CN111773882A - Micro positive pressure vacuum pressure swing adsorption system and method for safe concentration of low concentration gas - Google Patents

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 safe concentration of low concentration gas

technical field

The invention relates to a gas extraction system for concentration, in particular to a micro-positive pressure vacuum pressure swing adsorption system for safe concentration of low-concentration gas and a method thereof, belonging to the technical field of coal mine extraction gas concentration.

Background technique

Coal mine gas is an associated gas of coal, and its main component is methane. In recent years, my country's coal mine gas extraction volume has increased steadily year by year, reaching 17.8 billion cubic meters in 2018. However, due to the easy occurrence of air leakage in the process of underground gas extraction in coal mines, a large amount of air enters the extraction pipeline, resulting in generally low gas concentration (<30%) in underground coal mine extraction, which is explosive and difficult to use. The utilization rate of the extracted gas is low (<40%), and a large amount of gas is directly discharged into the atmosphere, resulting in huge energy waste and atmospheric greenhouse effect; the output after enriching the low-concentration gas extracted is easy to use and has high economic value. The higher concentration of gas can help to improve the utilization rate of coal mine gas, which is of great significance for promoting gas extraction, ensuring coal mine safety, increasing clean energy supply and reducing greenhouse gas emissions.

Low-concentration gas in coal mines is a mixture of methane and air. When the concentration of methane is 5% to 16%, it has the risk of explosion. Therefore, the gas separation and enrichment process must ensure safety. Existing gas separation and purification technologies mainly include cryogenic rectification separation technology, membrane separation technology and pressure swing adsorption technology. The cryogenic rectification separation technology utilizes the difference in the boiling point of different gases to achieve gas separation. Gas compression will greatly widen the limit range of gas explosion concentration. It is also very easy to generate high temperature ignition sources during compression, so it may lead to gas explosion, and low temperature rectification energy consumption is high, operating conditions are high, and equipment investment is large, especially the separation of methane content When there is very little low-concentration gas, the economy is very poor; the membrane separation technology uses the polymer membrane to selectively pass through different gases to achieve gas separation, and the membrane separation technology also needs to compress the gas to form a large pressure difference on both sides of the membrane Therefore, it also has a high risk of gas explosion. In addition, there are still many problems in membrane separation technology at this stage, such as low membrane selectivity, high membrane cost, and poor mechanical properties, which restrict the application of membrane separation technology in the field of coal mine gas separation and purification. ; It can be seen that both cryogenic rectification separation technology and membrane separation technology are not suitable for use in low-concentration gas separation and concentration; pressure swing adsorption technology utilizes the equilibrium adsorption capacity or kinetic adsorption rate difference of adsorbents for different gas components to achieve Gas separation, pressure swing adsorption technology has obvious advantages such as simple process, compact equipment, low operating cost, high reliability and strong adaptability, so it is widely used in coal mine gas concentration and purification.

At present, the method for purifying coal mine gas by pressure swing adsorption mainly uses the principle of adsorption equilibrium selectivity. Method for purifying methane in coalbed methane in mine area", a "pressure swing adsorption method for enriching methane in coal mine gas" published on October 29, 1986, a Chinese invention patent with a publication number of CN85103557, Chinese invention patent, December 2009 A kind of "a low-concentration gas pressure swing adsorption grading concentration method" disclosed on the 9th with the publication number of CN101596391A all utilizes the principle of adsorption equilibrium selectivity, and uses methane as a strong adsorption component, and the product gas with high methane concentration is in the desorption stage. get.

Using the principle of equilibrium selectivity to purify low-concentration gas with oxygen has obvious technical defects: (1) the oxygen concentration in the adsorption tower is high, and the mixture of methane and high-concentration oxygen has a high explosion risk; (2) a higher adsorption Only pressure can achieve better gas separation effect, such as "a method for separating and purifying methane in coalbed methane in coalbed methane by pressure swing adsorption method" published by Chinese invention patent on July 17, 2013, with the publication number CN103205297A, China The invention patent published on October 29, 1986 is a "pressure swing adsorption method for enriching methane in coal mine gas" with a publication number of CN85103557, and a Chinese invention patent published on December 9, 2009 with a publication number of CN101596391A. A low-concentration gas pressure swing adsorption graded concentration method" adopts the adsorption pressures of 0.5 MPa to 1 MPa, 0.4 MPa to 0.7 MPa and 0.8 MPa to 2.4 MPa, so the above methods all require the use of compressors to add gas to coal mine gas. The explosion concentration limit range of gas gas under high pressure is expanded, and the high temperature fire source generated during the pressurization process can detonate the gas gas, and the pressurization also greatly increases the gas separation cost; (3) High gas pressure easily leads to the pulverization of the adsorbent Ineffective, the service life of the adsorbent is greatly shortened, and the use of high adsorption pressure requires forward/reverse decompression steps (same as the above-mentioned published patents CN85103557A, CN103205297A, CN101596391A), which increases the complexity of the process; (4) The volume of the adsorption tower in the desorption stage contains A large number of weakly adsorbed components, so a large amount of impurity gas is mixed in the desorbed gas, resulting in a low concentration of methane in the product gas.

