Artificial coal synthesis method based on coal gangue-charcoal and biochar activation and pyrolysis synthesis

Abstract

The invention discloses an artificial coal synthesis method based on coal gangue-charcoal and biochar activation and pyrolysis synthesis, belongs to the technical field of artificial coal synthesis, and aims to solve the problems of low solid waste utilization rate, non-environment-friendly binder, unbalanced product performance and the like in the prior art. The method comprises the following steps: crushing and drying coal gangue, crushing and carbonizing more than two forestry and agricultural residues, and compounding the carbonized forestry and agricultural residues with charcoal with a specific index to form a composite carbon source; mixing the coal gangue powder with the composite carbon source in proportion, adding a KOH-H3PO4 composite activator, and heating and infiltrating; then pyrolyzing at the temperature of 650-750 DEG C under the protection of nitrogen, and purifying and recycling pyrolyzed combustible gas; and finally performing hydraulic forming and cooling to obtain a finished product. The solid waste utilization rate exceeds 60%, no chemical binders exist, the calorific value of the finished product is 22-26 MJ / kg, the compressive strength is larger than or equal to 15 MPa, and the product can be matched and linked with different existing devices, is suitable for industrial boilers and other scenes and has environment friendliness and practicability.

Description

Technical Field

[0001] This invention relates to the field of artificial coal synthesis technology, specifically to a method for synthesizing artificial coal through activated pyrolysis using coal gangue as solid waste raw material and charcoal and biochar as composite carbon sources. Background Technology

[0002] Artificial coal synthesis equipment refers to equipment systems that transform raw materials such as pulverized coal, coal gangue, agricultural and forestry waste, or plastics into artificial coal products with stable combustion performance and meeting specific usage requirements through physical mixing, pyrolysis, molding, and other processes. Its core function is to realize the resource utilization of low-value-added raw materials, make up for the supply gap of natural lump coal, and reduce pollutant emissions during fuel combustion. It is widely used in industrial boilers, civil heating, and other fields.

[0003] Existing artificial coal synthesis devices mainly include briquette forming devices, coal liquefaction devices, and biomass-based synthetic coal devices. Briquette forming devices have a basic structure of crushing unit-mixing unit-forming unit-drying unit, relying on binders such as asphalt and sodium humate to form pulverized coal. This results in increased pollutant emissions or insufficient forming strength due to the binders. Coal liquefaction devices consist of a coal gasification unit-hydrogenation reaction unit-separation and refining unit, requiring a high-temperature, high-pressure reaction environment, leading to extremely high equipment investment and energy consumption, and generating large amounts of high-concentration wastewater and CO2. Biomass-based synthetic coal devices are mostly simple crushing units-mixing units-hot pressing forming units, only coarsely crushing biomass raw materials without employing composite carbon sources and activation synergistic design. This results in low product calorific value, poor mechanical strength, and weak raw material adaptability. These structural defects in existing devices make it difficult to simultaneously achieve high-value utilization of solid waste, environmental protection, and product performance stability. Summary of the Invention

[0004] To address the problems in existing artificial coal synthesis methods, such as low solid waste utilization (e.g., pollution from coal gangue stockpiling), poor environmental performance of binders (e.g., asphalt binders increase pollutant emissions), imbalance between product calorific value and mechanical strength, unstable supply of biomass-based synthetic coal raw materials, and easy coking during pyrolysis, this invention aims to provide an artificial coal synthesis method with high solid waste utilization, no additional binders, and stable product performance, achieving the dual goals of reducing coal gangue volume and improving the quality of artificial coal.

[0005] To address the aforementioned technical problems, this invention provides the following technical solution: a method for synthesizing artificial coal based on coal gangue-charcoal, biochar activation and pyrolysis synthesis, comprising the following steps:

[0006] 1. Raw material pretreatment: Coal gangue is crushed to 80-120 mesh size and dried at 105-120℃ for 4-6 hours to remove free water, resulting in dried coal gangue powder; agricultural and forestry waste is pulverized to 60-80 mesh size, wherein the agricultural and forestry waste is a mixture of at least two of straw, sawdust, walnut shells or cottonseed hulls, with a mixing mass ratio of 1:1-2:1, and carbonized at 400-500℃ for 2-3 hours under an inert atmosphere to obtain biochar, and then the biochar is mixed with charcoal at a mass ratio of 3:1-5:1 to obtain a composite carbon source; the charcoal has a fixed carbon content ≥85%, ash content ≤5%, moisture content ≤3%, and particle size controlled at 60-100 mesh.

