Natural gas purification method and device based on propane replacement process and working method of natural gas purification device

Abstract

The invention relates to the technical field of pressure swing adsorption gas separation, and provides a natural gas purification method for realizing synchronous separation of methane, ethane and propane based on a propane replacement process, which comprises the following steps: S1, adsorption; removing ethane and propane in the natural gas by adopting an adsorption method to obtain a purified methane product gas; s2, propane replacement: after adsorption is completed, using propane to replace ethane in the adsorption bed; and S3, depressurization desorption: desorbing propane from the adsorption bed by using a vacuum pump to complete the regeneration of the adsorption bed. The invention also provides a device for purifying methane from natural gas by using the method and a working method of the device. The device for purifying natural gas is flexible and convenient to operate, low in cost and good in effect. On the premise of ensuring safety and stability, products with methane concentration of more than or equal to 99%, ethane concentration of more than or equal to 95% and propane concentration of more than or equal to 99% can be obtained, and the comprehensive yield of methane, ethane and propane is ensured to be more than or equal to 90%.

Description

Technical Field

[0001] This invention relates to the field of pressure swing adsorption gas separation technology, and in particular to a method, apparatus and working method of natural gas purification based on propane displacement process. Background Technology

[0002] Among various energy sources, natural gas, with its relatively abundant reserves in nature and superior eco-friendly characteristics compared to oil and coal, has become one of the most widely used energy forms. While the main component of natural gas is methane (CH4), it usually also contains a certain proportion of ethane (C2H6, 0-20%) and propane (C3H8, 0-5%). To improve the quality of natural gas, these associated components need to be recovered separately. The recovered ethane and propane can be converted into C2H4 and C3H6 through catalytic dehydrogenation reactions, thus serving as key raw materials for the production of various plastic products such as polyethylene, polyvinyl chloride, and polypropylene, and possessing significant industrial value.

[0003] Currently, the main technologies for industrial natural gas purification include cryogenic separation, solvent absorption, and membrane separation. However, these methods suffer from drawbacks such as high energy consumption and low separation efficiency. In particular, methane is highly similar to ethane and propane in various physicochemical properties, which means that there is currently a lack of both highly efficient adsorption materials and advanced separation technologies to achieve efficient purification of methane from natural gas and thus separate all the effective components from the natural gas one by one. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a natural gas purification method and apparatus based on propane replacement process to achieve simultaneous separation of methane, ethane and propane. By using propane replacement, after the adsorbent adsorption is completed, propane is injected into the adsorption tower from the inlet end of the adsorption tower to replace the ethane in the adsorption tower. Then, the adsorbent is desorbed by vacuum to recover the propane, thereby achieving efficient purification of methane in natural gas and separating all the effective components in natural gas one by one.

[0005] This invention relates to a natural gas purification method based on a propane displacement process for simultaneous separation of methane, ethane, and propane, comprising the following steps: S1. Adsorption: Ethane and propane are removed from natural gas by adsorption to obtain purified methane product gas. S2, Propane Replacement: After adsorption is complete, propane is used to replace ethane in the adsorption bed; S3. Depressurization desorption: Propane is desorbed from the adsorption bed using a vacuum pump, thus completing the regeneration of the adsorption bed.

