CN101596391A - A method for fractional concentration of low-concentration gas pressure swing adsorption - Google Patents

Abstract

The invention discloses a low-concentration gas pressure swing adsorption graded concentration method, the steps of which are: (1) gas pretreatment: A. to remove dust from the gas; B. to remove water, before entering the pressure swing adsorption tower Set up a drier to remove the moisture in the gas; C. In addition to CO ₂ , implement pre-filtration between the drier and the pressure swing adsorption device. The dynamic diameter of CO ₂ is 0.33nm, which is relatively small. Molecular sieves are _CO2 adsorbents, and _CO2 is discharged from methane and chain hydrocarbons with high selectivity; (2) Pressure swing adsorption fractional concentration of dry gas: low-concentration methane is divided into 2-6 levels, avoiding the gas explosion limit of 5-6 16%, exchanging 2~4 suction-desorption towers to continuously concentrate to high-concentration methane, and the suction-desorption towers are filled with 1~2 kinds of high-efficiency CH ₄ gas adsorbents. The methane recovery rate exceeds 90%, and the methane concentration exceeds 95%. It has a high calorific value, reduces the emission of methane gas with high greenhouse effect, and saves energy and reduces emissions.

Description

A method for fractional concentration of low-concentration gas pressure swing adsorption

technical field

The invention relates to the technical field of separation and purification of industrial gases. More specifically, it relates to a low-concentration gas pressure swing adsorption graded concentration method, which is suitable for concentrating low-concentration gas into high-concentration methane gas. The product of the present invention, methane, can be used as a chemical raw material, civil gas, and automobile fuel, which can save a lot of energy. At the same time, it reduces the emission of methane (21 times that of carbon dioxide) gas with high greenhouse effect, and has the global environmental significance of energy-saving economy and emission reduction.

Background technique

Coal mine gas (called coalbed methane) is the associated gas of coal mines. The main components of coalbed gas are: methane (CH ₄ ), carbon dioxide (CO ₂ ), carbon monoxide (CO), ethylene (C ₂ H ₄ ), propane (C ₂ H ₆ ), among which CO, C ₂ H ₄ , C ₂ H ₆ three kinds of gases have very little content in coalbed methane, and their typical components are as follows (expressed in volume percentage): methane (CH ₄ ): 20-60%, nitrogen (N ₂ ): 50-60%, oxygen + argon (O ₂ +Ar): 12-18%, saturated with water (H ₂ O). Every ^m3 of coal can produce 15-30 ^m3 of gas, and it is estimated that by 2010 methane emissions will increase to 28Mt, of which 70% come from mine return air flow with _CH4 concentration below 1%. U.S. CBM methane utilization The rate is only 27%.

However, 70-90% of the methane associated with coal mines in China is discharged because of low concentration (<20%) and no use value. This part of the methane is very close to the CH ₄ gas concentration due to its low CH ₄ gas concentration and high oxygen content. Explosive concentration (5-16%) range or just in the explosive concentration range of CH ₄ gas, so it is difficult to directly utilize. As a large coal-producing country, my country is rich in gas resources; the amount of coalbed methane within 2000 m in my country reaches 35 trillion cubic meters (equivalent to 45 billion tons of standard coal and 35 billion tons of standard oil), which is equivalent to onshore conventional natural gas resources. The "Coal Mine Safety Regulations" stipulates that the concentration of methane should not be lower than 30% when the gas is drained and utilized. In order to safely avoid the limit of gas explosion, when it is lower than 25%, it should be discharged without using it. In 2002, 193 mines of 53 mining groups in the country produced 4.31 billion m ³ of gas and 1.1461 billion m ³ of gas drainage.

The annual gas emission in Huainan City, Anhui Province is 500 million m ³ (converted to pure CH ₄ , the same below), 200 million m ³ of gas is extracted, 40 million m ³ is used, and there are three utilization methods: gas, power generation (3.5 degrees Electricity/m ³ CH ₄ ), boiler combustion gas, the total utilization rate is less than 10%, which represents the general situation of coalbed methane utilization in China.

