Method and system for purifying helium in natural gas with high sulfur content

Abstract

The invention provides a method and a system for purifying helium in natural gas with high sulfur content. The method comprises the following steps: converting trace H2 into CH4 by adopting methanation reaction, and replacing catalytic oxidative dehydrogenation reaction. The system comprises a membrane separator, a hydrogenation reactor and a methanation reactor, the membrane separator is used for concentrating the helium; the hydrogenation reactor is used for converting organic sulfur in raw material gas into H2S; the methanation reactor is used for performing exothermic reaction on trace H2 and CO2 in the raw material gas to generate CH4. Membrane separation pressure swing adsorption coupling equipment with a chemical method is adopted to extract and obtain high-purity helium from high-sulfur-content natural gas, conversion of organic sulfur and removal of H2S in the high-sulfur-content natural gas are carried out by adopting cobalt-molybdenum hydrogenation and dry absorption, and trace hydrogen in the natural gas is removed by utilizing methanation reaction. In the system, compression heat is used as an activation heat source for hydrogenation and methanation reactions, so that the compression heat is fully utilized, the heating power consumption is reduced, and cold and hot diseases are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of helium extraction, and in particular relates to a method and system for purifying helium from high-sulfur natural gas. Background Art

[0002] Helium is a vital commodity. Currently, the mainstream international helium extraction technology is cryogenic. This method, which is used for common helium-depleted and even extremely depleted helium fields, requires significant investment and energy consumption, making it unsuitable for industrialization. With the development of membrane technology in hydrogen recovery, research on its application to helium extraction has begun, but to date, it has not been widely adopted in industrial applications.

[0003] Domestic gas fields naturally contain trace amounts of sulfur. The current standard for the sulfur content of natural gas is no more than 100 mg / m 3 , mostly organic sulfur. None of the existing patented technologies have fully considered the removal scheme of organic sulfur (mainly COS, and also mercaptans, sulfides, thiophene, CS2, etc.). Whether it is VPSA, MDEA or dry desulfurization, the sulfur content of natural gas rich in organic sulfur cannot meet the requirements of subsequent dehydrogenation catalysts, which can easily cause catalyst poisoning. The existing technology does not consider the reasonable organization of heat exchange in the process, and there are hot and cold diseases. For example, the heat generated by the compressor is cooled for decarbonization, the dehydrogenation reaction requires heating, and the subsequent process requires cooling. If dehydrogenation is carried out at room temperature, it is difficult to ensure the removal rate of hydrogen, which directly affects the purity of helium. The existing technologies all use catalytic oxidative dehydrogenation. The dehydrogenation process requires excessive oxygen to participate in the reaction, and introduces impurities including O2 and Ar, which have an adverse effect on the subsequent PSA purification. The existing technology CN214087729U does not consider drying and dehydration, and the dew point of the product is difficult to guarantee. The existing CN215113528U technology uses MDEA for decarbonization, but fails to consider the impact of alcoholamine volatilization or carryover on the tolerance and performance of subsequent separation membranes. The existing CN215113528U membrane separator suffers from high backpressure downstream and a low operating pressure differential, resulting in poor separation performance and a significant increase in membrane equipment investment, making it economically unjustifiable.

[0004] Therefore, there is an urgent need for a method and system for purifying helium using membrane technology. Summary of the Invention

[0005] In order to solve the above problems in the prior art, the present invention proposes a method and system for purifying helium from high-sulfur natural gas. 3)Key technical issues for direct purification of helium from helium-containing natural gas. Scope of application: Natural gas helium content ≥ 300ppmv. Based on solving the overall technical solution for the purification of helium-poor natural gas. To solve the applicability problem of high-sulfur natural gas, hydrogenation conversion + dry removal of H2S + VPSA multi-layer is used to ensure the complete removal of total sulfur. In view of the characteristics of high CO2 content in gas field gas, methanation reaction is used to convert trace H2 into CH4, replacing the catalytic oxidative dehydrogenation reaction, avoiding the introduction of O2 and Ar impurities. At the same time, the cost of nickel-based catalysts used in the methanation reaction is only 1 / 10 to 1 / 20 of the cost of palladium-based oxidative dehydrogenation catalysts. The introduction of plate heat exchangers combines the heating requirements of the raw materials with the cooling requirements of the chemical reaction, optimizes the integrated heat exchange, and saves energy and reduces consumption.

