CN107694284A - A multi-tower replacement vacuum pressure swing adsorption method for concentrating coal bed methane methane - Google Patents

Abstract

It is a kind of method of the multitower Vacuum Pressure Swing Adsorption of carbon dioxide replacement the present invention relates to low concentration coal-bed gas methane concentration technical field, it is main to include pressurization, CH₄Absorption, CO₂The steps such as displacement, decompression, adsorbent vacuum desorption, vacuum purging.The present invention has following advantage：Carbon dioxide is Working medium gas and recycling, methane is used as overhead product by displacement and reaches about 90% purity and 80% rate of recovery；Carbon dioxide replacement stage not pure gas of the part containing methane of discharge is, respectively, used as vacuum desorption purge gass, and after purging, purge gass are back to charging source of the gas and carbon dioxide replacement source of the gas, circulation and stress, reduction methane losses amount respectively again；Multitower series connection carries out CH₄Absorption and CO₂Displacement, increase the adsorbent loading of packed bed, improve methane production；Multitower is in parallel to carry out adsorbent CO₂Regeneration, mobile phase pressure drop in tower is reduced, makes adsorbent reactivation easy.Present invention methane concentration suitable for the coal bed gas of different methane contents prepares the natural gas of high-quality.

Description

A multi-tower replacement vacuum pressure swing adsorption method for concentrating coal bed methane methane

technical field

The invention relates to the technical field of methane enrichment of coal bed gas, in particular to a method for concentrating low-concentration methane in coal bed gas by multi-tower vacuum pressure swing adsorption with carbon dioxide replacement.

Background technique

Methane is a high-quality fuel with large natural reserves, high calorific value, and the highest hydrogen/carbon ratio. It plays an important role in the energy system and is a cleaner energy source than coal and oil. Therefore, it is of great practical and strategic significance to separate and purify methane from coalbed methane, oil field gas, shale gas, biogas, landfill gas and other sources of low-quality methane gas resources to improve the energy structure and protect the atmospheric environment.

my country is rich in coalbed methane resources. According to the latest resource forecast, the total amount of coalbed methane resources in China is about 32 trillion cubic meters, making it the third country with the largest coalbed methane reserves after Russia and Canada. CBM can be divided into surface extraction and underground extraction according to the extraction methods. Surface drainage can obtain combustible gas with CH ₄ content above 95%, which can be directly used as high-energy fuel and chemical raw material, but the current drainage scale is small. Underground drainage is to extract coalbed methane from underground mines for the safety of coal mining. Since a large amount of air is mixed in the drainage process, the concentration of CH ₄ is only 10%-30%. The extraction volume of this part of coalbed methane is huge, more than up to 15 billion cubic meters. Due to the lack of advanced and practical methane concentration and separation technology, the utilization rate of low-concentration coalbed methane in China currently only accounts for 5%-10% of the total emissions, and most of them are directly discharged into the atmosphere, which not only wastes resources, but also causes serious atmospheric greenhouse effects (The greenhouse effect of CH ₄ is 21 times that of CO ₂ ).

An important factor restricting the utilization of low-concentration coalbed methane is its low CH ₄ content. If the CH ₄ concentration is increased to more than 80%, it can be used as high-energy fuel or chemical raw material; if the CH ₄ content reaches 95%, it can be directly incorporated into Natural gas pipeline network transmission. In addition to a certain amount of CH ₄ , low-concentration coalbed methane also contains a large amount of CO ₂ and N ₂ and a small amount of oxygen. The physical properties of CO ₂ and CH ₄ are very different, and they are easy to separate; CH ₄ and N ₂ are the most difficult to separate because of their similar kinetic diameters and similar physical properties. CBM methane separation and enrichment technologies include cryogenic rectification, membrane separation, absorption and adsorption methods. The adsorption method has attracted much attention due to its advantages of simple equipment, convenient operation, practical process and low energy consumption. It is considered to be the most industrially promising technology for methane concentration of low-concentration coalbed methane.

