Coal gangue and biomass staged gasification method

Abstract

The present application belongs to the field of bulk solid waste resource utilization, and discloses a coal gangue and biomass staged gasification method, which comprises: feeding coal gangue and biomass with a particle size less than 200 mm and a design amount as primary raw materials into a primary gasification furnace, using water vapor as a primary gasification agent, and performing preheating, pyrolysis and gasification in total three reactions during the sinking process of the primary raw materials; feeding coal gangue with a particle size of 200-500 mm and a design amount as secondary raw materials into a secondary gasification furnace, simultaneously feeding mixed gas of secondary water vapor and primary crude coal gas, and performing preheating, pyrolysis, gasification and coke removal in total four reactions during the sinking process of the secondary raw materials. The method can fully decompose macromolecular tar in the furnace into small molecule coal gas, improve the calorific value of the gas, the carbon conversion rate and the cold gas efficiency, the tar in the primary gasification furnace is catalytically reformed by the coke-removing zone coal gangue lime slag in the secondary gasification furnace, the tar removal rate of the whole process reaches more than 95%, and a separate tar removal device is not needed.

Description

Technical Field

[0001] This invention relates to the field of bulk solid waste resource utilization, specifically to a method for staged gasification of coal gangue and biomass. Background Technology

[0002] Coal gasification technology is one of the important methods for producing syngas. The main product of this technology is combustible gas, primarily composed of H2, CO, CH4, and CO2, which can be used as fuel or for synthesizing chemical products, and has a wide range of applications. Coal gangue is a solid industrial waste generated during coal mining, coal preparation, and extraction. It has low volatile matter and low carbon content. However, during coal gasification, it produces a large amount of tar, and to improve its gasification performance, it is necessary to increase the carbon content, enrich the pore structure, and enhance the efficiency of cold gasification. Biomass has high volatile matter and high carbon content, which will greatly improve the gasification performance of coal gangue. However, the interaction between coal gangue and biomass in the co-gasification process requires further in-depth research.

[0003] Co-gasification technology can not only improve the gasification efficiency of solid products, but also increase the yield of hydrogen-rich gas. However, the existing co-gasification process has the following problems: (1) Air is often used as the gasification agent. The gas contains a large amount of N2, the calorific value of the crude coal gas is low, and the purification cost is high. (2) At present, the proportion of coal gangue in the co-gasification of multiple raw materials is low. However, as an industrial solid waste, its emissions are much higher than the biomass. Therefore, the addition of low biomass is more meaningful for the study of coal gangue gasification efficiency. (3) A large amount of tar and dust can easily cause pipeline blockage, which poses a great challenge to the stability of the process. (4) In the co-gasification of multiple raw materials, the efficiency of cold coal gas is low and the interaction of raw material gasification process is weak. Therefore, a new gasification method is needed.

[0004] Chinese patent document CN108410513A describes a biomass staged gasification process that adds a reforming process to the conventional biomass gasification process to reform the tar, thereby achieving stepwise removal of tar and obtaining cleaner combustible gas. However, the gasification efficiency of biomass alone is lower than that of multi-source feedstocks, and its gasification efficiency cannot meet the needs of end-user power generation.

[0005] Chinese patent document CN102504877A describes a coal grading gasification process that solves technical problems such as high carbon dioxide and organic matter content, high carbon content in fly ash and slag, low cold gas efficiency, and difficulty in gas purification in the gas produced by fluidized bed or circulating fluidized bed pulverized coal gasification. However, its tar content is relatively high, and the problem of tar blockage has not been effectively solved.

[0006] According to Chinese patent document CN101970618A, the coal staged gasification process improves gasification efficiency through secondary air supply, but the syngas outlet temperature is too high, which easily causes problems such as fouling of the heating surface and low slag collection rate.

