heat exchange channel is connected to the end of the fourth heat exchange channel of the heat exchanger HX-2 through a pipeline, and the end of the sixth heat exchange channel is connected to the membrane separator OP-2 through a pipeline.

[0019] The above-mentioned membrane separation decarbonization process utilizing LNG cold energy is composed of compressor K-1, cooler E-1, cooler E-2, the second heat exchange channel of heat exchanger HX-1, the fourth heat exchange channel of heat exchanger HX-2, the sixth heat exchange channel of heat exchanger HX-3, membrane separator OP-2, separator S-1, membrane separator OP-1, and connecting pipes between adjacent components, which together constitute a natural gas decarbonization circuit.

[0020] The above-mentioned membrane separation decarbonization process for utilizing LNG cold energy, a two-stage membrane separation system, usually uses cellulose acetate as the membrane material. This material has a high CO2 permeability and a large permeability factor, so it is widely used in industry. The membrane separation method relies on the difference in solubility or diffusion rate of CO2 on both sides of the separation membrane to achieve the purpose of decarbonization.

[0021] The above-mentioned membrane separation decarbonization process for utilizing LNG cold energy is a two-stage membrane separation system, using cellulose acetate as the membrane material.

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] (1) The membrane separation decarbonization process suitable for utilizing cold energy of LNG provided by the present invention removes CO2 in the raw natural gas through a primary membrane separator, a heat exchange system and a secondary membrane separator to obtain purified natural gas. Based on the primary membrane separation decarbonization process, the present invention adds a secondary membrane separation system and utilizes the cold energy of LNG, thereby increasing the decarbonization efficiency and effectively utilizing the cold energy, and reducing the waste of resources.

[0024] (2) The membrane separation decarbonization process suitable for LNG cold energy utilization provided by the present invention adopts a two-stage membrane separation technology, and the produced natural gas has a low CO2 concentration, a high carbon removal rate, low overall energy consumption of the device, a simple process flow, and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart of membrane separation and decarbonization of LNG cold energy utilization according to the present invention;

[0026] Explanation of the reference numerals: S-1-gas-liquid separator; OP-1-membrane separator; K-1-compressor; E-1-cooler; E-2-cooler; HX-1-heat exchanger; HX-2-heat exchanger; HX-3-heat exchanger; OP-2-membrane separator; P-1-cryogenic pump. DETAILED DESCRIPTION

[0027] The following will be combined with the attached Figure 1 The membrane separation and decarbonization process technology scheme for utilizing LNG cold energy provided by the present invention is described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention.

[0028] This embodiment provides a membrane separation and decarbonization process for utilizing LNG cold energy, such as Figure 1 As shown, it includes a pre-separation unit, a primary membrane separation unit, a heat exchange unit, and a secondary membrane separation unit connected by pipelines.

[0029] The pre-separation unit includes separator S-1.

[0030] The primary membrane separation unit includes a membrane separator OP-1.

[0031] The heat exchange unit includes a compressor K-1, a cooler E-1, a cooler E-2, a heat exchanger HX-1, a heat exchanger HX-2, a heat exchanger HX-3, and a cryogenic pump P-1. The heat exchanger HX-1 is provided with a first heat exchange channel and a second heat exchange channel. The heat exchanger HX-2 is provided with a third heat exchange channel and a fourth heat exchange channel. The heat exchanger HX-3 is provided with a fifth heat exchange channel and a sixth heat exchange channel.

[0032] The secondary membrane separation unit includes a membrane separator OP-2.

[0033] The raw gas inlet pipeline is connected to the inlet of separator S-1; the top outlet of separator S-1 is connected to the inlet of membrane separator OP-1, and a small amount of water is discharged from the bottom outlet of separator S-1.

[0034] The top outlet of separator S-1 is connected to the inlet of membrane separator OP-1, the lower outlet of membrane separator OP-1 discharges the decarbonized residual gas, and the right outlet of membrane separator OP-1 is connected to the inlet of compressor K-1.

[0035] The right outlet of membrane separator OP-1 is connected to the inlet of compressor K-1; the outlet of compressor K-1 is connected to the inlet of cooler E-1; the outlet of cooler E-1 is connected to the inlet of cooler E-2; the first end of the second heat exchange channel is connected to cooler E-2 through a pipeline, and the end of the second heat exchange channel is connected to heat exchanger HX-2 through a pipeline; the first end of the fourth heat exchange channel is connected to the end of the second heat exchange channel of heat exchanger HX-1 through a pipeline, and the end of the fourth heat exchange channel is connected to heat exchanger HX-3 through a pipeline; the first end of the sixth heat exchange channel is connected to heat exchanger HX- 2The end of the fourth heat exchange channel is connected through a pipeline, and the end of the sixth heat exchange channel is connected to the membrane separator OP-2 through a pipeline; the head end of the first heat exchange channel produces NG through a pipeline, and the end of the first heat exchange channel is connected to the heat exchanger HX-2 through a pipeline; the head end of the third heat exchange channel is connected to the end of the first heat exchange channel of the heat exchanger HX-1 through a pipeline, and the end of the third heat exchange channel is connected to the heat exchanger HX-3 through a pipeline; the head end of the fifth heat exchange channel is connected to the end of the third heat exchange channel of the heat exchanger HX-2 through a pipeline, and the end of the fifth heat exchange channel is connected to the cryogenic pump P-1 through a pipeline.

