A system and method for purifying and separating raw coal gas from underground coal

Abstract

The present invention belongs to the technical field of coal gas purification, and specifically relates to a system and method for purifying and separating raw coal gas from underground coal. The technical scheme is as follows: a system for purifying and separating raw coal gas from underground coal, comprising a raw coal preliminary separation unit, the raw coal gas preliminary separation unit is connected to a membrane separation unit for methane concentration through a pipeline, the membrane separation unit is connected to a carbon dioxide purification unit through a pipeline, and the carbon dioxide purification unit is connected to a hydrogen purification unit through a pipeline. A method for purifying and separating raw coal gas from underground coal, comprising the following steps: preliminary separation of raw coal gas, carbon dioxide purification, hydrogen purification; methane concentration: the non-permeate gas from the first membrane separation device enters the second membrane separation assembly for methane concentration. The present invention provides a system and method for purifying and separating raw coal gas from underground coal.

Description

Technical Field

[0001] The invention belongs to the technical field of coal gas purification, and in particular relates to a system and method for purifying and separating raw coal gas from underground coal. Background Art

[0002] Underground coal gasification technology is a new clean energy technology that burns coal in a controlled manner underground without mining to produce gases such as coal gas.

[0003] The product gas (raw synthesis gas) generated by underground coal gasification usually contains synthesis gas (a mixture of CO, CO2, H2, CH4 and other gases) and other impurities (dust, water, tar, hydrocarbon vapor, and other trace components including H2S, COS, CS2, etc.). The complexity of its main components and impurities depends on many aspects: the oxidant used in underground coal gasification (air, pure oxygen, steam), the coal quality conditions and depth of the coal seam, and the operating parameters of the underground coal gasification process, including temperature, pressure, etc.

[0004] The main components of the raw coal gas obtained after pretreatment of the raw synthesis gas include H2, CH4, CO, CO2, N2, etc., among which H2 accounts for about 20-35% (v / v), CH4 accounts for about 30-50% (v / v), CO accounts for about 0.1-5% (v / v), CO2 accounts for about 6-50% (v / v), and N2 accounts for about 0.3-0.8% (v / v).

[0005] According to existing underground coal gasification plant engineering practices at home and abroad and existing patent literature, the main characteristics of the current underground coal gasification product gas are large changes in composition, pressure and flow rate. Therefore, its comprehensive utilization is mainly based on direct power generation, and there is a lack of a process flow system for simultaneously producing hydrogen, methane and CO2 according to downstream needs.

[0006] The main technologies for purifying and separating hydrogen, methane and CO2 from crude coal gas include membrane separation, pressure swing adsorption, cryogenic separation and absorption (amine absorption or low-temperature methanol washing). The membrane separation method has the advantages of low investment and simple operation, but the purity of the recovered hydrogen is not high and cannot meet the needs of industrial hydrogen. The pressure swing adsorption method can produce high-purity hydrogen, methane and CO2, but its recovery rate is not high and its adaptability to the fluctuation of raw gas components is not strong, which in turn affects the purity of the product. The hydrogen content finally obtained by the cryogenic separation method can only reach about 90% at most, and the purity still cannot meet the needs of downstream. The equipment used is complex and the production investment is high. The absorption method is generally used to remove acidic gases (absorb CO2) in crude coal gas, and then use the pressure swing adsorption process to recover H2. However, due to the complex composition of crude coal gas, the large change of CO2 components, the large investment of the absorption method, and the large energy consumption of the absorption liquid desorption, the process is complicated to operate, the investment is too large, and the economy is poor, which makes it difficult to be applied in actual engineering. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the object of the present invention is to provide a system and method for purifying and separating raw coal underground gas.

[0008] The technical solution adopted by the present invention is:

[0009] A system for purifying and separating underground raw coal gas comprises a raw coal preliminary separation unit, the raw coal gas preliminary separation unit is connected to a membrane separation unit for methane concentration via a pipeline, the membrane separation unit is connected to a carbon dioxide purification unit via a pipeline, and the carbon dioxide purification unit is connected to a hydrogen purification unit via a pipeline.

[0010] As a preferred embodiment of the present invention, the crude gas preliminary separation unit comprises a filter separator and a heater connected by a pipeline, the other end of the heater is connected to the membrane separation unit by a pipeline, and the filter separator is connected to a crude gas inlet pipeline.

[0011] As a preferred embodiment of the present invention, the membrane separation unit comprises a first membrane separation component and a second membrane separation component connected by pipelines, and the first membrane separation component is connected to the crude gas preliminary separation unit and the carbon dioxide purification unit respectively by pipelines.