The currently reported adsorbents for adsorption and separation of CH ₄ /N ₂ include activated carbon, carbon molecular sieves, silica-alumina molecular sieves, mesoporous molecular sieves, titanium-silicon molecular sieves and metal-organic framework materials. Since the CH ₄ /N ₂ equilibrium separation coefficient of the existing adsorption material is not high, it is difficult to concentrate the methane content below 50% to above 80% at one time based on the pressure swing adsorption process. When dealing with gas with a methane concentration of less than 10%, the concentration efficiency of traditional pressure swing adsorption will be very low, and the engineering application is uneconomical. The patent (CN101549240A) introduces the method of carbon dioxide displacement pressure swing adsorption to concentrate coalbed methane. In the pressure swing adsorption process, the step of replacing the adsorbed methane with carbon dioxide is added, so that methane becomes the top product, thereby improving the product gas methane. degrees and yields. Compared with methane and nitrogen adsorption, carbon dioxide is a strong adsorption component, and the energy consumption of adsorbent regeneration increases significantly. This method does not discuss the cycle process of carbon dioxide medium desorption and multi-tower series-parallel enhanced enrichment of low-concentration methane. At present, there are no other related patent reports on the carbon dioxide medium desorption and recycling process.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for concentrating low-concentration methane in coalbed methane through multi-tower vacuum pressure swing adsorption continuous circulation circulation.

The technical solution of the present invention is a vacuum pressure swing adsorption method for carbon dioxide replacement, which is characterized in that the coalbed methane with low concentration of methane is converted into high-quality natural gas fuel by adopting multi-tower continuous cycle adsorption, carbon dioxide replacement and vacuum desorption technologies; Each cycle of the method comprises the following specific steps:

Step (1) pressurization: pressurize the packed tower to the operating pressure set in the adsorption stage of 1.1atm to 10atm;

Step (2) Methane adsorption: Under the above-mentioned pressure conditions at a temperature of 10°C to 50°C, low-concentration coal-bed methane methane is input from the bottom of the packed tower into the packed tower containing adsorbents for adsorption and capture of methane. When the methane adsorption front reaches At the outlet of the packed tower, the adsorption stage ends;

Step (3) Carbon dioxide replacement: Under the conditions of temperature 10℃～50℃ and pressure 1.1atm～10atm, input carbon dioxide to replace the adsorbed methane and nitrogen in the tower. As the replacement progresses, the gases are sequentially discharged from the top of the packed tower and stored separately In the three buffer tanks, there are high-concentration methane product gas, high-concentration nitrogen with a small amount of methane, and high-concentration methane with a small amount of carbon dioxide; after the replacement of methane and nitrogen in the tower, the packed tower is basically full of carbon dioxide;

Step (4) depressurization: the packed tower is depressurized to normal pressure, and the carbon dioxide in the desorption tower is decompressed;

Step (5) Vacuum desorption: use a vacuum pump to reduce the pressure inside the packed tower to 1kPa-15kPa; this can increase the carbon dioxide desorption rate.

Step (6) Vacuum purge 1: Under vacuum pressure, use a small amount of high-concentration methane to purge from the top of the tower to replace carbon dioxide in the tower; purge gas 1 is the high-concentration methane obtained in step (3) containing a small amount of carbon dioxide;

Step (7) Vacuum purge 2: Under vacuum pressure, use a small amount of high-concentration nitrogen to purge from the top of the tower to replace methane in the tower; purge gas 2 is the high-concentration nitrogen obtained in step (3) containing a small amount of methane.

After completing step (7), cycle to step (1), repeat the operation, and perform the next cycle.

In the above method, in step (2), since the concentration of methane in coalbed methane is low, less than 20%, the methane adsorption partial pressure will be very low, and the methane adsorption capacity of the adsorbent is also low. This process recommends pressure adsorption to capture methane , the pressure is 1.1atm ~ 10atm, in order to improve the methane adsorption rate.

In step (5), under the conditions allowed by the vacuum pump, make the vacuum pressure as low as possible to improve the _CO desorption rate of the adsorbent.

In step (6), the high-concentration methane contains a small amount of carbon dioxide, which comes from the recovery of part of the gas from the top of the tower during the _CO2 replacement process. After vacuum purging, the gas is recovered and sent to the _CO2 replacement stage for recycling. The operation can reduce methane loss amount.

In step (7), the high-concentration nitrogen contains a small amount of methane, which is also part of the gas recovered from the top of the tower during the carbon dioxide replacement process. After purging, the gas is recovered and sent to the methane adsorption stage for recycling to reduce methane loss.

According to a carbon dioxide replacement vacuum pressure swing adsorption method of the present invention, preferably, the adsorbent filled in the multi-tower is selected from one or both of carbon-based materials and zeolite molecular sieves.

