CN114191939A - Methane and nitrogen mixture separation system and separation process - Google Patents
Methane and nitrogen mixture separation system and separation process Download PDFInfo
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- CN114191939A CN114191939A CN202010908029.5A CN202010908029A CN114191939A CN 114191939 A CN114191939 A CN 114191939A CN 202010908029 A CN202010908029 A CN 202010908029A CN 114191939 A CN114191939 A CN 114191939A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
- B01D53/047—Pressure swing adsorption
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/30—Fuel from waste, e.g. synthetic alcohol or diesel
Abstract
The invention belongs to the technical field of gas separation, and discloses a methane and nitrogen mixture separation system and a separation process. The active carbon separation material has the advantages of large specific surface area, developed microporous structure, large methane adsorption capacity, high nitrogen methane separation coefficient and the like, the double-reflux pressure swing adsorption can effectively overcome thermodynamic limitation, and simultaneously light component product gas and heavy component product gas with high purity and high recovery rate are obtained. The method can be operated at normal temperature and under the adsorption pressure of 0.2-0.5 MPa, so that the energy consumption and the cost are low; the method is suitable for the fields of coal bed gas development in industry, methane/nitrogen separation, methane heat value increase, gas concentration reduction in coal mines and the like.
Description
Technical Field
The invention belongs to the technical field of gas separation, and particularly relates to a separation system and a separation process for a mixture of methane and nitrogen.
Background
Methane is used as a high-efficiency clean energy source, can be used as a fuel and a chemical raw material for producing substances such as hydrogen, carbon black and the like, and is mainly present in coal bed gas, natural gas and oil field gas. Meanwhile, methane is a greenhouse effect gas, the greenhouse effect caused by the same volume of methane is 21 times that of carbon dioxide, and the destruction capability of the methane to ozone is 7 times that of the carbon dioxide. Therefore, under the international large background of lack of clean and efficient energy, the methane in resources such as low-concentration coal bed gas and the like is enriched and efficiently utilized, and the method has economic and environmental benefits.
After resources such as coal bed gas are pretreated by desulfurization, deoxidation and the like, components mainly comprise methane and nitrogen, so that the separation of the coal bed gas after the pretreatment is mainly the separation of the methane and the nitrogen. The current methane/nitrogen separation technology mainly comprises low-temperature cryogenic separation, pressure swing adsorption, membrane separation and the like. The low-temperature cryogenic separation technology has large basic investment and higher operating cost, and is more economic when the separation scale is larger (million cubic meters per day); the membrane separation has strong dependence on membrane preparation technology, and the membrane itself may have the problems of easy silting, easy damage, short service life and the like, and the technology is still in the development stage; the pressure swing adsorption separation technology has the advantages of simple equipment, single-stage operation, operability at room temperature and low pressure, no need of external heating or refrigeration source, large operation flexibility of the device, high automation degree, low cost and energy consumption, and obvious advantages in the field of methane/nitrogen separation.
The traditional pressure swing adsorption process comprises separation type pressure swing adsorption and enrichment type pressure swing adsorption, and the separation type pressure swing adsorption and the enrichment type pressure swing adsorption are both restricted by thermodynamics, wherein the separation type pressure swing adsorption can only obtain high-purity light component product gas, and the enrichment type pressure swing adsorption can only obtain high-purity heavy component product gas.
Disclosure of Invention
The invention discloses a methane and nitrogen mixture separation system and a separation process, aiming at the technical problems that the existing coal bed gas, oil field gas and other resource components are complex, and methane/nitrogen properties are similar and difficult to separate.