[0006] The present invention also provides an apparatus for the above-mentioned natural gas purification method based on propane replacement process to achieve simultaneous separation of methane, ethane and propane, comprising a compressor, an inlet buffer tank, several adsorption towers, several inlet programmable valves, several vacuum programmable valves, a vacuum pump, several propane replacement programmable valves, several ethane programmable valves, several pressure equalization programmable valves, several product gas programmable valves, a methane product gas buffer tank, a propane product gas buffer tank, an ethane product gas buffer tank, and a product gas flow regulating valve; One end of the air intake buffer tank is connected to the compressor, and the other end is connected to the air intake pipe of the adsorption tower through an air intake programmable valve; One end of the vacuum pump is connected to the adsorption tower inlet pipe via a vacuum programmable valve, and the other end of the vacuum pump is connected to the propane product gas buffer tank. One end of the equalizing control valve is connected to the adsorption tower, and the other end is connected to other equalizing control valves through the same pipeline. One end of the product gas control valve is connected to the gas outlet pipe of the adsorption tower, and the other end is connected to the methane product gas buffer tank. The methane product gas buffer tank is also connected to the product gas flow regulating valve. One end of the propane replacement programmable valve is connected to the inlet pipe of the adsorption tower, and the other end is connected to the propane product gas buffer tank through a pipeline. One end of the ethane programmable valve is connected to the gas outlet pipe of the adsorption tower, and the other end is connected to the ethane product gas buffer tank. The adsorption tower is filled with adsorbent.

[0007] Furthermore, the adsorbent is one of carbon molecular sieve, zeolite molecular sieve, or MOF.

[0008] Furthermore, each of the adsorption towers sequentially undergoes adsorption, pressure equalization, propane replacement, vacuuming, pressure equalization and pressure increase processes.

[0009] The present invention also provides a method for operating a single adsorption tower in the device, comprising the following steps: (1) The raw material gas is compressed by the compressor and flows into the adsorption tower through the inlet buffer tank and the inlet programmable valve. After the adsorbent in the adsorption tower adsorbs the strong adsorption components ethane and propane in the raw material gas, the separated methane-rich gas is used as product gas and enters the methane product gas buffer tank through the product gas programmable valve to complete the adsorption steps of the adsorption tower. (2) After adsorption is completed, close the inlet gas control valve and the product gas control valve, open the pressure equalization control valve, connect the adsorption tower that needs pressure equalization and the adsorption tower that has completed the adsorption step, and equalize the pressure drop of this adsorption tower. (3) After the pressure drop is equalized, the equalization control valve is closed and the propane replacement control valve and ethane control valve are opened. Propane flows into the adsorption tower through the propane replacement control valve, and the replaced ethane gas enters the ethane product gas buffer tank through the ethane control valve. Before propane penetration, the propane gas inlet is stopped. (4) After the replacement is completed, close the propane replacement control valve and the ethane control valve, open the vacuum control valve and the vacuum pump to evacuate the adsorption tower and depressurize it. The propane in the adsorption tower is extracted from the adsorption tower through the vacuum control valve under the action of the vacuum pump and enters the propane product gas buffer tank. (5) After the vacuuming is completed, open the pressure equalization control valve to connect the adsorption tower that needs pressure equalization and the adsorption tower that has completed the vacuuming, so as to realize the pressure equalization and rise operation of the adsorption tower. (6) Open the product gas process control valve to connect this adsorption tower with the adsorption tower that is currently adsorbing and perform a pressurization operation; (7) After the boosting operation is completed, return to step (1) and repeat the cycle.

[0010] Furthermore, the adsorption pressure in step (1) is maintained at 0.1 MPa to 2.0 MPa; In step (3), the displacement pressure is maintained at 0.1 MPa; In step (4), the desorption pressure is not lower than 0.01 MPa.

[0011] The beneficial technical effects of the present invention are as follows: (1) In natural gas purification, the method of this patent can obtain products with methane concentration ≥99%, ethane concentration ≥95% and propane concentration ≥99%. Through the synergistic effect of steps such as adsorption, propane replacement and depressurization desorption, ethane and propane are effectively separated from natural gas, thereby achieving high-purity purification of methane.

[0012] (2) This patent ensures that the overall yield of methane, ethane and propane is ≥90%. This effect indicates that most of the main effective components (methane, ethane and propane) in natural gas are recovered and utilized throughout the separation process. Compared with some traditional separation technologies that may result in a large loss of effective components, this patent improves product purity while minimizing the waste of effective components and increasing the overall utilization rate.