Further, the adsorbent can be in the shape of granular, fibrous, honeycomb or the like.

According to a carbon dioxide replacement vacuum pressure swing adsorption method of the present invention, preferably, the filling height of each tower is 0.8-1.2 meters. Due to vacuum desorption, the appropriate filling height of each tower is about 1 meter to reduce the pressure drop of the bed and improve the desorption efficiency.

According to a vacuum pressure swing adsorption method for carbon dioxide replacement of the present invention, preferably, the multi-tower continuous operation is three or more sets of packed tower cycle operations; each group contains a single tower, two towers, three towers, Four towers, or more towers.

Further, multiple towers in each group are connected in series for CH ₄ adsorption and capture and CO ₂ replacement; multiple towers in each group are connected in parallel for adsorbent CO ₂ regeneration.

Multiple towers in each group are connected in series for _CH4 adsorption and capture and _CO2 replacement to increase methane yield and purity, and multiple towers in each group are connected in parallel to regenerate adsorbent _CO2 to reduce the pressure drop of the mobile phase in the tower and make it easier to regenerate the adsorbent .

According to a carbon dioxide displacement vacuum pressure swing adsorption method of the present invention, preferably, the methane concentration of the low-concentration methane is 5%-20%.

According to a vacuum pressure swing adsorption method for carbon dioxide replacement of the present invention, preferably, the carbon dioxide input in step (3) consists of two parts, and in the early stage of the replacement stage, step (4), step (5) and step (6) are used ) decompression and vacuum desorption to recover the carbon dioxide, and use supplementary high-concentration carbon dioxide in the later stage of the replacement stage.

The carbon dioxide input in step (3) is high-concentration carbon dioxide with a purity of more than 90%. The high-concentration carbon dioxide is allowed to contain a small amount of methane, but nitrogen is not allowed to prevent pollution of the product gas methane purity.

Preferably, the carbon dioxide desorbed in step (4) is recovered and sent to the carbon dioxide replacement stage of step (3) for recycling; the carbon dioxide desorbed in step (5) is recycled and sent to the step (3) replacement stage for recycling; step (6) , after being purged, the obtained carbon dioxide gas is recovered and transported to the carbon dioxide replacement stage of step (3) for recycling.

The carbon dioxide gas source in step (3) is composed of two parts. The gas source in the early stage of the replacement stage comes from the carbon dioxide gas recovered in the previous cycle step (4), step (5) and step (6); the gas source in the later stage of the replacement stage is new Supplementary high-purity carbon dioxide (above 90%). The high-concentration carbon dioxide is allowed to contain a small amount of methane, but nitrogen is not allowed to prevent pollution of the product gas methane purity.

According to a carbon dioxide displacement vacuum pressure swing adsorption method of the present invention, preferably, in step (7), after purging, the gas is recovered and transported to step (2) to recover methane. This reduces the rate of methane loss.

Preferably, part of the methane-containing impure gas discharged from the carbon dioxide replacement stage of step (3) is used as vacuum desorption purge gas respectively. After purging, the purge gas 2 is returned to the feed gas source in step (2), The purge gas 1 is returned to the carbon dioxide replacement gas source in step (3), and the methane is recycled.

Preferably, step (5) uses a vacuum pump to evacuate to reduce the pressure in the packed tower to 5kPa-15kPa.

The beneficial effects of the present invention are:

In the carbon dioxide replacement process of the present invention, the gas discharged from the top of the tower is divided into three parts successively, high-concentration methane product gas, high-concentration nitrogen (slightly containing a small amount of methane) are used as follow-up vacuum purge gas 2, and high-concentration methane (slightly containing a small amount of carbon dioxide) is used For follow-up vacuum purge 1. After vacuum purging, the purge gas is recovered and recycled to reduce methane loss and increase methane recovery rate.

In the cyclic adsorption process, multiple towers are connected in series for _CH4 adsorption and capture and _CO2 replacement to increase methane yield and purity, and multiple towers are connected in parallel to regenerate the adsorbent _CO2 to reduce the pressure drop of the mobile phase in the tower and make the adsorbent Regeneration is easy. The adsorption and concentration efficiency of low-concentration methane (5% to 20%) in coalbed methane is remarkable, which is obviously superior to the traditional vacuum pressure swing adsorption technology.

