Process for extracting helium from low-grade natural gas

Abstract

The invention discloses a process for extracting helium from low-grade natural gas, and belongs to the field of rare gas chemical industry. According to the technical scheme, the process for extracting the helium from the low-grade natural gas comprises the following steps: 1, carrying out purification and impurity removal on raw natural gas; 2, the purified and impurity-removed raw natural gas passes through a centrifugal enrichment unit, so that the helium concentration of paraxial output gas flow of the centrifugal enrichment unit reaches the refining treatment concentration, and the paraxial output gas flow is collected; and 3, refining the paraxial output gas flow to obtain a high-purity helium product. The process for extracting the helium from the low-grade natural gas has the beneficial effects that the production difficulty is low, the process cost is low, the utilization rate of helium resources in China can be increased, and the supply and demand contradiction of the helium resources in China is solved.

Description

Technical Field

[0001] The invention relates to the technical field of rare gas chemical industry, and in particular to a process for extracting helium from low-quality natural gas. Background Art

[0002] Helium is a scarce strategic resource, widely used in cutting-edge technologies and frontier fields such as cryogenic technology, nuclear industry, national defense, clinical medicine, and deep-sea diving. It is also called "gas rare earth" and "golden gas". The main way to produce helium industrially is to extract it from natural gas. However, my country's helium resources are scarce, and the average helium concentration in natural gas is less than 0.2%, which is lower than the economic extraction concentration of existing large-scale helium extraction technology. At present, my country's self-produced helium is mainly obtained from the tail gas of liquefied natural gas (LNG) through deep cold liquefaction (BOG method), and then product-grade helium is obtained through adsorption and other methods. This process route consumes a lot of energy in the natural gas liquefaction stage, which increases the cost of natural gas and helium, and the output is limited, making it difficult to promote on a large scale.

[0003] The industrial way to obtain helium is to extract it from natural gas. The current mature extraction methods can be divided into cryogenic method and non-cryogenic method. The cryogenic method is mainly the flash liquefaction method (BOG), which uses the characteristic that the boiling point of helium is the lowest in nature to liquefy natural gas and extract helium. This method has no requirements for the concentration of helium in the raw gas, but it has high energy consumption and low output. Non-cryogenic methods include pressure swing adsorption (PSA) and membrane adsorption. Such methods have large output and low energy consumption, but have minimum requirements for the concentration of raw gas. Since the helium concentration in my country's natural gas is generally lower than the minimum concentration requirement of the non-cryogenic method, helium in my country's natural gas cannot be extracted. At present, some companies use the BOG method to liquefy natural gas first, and then extract helium from the tail gas. Although this route is feasible, the liquefaction process consumes a lot of energy, the output is limited, and it will increase the cost of natural gas and helium at the same time, making it difficult to promote the process.

[0004] The Chinese invention patent "A device and process for extracting helium from natural gas" with announcement number CN111170290B discloses a process for extracting helium by first removing most of the hydrogen and alkane gases in natural gas by combustion, and then removing carbon dioxide gas by spraying the exhaust gas mixture after combustion, removing water vapor by drying, filtering to remove methane, nitrogen and oxygen, removing residual methane, argon, residual oxygen and residual nitrogen by three-stage cooling, and removing residual hydrogen by centrifugation. However, the process has the following disadvantages: 1. The raw material for extracting helium in the process is natural gas exhaust gas, and removing other fuel gases in natural gas by combustion is a waste and not economical; 2. The process uses centrifugal method to separate hydrogen and helium, which is bound to use a centrifuge with extremely high speed, which will inevitably lead to extremely high energy consumption, making the process uncompetitive compared with the adsorption method; 3. The process seeks to directly obtain product-grade helium concentration, but if the helium output is increased and the device is enlarged, its increased production capacity will inevitably lead to a decrease in product quality, and if it is actually put into production, it will not be possible to obtain refining-grade helium concentration. Summary of the invention

[0005] In order to solve the problems in the above-mentioned prior art, the present invention proposes a new process route for helium extraction technology that is adapted to my country's national conditions. The present invention provides a process for extracting helium from low-quality natural gas, which can improve the utilization rate of my country's helium resources and solve the contradiction between supply and demand of my country's helium resources.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides a process for extracting helium from low-quality natural gas, characterized in that it comprises the following steps:

[0007] Step S1: purifying and removing impurities from the natural gas;

[0008] Step S2: passing the purified and impurity-removed natural gas through a centrifugal enrichment unit so that the helium concentration of the proximal output gas flow of the centrifugal enrichment unit reaches the refining treatment concentration, and collecting the proximal output gas flow;

[0009] Step S3: Refining the proximal output gas flow to obtain a high-purity helium product.