[0007] 2. Activation treatment: Dry coal gangue powder and composite carbon source are added to a mixer at a mass ratio of 2:1-3:1. At the same time, activator accounting for 5%-8% of the total raw material mass is added. The activator is a mixed aqueous solution of KOH and H3PO4, wherein the mass fraction of KOH is 10%-15%, the mass fraction of H3PO4 is 5%-8%, and the mass ratio of KOH to H3PO4 is 2:1-3:1. The stirring speed of the mixer is 200-300 r / min. During the stirring process, the material temperature is controlled at 40-50℃ by jacket heating. After stirring for 30-45 min, the mixture is allowed to stand for 10-15 min to impregnate with the activator, and the mixture is obtained.

[0008] 3. Pyrolysis Synthesis: The mixture is fed into an internally heated rotary kiln. Under a nitrogen protective atmosphere, the oxygen content in the kiln is controlled at ≤0.5%. The temperature is raised to 650-750℃ at a heating rate of 5-8℃ / min and held for pyrolysis for 2-3 hours. During this period, the pressure inside the kiln is controlled at 0.15-0.2MPa, and the kiln rotation speed is 1-2 r / min. The combustible gas generated by pyrolysis is purified by desulfurization and dust removal and then reused for kiln heating through a burner.

[0009] 4. Molding and Cooling: After pyrolysis, the product is quickly transferred to a hydraulic molding machine. The mold of the hydraulic molding machine is hexagonal or cylindrical. Molding is carried out under a pressure of 15-20 MPa for 30-60 seconds to obtain a bulk density of 1.2-1.4 g / cm³. 3 The blocky intermediate is naturally cooled to room temperature to obtain the artificial coal product, which has a calorific value of 22-26 MJ / kg, a compressive strength of ≥15 MPa, an ash content of ≤18%, a sulfur content of ≤0.8%, and a thermal stability of TS+6 ≥75%.

[0010] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages compared with the prior art:

[0011] Firstly, using coal gangue as the main raw material, the resource utilization rate of solid waste reaches over 60%, effectively reducing land occupation and environmental pollution caused by coal gangue stockpiling, and realizing high-value utilization of solid waste.

[0012] Secondly, a variety of agricultural and forestry wastes are mixed and carbonized to produce biochar, which is then compounded with high-fixed-carbon charcoal to form a composite carbon source, replacing traditional chemical binders such as asphalt. This not only avoids the pollutant emissions caused by binders, but also utilizes the porous structure of biochar to enhance the binding force between materials. Combined with the synergistic effect of KOH and H3PO4 composite activators, it significantly enhances the compressive strength and combustion reactivity of artificial coal.

[0013] Third, the pyrolysis process uses nitrogen protection to inhibit coking, and the combustible gas produced by pyrolysis is purified and reused for kiln heating, reducing external energy consumption by more than 30% and improving energy utilization efficiency.

[0014] Fourth, the product has excellent performance indicators, with a calorific value of 22-26 MJ / kg, compressive strength ≥15 MPa, and good thermal stability. It is suitable for combustion in industrial boilers and kilns, and is both environmentally friendly and practical.

[0015] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0016] Figure 1 This is a complete flow diagram of the artificial coal synthesis process of the present invention;

[0017] Figure 2 This is a timing diagram of the pyrolysis synthesis temperature and pressure control of the present invention;

[0018] Figure 3 This is a diagram showing the raw material ratio and composite carbon source composition of the present invention;

[0019] Figure 4 This is a schematic diagram showing the composition and proportion of the activator of the present invention;

[0020] Figure 5 This is a control diagram of the rotary kiln pyrolysis process parameters of the present invention;