[0006] In a first aspect, the present invention provides a method for purifying helium from high-sulfur natural gas, which comprises converting a trace amount of H2 into CH4 using a methanation reaction, replacing a catalytic oxidative dehydrogenation reaction.

[0007] As a specific embodiment of the present invention, the catalyst for catalyzing the oxidative dehydrogenation reaction includes a nickel-based catalyst and a palladium-based catalyst, preferably a nickel-based catalyst.

[0008] As a specific embodiment of the present invention, the following steps are included:

[0009] S1: High-sulfur and helium-containing natural gas is preheated and then concentrated. After pressurization, it is hydrogenated to convert organic sulfur into H2S, and the H2S is removed to obtain the first process gas;

[0010] S2: The process gas obtained in step S1 is subjected to a second concentration to remove hydrogen, and then cooled to remove carbon dioxide and water to obtain a second process gas;

[0011] S3: The second process gas obtained in step S2 is subjected to a third concentration to finally obtain high-purity helium.

[0012] As a specific embodiment of the present invention, in the step S1, the hydrogenation reaction temperature is 320°C to 450°C, and the pressure is 2.0 MPa to 5.0 MPa; the first concentration is 8-14 times.

[0013] As a specific embodiment of the present invention, in the step S2, the methanation reaction temperature is 280°C to 400°C, and the pressure is 1.5MPa to 3.0MPa; the second concentration is 5-8 times.

[0014] As a specific embodiment of the present invention, in the step S3, the third concentration is performed to 5-8 times.

[0015] In a second aspect, the present invention provides a system for purifying helium from high-sulfur natural gas, the system comprising a membrane separator, a hydrogenation reactor, and a methanation reactor; the membrane separator concentrates the helium; the hydrogenation reactor converts organic sulfur in the feed gas into H2S; and the methanation reactor causes trace amounts of H2 in the feed gas to react with CO2 in an exothermic reaction to generate CH4.

[0016] As a specific embodiment of the present invention, the system further includes an air-to-air heat exchanger, an absorption tower, and an adsorption tower; the number of the membrane separators is ≥3, which are respectively connected to the air-to-air heat exchanger, the absorption tower, and the adsorption tower.

[0017] As a specific embodiment of the present invention, the tail gas concentrated by the membrane separator can be recycled and then enter the inlet of the previous membrane separator to improve the helium yield.

[0018] As a specific embodiment of the present invention, the system further includes a compressor purification and refining unit and a tail gas circulation compressor.

[0019] As a specific embodiment of the present invention, the catalyst in the methanation reactor includes a nickel-based catalyst and a palladium-based catalyst, preferably a nickel-based catalyst.

[0020] As a specific embodiment of the present invention, a dehydration device may be added before the purification and refining unit for the water generated by the methanation reaction. The dehydration device may include a cold dryer or a molecular sieve dehydration process.

[0021] As a specific embodiment of the present invention, the absorption tower and the adsorption tower can be replaced by the alcohol amine absorption method, and an amine washing tower and a dehydration tower can be added to achieve the same purpose.

[0022] As a specific embodiment of the present invention, the system for purifying helium from high-sulfur natural gas described in the second aspect is used to complete the method for purifying helium from high-sulfur natural gas described in the first aspect, comprising the following steps:

[0023] S1: High-sulfur and helium-containing natural gas is preheated in a gas-to-gas heat exchanger to increase its dryness before entering the first membrane separator for the first concentration, where the helium is concentrated 8-14 times. At this point, the processed gas volume is reduced to 1 / 9-1 / 13 of the original. After being pressurized, it enters the hydrogenation reactor without cooling to convert organic sulfur into easily removable H2S. The H2S is then reduced to below 0.1ppm by an absorption tower to obtain the first process gas. The H2S removal rate in the first process gas is approximately 50%, and the organic sulfur removal rate is approximately 70%.

[0024] S2: The first process gas obtained in step S1 merges with the helium-rich tail gas from the third membrane separator and enters the second membrane separator for a second concentration, where the helium is concentrated by 5-8 times. The gas then enters the methanation reactor to remove hydrogen. After cooling in the gas-to-gas heat exchanger, the gas is sent to the VPSA adsorption tower to remove carbon dioxide and water, thereby obtaining the second process gas.