According to the Kowald triangle, the explosion concentration range of coal mine gas is determined. When the oxygen concentration in the gas under normal temperature and pressure is less than 12%, the coal mine gas loses the explosion risk.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a micro-positive pressure vacuum pressure swing adsorption system and method for safely enriching low-concentration gas, which can safely and efficiently remove oxygen and nitrogen in low-concentration gas under micro-positive pressure, and improve the safety of gas separation. It can increase the concentration of methane under natural conditions, and realize the safe transportation after gas enrichment.

In order to achieve the above purpose, the present invention provides a micro-positive pressure vacuum pressure swing adsorption system for the safe concentration of low-concentration gas, including a gas extraction water ring vacuum pump, a dust removal device, a dehydration device, and an intake buffer tank with a pressure gauge, The gas outlet of the gas extraction water-ring vacuum pump that outputs low-concentration gas gas is connected to the air inlet at the bottom of the air inlet buffer tank of the dedusting device and the dehydration device through pipelines in turn;

It also includes at least two adsorption towers with pressure gauges respectively. Adsorbents are arranged in each adsorption tower. The air inlet at the bottom of each adsorption tower is connected to the air outlet of the air inlet buffer tank through a pipeline. The inlet control valve is installed on the inlet pipeline at the bottom end of the tower, and the air outlet at the top of each adsorption tower is connected to the inlet end of the product gas buffer tank I with a pressure gauge through a pipeline, and is fed into the product gas buffer tank I. A gas production back pressure valve is installed on the pipeline at the gas port end, a gas outlet control valve is installed on the pipeline at the gas outlet at the top of each adsorption tower, and a pipe is connected to the pipeline connecting the gas outlet at the top of each adsorption tower with the gas outlet control valve One end of the pipeline, the other end of the pipeline is connected to the pipeline connecting the air outlet at the top of the adjacent adsorption tower and the air outlet control valve, and a pressure equalizing control valve is installed on the pipeline; the air outlet end of the intake buffer tank is also connected. There is a pipeline, the other end of the pipeline is connected to the front end of the gas production back pressure valve, and a back pressure control valve is installed on the pipeline; the vacuum water ring vacuum pump extracts the gas adsorbed inside each adsorption tower to a pressure The product gas buffer tank II shown in the table, and a vacuum control valve is installed on the pipeline connecting the vacuum water ring vacuum pump to each adsorption tower. Pipes are transported safely and flow controllers are installed on long-distance transmission lines.

As a further improvement of the present invention, the volume concentration of methane in the low-concentration gas output by the water-ring vacuum pump for gas extraction is 1% to 30%.

As a further improvement of the present invention, the micro-positive pressure of the output gas of the gas extraction water ring vacuum pump is 5kPa-40kPa, and the vacuum degree to be achieved by the vacuum desorption of the adsorption tower is 60kPa-80kPa.

As a further improvement of the present invention, the adsorbent is a commercial nitrogen carbon molecular sieve.

As a further improvement of the present invention, the explosion-proof and anti-static material is filled in the adsorption tower from the bottom up to 1/3-2/3 of the tower height, and the volume ratio of the explosion-proof and anti-static material to the adsorbent in the filling area is 6% to 10% .

As a further improvement of the present invention, the ratio of the height to the diameter of the adsorption tower is in the range of 10:1 to 30:1, and the ratio of the volume of the intake buffer tank to the adsorption tower is in the range of 7:1 to 12:1.