The present invention overcomes the defects of the existing pressure swing adsorption technology and has the following advantages: ① carbon dioxide is used as the working medium gas and is recycled, and about 10% CH ₄ gas passes through the adsorption and replacement process, making methane as the top product and reaching about 90% % purity and 80% recovery rate; ② Part of the impure gas containing methane discharged from the carbon dioxide replacement stage is used as vacuum desorption purge gas respectively. After purging, the purge gas is returned to the feed gas source and carbon dioxide replacement gas respectively ③Multiple packed towers are operated cyclically, and multiple towers are connected in series for CH ₄ adsorption and capture and CO ₂ replacement to improve methane yield and purity. Multi-towers are connected in parallel to regenerate adsorbent CO ₂ to reduce The pressure drop of the mobile phase in the tower makes it easy to regenerate the adsorbent. The present invention is suitable for methane concentration in coalbed methane with different methane contents, operates at normal temperature, can choose adsorption under pressure or near normal pressure and _CO2 replacement, commercial adsorbents such as activated carbon, zeolite and molecular sieve can all be used, so it can be used at a lower cost Turn low-methane coalbed methane into high-quality natural gas fuel.

Description of drawings

Figure 1. The activated carbon packed tower absorbs methane from 10% CH ₄ coalbed methane and then performs CO ₂ replacement. The composition of the gas outflow from the top of the filled tower and the division interval of product gas and vacuum desorption purge gas.

Figure 2. Schematic diagram of the process flow and program-controlled valves of multi-tower series for low-concentration _CH4 adsorption capture and _CO2 replacement steps and multi-tower parallel for adsorbent _CO2 regeneration (example of the first tower group).

Fig. 3 is a seven-step process cycle operation diagram of carbon dioxide replacement vacuum pressure swing adsorption concentration of low-concentration methane.

Fig. 4. Schematic diagram of the seven-step _CO replacement vacuum pressure swing adsorption process flow diagram for the enrichment of low-concentration CBM methane in the three-tower group.

detailed description

Figure 1 shows the composition of the gas outflow from the top of the filled tower when the activated carbon packed tower absorbs and captures 10% methane in the simulated coalbed methane after adsorption and capture of 10% methane in the simulated coalbed methane, and the division interval of the product gas and vacuum desorption purge gas, the operating pressure and The operating temperatures are near atmospheric pressure and room temperature, respectively. When the methane and nitrogen in the tower are replaced, they are discharged from the top of the tower in turn. The high-concentration nitrogen contains a small amount of methane (used as vacuum purge gas 2 in the present invention), and the high-concentration methane contains a small amount of nitrogen (recovered as product gas in the present invention). , high-concentration methane slightly contains a small amount of carbon dioxide (this invention is used as vacuum purge gas 1). As can be seen from Fig. 1, the purity of product gas methane can reach more than 90%; the gas containing methane in the other two parts is used as vacuum purge gas, and after the vacuum purge, the gas is returned to the feed gas source and the feed gas source of step (2) respectively. The carbon dioxide in step (3) replaces the gas source to further recover methane and reduce methane loss.

Since methane is a non-polar gas, the existing adsorbents have a small adsorption capacity for low-concentration methane, and it is necessary to increase the length of the packed bed (increase the amount of adsorbent) to increase the methane yield. However, the increase in the length of the packed bed will lead to a larger pressure drop of the mobile phase in the tower, which is not conducive to the depressurization regeneration of the adsorbent. Therefore, the present invention intends to use multiple towers connected in series to carry out the low-concentration _CH4 adsorption and capture and _CO2 replacement steps to increase the length of the packed bed (increase the amount of adsorbent) and increase the methane production rate; multiple towers are connected in parallel to carry out the regeneration of the adsorbent _CO2 , reducing the number of towers The pressure drop of the internal mobile phase makes the regeneration of the _CO2 adsorbent easy, as shown in Figure 2.

The carbon dioxide replacement multi-tower vacuum pressure swing adsorption method for concentrating low-concentration methane in coalbed methane of the present invention is a process of cyclic adsorption, replacement and desorption, and each cycle includes pressurization, adsorption, replacement, pressure reduction, vacuum desorption, and vacuum blowing. Sweep 1 and vacuum purge 2 seven steps (Figure 3), its specific steps:

Step (1) pressurization:

Open the intake valve, input low-concentration methane feed gas, pressurize the packed tower after vacuum regeneration, and pressurize to the set adsorption and capture methane pressure, such as 1 to 10 atmospheres, or higher. Due to the low concentration of methane in coalbed methane, the partial pressure of methane adsorption is very low, and the methane adsorption capacity of the adsorbent is also low. This process recommends pressure adsorption to capture methane.