[0021] Figure 6 This is a diagram showing the connection of the equipment system and the material flow of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that the terms "vertical," "horizontal," "up," "down," "left," "right," and similar expressions used in this article are for illustrative purposes only and do not represent the only possible implementation.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] As shown in the figure, in the specific implementation of this invention, each process unit is connected in series in the order of "raw material pretreatment unit → activation treatment unit → pyrolysis synthesis unit → molding and cooling unit". The raw material pretreatment unit includes coal gangue crushing equipment, drying equipment, agricultural and forestry waste crushing equipment, and carbonization furnace. The outlet of the carbonization furnace and the charcoal storage tank are connected to the mixer through a conveying pipeline to form a composite carbon source. The feed inlet of the mixer of the activation treatment unit is connected to the dry coal gangue powder storage tank and the outlet of the composite carbon source mixer of the raw material pretreatment unit. The discharge outlet of the mixer is connected to the feed end of the internally heated rotary kiln of the pyrolysis synthesis unit through a conveyor belt. The discharge end of the rotary kiln of the pyrolysis synthesis unit is connected to the feed inlet of the hydraulic molding machine of the molding and cooling unit. The discharge outlet of the hydraulic molding machine is equipped with a cooling conveyor belt.

[0026] In this implementation plan, the particle size of coal gangue and agricultural and forestry waste must be strictly controlled during the raw material pretreatment stage to ensure uniformity of subsequent mixing; during the activation treatment, the material temperature and mixing degree must be controlled by jacket heating and stirring speed to ensure full wetting of the activator; during the pyrolysis synthesis stage, the heating rate, kiln pressure and oxygen content must be precisely controlled to avoid local coking; during the molding and cooling stage, the transfer speed of pyrolysis products and molding pressure must be controlled to ensure the density and strength of the block intermediate.

[0027] Raw material pretreatment steps: Coal gangue is crushed to 80-120 mesh and dried to remove free water and avoid excessive water vapor during pyrolysis, which would affect the reaction. At the same time, the finer particle size increases the contact area with the composite carbon source. Agricultural and forestry waste is mixed, crushed, and then carbonized. On the one hand, the combination of multiple biomass solves the problem of unstable supply of single biomass raw materials. On the other hand, the biochar formed by carbonization has a rich pore structure, which provides a basis for subsequent activation and shaping. The high fixed carbon content of charcoal can improve the calorific value of artificial coal. This step achieves the dual effect of solid waste resource utilization and raw material performance optimization.

[0028] Activation process: Dry coal gangue powder and composite carbon source are mixed in a certain proportion, along with a specific ratio of KOH-H3PO4 activator. Under heating, stirring and static soaking, KOH can etch new pores on the surface of the raw materials, while H3PO4 can promote carbon structure reorganization. The two work synergistically to enhance the reactivity of the materials. Stirring parameters and temperature control ensure uniform distribution of the activator and avoid localized insufficient activation. This step solves the problem of traditional coal briquettes relying on chemical binders. Through the synergistic effect of physicochemical processes, the bonding force between materials is improved, laying the foundation for subsequent molding strength.

[0029] The pyrolysis synthesis process involves nitrogen protection and a low-oxygen environment to inhibit the oxidation and coking of raw materials. The controlled heating rate and pressure ensure that the raw materials are fully pyrolyzed at 650-750℃, which guarantees the synergistic reaction of organic matter and composite carbon sources in coal gangue while avoiding carbon loss due to over-pyrolysis. The slow rotation speed of the rotary kiln ensures that the material is tumbled evenly and heated uniformly. The purification and reuse of combustible gas converts pyrolysis byproducts into heating energy, reducing external energy consumption. This process achieves a balance between increasing the calorific value of manufactured coal and efficient energy utilization.

[0030] Molding and cooling steps: The pyrolysis products are quickly transferred to a hydraulic molding machine and molded under pressure of 15-20MPa. The plasticity of the hot material is used to improve the molding effect. The specific mold shape and volume density control give the artificial coal good storage and transportation performance. Natural cooling avoids structural cracking caused by rapid cooling. This step ensures the mechanical strength and stability of the finished artificial coal, so that the product meets the requirements of industrial boilers and kilns.

[0031] Based on the above specific implementation methods, the present invention can be flexibly adapted and linked with existing technologies and devices in different application scenarios. The following describes in detail the usage status of each structure and the connection, installation and linkage details with existing devices in three typical scenarios: small and medium-sized solid waste treatment plants, large industrial boiler supporting production lines and areas rich in biomass resources.

