CN114317052A - High-efficiency separation and purification method for low-concentration coal bed gas - Google Patents
High-efficiency separation and purification method for low-concentration coal bed gas Download PDFInfo
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- CN114317052A CN114317052A CN202111623990.0A CN202111623990A CN114317052A CN 114317052 A CN114317052 A CN 114317052A CN 202111623990 A CN202111623990 A CN 202111623990A CN 114317052 A CN114317052 A CN 114317052A
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Abstract
The invention belongs to the field of industrial gas separation and purification, and particularly relates to a method for efficiently separating and purifying low-concentration coal bed gas4Removing most of N2And O2In the second stage, CH is concentrated by means of displacement pressure-swing adsorption process4And obtaining the product with the methane concentration more than or equal to 90 percent. The method can obtain the product with the methane concentration of more than or equal to 90 percent on the premise of ensuring safety and stability, and the comprehensive yield of methane is more than or equal to 90 percent.
Description
Technical Field
The invention belongs to the field of industrial gas separation and purification, relates to gas separation and purification technologies in coal chemical industry, natural gas chemical industry and other fields, and particularly relates to a high-efficiency separation and purification method for low-concentration coal bed gas.
Background
The reserve of Chinese coal bed gas is equivalent to that of natural gas, and the geological resource quantity of the coal bed gas which is in the third world and deeply buried within 2000m is about 36.8 trillion m3Coal bed gas has attracted attention as the most realistic and reliable natural gas supplement. Because the explosion limit of methane is 5-15%, coal mine safety regulations require that coal bed gas with the concentration below 30% (low-concentration coal bed gas) cannot be utilized. Almost all coal mines vent coal bed gas with methane concentrations below 30% directly into the atmosphere. And more than 70% of the coal bed gas in China is low-concentration coal bed gas with the methane concentration of less than 30%.
Pressure Swing Adsorption (PSA) gas separation and purification technology utilizes the difference of Adsorption characteristics such as equilibrium Adsorption capacity and Adsorption rate of gas components on an adsorbent and the characteristic that the Adsorption capacity changes with Pressure to realize the alternation of Adsorption and desorption processes through periodic Pressure change, thereby realizing the separation or purification of gas, belonging to the physical process and being capable of realizing the separation or purification at normal temperature.
The conventional pressure swing adsorption separation of methane and nitrogen mostly uses combustible carbonaceous adsorbents, and because the oxygen content in the coal bed gas is higher, the carbonaceous adsorbents are easy to be ignited due to local temperature rise of a bed layer in production, so that serious potential safety hazards are brought. The concentration of the coal bed gas, especially the purification of the low-concentration coal bed gas, always has great difficulty.
The coal bed gas mainly comprises CH4、N2、O2Is CH4Mixed gas with air. Purification of CH using pressure swing adsorption technology4The adsorbent can be selected from activated carbon, carbon molecular sieve, molecular sieve and other adsorbents, and because combustible and explosive gas is contacted with the adsorbent in the adsorption tower in the purification process, the carbon-based adsorbent has a combustion-supporting effect, and the zeolite molecular sieve has a flame-retardant effect. The raw material gas does not contain O2Is used for separating CH4And N2Can select carbon-based absorptionAnd (4) an auxiliary agent. Because the coal bed gas contains O2For safety reasons, the adsorbent is selected to be a zeolite molecular sieve with flame retardant properties.
In the zeolite molecular sieve adsorbent, the average adsorption amount of CH4 of the common 5A molecular sieve is about 16.91ml/g, but the CH4-N2The separation factor is only 1.5 and can be used for separating CH4And N2But CH4Concentration and yield are not ideal and are not feasible, so that the development of a novel molecular sieve adsorbent is needed.
Disclosure of Invention
Aiming at the defects and shortcomings of the existing technology for purifying methane from low-concentration coal bed gas, the invention aims to provide the efficient separation and purification method for methane in low-concentration coal bed gas, the method can obtain products with the methane concentration of more than or equal to 90% on the premise of ensuring safety and stability, and the comprehensive yield of methane is more than or equal to 90%.
