CN111773882B - Micro-positive pressure vacuum pressure swing adsorption system and method for safely concentrating low-concentration gas - Google Patents

Micro-positive pressure vacuum pressure swing adsorption system and method for safely concentrating low-concentration gas Download PDF

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CN111773882B
CN111773882B CN202010739146.3A CN202010739146A CN111773882B CN 111773882 B CN111773882 B CN 111773882B CN 202010739146 A CN202010739146 A CN 202010739146A CN 111773882 B CN111773882 B CN 111773882B
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gas
concentration
adsorption tower
pressure
adsorption
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CN111773882A (en
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周福宝
王鑫鑫
刘宏
魏康伟
宋小林
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China University of Mining and Technology CUMT
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China University of Mining and Technology CUMT
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation 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
    • B01D53/02Separation 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
    • B01D53/04Separation 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
    • B01D53/047Pressure swing adsorption
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation 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
    • B01D53/02Separation 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
    • B01D53/04Separation 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
    • B01D53/047Pressure swing adsorption
    • B01D53/0476Vacuum pressure swing adsorption
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21FSAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
    • E21F7/00Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05FSTATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
    • H05F1/00Preventing the formation of electrostatic charges

Abstract

A micro-positive pressure vacuum pressure swing adsorption system and a method for safely concentrating low-concentration gas are disclosed, wherein the micro-positive pressure output by a coal mine gas extraction water ring vacuum pump (1) is used as gas source pressure; the low-concentration gas output by the gas extraction water ring vacuum pump enters an air inlet buffer tank (4) through a dust removal device (2) and a dehydration device (3), and then enters an adsorption tower (5); the adsorbent in the adsorption tower adsorbs a large amount of oxygen under micro positive pressure, simultaneously adsorbs nitrogen, and basically does not adsorb methane, the gas with high methane concentration and ultralow oxygen concentration discharged from the adsorption tower in the adsorption stage is a main product gas, and the gas with high oxygen concentration and ultralow methane concentration discharged in the vacuumizing desorption stage is a secondary product gas; the invention can safely and efficiently remove oxygen and nitrogen in low-concentration gas under micro positive pressure, improve the methane concentration under the condition of improving the gas separation safety, and realize the safe transportation of the concentrated gas.

Description

Micro-positive pressure vacuum pressure swing adsorption system and method for safely concentrating low-concentration gas
Technical Field
The invention relates to an extraction gas concentration system, in particular to a micro-positive pressure vacuum pressure swing adsorption system and a micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas, and belongs to the technical field of coal mine extraction gas concentration.
Background
Coal mine gas is associated gas of coal, and the main component is methane. In recent years, the gas extraction amount of coal mines in China steadily increases year by year, and reaches 178 billions of cubic meters in 2018. However, air leakage is easily caused in the process of extracting the underground coal mine gas, and a large amount of air enters an extraction pipeline, so that the concentration of the extracted underground coal mine gas is generally low (< 30%), the extracted underground coal mine gas has explosion risk and high utilization difficulty, the utilization rate of the extracted underground coal mine gas is low (< 40%) in China, and a large amount of gas is directly discharged into the atmosphere, so that huge energy waste and atmospheric greenhouse effect are caused; the method has the advantages that high-concentration gas which is easy to utilize and high in economic value is produced after low-concentration extracted gas is concentrated, the utilization rate of coal mine gas is improved, and the method has important significance for promoting gas extraction, guaranteeing coal mine safety, increasing clean energy supply, reducing greenhouse gas emission and the like.
The low-concentration gas in the coal mine is a mixed gas of methane and air, and when the concentration of the methane is 5-16%, the explosion risk exists, so that the safety of the gas separation and concentration process must be ensured. The existing gas separation and purification technology mainly comprises a low-temperature rectification separation technology, a membrane separation technology, a pressure swing adsorption technology and the like, wherein the low-temperature rectification separation technology utilizes the boiling point difference of different gases to realize gas separation, the gases need to be compressed to high pressure and then liquefied at low temperature, the gas compression can greatly widen the explosion concentration limit range of the gases, and a high-temperature ignition source is easily generated during compression, so that gas explosion can be caused, the low-temperature rectification energy consumption is high, the operating condition requirement is high, the equipment investment is large, and particularly, the economy is poor when low-concentration gas with little methane content is separated; the membrane separation technology utilizes the selective permeability of a polymer membrane to different gases to realize gas separation, and the membrane separation technology also needs to compress the gases so as to form larger pressure difference on two sides of the membrane, so that the membrane separation technology has higher gas explosion risk, and in addition, the membrane separation technology at the present stage has many problems, such as low membrane selectivity, high membrane cost, poor mechanical property and the like, which restrict the application of the membrane separation technology in the field of coal mine gas separation and purification; therefore, the low-temperature rectification separation technology and the membrane separation technology are not suitable for being adopted in the separation and concentration of low-concentration gas; the pressure swing adsorption technology utilizes the equilibrium adsorption capacity or the dynamic adsorption speed difference of the adsorbent to different gas components to realize gas separation, and has the obvious advantages of simple process, compact equipment, low operating cost, high reliability, strong adaptability and the like, so the pressure swing adsorption technology is more applied to the concentration and purification of the coal mine gas.