In order to solve the technical problems, the invention is realized by the following technical scheme:
according to one aspect of the invention, a methane and nitrogen mixture separation system is provided, which comprises a first compressor, a first adsorption tower, a second compressor, a methane product gas storage tank and a nitrogen product gas storage tank; active carbon separation materials are filled in the first adsorption tower and the second adsorption tower;
the inlet of the first compressor is connected with the feed inlet, the outlet of the first compressor is respectively connected with the middle feed inlet of the first adsorption tower through a first valve, and the second valve is connected with the middle feed inlet of the second adsorption tower;
a discharge port at the top of the first adsorption tower is connected with an inlet of a nitrogen product gas storage tank through a third valve, and an outlet of the nitrogen product gas storage tank is connected with a reflux port at the top of the first adsorption tower through a fourth valve;
a discharge port at the bottom of the tower of the first adsorption tower is connected with an inlet of the methane product gas storage tank through a fifth valve, an outlet of the methane product gas storage tank is connected with an inlet of the second compressor through a sixth valve, and an outlet of the second compressor is connected with a reflux port at the bottom of the tower of the first adsorption tower through a seventh valve;
a discharge port at the top of the second adsorption tower is connected with an inlet of the nitrogen product gas storage tank through an eighth valve, and an outlet of the nitrogen product gas storage tank is connected with a reflux port at the top of the second adsorption tower through a ninth valve;
a discharge port at the bottom of the second adsorption tower is connected with an inlet of the methane product gas storage tank through a tenth valve, an outlet of the methane product gas storage tank is connected with an inlet of the second compressor through a sixth valve, and an outlet of the second compressor is connected with a reflux port at the bottom of the second adsorption tower through an eleventh valve;
the nitrogen product gas storage tank is connected with the nitrogen product gas discharge port through a twelfth valve;
and the methane product gas storage tank is connected with the methane product gas discharge port through a thirteenth valve.
Furthermore, the weight of the active carbon separation materials in the first adsorption tower and the second adsorption tower is equal.
Further, the specific surface area of the active carbon separation material is 850-2/g。
Further, the pore volume of the active carbon separation material is 0.45-0.55cm3/g。
Further, the average pore diameter of the activated carbon separation material is 2.2-2.3 nm.
Further, the device also comprises a vacuum pump; a discharge hole at the bottom of the first adsorption tower is connected with an inlet of the vacuum pump through the fifth valve, and an outlet of the vacuum pump is connected with an inlet of the methane product gas storage tank; and a discharge hole at the bottom of the tower of the second adsorption tower is connected with an inlet of the vacuum pump through the tenth valve, and an outlet of the vacuum pump is connected with an inlet of the methane product gas storage tank.
According to another aspect of the invention, a separation process of the methane and nitrogen mixture separation system is provided, which comprises the following circulation processes:
opening the fifth valve, the eleventh valve, the sixth valve, the thirteenth valve, the first valve, the eighth valve, the fourth valve, the twelfth valve; feeding coal bed gas from a middle feeding hole of the first adsorption tower by the first compressor, introducing part of nitrogen in the nitrogen product gas storage tank into the first adsorption tower to complete tower top flushing, introducing methane discharged from the first adsorption tower into the methane product gas storage tank, discharging part of methane in the methane product gas storage tank from a methane product gas discharge hole, introducing the rest of methane into the second adsorption tower through the compressor, introducing a mixed gas of methane and nitrogen into the nitrogen product gas storage tank after the mixed gas is adsorbed by the second adsorption tower, and discharging part of nitrogen from a nitrogen product gas discharge hole;
after the set adsorption time is reached, closing the fifth valve, the eleventh valve, the sixth valve, the thirteenth valve, the first valve, the eighth valve, the fourth valve and the twelfth valve; opening the seventh valve and the tenth valve to finish the final pressure-rising work of the first adsorption tower and the pressure-reducing work of the second adsorption tower;
opening the seventh valve, the tenth valve, the sixth valve, the thirteenth valve, the second valve, the third valve, the ninth valve, the twelfth valve; feeding coal bed gas from a middle feeding hole of the second adsorption tower by the first compressor, introducing part of nitrogen in the nitrogen product gas storage tank into the second adsorption tower to complete tower top flushing, introducing methane discharged from the second adsorption tower into the methane product gas storage tank, discharging part of methane in the methane product gas storage tank from a methane product gas discharge hole, introducing the rest of methane into the first adsorption tower through the compressor, introducing a methane and nitrogen mixed gas into the nitrogen product gas storage tank after the methane and nitrogen mixed gas is adsorbed by the first adsorption tower, and discharging part of nitrogen from a nitrogen product gas discharge hole;
after the set adsorption time is reached, closing the seventh valve, the tenth valve, the sixth valve, the thirteenth valve, the second valve, the third valve, the ninth valve and the twelfth valve; and opening the eleventh valve and the fifth valve to finish the pressure reduction work of the first adsorption tower and the final pressure rise work of the second adsorption tower.