In order to achieve the technical effects, the specific technical scheme of the invention is as follows:
a process for efficiently separating and purifying low-concentration coalbed methane includes two-stage pressure-varying adsorption, and the first stage for concentrating CH by vacuumizing pressure-varying adsorption4Removing most of N2And O2In the second stage, CH is concentrated by means of displacement pressure-swing adsorption process4And obtaining the product with the methane concentration more than or equal to 90 percent.
As a preferred embodiment in the present application, the two-stage pressure swing adsorption method specifically comprises: the first section removes partial oxygen and nitrogen by pressure swing adsorption under low pressure, and the adsorbed methane is desorbed by evacuation, so that the obtained concentrated gas is not in the explosion limit, and the compression safety can be ensured; then the mixture enters a second section of pressure swing adsorption after compression and is concentrated, the purity of methane in the adsorption tower is concentrated through a replacement process, and finally a product with the methane concentration being more than or equal to 90 percent is obtained through evacuation; the displaced waste gas returns to the PSA inlet of the first section, the methane yield is improved, and the comprehensive methane yield is more than or equal to 90 percent.
As a preferred embodiment of the present invention, the first-stage pressure swing adsorption employs a continuously operated pressure swing adsorption system consisting of 3 or more adsorption towers, and each adsorption tower sequentially undergoes the steps of adsorption (a), multiple pressure Equalization (EiD), reverse pressure release (D), evacuation (V), multiple pressure Equalization (EiR), and final pressure increase (FR) in one cycle. Part of oxygen and nitrogen are removed by pressure swing adsorption under low pressure, and the adsorbed methane is desorbed by evacuation, so that the purity of the obtained semi-product concentrated gas is not within the explosion limit, and the compression safety can be ensured.
As a better implementation mode in the application, the adsorption pressure of the first stage pressure swing adsorption is 0.05-0.4 MPa (G), and the operation temperature of the pressure swing adsorption is 5-60 ℃.
As a preferred embodiment of the present invention, the second-stage pressure swing adsorption employs a continuously operating pressure swing adsorption system composed of 3 or more adsorption towers, and each adsorption tower sequentially undergoes the steps of adsorption (a), multiple pressure Equalization (EiD), displacement (RP), reverse pressure release (D), evacuation (V), multiple pressure Equalization (EiR), and final pressure increase (FR) in one cycle. The methane concentration in the adsorption tower is increased by a replacement process, and finally, a product with the methane concentration more than or equal to 90% is obtained by evacuation. The replacement waste gas returns to the inlet of the first PSA raw gas compressor to improve the methane yield, so that the comprehensive methane yield is more than or equal to 90 percent.
As a preferred embodiment of the present application, the adsorption pressure of the second stage of pressure swing adsorption is 0.2-2.0 MPa (G), and the operation temperature of the pressure swing adsorption is 5-60 ℃.
As a preferred embodiment of the present application, the adsorbent used in the first and second stages of pressure swing adsorption is CH4/N2The adsorbent is a non-carbonaceous molecular sieve adsorbent, has good hydrophobicity and flame retardance, can effectively solve the problem that saturated water contained in coal bed gas in the separation and purification process affects the performance of the adsorbent and gas components in the separation process are flammable and explosive, and ensures the safety and stability of the system.
As a preferred embodiment of the present application, the above-mentioned adsorbent is prepared by the following steps: mixing sodium hydroxide, tetrapropylammonium hydroxide, silica sol and deionized water, stirring and aging at room temperature, putting into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal treatment, cooling, fully washing with deionized water, filtering, drying, and roasting in an air atmosphere to obtain the catalyst.
In a preferred embodiment of the present invention, the molar ratio of sodium hydroxide, tetrapropylammonium hydroxide, silica sol and deionized water is 1: 35-46: 20-30: 600-800, wherein the silica sol is silica.
As a preferred embodiment in the present application, the aging time is 5 hours; the hydrothermal treatment conditions are that the temperature is 150-200 ℃, and the hydrothermal treatment time is 12-24 h.
As a preferred embodiment in this application, the number of deionized water washes is 3; the drying conditions were 80 ℃ for 24 hours.
As a better implementation mode in the application, the roasting condition is 500-700 ℃ for 24 hours.
As a preferred embodiment in this application, the methane content of the adsorption off-gas, the displacement off-gas, the semi-product gas and the product gas in the two-stage pressure swing adsorption are not within the explosive limits.
