Three-tower double-reflux pressure swing adsorption system

Abstract

The utility model discloses a three-tower double-reflux pressure swing adsorption system, and relates to the technical field of coal bed gas purification. Comprising a coal bed gas storage tank, a nitrogen storage tank, a methane storage tank, a first tower, a second tower, a third tower, a first compressor, a second compressor and a vacuum pump, every two of the tops of the three towers are connected through a pipeline; a gas inlet of the first compressor is respectively connected with the tops of the three towers and a coal bed gas storage tank pipeline; the exhaust port is connected with a first buffer structure and then is respectively connected with the middle parts of the three towers and a coal bed gas storage tank; a gas inlet of the second compressor is respectively connected with the bottoms of the three towers, a nitrogen gas storage tank and a methane gas storage tank through pipelines; the exhaust port is connected with the bottoms of the three towers after being connected with a second buffer structure; the vacuum pump is connected with the bottoms of the three towers and the methane storage tank through pipelines. The three-tower alternating operation is adopted, methane can be continuously generated, the methane production speed is improved, meanwhile, the starting and stopping frequency of the vacuum pump can be reduced, and the service life of a unit is prolonged.

Description

Technical Field

[0001] The utility model relates to the technical field of coal bed gas purification, in particular to a three-tower double-reflux pressure swing adsorption system. Background Art

[0002] Coalbed methane, also known as coal mine gas, is mainly adsorbed on the surface of coal matrix particles or partially free in coal pores. It is an important unconventional natural gas resource. The CH4 content of low-concentration coalbed methane is often less than 30%, and its calorific value is low and cannot be used directly. Therefore, low-concentration coalbed methane must be purified. However, the existing pressure swing adsorption technology faces problems such as high energy consumption, discontinuous methane output, frequent start-up and shutdown of units, and high maintenance costs. Therefore, it is necessary to design an efficient low-methane concentration coalbed methane enrichment system to solve the above problems. Utility Model Content

[0003] The main purpose of the utility model is to provide a three-tower double-reflux pressure swing adsorption system to solve the above problems.

[0004] To achieve the above-mentioned purpose, the utility model provides a three-tower double reflux pressure swing adsorption system, including a coalbed methane gas storage tank, a nitrogen gas storage tank, a methane gas storage tank, a first tower, a second tower, a third tower, a first compressor, a second compressor, a vacuum pump, a first buffer structure and a second buffer structure;

[0005] The tops of the first tower, the second tower and the third tower are connected in pairs via pipelines;

[0006] The air inlet of the first compressor is respectively connected to the top of the first tower, the second tower, the third tower and the coalbed methane storage tank pipeline; the exhaust port of the first compressor is connected to the first buffer structure and then to the middle of the first tower, the second tower, the third tower and the coalbed methane storage tank;

[0007] The air inlet of the second compressor is respectively connected to the bottom of the first tower, the second tower, and the third tower, as well as the nitrogen gas storage tank and the methane gas storage tank pipeline; the exhaust port of the second compressor is connected to the second buffer structure and then connected to the bottom of the first tower, the second tower, and the third tower;

[0008] The air inlet of the vacuum pump is connected to the bottom pipelines of the first tower, the second tower and the third tower respectively; the air outlet of the vacuum pump is connected to the pipeline of the methane gas storage tank;

[0009] All pipelines are equipped with gate valves.

[0010] Furthermore, the first tower, the second tower and the third tower are all independently controlled and are respectively in the adsorption process, the desorption process and the regeneration process during operation.

[0011] Furthermore, the fillers of the first tower, the second tower and the third tower are all lead ion modified zeolite molecular sieves.

[0012] Furthermore, the first buffer structure and the second buffer structure are both composed of a gate valve channel and a buffer tank channel connected in parallel, and a gate valve is connected to the front and rear of the buffer tank channel respectively.

[0013] Furthermore, the buffer tank channel in the first buffer structure is a coalbed methane buffer tank, and the buffer tank channel in the second buffer structure is a nitrogen buffer tank.