[0012] As a preferred embodiment of the present invention, a product natural gas pipeline is connected between the first membrane separation component and the second membrane separation component, and a product methane pipeline is connected to the second membrane separation component.

[0013] As a preferred embodiment of the present invention, the second membrane separation component is also connected to the pipeline between the first membrane separation component and the carbon dioxide purification unit through a pipeline.

[0014] As a preferred embodiment of the present invention, the carbon dioxide purification unit includes a front-end vacuum device, to which a product carbon dioxide pipeline is connected, and the front-end vacuum device is connected in parallel with several front-end adsorption towers, the top of the front-end adsorption tower is connected to the hydrogen purification unit through a pipeline, and the membrane separation unit is connected to the bottom of the several front-end adsorption towers through a pipeline.

[0015] As a preferred embodiment of the present invention, the hydrogen purification unit includes a rear-end vacuum pumping device, to which a fuel gas pipeline is connected, and the rear-end vacuum pumping device is connected in parallel with several rear-end adsorption towers, the top of the rear-end adsorption tower is connected to a product hydrogen pipeline, and the carbon dioxide purification unit is connected to the bottom of the several rear-end adsorption towers through a pipeline.

[0016] As a preferred embodiment of the present invention, both the first membrane separation component and the second membrane separation component are made of polyimide membrane material.

[0017] As a preferred embodiment of the present invention, the adsorbent in the carbon dioxide adsorption unit is a carbon dioxide-specific adsorbent; and the adsorbent in the hydrogen purification unit is a multi-bed adsorbent.

[0018] A method for purifying and separating raw coal underground gas, comprising the following steps:

[0019] Initial separation of raw gas: Solid particle impurities are separated from raw gas by the initial separation unit of raw gas;

[0020] Carbon dioxide purification: The gas after preliminary separation enters the membrane separation unit, and the permeate gas at the outlet of the tube side of the membrane separation unit enters the carbon dioxide purification unit for carbon dioxide purification;

[0021] Hydrogen purification: The raw coal gas from the carbon dioxide purification unit enters the hydrogen purification unit for hydrogen purification;

[0022] Methane concentration: The non-permeate gas from the first membrane separation device enters the second membrane separation component for methane concentration.

[0023] The beneficial effects of the present invention are:

[0024] The process flow of the present invention is simple, and effective components (hydrogen, methane and CO2) can be fully purified and separated. It has the advantages of strong adaptability to the components of raw gas and simple and flexible operation. In view of the problem that the raw gas produced by underground coal gasification cannot be comprehensively utilized, the present invention can purify and separate the raw coal gas from underground coal to obtain different products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the present invention.

[0026] In the figure, 1-raw coal preliminary separation unit; 2-membrane separation unit; 3-carbon dioxide purification unit; 4-hydrogen purification unit; 11-filter separator; 12-heater; 13-raw coal gas inlet pipeline; 21-first membrane separation component; 22-second membrane separation component; 23-product natural gas pipeline; 24-product methane pipeline; 31-front-end vacuum pumping device; 32-product carbon dioxide pipeline; 33-front-end adsorption tower; 41-rear-end vacuum pumping device; 42-fuel gas pipeline; 43-rear-end adsorption tower; 44-product hydrogen pipeline. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0028] like Figure 1 As shown, the system for purifying and separating raw coal gas from underground coal of this embodiment includes a raw coal preliminary separation unit 1, the raw gas preliminary separation unit is connected to a membrane separation unit 2 for methane concentration through a pipeline, the membrane separation unit 2 is connected to a carbon dioxide purification unit 3 through a pipeline, and the carbon dioxide purification unit 3 is connected to a hydrogen purification unit 4 through a pipeline.

[0029] The crude gas preliminary separation unit comprises a filter separator 11 and a heater 12 connected by a pipeline. The other end of the heater 12 is connected to the membrane separation unit 2 through a pipeline. The filter separator 11 is connected to a crude gas inlet pipeline 13.

[0030] The membrane separation unit 2 includes a first membrane separation assembly 21 and a second membrane separation assembly 22 connected by pipelines, and the first membrane separation assembly 21 is connected to the crude gas preliminary separation unit and the carbon dioxide purification unit 3 by pipelines, respectively. A product natural gas pipeline 23 is also connected between the first membrane separation assembly 21 and the second membrane separation assembly 22, and a product methane pipeline 24 is connected to the second membrane separation assembly 22. The second membrane separation assembly 22 is also connected to the pipeline between the first membrane separation assembly 21 and the carbon dioxide purification unit 3 by a pipeline.