[0025] S3: The second process gas obtained in step S2 is sent to the third-stage membrane separator for third concentration, the helium is concentrated by 5-8 times, and high-purity helium is obtained through a purification and refining unit.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention proposes a method for purifying helium from high-sulfur natural gas and high-CO2 natural gas, which specifically solves the technical problem that the organic sulfur content in gas field natural gas is high and the removal effect of physical methods such as MDEA and PSA is poor.

[0028] 2. The method of the present invention adopts the combination of "cobalt-molybdenum hydrogenation + dry absorption" to remove organic sulfur and inorganic sulfur, which not only completely removes organic sulfur but also effectively avoids the adverse effects of MDEA alcoholamine solvent entrainment on the subsequent membrane separator.

[0029] 3. The method of the present invention cleverly utilizes the methanation reaction to remove trace hydrogen from natural gas, which not only avoids the problem of difficult removal of impurities O2 and Ar, but also reduces the cost of the catalyst.

[0030] 4. The system of the present invention utilizes an air-to-air heat exchanger to solve the integration problem of chemical reaction heat release and feed gas preheating, fully utilizes compression heat, avoids the disadvantage of "hot and cold disease" in the process flow, and at the same time avoids separate heating equipment and reduces cooling water consumption.

[0031] 5. The system of the present invention adopts a three-stage membrane separator for helium concentration. The third membrane separator is not segmented, and the non-permeate gas is directly circulated to the inlet of the second membrane separator, which reduces the number of equipment, reduces membrane investment, and significantly reduces compression power. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a cross-sectional schematic diagram of an embodiment of the present invention;

[0033] Figure 2 This is a process flow chart for purifying helium from high-sulfur natural gas and high-CO2 natural gas provided in another embodiment of the present invention.

[0034] Among them, 1-gas-gas heat exchanger, 2-first membrane separator, 3-first compressor, 4-hydrogenation reactor, 5-absorption tower, 6-adsorption tower, 7-second membrane separator, 8-second compressor, 9-methanation reactor, 10-third membrane separator, 11-third compressor, 13-purification and refining unit, and 15 is the tail gas compressor. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific examples, but they do not constitute any limitation to the present invention.

[0036] Example 1

[0037] This embodiment provides a method and system for purifying helium from high-sulfur natural gas. The specific details are as follows:

[0038] High-sulfur and helium-containing natural gas from a gas field processing plant first enters a gas-to-gas heat exchanger (1) for preheating and then increases its dryness. It then enters a first membrane separator (2). The non-permeated tail gas is directly returned to the natural gas network with almost no pressure reduction. The permeated gas is at normal pressure, with an increased helium concentration and a significantly reduced flow rate. It is then pressurized to a suitable pressure by a first compressor (3) without cooling, and sent to a hydrogenation reactor (4) where organic sulfur is converted into H2S under the action of a cobalt-molybdenum catalyst. The H2S is then completely removed by an absorption tower (5). The gas is cooled to room temperature by the gas-to-gas heat exchanger (1) and enters a second membrane separator (7). The helium concentration of the permeated gas is further concentrated. The second compressor (8) increases the pressure to a certain level and directly enters the methanation reactor (9) without cooling. Under the action of a nickel-based catalyst, a trace amount of H2 in the raw material reacts with CO2 to produce CH4 in an exothermic reaction. The CH4 is cooled to room temperature by the gas-to-gas heat exchanger (1) and enters the adsorption tower (6) to remove most of the CO2. The CH4 then enters the third membrane separator (10). The helium concentration is concentrated to the required concentration (≥50%) for the low-temperature purification unit. The CH4 is then increased to the required pressure by the 3# compressor (11) and sent to the purification and refining unit (13). The remaining CH4, N2, Ne and other impurities are removed to obtain helium with a purity of 99.999%.

[0039] The non-permeate gas from the second membrane separator (7) is pressurized by the tail gas compressor (15) and then merged into the tail gas network. The non-permeate gas from the third membrane separator (10) contains a large amount of helium and is returned to the inlet of the second membrane separator (7) for recovery. The tail gas from the purification unit (13) is circulated to the second compressor (8) to recover the helium.

[0040] The helium recovery rate of the entire process is above 92%.

[0041] Example 2

[0042] Combine Figure 2 As shown, the difference between this embodiment and embodiment 1 is that the adsorption tower (6) is moved to the inlet of the second membrane separator (7) and the methanation reactor (9) is moved to the third compressor (11), and the same purpose can be achieved. In this case, in order to remove the water generated by the methanation reaction, a dehydration device (12) needs to be added before the purification unit (13), and the dehydration adopts a cold dryer or molecular sieve dehydration process.