Further, the adsorption pressure of the first adsorption tower and the second adsorption tower is set to be 0.2-0.5 MPa.
Further, the desorption process adopts normal pressure desorption or vacuum desorption.
The invention has the beneficial effects that:
the invention fully utilizes the excellent separation performance of the activated carbon on nitrogen and methane, combines the characteristics of a double reflux device, reasonably sets a time sequence, can sort out high-purity nitrogen and methane gas, and keeps higher recovery rate:
the methane and nitrogen mixture separation system and the separation process comprise a first compressor, a first adsorption tower, a second compressor, a methane product gas storage tank and a nitrogen product gas storage tank; the separation system provided by the invention adopts the activated carbon with large specific surface area and developed microporous structure as the methane/nitrogen adsorption separation material, the methane adsorption capacity on the activated carbon is large, and the separation coefficient of the activated carbon to methane/nitrogen is more than 3.5, so that the methane/nitrogen mixture can be effectively separated through pressure swing adsorption.
Compared with low-temperature cryogenic rectification and membrane separation technologies, the pressure swing adsorption separation system and separation process for the mixture of methane and nitrogen have the advantages of more flexible device, smaller scale, lower cost and energy consumption, and are more suitable for the fields of coal bed gas resource development and methane enrichment and recovery in China.
And (III) the methane and nitrogen mixture separation system and the separation process provided by the invention have the advantages that double-reflux pressure swing adsorption is used as a novel pressure swing adsorption technology, thermodynamic limitations can be overcome, the traditional pressure swing adsorption can only obtain a product gas with higher purity, the double-reflux pressure swing adsorption can simultaneously obtain two product gases with high purity and high recovery rate, and a high-purity nitrogen product can be obtained by separation while methane is enriched.
And (IV) the methane and nitrogen mixture separation system and the separation process can be operated at normal temperature and under the adsorption pressure of 0.2-0.5 MPa, so that the energy consumption and the cost are low, and the methane and nitrogen mixture separation system and the separation process are suitable for the fields of coal bed gas development, methane/nitrogen separation, methane heat value improvement, gas concentration reduction in coal mines and the like in industry.
Drawings
FIG. 1 is a schematic diagram of a methane and nitrogen mixture separation system provided by the present invention;
in the figure: 1-a first compressor, 2-a seventh valve, 3-a first adsorption tower, 4-a fifth valve, 5-a second adsorption tower, 6-a tenth valve, 7-an eleventh valve, 8-a vacuum pump, 9-a second compressor, 10-a sixth valve, 11-a methane product gas storage tank, 12-a thirteenth valve, 13-a second valve, 14-a first valve, 15-a third valve, 16-an eighth valve, 17-a fourth valve, 18-a ninth valve, 19-a nitrogen product gas storage tank, and 20-a twelfth valve.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "horizontal", "inside", "outside", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments.
As shown in fig. 1, in the present embodiment, a methane and nitrogen mixture separation system is provided, in which activated carbon with a large specific surface area and a developed microporous structure is used as a separation material, a double reflux pressure swing adsorption process of two adsorption towers is used as a separation technology, and a methane/nitrogen mixture is separated, so that a high-purity nitrogen product gas is obtained while methane is enriched.
