Hydrogen gas purification system and method for hydrogen-doped natural gas

Abstract

The application discloses a hydrogen-containing natural gas hydrogen purification system and method, which comprises a natural gas pressure energy utilization system and a hydrogen extraction system. The natural gas pressure energy utilization system comprises a three-way valve, an expander, a first heat exchanger and a second heat exchanger connected in sequence, the three-way valve is connected with a high-pressure hydrogen-containing natural gas pipe network, and the second heat exchanger is connected with a medium-low pressure natural gas pipe network. The natural gas hydrogen extraction system comprises a three-way valve, a membrane separator, a back pressure valve, a first heat exchanger, a first adsorption tower, a second adsorption tower, a compressor and a second heat exchanger connected in sequence, and the compressor is connected with the expander through a shaft coupling. The application utilizes the high-pressure natural gas expansion work to drive the compressor for re-compressing and desorbing the natural gas. Meanwhile, the low-temperature natural gas after expansion is used for cooling the hydrogen-containing natural gas, and low-temperature pressure swing adsorption is realized to improve the adsorption efficiency. The application fully applies the natural gas pressure energy to the hydrogen extraction process, effectively reduces the hydrogen extraction and compression costs, and reduces the equipment investment.

Description

Technical Field

[0001] This invention relates to the field of natural gas processing technology, and in particular to a hydrogen purification system and method for hydrogen-blended natural gas. Background Technology

[0002] Compared to other hydrogen transportation methods, using natural gas pipelines for long-distance hydrogen transport has the advantages of low transportation costs and reduced infrastructure investment. However, in order to use hydrogen as a chemical feedstock or fuel for fuel cells, it is crucial to separate pure hydrogen from hydrogen-blended natural gas (according to ISO 14687-2:2012, the purity of hydrogen used in fuel cells must be at least 99.97%).

[0003] Given the current safety operation of hydrogen-blended natural gas pipelines and the limitations on the amount of hydrogen blending that downstream users can tolerate, the hydrogen concentration in hydrogen-blended natural gas is generally less than 20%. A combination of membrane separation and pressure swing adsorption (PSA) is commonly used to extract hydrogen from this natural gas. Most zeolite adsorbents exhibit higher adsorption capacity and separation coefficients at low temperatures; for example, 5A zeolite molecular sieve achieves its highest saturation adsorption capacity at -30°C. However, while PSA obtains pure hydrogen, the desorbed natural gas needs to be further pressurized and injected into the pipeline network. Therefore, reducing the energy consumption of natural gas recompression and minimizing the amount of adsorbent required are crucial factors in reducing the cost of hydrogen extraction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hydrogen purification system and method for blended natural gas that can make full use of natural gas pressure energy and reduce hydrogen extraction costs.

[0005] The present invention provides a technical solution for a hydrogen purification system for hydrogen-blended natural gas, comprising a natural gas pressure energy utilization system and a hydrogen extraction system. The natural gas pressure energy utilization system includes a three-way valve, the inlet of which is connected to a high-pressure hydrogen-blended natural gas pipeline network, the first outlet of which is connected to the inlet of an expander, the outlet of which is connected to the first inlet of a first heat exchanger, the first outlet of which is connected to the first inlet of a second heat exchanger, and the first outlet of which is connected to a low-pressure natural gas pipeline network.

[0006] The natural gas hydrogen extraction system includes a membrane separator, an adsorption tower, and a compressor. The second outlet of a three-way valve is connected to the inlet of the membrane separator. The first outlet of the membrane separator is connected to the second inlet of the first heat exchanger. The second outlet of the first heat exchanger is connected to the inlet valves of the first and second adsorption towers. The second outlet valves of the first and second adsorption towers are connected to the inlet of the compressor. The outlet of the compressor is connected to the second inlet of the second heat exchanger. The second outlet of the second heat exchanger is connected to the low-pressure natural gas pipeline network. The compressor is connected to an expander via a coupling.

[0007] The present invention relates to a hydrogen purification system for hydrogen-blended natural gas, wherein the second outlet of the membrane separator is connected to the inlet of a back pressure valve, and the outlet of the back pressure valve is connected to the inlet of an expander.

[0008] The present invention relates to a hydrogen purification system for hydrogen-blended natural gas, wherein the first adsorption tower is provided with a first adsorption tower first outlet valve, and the first adsorption tower first outlet valve is connected to the downstream hydrogen supply end.

[0009] The present invention relates to a hydrogen purification system for hydrogen-blended natural gas, wherein the second adsorption tower is provided with a first outlet valve for the second adsorption tower, and the first outlet valve for the second adsorption tower is connected to the downstream hydrogen supply end.

[0010] The present invention relates to a hydrogen purification system for hydrogen-blended natural gas, wherein the membrane separator and adsorption tower comprise multiple sets.