Step (2) methane adsorption:

Open the inlet valve, input low-concentration methane raw material gas, fill the tower with adsorbent to capture methane, and the gas discharged from the top of the tower is mainly nitrogen. It is necessary to control the methane discharge rate in order to improve the methane recovery rate in coalbed methane. If the desorption of carbon dioxide in the packed tower is insufficient, at this time, the exhaust gas will contain carbon dioxide. Carbon dioxide is a greenhouse gas, and its emission needs to be strictly controlled.

Step (3) carbon dioxide replacement:

When the methane adsorption front in the packed tower is close to the outlet at the top of the tower, the valve for coalbed methane inlet is closed, and the carbon dioxide inlet valve is opened to replace and enrich the adsorbed methane in the tower with carbon dioxide. After methane and nitrogen are replaced, they are discharged from the top of the tower in sequence. Most of the high-concentration methane gas is recovered as product gas, part of the high-concentration nitrogen gas contains a small amount of methane, and is recovered as subsequent vacuum purge gas 2, and part of the high-concentration methane gas contains a small amount of carbon dioxide. Recycled as subsequent vacuum purge gas 1. The carbon dioxide displacement is a pressure displacement, and the pressure is the same as that of the methane adsorption and capture stage.

Step (4) step down

Open the exhaust valve at the bottom of the tower to reduce the pressure of the packed tower, and the carbon dioxide adsorbed in the tower is desorbed and discharged from the bottom of the tower. The discharged carbon dioxide is recovered for replacement step (3). The packed tower is depressurized to near normal pressure, and enters the vacuum to desorb carbon dioxide.

Step (5) vacuum desorption

Open the vacuum valve at the bottom of the tower to vacuum desorb the carbon dioxide adsorbed in the tower. Under the conditions allowed by the vacuum pump, reduce the vacuum pressure as much as possible to increase the carbon dioxide desorption rate.

Step (6) vacuum high-concentration methane purging

Under vacuum conditions, a small amount of high-concentration methane is used to purge from the top of the tower to replace carbon dioxide in the tower. Because the amount of high-concentration methane gas is not much, this method adopts the gas recovered from the top of the tower in the carbon dioxide replacement process (high-concentration methane slightly contains a small amount of carbon dioxide)

Step (7) Vacuum high-concentration nitrogen purging

Under vacuum conditions, a small amount of high-concentration nitrogen is used to purge from the top of the tower to recover methane in the tower. The method adopts the gas recovered from the top of the tower during the carbon dioxide replacement process (the high-concentration nitrogen slightly contains a small amount of methane).

The continuous adsorption and capture of low-concentration methane in the coalbed methane of the present invention requires multiple adsorption tower groups to operate in parallel. Figure 4 shows a typical three-tower group (each group contains four towers, as shown in Figure 2, a total of twelve towers) seven-step carbon dioxide displacement vacuum pressure swing adsorption operation process, the functions and operating states of each valve are shown in Table 1. The seven operating steps of each cycle are divided into three equal time periods, mainly _CH4 adsorption, _CO2 replacement and _CO2 desorption. Specifically, time period 1 includes pressurization and CH adsorption, time period ₂ is _CO replacement, and time period 3 includes depressurization, vacuum desorption, vacuum purge 1 and vacuum purge 2.

Table 1 The operating status and time sequence of each adsorption tower when _CO2 is replaced by vacuum pressure swing adsorption for enrichment of low-concentration CBM methane

Table 2 Function description of automatic control valve in multi-tower continuous cycle operation when _CO2 is replaced by vacuum pressure swing adsorption for enrichment of low-concentration coalbed methane methane

The method for concentrating coalbed methane by vacuum pressure swing adsorption with carbon dioxide replacement provided by the present invention overcomes the defects of the existing vacuum pressure swing adsorption technology and has the following advantages:

(1) The step of adding carbon dioxide to replace the adsorbed methane, so that methane becomes the top product, thereby increasing the concentration and yield of the product gas methane.

(2) Carbon dioxide is used as a working gas and recycled, which maintains a high separation coefficient of key components, and makes methane as a tower top product and achieves a high concentration and recovery rate.

