JPS58198591A - Method and apparatus for concentrating methane - Google Patents

Abstract

PURPOSE:To efficiently concentrate methane at a low cost, by repeating methane concn. collection operation of a non-equibrium press. method and operation for vacuum regeneration of an absorbent one after the other by using a concn. column filled with natural zeolite adsorbent. CONSTITUTION:An air/methane-base mixed gas/such as coal mine exhaust gas contg. moisture and CO2 is pretreated by successive introduction into dehumidification columns C1, C2 and a CO2-removing column B. Then it is introduced into the bottom of a concn. column A filled with natural zeolite adsorbent and regenerated in vacuum to separate high-conc. methane from the top of the column A. When the concn. column A reaches a predetermined press., the introduction of the gas is stopped, the press. is reduced nearly to the atmospheric press. by opening the top, and the released gas is collected as methane. When the press. becomes atmospheric, the release of the gas is stopped and the natural zeolite adsorbent is regenerated by reducing the press. to vacuum. Methane is is conc. by repeating the above procedure.

Description

DETAILED DESCRIPTION OF THE INVENTION At present, degassed methane from coal mines and the like is used for private power generation, private consumption such as heating, and in some cases is supplied to city gas. When used for power generation, power generation efficiency decreases when the methane concentration falls below 50%, and when used for city gas, when the methane concentration decreases, it is necessary to adjust the calorie content by mixing high-calorie gas. Therefore, improving the utilization rate by concentrating 30 to 40 inches of methane gas from these coal mine exhaust gases is important from the perspective of effective use of valuable energy resources, and simple, low-cost methane concentrators are attracting attention. .

On the other hand, the conventional cryogenic separation method is a method for concentrating and separating mixed gases, but although this method has the advantage of producing high-purity gas, it requires a huge amount of electricity and equipment, so it is not suitable for simple methane concentration. It is economically impractical as a law. In addition, the method of separating gases by repeating pressurization and depressurization using an adsorbent is called the PSA (prenosher swing adsorption) method, and various operating methods have been devised. It has been put into practical use for removing moisture from the air and purifying other gases, with nitrogen separation being a typical example. However, the known PSA method has the disadvantage of reducing the recovery rate of product gas with respect to the raw gas that captures gas due to its pressurized ability. Taking the separation of oxygen and nitrogen in the air as an example, the recovery rate of product oxygen is as low as 20 to 65% relative to the oxygen in the introduced raw material air. Also, these known PS
Method A produces coal mine exhaust gas (30-40% methane).

The above-mentioned disadvantages also occur when attempting to concentrate methane (12-14% oxygen, 48-56% nitrogen).

Furthermore, trace amounts of moisture and carbon dioxide present in the gas reduce the concentration efficiency, making it impractical.

Moreover, if the adsorption pressure is operated at 10 kgZα2 (absolute pressure) or higher, the power cost of the compressor will increase and the maintenance of the device will be difficult. For this reason, a practical device for concentrating methane using the PSA method for air-methane mixed gas has not yet appeared.

The present invention was based on the knowledge that among the natural zeolite adsorbents produced in the Nagatabu area of Hokkaido, clinoptilolite exhibits unique adsorption characteristics in that the adsorption rate of methane is extremely slow compared to nitrogen.
Taking advantage of this characteristic and applying the principle of the well-known PSA method, we have created a non-equilibrium pressure operation method in which the concentration and collection operations are constantly varied in a non-equilibrium pressure state from vacuum to a predetermined pressure and from a predetermined pressure to near atmospheric pressure. By repeating vacuum regeneration alternately, we aim to improve the methane recovery rate and downsize the tower. Furthermore, by adding a pre-treatment tower that removes moisture and carbon dioxide without adversely affecting methane concentration, it is possible to concentrate low-concentration methane gas from coal mine exhaust gas to about 50-60%, which can be used as fuel for city gas etc. It was intended as a practical device.

The present invention will be explained in detail with reference to FIG. Concentration tower A packed with natural zeolite adsorbent, decarbonization tower B packed with the same adsorbent as tower A but with a smaller volume than tower A (volume of V1 to 1/th), pressurized adsorption-thermal regeneration , a dehumidification tower C5 is operated, and a dehumidification tower C2 is operated by atmospheric pressure adsorption and thermal regeneration. When the air-methane mixed gas dehumidified in the C2 and C2 towers is injected from the bottom of the A tower through the B tower, In the B tower, carbon dioxide contained in the raw gas is removed, and in the A tower, the gas composition in the voids in the tower changes due to the difference in the diffusion rate of nitrogen, oxygen, and methane in the natural zeolite adsorbent particles, and the methane concentration in the upper part of the tower changes. An increasing concentration gradient is formed. When the internal pressure of the tower reaches a predetermined pressure, the pulp V is closed, V, , V,
Open the A and B towers to reduce the pressure inside them. At the beginning, gas with high methane concentration is released. This gas is collected in a tank as concentrated methane gas. A.

