A process for co-production of ethane from natural gas cryogenic-membrane separation helium extraction

Abstract

The application provides a kind of natural gas cryogenic-membrane separation helium extraction process for co-production of ethane, which comprises the following steps: (1) raw material gas heat exchange separation; (2) expansion throttling; (3) rich methane gas backflow; (4) ethane recovery; (5) ethane secondary recovery; (6) preliminary helium extraction; (7) crude helium extraction; (8) crude helium membrane separation; (9) fine helium extraction. The application provides a natural gas cryogenic-membrane separation helium extraction process for co-production of ethane, which can simultaneously extract high-concentration helium and ethane, and the recovery rate is higher than 90%, meeting the process design requirements; compared with single cryogenic separation process and RSV process, the application can significantly reduce the comprehensive energy consumption and unit energy consumption of the process, improve the economy of the process, reduce production cost, play an important role in gas field multi-energy utilization and overall benefit improvement.

Description

Technical Field

[0001] This invention relates to the field of natural gas helium extraction technology, specifically a cryogenic-membrane separation helium extraction process for natural gas co-producing ethane. Background Technology

[0002] Helium, a special and rare industrial and electronic gas, is widely used in semiconductor manufacturing and is a crucial strategic and scarce resource related to the development of high-tech industries. Helium density (0.1786 kg / m³) 3 Helium has an extremely low boiling point (-268.85°C) and is chemically inert, making it the most difficult gas to liquefy. With the development of technology, helium is widely used in low-temperature superconductivity, medical imaging, semiconductors, equipment leak detection, and welding. Currently, global helium resources are mainly concentrated in countries such as the United States, Qatar, Russia, and Canada. China's helium resources account for only 2% to 3% of the global total, and its production is far from meeting demand, with most of its helium resources relying on imports.

[0003] Helium is primarily extracted from helium-rich natural gas using helium extraction equipment, a technology that originated in the 1920s. Currently, commonly used helium production methods include conventional natural gas helium extraction and unconventional methods. Conventional natural gas helium extraction methods include cryogenic extraction, membrane separation, adsorption, absorption, diffusion, and hydrate methods. Unconventional methods mainly include BOG (Bottle-Oxide-Gas) helium extraction, ammonia synthesis, air fractionation, uranium ore extraction, and geothermal gas extraction. Among these, cryogenic extraction is the most widely used method in industrial production. Cryogenic extraction generally refers to processes where equipment temperatures are below -100℃. The processes, from highest to lowest temperature, include ethane recovery (-100℃), natural gas liquefaction (-160℃), natural gas denitrification (-190℃), natural gas helium extraction (-190℃), and helium liquefaction (-269℃). Currently, the cryogenic helium extraction method in China has low efficiency and the final extracted product gas has a low helium concentration, resulting in high production costs and energy consumption. Furthermore, if a higher helium concentration is required in the product gas, helium purification is necessary, necessitating the installation of costly equipment such as membrane separators or pressure swing adsorption (PSA) systems.

[0004] To address the problems of high energy consumption, high investment, and low helium extraction efficiency in traditional cryogenic helium extraction processes from natural gas, this invention proposes a cryogenic-membrane separation helium extraction process that combines cryogenic separation with membrane separation and considers the co-production of ethane. This process improves the economics of helium extraction, significantly reduces energy consumption and equipment investment costs, optimizes the design of gas field surface processing technology, achieves comprehensive development and improves overall efficiency, avoids redundant construction and investment waste, alleviates the urgent need for national helium resource supply, and plays an important role in the multi-energy utilization and overall efficiency improvement of gas fields. Summary of the Invention