[0011] The present invention relates to a hydrogen purification system for hydrogen-blended natural gas, wherein multiple sets of expanders and compressors are provided.

[0012] Another technical solution provided by the present invention is a method for purifying hydrogen from hydrogen-blended natural gas, comprising the following steps:

[0013] S10: Part of the high-pressure hydrogen-blended natural gas is fed into the membrane separator for gas separation, and part is fed into the expander to provide pressure energy;

[0014] S20, the hydrogen-blended natural gas separated and purified by the membrane separator and the low-temperature natural gas that has expanded and done work after releasing pressure energy in the expander exchange heat in the first heat exchanger and then enter the first adsorption tower in the adsorption state for gas separation, and the standard pure hydrogen is sent to the downstream hydrogen use end.

[0015] S30, when the first adsorption tower reaches adsorption equilibrium, it switches to desorption state, and the second adsorption tower continues to adsorb. The first adsorption tower and the second adsorption tower alternately are in adsorption and desorption states.

[0016] S40, the natural gas desorbed from the adsorption tower is compressed using the pressure energy from step S10 and then sent downstream to the hydrogen end.

[0017] The present invention relates to a method for purifying hydrogen from hydrogen-blended natural gas, wherein the desorbed natural gas from the first adsorption tower or the second adsorption tower is compressed using pressure energy and then enters the second heat exchanger to exchange heat with the natural gas that has lost pressure energy and has passed through the first heat exchanger, and then goes to the downstream low-pressure natural gas pipeline network.

[0018] The present invention provides a method for purifying hydrogen from hydrogen-blended natural gas, wherein in step S40, the equipment utilizing pressure energy is an expander and a compressor.

[0019] The hydrogen purification system and method for blended natural gas of this invention differ from existing technologies in that the hydrogen purification system for blended natural gas of this invention fully utilizes the pressure energy of high-pressure natural gas for the hydrogen extraction system. On the one hand, the pressure energy is used for the recompression of the desorbed natural gas entering the natural gas pipeline network, without additional compression energy consumption, reducing equipment investment and lowering the cost of the hydrogen extraction system. On the other hand, the cold energy after expansion is used to cool the blended natural gas, reducing the impact of adsorption heat on performance, increasing the adsorption capacity of the adsorbent, effectively reducing the adsorbent dosage in the adsorption tower, and improving adsorption efficiency.

[0020] The hydrogen purification system and method for hydrogen-blended natural gas of the present invention will be further described below with reference to the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the hydrogen purification system for hydrogen-doped natural gas according to the present invention;

[0022] The markings in the diagram are as follows: 1-Three-way valve; 2-Expander; 3-First heat exchanger; 4-Second heat exchanger; 5-Compressor; 6-Membrane separator; 7-Back pressure valve; 8-Inlet valve of the first adsorption tower; 9-First adsorption tower; 10-First outlet valve of the first adsorption tower; 11-Second outlet valve of the first adsorption tower; 12-Inlet valve of the second adsorption tower; 13-Second adsorption tower; 14-First outlet valve of the second adsorption tower; 15-Second outlet valve of the second adsorption tower. Detailed Implementation

[0023] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0024] Example 1

[0025] like Figure 1 As shown, the hydrogen purification system for blended natural gas of the present invention includes a natural gas pressure energy utilization system and a hydrogen extraction system. The natural gas pressure energy utilization system can use the pressure energy in the natural gas for cooling and recompression of the desorbed natural gas by low-temperature pressure swing adsorption in the hydrogen extraction system.

[0026] The natural gas pressure energy utilization system includes a three-way valve 1, an expander 2, a first heat exchanger 3, and a second heat exchanger 4 connected in sequence. The inlet of the three-way valve 1 is connected to the upstream high-pressure hydrogen-blended natural gas pipeline, and the first outlet of the three-way valve 1 is connected to the inlet of the expander 2. The outlet of the expander 2 is connected to the first inlet of the first heat exchanger 3, the first outlet of the first heat exchanger 3 is connected to the first inlet of the second heat exchanger 4, and the first outlet of the second heat exchanger 4 is connected to the downstream medium- and low-pressure natural gas pipeline. The upstream high-pressure hydrogen-blended natural gas enters the expander 2, expands, and performs work, then undergoes two heat exchanges in sequence through the first heat exchanger 3 and the second heat exchanger 4.

[0027] The natural gas hydrogen extraction system includes, in sequence, a three-way valve 1, a membrane separator 6, a back pressure valve 7, a first heat exchanger 3, a first adsorption tower 9, a second adsorption tower 13, a compressor 5, and a second heat exchanger 4. The second outlet of the three-way valve 1 is connected to the membrane separator 6. The first outlet of the membrane separator 6 is connected to the second inlet of the first heat exchanger 3. The second outlet of the membrane separator 6 is connected to the inlet of the back pressure valve 7, and the outlet of the back pressure valve 7 is connected to the inlet of the expander 2. The second outlet of the first heat exchanger 3 is connected to both the first adsorption tower 9 and the second adsorption tower 13.