As a better implementation mode in the application, the method is suitable for separating and purifying CH in the coal bed gas by pressure swing adsorption gas4The field of the technology.
Compared with the prior art, the positive effects of the invention are as follows:
the method comprises the following steps of (I) solving the problem that saturated water contained in the coal bed gas influences the performance of the adsorbent in the separation and purification process by using a hydrophobic adsorbent, and ensuring the stability of the separation performance.
And (II) by using the flame-retardant non-carbon molecular sieve adsorbent, the problem that gas components are flammable and explosive in the separation process is solved under the condition that explosion suppression materials are not additionally arranged in equipment and pipelines, and the safety and stability of the system are ensured.
(III) by using CH4/N2、CH4/O2The adsorbent with high separation coefficient can obtain high-purity natural gas product.
(IV) by using a two-stage pressure swing adsorption process, after the first stage of pressurization, concentrating CH by a vacuum pressure swing adsorption process4Removing most of N2And O2In the second stage, CH is concentrated by means of displacement pressure-swing adsorption process4To obtain CH4The purity is more than or equal to 90 percent.
(V) increasing CH by partial waste gas pressurization and return in the second stage4The yield is more than or equal to 90 percent of the comprehensive yield of the system.
And (VI) by using a two-stage pressure swing adsorption process, the methane contents of the adsorption waste gas (nitrogen-rich gas), the replacement waste gas, the semi-product gas and the product gas of the pressure swing adsorption system are not within the explosion limit.
Drawings
FIG. 1 is a flow chart of a method for efficiently separating and purifying low-concentration coal bed gas according to the present invention
FIG. 2 is a flow chart of PSA1 process in EXAMPLE 1 of the present invention
FIG. 3 is a flow chart of PSA2 process in EXAMPLE 1 of the present invention
Detailed Description
The present invention will be described in further detail below by way of specific examples, but it should not be construed that the scope of the above-described subject matter of the present invention is limited to the following examples. Various substitutions and alterations made on the basis of the general knowledge and the conventional means in the art without departing from the technical idea of the invention as described above are intended to be included in the scope of the invention.
All% described in the present application mean volume percentage, i.e., v%, unless otherwise specified.
Example 1: preparation of adsorbent No. 1
Mixing sodium hydroxide, tetrapropylammonium hydroxide, silica sol (calculated by silicon dioxide) and deionized water according to the molar ratio of 1: 40: 20: 600, stirring and aging for 5 hours at room temperature, then filling the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, carrying out hydrothermal treatment for 14 hours at the temperature of 150 ℃, fully washing the mixture for 3 times by using the deionized water after cooling, filtering and drying the mixture for 24 hours at the temperature of 80 ℃, and then roasting the dried mixture for 24 hours at the temperature of 550 ℃ in an air atmosphere to obtain the molecular sieve adsorbent.
Example 2:
preparation of adsorbent No. 2
Mixing sodium hydroxide, tetrapropylammonium hydroxide, silica sol (calculated by silicon dioxide) and deionized water according to the molar ratio of 1: 42: 25: 650, stirring and aging for 5 hours at room temperature, then filling the mixture into a polytetrafluoroethylene-lined high-pressure reaction kettle, carrying out hydrothermal treatment for 18 hours at the temperature of 160 ℃, fully washing the mixture for 3 times by using the deionized water after cooling, filtering and drying the mixture for 24 hours at the temperature of 80 ℃, and then roasting the dried mixture for 24 hours at the temperature of 600 ℃ in an air atmosphere to obtain the molecular sieve adsorbent.
Example 3:
preparation of adsorbent No. 3
Mixing sodium hydroxide, tetrapropylammonium hydroxide, silica sol (calculated by silicon dioxide) and deionized water according to the molar ratio of 1: 42: 30: 800, stirring and aging for 5 hours at room temperature, then putting into a polytetrafluoroethylene-lined high-pressure reaction kettle, carrying out hydrothermal treatment for 20 hours at the temperature of 180 ℃, cooling, fully washing for 3 times by using deionized water, filtering, drying for 24 hours at the temperature of 80 ℃, and then roasting for 24 hours at the temperature of 700 ℃ in an air atmosphere to obtain the molecular sieve adsorbent.