[0043] In this embodiment, the non-permeate gas of the third membrane separator (11) is directly returned to the inlet of the second membrane separator (7). In fact, it can also be returned to the first compressor (3) to achieve the same purpose.

[0044] In summary, the method and apparatus for purifying helium from high-sulfur natural gas of the present invention utilizes membrane separation and pressure swing adsorption coupled equipment with a chemical method to extract and obtain high-purity helium from high-sulfur natural gas. Cobalt-molybdenum hydrogenation followed by dry absorption is used to convert organic sulfur in the high-sulfur natural gas and remove H2S. The process can be segmented into a "hydrogenation-absorption-hydrogenation-absorption" process as needed. Compression heat is utilized as the activation heat source for the hydrogenation and methanation reactions, fully utilizing the compression heat to save heating power and avoid the "hot and cold syndrome." Multi-stream or plate-fin gas-to-gas heat exchangers are used to integrate reaction exotherm with feedstock preheating. The methanation reaction is used to remove trace hydrogen from the natural gas. Non-permeate gas from the third membrane separator is directly returned to the inlet of the second membrane separator for recovery. The tail gas from the purification and refining unit is circulated to the second compressor for helium recovery.

[0045] Any numerical value mentioned in the present invention includes all values that increase by one unit each time from the lowest value to the highest value if there is only a gap of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is stated to be 50-90, it is meant in this specification to specifically list values such as 51-89, 52-88... and 69-71 and 70-71. For non-integer values, it is appropriate to consider units of 0.1, 0.01, 0.001 or 0.0001. These are just some special examples. In this application, in a similar manner, all possible combinations of numerical values between the listed lowest value and the listed highest value are considered to have been disclosed.

[0046] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for purifying helium from high-sulfur natural gas, characterized in that: The method includes using a methanation reaction to convert a trace amount of H2 into CH4, replacing the catalytic oxidative dehydrogenation reaction.

2. The method according to claim 1, characterized in that The catalyst for the methanation reaction includes a nickel-based catalyst and a palladium-based catalyst, preferably a nickel-based catalyst.

3. The method according to claim 1 or 2, characterized in that The following steps are involved: S1: High-sulfur and helium-containing natural gas is preheated and then concentrated. After pressurization, it is hydrogenated to convert organic sulfur into H2S, and the H2S is removed to obtain the first process gas; S2: The process gas obtained in step S1 is subjected to a second concentration, a methanation reaction is performed to remove hydrogen, and carbon dioxide and water are removed after cooling to obtain a second process gas; S3: The second process gas obtained in step S2 is subjected to a third concentration to finally obtain high-purity helium.

4. The method according to any one of claims 1 to 3, characterized in that In the step S1, the hydrogenation reaction temperature is 320° C. to 450° C., and the reaction pressure is 2.0 MPa to 5.0 MPa; and the first concentration is 8-14 times.

5. The method according to any one of claims 1 to 4, characterized in that In the step S2, the methanation reaction temperature is 280°C to 400°C, and the reaction pressure is 1.5MPa to 3.0MPa; the second concentration is 5-8 times; And / or, in step S3, the third concentration is to 5-8 times.

6. A system for purifying helium from high-sulfur natural gas, characterized in that: The system includes a membrane separator, a hydrogenation reactor, and a methanation reactor; the membrane separator concentrates helium; the hydrogenation reactor converts organic sulfur in the raw gas into H2S; and the methanation reactor causes trace amounts of H2 in the raw gas to react with CO2 in an exothermic reaction to generate CH4.

7. The system according to claim 6, characterized in that The system also includes an air-to-air heat exchanger, an absorption tower, and an adsorption tower; the number of the membrane separators is ≥3, which are respectively connected to the air-to-air heat exchanger, the absorption tower, and the adsorption tower.

8. The system according to claim 6 or 7, characterized in that The tail gas concentrated by the membrane separator can be recycled and then enter the inlet of the previous membrane separator.

9. The system according to any one of claims 6 to 8, characterized in that: The system also includes a compressor purification and refining unit and a tail gas circulation compressor.

10. The system according to any one of claims 6 to 9, characterized in that: The catalyst in the methanation reactor includes a nickel-based catalyst and a palladium-based catalyst, preferably a nickel-based catalyst.

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