At present, a pressure swing adsorption coal mine gas purification method mainly utilizes an adsorption equilibrium selectivity principle, for example, "a method for separating and purifying coal bed methane in a mine area by using a pressure swing adsorption method" disclosed by Chinese invention patent 2013, 7, 17, related to coal mine gas purification, with a publication number of CN103205297A, "a method for enriching methane in coal mine gas by using a pressure swing adsorption method" disclosed by Chinese invention patent 1986, 10, 29, and "a method for performing pressure swing adsorption fractional concentration on low-concentration gas with a publication number of CN 101596391A" disclosed by Chinese invention patent 2009, 12, 9, all utilize the adsorption equilibrium selectivity principle to take methane as a strong adsorption component, and product gas with high methane concentration is obtained in a desorption stage.
The purification of the oxygen-containing low-concentration gas by utilizing the equilibrium selectivity principle has obvious technical defects: (1) the concentration of oxygen in the adsorption tower is high, and the mixture of methane and high-concentration oxygen has higher explosion risk; (2) the method for separating and purifying methane in coal bed gas in mine areas by using pressure swing adsorption method disclosed in patent number CN103205297A published in patent number 7.17.2013, the method for enriching methane in coal bed gas in mine areas by using pressure swing adsorption method disclosed in patent number CN85103557 published in patent number 10.29.1986, and the method for fractional concentration by pressure swing adsorption of low-concentration gas disclosed in patent number CN101596391A published in patent number 2009, 12.9.9.4 are respectively provided with adsorption pressures of 0.5 MPa-1 MPa, 0.4 MPa-0.7 MPa and 0.8 MPa-2.4 MPa, so that the methods all need to use a compressor to pressurize the gas, the limit range of the explosion concentration of the gas is expanded under high pressure, and high-temperature fire source generated in the pressurizing process can detonate the gas, pressurization also greatly increases the cost of gas separation; (3) the high air pressure easily causes the pulverization failure of the adsorbent, greatly shortens the service life of the adsorbent, and increases the process complexity by adopting the forward/reverse pressure reduction step (the same as the above-mentioned published patents CN85103557A, CN103205297A and CN101596391A) required by high adsorption pressure; (4) the volume of the adsorption tower at the desorption stage contains a large amount of weakly adsorbed components, so that a large amount of impurity gas is mixed in the desorbed gas, and the methane concentration of the product gas is low.
And (4) judging the explosion concentration range of the coal mine gas according to the Coval triangle, wherein when the oxygen concentration in the gas is less than 12% at normal temperature and normal pressure, the coal mine gas loses the explosion risk.
Disclosure of Invention
The invention aims to provide a micro-positive pressure vacuum pressure swing adsorption system and a method for safely concentrating low-concentration gas, which can safely and efficiently remove oxygen and nitrogen in the low-concentration gas under micro-positive pressure, improve the methane concentration under the condition of improving the gas separation safety, and realize the safe transportation of the gas after concentration.
In order to achieve the aim, the invention provides a micro-positive pressure vacuum pressure swing adsorption system for safely concentrating low-concentration gas, which comprises a gas extraction water ring vacuum pump, a dust removal device, a dehydration device and an air inlet buffer tank with a pressure gauge, wherein an air outlet of the gas extraction water ring vacuum pump for outputting the low-concentration gas is sequentially connected with air inlets at the bottoms of the dust removal device and the dehydration device air inlet buffer tank through pipelines;
the adsorption tower is characterized by also comprising at least two adsorption towers with pressure gauges respectively, an adsorbent is arranged in each adsorption tower, a gas inlet at the bottom end of each adsorption tower is connected with a gas outlet of a gas inlet buffer tank through a pipeline, a gas inlet control valve is arranged on the gas inlet pipeline at the bottom end of each adsorption tower respectively, a gas outlet at the top end of each adsorption tower is connected with a gas inlet end of a product gas buffer tank I with a pressure gauge through a pipeline, a gas production back pressure valve is arranged on the pipeline of the gas inlet end of the product gas buffer tank I, a gas outlet control valve is arranged on the pipeline at the gas outlet at the top end of each adsorption tower respectively, one end of the pipeline is connected on the pipeline connecting the gas outlet at the top end of each adsorption tower and the gas outlet control valve in parallel, the other end of the pipeline is connected on the pipeline connecting the gas outlet at the top end of the adjacent adsorption tower and the gas outlet control valve in parallel, and a pressure equalizing control valve is arranged on the pipeline; the air outlet end of the air inlet buffer tank is also connected with a pipeline in parallel, the other end of the pipeline is connected with the front end of the gas production back pressure valve, and the pipeline is provided with a back pressure regulating control valve; and the vacuumizing water ring vacuum pump pumps the gas adsorbed in each adsorption tower out to a product gas buffer tank II with a pressure gauge, vacuumizing control valves are respectively arranged on pipelines connected with the vacuumizing water ring vacuum pump and each adsorption tower, the gas in the product gas buffer tank I and the gas in the product gas buffer tank II are respectively and safely transported through a remote transmission pipeline, and a flow controller is arranged on the remote transmission pipeline.