The molecular sieve adsorbents prepared in examples 1 to 3 were subjected to adsorption amount tests, and the results were as follows:
adsorption capacity under pressure of 7-100kPa
| Molecular sieve adsorbent | N2Adsorption capacity (ml/g) | CH4(ml/g) | O2(ml/g) |
| 1# | 3.15 | 10.5 | 3.14 |
| 2# | 3.3 | 11.1 | 3.15 |
| 3# | 3.35 | 11.15 | 3.15 |
Through tests, the bulk specific gravity of the molecular sieve adsorbent prepared in the application is 1.3-1.5 times that of the activated carbon adsorbent, and CH is obtained4-N2/O2Separation factor 3.33, CH4The equilibrium adsorption capacity is 11.08ml/g, and the catalyst has hydrophobicity and is used for separating and purifying CH from coal bed gas4The preferred adsorbent of (1).
Example 4:
the adsorbents used in the first and second stages of pressure swing adsorption were obtained according to the method of example 2.
CH in raw material gas (coal bed gas)4Content-25%, N2Content of-60%, O2The content is 15 percent, the pressure is normal pressure, and the temperature is 20 to 40 ℃.
The raw material gas is compressed to 0.25MPa (G) by a raw material gas compressor under normal pressure and then enters a 4-tower PSA1 system. The PSA1 system consists of 1 gas-liquid separator, 4 adsorption columns, 2 stripping gas buffer tanks and a series of program control valves (see fig. 2 for a process flow diagram). In PSA1 system, one adsorber is always in different stages of adsorption step at any time, raw material is introduced from inlet end, nitrogen-rich gas obtained from outlet end is sent out, and adsorbed CH is obtained4The semi-product gas compressor after desorption is obtained by reverse discharge and evacuation, and the rest adsorbers are in different stages of regeneration.
The PSA1 desorption gas (semi-product gas) is compressed by a semi-product gas compressor to 0.4MPa (G) and enters a 6-tower PSA2 system. PSA2The system consists of 6 adsorbers, 1 displacement waste gas buffer tank, 2 product gas buffer tanks and a series of program control valves (the process flow chart is shown in figure 3). In a PSA2 system, one adsorber is always in different stages of adsorption step at any time, raw material is introduced from inlet end, nitrogen-rich gas obtained from outlet end is sent out, part of product gas is returned to adsorber by blower for replacement, replaced waste gas is returned to inlet of raw material gas compressor, adsorbed CH4The desorbed product is obtained by reverse discharge and evacuation and is output to the outside as a product.
Table 1: PSA1 operating schedule
The operating process of the PSA1 system is shown in Table 1, and the specific process is as follows:
1. an adsorption (A) step: the raw material gas is compressed to 0.25MPa (G) by a raw material gas compressor under normal pressure, most of water is removed by a gas-liquid separator, and then the raw material gas enters a PSA1 adsorption tower under the conditions of 0.25MPa (G) and the temperature of less than or equal to 40 ℃, and CH in the raw material gas4Weakly adsorbed component (N) adsorbed by the adsorbent2、O2) And part of CH4Delivering the mixture from the upper part of the adsorption tower to a boundary area;
2. pressure drop (EiD) step: after the step (A) of adsorption is completed, opening a pressure equalizing program control valve, transferring the adsorbent gap in the tower and the gas components adsorbed by the adsorbent to an adsorption tower with increased pressure, closing the pressure equalizing program control valve after the pressure increase is basically equal to the pressure of the pressure reduction adsorption tower, and uniformly reducing the pressure of PSA1 for 1 time;
3. and (D) reversely releasing pressure: after the step of equalizing and dropping (EiD) is finished, the adsorption tower adsorbs CH by the adsorbent4The concentration reaches the requirement of semi-product gas, and the semi-product gas is discharged through a reverse-discharge program control valve at the bottom of the adsorption tower and enters a desorption gas buffer tank A;
4. evacuation (V) step: for further recovery of CH adsorbed in the adsorbent4Using a vacuum pump to pump CH4Desorbing from the adsorbent, pumping air into the desorption gas buffer tank B to mix with the reverse-discharge gas discharged from the desorption gas buffer tank AThe obtained product is used as semi-product gas and sent to a semi-product gas compressor;
5. a pressure rising (EiR) step, which corresponds to the pressure falling (EiD) step, wherein after the step of evacuating (V) is completed, the pressure of the adsorption tower ending the step of evacuating (V) is uniformly raised by using the gas in the step of pressure falling (EiD), and the pressure of PSA1 is uniformly raised by 1 time;
6. final boost (FR) step: because the pressure of the adsorption tower can not reach the adsorption pressure through the pressure rising (EiR) step, the nitrogen-rich gas discharged from the top of the adsorption tower needs to be used for increasing the pressure from the top of the adsorption tower to reach the adsorption operation pressure, and after the pressure of the adsorption tower is increased to reach the adsorption operation pressure, the adsorption tower enters the next cycle process according to the operation program.