A micro-positive pressure vacuum pressure swing adsorption method for safely enriching low-concentration gas, comprising the following steps for one operation cycle of one of the adsorption towers:

(1) Adsorption gas production: Adjust the pressure of the gas production back pressure valve connected to the gas outlet of the adsorption tower to 1kPa ~ 10kPa, connect the intake buffer tank and the bottom of the adsorption tower that has been boosted and pressure equalized, so that the gas can be used for water extraction. The low-concentration gas output by the ring vacuum pump enters the adsorption tower from the bottom of the adsorption tower through the dust removal device, the dehydration device, and the intake buffer tank in turn. Most of the oxygen and part of the nitrogen in the low-concentration gas are adsorbed by the adsorbent inside the adsorption tower. , the main product gas with high methane concentration and ultra-low oxygen concentration continuously discharged from the top of the adsorption tower enters the product gas buffer tank I, and the main product gas can be continuously output from the product gas buffer tank I; the oxygen concentration in the exhaust gas rises to Before 5% to 10%, stop feeding low-concentration gas gas into the adsorption tower, and the adsorption gas production ends;

(2) Depressurization and pressure equalization: Connect the top of the adsorption tower that has completed adsorption gas production with the top of the adjacent adsorption tower that has just completed vacuuming and gas production, and the gas flows from the adsorption tower with higher pressure to the adjacent adsorption tower that has just completed vacuuming and gas production. adsorption tower;

(3) Evacuation and gas production: use a vacuuming water ring vacuum pump to evacuate the bottom of the adsorption tower that has completed depressurization and pressure equalization to a predetermined degree of vacuum, so that the adsorbent in the adsorption tower is regenerated, and the extracted high oxygen concentration, ultra-high oxygen concentration The secondary product gas with low methane concentration is passed into the product gas buffer tank II, and the secondary product gas can be continuously output from the product gas buffer tank II;

(4) Boost and equalize: connect the top of the adsorption tower that has just completed vacuuming and gas production and the top of the adjacent adsorption tower that has just completed adsorption and gas production, and the gas flows from the adjacent adsorption tower with higher pressure to the adsorption tower in a vacuum state, so far Complete one cycle of operation of the adsorption tower.

As a further improvement of the present invention, the maintenance time of the adsorption gas production and the vacuum gas production steps are both 100s-200s.

As a further improvement of the present invention, when it is necessary to increase the methane concentration of the main product gas in the product gas buffer tank 1, reduce the oxygen concentration or simplify the operation steps, the pressure equalization step of step (2) and step (4) can be omitted, and the adsorption product The gas step directly passes the low-concentration gas into the adsorption tower that has just been evacuated, and the vacuum step directly evacuates the adsorption tower that has just completed the adsorption gas production to a vacuum state, but omitting the pressure equalization steps of steps 2) and 4) will cause The methane recovery rate is reduced and the vacuum energy consumption is increased.

As a further improvement of the present invention, the volume concentration of methane in the main product gas in the product gas buffer tank I is 7% to 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 It is 30% to 80%, and the volume concentration of methane is less than 1%; the main and secondary product gases are not explosive, can be safely transported over long distances, and can be used as combustible gas and combustion-supporting gas respectively.

Compared with the prior art, the present invention only realizes the separation and concentration of the low-concentration gas extracted under the slight positive pressure output by the existing gas extraction water-ring vacuum pump in the coal mine, and the low-concentration gas output by the gas extraction water-ring vacuum pump is processed through the gas extraction system. After dust removal and dehydration, it enters the intake buffer tank, and then enters the adsorption tower to realize the adsorption of most oxygen and part of nitrogen by the adsorbent, without the need for gas compression, which avoids the danger of low-concentration gas explosion caused by gas compression, and can prevent The adsorbent is pulverized and fails under high pressure, thereby improving the safety of gas separation, reducing energy consumption costs, and prolonging the service life of the adsorbent; in addition, the adsorbent in the adsorption tower adsorbs a large amount of oxygen, and the oxygen concentration in the adsorption tower is low, reducing the There is a risk of gas explosion in the adsorption tower. The explosion-proof and anti-static material is filled in the explosion-hazardous area where the oxygen concentration in the tower may be higher than 12%, which further increases the safety; the weak adsorption component gases discharged in the adsorption stage are high methane concentration and ultra-low oxygen. Compared with the technology of recovering methane in the desorption stage, the concentration of the main product gas improves the methane recovery rate and the methane separation and concentration effect; the operation process of the invention is simple, and steps such as forward/reverse decompression and gas replacement are not required, which is helpful for The gas processing efficiency is improved, the reliability and stability of the system operation are increased, and the main product gas and the secondary product gas produced by the present invention do not have the danger of explosion, and can realize the long-distance safe transportation after gas concentration. Used as combustible gas and combustion-supporting gas.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the process cycle sequence diagram of the invention taking two adsorption towers as an example;

Fig. 3 is the variation diagram of methane concentration and oxygen concentration in 6 circulation periods with time in the main product gas of the embodiment of the present invention 1;

Fig. 4 is the time-space distribution change diagram of free oxygen and methane concentration in the adsorption tower in Example 1 of the present invention: wherein (a) is the distribution diagram at 20s, wherein (b) is the distribution at 40s, and (c) is 60s distribution at 120s, where (d) is the distribution at 120s;

Fig. 5 is the variation diagram of methane concentration over time in the main product gas of Example 2 of the present invention;

FIG. 6 is a graph showing the variation of oxygen concentration with time in the main product gas in Example 2 of the present invention.