Coalbed methane not only has huge resource potential, but also has a wide range of uses. It can be used as residential gas, industrial fuel and chemical raw material gas, vehicle fuel, and power generation. Among them, the use of coalbed methane to generate electricity is a technology that is currently being actively developed. If the country uses 80% of the annual 4.31 billion m ³ of gas, it is equivalent to an annual increase of 4.68 million tons of standard coal.

The impact of CH ₄ on the greenhouse effect of the atmosphere accounts for 15-20%. CH ₄ is 21 times the greenhouse effect of CO ₂ molecules, and its ability to destroy the ozone layer is 7 times that of carbon dioxide. The emission of CH ₄ into the atmosphere has caused serious resource losses on the one hand. Waste, on the other hand, leads to the greenhouse effect. Therefore, rational enrichment and utilization of CH ₄ in low-concentration gas has dual meanings of energy saving and environmental protection, and there is an urgent need for a technology that can safely concentrate and enrich low-concentration gas into high-concentration gas.

Contents of the invention

The purpose of the present invention is to provide a low-concentration gas pressure swing adsorption fractional concentration method to provide a high-concentration methane gas. Make the methane recovery rate ≥ 90%, can obtain high-concentration methane with different concentrations (≥ 25%), and the concentration can be ≥ 95%; the method of the present invention can enrich the abandoned coal mine gas with low calorific value value and has a wide range of high-concentration methane gas.

The present invention firstly pretreats the gas, and then adopts pressure swing adsorption and step-by-step concentration technology to utilize multi-components of the gas (CH ₄ , N ₂ , O ₂ , CO ₂ , H ₂ O, etc.) on the adsorbent. The principle of the adsorption capacity changing with the pressure, the pressure swing adsorption is concentrated step by step, from low-concentration methane to 2~6 stages, exchange 2~4 absorption-extraction towers to continuously concentrate to the enrichment method of high-concentration methane, using high-concentration methane gas and The method of mixing low-concentration methane gas to increase the methane gas concentration avoids the gas explosion limit (5-16%), so that the methane recovery rate in the gas exceeds 90%, and the methane concentration exceeds 95%.

A method for fractional concentration of low-concentration gas pressure swing adsorption, the steps of which are:

(1) Gas pretreatment:

A. Dust removal:

Use a gas dust filter to remove dust. Dust has a great impact on the protection and maintenance of equipment and the regeneration of CH ₄ gas adsorbents in the subsequent process. A gas dust filter must be installed to remove dust from the gas to reduce corrosion of equipment , to improve the separation effect; the gas dust filter is a bag filter, which passes the dusty flue gas through the filter material, and the dust particles are filtered, and the filter material captures coarse dust mainly by inertial collision, and captures fine dust Mainly rely on diffusion and sieving, the dust layer of the filter material also has a certain filtering effect.

B. Dewatering the gas after dedusting:

In order to obtain dry methane-enriched product gas, a MAD micro-heat regenerative adsorption dryer is installed before entering the pressure swing adsorption tower to remove moisture in the gas. The desiccant used in the desiccator can be any one of fine-pore spherical silica gel, spherical blue gel, alumina molecular sieve or a combination of two to three thereof.

C. In addition to carbon dioxide (CO ₂ ):

Before gas concentration in coal mine gas, carbon dioxide (CO ₂ ) must be removed from the coal mine gas, and pre-filtered between the dryer and the pressure swing adsorption device. The kinetic diameter of carbon dioxide (CO ₂ ) is 0.33nm, which is relatively small , using fine-pore carbon molecular sieves as _CO2 adsorbents, _CO2 is discharged from methane and chain hydrocarbons with high selectivity. pressure adsorption device.