[0028] The inlet and outlet pipes of the first adsorption tower 9 are equipped with a first adsorption tower inlet valve 8, a first adsorption tower first outlet valve 10, and a first adsorption tower second outlet valve 11. The first adsorption tower inlet valve 8 is connected to the second outlet of the first heat exchanger 3, and the first adsorption tower first outlet valve 10 is connected to the downstream hydrogen supply end.

[0029] The inlet and outlet pipes of the second adsorption tower 13 are equipped with a second adsorption tower inlet valve 12, a second adsorption tower first outlet valve 14, and a second adsorption tower second outlet valve 15. The second adsorption tower inlet valve 12 is connected to the second outlet of the first heat exchanger 3, and the second adsorption tower first outlet valve 14 is connected to the downstream hydrogen supply end.

[0030] The second outlet valve 11 of the first adsorption tower and the second outlet valve 15 of the second adsorption tower are both connected to the inlet of the compressor 5. The outlet of the compressor 5 is connected to the second inlet of the second heat exchanger 4, and the second outlet of the second heat exchanger 4 is connected to the downstream medium- and low-pressure natural gas pipeline network. The compressor 5 is connected to the expander 2 via a coupling, and the expander 2 drives the compressor 5 to compress and desorb natural gas to the set pressure.

[0031] When the hydrogen-blended natural gas hydrogen purification system of this invention is used, the natural gas pressure energy utilization system and the hydrogen extraction system work together to carry out the working cycle.

[0032] The working process of the natural gas pressure energy utilization system is as follows: High-pressure hydrogen-blended natural gas with a set flow rate is introduced into expander 2 through three-way valve 1. The temperature and pressure of the natural gas decrease, expander 2 recovers pressure energy, and transfers the energy to compressor 5 through coupling. Subsequently, the low-temperature natural gas exchanges heat with the natural gas before entering the first adsorption tower 9 and the second adsorption tower 13 in the first heat exchanger 3, and exchanges heat with the desorbed natural gas compressed by compressor 5 in the second heat exchanger 4.

[0033] The hydrogen extraction system operates as follows: When the first adsorption tower 9 adsorbs natural gas, the inlet valve 8 of the first adsorption tower opens, the first outlet valve 10 of the first adsorption tower opens, and the second outlet valve 11 of the first adsorption tower closes. At this time, the second adsorption tower 13 desorbs natural gas, and the inlet valve 12 of the second adsorption tower closes, the first outlet valve 14 of the second adsorption tower closes, and the second outlet valve 15 of the second adsorption tower opens. High-pressure hydrogen-blended natural gas at a set flow rate is introduced into the membrane separator 6 through the three-way valve 1. Non-permeable gas (mainly natural gas) leaves from the second outlet of the membrane separator 6 and enters the expander 2 through the back pressure valve 7. The permeated hydrogen-rich natural gas (with increased hydrogen concentration) enters the first heat exchanger 3 to exchange heat with the low-temperature natural gas that has expanded and performed work in the expander 2. Subsequently, the hydrogen-rich natural gas enters the first adsorption tower 9 through the inlet valve 8 of the first adsorption tower, where the natural gas is adsorbed. The pure hydrogen, reaching the standard, goes to the downstream hydrogen-using end through the first outlet valve 10 of the first adsorption tower. The pressure in the second adsorption tower 13 decreases, the natural gas desorbs, and enters the compressor 5 through the second outlet valve 15 of the second adsorption tower. After being compressed, the natural gas enters the second heat exchanger 4 to be cooled, and then enters the downstream low-pressure natural gas pipeline network. When the first adsorption tower 9 reaches adsorption equilibrium, the inlet valve 8 of the first adsorption tower closes, the first outlet valve 10 of the first adsorption tower closes, and the second outlet valve 11 of the first adsorption tower opens, causing the first adsorption tower 9 to desorb natural gas. At this time, the second adsorption tower 13 begins to absorb natural gas, and the inlet valve 12 of the second adsorption tower opens, the first outlet valve 14 of the second adsorption tower opens, and the second outlet valve 15 of the second adsorption tower closes. This cycle repeats.

[0034] In other embodiments, the natural gas hydrogen purification system may consist of multiple membrane separators and adsorption towers; the natural gas pressure energy utilization system may include multiple expanders and multiple compressors to perform multi-stage compression or multi-stage expansion of natural gas.