[0007] In view of the above, there is an urgent need to develop a new staged gasification process for coal gangue and biomass that can not only produce hydrogen-rich gas and improve the efficiency of cold coal gas, but also directly remove long fatty chain tar molecules without the need for an external tar removal device, thus avoiding the impact of gas pipeline blockage on process stability. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and provide a method for graded gasification of coal gangue and biomass. The method uses steam as the gasifying agent and feeds multiple raw materials in stages, so that the raw materials are preheated, pyrolyzed, gasified and decoked to obtain combustible gas with low tar content. This eliminates the investment in decoking equipment and enhances the application value of multiple bulk solid wastes.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] This invention provides a method for staged gasification of coal gangue and biomass, comprising the following steps:

[0011] Step S1, pretreatment: crush and screen the coal gangue and biomass raw materials to obtain coal gangue and biomass with a particle size of less than 200mm and coal gangue with a particle size of 200-500mm respectively (the specific pretreatment method is to control the screening rate of coal gangue to be above 85%, the screen size to be 200mm, and collect the oversize and undersize raw materials respectively); the volatile matter content of the coal gangue raw materials should be less than 15%, and the ash content should be between 40-60%.

[0012] Specifically, biomass can be one or more of straw, wood, peanut shells, and cottonseed hulls. Coal gangue can be one or more of coal roadway gangue, spontaneously combusting gangue, washed gangue, hand-sorted gangue, and stripped gangue.

[0013] Step S2: The pretreated raw materials are fed into a staged gasification unit, which consists of a two-stage gasifier, including a primary gasifier and a secondary gasifier. The primary gasifier uses steam as the gasifying agent, which is fed into the primary gasifier from the bottom. A mixture of coal gangue and biomass with a particle size less than 200mm is used as the primary raw material, fed from the top of the primary gasifier and sinking from top to bottom, sequentially passing through three reaction layers: preheating, pyrolysis, and gasification, and undergoing the corresponding reactions. A mixture of coal gangue and biomass with a particle size of 200-500mm is also used as the primary raw material. Coal gangue, as a secondary feedstock, is fed into the secondary gasifier from the top. It sinks from top to bottom within the gasifier, undergoing preheating, pyrolysis, gasification, and decoking in four reaction layers. Simultaneously, secondary steam is mixed with primary crude gas discharged from the top of the primary gasifier and fed into the bottom of the secondary gasifier. It then rises and is catalytically reformed by the secondary coal gangue and lime slag, thus completing the secondary gasification and decoking reactions. Biomass accounts for 30%–40% of the total mass of the primary and secondary feedstocks, while the secondary feedstock accounts for 10%–20%.

[0014] In step S3, the secondary crude gas discharged from the top of the secondary gasifier is cooled, heat exchanged, and purified by dust removal to obtain fuel gas.

[0015] Further, in step S2, the preheating temperature is 300–500℃; the pyrolysis temperature is 500–1000℃; the gasification temperature is 1000–1100℃; the decoking temperature is 900–1000℃; the height range of the preheating:pyrolysis:gasification:decoking reaction zone is 1.8–2.2:1–1.4:2–2.5:2–3; the primary crude gas holding temperature is 250–330℃, and the secondary crude gas holding temperature is 180–280℃. Even further, in step S2, both the primary and secondary gasifiers employ radiant heating to heat their internal raw materials in an air-isolated manner, ensuring that the internal temperature meets the reaction conditions for preheating, pyrolysis, gasification, and decoking. Specifically, the radiant heating is achieved by installing heating devices around the exterior of the primary and secondary gasifiers, respectively, and embedding heating pipes in the gasification layer of both the primary and secondary gasifiers, with heated flue gas circulating within the heating pipes. By using external and buried pipe radiant heating, the internal temperature of the primary and secondary gasifiers is effectively controlled, allowing the raw materials to complete the pyrolysis and gasification process in the high-temperature zone inside the furnace. The process is simple and the control is flexible.

[0016] Preferably, in step S2, the mass ratio of water vapor to raw material in each gasifier is 1.6 to 1.7:1, and the water vapor in the first-stage gasifier accounts for 70% to 85% of the total water vapor mass.