[0005] This invention addresses the technical problems of high energy consumption, high investment, low helium extraction efficiency, and high production cost in traditional cryogenic natural gas helium extraction processes. It combines cryogenic separation and membrane separation for helium extraction and considers the co-production of ethane, providing a cryogenic-membrane separation helium extraction process for natural gas with ethane co-production.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A cryogenic membrane separation helium extraction process for natural gas co-producing ethane is characterized by comprising the following steps: (1) Raw gas heat exchange and separation: The raw gas is subcooled to -55°C to -58°C by the main heat exchanger (LNG-100) and then enters the filter separator for gas-liquid separation to obtain two gas phases and two liquid phases. (2) Expansion and throttling: The first gas phase expands and cools to -85°C to -88°C through the expander, and then enters the top of the demethanizer; the second gas phase merges with the first liquid phase and enters the heat exchanger (LNG-101) to exchange heat to -70°C to -72°C, and then enters the middle of the demethanizer after passing through the throttling valve; the second liquid phase directly enters the middle of the demethanizer after passing through the throttling valve. (3) Methane-rich gas reflux: A stream of methane-rich gas is extracted from the external dry gas after being pressurized by the external gas compressor and refluxed. The methane-rich gas is heated to -70°C to -72°C by the heat exchanger (LNG-101) and then throttled before entering the demethanizer tower. (4) Ethane recovery: The above stream enters the demethanizer for gaseous methane separation. The liquid flowing out from the bottom of the demethanizer is ethane-rich liquid, and the gas flowing out from the top of the tower is methane-rich gas. (5) Ethane secondary recovery: After the methane-rich gas is heated by the main heat exchanger (LNG-100) and the heat exchanger (LNG-101), it is divided into two streams. One stream is pressurized by the ethane compressor, then heated by the heat exchanger (LNG-101), and then separated into two streams by the demethanizer. (6) Preliminary helium extraction: Another stream exchanges heat with the subcooling heat exchanger (LNG-102) to -115℃ to -118℃, and then enters the first helium extraction tower for preliminary helium extraction; (7) Crude helium extraction: After the overhead stream of the first helium extraction tower is cooled to -153°C to 155°C by the refrigeration cycle, it enters the second helium extraction tower for crude helium extraction to obtain crude helium; (8) Crude helium membrane separation: After the cold energy is recovered by the cold heat exchanger (LNG-102) and the main heat exchanger (LNG-100), the crude helium enters the first-stage membrane separator to obtain tail gas and helium-rich gas. (9) Helium extraction: Helium-rich gas enters a secondary membrane separator for purification to obtain refined helium with a helium content >99 vol%.

[0007] Furthermore, in a cryogenic membrane separation helium extraction process for co-producing ethane from natural gas, the methane-rich gas extracted from the exported dry gas in step (3) requires a methane content >90 vol% and a reflux ratio of 0.18~0.20.

[0008] Furthermore, in a cryogenic membrane separation helium extraction process for co-producing ethane from natural gas, the ethane-rich liquid flowing out from the bottom of the tower in step (4) has an ethane content of >60 vol, and the methane-rich gas flowing out from the top of the tower has a methane content of >94 vol.

[0009] Furthermore, in a natural gas cryogenic-membrane separation helium extraction process for co-producing ethane, the refrigeration cycle in step (7) adopts a nitrogen refrigeration cycle.

[0010] Furthermore, in a cryogenic membrane separation helium extraction process for co-producing ethane from natural gas, the crude helium content in step (7) is >65 vol%, and the helium-rich helium content in step (8) is >90 vol.

[0011] Furthermore, in a cryogenic membrane separation helium extraction process for co-producing ethane from natural gas, the primary and secondary membrane separators in steps (8) and (9) employ highly selective Poly membranes with a helium permeation rate of up to 170 GPUs.

[0012] Furthermore, in a cryogenic membrane separation helium extraction process for co-producing ethane from natural gas, the helium-rich gas described in step (9) should be cooled and pressurized before entering the secondary membrane separator, with the temperature reduced to -190°C to -192°C and the pressure increased to 1.5 MPa. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be explained below: Figure 1 This is a simplified flow chart of the cryogenic-membrane separation helium extraction process for co-producing ethane from natural gas provided by the present invention; Figure 2 This is a flow chart of the cryogenic membrane separation helium extraction process for co-producing ethane from natural gas provided by the present invention; Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0015] like Figure 1The provided flow chart shows a cryogenic-membrane separation helium extraction process for natural gas co-producing ethane. The process is characterized by the following steps: (1) Raw material gas heat exchange and separation: The raw material gas is subcooled to -55°C to -58°C by the main heat exchanger (LNG-100), and then enters the filter separator (V-100) for gas-liquid separation to obtain two gas phases and two liquid phases; (2) Expansion and throttling: The first gas phase expands and cools to -85°C to -88°C through the expander (K-100) and enters the top of the demethanizer (T-100); the second gas phase merges with the first liquid phase and enters the heat exchanger (LNG-101) to exchange heat to -70°C to -72°C, and then enters the middle of the demethanizer (T-100) through the throttling valve (VLV-100); the second liquid phase enters the middle of the demethanizer (T-100) directly after passing through the throttling valve (VLV-101); (3) Methane-rich gas reflux: In order to improve the ethane recovery rate, a stream of methane-rich gas with a methane content >90 vol% is extracted from the dry gas after the external gas compressor and refluxed. The reflux ratio is 0.18~0.20. The refluxed methane-rich gas is heated to -70℃ to -72℃ by the heat exchanger (LNG-101), and then throttled by the throttling valve (VLV-102) before entering the demethanizer (T-100). (4) Ethane recovery: After the above stream enters the demethanizer (T-100), gaseous methane is separated. The liquid flowing out from the bottom of the demethanizer (T-100) is ethane-rich liquid with an ethane content >60 vol%. The gas flowing out from the top of the tower is methane-rich gas with a methane content >94 vol%. (5) Ethane secondary recovery: After the methane-rich gas exchanges heat with the main heat exchanger (LNG-100) and the heat exchanger (LNG-101), it is divided into two streams. One stream is pressurized to 4.75 MPa by the ethane compressor (K-101), enters the heat exchanger (LNG-101) to exchange heat to -70℃ to -72℃, and then enters the demethanizer (T-100) for secondary methane separation. (6) Preliminary helium extraction: Another stream exchanges heat with the subcooling heat exchanger (LNG-102) to -115℃ to -118℃, and enters the first helium extraction tower (T-101); (7) Rough helium extraction: The overhead stream of the first helium extraction tower (T-101) is cooled to -153℃ to 155℃ through a nitrogen refrigeration cycle (LNG-103) and then enters the second helium extraction tower (T-102) for rough helium extraction; (8) Crude helium membrane separation: The gas flowing out of the top condenser of the second helium extraction tower (T-102) is crude helium with a helium content >65 vol%. The crude helium passes through the cold heat exchanger (LNG-102) and the main heat exchanger (LNG-100) to recover the cold energy, and then enters the first-stage membrane separator (OP-100) to separate the tail gas and helium-rich gas, in which the helium-rich gas has a helium content >90 vol%. (9) Helium extraction: At this time, the pressure of the helium-rich gas is only 0.01 MPa. Therefore, it should be cooled and pressurized before entering the secondary membrane separator. The temperature of the helium-rich gas should be reduced to -190℃ to -192℃, and the pressure should be increased to 1.5 MPa. Then, it should be purified by the secondary membrane separator to obtain refined helium with a helium content >99 vol%.