In the picture: 1. Water ring vacuum pump for gas extraction, 2. Dust removal device, 3. Dehydration device, 4. Inlet buffer tank, 5. Adsorption tower, 5.1, Inlet control valve, 5.2, Outlet control valve, 6. Products Gas buffer tank I, 7, gas production back pressure valve, 8, pressure equalizing control valve, 9, back pressure regulating control valve, 10, vacuum water ring vacuum pump, 11, vacuum pump control valve, 12, product gas buffer tank II , 13, flow controller.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings.

As shown in Figure 1, a micro-positive pressure vacuum pressure swing adsorption system for safe concentration of low-concentration gas includes a gas extraction water ring vacuum pump 1, a dust removal device 2, a dehydration device 3, and an intake buffer tank with a pressure gauge. 4. The gas outlet of the gas extraction water ring vacuum pump 1 that outputs low-concentration gas gas is connected to the air inlet at the bottom of the dust removal device 2, the dehydration device 3, and the inlet buffer tank 4 in turn through pipelines;

Also include at least two adsorption towers 5 with pressure gauges, each adsorption tower 5 is provided with an adsorbent material, and the air inlet at the bottom of each adsorption tower 5 is connected to the air outlet of the air intake buffer tank 4 through a pipeline , install the intake control valve 5.1 on the intake pipeline at the bottom end of each adsorption tower 5, and the air outlet at the top of each adsorption tower 5 is connected to the intake port end of the product gas buffer tank I6 with a pressure gauge through a pipeline , and install a gas production back pressure valve 7 on the pipeline at the inlet end of the product gas buffer tank I6, and install a gas outlet control valve 5.2 on the pipeline at the gas outlet at the top of each adsorption tower 5. One end of the pipeline is connected to the pipeline connecting the gas outlet and the gas outlet control valve 5.2 in parallel, and the other end of the pipeline is parallelly connected to the pipeline connecting the gas outlet at the top of the adjacent adsorption tower 5 and the gas outlet control valve 5.2, and is installed on the pipeline. Pressure equalizing control valve 8; a pipeline is also connected in parallel at the air outlet end of the intake buffer tank 4, the other end of the pipeline is connected to the front end of the gas production back pressure valve 7, and a back pressure regulating control valve 9 is installed on the pipeline ; Evacuation water ring vacuum pump 10 extracts the secondary product gas adsorbed in each adsorption tower 5 to the product gas buffer tank II12 with a pressure gauge, and on the pipeline connecting the evacuated water ring vacuum pump 10 and each group of adsorption towers The vacuum control valve 11 is installed respectively, and the gas in the product gas buffer tank I6 and the product gas buffer tank II12 are safely transported through the long-distance transmission pipeline, and the flow controller 13 is installed on the long-distance transmission pipeline.

The volume concentration of methane in the low-concentration gas output by the water-ring vacuum pump 1 for gas extraction is 1% to 30%.

The micro-positive pressure of the output gas of the water-ring vacuum pump 1 for gas extraction is 5kPa~40kPa, and the water-ring vacuum pump 1 for coal mine gas extraction outputs low-concentration gas with a micro-positive pressure of 5kPa~40kPa, and the volume concentration of methane is 1%~30%. The concentration gas is sent to the dust removal device 2 and the dehydration device 3, the dust and water vapor therein are removed, and the purified gas directly enters the intake buffer tank 4 as the raw material gas for pressure swing adsorption, without going through the gas compression link; the adsorption tower The vacuum degree that needs to be reached for vacuum desorption is 60kPa ~ 80kPa.

The adsorbent of the present invention is a commercial nitrogen carbon molecular sieve, the gas in the intake buffer tank 4 enters the adsorption tower 5, and the commercial nitrogen carbon molecular sieve is filled in the adsorption tower 5, and the specific models include CMS-3KT, 1.5GN-H, CMS-F , CMS-260, CMS-240, CMS-220 and CMS-180, the above adsorbents can adsorb a large amount of oxygen in low-concentration gas under the slight positive pressure of 5kPa ~ 40kPa, and also adsorb nitrogen, and basically do not adsorb methane gas.