(2) Pressure swing adsorption fractional concentration of dry gas:

Low-concentration methane is divided into 2-6 levels, and the method of mixing high-concentration methane gas and low-concentration methane gas to increase the concentration of methane gas avoids the limit of gas explosion (5-16%), and exchanges 2-4 absorption-extraction towers for continuous concentration Methane, to obtain high-concentration methane with different concentrations (≥25%), the concentration can be ≥95%, and the absorption-desorption tower is filled with 1 to 2 kinds of high-efficiency _CH4 gas adsorbents. The CH ₄ gas adsorbent in the absorption-desorption tower can be any one of zeolite molecular sieve, carbon molecular sieve or a combination of both.

Take 4 levels of concentration as an example:

A. The first pressure swing adsorption:

Pressure swing adsorption is based on the fact that the adsorbent has a large adsorption capacity for the adsorbate under high pressure (adsorption pressure), but has a small adsorption capacity under low pressure (desorption pressure). It consists of two stages of selective adsorption and desorption regeneration. Switch cycle process.

Based on the current mature air separation technology, when the adsorbent is used to pressurize, the gas (methane) in the mixed gas will be adsorbed, and the unadsorbed air will be discharged from the outlet of the adsorption tower. The adsorbed gas will be desorbed and then discharged, concentrated step by step into high-concentration product gas-methane, and then vacuumed to restore the adsorption capacity of the adsorbent. The CH ₄ gas adsorbent in the absorption-desorption tower can be any one of zeolite molecular sieve, carbon molecular sieve or a combination of both.

After the dry gas is subjected to pressure swing adsorption for the first time, methane gas with a concentration of less than 5% is obtained.

B. Mixing, avoiding gas explosion limit:

Mixing methane gas with a concentration of 30-95% and step A product (methane gas with a concentration of less than 5%) to increase the methane gas concentration, increasing the gas concentration of the step A product to 20%-35%, thereby effectively avoiding gas explosion limit;

C. The second pressure swing adsorption:

After the product gas (20%-35% methane concentration) of step B is subjected to pressure swing adsorption for the second time, the methane concentration is increased to 25%-50%;

D. The third pressure swing adsorption:

After the third pressure swing adsorption is performed on the product gas (25%-50% methane gas concentration) of step C, the methane concentration is increased to 40%-85%;

E. The fourth pressure swing adsorption:

After the product gas (concentration is 40%～85% methane gas) of step D is subjected to pressure swing adsorption for the fourth time, the methane concentration is increased to 95% or greater than 95%

The low-concentration methane gas is methane gas with a concentration less than 5%.

The CH ₄ pressure swing adsorption process parameters are as follows: the pressure of pressurized adsorption is controlled within the range of 0.8-2.4 MPa, the pressure of decompression desorption is controlled within the range of negative pressure of 0.1-0.02 MPa, and the temperature is 4-25°C.

The low-concentration gas pressure swing adsorption fractional concentration technology for realizing the purpose of the present invention is characterized in that: if the required high-concentration methane product gas is allowed to contain saturated moisture, the gas may not be dehydrated before entering the pressure swing adsorption tower. deal with.

The low-concentration gas pressure swing adsorption fractional concentration technology for realizing the object of the present invention is characterized in that: according to the requirements for methane gas concentration, the corresponding fractional concentration can be selected to obtain methane gas within a certain concentration range.

The low-concentration gas pressure swing adsorption fractional concentration technology for realizing the purpose of the present invention is characterized in that: the methane recovery rate exceeds 90%, and high-concentration methane with different concentrations (≥25%) can be obtained, and the concentration can be ≥95%. The beneficial effects of the present invention are:

(1) The present invention adopts pressure swing adsorption and graded concentration technology to concentrate CH ₄ , enrich the discarded coal mine gas with low calorific value into methane-rich gas with high calorific value and wide application, and realize low-concentration coal seam drainage Comprehensive utilization of gas;

(2) The present invention can make the methane recovery rate ≥ 90%, can obtain high-concentration methane of different concentrations (≥ 25%), and the concentration can be ≥ 95%;

(3) The product of the present invention-methane can be used as chemical raw materials, civil gas, automobile fuel, etc., saving a lot of energy, and simultaneously reducing the emission of high greenhouse effect methane (21 times that of CO ₂ ) gas.