The methane concentration of the released gas decreases as the internal pressure of the B tower decreases, but when the internal pressure of the tower reaches atmospheric pressure, the vacuum pump opens the exhaust pipes Perform vacuum regeneration in steps 5 and 4. In this way, methane concentration is performed by repeating pressure adsorption (gas introduction) - gas collection - vacuum regeneration, but by adjusting the collection time (or collection pressure range) in the gas collection process, it is possible to achieve an arbitrary concentration. Although methane gas can be obtained, it is also preferable that the methane recovery rate decreases as the concentration increases. Gas having a methane concentration higher than that of the raw gas by 50% or less is recovered into the raw gas tank through the recovery pipe 8, and an operation may be added to prevent loss of the raw gas. In this way, by collecting or recovering the product gas from a pressurized state during the depressurization process of atmospheric forging, the gas is prevented from being released outside the system, and improvements have been made to increase the recovery rate of concentrated methane gas relative to the raw gas introduced. The present invention provides a method for concentrating methane.

Furthermore, using pressurized gas to introduce gas from vacuum to atmospheric pressure in the pressurization process (gas introduction, concentration process) increases the power cost of the compressor, which is inconvenient.

Therefore, we decided to reduce the power cost of the compressor by using two lines for gas introduction, introducing gas at atmospheric pressure from vacuum to atmospheric pressure, and using pressurized gas only for introducing gas above atmospheric pressure. An improved device is provided. Furthermore, due to the methane, nitrogen, and oxygen adsorption properties of the natural zeola and nitride adsorbents selected as the adsorbents to be filled in the A and B columns of the present invention, methane concentration of 2 can be recovered even if the column internal pressure is increased to 5 kg/Crn2 (absolute pressure) or higher. The increase in rate is not significant and only increases the cost of powering the compressor. For this reason, the upper limit of the predetermined pressure in the concentration column is 5 k1M.
About m2 is preferable. This relatively low pressure operating condition is also an advantage of Kenpo.

Next, in the vacuum regeneration step, which is particularly important in the present invention, nitrogen is removed from the adsorbent in the A column by a vacuum regeneration operation.

Desorption of oxygen and carbon dioxide are mainly carried out in tower B, but the natural zeolite adsorbent packed in towers A and B exhibits remarkable adsorption of nitrogen, oxygen, and carbon dioxide in the low pressure range below atmospheric pressure. , the increase in adsorption is small in the high pressure range above atmospheric pressure. That is, gas desorption occurs significantly in a vacuum region below atmospheric pressure, and the higher the degree of vacuum, the more convenient it is for regeneration. Both towers A and B] A vacuum of 0 mm (mercury column) or less is preferable. Furthermore, since the adsorption power of carbon dioxide is greater than that of nitrogen and oxygen, it is impossible to directly connect towers A and B and regenerate the adsorbent in both towers in a fixed period of time using one vacuum pump.

For this reason, the valve v4 installed between the B tower and the A tower, which is designed to be smaller than the A tower, is closed and the A and B towers are vacuum regenerated individually, so that the regeneration of both towers is completed in a certain amount of time. The purpose of this invention is to provide an improved device. The smaller the volume of the screening tower compared to the A tower, the better the results for regeneration, but it is determined by the amount of carbon dioxide in the raw gas, the amount of gas introduced into the A tower in one cycle, etc. In the case of coal mine exhaust gas, the amount of carbon dioxide is 2
%, it is sufficient for the B column to be 1/1 to 1/1 of the A column.

Further, the adsorbent filled in the A and B towers of the present invention is nitrogen.

The larger the difference in the adsorption characteristics of carbon dioxide and methane, the better the natural zeolite (natural zeolite) is suitable for the two conditions.
(Oshamambu, Hokkaido) was selected. From the X-ray diffraction results of this zeolite mountain, the adsorbent belonging to clinoptilolite (hereinafter referred to as clinoptilolite), 6804% silicic acid, 11.66% aluminum oxide, 003% titanium oxide, 28% iron oxide
12%, manganese oxide 004%, magnesium oxide 06
2%, calcium oxide 2.24%, sodium oxide 28
It has a composition of 8% potassium oxide, 214% potassium oxide, 510% attached water, and 5.36% crystallized water, which is crushed, refined and washed with water to remove the powder on the particle surface, or granulated)
.

It is used after being heated and activated at 400-500°C. If the heating temperature exceeds 500° C., the crystal structure will be destroyed, which is disadvantageous.