As a further improvement of the invention, the volume concentration of methane in the low-concentration gas output by the gas extraction water ring vacuum pump is 1-30%.
As a further improvement of the invention, the micro-positive pressure of the gas output by the gas extraction water ring vacuum pump is 5 kPa-40 kPa, and the vacuum degree required by the vacuum pumping desorption of the adsorption tower is 60 kPa-80 kPa.
As a further improvement of the invention, the adsorbent is a commercial nitrogen-producing carbon molecular sieve.
As a further improvement of the invention, an explosion-proof and anti-static material is filled in the adsorption tower from the bottom to the height 1/3-2/3 of the tower, and the volume ratio of the explosion-proof and anti-static material to the adsorbent in a filling area is 6-10%.
As a further improvement of the invention, the ratio of the height to the diameter of the adsorption tower is 10:1 to 30:1, and the ratio of the volume of the gas inlet buffer tank to the volume of the adsorption tower is 7:1 to 12: 1.
A micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas comprises the following steps aiming at one operation cycle of one adsorption tower:
(1) gas is produced through adsorption: adjusting the pressure of a gas production backpressure valve connected with a gas outlet of an adsorption tower to 1-10 kPa, communicating an air inlet buffer tank with the bottom of the adsorption tower which is subjected to pressure boosting and pressure equalizing, enabling low-concentration gas output by a gas extraction water ring vacuum pump to sequentially pass through a dust removal device, a dehydration device and the air inlet buffer tank and then enter the adsorption tower from the bottom of the adsorption tower, enabling most of oxygen and part of nitrogen in the low-concentration gas to be adsorbed by an adsorbent in the adsorption tower, enabling main product gas with high methane concentration and ultralow oxygen concentration continuously discharged from the top of the adsorption tower to enter a product gas buffer tank I, and enabling the main product gas to be continuously output from the product gas buffer tank I; stopping introducing low-concentration gas into the adsorption tower before the oxygen concentration of the exhaust gas is increased to 5-10%, and finishing the gas production through adsorption;
(2) pressure reduction and pressure equalization: communicating the top of the adsorption tower which finishes the gas production by adsorption with the top of the adjacent adsorption tower which just finishes the gas production by vacuumizing, wherein the gas flows from the adsorption tower with higher pressure to the adjacent adsorption tower which just finishes the gas production by vacuumizing;
(3) vacuumizing to produce gas: vacuumizing from the bottom of the adsorption tower after pressure reduction and pressure equalization to a preset vacuum degree by using a vacuumizing water ring vacuum pump to regenerate the adsorbent in the adsorption tower, introducing the extracted secondary product gas with high oxygen concentration and ultralow methane concentration into a product gas buffer tank II, and continuously outputting the secondary product gas from the product gas buffer tank II;
(4) boosting and pressure equalizing: the top of the adsorption tower which just finishes vacuumizing to generate gas and the top of the adjacent adsorption tower which just finishes adsorbing to generate gas are communicated, and the gas flows to the adsorption tower in a vacuum state from the adjacent adsorption tower with higher pressure, so that the operation of one period of the adsorption tower is finished.
As a further improvement of the invention, the holding time of the steps of gas generation by adsorption and gas generation by vacuumizing is 100-200 s.
As a further improvement of the invention, when the main product gas methane concentration in the product gas buffer tank I needs to be increased, the oxygen concentration is reduced or the operation steps are simplified, the pressure equalizing step of the step (2) and the step (4) can be omitted, the gas with low concentration is directly introduced into the adsorption tower which is just vacuumized in the gas production adsorption step, the adsorption tower which is just vacuumized is directly vacuumized in the gas production adsorption step, but the methane recovery rate is reduced and the vacuum energy consumption is increased due to the omission of the pressure equalizing step of the step 2) and the step 4).
As a further improvement of the invention, the volume concentration of methane in the main product gas in the product gas buffer tank I is 7-90%, and the volume concentration of oxygen is less than 3%; the volume concentration of oxygen in the secondary product gas in the product gas buffer tank II is 30-80%, and the volume concentration of methane is less than 1%; the primary product gas and the secondary product gas have no explosion danger, can be safely conveyed in a long distance, and can be respectively used as combustible gas and combustion-supporting gas for utilization.