[0014] The utility model has the following beneficial effects:

[0015] 1. The three-tower rotation operation can produce methane continuously, increase the methane production speed, reduce the start and stop frequency of the vacuum pump, and extend the life of the unit.

[0016] 2. Multiple double reflux operations can reduce energy consumption by about 20% and improve methane recovery rate and purity;

[0017] 3. Using a buffer device can reduce energy consumption, reduce the start and stop frequency of the compressor, and extend the life of the compressor;

[0018] 4. The pipeline connection method and process flow are cleverly combined, and only two necessary compressor units are used, which can effectively reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of a three-tower double-reflux pressure swing adsorption system proposed by the utility model;

[0020] Figure 2 This is a schematic diagram of the first four steps in a working cycle of a three-tower double-reflux pressure swing adsorption system proposed by the utility model.

[0021] In the figure: 1-coalbed methane gas storage tank; 2-nitrogen gas storage tank; 3-methane gas storage tank; 4-first tower; 5-second tower; 6-third tower; 7-first compressor; 8-second compressor; 9-vacuum pump; 10-nitrogen buffer tank; 11-coalbed methane buffer tank. DETAILED DESCRIPTION

[0022] In order to achieve the above-mentioned purpose and effect, the technical means and structure adopted by the utility model are described in detail with reference to the accompanying drawings for the preferred embodiments of the utility model and their features and functions.

[0023] like Figure 1As shown, the utility model provides a three-tower double reflux pressure swing adsorption system, including a coalbed methane gas storage tank 1, a nitrogen gas storage tank 2, a methane gas storage tank 3, a first tower 4, a second tower 5, a third tower 6, a first compressor 7, a second compressor 8, a vacuum pump 9, a first buffer structure and a second buffer structure; wherein the three towers refer to the first tower 4, the second tower 5, and the third tower 6, respectively, and the three towers work together and the processes are rotated; the double reflux process refers to the reflux of the heavy component gas and the light component gas of the tower in the adsorption process and the tower in the regeneration process during the working process; the pressure swing refers to the different pressure states of the three towers during the working process, and the pressure state of the same tower in different working steps is also different; the adsorption means that, compared with nitrogen, more methane gas is adsorbed in the zeolite material to be enriched.

[0024] Specifically, the light component gas refers to nitrogen that is less absorbed by the zeolite material, and the heavy component gas refers to methane that is more absorbed by the zeolite material.

[0025] The tops of the three towers are connected in pairs through pipelines, providing a path for the pressure equalization and double reflux process. The air inlet of the second compressor 8 is connected to the bottom of the three towers, the nitrogen gas storage tank 2 and the methane gas storage tank 3 through pipelines, and the exhaust port of the second compressor 8 is connected to the second buffer structure and then to the bottom of the three towers; the air inlet of the first compressor 7 is connected to the top of the three towers and the coalbed methane gas storage tank 1 through pipelines, and the exhaust port of the first compressor 7 is connected to the first buffer structure and then to the middle of the three towers and the coalbed methane gas storage tank 1. The vacuum pump 9 is connected to the bottom of the three towers and the methane gas storage tank 3, and the high-concentration methane gas in the tower in the desorption process is continuously recovered.

[0026] The first tower 4, the second tower 5 and the third tower 6 are all independently controlled and are in the adsorption process, the desorption process and the regeneration process respectively during operation. The adsorption process refers to the introduction of a methane-nitrogen mixed gas, the adsorption of methane and the discharge of high-purity nitrogen. The desorption process refers to negative pressure analysis, in which the high-concentration methane adsorbed in the zeolite is released and stored in the methane gas storage bottle 3. The regeneration process refers to the complete desorption of methane in the zeolite by purging with high-purity nitrogen.

[0027] The three towers rotate during operation, and the rotation order is: regeneration → adsorption → desorption. During the regeneration process, the inside of the tower is filled with high-purity nitrogen with very little methane content. The next step will be adsorption. During the adsorption process, the nitrogen adsorbed in the zeolite molecular sieve in the tower flows out, and methane is adsorbed, making the nitrogen content in the exhaust gas higher. After complete adsorption, desorption is carried out, and vacuum negative pressure is pumped to desorb the gas molecules adsorbed by the zeolite and collected in the methane gas storage tank 3.