[0031] The carbon dioxide purification unit 3 includes a front-end vacuum device 31, to which a product carbon dioxide pipeline 32 is connected. The front-end vacuum device 31 is connected in parallel with a plurality of front-end adsorption towers 33. The top of the front-end adsorption tower 33 is connected to the hydrogen purification unit 4 through a pipeline, and the membrane separation unit 2 is connected to the bottom of the plurality of front-end adsorption towers 33 through a pipeline.

[0032] The hydrogen purification unit 4 includes a rear-end vacuum pumping device 41, to which a fuel gas pipeline 42 is connected. The rear-end vacuum pumping device 41 is connected in parallel with a plurality of rear-end adsorption towers 43, and the top of the rear-end adsorption tower 43 is connected with a product hydrogen pipeline 44. The carbon dioxide purification unit 3 is connected to the bottom of the plurality of rear-end adsorption towers 43 through a pipeline.

[0033] 1. Raw gas preliminary separation part: This part is to perform preliminary separation of hydrogen, methane and CO2 in the raw gas according to the different permeability of each component in the raw gas to ensure the stability of the products of the downstream purification device.

[0034] The filter separator 11 is a simple physical pretreatment site for the raw gas, and the filter separator 11 is connected to the heater 12 in turn.

[0035] The outlet of the heater 12 is directly connected to the first membrane separation assembly 21 to provide heat to ensure the membrane separation effect.

[0036] The shell side of the first membrane separation component 21 is non-permeate gas, and is directly connected to the second membrane separation component 22 , and the tube side is permeate gas, and is directly connected to the front-end adsorption tower 33 .

[0037] 2. CO2 purification part: This part mainly purifies CO2 in the permeate gas during membrane separation and transmits it to the downstream.

[0038] The top outlet of the front-end adsorption tower 33 is non-adsorbed gas that does not contain CO 2 and is directly connected to the rear-end adsorption tower 43 .

[0039] The bottom outlet of the front-end adsorption tower 33 is the analytical gas with a CO2 concentration greater than 99%, which is directly connected to the front-end vacuum pumping device 31 and is sent to the downstream device after vacuum analysis.

[0040] 3. Hydrogen purification part: This part mainly purifies the hydrogen in the permeate gas during membrane separation and transmits it to the downstream.

[0041] The top outlet of the rear end adsorption tower 43 is non-adsorbed gas with a hydrogen purity greater than 99%, which is directly transported to the downstream.

[0042] The bottom outlet of the rear-end adsorption tower 43 is the analytical gas, which is directly connected to the rear-end vacuum pumping device 41 and is sent to the downstream device after vacuum pumping and analysis.

[0043] 4. Methane concentration section: This section is mainly used to concentrate the methane in the non-permeate gas during membrane separation and transmit it to the downstream.

[0044] The shell-side outlet of the second membrane separation component 22 is non-permeate gas with a methane purity greater than 95%, which is directly transported to the downstream.

[0045] The outlet of the tube side of the second membrane separation component 22 is the permeate gas, which is directly connected to the front-end adsorption tower 33 to recover hydrogen and improve the recovery rate of hydrogen.

[0046] The present invention also provides a method for purifying and separating raw coal gas from underground coal gasification, comprising the following steps:

[0047] 1. Preliminary separation of raw gas

[0048] The raw coal gas of 2.0-4.0 MPa.g is connected to the filter separator 11. After the solid particle impurities that may be carried are separated by the filter separator 11, it enters the heater 12. After the raw coal gas is heated to 30-60°C by the heater 12, it enters the first membrane separation component 21. The shell side outlet of the first membrane separation component 21 is non-permeate gas with a pressure of 2.0-4.0 MPa.g, which enters the second membrane separation component 22. The tube side outlet of the first membrane separation component 21 is permeate gas with a pressure of 0.2-0.6 MPa.g, which enters the front-end adsorption tower 33.

[0049] 2. CO2 purification part

[0050] The raw coal gas with a non-permeate pressure of 0.2-0.6 MPa.g from the first membrane separation module 21 enters from the bottom of the front adsorption tower 33, CO2 in the raw coal gas is adsorbed by the adsorbent, and the non-adsorbed gas enters the hydrogen purification part from the top outlet of the tower. The adsorbed CO2 is extracted by the front vacuum device 31 and sent to the downstream device.

[0051] 3. Hydrogen purification part

[0052] The crude gas from the top of the front adsorption tower 33 is 0.2-0.6 MPa.g, and enters from the bottom of the rear adsorption tower 43. Impurities in the crude gas are adsorbed, and hydrogen is collected from the top of the rear adsorption tower 43 as a non-adsorbed component and sent to the downstream device. The adsorbed impurities are analyzed by the rear vacuum device 41 and sent to the downstream device.