Each adsorption tower passes through the same step sequence, and only the process steps are staggered with each other by a sub-period in operation so as to ensure that the separation process is continuously carried out.
Table 2: PSA2 operating schedule
The operating process of the PSA2 system is shown in Table 2, and the specific process is as follows:
1. an adsorption (A) step: PSA1 desorption gas (semi-product gas) is compressed to 0.4MPa by a compressor (G) and enters a PSA2 adsorption tower at the temperature of 20-40 ℃, and CH in the feed gas4Weakly adsorbed component (N) adsorbed by the adsorbent2、O2) And part of CH4Sending the nitrogen-rich gas out of the battery limits;
2. pressure drop (EiD) step: after the step (A) of adsorption is completed, opening a pressure equalizing program control valve, transferring the adsorbent gap in the tower and the gas components adsorbed by the adsorbent to an adsorption tower with increased pressure, closing the pressure equalizing program control valve after the pressure increase is basically equal to the pressure of the adsorption tower with reduced pressure, and completing the pressure reduction of PSA2 for 2 times;
3. replacement (RP) step: after the step of pressure equalizing drop (EiD) is finished, the product gas is used for replacement, partial product gas is boosted by a replacement gas blower and then returns to the adsorption tower to adsorb residual impurities (N) in the adsorbent2、O2) Device for placingAnd (4) exchanging the waste gas to ensure that the product gas adsorbed in the adsorption tower reaches the designed concentration, and exchanging the waste gas to enter the waste gas exchanging buffer tank from the top of the adsorption tower and then return to the feed gas compressor.
4. And (D) reversely releasing pressure: after the Replacement (RP) step is completed, adsorbing CH in the column4The concentration of the product gas reaches the requirement of the product gas, and the product gas is discharged through a reverse-discharge program control valve at the bottom of the adsorption tower and enters a product gas buffer tank;
5. evacuation (V) step: for further recovery of CH adsorbed in the adsorbent4Using a vacuum pump to pump CH4Desorbing from the adsorbent, pumping air into a product gas mixing tank to be mixed with the reverse exhaust gas discharged from the product gas buffer tank to be used as product gas to be discharged;
6. a pressure rising (EiR) step corresponding to the pressure dropping (EiD) step, wherein after the evacuation (V) step is completed, the pressure of the adsorption tower ending the evacuation (V) step is uniformly raised by using the gas in the pressure dropping (EiD) step, and the step is completed in 2 times;
7. final boost (FR) step: because the pressure of the adsorption tower can not reach the adsorption pressure through a plurality of pressure rising (EiR) steps, the nitrogen-rich gas discharged from the top of the adsorption tower needs to be used for increasing the pressure from the top of the adsorption tower to reach the adsorption operation pressure, and when the pressure of the adsorption tower is increased to reach the adsorption operation pressure, the adsorption tower enters the next cycle process according to the operation program.
Each adsorption tower passes through the same step sequence, and only the process steps are staggered with each other by a sub-period in operation so as to ensure that the separation process is continuously carried out.
Example 5:
the adsorbents used in the first and second stages of pressure swing adsorption were obtained according to the method in example 3.
CH in raw material gas (coal bed gas)4Content 20% N2Content of-64%, O2The content is 16 percent, the pressure is normal pressure, and the temperature is 20 to 40 ℃.
The raw material gas is compressed to 0.35MPa (G) by a raw material gas compressor under normal pressure and then enters a 6-tower PSA1 system. The PSA1 system consists of 1 gas-liquid separator, 6 adsorbers, 2 desorbent gas buffer tanks and a series of program control valves. In the PSA1 system, one adsorber is always in different stages of adsorption step, the raw material is introduced from the inlet end, the nitrogen-rich gas obtained from the outlet end is discharged, the adsorbed CH4 is desorbed by reverse discharge and evacuation and then sent to the semi-product gas compressor, and the other adsorbers are in different stages of regeneration.