[0017] The beneficial effects of this invention are:

[0018] 1. The coal gangue and biomass staged gasification process of the present invention does not require the biomass raw material to be shaped, but only needs to be crushed to a suitable size, which improves the adaptability of raw materials, simplifies the pretreatment process, and helps to reduce investment costs and engineering energy consumption;

[0019] 2. The coal gangue and biomass staged gasification process of the present invention uses primary and secondary raw materials in synergy, and combines primary gasifying agent (steam) and secondary gasifying agent (composed of secondary steam and hot crude gas from the primary gasifier) ​​for staged gas supply. At the same time, the temperature of both gasification layers is controlled to reach 1000-1100℃, so that the large tar molecules in the furnace are fully decomposed into small molecule gases, which improves the calorific value of the fuel gas, carbon conversion rate and cold gas efficiency. The tar from the primary gasifier is adsorbed and catalytically reformed by the coal gangue and lime slag in the decoking zone in the secondary gasifier, so that the tar removal rate of the entire process reaches more than 95%, and there is no need to configure a separate tar removal device.

[0020] 3. The staged gasification process of coal gangue and biomass of the present invention provides gas that can be used for direct combustion power generation, synthesis of aviation fuel, or other applications that replace fossil fuels. Attached Figure Description

[0021] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0022] Figure 1 This is a flowchart of the staged gasification process for coal gangue and biomass of the present invention.

[0023] Figure 2 This is a schematic diagram of the device used in the embodiments of the present invention.

[0024] The attached diagram is labeled as follows: 1. Primary feed inlet, 2. Primary preheating layer, 3. Primary furnace heating layer, 4. Primary pyrolysis layer, 5. Primary gasification layer, 6. Primary heating tube, 7. Primary crude gas outlet, 8. Primary slag outlet, 9. Secondary gasifying agent inlet, 10. Secondary feed inlet, 11. Secondary crude gas outlet, 12. Secondary preheating layer, 13. Secondary pyrolysis layer, 14. Secondary gasification layer, 15. Secondary furnace heating layer, 16. Secondary heating tube, 17. Secondary slag outlet, 18. Primary gasifying agent inlet, 19. Decoking layer. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments:

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0027] Figure 1As shown, the staged gasification process for coal gangue and biomass provided by this invention includes the following steps:

[0028] S1, Pretreatment: The coal gangue and biomass raw materials are pretreated to obtain coal gangue and biomass with a particle size of less than 200 mm and coal gangue with a particle size of 200-500 mm, respectively. The volatile matter content of the coal gangue raw material should be less than 15% and the ash content should be between 40-60%.

[0029] The specific operation process is as follows: the moisture content of coal gangue and biomass raw materials is controlled to below 10wt% by air drying or baking. The coal gangue and biomass raw materials are pre-treated by crushing or shredding using a crusher or shredder to obtain raw materials with a particle size of less than 200mm. The screening rate of coal gangue is above 85% (coarse particles that are not screened are used as secondary raw materials). Among them, the coal gangue raw materials include one or more of coal roadway gangue, spontaneous combustion gangue, washed gangue, hand-sorted gangue, and stripped gangue, and the volatile matter content should be less than 15% and the ash content should be between 40-60%. The biomass raw materials include one or more of straw, wood, peanut shells, and cottonseed hulls.

[0030] S2. The pretreated raw materials are fed into a staged gasification unit, which consists of a two-stage gasifier, including a primary gasifier and a secondary gasifier. The primary gasifier uses steam as the gasifying agent, which enters from the bottom. A designed amount of coal gangue and biomass with a particle size of less than 200mm is mixed as the primary raw material, fed from the top of the primary gasifier and sinking from top to bottom, passing through three reaction layers: preheating, pyrolysis, and gasification, and undergoing corresponding reactions. A designed amount of coal gangue with a particle size of 200-500mm is fed from the top of the secondary gasifier and sinking from top to bottom, passing through four reaction layers: preheating, pyrolysis, gasification, and decoking, and undergoing corresponding reactions. Biomass accounts for 30% to 40% of the total mass of the primary and secondary raw materials, and the secondary raw material accounts for 10% to 20% of the total mass of the primary and secondary raw materials.