Specifically, the methane and nitrogen mixture separation system comprises a first compressor 1, a seventh valve 2, a first adsorption tower 3, a fifth valve 4, a second adsorption tower 5, a tenth valve 6, an eleventh valve 7, a vacuum pump 8, a second compressor 9, a sixth valve 10, a methane product gas storage tank 11, a thirteenth valve 12, a second valve 13, a first valve 14, a third valve 15, an eighth valve 16, a fourth valve 17, a ninth valve 18, a nitrogen product gas storage tank 19 and a twelfth valve 20.
Wherein the first adsorption tower 3 and the second adsorption tower 5 are filled with equal weight of active carbon separation materials, and the specific surface of the active carbon separation materialsThe volume is preferably 850-2The pore volume is preferably 0.45-0.55 cm/g3The average pore diameter is preferably from 2.2 to 2.3 nm/g. The specific surface area is 850-2When the concentration is between the concentration of the water and the concentration of the water, the system can achieve better purity and recovery rate, and the pore volume is 0.45-0.55cm3The effect of separating the nitrogen/methane mixed gas is the best when the/g and the average pore diameter are between 2.2 and 2.3nm, so when the activated carbon material with the parameter is selected, the better separation effect can be kept under the condition of lower economic investment.
The feed inlet is connected with the inlet of the first compressor 1, the outlet of the first compressor 1 is respectively connected with the middle feed inlet of the first adsorption tower 3 through a first valve 14, and the second valve 13 is connected with the middle feed inlet of the second adsorption tower 5.
The discharge port at the top of the first adsorption tower 3 is connected with the inlet of a nitrogen product gas storage tank 19 through a third valve 15, and the outlet of the nitrogen product gas storage tank 19 is connected with the top reflux port of the first adsorption tower 3 through a fourth valve 17.
The discharge hole at the bottom of the tower of the first adsorption tower 3 is connected with the inlet of a vacuum pump 8 through a fifth valve 4, the outlet of the vacuum pump 8 is connected with the inlet of a methane product gas storage tank 11, the outlet of the methane product gas storage tank 11 is connected with the inlet of a second compressor 9 through a sixth valve 10, and the outlet of the second compressor 9 is connected with the reflux hole at the bottom of the tower of the first adsorption tower 3 through a seventh valve 2.
The discharge hole at the top of the second adsorption tower 5 is connected with the inlet of a nitrogen product gas storage tank 19 through an eighth valve 16, and the outlet of the nitrogen product gas storage tank 19 is connected with the top reflux hole of the second adsorption tower 5 through a ninth valve 18.
The outlet at the bottom of the second adsorption tower 5 is connected with the inlet of a vacuum pump 8 through a tenth valve 6, the outlet of the vacuum pump 8 is connected with the inlet of a methane product gas storage tank 11, the outlet of the methane product gas storage tank 11 is connected with the inlet of a second compressor 9 through a sixth valve 10, and the outlet of the second compressor 9 is connected with the reflux port at the bottom of the second adsorption tower 5 through an eleventh valve 7.
The nitrogen product gas storage tank 19 is connected with the nitrogen product gas discharge port through a twelfth valve 20.
The methane product gas storage tank 11 is connected with the methane product gas discharge port through a thirteenth valve 12.