The PSA1 desorption gas (semi-product gas) is compressed by a semi-product gas compressor to 1.0MPa (G) and enters a 10-tower PSA2 system. The PSA2 system consists of 10 adsorbers, 1 displacement waste gas buffer tank, 2 product gas buffer tanks, and a series of programmed valves. In a PSA2 system, one adsorber is always in different stages of adsorption step at any time, raw material is introduced from inlet end, nitrogen-rich gas obtained from outlet end is sent out, part of product gas is returned to adsorber by blower for replacement, replaced waste gas is returned to inlet of raw material gas compressor, adsorbed CH4The desorbed product is obtained by reverse discharge and evacuation and is output to the outside as a product.
Table 3: PSA1 operating schedule
The operating process of the PSA1 system is shown in Table 3, and the specific process is as follows:
1. an adsorption (A) step: the raw material gas is compressed to 0.35MPa (G) by a raw material gas compressor under normal pressure, most of water is removed by a gas-liquid separator, and then the raw material gas enters a PSA1 adsorption tower under the conditions of 0.35MPa (G) and the temperature of less than or equal to 40 ℃, and CH in the raw material gas4Weakly adsorbed component (N) adsorbed by the adsorbent2、O2) And part of CH4Delivering the mixture from the upper part of the adsorption tower to a boundary area;
2. pressure drop (EiD) step: after the step (A) of adsorption is completed, opening a pressure equalizing program control valve, transferring the adsorbent gap in the tower and the gas components adsorbed by the adsorbent to an adsorption tower with increased pressure, closing the pressure equalizing program control valve after the pressure increase is basically equal to the pressure of the adsorption tower with reduced pressure, and completing the pressure reduction of PSA1 for 2 times;
3. and (D) reversely releasing pressure: after the step of homogenizing and descending (EiD) is finished, the adsorption tower adsorbs CH by the adsorbent4The concentration of the semi-product gas reaches the requirement of the semi-product gas, and the semi-product gas is discharged through a reverse-release program control valve at the bottom of the adsorption tower and enters a desorption gas buffer tank A;
4. evacuation (V) step: for further recovery of CH adsorbed in the adsorbent4Using a vacuum pump to pump CH4Desorbing from the adsorbent, pumping air into a desorption gas buffer tank B, mixing with the reverse vent gas discharged from the desorption gas buffer tank A, and delivering the mixture as semi-product gas to a semi-product gas compressor;
5. a pressure rising (EiR) step, which corresponds to the pressure falling (EiD) step, wherein after the step of evacuating (V) is completed, the pressure of the adsorption tower ending the step of evacuating (V) is uniformly raised by using the gas in the step of pressure falling (EiD), and the pressure of PSA1 is uniformly raised for 2 times;
6. final boost (FR) step: because the pressure of the adsorption tower can not reach the adsorption pressure through the pressure rising (EiR) step, the nitrogen-rich gas discharged from the top of the adsorption tower needs to be used for increasing the pressure from the top of the adsorption tower to reach the adsorption operation pressure, and after the pressure of the adsorption tower is increased to reach the adsorption operation pressure, the adsorption tower enters the next cycle process according to the operation program.
Each adsorption tower passes through the same step sequence, and only the process steps are staggered with each other by a sub-period in operation so as to ensure that the separation process is continuously carried out.
Table 4: PSA2 operating schedule
The operating process of the PSA2 system is shown in Table 4, and the specific process is as follows:
1. an adsorption (A) step: PSA1 desorption gas (semi-product gas) is compressed to 1.0MPa by a compressor (G) and enters a PSA2 adsorption tower at the temperature of 20-40 ℃, and CH in the feed gas4Weakly adsorbed component (N) adsorbed by the adsorbent2、O2) And part of CH4Sending the nitrogen-rich gas out of the battery limits;
2. pressure drop (EiD) step: after the step (A) of adsorption is completed, opening a pressure equalizing program control valve, transferring the adsorbent gap in the tower and the gas components adsorbed by the adsorbent to an adsorption tower with increased pressure, closing the pressure equalizing program control valve after the pressure increase is basically equal to the pressure of the adsorption tower with reduced pressure, and completing the pressure reduction of PSA2 for 4 times;
3. replacement (RP) step: after the step of pressure equalizing drop (EiD) is finished, the product gas is used for replacement, partial product gas is pressurized by a replacement blower and then returns to the adsorption tower to adsorb residual impurities (N) in the adsorbent2、O2) And (4) the product gas adsorbed in the adsorption tower reaches the designed concentration, and the displacement waste gas enters the displacement waste gas buffer tank from the top of the adsorption tower and then returns to the feed gas compressor.