[0013] (3) This application uses a single adsorbent (which may be carbon molecular sieve, zeolite molecular sieve or MOF). These adsorbents are relatively common and may be low in cost. Moreover, the entire process does not require complex low-temperature equipment like cryogenic separation, nor does it rely on special membrane materials like membrane separation, thus reducing costs.

[0014] (4) The device of this patent includes a compressor, an inlet buffer tank, four adsorption towers, multiple programmable valves (inlet programmable valve, vacuum programmable valve, propane replacement programmable valve, ethane programmable valve, pressure equalization programmable valve, and product gas programmable valve), multiple product gas buffer tanks (methane product gas buffer tank, ethane product gas buffer tank, and propane product gas buffer tank), and product gas flow regulating valves, vacuum pumps, etc. All the equipment is connected by reasonable pipelines and valves, forming a complete natural gas purification system. All components in the device work collaboratively. The adsorbent in the adsorption tower can adsorb ethane and propane from natural gas, achieving preliminary purification of methane; the programmable valve can precisely control the direction and flow rate of the gas, ensuring the smooth progress of each process step (such as adsorption, pressure equalization, propane replacement, and depressurization desorption); the product gas buffer tank can collect methane, ethane, and propane product gases separately for subsequent processing and use; the vacuum pump plays a key role in the depressurization desorption step, desorbing propane from the adsorption bed and regenerating the adsorption bed, thereby ensuring the sustainability of the entire purification process. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of an apparatus for a natural gas purification method that simultaneously separates methane, ethane, and propane based on a propane displacement-assisted process.

[0016] In the diagram: 1 - Compressor; 2-Intake buffer tank; 3-Intake control valve, 31-Intake control valve I, 32-Intake control valve II, 33-Intake control valve III, 34-Intake control valve IV; 4-Vacuum programmable valve, 41-Vacuum programmable valve I, 42-Vacuum programmable valve II, 43-Vacuum programmable valve III, 44-Vacuum programmable valve IV; 5-Adsorption tower, 51-Adsorption tower I, 52-Adsorption tower II, 53-Adsorption tower III, 54-Adsorption tower IV; 6-Product air control valve, 61-Product air control valve I, 62-Product air control valve II, 63-Product air control valve III, 64-Product air control valve IV; 7-Equalizing control valve, 71-Equalizing control valve I, 72-Equalizing control valve II, 73-Equalizing control valve III, 74-Equalizing control valve IV; 8-Propane replacement control valve, 81-Propane replacement control valve I, 82-Propane replacement control valve II, 83-Propane replacement control valve III, 84-Propane replacement control valve IV; 9-Ethane programmable valve, 91-Ethane programmable valve I, 92-Ethane programmable valve II, 93-Ethane programmable valve III, 94-Ethane programmable valve IV; 10-Methane product gas buffer tank; 11-Ethane product gas buffer tank; 12-Propane product gas buffer tank; 13-Product gas flow regulating valve; 14-Vacuum pump. Detailed Implementation

[0017] Example 1 A natural gas purification method based on a propane displacement-assisted process for simultaneous separation of methane, ethane, and propane includes the following steps: Step 1, Adsorption: Ethane and propane are removed from natural gas in an adsorption tower using an adsorption method to obtain purified methane product gas; Step 2, Propane Replacement: After adsorption is complete, propane replacement is used to remove ethane from the adsorption tower. Step 3, depressurization desorption: In order to further recover propane in the adsorption tower, vacuum pump 14 is used to desorb propane from the adsorption bed, thus completing the regeneration of the adsorption bed.

[0018] Natural gas flows into the adsorption tower under high pressure. Ethane, propane, and a small amount of methane are adsorbed by the adsorbent. The gas that is not adsorbed by the adsorbent is purified methane product gas and flows out from the exhaust end of the adsorption tower. After the adsorption process is completed, propane is introduced from the inlet end of the adsorption tower, at which point the ethane in the adsorbent gaps and the exhaust end of the adsorption tower is displaced. Before propane breakthrough, the propane intake is stopped, and then the adsorption tower is depressurized and the desorption step is completed.