Through the methane and nitrogen mixture separation system, the feed gas of low-concentration coal bed gas is compressed by the first compressor 1 and then fed from the middle feed inlet of the first adsorption tower 3, the top of the first adsorption tower 3 is flushed with nitrogen product gas, methane with higher concentration is extracted from the bottom of the tower, one part of methane is output as heavy component product gas, the other part of methane is reflux to the second adsorption tower 5 as heavy component reflux gas for replacement, high-purity nitrogen is extracted from the top of the second adsorption tower 5, one part of nitrogen is output as light component product gas, and the other part of nitrogen is reflux flushed with the first adsorption tower 3 as light component reflux gas. At this point, the first adsorption tower 3 has completed the low-pressure feeding/flushing step, methane with higher concentration is extracted at the bottom of the tower, the second adsorption tower 5 has completed the heavy component reflux replacement step, and high-purity nitrogen is extracted at the top of the tower. Then, the second adsorption tower 5 is reversely discharged or evacuated, and the gas is reversely discharged from the bottom of the second adsorption tower 5, compressed by the second compressor 9, and then pressurized in the first adsorption tower 3. At this point, the second adsorption tower 5 completes the reverse discharging or vacuumizing step, the pressure in the tower is reduced to low pressure, the first adsorption tower 3 completes the pressure increasing step, and the pressure in the tower is increased to high pressure. And finally, interchanging time sequences of the two towers to finish the rest steps.
In the pressure swing adsorption cycle, the adsorption pressure of the first adsorption tower 3 and the second adsorption tower 5 can be set to be 0.2-0.5 MPa, and the desorption process adopts normal pressure desorption or vacuum-pumping desorption.
The preferred timing scheme is as follows:
| phases | (A) | (II) | (III) | (IV) |
| Setting the adsorption time | 100s | 90s | 100s | 90s |
| |
Rinsing | Pressure equalization rise | Adsorption | Pressure equalizing drop |
| |
Adsorption | Pressure equalizing drop | Rinsing | Pressure equalization rise |
The method comprises the following specific operation steps:
opening the fifth valve 4, the eleventh valve 7, the sixth valve 10, the thirteenth valve 12, the first valve 14, the eighth valve 16, the fourth valve 17, and the twelfth valve 20: feeding low-concentration coal bed gas with 10-30% of methane content from a first compressor 1 through a pipeline and a first valve 14 from a middle feeding hole of a first adsorption tower 3, introducing a small part of nitrogen in a nitrogen product gas storage tank 19 into the first adsorption tower 3 through a fourth valve 17 by the first adsorption tower 3 to complete top washing, and the methane discharged and replaced from the fifth valve 4 by the first adsorption tower 3 is introduced into a methane product gas storage tank 11 through a vacuum pump 8, most of the methane in the methane product gas storage tank 11 is discharged from a methane product gas discharge port through a thirteenth valve 12, a small part of the methane is introduced into a compressor 9 through a sixth valve 10 and then enters the second adsorption tower 5 through an eleventh valve 7, and the mixed gas of the methane and the nitrogen is adsorbed by the second adsorption tower 5, the eighth valve 16 feeds a nitrogen product gas reservoir 19, at which point most of the nitrogen is removed from the nitrogen product gas outlet via a twelfth valve 20.
And after the set adsorption time is reached, closing the fifth valve 4, the eleventh valve 7, the sixth valve 10, the thirteenth valve 12, the first valve 14, the eighth valve 16, the fourth valve 17 and the twelfth valve 20.
The set adsorption time is determined according to the process purity requirement and the breakthrough time, and the adsorption time which can maximally utilize the adsorbent and cannot cause the purity of the heavy component to exceed the standard is selected according to the breakthrough time; for example, the time for which the methane purity was set to 66.6% in this example was 100S.
(ii) opening only the seventh valve 2 and the tenth valve 6: the final pressure-raising operation of the first adsorption tower 3 and the pressure-lowering operation of the second adsorption tower 5 are completed.
(iii) opening the seventh valve 2, the tenth valve 6, the sixth valve 10, the thirteenth valve 12, the second valve 13, the third valve 15, the ninth valve 18, the twelfth valve 20:
feeding low-concentration coal bed gas with 10-30% of methane content from a first compressor 1 through a pipeline through a second valve 13 from a middle feed inlet of a second adsorption tower 5, introducing a small part of nitrogen in a nitrogen product gas storage tank 19 into the second adsorption tower 5 through a ninth valve 18 by the second adsorption tower 5 to complete top washing, meanwhile, the methane discharged and replaced from the tenth valve 6 by the second adsorption tower 5 is introduced into a methane product gas storage tank 11 through a vacuum pump 8, most of the methane in the methane product gas storage tank 11 is discharged from a methane product gas discharge port through a thirteenth valve 12, a small part of the methane is introduced into a compressor 9 through a sixth valve 10 and then enters the first adsorption tower 3 through a seventh valve 2, and the mixed gas of the methane and the nitrogen is adsorbed by the first adsorption tower 3, the nitrogen product gas storage tank 19 is fed through the third valve 15, and most of the nitrogen is discharged from the nitrogen product gas outlet through the twelfth valve 20.