The explosion-proof and anti-static material is filled in the adsorption tower from the bottom up to 1/3-2/3 of the tower height, and the volume ratio of the explosion-proof and anti-static material to the adsorbent in the filling area is 6% to 10%. It is preferably a reticulated aluminum alloy material.

In order to ensure better gas adsorption effect and lower gas flow resistance at the same time, the ratio of the height to the diameter of the adsorption tower 5 of the present invention ranges from 10:1 to 30:1.

It is ensured that the gas pressure in the buffer tank remains stable, and the gas can be output to the adsorption tower stably.

A micro-positive pressure vacuum pressure swing adsorption method for safely enriching low-concentration gas, characterized in that an operation cycle of a certain adsorption tower 5 comprises the following steps:

(1) Adsorption gas production: open the back pressure regulating control valve 9, connect the intake buffer tank 4 and the front end of the gas production back pressure valve 7, and adjust the pressure of the gas production back pressure valve 7 to 1kPa～10kPa (relative pressure), The gas-producing back pressure valve 7 can rapidly increase the pressure in the adsorption tower 5 to the specified adsorption pressure and keep it stable, then close the back pressure regulating control valve 9 and open the intake control valve 5.1 at the bottom of the two adjacent adsorption towers 5, Close other valves, connect the intake buffer tank 4 and the bottom of the adsorption tower 5 that has been boosted and pressure equalized, so that low-concentration gas enters the interior of the adsorption tower 5 from the bottom of the adsorption tower 5, and most of the oxygen and Part of the nitrogen is adsorbed by the adsorbent inside the adsorption tower 5, and the main product gas with high methane concentration and ultra-low oxygen concentration continuously discharged from the top of the adsorption tower 5 enters the product gas buffer tank I6, and the main product gas can be from the product gas buffer tank I6. Continuous output; stop feeding low-concentration gas gas into the adsorption tower 5 before the oxygen concentration of the exhaust gas rises to 5% to 10%, and the adsorption gas production ends, and the main product gas can be continuously output from the product gas buffer tank I6. for use;

(2) pressure reduction and pressure equalization: open the pressure equalization control valve 8, close other valves, and connect the top of the adsorption tower 5 that has completed adsorption gas production with the top of the adjacent adsorption tower 5 that has just completed vacuuming and gas production, and the gas from the higher pressure The adsorption tower flows to the adjacent adsorption tower that has just completed vacuuming and gas production;

(3) Evacuation and gas production: open the evacuation control valve 11, close other valves, and use the evacuation water ring vacuum pump 10 to evacuate from the bottom of the adsorption tower 5 that has completed depressurization and pressure equalization to a degree of vacuum of 60kPa～80kPa, so that the adsorption tower The adsorbent in 5 is regenerated, and the extracted secondary product gas with high oxygen concentration and ultra-low methane concentration is passed into the product gas buffer tank II12, and the secondary product gas can be continuously output from the product gas buffer tank II12 for utilization;

(4) Boosting and equalizing: open the equalizing control valve 8, close other valves, and connect the top of the adsorption tower that has just completed vacuuming and gas production with the top of the adjacent adsorption tower that has just completed adsorption and gas production. The adjacent adsorption tower flows to the adsorption tower in the vacuum state, thus completing one cycle of operation of the adsorption tower.

The maintenance time of the adsorption gas production and the vacuum gas production steps are both 100s to 200s.

The volume concentration of methane in the main product gas in the product gas buffer tank I6 is 7% to 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% to 80%, The volume concentration of methane is less than 1%; the main and secondary product gases are non-explosive and can be safely transported over distances, and are used as combustible gas and combustion-supporting gas respectively. The main product gas can also be used to manufacture chemical products such as graphite and methanol.

A plurality of adsorption towers can be used, and each adsorption tower can be cycled to perform the operations from step 1) to step 4) in turn, so as to realize continuous treatment of raw gas and continuous output of product gas. In order to clearly illustrate the process sequence arrangement of each adsorption tower, taking two adsorption towers as an example, the process cycle sequence diagram of the method of the present invention is shown in FIG. 2 .