[0016] Example: To verify the effectiveness of the process provided by the present invention in extracting helium and co-producing ethane from natural gas, natural gas from a gas field in Shaanxi Province was used as the research object. The co-production process described in the present invention was compared and analyzed with the traditional cryogenic separation process and RSV process.

[0017] Before entering the cryogenic process, the feed gas must be treated. The maximum allowable impurities in the cryogenic process feed gas are shown in Table 1.

[0018] Table 1 Maximum Permissible Impurity Content in Raw Gas Note: H2O, CO2, H2S, and aromatics are all volume fractions.

[0019] For natural gas from a gas field in Shaanxi Province, the average CO2 content is 1.1084%, and it contains no H2S or H2O. The composition of the natural gas entering the natural gas processing plant is shown in Table 2. Feed gas processing capacity: 2.8 × 10⁻⁶ 5 Nm 3 / d, raw material gas pressure: 5.75MPa, inlet temperature: 30℃.

[0020] Table 2. Composition of Raw Gas Compared with the maximum allowable mass of the raw gas in Table 1, it needs to be decarbonized before entering the helium extraction unit. The composition of the raw gas after decarbonization is shown in Table 3.

[0021] Table 3 Composition of feed gas after decarbonization treatment The superiority of the co-production process is demonstrated by comparing the product recovery rate and overall system energy consumption of the co-production process provided by this invention with those of traditional single processes. The crude helium recovery rate and ethane recovery rate, as scientific indicators for measuring process efficiency, can quickly assess process operating costs and are of great significance. The formula for the crude helium recovery rate is shown in equation (1), and the formula for the ethane recovery rate is shown in equation (2).

[0022] (1) In the formula: R 粗氦 For crude helium recovery rate; x 粗氦 The crude helium molar fraction (%) in the recovered product; y 粗氦 The crude helium mole fraction (%) in the feed gas; X 粗氦 The molar flow rate (kmol) of the recovered product; Y The molar flow rate (kmol) of the recovered product.

[0023] (2) In the formula: Ethane recovery rate; The molar fraction of ethane in the recovered product (%); The molar fraction of ethane in the feed gas (%); Z The molar flow rate (kmol) of the recovered product; V The molar flow rate (kmol) of the recovered product.

[0024] The product recovery rate and comprehensive energy consumption simulation results of the co-production process provided by this invention compared with traditional cryogenic separation process and RSV process are shown in Table 4.

[0025] Table 4 Process simulation results As shown in Table 4, the cryogenic-membrane separation helium extraction process for ethane co-production provided by this invention can simultaneously extract high concentrations of helium and ethane, with recovery rates exceeding 90%, meeting the process design requirements. Compared with traditional single processes, the co-production process significantly reduces energy consumption: the overall energy consumption of the co-production process is 5669.24 kW lower than that of single cryogenic separation and RSV processes, a reduction of 22.83%; the unit energy consumption is 29.66 kW / kmol lower than that of single cryogenic separation and RSV processes, a reduction of 15.94%.

[0026] The cryogenic membrane separation helium extraction process for co-producing ethane provided by this invention mainly uses equipment such as a demethanizer, a helium extraction tower, a compressor, an expander, a heat exchanger, and a cooler. The equipment energy consumption simulation results are shown in Table 5.