[0019] In this embodiment, the purified product gas includes methane, ethane and propane, wherein the methane concentration is ≥99%, the ethane concentration is ≥95% and the propane concentration is ≥99%, and the overall yield of methane, ethane and propane is ≥90%.

[0020] Example 2 An apparatus for the above-mentioned natural gas purification method based on propane replacement process to achieve simultaneous separation of methane, ethane and propane includes a compressor 1, an inlet buffer tank 2, four adsorption towers 5, four inlet programmable valves 3, four vacuum programmable valves 4, four propane replacement programmable valves 8, four ethane programmable valves 9, four product gas programmable valves 6, four pressure equalization programmable valves 7, a methane product gas buffer tank 10, a propane product gas buffer tank 12, an ethane product gas buffer tank 11, and a product gas flow regulating valve 13; One end of the air intake buffer tank 2 is connected to the compressor 1, and the other end is connected to the air intake pipe of the adsorption tower through the air intake programmable valve; One end of the vacuum pump 14 is connected to the inlet pipe of the adsorption tower 5 through the vacuum programmable valve 4, and the other end of the vacuum pump 14 is connected to the propane product gas buffer tank 12. One end of the equalizing control valve 7 is connected to the adsorption tower (5), and the other end is connected to other equalizing control valves 7 through the same pipeline. One end of the product gas control valve 6 is connected to the outlet pipe of the adsorption tower 5, and the other end is connected to the methane product gas buffer tank 10. The methane product gas buffer tank 10 is also connected to the product gas flow regulating valve 13. One end of the propane replacement programmable valve 8 is connected to the inlet pipe of the adsorption tower 5, and the other end is connected to the propane product gas buffer tank 12 through a pipeline. One end of the ethane programmable valve 9 is connected to the gas outlet pipe of the adsorption tower 5, and the other end is connected to the ethane product gas buffer tank 11. The adsorption tower 5 is filled with an adsorbent. The adsorbent is a single adsorbent, which is one of carbon molecular sieve, zeolite molecular sieve or MOF.

[0021] In this embodiment, each adsorption tower 5 sequentially performs six steps: adsorption, pressure equalization and reduction, propane replacement, vacuum depressurization and desorption, pressure equalization and increase, and pressure increase.

[0022] When using the apparatus of this embodiment to purify natural gas by simultaneously separating methane, ethane, and propane based on propane replacement-assisted technology, the feed gas is compressed by compressor 1 and flows into adsorption tower 5 through inlet buffer tank 2 and inlet programmable valve. After the adsorbent in adsorption tower 5 adsorbs the strongly adsorbed components ethane and propane in the feed gas, the methane-rich gas flows out from the exhaust end of adsorption tower 5 as product gas through product gas programmable valve 6. After adsorption, pressure equalization programmable valve 7 is opened to equalize the pressure in adsorption tower 5. After pressure equalization, propane flows into adsorption tower 5 through propane replacement programmable valve 8, and the displaced ethane gas flows out from the exhaust end of adsorption tower 5 through ethane programmable valve 9. After replacement, propane replacement programmable valve 8 and ethane programmable valve 9 are closed, and propane in adsorption tower 5 is extracted from adsorption tower 5 by vacuum pump 14 through vacuum programmable valve 4. The pressure equalization process is achieved by pressure equalization programmable valve 7. Propane replacement programmable valve 8 controls the propane replacement step in adsorption tower 5.