Compared with the prior art, the low-concentration extracted gas is separated and concentrated only under the micro-positive pressure output by the existing gas extraction water ring vacuum pump in the coal mine, the low-concentration gas output by the gas extraction water ring vacuum pump enters the gas inlet buffer tank after dust removal and dehydration, and then enters the adsorption tower, so that most of oxygen and part of nitrogen are adsorbed by the adsorbent, a gas compression link is not needed, the low-concentration gas explosion danger caused by gas compression is avoided, the adsorbent can be prevented from being pulverized and failed under high pressure, the gas separation safety is improved, the energy consumption cost is reduced, and the service life of the adsorbent is prolonged; in addition, the adsorbent in the adsorption tower adsorbs a large amount of oxygen, the concentration of the oxygen in the adsorption tower is low, the risk of gas explosion in the adsorption tower is reduced, and explosion-proof and anti-static materials are filled in an explosion danger area with the concentration of the oxygen possibly higher than 12% in the tower, so that the safety is further improved; the weakly adsorbed component gas discharged in the adsorption stage is a main product gas with high methane concentration and ultralow oxygen concentration, and compared with the technology for recovering methane in the desorption stage, the methane recovery rate and the methane separation and concentration effect are improved; the method has simple operation flow, does not need steps of forward/reverse pressure reduction, gas replacement and the like, is beneficial to improving the gas treatment efficiency, and increases the reliability and the stability of system operation.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a timing diagram illustrating a process cycle of the present invention using two adsorption columns as an example;
FIG. 3 is a graph of methane concentration and oxygen concentration in the main product gas over a 6 cycle period as a function of time for example 1 of the present invention;
FIG. 4 is a graph showing the temporal and spatial distribution of the concentration of free oxygen and methane in the adsorption column in example 1 of the present invention: wherein (a) is a profile at 20s, wherein (b) is a profile at 40s, wherein (c) is a profile at 60s, wherein (d) is a profile at 120 s;
FIG. 5 is a graph showing the change in methane concentration in the main product gas with time according to example 2 of the present invention;
FIG. 6 is a graph showing the change of the oxygen concentration in the main product gas with time according to example 2 of the present invention.
In the figure: 1. the device comprises a gas extraction water ring vacuum pump, 2, a dust removal device, 3, a dehydration device, 4, a gas inlet buffer tank, 5, an adsorption tower, 5.1, a gas inlet control valve, 5.2, a gas outlet control valve, 6, product gas buffer tanks I and 7, a gas production back pressure valve, 8, a pressure equalizing control valve, 9, a back pressure regulating control valve, 10, a vacuumizing water ring vacuum pump, 11, a vacuumizing control valve, 12, product gas buffer tanks II and 13 and a flow controller.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, a micro-positive pressure vacuum pressure swing adsorption system for safely concentrating low-concentration gas comprises a gas extraction water ring vacuum pump 1, a dust removal device 2, a dehydration device 3 and an air inlet buffer tank 4 with a pressure gauge, wherein an air outlet of the gas extraction water ring vacuum pump 1 for outputting the low-concentration gas is sequentially connected with the dust removal device 2, the dehydration device 3 and an air inlet at the bottom of the air inlet buffer tank 4 through pipelines;
also comprises at least two adsorption towers 5 respectively provided with a pressure gauge, an adsorbent material is arranged in each adsorption tower 5, an air inlet at the bottom end of each adsorption tower 5 is connected with an air outlet of the air inlet buffer tank 4 through a pipeline, an air inlet control valve 5.1 is respectively arranged on an air inlet pipeline at the bottom end of each adsorption tower 5, an air outlet at the top end of each adsorption tower 5 is connected with an air inlet end of a product gas buffer tank I6 with a pressure gauge through a pipeline, a gas production back pressure valve 7 is arranged on the pipeline of the air inlet end of the product gas buffer tank I6, an air outlet control valve 5.2 is respectively arranged on a pipeline at the air outlet at the top end of each adsorption tower 5, one end of the pipeline is connected to the pipeline connecting the air outlet at the top end of each adsorption tower 5 with the air outlet control valve 5.2 in parallel, the other end of the pipeline is connected to the pipeline connecting the air outlet at the top end of the adjacent adsorption tower 5 with the air outlet control valve 5.2 in parallel, and a pressure equalizing control valve 8 is arranged on the pipeline; the air outlet end of the air inlet buffer tank 4 is also connected with a pipeline in parallel, the other end of the pipeline is connected with the front end of the gas production back pressure valve 7, and a back pressure regulating control valve 9 is installed on the pipeline; and the secondary product gas adsorbed in each adsorption tower 5 is pumped out to a product gas buffer tank II12 with a pressure gauge by a vacuumizing water ring vacuum pump 10, vacuumizing control valves 11 are respectively arranged on pipelines connected with each group of adsorption towers by the vacuumizing water ring vacuum pump 10, the gases in the product gas buffer tank I6 and the product gas buffer tank II12 are respectively and safely transported through a remote transmission pipeline, and a flow controller 13 is arranged on the remote transmission pipeline.