Next, the configuration of a practical device in which each unit is made into multiple towers for continuous gas introduction will be explained with reference to FIG. 2 and its operating procedure with reference to FIG. 3. A and A' are methane concentration towers filled with clinoptilolite, B and B' are filled with the same adsorbent as the concentration tower,
Concentration tower fortress ~ Carbon dioxide removal tower with rare capacity + C1+
C1' + C2+ C2' is a dehumidification tower filled with silica gel, and C1 and C12 are operated by pressurized adsorption and thermal regeneration.
C21C2' is also operated with atmospheric pressure adsorption-thermal regeneration. 2 is a compressor, 4 and 5 are vacuum pumps, ■1~
■14 consists of automatic valves, etc. A, A',
Both B and B' refer to the gas introduction step from vacuum to atmospheric pressure (first step), the pressure introduction step from atmospheric pressure to a predetermined pressure (5 kg/i) (second step), and the predetermined pressure (5 kg/cm'). ) to near atmospheric pressure (third step) and vacuum regeneration step (fourth step) below atmospheric pressure. And in the first step, A and B are in the second step, A' and B'
The first step is performed.

In the second step, A and B are in the third step, A' and B'
The first step is performed.

In the third step, A and B are in the fourth step, A', B'
The second step is performed.

In the fourth step, A and B are the first step, A' and B'
is operated so that the third step is carried out. In other words, let's explain it in terms of pulp operation.

First, the air-methane mixed gas pressurized by the compressor 2 is dehumidified through the C8 and introduced into the pressurized tank 9.

In the first step, pulp V, , V3. V4゜V,
1. Open V, 4 l ■21 Vll + VQ I
VIQ is closed and pressurized gas from pressurized tank 9 is introduced from B to tower A. At the same time, atmospheric pressure A1. BI tower has vacuum pump 4
．． 5 is vacuum regenerated. In the second step, pulp v,
, v3. v, 3. v, close 4°, v2. v
, , v, , v8. v, opening is at a predetermined pressure A, B
The tower is depressurized to near atmospheric pressure, and the released gas is collected in a collection tank 3. At the same time, B' was vacuum regenerated.

Raw gas at atmospheric pressure, which has been dehumidified with C2, is introduced into the A' tower. In the third step, pulp v2. v4. v, ,
V, is closed and TV, , V, , , V, 2 is opened to atmospheric pressure (7) and the A and B columns are individually vacuum regenerated. At the same time, pressurized gas is introduced from the pressurized tank 9 to a predetermined pressure from the atmospheric pressure B' to the A' column.

In the fourth step, pulp Vl + VB + VH+
Close VH2 ■2゜v, , v4. v, , v,
The gas released from the A' tower is collected in the tank 3 by opening the A' and B' towers, and the pressure of the A' and B' towers is reduced to near atmospheric pressure.

Atmospheric pressure gas dehumidified in C2 is introduced into the A and B towers which have been vacuum-regenerated at the same time. Then, return to the first step and repeat each step in sequence. The opening and closing of the pulp is performed by an automatic opening/closing device using a timer, but the setting of each step time is determined by selecting the optimal gas flow rate of the tower and designing the tower so that each process has a specified pressure fluctuation within the set time. It will be done. One example would be number 1. The third step is 12
0 seconds, 2nd. The third step is set as 20 seconds.

Next, the present invention will be explained in detail by way of examples.

Example 1 2.3 to 2.8 m in a concentration tower with a diameter of 30 mm and a height of 500 mm.
Clinoptilolite 280I, which had been finely milled, washed with water, and activated by heating at 450°C for 2 hours, was charged, and the pressure inside the tower was reduced to 5 mercury columns using a vacuum pump. Then from the bottom of the tower 1.3
At a flow rate of 11 Anin (standard state), the inside of the column changes from 3 to 12 (
Low concentration methane gas (adjusted gas of 44% methane, 44% nitrogen, and 12% oxygen) was introduced until the absolute pressure was reached.

Then, the gas introduction is stopped, the upper part of the tower is opened, and the gas released at that time is collected in a tank. Then, the inside of the tower is regenerated under vacuum. This operation was repeated for 1 hour for about 20 cycles) The composition of the collected gas was determined by gas chromatography. This test was conducted by varying the amount of collected gas to determine the relationship between methane concentration and recovery rate.

As a result, when the methane concentration was concentrated from 44% to 60%, the recovery rate was 88%, and when it was concentrated to 64%, the recovery rate was 73%.
%Met. In addition, synthetic zeolites) 4A, 5A,
When a natural zeolite such as mordenite was used as an adsorbent, methane adsorption occurred to the same extent as nitrogen, making it impossible to concentrate methane.