[0031] The specific operation process is as follows: The structure of the staged gasification device in this embodiment is shown in [reference needed]. Figure 2 The primary gasifier is equipped with a primary feed inlet 1, a primary preheating layer 2, a primary furnace heating layer 3, a primary pyrolysis layer 4, a primary gasification layer 5, a primary heating tube 6, a primary crude gas outlet 7, a primary slag outlet 8, and a primary gasifying agent inlet 18. The secondary gasifier is equipped with a secondary gasifying agent inlet 9, a secondary feed inlet 10, a secondary crude gas outlet 11, a secondary preheating layer 12, a secondary pyrolysis layer 13, a secondary gasification layer 14, a secondary furnace heating layer 15, a secondary heating tube 16, a secondary slag outlet 17, and a decoking layer 19.

[0032] The raw materials for each stage of the gasifier are pushed into the furnace from top to bottom using feeding equipment. Both the primary and secondary gasifiers use radiant heating to heat the raw materials inside the furnace in the absence of air, so that the internal temperature meets the reaction conditions for preheating, pyrolysis, gasification, and decoking. Specifically, the radiant heating is achieved by setting heating devices (i.e., primary furnace heating layer 3 and secondary furnace heating layer 15) around the outside of the primary and secondary gasifiers, respectively. At the same time, primary heating pipes 6 and secondary heating pipes 16 are pre-embedded in the gasification layers of the primary and secondary gasifiers, respectively. Multiple primary heating pipes 6 and secondary heating pipes 16 are provided and are arranged in parallel and spaced apart in the horizontal and vertical directions. Hot flue gas is passed through the heating pipes. In use, the hot flue gas enters the primary heating pipes 6 and secondary heating pipes 16 through the primary furnace heating layer 3 and the secondary furnace heating layer 15, respectively, forming a common radiant heating between the inside and the outside. By using external and internal buried pipe radiant heating, the internal temperature of the primary and secondary gasifiers is effectively controlled, allowing the raw materials to complete the pyrolysis and gasification processes in the high-temperature zone within the furnace. The process is simple and the control is flexible. In step S2, the preheating temperature is 300–500℃; the pyrolysis temperature is 500–1000℃; the gasification temperature is 1000–1100℃; the decoking temperature is 900–1000℃; the height range of the preheating:pyrolysis:gasification:decoking reaction zone is 1.8–2.2:1–1.4:2–2.5:2–3; the primary crude gas temperature is maintained at 250–330℃, and the secondary crude gas temperature is maintained at 180–280℃.

[0033] Specifically, the primary raw material is first pyrolyzed to generate pyrolysis gas, coal gangue coke, and biochar. Then, the carbon gasification reaction C + H2O → CO + H2 occurs. At 1000℃, the carbon gasification reaction is very obvious. Above 1000℃, the tar cracking and conversion is even faster. Some of the tar in the pyrolysis gas is cracked and converted into H2, CO, CH4, or CO2 (i.e., the main components of primary crude coal gas) under the action of primary gasification agent water vapor (i.e., water vapor directly introduced into the primary gasifier) ​​and biochar (where biochar acts as a catalyst, and when the contact time is greater than 2s, the primary tar removal rate can reach more than 84%). Subsequently, the primary crude coal gas is mixed with the secondary gasifying agent (steam) and introduced into the bottom of the secondary gasifier. Under the catalytic action of the secondary coal gangue coke (when the contact time is greater than 2 seconds, the overall tar removal rate can reach more than 95%). Furthermore, the steam-to-raw material ratio (mass ratio) in each gasifier is 1.6 to 1.7, and the steam volume in the primary gasifier accounts for 70% to 85% of the total steam mass.

[0034] S3, the crude coal gas discharged from the top of the secondary gasifier is cooled, heat exchanged, and purified by dust removal to obtain fuel gas.