[0036] The end of the sixth heat exchange channel is connected to the inlet of the membrane separator OP-2 through a pipeline, the right outlet of the membrane separator OP-2 discharges CO2 permeate gas, and the lower outlet of the membrane separator OP-2 is connected to the inlet of the separator S-1.

[0037] The above-mentioned membrane separation decarbonization process utilizing LNG cold energy is composed of compressor K-1, cooler E-1, cooler E-2, the second heat exchange channel of heat exchanger HX-1, the fourth heat exchange channel of heat exchanger HX-2, the sixth heat exchange channel of heat exchanger HX-3, membrane separator OP-2, separator S-1, membrane separator OP-1, and connecting pipes between adjacent components, which together constitute a natural gas decarbonization circuit.

[0038] In the above-mentioned membrane separation and decarbonization process for utilizing LNG cold energy, a two-stage membrane separation system is used to decarbonize natural gas, and cellulose acetate is used as the membrane material.

[0039] The membrane separation and decarbonization process for utilizing LNG cold energy provided by the present invention uses a room-temperature, high-pressure natural gas with a high CO2 content, and is suitable for natural gas with a high CO2 content in the raw gas.

[0040] The above is to help readers understand the principles of the present invention, and the protection scope of the present invention is not limited to such specific statements and embodiments. For ordinary technicians in this technical field, several combinations and improvements can be made without departing from the principles of the present invention, and these combinations and improvements are also within the protection scope of the present invention.

Claims

1. A membrane separation and decarbonization process for utilizing LNG cold energy, characterized in that: It includes a pre-separation unit, a primary membrane separation unit, a heat exchange unit, and a secondary membrane separation unit; The pre-separation unit includes a separator S-1; the primary membrane separation unit includes a membrane separator OP-1; the heat exchange unit includes a compressor K-1, a cooler E-1, a cooler E-2, a heat exchanger HX-1, a heat exchanger HX-2, a heat exchanger HX-3, and a cryogenic pump P-1; the secondary membrane separation unit includes a membrane separator OP-2; In the pre-separation unit, the feed gas inlet pipeline is connected to the separator S-1 inlet, and the top outlet of the separator S-1 is connected to the membrane separator OP-1 inlet; In the first-stage membrane separation unit, the top outlet of the separator S-1 is connected to the inlet of the membrane separator OP-1, the bottom outlet of the membrane separator OP-1 discharges the decarbonized retentate gas, and the right outlet of the membrane separator OP-1 is connected to the inlet of the compressor K-1; In the heat exchange unit, the right outlet of the membrane separator OP-1 is connected to the inlet of the compressor K-1, the cooler E-1, the cooler E-2, the heat exchanger HX-1, the heat exchanger HX-2, and the heat exchanger HX-3 in sequence; the LNG inlet pipeline is connected to the inlet of the cryogenic pump P-1, the heat exchanger HX-3, the heat exchanger HX-2, and the heat exchanger HX-1 in sequence; In the secondary membrane separation unit, the outlet of the heat exchanger HX-3 is connected to the inlet of the membrane separator OP-2, the right outlet of the membrane separator OP-2 discharges CO2 permeate gas, and the lower outlet of the membrane separator OP-2 is connected to the inlet of the separator S-1, and the cycle continues.

2. The membrane separation and decarbonization process for utilizing LNG cold energy according to claim 1 is characterized in that: The heat exchanger HX-1 is provided with a first heat exchange channel and a second heat exchange channel; The head end of the second heat exchange channel is connected to the cooler E-2 through a pipeline, and the end of the second heat exchange channel is connected to the heat exchanger HX-2 through a pipeline; the head end of the first heat exchange channel produces NG through a pipeline, and the end of the first heat exchange channel is connected to the heat exchanger HX-2 through a pipeline.

3. The membrane separation and decarbonization process for utilizing LNG cold energy according to claim 2 is characterized in that: The heat exchanger HX-2 is provided with a third heat exchange channel and a fourth heat exchange channel; The first end of the third heat exchange channel is connected to the end of the first heat exchange channel of the heat exchanger HX-1 through a pipeline, and the end of the third heat exchange channel is connected to the heat exchanger HX-3 through a pipeline; the first end of the fourth heat exchange channel is connected to the end of the second heat exchange channel of the heat exchanger HX-1 through a pipeline, and the end of the fourth heat exchange channel is connected to the heat exchanger HX-3 through a pipeline.

4. The membrane separation and decarbonization process for utilizing LNG cold energy according to claim 3 is characterized in that: The heat exchanger HX-3 is provided with a fifth heat exchange channel and a sixth heat exchange channel; The first end of the fifth heat exchange channel is connected to the end of the third heat exchange channel of the heat exchanger HX-2 through a pipeline, and the end of the fifth heat exchange channel is connected to the low-temperature pump P-1 through a pipeline; the first end of the sixth heat exchange channel is connected to the end of the fourth heat exchange channel of the heat exchanger HX-2 through a pipeline, and the end of the sixth heat exchange channel is connected to the membrane separator OP-2 through a pipeline.

5. A membrane separation and decarbonization process for utilizing cold energy of LNG according to any one of claims 1 to 4, characterized in that: The two-stage membrane separation system comprises membrane separators OP-1 and OP-2 for decarbonizing natural gas, and uses cellulose acetate as the membrane material.

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