(3) When carbon dioxide is replaced, the gas discharged from the top of the tower is divided into three parts, high-concentration nitrogen (slightly containing a small amount of methane) is used for subsequent vacuum purge gas 2, high-concentration methane (slightly containing a small amount of nitrogen) is collected as product gas, high-concentration Methane (with a small amount of carbon dioxide) was used for subsequent vacuum purge gas 1.

(4) The purge gas from the carbon dioxide replacement section contains methane. After vacuum purge, the gas returns to the feed gas source and the carbon dioxide replacement gas source respectively to reduce the loss of methane.

(5) Multiple groups of packed towers are operated cyclically, and each group contains multiple packed towers. Multiple towers in each group are connected in series for CH ₄ adsorption and capture and CO ₂ replacement, increasing the length of the packed bed (increasing the amount of adsorbent) and increasing the methane yield; multiple towers in each group are connected in parallel to regenerate the adsorbent CO ₂ to reduce the mobile phase in the tower pressure drop, making regeneration of the _CO2 sorbent easy.

(6) The present invention is applicable to the concentration of methane in coalbed methane with different methane content. It operates at normal temperature and can choose adsorption and replacement under pressure or near normal pressure. Commercial adsorbents such as activated carbon, zeolite and molecular sieve can be used.

(7) The methane concentration obtained by the present invention is high, the yield is high, and the separation conditions are mild, so the coalbed methane with low methane concentration can be turned into high-quality natural gas fuel at a relatively low cost, and the product gas can be transported by pipeline or installed tank storage.

The following provides a specific example of a method for concentrating low-concentration methane in coalbed methane by vacuum pressure swing adsorption for carbon dioxide replacement in the present invention.

Example 1

The packed tower is filled with asphalt-based activated carbon pellets, the diameter of the packed tower is 27mm, the filling height is 0.617m, and the asphalt-based activated carbon pellets are filled with 0.1804kg. Using this packed tower to adsorb and capture coalbed methane with a methane concentration of 10%, the experimental results of the traditional vacuum pressure swing adsorption process and the carbon dioxide replacement vacuum pressure swing adsorption process are compared as follows:

(1) Traditional vacuum pressure swing adsorption: the adsorption pressure is 150kPa, the vacuum desorption pressure is 5.1kPa, the temperature is about 298K, the methane concentration of coalbed gas is 10%, the methane concentration of the product gas is 25.3%, and the methane recovery rate is 87.7%.

(2) Carbon dioxide displacement vacuum pressure swing adsorption: adsorption pressure 150kPa, vacuum desorption pressure 5.1kPa, temperature about 298K, coalbed methane methane concentration 10%, product gas methane concentration 83.3%, methane recovery rate 90.7%

Carbon dioxide displacement vacuum pressure swing adsorption will concentrate 10% methane to 83.3%, while traditional vacuum pressure swing adsorption can only concentrate to 25.3%. The experimental results show that carbon dioxide displacement vacuum pressure swing adsorption has obvious advantages.

Example 2

The packed tower is filled with commercial coconut shell activated carbon, the diameter of the packed tower is 27mm, the filling height is 0.657m, and the coconut shell activated carbon is filled with 0.2103kg. Using this packed tower to adsorb and capture coalbed methane with a methane concentration of 10%, the experimental results of the traditional vacuum pressure swing adsorption process and the carbon dioxide replacement vacuum pressure swing adsorption process are compared as follows:

(1) Traditional vacuum pressure swing adsorption: adsorption pressure is 150kPa, vacuum desorption pressure is 6.5kPa, temperature is about 298K, coalbed methane methane concentration is 10%, product gas methane concentration is 22.2%, methane recovery rate is 93.0%

(2) Vacuum pressure swing adsorption for carbon dioxide replacement: adsorption pressure 150kPa, vacuum desorption pressure 13.8kPa, temperature about 298K, coalbed methane methane concentration 10%, product gas methane concentration 90.0%, methane recovery rate 82.3%

Carbon dioxide displacement vacuum pressure swing adsorption will concentrate 10% methane to 90.0%, while traditional vacuum pressure swing adsorption can only concentrate to 22.2%. The experimental results show that carbon dioxide displacement vacuum pressure swing adsorption has obvious advantages.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Within the protection scope of the present invention.