The volume concentration of methane in the low-concentration gas output by the gas extraction water ring vacuum pump 1 is 1-30%.
The micro-positive pressure of the gas output by the gas extraction water ring vacuum pump 1 is 5 kPa-40 kPa, the coal mine gas extraction water ring vacuum pump 1 outputs low-concentration gas at the micro-positive pressure of 5 kPa-40 kPa, the low-concentration gas with the methane volume concentration of 1% -30% is sent to the dust removal device 2 and the dehydration device 3, dust and water vapor are removed, and the purified gas directly enters the gas inlet buffer tank 4 to be used as a raw gas for pressure swing adsorption without passing through a gas compression link; the vacuum degree required by the vacuum pumping desorption of the adsorption tower is 60 kPa-80 kPa.
The adsorbent is a commercial nitrogen-carbon molecular sieve, gas in an air inlet buffer tank 4 enters an adsorption tower 5, the adsorption tower 5 is filled with the commercial nitrogen-carbon molecular sieve, the specific types of the commercial nitrogen-carbon molecular sieve comprise CMS-3KT, 1.5GN-H, CMS-F, CMS-260, CMS-240, CMS-220 and CMS-180, and the adsorbent can adsorb a large amount of oxygen in low-concentration gas under the micro-positive pressure of 5 kPa-40 kPa, and can adsorb nitrogen at the same time, so that methane gas is not adsorbed basically.
Filling an explosion-proof and anti-static material from the bottom to 1/3-2/3 positions in the adsorption tower, wherein the volume ratio of the explosion-proof and anti-static material to the adsorbent in a filling area is 6% -10%, and the explosion-proof and anti-static material is preferably a net-shaped aluminum alloy material.
In order to simultaneously ensure a better gas adsorption effect and lower gas flow resistance, the ratio of the height to the diameter of the adsorption tower 5 is 10: 1-30: 1.
The gas pressure in the buffer tank is kept stable, gas can be stably output to the adsorption tower, and the volume ratio of the gas inlet buffer tank 4 to the adsorption tower 5 is 7: 1-12: 1.
A micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas comprises the following steps aiming at one operation period of an adsorption tower 5:
(1) gas is produced through adsorption: opening a back pressure regulating control valve 9, communicating the front ends of the gas inlet buffer tank 4 and the gas production back pressure valve 7, regulating the pressure of the gas production back pressure valve 7 to 1 kPa-10 kPa (relative pressure), enabling the gas production back pressure valve 7 to rapidly raise the pressure in the adsorption tower 5 to a specified adsorption pressure and keep stable, then closing the back pressure regulating control valve 9, opening gas inlet control valves 5.1 at the bottoms of two adjacent adsorption towers 5, closing other valves, communicating the gas inlet buffer tank 4 with the bottoms of the adsorption towers 5 which have completed pressure raising and pressure equalizing, enabling low-concentration gas to enter the adsorption towers 5 from the bottoms of the adsorption towers 5, enabling most of oxygen and part of nitrogen in the low-concentration gas to be adsorbed by an adsorbent in the adsorption towers 5, and continuously discharging high methane concentration from the tops of the adsorption towers 5, the main product gas with ultra-low oxygen concentration enters a product gas buffer tank I6, and the main product gas can be continuously output from a product gas buffer tank I6; stopping introducing low-concentration gas into the adsorption tower 5 before the oxygen concentration of the exhaust gas is increased to 5-10%, and continuously outputting main product gas for utilization from a product gas buffer tank I6 after the adsorption gas production is finished;
(2) pressure reduction and pressure equalization: opening the pressure equalizing control valve 8, closing other valves, communicating the top of the adsorption tower 5 which finishes the gas production by adsorption with the top of the adjacent adsorption tower 5 which just finishes the gas production by vacuumizing, and enabling the gas to flow from the adsorption tower with higher pressure to the adjacent adsorption tower which just finishes the gas production by vacuumizing;
(3) vacuumizing to produce gas: opening a vacuumizing control valve 11, closing other valves, vacuumizing from the bottom of the adsorption tower 5 subjected to pressure reduction and pressure equalization by using a vacuumizing water ring vacuum pump 10 until the vacuum degree is 60-80 kPa, so that an adsorbent in the adsorption tower 5 is regenerated, introducing the extracted secondary product gas with high oxygen concentration and ultralow methane concentration into a product gas buffer tank II12, and continuously outputting the secondary product gas from a product gas buffer tank II12 for utilization;
(4) boosting and pressure equalizing: and opening the pressure equalizing control valve 8, closing other valves, communicating the top of the adsorption tower which just completes vacuumizing gas production with the top of the adjacent adsorption tower which just completes adsorption gas production, and allowing gas to flow to the adsorption tower in a vacuum state from the adjacent adsorption tower with higher pressure, so that one period of operation of the adsorption tower is completed.