[0010] Furthermore, the centrifugal unit comprises a plurality of gas centrifuges installed in cascade.

[0011] Furthermore, when the proximal output gas flow reaches the refining treatment concentration, the volume concentration of helium is C 氦 ≥7%.

[0012] Furthermore, the refining process is an adsorption method.

[0013] Furthermore, the near-wall output airflow of the centrifugal unit is collected as a by-product.

[0014] A system for implementing the process of extracting helium from low-grade natural gas, comprising:

[0015] Gas washing and purification unit, used to purify and remove impurities from natural gas;

[0016] A centrifugal enrichment unit, used for centrifugally treating and purifying the raw natural gas after impurities removal, and obtaining a near-axial output gas flow with a helium concentration reaching a refining treatment concentration;

[0017] And a refining processing unit is used for refining the proximal output gas flow to obtain a high-purity helium product.

[0018] Furthermore, the centrifugal enrichment unit comprises a plurality of gas centrifuges installed in cascade, the input end of the first-stage gas centrifuge is connected to the output end of the gas washing and purification unit, the input end of the latter-stage gas centrifuge is connected to the proximal output end of the adjacent previous-stage gas centrifuge, and the output end of the latter-stage gas centrifuge is connected to the input end of the refining processing unit.

[0019] Furthermore, the refining processing unit uses an adsorption method to refine the proximal output airflow.

[0020] Furthermore, a byproduct collection unit is provided at the near-wall output end of the centrifugal enrichment unit.

[0021] The beneficial effects of the present invention are as follows: 1. The process of the present invention does not include the cryogenic liquefaction process in the BOG process, which is suitable for my country, which is not an exporter of liquefied natural gas (LNG). The cost of natural gas and helium is limited when the process is used to extract helium;

[0022] 2. The process provided by the present invention does not seek to directly obtain a high-concentration helium product in the centrifugal enrichment stage, but only aims to increase the helium concentration in the product gas to a limited extent. Therefore, the design difficulty and energy consumption of the centrifugal device are relatively low, further reducing the difficulty and cost of production.

[0023] 3. Compared with the gas centrifuge used for uranium enrichment, the gas centrifuge used in the centrifugal unit of the present invention does not require the use of special materials, has low operating difficulty, low construction cost, and is highly advanced. In addition, the operating parameters of the gas centrifuge used in the present invention are significantly lower than those of the uranium enrichment centrifuge, and the design difficulty is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the process route and system structure of the present invention.

[0025] Among them, the reference numerals are: 100, gas washing and purification unit; 200, centrifugal enrichment unit; 201, near-wall output airflow; 202, near-axis output airflow; 210, gas centrifuge; 300, refining processing unit. DETAILED DESCRIPTION

[0026] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0027] See also Figure 1 The embodiment of the present invention provides a process for extracting helium from low-quality natural gas, which is characterized by comprising the following steps:

[0028] Step S1: purifying and removing impurities from the natural gas;

[0029] Step S2: passing the purified and impurity-removed natural gas through a centrifugal enrichment unit so that the helium concentration of the proximal output gas flow of the centrifugal enrichment unit reaches the refining treatment concentration, and collecting the proximal output gas flow;

[0030] Step S3: Refining the proximal output gas flow to obtain a high-purity helium product.