Example 2 A concentration tower with a diameter of 60 mm and a height of 2000 mm was filled with 3.7 kg of clinoptilolite activated in the same manner as in Example 1, and coal mine exhaust gas (40.0% methane, 443% nitrogen) was charged. , oxygen 120%, carbon dioxide 2.5%, moisture 1.2%)
A column filled with silica gel (diameter 60 x height 300+++
m) to remove moisture up to 0.001%) 151/, f
A test was conducted by repeating the same operation as described in Example 1, introducing the sample at a flow rate of i (standard condition). The opening and closing of the pulp was performed automatically using a pulp automatic opening/closing device set to a gas introduction time of 120 seconds, a gas collection time of 15 seconds, a gas recovery time of 5 seconds, and a vacuum regeneration time of 120 seconds. Upper limit is 4 to 9A-rrL2 (absolute pressure), lower limit is 1
The condition is 0 (mercury column).

As a result, when there was no carbon dioxide removal group, the raw gas methane concentration of 40 cm was concentrated to 55%, and the methane recovery rate was 50%. By adding 300 mrtr) and removing carbon dioxide to 0.25%, a methane recovery rate of 90 cm can be achieved at the same concentration rate, and the same methane concentration over 10'O hours.

We were able to maintain the recovery rate. Furthermore, carbon dioxide is reduced to 0
By removing it to about 1%, it is possible to increase the concentration 1 recovery rate. In addition, by using two lines of gas inlet pipes, one for the pressurized system and one for the atmospheric pressure system, we were able to reduce the electricity cost of the compressor by about 20%.

As mentioned above, the methane concentrator, which has a concentrator filled with clinoptilolite and a pretreatment column for dehumidification and carbon dioxide removal, can easily produce low-concentration methane such as coal mine exhaust gas.
50 to 60, which can fully use air-based mixed gas as fuel
%, making effective use of valuable resources possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of implementing the method of the present invention, FIG. 2 is a system diagram of a practical device for implementing the present invention, and FIG.
The figure is a process explanatory diagram of a practical device. Code A, A': Concentration column, B, B': Decarbonization group +
CI+ C1'+ C2+ C2': Dehumidification tower. 1: Raw gas tank at atmospheric pressure, 2: Compressor. 3: Atmospheric pressure gas collection tank, 4.5: Vacuum pump. 6: ° atmospheric pressure gas introduction pipe, 7: pressurized gas introduction pipe. 8: Gas recovery pipe, 9: Pressurized tank, 10.11: Vacuum tank lV, ~V2. : Automatic valve ↑2 (21 1! JJ times 1, -, -, - 8

Claims (1)

[Claims] (11) Air-methane mixed gas containing moisture and carbon dioxide, such as coal mine exhaust gas, is pretreated in a dehumidification tower and carbon dioxide removal group, then filled with natural zeolite adsorbent, and vacuum regenerated. The gas is introduced from the lower part of the condensation tower at a predetermined pressure of 1, and as soon as the internal pressure of the tower reaches the predetermined pressure, the gas introduction is stopped, the upper part is opened and the pressure is reduced to near atmospheric pressure, and the gas released during this time is captured as concentrated methane gas. The gas is collected and stops releasing gas when it reaches atmospheric pressure.The natural zeolite adsorbent is regenerated by reducing the pressure to vacuum.Methane concentration using the non-equilibrium pressure operation method in the above concentration tower,
A methane concentration method and device characterized by alternately repeating a collection operation and a vacuum regeneration operation. (2) A concentrating column filled with natural zeolite adsorbent and a decarbonization group filled with the same adsorbent as the same column and with a smaller volume than the same column, with pulp installed between them to connect the nine columns. Furthermore, the air-methane mixed gas dehumidified in the dehumidifying tower is introduced from the carbon dioxide group to the concentrating tower (
The pressurization process) is divided into gas introduction from vacuum to atmospheric pressure (first process) and pressurization introduction from atmospheric pressure to a predetermined pressure (second process). The pressure reduction process is divided into gas collection from a predetermined pressure to atmospheric pressure (third step) and vacuum regeneration to reduce the pressure to below atmospheric pressure (fourth step), and from the first step to the third step, both towers are directly connected. operate,
The method and apparatus for concentrating methane according to claim 1, characterized in that only the fourth step is operated with both columns separated. 131 Claim 1 characterized in that the system is a mechanism for introducing the air-methane mixed gas into the carbon dioxide removal group in two systems, a pressurized system and an atmospheric pressure system, to reduce the power cost of the compressor. The method and apparatus for concentrating methane according to item 1 or 2. (1) Claims 1 or 2, characterized in that clinoptilolite selected as one suitable for the present invention among the natural zeolite adsorbents packed in the concentration column to remove carbon dioxide groups is used. Methane concentration method and apparatus described.