The maintaining time of the steps of gas production by adsorption and gas production by vacuum pumping is 100-200 s.
The volume concentration of methane in the main product gas in the product gas buffer tank I6 is 7-90%, and the volume concentration of oxygen is less than 3%; the volume concentration of oxygen in the secondary product gas in the product gas buffer tank II12 is 30-80%, and the volume concentration of methane is less than 1%; the main product gas and the secondary product gas have no explosion danger, can be safely transported at a distance and are respectively used as combustible gas and combustion-supporting gas, and the main product gas can also be used for manufacturing chemical products such as graphite, methanol and the like.
A plurality of adsorption columns may be used, each of which is sequentially circulated to perform the operations from step 1) to step 4), thereby achieving continuous treatment of the feed gas and continuous output of the product gas. In order to clearly illustrate the process timing of each adsorption tower, two adsorption towers are taken as an example, and the process cycle timing chart of the method of the invention is shown in FIG. 2.
When the main product gas methane concentration in the product gas buffer tank I6 needs to be increased, the oxygen concentration needs to be reduced or the operation steps need to be simplified, the pressure equalizing step of the step 2 and the step 4 can be omitted, the gas generating adsorption step directly leads low-concentration gas into the adsorption tower which is just vacuumized, the vacuumizing step directly pumps the adsorption tower which is just vacuumized to a vacuum state, but the pressure equalizing step of the step (2) and the step (4) is omitted, so that the methane recovery rate is reduced, and the vacuumizing energy consumption is increased.
As shown in fig. 1, taking two adsorption towers as an example, when the system of the invention is used for carrying out micro-pressure vacuum pressure swing adsorption for safely and efficiently concentrating low-concentration extracted gas, the low-concentration gas is extracted to the ground by a gas extraction water ring vacuum pump 1, is output at micro-positive pressure, passes through a dust removal device 2 and a dehydration device 3, enters an inlet buffer tank 4, opens a back pressure regulating control valve 9, regulates the pressure of a gas production back pressure valve 7, and then the gas in the inlet buffer tank 4 respectively enters the bottoms of an adsorption tower i or an adsorption tower ii after passing through an inlet control valve 5.1; the adsorbent in the adsorption tower I or the adsorption tower II adsorbs most of oxygen and part of nitrogen in the low-concentration gas, the residual high-methane-concentration gas flows out of the top of the adsorption tower I or the adsorption tower II and sequentially passes through the gas outlet control valve 5.2 and the gas production back pressure valve 7, and the gas pressure in the adsorption tower can be quickly increased to the set adsorption pressure and kept stable under the control of the gas production back pressure valve 7; the main product gas with high methane concentration and ultra-low oxygen concentration flowing out through the gas production back pressure valve 7 in the adsorption stage enters a product gas buffer tank I6, and then is safely transported to a gas utilization place through a remote delivery pipeline and a flow controller 13; after the adsorption stage is finished, opening the pressure equalizing control valve 8, and communicating the top of the adsorption tower I/II with the top of the adjacent adsorption tower II/I after the vacuumizing is finished; after the pressure equalization is finished, the pressure equalization control valve 8 is closed, the vacuumizing control valve 11 is opened, the secondary product gas with high oxygen concentration and ultralow methane concentration enters the product gas buffer tank II12 through the vacuumizing water ring vacuum pump 10, meanwhile, the adsorbent in the adsorption tower is regenerated, and then the secondary product gas is safely transported to a gas using place through a remote transmission pipeline and the flow controller 13.
Example 1
To illustrate the technical effects of the present invention, in this example 1, low-concentration gas with a methane concentration of 3.5%, an oxygen concentration of 19%, and a nitrogen concentration of 77.5% is selected as a raw material gas, a micro-positive pressure output by the gas extraction water ring vacuum pump 1 is 20kPa, a vacuum degree of evacuation of the adsorption tower 5 is 80kPa, a height and a diameter ratio of the adsorption tower 5 is 12:1, a volume ratio of the gas inlet buffer tank 4 to the adsorption tower 5 is 8:1, CMS-260 is used as an adsorbent, a pressure of the gas production back pressure valve 7 is 1kPa, an adsorption time is 120s, an explosion-proof and static-proof material is filled in the adsorption tower from the bottom to a tower height of 2/3, a volume ratio of the explosion-proof and static-proof material to the adsorbent in a filling area is 6%, the separation and concentration of the low-concentration gas are performed by the above separation steps of the present invention, and an experimental graph showing changes of the methane concentration and the oxygen concentration in the main product, as can be seen from FIG. 3, the concentration of oxygen in the gas after the separation and concentration method of the present invention is reduced from 19% to about 1% -2%, the concentration of methane is increased from 3.5% to 7.5% -9.5%, the separation and concentration effect of methane is obvious, and the methane concentration required by gas combustion power generation is achieved. The space-time variation law of the free oxygen concentration in the adsorption tower under the working condition of the embodiment is shown in fig. 4, and it can be known from (a), (b), (c) and (c) of fig. 4 that the oxygen concentration in the adsorption tower is very low, and the oxygen concentration in only the 2/3 area at the lower part of the adsorption tower is higher than 12% (the explosive-free oxygen concentration) in the adsorption time of 120s, so that the explosion risk can be avoided by filling the explosion-proof and anti-static material from the bottom to the 2/3 position in the adsorption tower, thereby explaining that the low-concentration gas separation and concentration method provided by the invention has very high safety.
