Method for separating and purifying hydrogen from middle-low pressure hydrogen-doped natural gas

Abstract

The invention belongs to the technical field of gas separation, and particularly relates to a method for separating and purifying hydrogen from middle and low pressure hydrogen-doped natural gas. According to the method, a membrane separation process and a pressure swing adsorption process are coupled for purifying hydrogen. In order to solve the technical problems of low hydrogen doping proportion, high purification difficulty and the like in the middle-low pressure hydrogen-doped natural gas, a membrane separation and pressure swing adsorption combined process flow is adopted, hydrogen is separated and concentrated from the hydrogen-doped natural gas by using a membrane separation method, then the hydrogen is purified by using a pressure swing adsorption method, the purity of the obtained hydrogen can reach 99.999%, and the purity of the obtained hydrogen can reach 99.999%. And the requirements of high-purity hydrogen and hydrogen for fuel cell vehicles are met.

Description

Technical Field

[0001] The invention belongs to the technical field of gas separation, and in particular relates to a method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas. Background Art

[0002] Due to the limited reserves of fossil fuels and the environmental pollution and carbon dioxide emissions caused by their use, the search for clean energy is urgent. Hydrogen, as a clean secondary energy carrier, has received widespread attention at home and abroad in recent years. At present, large-scale hydrogen production and purification technologies have been widely used in industrial production, and the safe, efficient and economical transportation of hydrogen is one of the technical bottlenecks for the promotion and application of hydrogen energy. Compared with high-pressure gas hydrogen, liquid hydrogen and other hydrogen transportation methods, pipeline hydrogen transportation has low cost, large transportation volume and the greatest development potential. However, there is a lack of dedicated hydrogen transportation pipelines, and it is difficult to build a large number of dedicated hydrogen transportation pipelines in the short term. By the end of 2018, the total length of my country's natural gas trunk pipelines reached 76,000 km, and the primary gas transmission capacity reached 320 billion m 3 / a, natural gas pipeline facilities are complete, the transportation volume is large, and the transportation cost is low. Therefore, mixing hydrogen with natural gas to form mixed hydrogen natural gas and then transporting hydrogen through the natural gas pipeline network can achieve low-cost, long-distance transportation of hydrogen, improve the overall efficiency of the energy system, and can be combined with a variety of hydrogen energy technologies at the terminal. It is considered a low-cost way to transport hydrogen and has become a research hotspot.

[0003] Hydrogen-mixed natural gas itself is a low-carbon gas fuel that can be used for direct combustion to obtain heat energy or generate electricity. However, hydrogen end users have certain requirements for hydrogen purity. Fuel cells using high-purity hydrogen have high energy conversion efficiency. Therefore, it is necessary to separate the hydrogen from medium and low-pressure natural gas at the natural gas terminal gate station and obtain higher-purity hydrogen, which can meet the needs of hydrogen users and the demand for hydrogen sources for hydrogen energy development.

[0004] The proportion of hydrogen in hydrogen-blended natural gas in various countries around the world is mainly between 5% and 30%. Hydrogen separation methods include pressure swing adsorption, membrane separation, cryogenic separation, hydrogen storage alloy separation and electrochemical separation. Since hydrogen separation and purification of hydrogen-blended natural gas is an emerging technology field, there is still little research on hydrogen separation technology for hydrogen-blended natural gas.

[0005] Electrochemical separation methods are still in the early stages of research. The boiling points of hydrogen, methane, and ethane are very different, so it is feasible to separate hydrogen from hydrogen-blended natural gas by cryogenic methods. However, since the hydrogen content in hydrogen-blended natural gas is not high, cryogenic separation requires a low-temperature liquefaction process, which requires complex process equipment, high energy consumption, inconvenient maintenance, and high public engineering requirements. Hydrogen storage alloy materials have strong chemical activity, and polar impurity gases in hydrogen-blended natural gas will cause alloy poisoning and hydrogen storage performance degradation.

[0006] At present, the large-scale economic hydrogen separation methods that have been applied in industry are mainly pressure swing adsorption and membrane separation. Pressure swing adsorption separation of hydrogen has the advantages of clean process, long service life of adsorbent, and high purity of hydrogen. It is mainly used to separate and purify hydrogen from hydrogen-containing mixed gas. Pressure swing adsorption devices are usually used in the case where the hydrogen content in the mixed gas is high (usually greater than 50%), and the hydrogen content of hydrogen-blended natural gas is low (usually between 5% and 30%), while hydrocarbon gases such as methane are the main components and are strongly adsorbed components. Therefore, in the pressure swing adsorption separation process, methane and other hydrocarbons belong to the adsorption phase, and the adsorption bed needs to be repeatedly adsorbed and low-pressure desorbed to desorb methane and other hydrocarbons, and then the methane and other hydrocarbons are pressurized and returned to the pipeline network, resulting in complex processes, high compression energy consumption, and poor economy.