[0035] The specific operation process is as follows: The temperature of the crude gas discharged from the top of the secondary gasifier is 180-280℃. It is first cooled down to facilitate subsequent processing. On the one hand, the temperature of the high-temperature gas is reduced to about 70℃, and on the other hand, the high-temperature and high-pressure water vapor generated by the waste heat of the crude gas can be recovered. The low-temperature crude gas is purified by a dust removal device to obtain fuel gas, which is then stored in a gas holder. The dust removal device can be set as a cyclone dust collector and / or a bag dust collector / or an electrostatic precipitator, etc. Part of the fuel gas in the gas holder is used as fuel for the radiant heating of the two-stage gasifier to achieve continuous heating. The fuel gas can be sold directly or directly used for power generation and then connected to the national power grid.

[0036] The biomass gasification process of this invention will be further described below with specific examples:

[0037] Example

[0038] The coal gangue raw materials in this embodiment are: self-igniting gangue (Mad, 7.6%, CFad, 36.7%, Vad, 10.5%, Aad, 45.2%); and the biomass raw materials are: corn stalks (Mad, 6.8%, CFad, 13.7%, Vad, 75.1%, Aad, 4.4%).

[0039] like Figure 1 As shown, the coal gangue and biomass raw materials in this embodiment are processed in the following manner:

[0040] After the raw materials are simply dried in the yard until the moisture content is less than 10%, the coal gangue and biomass raw materials are crushed and pulverized by a crusher. The particle size after pulverization is controlled within 200mm as the first-grade raw material, and the screening rate of coal gangue is guaranteed to be above 85%. The remaining coarse coal gangue is used as the second-grade raw material.

[0041] The pre-crushed raw materials are fed to the first and second stage gasifiers using feeding equipment and other facilities. Primary fuel (a mixture of fine-particle coal gangue and needle-shaped biomass) is transported to the top of the primary gasifier by a feeding trolley, while secondary fuel (coarse-particle coal gangue) is simultaneously transported to the top of the secondary gasifier. The raw material quantity (the mixture of biomass and fine-particle coal gangue) in the primary gasifier accounts for 80% of the total, of which primary biomass accounts for 40%. In addition, the raw material quantity (coarse-particle coal gangue) in the secondary gasifier accounts for 20% of the total, and the secondary gasification agent (water vapor) accounts for 26% of the total.

[0042] The raw materials gradually heat up as they sink from top to bottom within the furnace. In the primary gasifier, they sequentially undergo three reaction layers: preheating, pyrolysis, and gasification. In the secondary gasifier, they sequentially undergo four reaction layers: preheating, pyrolysis, gasification, and decoking, ultimately yielding crude coal gas and ash. The preheating temperature is 300℃~500℃, the pyrolysis temperature is 500-1000℃, the gasification temperature is 1000~1100℃, and the decoking temperature is 900~1000℃. The height range of the preheating:pyrolysis:gasification:decoking reaction zones is 1.8~2.2:1~1.4:2~2.5:2~3. The primary crude coal gas temperature is maintained at 250-330℃, and the secondary crude coal gas temperature is maintained at 180-280℃. During the gasification and decoking process, under the supply of steam, the gasification of coal gangue coke and biomass char (intermediate products of coal gangue and biomass gasification) and the decomposition and removal of large molecular tar are completed. Most of the tar is cracked and converted into small molecular gas. The tar removal rate reaches 95%, the carbon conversion rate reaches 86.75%, the cold gas efficiency reaches 0.4734, and the hydrogen production reaches 48.36 mmol / g.

[0043] The effect of primary biomass content and the proportion of secondary fuel (coarse-grained coal gangue) on cold gas efficiency

[0044]

[0045] The impact of the proportion of primary fuel biomass and the proportion of secondary fuel (coarse-grained coal gangue) on hydrogen production.

[0046]

[0047] After the secondary crude gas is cooled, the high-temperature gas is purified by a bag filter to obtain fuel gas, which is then stored in a fuel tank for later use. Of this, 15% (by volume) of the fuel gas is used as fuel for the radiant heating of the two-stage gasifier, burning with combustion air to achieve continuous heating for the two-stage gasifier. The heating temperature is controlled by the supply of fuel gas and combustion air, keeping it within the reasonable temperature range for preheating, pyrolysis, gasification, and decoking. The remaining 85% (by volume) of the fuel gas is sold externally.