When it is necessary to increase the methane concentration of the main product gas in the product gas buffer tank I6, reduce the oxygen concentration or simplify the operation steps, the pressure equalization steps of steps 2 and 4 can be omitted, and the adsorption gas production step directly passes the low-concentration gas into the freshly pumped gas. After vacuuming the adsorption tower, the vacuuming step directly evacuates the adsorption tower that has just completed adsorption and gas production to a vacuum state, but omitting the pressure equalization step of step (2) and step (4) will lead to a reduction in methane recovery rate and vacuum energy consumption. improve.

As shown in Figure 1, taking two adsorption towers as an example, when using the system of the present invention to carry out the micro-pressure vacuum pressure swing adsorption of the safe and efficient concentration of low-concentration gas extraction, the low-concentration gas is pumped by the gas extraction water ring vacuum pump 1 Mined to the ground, and output with a slight positive pressure, after passing through the dust removal device 2 and the dehydration device 3, it enters the intake buffer tank 4, opens the back pressure control valve 9, adjusts the pressure of the gas production back pressure valve 7, and then enters the intake buffer tank. The gas in 4 enters the bottom of adsorption tower I or adsorption tower II respectively after passing through the intake control valve 5.1; the adsorbent in adsorption tower I or adsorption tower II adsorbs most of the oxygen and part of nitrogen in the low-concentration gas, and the rest is high. The methane concentration gas flows out from the top of the adsorption tower I or adsorption tower II, and passes through the gas outlet control valve 5.2 and the gas production back pressure valve 7 in turn. Under the control of the gas production back pressure valve 7, the gas pressure in the adsorption tower can be rapidly increased to the set 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 the product gas buffer tank 16, and then passes through the long-distance conveying pipeline and the flow controller 13. It is safely transported to the place where the gas is used; after the end of the adsorption stage, open the pressure equalizing control valve 8, and the top of the adsorption tower I/II is connected to the top of the adjacent adsorption tower II/I after vacuuming; Press the control valve 8, open the vacuum control valve 11, the secondary product gas with high oxygen concentration and ultra-low methane concentration enters the product gas buffer tank II 12 through the vacuum water ring vacuum pump 10, and the adsorbent in the adsorption tower is regenerated at the same time. Secondary product gas is safely transported to the point of use via long-distance transmission lines and flow controllers 13 .

Example 1

In order to illustrate the technical effect of the present invention, the present embodiment 1 selects low-concentration gas with a methane concentration of 3.5%, an oxygen concentration of 19%, and a nitrogen concentration of 77.5% as the raw material gas, and the micro-positive pressure output by the gas extraction water ring vacuum pump 1 is 20kPa, The vacuum degree of the adsorption tower 5 is 80kPa, the height and diameter ratio of the adsorption tower 5 is 12:1, the volume ratio of the intake buffer tank 4 and the adsorption tower 5 is 8:1, the adsorbent adopts CMS-260, and the gas producing back The pressure of the pressure valve 7 is 1kPa, the adsorption time is 120s, and the explosion-proof and anti-static material is filled inside the adsorption tower from the bottom to 2/3 of the tower height. The volume ratio of the explosion-proof and anti-static material to the adsorbent in the filling area is 6%. The above-mentioned separation step of the present invention carries out low-concentration gas separation and concentration, and then the methane concentration and oxygen concentration in the main product gas obtained by the experiment are shown in Figure 3 as a function of time in 6 cycles. It can be seen from Figure 3 that the present invention The oxygen concentration in the gas is reduced from 19% to about 1% to 2%, and the methane concentration is increased from 3.5% to 7.5% to 9.5%. The methane separation and concentration effect is obvious, and the methane concentration required for gas combustion power generation is achieved. . The temporal and spatial variation of the free oxygen concentration in the adsorption tower under the working conditions of this example is shown in Figure 4. From Figure 4 (a), (b), (c), and (c), it can be seen that the oxygen concentration in the adsorption tower is very low , in the adsorption time of 120s, only the oxygen concentration in the lower 2/3 area of the adsorption tower is higher than 12% (detonation oxygen concentration), so the explosion-proof and anti-static materials are filled inside the adsorption tower from the bottom up to 2/3 of the tower height. The risk of explosion is avoided, which shows that the low-concentration gas separation and concentration method proposed by the present invention has high safety.