[0007] Membrane separation technology uses the difference in permeability of each component in the mixed gas in the membrane and uses the pressure difference on both sides of the membrane as the driving force to separate hydrogen. It has become one of the widely used hydrogen separation technologies. It has more advantages in recovering hydrogen from mixed gases with low hydrogen concentration (<30%), but it is difficult to obtain high-purity hydrogen using only organic gas membrane separation. Palladium-based separation membranes are mostly used to prepare high-purity hydrogen, but the impurity composition of hydrogen-doped natural gas is complex and the hydrogen content is low, which makes its separation process and equipment cost high, and the scale of hydrogen doping is small, making it difficult to achieve large-scale hydrogen separation and purification.

[0008] Chinese patent CN 113735060 A discloses a system for adjusting the hydrogen-carbon ratio of synthesis gas and producing hydrogen as a by-product by coupling membrane separation and pressure swing adsorption, which is mainly used for adjusting the carbon-hydrogen ratio of carbonyl synthesis gas and producing hydrogen as a by-product.

[0009] Chinese patent CN 115584290 A discloses a hydrogen-blended natural gas separation system, including: a separation device, a purification device, a combustion reactor and a first vacuum pump, which can effectively utilize the exhaust gas discharged from the separation device to provide heat energy for the purification device. The separation device uses the method of adsorbing and desorbing hydrogen to separate natural gas and hydrogen, and the separated hydrogen is transported to the purification device, so that the separation system can output high-purity hydrogen; and the exhaust gas discharged from the separation device is transported to the combustion reactor, and the purification device is located in the combustion reactor. The exhaust gas discharged from the separation device can be burned and released in the combustion reactor, thereby providing heat energy for the purification device, and the natural gas cannot be returned to the pipeline system. The purification device 30 uses a palladium membrane separation device, and the temperature swing adsorption (TSA) method can be used to purify hydrogen.

[0010] Chinese patent CN 115108531 A discloses a continuous hydrogen purification system for hydrogen-doped natural gas and its purification process, which uses a purification tank equipped with a hydrogen storage alloy to absorb hydrogen. The hydrogen-doped natural gas enters the purification tank through the mixed gas inlet pipe to undergo a hydrogen absorption reaction. When the hydrogen storage alloy is saturated with adsorption, the valve is switched to enter a dehydrogenation state. According to the required hydrogen purity requirements, the initial desorbed hydrogen can be used for purging. After the purging is completed, high-purity hydrogen is produced.

[0011] Chinese patent CN 114561235 A discloses a hydrogen-natural gas mixed transmission and separation device and method based on pressure energy recovery. The device uses a pressure energy recovery module, a membrane separation module and a boost module to convert the pressure energy of the hydrogen-blended natural gas into mechanical energy, providing power for pressurizing the separated hydrogen / natural gas, recovering pressure energy and reducing the energy consumption of system operation.

[0012] Chinese patent CN 113566113 A discloses an apparatus and method for extracting and transporting hydrogen from hydrogen-blended natural gas, comprising at least one magnesium-based solid-state hydrogen storage and transportation device, and heat transfer oil is heated to release hydrogen.

[0013] Chinese patent CN 112628602 A discloses a hydrogen-blended natural gas transportation and separation system and a control method thereof, the system comprising a hydrogen buffer tank, a natural gas pressure regulator, a natural gas hydrogen blending device, a monitoring module, a hydrogen-blended natural gas separation and purification device, and a hydrogen storage device. The hydrogen-blended natural gas separation and purification device uses pressure swing adsorption to separate the hydrogen-blended natural gas. Summary of the invention

[0014] The purpose of the present invention is to overcome the shortcomings of using membrane separation and pressure swing adsorption alone to separate and purify hydrogen from hydrogen-blended natural gas, and to provide a method for purifying hydrogen by coupling membrane separation and pressure swing adsorption technology, so as to reduce the difficulty of hydrogen separation and purification and improve the economy and practicality of hydrogen separation and purification of hydrogen-blended natural gas.

[0015] In order to achieve the above invention objectives, the specific technical solution adopted by the present invention is:

[0016] A method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas, the method coupling a membrane separation process and a pressure swing adsorption process to purify hydrogen.