And after the set adsorption time is reached, closing the fifth valve 4, the eleventh valve 7, the sixth valve 10, the thirteenth valve 12, the first valve 14, the eighth valve 16, the fourth valve 17 and the twelfth valve 20.
The adsorption time was set to be the same as in stage (one).
(iv) opening only the eleventh valve 7 and the fifth valve 4: the pressure-reducing operation of the first adsorption tower 3 and the final pressure-increasing operation of the second adsorption tower 5 are completed.
At this point, a complete cycle is completed.
It can be seen that the first adsorption tower 3 is used as a low pressure tower at the beginning of the first cycle, the second adsorption tower 5 is used as a high pressure tower at the beginning of the first cycle, and after the time sequence interchange, the first adsorption tower 3 becomes the high pressure tower, and the second adsorption tower 5 becomes the low pressure tower.
Experiments prove that the separation process adopts double-reflux pressure swing adsorption with four steps of two towers to separate feed gas with the methane content of 10-30%, the first adsorption tower 3 and the second adsorption tower 5 sequentially undergo four steps of low-pressure feeding/flushing, pressure boosting, heavy component reflux replacement, reverse discharging or vacuum pumping and the like, finally, methane with the concentration of 50-70% is obtained at the tower bottom, the recovery rate is 95-99%, nitrogen with the concentration of 95-99% is obtained at the tower top, and the recovery rate is 85-90%.
The foregoing is considered as illustrative only of the preferred embodiments of the invention, and is presented merely for purposes of illustration and description of the principles of the invention and is not intended to limit the scope of the invention in any way. Any modifications, equivalents and improvements made within the spirit and principles of the invention and other embodiments of the invention without the creative effort of those skilled in the art are included in the protection scope of the invention based on the explanation here.
Claims (9)
1. A methane and nitrogen mixture separation system is characterized by comprising a first compressor, a first adsorption tower, a second compressor, a methane product gas storage tank and a nitrogen product gas storage tank; active carbon separation materials are filled in the first adsorption tower and the second adsorption tower;
the inlet of the first compressor is connected with the feed inlet, the outlet of the first compressor is respectively connected with the middle feed inlet of the first adsorption tower through a first valve, and the second valve is connected with the middle feed inlet of the second adsorption tower;
a discharge port at the top of the first adsorption tower is connected with an inlet of a nitrogen product gas storage tank through a third valve, and an outlet of the nitrogen product gas storage tank is connected with a reflux port at the top of the first adsorption tower through a fourth valve;
a discharge port at the bottom of the tower of the first adsorption tower is connected with an inlet of the methane product gas storage tank through a fifth valve, an outlet of the methane product gas storage tank is connected with an inlet of the second compressor through a sixth valve, and an outlet of the second compressor is connected with a reflux port at the bottom of the tower of the first adsorption tower through a seventh valve;
a discharge port at the top of the second adsorption tower is connected with an inlet of the nitrogen product gas storage tank through an eighth valve, and an outlet of the nitrogen product gas storage tank is connected with a reflux port at the top of the second adsorption tower through a ninth valve;
a discharge port at the bottom of the second adsorption tower is connected with an inlet of the methane product gas storage tank through a tenth valve, an outlet of the methane product gas storage tank is connected with an inlet of the second compressor through a sixth valve, and an outlet of the second compressor is connected with a reflux port at the bottom of the second adsorption tower through an eleventh valve;
the nitrogen product gas storage tank is connected with the nitrogen product gas discharge port through a twelfth valve;
and the methane product gas storage tank is connected with the methane product gas discharge port through a thirteenth valve.