4. And (D) reversely releasing pressure: after the Replacement (RP) step is completed, adsorbing CH in the column4The concentration of the product gas reaches the requirement of the product gas, and the product gas is discharged through a reverse-discharge program control valve at the bottom of the adsorption tower and enters a product gas buffer tank;
5. evacuation (V) step: for further recovery of CH adsorbed in the adsorbent4Using a vacuum pump to pump CH4Desorbing from the adsorbent, pumping air into a product gas mixing tank to be mixed with the reverse exhaust gas discharged from the product gas buffer tank to be used as product gas to be discharged;
6. a pressure rising (EiR) step corresponding to the pressure dropping (EiD) step, wherein after the evacuation (V) step is completed, the pressure of the adsorption tower ending the evacuation (V) step is uniformly raised by using the gas in the pressure dropping (EiD) step, and the step is completed in 4 times;
7. final boost (FR) step: because the pressure of the adsorption tower can not reach the adsorption pressure through a plurality of pressure rising (EiR) steps, the nitrogen-rich gas discharged from the top of the adsorption tower needs to be used for increasing the pressure from the top of the adsorption tower to reach the adsorption operation pressure, and when the pressure of the adsorption tower is increased to reach the adsorption operation pressure, the adsorption tower enters the next cycle process according to the operation program.
Each adsorption tower passes through the same step sequence, and only the process steps are staggered with each other by a sub-period in operation so as to ensure that the separation process is continuously carried out.
Comparative example 1:
1. single-stage VPSA
Preparing raw material gas with the components close to those of coal bed gas, and testing CH (carbon nitride) by a single-section VPSA (vacuum pressure swing adsorption) process4And (4) concentration effect.The experimental conditions were: the adsorption pressure is 0.25MPa, the pressure is equalized for 1 time, and the regeneration is pumped to-0.08 MPa, so that the following experimental data are obtained:
the experimental result shows that the CH in the product gas is increased along with the increase of the air input of the raw material gas4The content may be slightly increased, but CH4The yield of (A) is reduced obviously, which indicates that CH cannot be concentrated by single-stage VPSA4The requirement of natural gas is met.
Comparative example 2:
two-stage VPSA
It can be seen from the single-stage VPSA experiment (comparative example 1) that4CH when the content is concentrated to more than 50%4The yield of the product can still only reach more than 93 percent. On the basis, a two-stage VPSA experiment is added to prepare CH4Feed gas with a content of about 50%, tested for CH by VPSA procedure4And (4) concentration effect. The experimental conditions were: the adsorption pressure is 0.4MPa, the pressure is equalized for 2 times, and the regeneration is pumped out to-0.08 MPa, so that the following experimental data are obtained:
the experimental result shows that the CH in the product gas is increased along with the increase of the air input of the raw material gas4The content can be increased to more than 80 percent, CH4The yield is also higher, but the natural gas requirement can not be met.
Comparative example 3:
one-stage VPSA + one-stage tape replacement VPSA
On the basis of two stages of VPSA experiments of comparative example 2, a replacement step is added to the two stages of VPSA, and the experimental conditions are as follows: the adsorption pressure is 0.4MPa, the pressure is equalized for 2 times, the pressure is equalized and then the pressure is replaced, the replacement pressure is 0.06MPa, and the regeneration is pumped out to-0.08 MPa. At the same time, due to the replacement of CH in the exhaust gas4Higher content of CH in order to increase4Yield, the displaced waste gas of the two-stage VPSA was returned to the first-stage feed gas inlet, yielding the following experimental data:
the experimental result shows that the coal bed gas is concentrated through a new process, and CH in the product gas4The content can be increased to more than 90 percent, the requirement of natural gas is met, and simultaneously, CH4The yield can reach more than 90 percent, and simultaneously the product gas, the semi-product gas, the adsorption waste gas and the replacement of CH in the waste gas4The contents are not within the explosion limit.