[0023] Example 3 The separation process is illustrated using adsorption tower I51 as an example: 1. The raw material gas passes through compressor 1 and inlet buffer tank 2, and enters adsorption tower I51 through inlet programmable valve I31. The unadsorbed methane gas passes through product gas programmable valve I61, methane product gas buffer tank 10, and product gas flow regulating valve 13 before entering the methane product gas pipeline, thus completing the adsorption step. 2. Close the inlet gas control valve I31 and the product gas control valve I61, open the equalizing control valve I71 and the equalizing control valve III73, and connect the adsorption tower I51 and the adsorption tower III53 to complete the equalization of pressure drop. 3. After the pressure equalization is completed, close the pressure equalization control valve I71 and the pressure equalization control valve III73, and open the propane replacement control valve I81 and the ethane control valve I91. The propane replacement gas flows into the adsorption tower I51 through the propane replacement control valve I81 for replacement. The gas replaced is mainly ethane, which flows through the ethane control valve I91 and the ethane product gas buffer tank 11 to the ethane product gas pipeline. 4. Stop the propane replacement step before propane penetration. At this time, close the propane replacement programmable valve I81 and the ethane programmable valve I91, and open the vacuum programmable valve I41 to evacuate the adsorption tower I51. The gas extracted at this time is the propane product gas, which flows to the propane product gas pipeline through the vacuum pump 14 and the propane product gas buffer tank 12. 5. After the vacuuming is completed, open the equalization control valve I71 and the equalization control valve III73; the adsorption tower III53, which has completed the adsorption process, will equalize the pressure of the adsorption tower I51. 6. Open product gas control valve I61 and product gas control valve IV64 to allow some methane product gas to flow from adsorption tower IV54 through product gas control valve I61 and product gas control valve IV64 to adsorption tower I51, thus completing the pressurization step of adsorption tower I51. 7. Repeat step 1.

[0024] The cyclic timing of this process is shown in Table 1.

[0025] Table 1. Cycle Time Sequence Table of Four Adsorption Towers Adsorption Tower I Adsorption Adsorption Adsorption Average decline Replacement Replacement Replacement vacuum vacuum average rise Boost Boost Adsorption Tower II average rise Boost Boost Adsorption Adsorption Adsorption Average decline Replacement Replacement Replacement vacuum vacuum Adsorption Tower III Replacement vacuum vacuum average rise Boost Boost Adsorption Adsorption Adsorption Average decline Replacement Replacement Adsorption Tower IV Average decline Replacement Replacement Replacement vacuum vacuum average rise Boost Boost Adsorption Adsorption Adsorption In this embodiment, the natural gas composition is 85% CH4 / 10% C2H6 / 5% C3H8. The process parameters in this embodiment are as follows: adsorption pressure is 0.1 MPa to 2.0 MPa, propane replacement pressure is 0.1 MPa, and minimum desorption pressure is 0.01 MPa. In this embodiment, the purified methane concentration is greater than 99%, ethane concentration is greater than 95%, and propane concentration is greater than 99%, with a combined yield of over 90% for methane, ethane, and propane. In summary, the device of this invention can achieve efficient purification of methane from natural gas while simultaneously recovering high-value hydrocarbons such as ethane and propane.

Claims

1. A natural gas purification method based on propane displacement process for simultaneous separation of methane, ethane, and propane, characterized in that: Includes the following steps: S1. Adsorption: Ethane and propane are removed from natural gas by adsorption to obtain purified methane product gas. S2, Propane Replacement: After adsorption is complete, propane is used to replace ethane in the adsorption bed; S3. Depressurization desorption: Propane is desorbed from the adsorption bed using a vacuum pump, thus completing the regeneration of the adsorption bed.