[0035] Example 2

[0036] This embodiment describes a method for purifying hydrogen from hydrogen-blended natural gas, including the following steps:

[0037] S10: Part of the high-pressure hydrogen-blended natural gas is fed into the membrane separator for gas separation, and part is fed into the expander to provide pressure energy;

[0038] S20, the hydrogen-blended natural gas separated and purified by the membrane separator and the low-temperature natural gas that has expanded and done work after releasing pressure energy in the expander exchange heat in the first heat exchanger and then enter the first adsorption tower in the adsorption state for gas separation, and the standard pure hydrogen is sent to the downstream hydrogen use end.

[0039] S30, when the first adsorption tower reaches adsorption equilibrium, it switches to desorption state, and the second adsorption tower continues to adsorb. The first adsorption tower and the second adsorption tower alternately are in adsorption and desorption states.

[0040] S40, the natural gas desorbed from the adsorption tower is compressed using the pressure energy from step S10 and then sent downstream to the hydrogen end.

[0041] The natural gas desorbed from the first or second adsorption tower is compressed using pressure energy and then enters the second heat exchanger to exchange heat with the natural gas that has lost pressure energy and has passed through the first heat exchanger. It then goes to the downstream low-pressure natural gas pipeline network.

[0042] In step S40, the devices that utilize pressure energy are an expander and a compressor.

[0043] This invention relates to a hydrogen purification system for blended natural gas. It fully utilizes the pressure energy of the natural gas before and after pressure regulation for hydrogen extraction. On one hand, the pressure energy is used for desorbing and recompressing the natural gas; on the other hand, the expanded, low-temperature natural gas is used to maintain the low-temperature environment for pressure swing adsorption. This invention applies the pressure energy of high-pressure blended natural gas to hydrogen purification, effectively improving adsorption / separation efficiency, reducing investment costs, and lowering operating costs.

[0044] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A hydrogen purification system for hydrogen-blended natural gas, characterized in that: It includes a natural gas pressure energy utilization system and a hydrogen extraction system. The natural gas pressure energy utilization system includes a three-way valve. The inlet of the three-way valve is connected to the high-pressure hydrogen-blended natural gas pipeline network. The first outlet of the three-way valve is connected to the inlet of the expander. The outlet of the expander is connected to the first inlet of the first heat exchanger. The first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger. The first outlet of the second heat exchanger is connected to the low-pressure natural gas pipeline network. The natural gas hydrogen extraction system includes a membrane separator, an adsorption tower, and a compressor. The second outlet of a three-way valve is connected to the inlet of the membrane separator. The first outlet of the membrane separator is connected to the second inlet of the first heat exchanger. The second outlet of the first heat exchanger is connected to the inlet valves of the first and second adsorption towers. The second outlet valves of the first and second adsorption towers are connected to the inlet of the compressor. The outlet of the compressor is connected to the second inlet of the second heat exchanger. The second outlet of the second heat exchanger is connected to the low-pressure natural gas pipeline network. The compressor is connected to an expander via a coupling. The second outlet of the membrane separator is connected to the inlet of a back pressure valve. The outlet of the back pressure valve is connected to the inlet of the expander.

2. The hydrogen purification system for hydrogen-blended natural gas according to claim 1, characterized in that: The first adsorption tower is equipped with a first outlet valve, which is connected to the downstream hydrogen supply end.

3. The hydrogen purification system for hydrogen-blended natural gas according to claim 1 or 2, characterized in that: The second adsorption tower is equipped with a first outlet valve, which is connected to the downstream hydrogen supply end.

4. The hydrogen purification system for hydrogen-blended natural gas according to claim 1, characterized in that: The membrane separator and adsorption tower comprise multiple sets.

5. The hydrogen purification system for hydrogen-blended natural gas according to claim 1, characterized in that: The expander and compressor are provided in multiple sets.

6. A method for purifying hydrogen from hydrogen-blended natural gas, characterized in that: Includes the following steps: S10: Part of the high-pressure hydrogen-blended natural gas is fed into the membrane separator for gas separation, and part is fed into the expander to provide pressure energy; S20, after being purified by the membrane separator, the hydrogen-blended natural gas and the low-temperature natural gas that has been expanded and worked in the expander exchange heat in the first heat exchanger and then enter the first adsorption tower in the adsorption state for gas separation, and the standard pure hydrogen is sent to the downstream hydrogen use end. S30, when the first adsorption tower reaches adsorption equilibrium, it switches to the desorption state, and the second adsorption tower continues to adsorb. The first adsorption tower and the second adsorption tower alternately are in the adsorption and desorption states. S40, the desorbed natural gas in the adsorption tower is compressed using the pressure energy from step S10, and then enters the second heat exchanger to exchange heat with the natural gas that has lost pressure energy and has passed through the first heat exchanger. Then it goes to the downstream low-pressure natural gas pipeline network. The equipment that utilizes pressure energy is an expander and a compressor.

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