Claims (10)

1. a vacuum pressure swing adsorption method for carbon dioxide replacement, characterized in that, adopting multi-tower continuous cycle adsorption, carbon dioxide replacement and vacuum desorption technology makes the coal-bed methane of low-concentration methane become high-quality natural gas fuel; A cycle includes the following specific steps: Step (1) pressurization: pressurize the packed tower to the operating pressure set in the adsorption stage of 1.1atm to 10atm; Step (2) Methane adsorption: Under the above-mentioned pressure conditions at a temperature of 10°C to 50°C, low-concentration coal-bed methane methane is input from the bottom of the packed tower into the packed tower containing adsorbents for adsorption and capture of methane. When the methane adsorption front reaches At the outlet of the packed tower, the adsorption stage ends; Step (3) Carbon dioxide replacement: Under the conditions of temperature 10℃～50℃ and pressure 1.1atm～10atm, input carbon dioxide to replace the adsorbed methane and nitrogen in the tower. As the replacement progresses, the gases are sequentially discharged from the top of the packed tower and stored separately In the three buffer tanks, there are high-concentration methane product gas, high-concentration nitrogen with a small amount of methane, and high-concentration methane with a small amount of carbon dioxide; after the replacement of methane and nitrogen in the tower, the packed tower is basically full of carbon dioxide; Step (4) depressurization: the packed tower is depressurized to normal pressure, and the carbon dioxide in the desorption tower is decompressed; Step (5) vacuum desorption: use a vacuum pump to evacuate, so that the pressure in the packed tower is reduced to 1kPa～15kPa; Step (6) Vacuum purge 1: Under vacuum pressure, use a small amount of high-concentration methane to purge from the top of the tower to replace carbon dioxide in the tower; purge gas 1 is the high-concentration methane obtained in step (3) containing a small amount of carbon dioxide; Step (7) Vacuum purge 2: Under vacuum pressure, use a small amount of high-concentration nitrogen to purge from the top of the tower to replace methane in the tower; purge gas 2 is the high-concentration nitrogen obtained in step (3) containing a small amount of methane. 2. the vacuum pressure swing adsorption method of a kind of carbon dioxide displacement as claimed in claim 1, it is characterized in that, the adsorbent filled in the described multi-tower is selected from one or both of carbon-based materials and zeolite molecular sieves. kind. 3. the vacuum pressure swing adsorption method of a kind of carbon dioxide replacement as claimed in claim 1, is characterized in that, the filling height of each tower is 0.8-1.2 meter. 4. the vacuum pressure swing adsorption method of a kind of carbon dioxide displacement as claimed in claim 1, it is characterized in that, described multi-tower continuous operation is three groups or more than three groups of packed tower circulation operation, each group contains single tower, two Towers, triple towers, quadruple towers, or more towers. 5. the vacuum pressure swing adsorption method of a kind of carbon dioxide displacement as claimed in claim 1 or ₄ , it is characterized in that, in each group, many towers are connected in series to carry out CH Adsorption capture and _CO Replacement; In each group, many towers are connected in parallel Sorbent _CO2 regeneration. 6 . The vacuum pressure swing adsorption method for carbon dioxide replacement as claimed in claim 1 , wherein the methane concentration of the low-concentration methane is 5% to 20%. 7. the vacuum pressure swing adsorption method of a kind of carbon dioxide replacement as claimed in claim 1, is characterized in that, the carbon dioxide that step (3) imports is made of two parts, and in the early stage of replacement stage, use step (4), step (5 ) and step (6) depressurization and the carbon dioxide recovered by vacuum desorption, and in the later stage of the replacement stage, supplementary high-concentration carbon dioxide is used. 8 . The vacuum pressure swing adsorption method for carbon dioxide replacement as claimed in claim 7 , wherein the purity of the high-concentration carbon dioxide is more than 90%. 9. the vacuum pressure swing adsorption method of a kind of carbon dioxide replacement as claimed in claim 1, it is characterized in that, step (3) the impure gas containing methane that the part of carbon dioxide replacement stage discharges is respectively used as vacuum desorption purge gas, After purging, the purge gas 2 is returned to the feed gas source in step (2), and the purge gas 1 is returned to the carbon dioxide replacement gas source in step (3), and methane is recycled. 10. A vacuum pressure swing adsorption method for carbon dioxide replacement as claimed in claim 1, characterized in that step (5) adopts a vacuum pump to evacuate to reduce the pressure in the packed tower to 5kPa˜15kPa.