[0053] 4. Methane enrichment part

[0054] The raw coal gas with a pressure of 2.0-4.0 MPa.g from the first membrane separation module 21 enters the second membrane separation module 22. The tube-side outlet of the second membrane separation module 22 is permeate gas with a pressure of 0.2-0.6 MPa.g, which enters the front-end adsorption tower 33. The shell-side outlet of the second membrane separation module 22 is non-permeate gas with a pressure of 2.0-4.0 MPa.g, which is sent to the downstream device as a natural gas product.

[0055] In the present invention, the first membrane separation component 21 and the second membrane separation component 22 are made of polyimide membrane material.

[0056] The heater 12 in the present invention can be an electric heater 12, steam heating or other heat sources.

[0057] In the present invention, the front-end vacuum pumping device 31 and the rear-end vacuum pumping device 41 are both water ring vacuum pumps.

[0058] The adsorbent in the front-end adsorption tower 33 of the present invention is a CO2-specific adsorbent.

[0059] The adsorbent in the rear end adsorption tower 43 of the present invention is a multi-bed adsorbent, which can adsorb N2, CO, CO2 and methane respectively.

[0060] The present invention is not limited to the above-mentioned optional implementation modes. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that fall within the scope defined by the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A system for purifying and separating raw coal gas from underground coal. It is characterized in that The invention comprises a crude coal preliminary separation unit (1), the crude coal gas preliminary separation unit is connected to a membrane separation unit (2) for methane concentration via a pipeline, the membrane separation unit (2) is connected to a carbon dioxide purification unit (3) via a pipeline, and the carbon dioxide purification unit (3) is connected to a hydrogen purification unit (4) via a pipeline; The crude coal gas preliminary separation unit comprises a filter separator (11) and a heater (12) connected by a pipeline, the other end of the heater (12) is connected to the membrane separation unit (2) by a pipeline, and the filter separator (11) is connected to a crude coal gas inlet pipeline (13); The membrane separation unit (2) comprises a first membrane separation component (21) and a second membrane separation component (22) connected via a pipeline, and the first membrane separation component (21) is connected to a crude gas preliminary separation unit and a carbon dioxide purification unit (3) via pipelines respectively; A product natural gas pipeline (23) is also connected between the first membrane separation component (21) and the second membrane separation component (22), and a product methane pipeline (24) is connected to the second membrane separation component (22); The second membrane separation component (22) is also connected to the pipeline between the first membrane separation component (21) and the carbon dioxide purification unit (3) through a pipeline; The carbon dioxide purification unit (3) comprises a front-end vacuum pumping device (31), the front-end vacuum pumping device (31) is connected to a product carbon dioxide pipeline (32), the front-end vacuum pumping device (31) is connected in parallel to a plurality of front-end adsorption towers (33), the top of the front-end adsorption tower (33) is connected to the hydrogen purification unit (4) via a pipeline, and the membrane separation unit (2) is connected to the bottom of the plurality of front-end adsorption towers (33) via a pipeline; The hydrogen purification unit (4) comprises a rear-end vacuum pumping device (41), the rear-end vacuum pumping device (41) is connected to a fuel gas pipeline (42), the rear-end vacuum pumping device (41) is connected in parallel to a plurality of rear-end adsorption towers (43), the top of the rear-end adsorption tower (43) is connected to a product hydrogen pipeline (44), and the carbon dioxide purification unit (3) is connected to the bottom of the plurality of rear-end adsorption towers (43) via pipelines.

2. A system for purifying and separating raw coal underground gas according to claim 1, It is characterized in that The first membrane separation component (21) and the second membrane separation component (22) are both made of polyimide membrane material.

3. A system for purifying and separating raw coal underground gas according to claim 1, It is characterized in that The adsorbent in the carbon dioxide adsorption unit is a special adsorbent for carbon dioxide; the adsorbent in the hydrogen purification unit (4) is a multi-bed adsorbent.

4. A method for purifying and separating raw coal underground gas using the system of claim 1, It is characterized in that The steps include: Initial separation of raw gas: Solid particle impurities are separated from raw gas by the initial separation unit of raw gas; Carbon dioxide purification: the gas after preliminary separation enters the membrane separation unit (2), and the permeate gas at the outlet of the tube side of the membrane separation unit (2) enters the carbon dioxide purification unit (3) for carbon dioxide purification; Hydrogen purification: The raw coal gas from the carbon dioxide purification unit (3) enters the hydrogen purification unit (4) for hydrogen purification; Methane concentration: The non-permeate gas from the first membrane separation device enters the second membrane separation module (22) for methane concentration.

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