Example 2

In this embodiment, low-concentration gas with a methane concentration of 4.5%, an oxygen concentration of 19%, and a nitrogen concentration of 76.5% is selected as the raw material gas, the micro-positive pressure output by the gas extraction water ring vacuum pump 1 is 20kPa, and the vacuum degree of the adsorption tower is 80kPa , the height and diameter ratio of the adsorption tower 5 is 24:1, the volume ratio of the intake buffer tank 4 and the adsorption tower 5 is 8:1, the pressure of the gas production back pressure valve 7 is 1kPa, and the adsorbents are made of different types. Nitrogen-carbon molecular sieves CMS-3KT, CMS-F, CMS-260, CMS-240, CMS-220 and CMS-180 are filled with explosion-proof and anti-static materials from the bottom up to 2/3 of the tower height inside the adsorption tower. The volume ratio of explosion-proof and anti-static material to adsorbent in the area is 6%, and the steps shown in the above embodiment are used to separate and concentrate low-concentration gas, and the experiment shows the changes of methane concentration and oxygen concentration in the main product gas when different adsorbents are used. As shown in Figure 5 and Figure 6 respectively, the methane concentration can be increased to 15% at the highest, and the oxygen concentration can be reduced to 0.5%. Comparing Figure 5, Figure 6 with Figure 4, it can be seen that the same adsorbent CMS-260 is used, Example 2 The methane concentration of the main product gas is higher than that of Example 1, and the oxygen concentration of the main product gas of Example 2 is lower than that of Example 1, so the separation and concentration effect of Example 2 is better than that of Example 1. This is mainly because the height and diameter ratio of the adsorption tower used in Example 2 are significantly larger than those in Example 1, which leads to the improvement of the gas separation effect of the adsorption tower in Example 2, which shows that the reasonable selection of the height and diameter ratio of the adsorption tower has the advantages of low concentration gas separation and concentration. Significant influence. In addition, it can be seen from Figure 5 and Figure 6 that different types of nitrogen-producing carbon molecular sieves can play a better low-concentration gas separation and concentration effect in the method of the present invention. CMS-3KT, CMS-F, CMS-260 and CMS-240 The effect of CMS180 and CMS220 is obviously better than that of CMS180 and CMS220, especially the separation and concentration effect of CMS-260 is the best, so the present invention can choose various carbon molecular sieves for nitrogen production, such as CMS-260, CMS-3KT, CMS-F and CMS-240. The effect is better.

Claims (10)