[0048] In addition, the fly ash obtained after cooling, heat exchange, purification, and separation (accounting for approximately 40 wt% of the total ash) in this embodiment is about 38.41 wt% of the raw material. Analysis of its composition shows that the main components are SiO: 53.42 wt%, K2O: 8.54 wt%, CaO: 20.67 wt%, Na2O: 0.96 wt%, MgO: 8.5 wt%, Al2O3: 5.73 wt%, and Fe2O3: 2.18 wt%. The melting point of the ash is 1436°C. It did not undergo melting and adhesion in the gasifier and was sent to the stockpile for storage. It can be used as a raw material for building materials in the future.

[0049] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A method for staged gasification of coal gangue and biomass, characterized in that: Includes the following steps: Step S1, pretreatment: The coal gangue and biomass raw materials are crushed and screened to obtain coal gangue and biomass with a particle size of less than 200 mm, and coal gangue with a particle size of 200-500 mm; the volatile matter content of the coal gangue raw material is less than 15 wt%, and the ash content is 40-60 wt%. Step S2: The pretreated raw materials are fed into a staged gasification unit, which consists of a two-stage gasifier, including a primary gasifier and a secondary gasifier. The primary gasifier uses steam as the gasifying agent, which is fed into the furnace from the bottom. A designed amount of coal gangue and biomass with a particle size less than 200mm is mixed as the primary raw material and fed into the primary gasifier from the top, sinking from top to bottom and passing through three reaction layers: preheating, pyrolysis, and gasification, undergoing the corresponding reactions. A designed amount of coal gangue with a particle size of 200-500mm... Biomass, as a secondary feedstock, is fed into the secondary gasifier from the top. Within the secondary gasifier, the feedstock sinks from top to bottom, undergoing preheating, pyrolysis, gasification, and decoking in four reaction layers. Simultaneously, secondary steam is mixed with primary crude gas discharged from the top of the primary gasifier and fed into the bottom of the secondary gasifier. The mixture then rises and is catalytically reformed by secondary coal gangue and lime slag, thus completing the secondary gasification and decoking reactions. Biomass constitutes 30%–40% of the total mass of the primary and secondary feedstocks, while the secondary feedstock constitutes 10%–20%. Step S3: The secondary crude gas discharged from the top of the secondary gasifier is cooled, heat exchanged, and purified by dust removal to obtain fuel gas; In step S2, the preheating temperature is 300~500°C, the pyrolysis temperature is 500-1000°C, the gasification temperature is 1000~1100°C, the decoking temperature is 900~1000°C, the height range of the preheating:pyrolysis:gasification:decoking reaction zone is 1.8~2.2:1~1.4:2~2.5:2~3, the primary crude gas holding temperature is 250-330°C, and the secondary crude gas holding temperature is 180-280°C. In step S2, the mass ratio of water vapor to raw material in each gasifier is 1.6 to 1.7:1, and the water vapor in the first gasifier accounts for 70% to 85% of the total water vapor mass.

2. The method for staged gasification of coal gangue and biomass according to claim 1, characterized in that: The specific pretreatment method for step S1 is as follows: control the coal gangue screening rate to be above 85%, the screen aperture size to be 200mm, and collect the oversize and undersize materials separately.

3. The method for staged gasification of coal gangue and biomass according to claim 1, characterized in that: In step S2, both the primary gasifier and the secondary gasifier use radiant heating to heat the raw materials inside them in an air-isolated manner. The radiant heating is achieved by setting heating devices around the outside of the primary gasifier and the secondary gasifier, respectively, and pre-embedding heating pipes in the gasification layer of the primary gasifier and the secondary gasifier, with heated flue gas passing through the heating pipes.

4. The method for staged gasification of coal gangue and biomass according to claim 1, characterized in that: Biomass can be one or more of the following: straw, wood, peanut shells, and cottonseed hulls.

5. The method for staged gasification of coal gangue and biomass according to claim 1, characterized in that: Coal gangue can be one or more of the following: coal roadway gangue, spontaneously combusting gangue, washed gangue, hand-sorted gangue, and stripped gangue.

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