[0028] The fillers of the three towers are all lead ion modified zeolite molecular sieves. Experiments have shown that the lead ion modified zeolite molecular sieves have higher methane enrichment capacity.

[0029] All three towers adopt the middle feeding method, and the middle feeding position must meet the requirements: when the reflux heavy component gas reaches this position, the methane concentration is close to the feed methane concentration; at the same time, during the feeding process, there is a gas reflux process between the tower in the adsorption process and the tower in the regeneration process, that is, a double reflux process, which can improve the methane recovery rate and production efficiency. Compared with the single-tower system, it can reduce the operating steps and save energy.

[0030] The first buffer structure and the second buffer structure are both composed of a gate valve channel and a buffer tank channel in parallel, and a gate valve is connected to the front and back of the buffer tank channel; the buffer tank channel in the first buffer structure is a coalbed methane buffer tank 11, and the buffer tank channel in the second buffer structure is a nitrogen buffer tank 10. During the action of the buffer structure, the working power of the compressor will produce slow fluctuations to meet the normal operation of the system. The existence of the buffer system can greatly reduce the start and stop frequency of the compressor, save start and stop energy consumption, and extend the life of the unit.

[0031] Taking the initial state, the first tower 4 is in the adsorption process, the second tower 5 is in the regeneration process, and the third tower 6 is in the desorption process as an example, the system operation process is:

[0032] Step 1, the coalbed methane gas storage tank 1 is filled with gas into the middle of the first tower 4 through the gate valve channel through the first compressor 7, the first tower 4 is in a high-pressure adsorption state, the zeolite material adsorbs methane under high pressure and discharges nitrogen, a part of the nitrogen is passed into the nitrogen gas storage tank 2, and the other part is purged into the second tower 5 through the throttle valve, the residual methane in the zeolite material in the second tower 5 is preliminarily resolved, the discharged methane and nitrogen mixed gas is pressurized by the second compressor 8 and enters the first tower 4 through the gate valve channel for reflux adsorption to improve the methane recovery rate, and the third tower 6 pumps high-purity methane gas into the methane gas storage tank 3 through the vacuum pump 9;

[0033] Step 2, the tops of the first tower 4 and the second tower 5 are connected through a gate valve and a throttle valve to perform a pressure equalization operation. Since the gas pressure of the first tower 4 is higher than that of the second tower 5, a small portion of the high-concentration nitrogen remaining at the top of the first tower 4 enters the second tower 5, the second tower 5 completes the initial pressure increase, and the first tower 4 completes the initial pressure reduction, which can improve the purity of methane and save unit energy consumption. The coalbed methane storage tank 1 pumps the gas into the coalbed methane buffer tank 11 through the first compressor 7, and the nitrogen storage tank 2 pumps the gas into the nitrogen buffer tank 10 through the second compressor 8. The third tower 6 continues to pump gas into the methane storage tank 3 through the vacuum pump 9;

[0034] Step 3: The second compressor 8 passes the gas in the methane gas storage tank 3 into the bottom of the first tower 4, and the first compressor 7 passes the gas at the top of the first tower 4 into the coalbed methane gas storage tank 1. The third tower 6 continues to pump gas into the methane gas storage tank 3 through the vacuum pump 9, and the nitrogen buffer tank 10 is connected to the bottom of the second tower 5 to achieve re-pressurization;

[0035] Step 4: The second compressor 8 passes the gas in the nitrogen gas storage tank 2 into the bottom of the second tower 5, and the second tower 5 completes the final pressure increase and complete regeneration. The first compressor 7 passes the coal-bed methane in the coal-bed methane gas storage tank 1 into the coal-bed methane buffer tank 11 for temporary storage. The third tower 6 continues to pump gas into the methane gas storage tank 3 through the vacuum pump 9. This step is mainly to achieve complete regeneration of the second tower 5, which takes a short time.

[0036] Step 5, process rotation; the first tower 4 enters the desorption process, the second tower 5 enters the adsorption process, the third tower 6 enters the regeneration process, and step 1 is repeated.