[0031] The raw natural gas is first purified and cleaned by basic gas washing and purification to remove the main impurities. The purified and cleaned raw natural gas is then centrifugally enriched by a centrifugal unit. The core device of the centrifugal enrichment process is a low-energy gas centrifuge. The gas centrifuge uses the centrifugal force generated by high-speed rotation to make gases such as methane with larger molecular weight gather near the wall of the gas centrifuge, while helium, due to its smaller molecular weight, gathers near the axis of the gas centrifuge. Through the guide pipe, the near-wall output airflow and the near-axis output airflow are respectively discharged, and then the near-axis output airflow with high helium concentration is refined and purified. This process can directly use the existing mature helium extraction technology to reduce operating costs and finally obtain high-purity helium products. This process does not include a cryogenic process and does not seek to directly obtain product-grade helium purity. It only makes a limited improvement in the helium concentration and is only committed to increasing the helium concentration in the raw natural gas to an economical extraction concentration, i.e., a refining treatment concentration, in an economical and practical way. It serves as a bridge to improve the economy of the overall helium extraction process, and then uses mature and reliable methods (such as adsorption method, etc.) to extract helium and obtain refined products in a more economical way.

[0032] In one of the preferred embodiments, the centrifugal unit includes several gas centrifuges installed in cascade, the proximal output end of the previous stage gas centrifuge is connected to the input end of the next stage gas centrifuge, the purified and impurity-free raw natural gas is input from the input end of the first stage gas centrifuge, and the proximal output gas flow is processed in sequence by several stages of gas centrifuges to increase the helium concentration of the final proximal output gas flow.

[0033] In one preferred embodiment, the volume concentration of helium when the proximal output gas flow reaches the refining concentration is C 氦 ≥7%, meeting the minimum concentration requirement of non-cryogenic method.

[0034] In one of the preferred embodiments, the refining process is an adsorption method, which is mature and reliable and ensures the economy of the process.

[0035] In one preferred embodiment, the near-wall output gas flow of the centrifugal unit is collected as a by-product. The near-wall output gas flow 201 is a helium-depleted natural gas gas flow from which helium is removed, which does not affect the normal use of natural gas and further reduces the process cost.

[0036] In one of the preferred embodiments, a uranium enrichment centrifuge is used as the gas centrifuge in the centrifugal unit of this embodiment. According to relevant information, the uranium compounds used in the uranium enrichment process have characteristics such as highly toxic and highly corrosive, which puts forward extremely high performance requirements for the uranium enrichment centrifuge, resulting in special structural materials, harsh operating conditions, high construction difficulty and high cost for the uranium enrichment centrifuge. However, the gas centrifuge used in the centrifugal unit of the present invention does not need to use special materials, has low operating difficulty and low construction cost, and is highly advanced;

[0037] According to the principle of centrifugal separation operation, use the same centrifuge, control the centrifuge specifications and environmental parameters to keep the same, and calculate the centrifugal separation efficiency according to the formula:

[0038]

[0039] Where, M1 is the molar mass of the substance in the near-axis output airflow, M2 is the molar mass of the substance in the near-wall output airflow, r1 is the rotation radius of the near-axis output end on the centrifuge cross section, r2 is the rotation radius of the near-wall output end on the centrifuge cross section, and ω is the angular velocity of the centrifuge;

[0040] The centrifugal separation coefficient α1 for separation of enriched uranium (taking uranium hexafluoride as an example) and the centrifugal separation coefficient α2 for separation of helium from low-grade natural gas can be calculated as follows:

[0041]

[0042]

[0043] If the two have the same centrifugal efficiency, that is, α1 = α2, we can deduce:

[0044] ω1=2ω2,

[0045] That is, when the angular velocity of a gas centrifuge used to separate helium from low-grade natural gas is only half of that of a uranium enrichment centrifuge, the two centrifuges have the same separation efficiency.

[0046] According to the power formula of rotating machinery:

[0047]

[0048] According to the gas state equation:

[0049] pV=nRT,

[0050]

[0051] In the formula, m is the mass of the separated mixture, M is the molar mass of the separated mixture, R is the radius of the centrifuge, V is the volume of the centrifuge, p is the working pressure of the centrifuge, and T is the working temperature of the centrifuge.

[0052]

[0053] Therefore, using the same centrifuge, under the same conditions such as gas temperature, we can get P∝Mω 2 The power of the uranium enrichment centrifuge is P1, and the power of the centrifuge used to separate helium from low-quality natural gas is P2. At this time, P1 / P2 = 44. In other words, under the same centrifugal separation efficiency, the power required to separate helium from low-quality natural gas is only 1 / 44 of the power required for uranium enrichment.