2. A methane and nitrogen mixture separation system according to claim 1, wherein the activated carbon separation materials in the first adsorption tower and the second adsorption tower are of equal weight.
3. The system for separating a mixture of methane and nitrogen as claimed in claim 1, wherein said activated carbon separation materialSpecific surface area of 850-2/g。
4. A methane and nitrogen mixture separation system according to claim 1, wherein the pore volume of said activated carbon separation material is 0.45-0.55cm3/g。
5. A methane and nitrogen mixture separation system according to claim 1, wherein said activated carbon separation material has an average pore size of 2.2-2.3 nm.
6. A methane and nitrogen mixture separation system according to claim 1, further comprising a vacuum pump; a discharge hole at the bottom of the first adsorption tower is connected with an inlet of the vacuum pump through the fifth valve, and an outlet of the vacuum pump is connected with an inlet of the methane product gas storage tank; and a discharge hole at the bottom of the tower of the second adsorption tower is connected with an inlet of the vacuum pump through the tenth valve, and an outlet of the vacuum pump is connected with an inlet of the methane product gas storage tank.
7. A separation process based on a methane and nitrogen mixture separation system according to any one of claims 1 to 6, characterized by comprising the following cyclic processes:
opening the fifth valve, the eleventh valve, the sixth valve, the thirteenth valve, the first valve, the eighth valve, the fourth valve, the twelfth valve; feeding coal bed gas from a middle feeding hole of the first adsorption tower by the first compressor, introducing part of nitrogen in the nitrogen product gas storage tank into the first adsorption tower to complete tower top flushing, introducing methane discharged from the first adsorption tower into the methane product gas storage tank, discharging part of methane in the methane product gas storage tank from a methane product gas discharge hole, introducing the rest of methane into the second adsorption tower through the compressor, introducing a mixed gas of methane and nitrogen into the nitrogen product gas storage tank after the mixed gas is adsorbed by the second adsorption tower, and discharging part of nitrogen from a nitrogen product gas discharge hole;
after the set adsorption time is reached, closing the fifth valve, the eleventh valve, the sixth valve, the thirteenth valve, the first valve, the eighth valve, the fourth valve and the twelfth valve; opening the seventh valve and the tenth valve to finish the final pressure-rising work of the first adsorption tower and the pressure-reducing work of the second adsorption tower;
opening the seventh valve, the tenth valve, the sixth valve, the thirteenth valve, the second valve, the third valve, the ninth valve, the twelfth valve; feeding coal bed gas from a middle feeding hole of the second adsorption tower by the first compressor, introducing part of nitrogen in the nitrogen product gas storage tank into the second adsorption tower to complete tower top flushing, introducing methane discharged from the second adsorption tower into the methane product gas storage tank, discharging part of methane in the methane product gas storage tank from a methane product gas discharge hole, introducing the rest of methane into the first adsorption tower through the compressor, introducing a methane and nitrogen mixed gas into the nitrogen product gas storage tank after the methane and nitrogen mixed gas is adsorbed by the first adsorption tower, and discharging part of nitrogen from a nitrogen product gas discharge hole;
after the set adsorption time is reached, closing the seventh valve, the tenth valve, the sixth valve, the thirteenth valve, the second valve, the third valve, the ninth valve and the twelfth valve; and opening the eleventh valve and the fifth valve to finish the pressure reduction work of the first adsorption tower and the final pressure rise work of the second adsorption tower.
8. The separation process according to claim 7, wherein the adsorption pressure of the first adsorption column and the second adsorption column is set to 0.2 to 0.5 MPa.
9. A separation process according to claim 7, wherein the desorption is carried out by atmospheric desorption or vacuum desorption.
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