1. A micro-positive pressure vacuum pressure swing adsorption system for safely enriching low-concentration gas, comprising a gas extraction water ring vacuum pump (1), a dust removal device (2), a dehydration device (3), an air intake with a pressure gauge The buffer tank (4), the gas outlet of the gas extraction water ring vacuum pump (1) that outputs low-concentration gas gas is connected to the dust removal device (2), the dehydration device (3), and the bottom of the intake buffer tank (4) through the pipeline in turn. Air port connection; characterized in that, It also includes at least two adsorption towers (5) with pressure gauges respectively, an adsorbent is arranged in each adsorption tower (5), and the air inlet at the bottom end of each adsorption tower (5) is connected to an air intake buffer through a pipeline At the air outlet of the tank (4), an air inlet control valve (5.1) is installed on the air inlet pipeline at the bottom of each adsorption tower (5), and the top air outlet of each adsorption tower (5) is connected with a pressure via a pipeline. The inlet end of the product gas buffer tank I (6) shown in the table, and install the gas production back pressure valve (7) on the pipeline of the inlet end of the product gas buffer tank I (6), in each adsorption tower (5) The gas outlet control valve (5.2) is installed on the pipeline at the top gas outlet respectively, and one end of the pipeline is connected to the pipeline connecting the top gas outlet of each adsorption tower (5) with the gas outlet control valve (5.2), and the other side of the pipeline is connected. One end is connected in parallel to the pipeline connecting the air outlet at the top of the adjacent adsorption tower (5) with the air outlet control valve (5.2), and a pressure equalizing control valve (8) is installed on the pipeline; The gas port end is also connected with a pipeline, the other end of the pipeline is connected to 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 gas adsorbed inside each adsorption tower (5) is pumped out to the product gas buffer tank II (12) with a pressure gauge, and a vacuum pump is installed on the pipeline connecting the vacuum water ring vacuum pump (10) with each adsorption tower. The control valve (11), the gas in the product gas buffer tank I (6) and the product gas buffer tank II (12) are respectively safely transported through the long-distance transmission pipeline, and a flow controller (13) is installed on the long-distance transmission pipeline. . 2. the slightly positive pressure vacuum pressure swing adsorption system of a kind of low-concentration gas safety enrichment according to claim 1, is characterized in that, the methane volume concentration in the low-concentration gas output by the gas extraction water ring vacuum pump (1) is: 1% to 30%. 3. the micro positive pressure vacuum pressure swing adsorption system of a kind of low concentration gas safety enrichment according to claim 1 and 2, is characterized in that, the micro positive pressure of gas extraction water ring vacuum pump (1) output gas is 5kPa ～40kPa, and the vacuum degree to be achieved by the vacuum desorption of the adsorption tower is 60kPa～80kPa. 4. The micro-positive pressure vacuum pressure swing adsorption system of a low-concentration gas safe concentration according to claim 1 or 2, wherein the adsorbent is a commercial nitrogen-producing carbon molecular sieve. 5 . The micro-positive pressure vacuum pressure swing adsorption system for safely enriching low-concentration gas according to claim 1 or 2, characterized in that, in the adsorption tower, from the bottom up to 1/3～2/3 of the tower height The explosion-proof and anti-static material is filled at the place, and the volume ratio of the explosion-proof and anti-static material to the adsorbent in the filling area is 6% to 10%. 6. the micro positive pressure vacuum pressure swing adsorption system of a kind of low concentration gas safety enrichment according to claim 1 and 2, is characterized in that, the scope of the ratio of the height of adsorption tower (5) and diameter is 10:1 ~30:1, and the volume ratio of the intake buffer tank (4) to the adsorption tower (5) is in the range of 7:1 to 12:1. 7. the slightly positive pressure vacuum pressure swing adsorption method of a kind of low-concentration gas safety enrichment according to claim 1, is characterized in that, comprises the following steps for an operation cycle of wherein one adsorption tower (5): (1) Adsorption gas production: adjust the pressure of the gas production back pressure valve (7) connected to the air outlet of the adsorption tower (5) to 1kPa ~ 10kPa, and connect the intake buffer tank (4) with the adsorption that has been boosted and pressure equalized. At the bottom of the tower (5), the low-concentration gas output by the gas extraction water ring vacuum pump (1) passes through the dust removal device (2), the dehydration device (3), and the intake buffer tank (4) in sequence, and then flows out of the adsorption tower (5). The bottom of the gas enters the adsorption tower (5), most of the oxygen and part of the nitrogen in the low-concentration gas are adsorbed by the adsorbent inside the adsorption tower (5), and the high methane concentration, ultra-low concentration continuously discharged from the top of the adsorption tower (5) The main product gas with oxygen concentration enters the product gas buffer tank I (6), and the main product gas can be continuously output from the product gas buffer tank I (6); before the oxygen concentration of the exhaust gas rises to 5% to 10%, stop to Low-concentration gas gas is introduced into the adsorption tower (5), and the adsorption gas production ends; (2) Depressurization and pressure equalization: Connect the top of the adsorption tower (5) that has completed the adsorption and gas production with the top of the adjacent adsorption tower (5) that has just completed vacuuming and gas production, and the gas flows from the adsorption tower with higher pressure to the just completed pumping. Adjacent adsorption tower (5) for vacuum gas production; (3) Evacuation and gas production: use the vacuum water ring vacuum pump (10) to evacuate the bottom of the adsorption tower (5) where the pressure reduction and pressure equalization is completed to a predetermined degree of vacuum, so that the adsorbent in the adsorption tower (5) is regenerated , the extracted secondary product gas with high oxygen concentration and ultra-low methane concentration is passed into the product gas buffer tank II (12), and the secondary product gas can be continuously output from the product gas buffer tank II (12); (4) Boost and equalize: connect the top of the adsorption tower that has just completed vacuuming and gas production and the top of the adjacent adsorption tower that has just completed adsorption and gas production, and the gas flows from the adjacent adsorption tower with higher pressure to the adsorption tower in a vacuum state, so far Complete one cycle of operation of the adsorption tower. 8 . The micro-positive pressure vacuum pressure swing adsorption method for safe enrichment of low-concentration gas according to claim 7 , wherein the maintenance time of the steps of adsorption gas production and vacuum gas production are both 100s to 200s. 9 . 9. the slightly positive pressure vacuum pressure swing adsorption method of a kind of low concentration gas safety enrichment according to claim 7, is characterized in that, when the main product gas methane concentration in the product gas buffer tank 1 (6) needs to be improved, When reducing the oxygen concentration or simplifying the operation steps, the pressure equalization steps of steps (2) and (4) can be omitted. 10. the slightly positive pressure vacuum pressure swing adsorption method of a kind of low concentration gas safety enrichment according to claim 7, is characterized in that, in the main product gas in the product gas buffer tank 1 (6), the methane volume concentration 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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