The foregoing basic embodiments of the invention and their various further alternatives can be freely combined to form multiple embodiments, all of which are contemplated and claimed herein. In the scheme of the invention, each selection example can be combined with any other basic example and selection example at will. Numerous combinations will be known to those skilled in the art.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The efficient separation and purification method of low-concentration coal bed gas is characterized by adopting two-stage pressure swing adsorption process, and concentrating CH by using evacuation pressure swing adsorption process after pressurization in the first stage4Removing most of N2And O2In the second stage, CH is concentrated by means of displacement pressure-swing adsorption process4And obtaining the product with the methane concentration more than or equal to 90 percent.
2. The method for efficiently separating and purifying low-concentration coal bed gas according to claim 1, wherein the two-stage pressure swing adsorption comprises the following specific steps: the first section removes partial oxygen and nitrogen by pressure swing adsorption under low pressure, and the adsorbed methane is desorbed by evacuation, so that the obtained concentrated gas is not in the explosion limit, and the compression safety can be ensured; then the mixture enters a second section of pressure swing adsorption after compression and is concentrated, the purity of methane in the adsorption tower is concentrated through a replacement process, and finally a product with the methane concentration being more than or equal to 90 percent is obtained through evacuation; the displaced waste gas returns to the PSA inlet of the first section, the methane yield is improved, and the comprehensive methane yield is more than or equal to 90 percent.
3. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in claim 1 or 2, wherein the method comprises the following steps: the first stage of pressure swing adsorption adopts a continuously operating pressure swing adsorption system consisting of 3 or more than 3 adsorption towers, and each adsorption tower sequentially undergoes the steps of adsorption, pressure drop for multiple times, reverse pressure release, vacuumizing, pressure rise for multiple times and final pressure rise in one cycle.
4. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in claim 1 or 2, wherein the method comprises the following steps: the second stage pressure swing adsorption adopts a continuous operation pressure swing adsorption system consisting of 3 or more than 3 adsorption towers, and each adsorption tower sequentially undergoes the steps of adsorption, multiple pressure reduction, replacement, reverse pressure release, vacuumizing, multiple pressure increase and final pressure increase in one cycle.
5. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in claim 3, wherein the method comprises the following steps: the adsorption pressure of the first-stage pressure swing adsorption is 0.05-0.4 MPa (G), and the operation temperature of the pressure swing adsorption is 5-60 ℃.
6. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in claim 4, wherein the adsorption pressure of the second stage pressure swing adsorption is 0.2-2.0 MPa (G), and the operation temperature of the pressure swing adsorption is 5-60 ℃.
7. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in claim 1 or 2, wherein the method comprises the following steps: the adsorbent used in the first and second pressure swing adsorption stages is CH4/N2Close to 4.
8. The method for efficiently separating and purifying low-concentration coal bed gas according to claim 7, wherein the preparation method of the adsorbent comprises the following steps: mixing sodium hydroxide, tetrapropylammonium hydroxide, silica sol and deionized water, stirring and aging at room temperature, putting into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal treatment, cooling, fully washing with deionized water, filtering, drying, and roasting in an air atmosphere to obtain the catalyst.
9. The method for efficiently separating and purifying low-concentration coal bed gas according to claim 8, wherein the preparation method of the adsorbent comprises the following steps: the molar ratio of the sodium hydroxide to the tetrapropylammonium hydroxide to the silica sol to the deionized water is 1: 35-46: 20-30: 600-800, wherein the silica sol is calculated by silicon dioxide; the aging time is 5 hours; the hydrothermal treatment conditions are that the temperature is 150-200 ℃, and the hydrothermal treatment time is 12-24 h; the washing times of deionized water are 3 times; the drying condition is 80 ℃ and 24 hours; the roasting condition is 500-700 ℃ for 24 hours.
10. The method for efficiently separating and purifying low-concentration coal bed gas as claimed in any one of claims 1 to 9, wherein: the methane content of the adsorption waste gas, the replacement waste gas, the semi-product gas and the product gas in the two-stage pressure swing adsorption is not within the explosion limit.
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