[0054] In summary, if the two centrifuges have the same separation efficiency, the power required by the gas centrifuge for extracting helium from low-quality natural gas is much less than that of the uranium enrichment centrifuge. When the centrifuge speeds are the same, the centrifugal separation efficiency of separating helium from low-quality natural gas is more than 8,000 times that of the uranium enrichment centrifuge.

[0055] A system for implementing a process for extracting helium from low-grade natural gas, comprising:

[0056] The gas washing and purification unit 100 is used to purify and remove impurities from the natural gas;

[0057] The centrifugal enrichment unit 200 is used to centrifugally purify the natural gas after impurities are removed, and obtain a near-axial output gas flow 202 with a helium concentration reaching a refining treatment concentration;

[0058] And a refining processing unit 300 is used for refining the proximal output gas flow 202 to obtain a high-purity helium product.

[0059] In one preferred embodiment, the centrifugal enrichment unit 200 includes a plurality of gas centrifuges 210 installed in cascade, the input end of the first-stage gas centrifuge 210 is connected to the output end of the gas washing and purification unit 100, the input end of the second-stage gas centrifuge 210 is connected to the proximal output end of the adjacent first-stage gas centrifuge 210, and the output end of the last-stage gas centrifuge 210 is connected to the input end of the refining treatment unit 300. Due to the reduction of the flow rate at the proximal output end, the input end of the next-stage gas centrifuge may be connected to the proximal output ends of multiple previous-stage gas centrifuges, that is, an immediate connection installation.

[0060] In one of the preferred embodiments, the refining unit 300 uses an adsorption method to refine the proximal output gas flow. The adsorption method is a mature and reliable helium extraction process, which ensures the economy of the process.

[0061] In one preferred embodiment, a byproduct collection unit is provided at the near-wall output end of the centrifugal enrichment unit 200 for collecting the near-wall output gas flow 201, that is, for collecting the helium-depleted natural gas gas flow from which helium has been removed.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A process for extracting helium from low-quality natural gas, characterized in that: The following steps are involved: Step S1: purifying and removing impurities from the natural gas; Step S2: passing the purified and impurity-removed natural gas through a centrifugal enrichment unit so that the helium concentration of the proximal output gas flow of the centrifugal enrichment unit reaches the refining treatment concentration, and collecting the proximal output gas flow; Step S3: Refining the proximal output gas flow to obtain a high-purity helium product.

2. The process for extracting helium from low-quality natural gas according to claim 1, characterized in that: The centrifugal unit comprises a plurality of gas centrifuges installed in cascade.

3. The process for extracting helium from low-quality natural gas according to claim 1 or 2, characterized in that: When the proximal output gas flow reaches the refining treatment concentration, the volume concentration of helium is C 氦 ≥7%.

4. The process for extracting helium from low-quality natural gas according to any one of claims 1 to 3, characterized in that: The refining process is an adsorption method.

5. The process for extracting helium from low-quality natural gas according to any one of claims 1 to 4, characterized in that: The near-wall output airflow of the centrifugal unit is collected as a by-product.

6. A system for implementing the process of extracting helium from low-quality natural gas as described in any one of claims 1 to 5, characterized in that: include: Gas washing and purification unit, used to purify and remove impurities from natural gas; A centrifugal enrichment unit, used for centrifugally treating and purifying the raw natural gas after impurities removal, and obtaining a near-axial output gas flow with a helium concentration reaching a refining treatment concentration; And a refining processing unit is used for refining the proximal output gas flow to obtain a high-purity helium product.

7. The system according to claim 6, characterized in that The centrifugal enrichment unit comprises a plurality of gas centrifuges installed in cascade, wherein the input end of the first-stage gas centrifuge is connected to the output end of the gas washing and purification unit, the input end of the second-stage gas centrifuge is connected to the proximal output end of the gas centrifuge of the adjacent previous stage, and the output end of the last-stage gas centrifuge is connected to the input end of the refining processing unit.

8. The system according to claim 6 or 7, characterized in that: The refining processing unit refines and processes the proximal output airflow by an adsorption method.

9. The system according to any one of claims 6 to 8, characterized in that: A byproduct collection unit is arranged at the output end near the wall of the centrifugal enrichment unit.

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