[0037] Process optimization and pipeline design in this process flow (refer to Figure 1 ), the vacuum pump 9 can be started without damage, the service life of the vacuum pump can be greatly increased, the energy consumption of starting and stopping can be reduced, and only two compressor units are used, which reduces the compressor production cost and saves about 20% of the comprehensive budget.

[0038] For the sake of convenience, the tower in the adsorption process is called the adsorption tower, the tower in the regeneration process is called the regeneration tower, and the tower in the desorption process is called the desorption tower.

[0039] In step one, the air pressure of the adsorption tower is controlled at about 0.4MPa, the air pressure of the regeneration tower is controlled at about 0.1MPa, the air pressure of the coalbed methane buffer tank 11 slowly drops to 0.4MPa, and the air pressure of the desorption tower is controlled at about 0.05MPa, which takes a long time; in step two, the air pressure of the adsorption tower and the regeneration tower is about 0.25MPa after equalization, the air pressure of the coalbed methane buffer tank 11 does not exceed 0.5MPa, the air pressure of the nitrogen buffer tower 10 does not rise by more than 0.6MPa, and the air pressure of the desorption tower is controlled at about 0.05MPa, which takes a very short time; in step three, the air pressure of the adsorption tower is controlled at about 0.25MPa, the air pressure of the regeneration tower is increased by no more than 0.3MPa from the nitrogen buffer tank, and the air pressure of the desorption tower is controlled at about 0.05MPa, which takes a long time; in step four, the air pressure of the regeneration tower is controlled at about 0.4MPa, the air pressure of the coalbed methane buffer tank 11 does not exceed 0.6MPa, and the air pressure of the desorption tower is controlled at about 0.05MPa, which takes a short time.

[0040] The above description is only the preferred embodiment of the utility model, not all embodiments. Anyone should be aware that structural changes made under the inspiration of the utility model, and all technical solutions that are the same or similar to the utility model, belong to the protection scope of the utility model.

Claims

1. A three-tower double reflux pressure swing adsorption system, characterized in that: It includes a coalbed methane gas storage tank, a nitrogen gas storage tank, a methane gas storage tank, a first tower, a second tower, a third tower, a first compressor, a second compressor, a vacuum pump, a first buffer structure and a second buffer structure; The tops of the first tower, the second tower and the third tower are connected in pairs through pipelines; The air inlet of the first compressor is respectively connected to the top of the first tower, the second tower, the third tower and the coalbed methane storage tank pipeline; the exhaust port of the first compressor is connected to the first buffer structure and then to the middle of the first tower, the second tower, the third tower and the coalbed methane storage tank; The air inlet of the second compressor is respectively connected to the bottom of the first tower, the second tower, and the third tower, as well as the nitrogen gas storage tank and the methane gas storage tank pipeline; the exhaust port of the second compressor is connected to the second buffer structure and then connected to the bottom of the first tower, the second tower, and the third tower; The air inlet of the vacuum pump is connected to the bottom pipelines of the first tower, the second tower and the third tower respectively; the air outlet of the vacuum pump is connected to the pipeline of the methane gas storage tank; All pipelines are equipped with gate valves.

2. A three-tower double reflux pressure swing adsorption system as claimed in claim 1, characterized in that: The first tower, the second tower and the third tower are all independently controlled and are respectively in the adsorption process, the desorption process and the regeneration process during operation.

3. A three-tower double reflux pressure swing adsorption system as claimed in claim 1 or 2, characterized in that: The fillers of the first tower, the second tower and the third tower are all lead ion modified zeolite molecular sieves.

4. A three-tower double reflux pressure swing adsorption system as claimed in claim 3, characterized in that: The first buffer structure and the second buffer structure are both composed of a gate valve channel and a buffer tank channel connected in parallel, and a gate valve is connected to the front and rear of the buffer tank channel respectively.

5. A three-tower double reflux pressure swing adsorption system as claimed in claim 4, characterized in that: The buffer tank channel in the first buffer structure is a coalbed methane buffer tank, and the buffer tank channel in the second buffer structure is a nitrogen buffer tank.

Images