[0017] As a preferred embodiment of the present application, the method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas comprises the following steps:

[0018] S1. Passing hydrogen-blended natural gas through a gas-liquid separator to remove liquid foam from the gas;

[0019] S2, using membrane separation technology to separate the gas obtained in S1, so that the hydrogen is concentrated to a certain volume percentage to obtain hydrogen-rich gas, and the remaining gas is transported to the natural gas pipeline;

[0020] S3, using the PSA separation method to separate and purify the hydrogen-rich gas obtained in S2 to obtain high-purity hydrogen; the residual gas generated in the PSA process is transported to the natural gas pipeline after being compressed.

[0021] As a preferred embodiment of the present application, the raw material hydrogen-blended natural gas in S1 has a hydrogen volume percentage of 5-30% (specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.), and a pressure of 0. Hydrogen-blended natural gas with a pressure of 4 to 4.0 MPa (specifically 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa, 2.0 MPa, 2.2 MPa, 2.4 MPa, 2.6 MPa, 2.8 MPa, 3.0 MPa, 3.2 MPa, 3.4 MPa, 3.6 MPa, 3.8 MPa, 4.0 MPa, etc.).

[0022] As a better embodiment of the present application, the hydrogen in S2 is concentrated to a volume percentage of 50% to 80% (specifically 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.).

[0023] As a preferred embodiment of the present application, the volume percentage of the high-purity hydrogen in S3 is 99% to 99.999%.

[0024] Compared with the prior art, the positive effects of the present invention are embodied in:

[0025] The present invention combines liquid separation, membrane separation and PSA method, which can reduce the energy consumption of gas pressurization and recover and purify hydrogen to the greatest extent. The purity of hydrogen can reach 99.999%, meeting the requirements of high-purity hydrogen and hydrogen for fuel cell vehicles, and solving the problem of hydrogen separation and purification at hydrogen-blended natural gas terminal gate stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic flow chart of a method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas. DETAILED DESCRIPTION

[0027] A method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas, comprising: using hydrogen-blended natural gas transported by a natural gas pipeline network, and using a physical separation method at a medium- and low-pressure natural gas transmission and distribution gate station to obtain high-purity hydrogen and residual gas, wherein the high-purity hydrogen can be used by downstream users, and the residual gas is returned to the natural gas pipeline.

[0028] For hydrogen-doped natural gas with a hydrogen content of 5 to 30% and a pressure of 0.4 to 4.0 MPa, the first step is to remove free liquid droplets through a gas-liquid separator. In the second step, the hydrogen-doped natural gas enters a membrane separation device to concentrate the hydrogen on the permeate side to a volume percentage of 50% to 80%, and the remaining gas is transported to a natural gas pipeline. In the third step, the concentrated hydrogen in the second step is input into a pressure swing adsorption device to obtain high-purity hydrogen (volume percentage of 99% to 99.999%), and the remaining gas is returned to the inlet of the membrane separation device.

[0029] The method comprises the following steps:

[0030] S1. Passing hydrogen-blended natural gas through a gas-liquid separator to remove liquid foam from the gas;

[0031] S2. Separate the high-temperature gas in S1 by using membrane separation technology to concentrate the hydrogen to a volume percentage of 50% to 80%, and transport the remaining gas to a natural gas pipeline;

[0032] S3. Separating and purifying the hydrogen-rich gas in S2 by PSA separation method to obtain high-purity hydrogen (volume percentage 99% to 99.999%).

[0033] In order to make the content of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. However, this should not be understood as the scope of the above-mentioned subject matter of the present invention being limited to the following embodiments. All features disclosed in this application, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way.

[0034] In the present application, the pressure swing adsorption device and the membrane separation system are both conventional technologies, and the specific operation process is not repeated; for example, the membrane separation system can refer to the Chinese patent CN 112628602 A.

[0035] Embodiment 1:

[0036] For hydrogen-enriched natural gas with 30% hydrogen and 4.0MPa pressure, the gas-liquid separator removes the liquid droplets and enters the membrane separation system to obtain hydrogen-rich gas with 57% hydrogen volume content and 0.4MPa pressure, and the remaining gas returns to the natural gas pipeline at a pressure of 4.0MPa. The hydrogen-rich gas enters the pressure swing adsorption device at a pressure of 0.4MPa to be purified to obtain hydrogen with a volume content of 99.99%, and the pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0037] Embodiment 2:

[0038] For natural gas with 30% hydrogen blend and 0.4MPa pressure, after the liquid droplets are removed by the gas-liquid separator, it enters the membrane separation system to obtain hydrogen-rich gas with 54% hydrogen volume content and 0.02MPa pressure, and the remaining gas returns to the natural gas pipeline at a pressure of 0.4MPa. The hydrogen-rich gas is pressurized to 0.8MPa and then enters the pressure swing adsorption device to purify the hydrogen with a volume content of 99.999%, and the pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0039] Embodiment 3:

[0040] For natural gas with 20% hydrogen blend and 4.0MPa pressure, the gas-liquid separator removes the liquid droplets and enters the membrane separation system to obtain hydrogen-rich gas with 48% hydrogen volume content and 0.5MPa pressure. The remaining gas returns to the natural gas pipeline at a pressure of 4.0MPa. The hydrogen-rich gas enters the pressure swing adsorption device at a pressure of 0.5MPa to be purified to obtain hydrogen with a volume content of 99.9%. The pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0041] Embodiment 4:

[0042] For natural gas with 10% hydrogen blend and 0.4MPa pressure, the gas-liquid separator removes the liquid droplets and enters the membrane separation system to obtain hydrogen-containing gas with 27% hydrogen volume content and 0.02MPa pressure, and the remaining gas returns to the natural gas pipeline at a pressure of 0.4MPa. The hydrogen-containing gas with 24% hydrogen volume content and 0.02MPa pressure is pressurized to 0.4MPa, and then membrane separation is performed to obtain hydrogen-rich gas with 51% volume content and 0.02MPa pressure. The hydrogen-rich gas enters the pressure swing adsorption device at a pressure of 0.5MPa, and is purified to obtain hydrogen with a volume content of 99.95%, and the pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0043] Embodiment 5:

[0044] For natural gas with 5% hydrogen content and 4.0MPa pressure, the gas-liquid separator removes the liquid droplets and enters the membrane separation system to obtain hydrogen-containing gas with a hydrogen volume content of 28% and a pressure of 0.4MPa. The remaining gas returns to the natural gas pipeline at a pressure of 4.0MPa. The hydrogen-containing gas with a hydrogen volume content of 20% and a pressure of 0.4MPa is further separated by a membrane to obtain hydrogen-rich gas with a volume content of 50% and a pressure of 0.02MPa. The hydrogen-rich gas enters the pressure swing adsorption device at a pressure of 0.8MPa to purify the hydrogen with a volume content of 99.99%. The pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0045] Embodiment 6:

[0046] For natural gas with 5% hydrogen and 0.6MPa pressure, the gas-liquid separator removes the liquid droplets and then enters the membrane separation system to obtain hydrogen-containing gas with a hydrogen volume content of 21% and a pressure of 0.02MPa, and the remaining gas returns to the natural gas pipeline. The hydrogen-containing gas with a hydrogen volume content of 21% and a pressure of 0.02MPa is pressurized to 1.0MPa and then separated by a membrane to obtain hydrogen-rich gas with a hydrogen volume content of 51% and a pressure of 0.02MPa. The hydrogen-rich gas is pressurized to 0.8MPa, and the remaining gas returns to the natural gas pipeline. The hydrogen-rich gas enters the pressure swing adsorption device at a pressure of 0.8MPa, and is purified to obtain hydrogen with a volume content of 99.99%. The pressure swing adsorption desorbed gas is pressurized and returned to the natural gas pipeline.

[0047] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas, characterized in that The method couples the membrane separation process and the pressure swing adsorption process to purify hydrogen.

2. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas according to claim 1, characterized in that The following steps are involved: S1. Passing hydrogen-blended natural gas through a gas-liquid separator to remove liquid foam from the gas; S2, using membrane separation technology to separate the gas obtained in S1, so that the hydrogen is concentrated to a certain volume percentage to obtain hydrogen-rich gas, and the remaining gas is transported to the natural gas pipeline; S3, using the PSA separation method to separate and purify the hydrogen-rich gas obtained in S2 to obtain high-purity hydrogen; the residual gas generated in the PSA process is transported to the natural gas pipeline after being compressed.

3. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 2, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 5 to 30% and a pressure of 0.4 to 4.0 MPa.

4. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 2, characterized in that: In S2, hydrogen is concentrated to a volume percentage of 50% to 80%.

5. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 2, characterized in that: The volume percentage of the high-purity hydrogen in S3 is 99% to 99.999%.

6. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 3, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 30% and a pressure of 4.0 MPa.

7. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 3, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 5 to 30% and a pressure of 0.4 to 4.0 MPa.

8. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 3, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 30% and a pressure of 0.4 MPa.

9. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 3, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 20% and a pressure of 4.0 MPa.

10. The method for separating and purifying hydrogen from medium- and low-pressure hydrogen-blended natural gas as claimed in claim 3, characterized in that: The raw material hydrogen-blended natural gas in S1 is hydrogen-blended natural gas with a hydrogen volume percentage of 10% and a pressure of 0.4 MPa.

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