Example 2
In this embodiment, low-concentration gas having a methane concentration of 4.5%, an oxygen concentration of 19%, and a nitrogen concentration of 76.5% is used as a raw material gas, the micro-positive pressure output by the gas extraction water ring vacuum pump 1 is 20kPa, the vacuum degree of the adsorption tower for vacuumizing is 80kPa, and the height and diameter ratio of the adsorption tower 5 is 24: 1, the volume ratio of the gas inlet buffer tank 4 to the adsorption tower 5 is 8:1, the pressure of the gas production back pressure valve 7 is 1kPa, the adsorbents respectively adopt different types of nitrogen-making carbon molecular sieves CMS-3KT, CMS-F, CMS-260, CMS-240, CMS-220 and CMS-180, explosion-proof and anti-static materials are filled in the adsorption tower from the bottom to the tower height 2/3, the volume ratio of the explosion-proof and anti-static materials to the adsorbents in the filling area is 6%, the low-concentration gas separation and concentration are carried out by adopting the steps shown in the above embodiment, then the experiment shows that the changes of the methane concentration and the oxygen concentration in the main product gas when different adsorbents are used are respectively shown in figures 5 and 6, the methane concentration is increased to 15% at most, the oxygen concentration can be reduced to 0.5%, and as can be known by comparing figures 5 and 6 with figure 4, the same adsorbent is adopted for CMS-260, the concentration of methane in the main product gas of the embodiment 2 is higher than that of the embodiment 1, and the concentration of oxygen in the main product gas of the embodiment 2 is lower than that of the embodiment 1, so the separation and concentration effects of the embodiment 2 are better than that of the embodiment 1. This is mainly because the height and diameter ratio of the adsorption tower used in example 2 is significantly larger than that of example 1, which results in the improved gas separation effect of the adsorption tower in example 2, and illustrates that the reasonable selection of the height and diameter ratio of the adsorption tower has an important influence on the separation and concentration of low-concentration gas. In addition, as can be seen from fig. 5 and 6, different types of nitrogen making carbon molecular sieves can achieve better low-concentration gas separation and concentration effects in the method, the effects of CMS-3KT, CMS-F, CMS-260 and CMS-240 are obviously better than those of CMS180 and CMS220, and particularly the separation and concentration effects of CMS-260 are the best, so that different types of nitrogen making carbon molecular sieves, namely CMS-260, CMS-3KT, CMS-F and CMS-240, can be selected in the method.

Claims (7)

1. A micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas comprises a gas extraction water ring vacuum pump (1), a dust removal device (2), a dehydration device (3) and an air inlet buffer tank (4) with a pressure gauge, wherein an air outlet of the gas extraction water ring vacuum pump (1) for outputting the low-concentration gas is sequentially connected with the dust removal device (2), the dehydration device (3) and an air inlet at the bottom of the air inlet buffer tank (4) through pipelines;
the adsorption tower comprises at least two adsorption towers (5) with pressure gauges respectively, an adsorbent is arranged in each adsorption tower (5), an air inlet at the bottom end of each adsorption tower (5) is connected with an air outlet of an air inlet buffer tank (4) through a pipeline, an air inlet control valve (5.1) is arranged on an air inlet pipeline at the bottom end of each adsorption tower (5), an air outlet at the top end of each adsorption tower (5) is connected with an air inlet end of a product air buffer tank I (6) with a pressure gauge through a pipeline, a back pressure valve (7) is arranged on a pipeline at the air inlet end of the product air buffer tank I (6), an air outlet control valve (5.2) is arranged on a pipeline at the air outlet at the top end of each adsorption tower (5), one end of the pipeline is connected on a pipeline connecting the air outlet at the top end of each adsorption tower (5) with the air outlet control valve (5.2) in parallel, the other end of the pipeline is connected on a pipeline connecting the air outlet at the top end of the adjacent adsorption tower (5) with the air outlet control valve (5.2), and a pressure equalizing control valve (8) is arranged on the pipeline; the air outlet end of the air inlet buffer tank (4) is also connected with a pipeline in parallel, the other end of the pipeline is connected with the front end of the gas production back pressure valve (7), and a back pressure regulating control valve (9) is installed on the pipeline; the vacuumizing water ring vacuum pump (10) pumps the gas adsorbed in each adsorption tower (5) to a product gas buffer tank II (12) with a pressure gauge, vacuumizing control valves (11) are respectively installed on pipelines connected with the vacuumizing water ring vacuum pump (10) and each adsorption tower, the gas in the product gas buffer tank I (6) and the gas in the product gas buffer tank II (12) are respectively and safely transported through remote transmission pipelines, and a flow controller (13) is installed on the remote transmission pipelines; the volume concentration of methane in the low-concentration gas output by the gas extraction water ring vacuum pump (1) is 1-30%; the micro-positive pressure of the gas output by the gas extraction water ring vacuum pump (1) is 5 kPa-40 kPa, and the required vacuum degree of the vacuum extraction desorption of the adsorption tower is 60 kPa-80 kPa;