[0027] Table 5 Energy consumption of various equipment in the cryogenic-membrane separation helium extraction process for ethane co-production As shown in Table 5, the main energy consumption in this process is in the nitrogen compressor (57%), the tail gas compressor (22%), the reboiler at the bottom of the demethanizer (T-100) (8%), and the reboiler at the bottom of the helium stripping tower (T-101) (8%). The energy consumption of the condenser at the top of the helium stripping tower (T-102) and the reboiler at the bottom is relatively small because the flow rate of the stream entering the helium stripping tower (T-102) accounts for only 2.11% of the initial feed gas flow rate, resulting in a small processing capacity for the helium stripping tower (T-102). The energy consumption of the membrane compressor is also relatively small because the flow rate of the crude helium extracted by the helium stripping tower (T-102) accounts for only 0.12% of the initial feed gas flow rate, resulting in a small processing capacity for the membrane compressor, and the membrane permeation rate remains constant.

[0028] In summary, the cryogenic membrane separation helium extraction process for co-producing ethane provided by this invention integrates helium extraction and ethane recovery, achieving recovery rates of over 90% for both helium and ethane, meeting basic process requirements. Compared to traditional single-product processes, it overcomes the technical bottlenecks of high energy consumption and investment in single-product production processes, reduces the overall energy consumption and unit energy consumption of the process, effectively improves the production performance of the process, and has practical application value.

[0029] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A cryogenic membrane separation helium extraction process for natural gas co-producing ethane, characterized in that, Includes the following steps: (1) Raw gas heat exchange and separation: The raw gas is subcooled to -55°C to -58°C by the main heat exchanger (LNG-100) and then enters the filter separator for gas-liquid separation to obtain two gas phases and two liquid phases. (2) Expansion and throttling: The first gas phase expands and cools to -85°C to -88°C through the expander, and then enters the top of the demethanizer; the second gas phase merges with the first liquid phase and enters the heat exchanger (LNG-101) to exchange heat to -70°C to -72°C, and then enters the middle of the demethanizer after passing through the throttling valve; the second liquid phase directly enters the middle of the demethanizer after passing through the throttling valve. (3) Methane-rich gas reflux: A stream of methane-rich gas is extracted from the external dry gas after being pressurized by the external gas compressor and refluxed. The methane-rich gas is heated to -70°C to -72°C by the heat exchanger (LNG-101) and then throttled before entering the demethanizer tower. (4) Ethane recovery: The above stream enters the demethanizer for gaseous methane separation. The liquid flowing out from the bottom of the demethanizer is ethane-rich liquid, and the gas flowing out from the top of the tower is methane-rich gas. (5) Ethane secondary recovery: After the methane-rich gas is heated by the main heat exchanger (LNG-100) and the heat exchanger (LNG-101), it is divided into two streams. One stream is pressurized by the ethane compressor, then heated by the heat exchanger (LNG-101), and then separated into two streams by the demethanizer. (6) Preliminary helium extraction: Another stream exchanges heat with the subcooling heat exchanger (LNG-102) to -115℃ to -118℃, and then enters the first helium extraction tower for preliminary helium extraction; (7) Crude helium extraction: After the overhead stream of the first helium extraction tower is cooled to -153°C to 155°C by the refrigeration cycle, it enters the second helium extraction tower for crude helium extraction to obtain crude helium; (8) Crude helium membrane separation: After the cold energy is recovered by the cold heat exchanger (LNG-102) and the main heat exchanger (LNG-100), the crude helium enters the first-stage membrane separator to obtain tail gas and helium-rich gas. (9) Helium extraction: Helium-rich gas enters a secondary membrane separator for purification to obtain refined helium with a helium content >99 vol%.

2. The process as described in claim 1, characterized in that, The methane-rich gas extracted from the dry gas in step (3) requires a methane content > 90 vol% and a reflux ratio of 0.18 to 0.

20.

3. The process as described in claim 1, characterized in that, In step (4), the ethane-rich liquid flowing out from the bottom of the tower has an ethane content of >60 vol, and the methane-rich gas flowing out from the top of the tower has a methane content of >94 vol.

4. The process as described in claim 1, characterized in that, The refrigeration cycle described in step (7) adopts a nitrogen refrigeration cycle.

5. The process as described in claim 1, characterized in that, The crude helium in step (7) has a helium content of >65 vol%, and the rich helium in step (8) has a helium content of >90 vol.

6. The process as described in claim 1, characterized in that, The primary and secondary membrane separators described in steps (8) and (9) use highly selective Poly membranes with a helium permeation rate of 170 GPUs.

7. The process as described in claim 1, characterized in that, Before the helium-rich gas mentioned in step (9) enters the secondary membrane separator, it should be cooled and pressurized, with the temperature reduced to -190°C to -192°C and the pressure increased to 1.5 MPa.

Images