2. An apparatus for the natural gas purification method based on propane displacement process for simultaneous separation of methane, ethane, and propane as described in claim 1, characterized in that: Includes a compressor (1), an inlet buffer tank (2), several adsorption towers (5), several inlet programmable valves (3), several vacuum programmable valves (4), a vacuum pump (14), several propane replacement programmable valves (8), several ethane programmable valves (9), several equalizing programmable valves (7), several product gas programmable valves (6), a methane product gas buffer tank (10), a propane product gas buffer tank (12), an ethane product gas buffer tank (11), and a product gas flow regulating valve (13); One end of the air intake buffer tank (2) is connected to the compressor (1), and the other end is connected to the air intake pipe of the adsorption tower (5) through the air intake program control valve (3); One end of the vacuum pump (14) is connected to the inlet pipe of the adsorption tower (5) through the vacuum programmable valve (4), and the other end of the vacuum pump (14) is connected to the propane product gas buffer tank (12). One end of the equalizing control valve (7) is connected to the adsorption tower (5), and the other end is connected to other equalizing control valves (7) through the same pipeline; One end of the product gas process control valve (6) is connected to the gas outlet pipe of the adsorption tower (5), and the other end is connected to the methane product gas buffer tank (10). The methane product gas buffer tank (10) is also connected to the product gas flow regulating valve (13). One end of the propane replacement programmable valve (8) is connected to the inlet pipe of the adsorption tower (5), and the other end is connected to the propane product gas buffer tank (12) through a pipeline; One end of the ethane programmable valve (9) is connected to the gas outlet pipe of the adsorption tower (5), and the other end is connected to the ethane product gas buffer tank (11); The adsorption tower (5) is filled with adsorbent.

3. The apparatus for a natural gas purification method based on propane replacement process for simultaneous separation of methane, ethane, and propane, as described in claim 2, is characterized in that: The adsorbent is one of carbon molecular sieve, zeolite molecular sieve or MOF.

4. The apparatus for a natural gas purification method based on propane replacement process for simultaneous separation of methane, ethane, and propane, as described in claim 2, is characterized in that: Each adsorption tower (5) sequentially undergoes adsorption, pressure equalization, propane replacement, vacuuming, pressure equalization and pressure increase processes.

5. A method of operating a single adsorption tower in the apparatus according to any one of claims 2-4, characterized in that: Includes the following steps: S1. The raw material gas is compressed by the compressor (1) and flows into the adsorption tower (5) through the inlet buffer tank (2) and the inlet programmable valve (3). After the adsorbent in the adsorption tower (5) adsorbs the strong adsorption components ethane and propane in the raw material gas, the separated methane-rich gas is used as product gas and enters the methane product gas buffer tank (10) through the product gas programmable valve (6) to complete the adsorption step of the adsorption tower (5). S2. After adsorption is completed, close the inlet control valve (3) and the product gas control valve (6), open the equalization control valve (7), connect the adsorption tower (5) that needs to equalize the pressure and the adsorption tower (5) that has completed the adsorption step, and equalize the pressure drop of this adsorption tower (5). S3. After the pressure drop is equalized, the equalization control valve (7) of the adsorption tower (5) is closed, and the propane replacement control valve (8) and the ethane control valve (9) are opened. Propane flows into the adsorption tower (5) through the propane replacement control valve (8), and the ethane gas that is replaced enters the ethane product gas buffer tank (11) through the ethane control valve (9). Before propane penetration, the propane gas intake is stopped. S4. After the replacement is completed, close the propane replacement control valve (8) and the ethane control valve (9), open the vacuum control valve (4) and the vacuum pump (14) to evacuate the adsorption tower (5) to reduce pressure and desorb. Under the action of the vacuum pump (14), the propane in the adsorption tower (5) is extracted from the adsorption tower (5) through the vacuum control valve (4) and enters the propane product gas buffer tank (12). S5. After the vacuuming is completed, open the equalization control valve (7) to connect the adsorption tower (5) that needs equalization and the adsorption tower (5) that has completed the vacuuming, and perform equalization and pressure increase operation on the adsorption tower (5). S6. Open the product gas control valve (6) to connect this adsorption tower (5) with the adsorption tower (5) that is currently adsorbing, and perform a pressurization operation. S7. After completing the boost operation, repeat step (1) to cycle through the process.

6. The method of operating a single adsorption tower in the apparatus according to claim 5, characterized in that: The adsorption pressure of S1 is maintained between 0.1 MPa and 2.0 MPa; The displacement pressure in S3 is maintained at 0.1 MPa; The desorption pressure in S4 is not lower than 0.01 MPa.

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