(4) The comprehensive utilization of coalbed methane resources in the present invention has important economic and environmental significance for improving and optimizing energy structure, ensuring safe production of coal mines, reducing production costs of coal mines, and reducing air pollution.

Detailed ways

Example 1:

A method for fractional concentration of low-concentration gas pressure swing adsorption, the steps of which are:

(1) Pretreatment of gas:

A. Dust removal: Use the gas dust removal filter to first remove dust from the gas:

Dust has a great influence on the protection and maintenance of equipment and the regeneration of CH ₄ gas adsorbent in the follow-up process. The gas dedusting filter is used to remove dust from the gas gas first, so as to reduce the corrosion of equipment and improve the separation effect; the CH _4. The gas adsorbent can be any one of zeolite molecular sieve, carbon molecular sieve or a combination of the two. The gas dust removal filter is a bag filter, which passes the dusty flue gas through the filter material, and the dust particles are filtered out. The filter material captures coarse dust mainly by inertial collision, and captures fine dust mainly by diffusion and sieving. The dust layer of the filter material also has a certain filtering effect.

B. Dewatering the gas after dedusting:

In order to obtain dry methane-enriched product gas, a MAD micro-thermal regenerative adsorption dryer is installed before entering the pressure swing adsorption tower to remove the moisture in the gas. The desiccant used in the desiccator can be any one of fine-pore spherical silica gel, spherical blue gel, alumina molecular sieve or a combination of two to three thereof.

C. In addition to carbon dioxide (CO ₂ ):

Before gas concentration in coal mine gas, carbon dioxide (CO ₂ ) must be removed from coal mine gas and pre-filtered between the drier and pressure swing adsorption device _. Porous carbon molecular sieves are _CO2 adsorbents, and _CO2 is discharged from methane and chain hydrocarbons with high selectivity. The pressure swing adsorption device is divided into 2 to 6 stages, and the pressure swing adsorption device is exchanged with 2 to 4 absorption-desorption towers. .

(2) Pressure swing adsorption fractional concentration of dry gas:

Pressure swing adsorption uses any one of zeolite molecular sieve, carbon molecular sieve or their combination as _CH4 gas adsorbent, the pressure of pressurized adsorption is 0.9 or 1.2 or 1.8 or 2.3 MPa, and the pressure of decompression desorption is 0.09 or 0.08 or 0.06 or 0.03MPa negative pressure, temperature 4 or 10 or 15 or 20°C, concentrate in 3 stages to obtain methane gas with a concentration of 40 or 50 or 60 or 70 or 75 or 80 or 88 or 95%. Specifically:

A. The first pressure swing adsorption:

After the first pressure swing adsorption of dry gas, the methane concentration is 2 or 3%;

B. Rinse to avoid gas explosion limit:

Wash the product gas of step A with 30 or 40 or 50 or 60% methane gas, and increase the concentration of the product gas of step A to 20 or 30 or 40 or 50%, thereby effectively avoiding the gas explosion limit;

C. The second pressure swing adsorption:

After the product gas in step B is subjected to pressure swing adsorption for the second time, the methane concentration is increased to 25 or 40 or 50 or 60%;

D. The third pressure swing adsorption:

After the product gas of step C is subjected to pressure swing adsorption for the third time, the concentration of methane is increased to 40 or 50 or 60 or 70 or 75 or 80 or 88 or 95%, that is, the concentration is 40 or 50 or 60 or 70 or 75 or 80 or 88 or 95% methane gas.