characterized in that it comprises the following steps for one operating cycle of one of the adsorption columns (5):
(1) gas is produced through adsorption: adjusting the pressure of a gas production backpressure valve (7) connected with a gas outlet of an adsorption tower (5) to 1 kPa-10 kPa, communicating a gas inlet buffer tank (4) with the bottom of the adsorption tower (5) after pressure boosting and pressure equalizing are completed, enabling low-concentration gas output by a gas extraction water ring vacuum pump (1) to sequentially pass through a dust removal device (2), a dehydration device (3) and the gas inlet buffer tank (4) and then enter the adsorption tower (5) from the bottom of the adsorption tower (5), enabling most of oxygen and part of nitrogen in the low-concentration gas to be adsorbed by an adsorbent in the adsorption tower (5), enabling main product gas with high methane concentration and ultra-low oxygen concentration continuously discharged from the top of the adsorption tower (5) to enter a product gas buffer tank I (6), and enabling the main product gas to be continuously output from the product gas buffer tank I (6); stopping introducing low-concentration gas into the adsorption tower (5) before the oxygen concentration of the exhaust gas is increased to 5-10%, and finishing the adsorption gas production;
(2) pressure reduction and pressure equalization: communicating the top of the adsorption tower (5) which finishes the gas production by adsorption with the top of the adjacent adsorption tower (5) which just finishes the gas production by vacuumizing, wherein the gas flows from the adsorption tower with higher pressure to the adjacent adsorption tower (5) which just finishes the gas production by vacuumizing;
(3) vacuumizing to produce gas: vacuumizing from the bottom of the adsorption tower (5) which completes pressure reduction and pressure equalization to a preset vacuum degree by using a vacuumizing water ring vacuum pump (10), so that an adsorbent in the adsorption tower (5) is regenerated, pumping secondary product gas with high oxygen concentration and ultralow methane concentration into a product gas buffer tank II (12), and continuously outputting the secondary product gas from the product gas buffer tank II (12);
(4) boosting and pressure equalizing: the top of the adsorption tower which just finishes vacuumizing to generate gas and the top of the adjacent adsorption tower which just finishes adsorbing to generate gas are communicated, and the gas flows to the adsorption tower in a vacuum state from the adjacent adsorption tower with higher pressure, so that the operation of one period of the adsorption tower is finished.
2. The micro-positive pressure vacuum pressure swing adsorption process of claim 1, wherein the adsorbent is a commercial nitrogen-producing carbon molecular sieve.
3. The micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas as claimed in claim 1, wherein the explosion-proof and static-electricity-proof material is filled in the adsorption tower from the bottom to the tower height 1/3-2/3, and the volume ratio of the explosion-proof and static-electricity-proof material to the adsorbent in the filling area is 6% -10%.
4. The micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas according to claim 1, wherein the ratio of the height to the diameter of the adsorption tower (5) is 10:1 to 30:1, and the ratio of the volume of the inlet buffer tank (4) to the volume of the adsorption tower (5) is 7:1 to 12: 1.
5. The micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas according to claim 1, wherein the duration of the gas production by adsorption and the gas production by vacuum pumping is 100 s-200 s.
6. The micro-positive pressure vacuum pressure swing adsorption process of low-concentration gas safety concentration according to claim 1, characterized in that the pressure equalizing step of step (2) and step (4) can be omitted when it is required to increase the methane concentration, decrease the oxygen concentration or simplify the operation steps of the main product gas in the product gas buffer tank I (6).
7. The micro-positive pressure vacuum pressure swing adsorption method for safely concentrating low-concentration gas as claimed in claim 1, wherein the volume concentration of methane in the main product gas in the product gas buffer tank I (6) is 7-90%, and the volume concentration of oxygen is less than 3%; the volume concentration of oxygen in the secondary product gas in the product gas buffer tank II (12) is 30-80%, and the volume concentration of methane is less than 1%.
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