Example 2:

Coal mine gas is pretreated by dust removal, water removal and _CO2 removal (same example 1), and pressure swing adsorption uses any one of zeolite molecular sieve, carbon molecular sieve or their combination as _CH4 gas adsorbent, and the pressure of pressurized adsorption is 0.8 Or 1.2 or 1.8 or 2.0MPa, the pressure of decompression and desorption is 0.1 or 0.08 or 0.06 or 0.04MPa negative pressure, the temperature is 4 or 8 or 15 or 20°C, and it is concentrated in 4 stages to obtain a concentration of 50 or 60 or 70 or 85 or 90 or 95 or 96 percent methane gas. Specifically:

A. The first pressure swing adsorption:

After the first pressure swing adsorption of dry gas, the methane concentration is 2 or 3%;

B. Rinse to avoid gas explosion limit:

Wash the product gas of step A with 30 or 40 or 50 or 60% methane gas, and increase the concentration of the product gas of step A to 20 or 30 or 40 or 50%, thereby effectively avoiding the gas explosion limit;

C. The second pressure swing adsorption:

After the product gas in step B is subjected to pressure swing adsorption for the second time, the methane concentration is increased to 25 or 40 or 50 or 60%;

D. The third pressure swing adsorption:

After the product gas in step C is subjected to pressure swing adsorption for the third time, the methane concentration is increased to 40 or 50 or 60 or 70%;

E. The fourth pressure swing adsorption:

After the product gas of step D is subjected to pressure swing adsorption for the fourth time, the concentration of methane is increased to 50 or 60 or 70 or 85 or 90 or 95 or 96%, that is, the concentration is 50 or 60 or 70 or 85 or 90 or 95 or 96% methane gas.

Example 3:

Coal mine gas is pretreated by dust removal, water removal and _CO2 removal (same example 1), and pressure swing adsorption uses any one of zeolite molecular sieve, carbon molecular sieve or their combination as _CH4 gas adsorbent, and the pressure of pressurized adsorption is 0.8 Or 1.5 or 2.0 or 2.4MPa, the pressure of decompression desorption is 0.1 or 0.08 or 0.06 or 0.04MPa negative pressure, the temperature is 5 or 10 or 18 or 25°C, and it is concentrated in 5 stages, and the concentration is 60 or 70 or 80 or 90 or 95 or 95.5 or 97% methane gas. Specifically:

A. The first pressure swing adsorption:

After the first pressure swing adsorption of dry gas, the methane concentration is 2 or 3%;

B. Rinse to avoid gas explosion limit:

Wash the product gas of step A with 30 or 40 or 50 or 60% methane gas, and increase the concentration of the product gas of step A to 20 or 30 or 40 or 50%, thereby effectively avoiding the gas explosion limit;

C. The second pressure swing adsorption:

After the product gas in step B is subjected to pressure swing adsorption for the second time, the methane concentration is increased to 25 or 35 or 45 or 60%;

D. The third pressure swing adsorption:

After the product gas in step C is subjected to pressure swing adsorption for the third time, the methane concentration is increased to 45 or 50 or 65 or 70%;

E. The fourth pressure swing adsorption:

After the product gas in step D is subjected to pressure swing adsorption for the fourth time, the methane concentration is increased to 50 or 60 or 70 or 85% or greater than 85%;

F. The fifth pressure swing adsorption:

After the product gas of step E is subjected to pressure swing adsorption for the fifth time, the concentration of methane is increased to 60 or 70 or 80 or 90 or 95 or 95.5 or 97%, that is, the concentration is 60 or 70 or 80 or 90 or 95 or 95.5 or 97% methane gas.

Example 4

Coal mine gas is pretreated by dust removal, water removal, and _CO2 removal (same example 1). Pressure swing adsorption uses any one of zeolite molecular sieve, carbon molecular sieve or a combination thereof as an adsorbent, and the pressure of pressurized adsorption is 0.9 or 1.5 or 1.8 or 2.2MPa, decompression desorption pressure is 0.1 or 0.09 or 0.07 or 0.05MPa negative pressure, temperature is 6 or 12 or 15 or 24 ° C, concentrated in 6 stages, the concentration is 65 or 75 or 85 or 95 or 96 Or 96.5% methane gas. Specifically:

A. The first pressure swing adsorption:

After the first pressure swing adsorption of dry gas, the methane concentration is 2 or 3%;

B. Rinse to avoid gas explosion limit:

Wash the product gas of step A with 30 or 40 or 50 or 60% methane gas, and increase the concentration of the product gas of step A to 20 or 30 or 40 or 50%, thereby effectively avoiding the gas explosion limit;

C. The second pressure swing adsorption:

After the product gas in step B is subjected to pressure swing adsorption for the second time, the methane concentration is increased to 25 or 35 or 45 or 55%;

D. The third pressure swing adsorption:

After the product gas in step C is subjected to pressure swing adsorption for the third time, the methane concentration is increased to 45 or 50 or 60 or 72%;

E. The fourth pressure swing adsorption:

After the product gas in step D is subjected to pressure swing adsorption for the fourth time, the methane concentration is increased to 55 or 60 or 70 or 83%;

F. The fifth pressure swing adsorption:

After the product gas in step E is subjected to pressure swing adsorption for the fifth time, the methane concentration is increased to 60 or 70 or 80 or 90%;

G. The sixth pressure swing adsorption:

After the product gas of step F is subjected to pressure swing adsorption for the fifth time, the concentration of methane is increased to 65 or 75 or 85 or 95 or 96 or 96.5%, that is, the concentration is 65 or 75 or 85 or 95 or 96 or 96.5% of methane gas.

Claims (4)

1, a kind of low-concentration gas pressure swing adsorption graded concentration method, its steps are: (1) Gas pretreatment: A. Dust removal, use a gas dust removal filter to remove dust, set a gas dust removal filter to first remove dust from the gas, the gas dust removal filter is a bag filter, the dusty flue gas passes through the filter material, and the dust particles are filtered down; B. To remove water from the gas after dedusting, in order to obtain dry methane-enriched product gas, a MAD micro-heat regenerative adsorption dryer is installed before entering the pressure swing adsorption tower to remove the moisture in the gas; C. In addition to carbon dioxide, before the coal mine gas is concentrated, carbon dioxide must be removed from the coal mine gas, and pre-filtered between the dryer and the pressure swing adsorption device. The kinetic diameter of carbon dioxide is 0.33nm, and the fine-pore carbon molecular sieve is _CO2 adsorbent, _CO2 is discharged from methane and chain hydrocarbons, and the pressure swing adsorption device is divided into 2 to 6 stages, and the pressure swing adsorption device with 2 to 4 suction-extraction towers is exchanged; (2) Pressure swing adsorption fractional concentration of dry gas: Low-concentration methane is divided into 2 to 6 grades, and methane gas with a concentration of 30-95% is mixed with low-concentration methane gas to increase the concentration of methane gas, avoiding the gas explosion limit of 5-16%, and exchanging 2-4 suction-degassing The tower is continuously concentrated to a high concentration of methane, and the absorption-desorption tower is filled with 1 to 2 kinds of CH ₄ gas adsorbents; The desiccant used in the desiccator is any one of fine-pore spherical silica gel, spherical blue gel, alumina molecular sieve or a combination of two to three. 2. A method for fractional concentration of low-concentration gas pressure swing adsorption according to claim 1, characterized in that: the CH _gas adsorbent in the absorption-desorption tower is any one of zeolite molecular sieve and carbon molecular sieve or a combination thereof. 3. A low-concentration gas pressure swing adsorption fractional concentration method according to claim 1, characterized in that: the high-concentration methane product gas contains saturated water, and the gas is not removed before entering the pressure swing adsorption tower. Water pretreatment. 4. A method for fractional concentration of low-concentration gas pressure swing adsorption according to claim 1, characterized in that: said CH ₄ pressure swing adsorption process parameters are as follows: the pressure of pressurized adsorption is controlled within the range of 0.8-2.4 MPa Inside, the pressure of decompression desorption is controlled within the negative pressure range of 0.1-0.02MPa, and the temperature is 4-25°C.