[0032] Scenario 1: Application scenarios of small and medium-sized solid waste treatment plants

[0033] In this scenario, small-scale coal gangue crushing equipment, simple biomass pulverizing equipment, and hot air drying furnaces are typically already in place. The connection and installation of this invention with existing equipment is as follows: the feed inlet of the coal gangue crushing equipment in the raw material pretreatment unit is connected to the discharge outlet of the existing coal gangue crushing equipment via a vibrating conveyor belt; the hot air outlet of the existing hot air drying furnace is connected to the air inlet of the drying equipment of this invention via a duct flange; the inlet of the agricultural and forestry waste pulverizing equipment is connected to the outlet of the existing biomass pulverizing equipment via a belt conveyor. If the discharge particle size of the existing pulverizing equipment has reached 60-80 mesh, it can be directly connected to the feed end of the carbonization furnace via a pipeline.

[0034] Structural Usage: The coal gangue crushing equipment maintains a vibration frequency of 20-30Hz during operation to ensure that the coal gangue is crushed to 80-120 mesh; the temperature sensor in the drying equipment monitors the temperature in real time and is linked with the temperature control valve of the existing hot air drying oven to maintain a drying environment of 105-120℃; nitrogen is introduced into the carbonization furnace as an inert atmosphere, the heating element maintains a carbonization temperature of 400-500℃, and the stirring paddle in the furnace stirs the material at a speed of 30r / min; the spiral stirrer in the composite carbon source mixer runs at a speed of 100r / min to mix biochar and charcoal in a ratio of 3:1-5:1.

[0035] Linkage details: An electromagnetic flowmeter is installed at the feed inlet of the mixer in the activation treatment unit, which is linked with the discharge valve of the dry coal gangue powder storage tank and the composite carbon source mixer in the raw material pretreatment unit to precisely control the feed ratio of the two to 2:1-3:1; The jacket heating device of the mixer is linked with the combustible gas purification and reuse device of the pyrolysis synthesis unit. After desulfurization and dust removal, part of the combustible gas generated by pyrolysis is introduced into the jacket heating chamber of the mixer to provide a heat source of 40-50℃ for activation treatment. The insufficient heat is supplemented by the existing electric heating auxiliary; The exhaust gas outlet of the rotary kiln of the pyrolysis synthesis unit is connected to the spray tower of the existing solid waste treatment plant through a pipeline to achieve compliant exhaust gas emissions.

[0036] Scenario 2: Production line supporting large industrial boilers

[0037] The setup includes a large industrial boiler, a boiler fuel conveying scraper conveyor, a flue gas desulfurization and denitrification device, and a waste heat recovery system. The connection and installation of this invention with existing equipment is as follows: the end of the cooling conveyor belt of the forming and cooling unit connects to the feed hopper of the existing boiler fuel conveying scraper conveyor via an inclined chute; a gate valve is installed at the bottom of the chute to control the material discharge; the flue gas outlet of the rotary kiln of the pyrolysis synthesis unit is connected to the inlet pipe of the existing flue gas desulfurization and denitrification device via a corrugated compensator; the hot water outlet of the existing boiler's waste heat recovery system is connected to the heating coil of the drying equipment of this invention via a pipe.

[0038] Structural and operational status: The hydraulic molding machine uses a cylindrical mold and continuously forms blocks at a pressure of 15-20 MPa, with a forming cycle controlled at 40-60 seconds per block. During the cooling conveyor belt transport, the intermediate blocks are cooled to below 60°C by an air-cooled fan. The internally heated rotary kiln maintains a pyrolysis temperature of 650-750°C at a heating rate of 5-8°C / min, with a kiln rotation speed of 1.5-2 r / min. A thermocouple at the kiln tail monitors the temperature in real time. The desulfurizing agent slurry circulation pump in the desulfurization tower of the combustible gas purification and reuse unit operates continuously to ensure that the sulfur content of the combustible gas is reduced to 50 mg / m³. 3 the following.

[0039] Linkage details: The load control system of the existing industrial boiler is linked with the molding and cooling unit of this invention. When the boiler load increases, the molding pressure of the hydraulic molding machine is automatically increased by 0.5-1MPa, and the speed of the cooling conveyor belt is increased by 10%-15%, increasing the supply of artificial coal. The feed rate of the rotary kiln in the pyrolysis synthesis unit is linked with the boiler fuel consumption through the PLC control system to achieve "production based on demand". The hot water temperature sensor of the existing waste heat recovery system is linked with the temperature control system of the drying equipment of this invention. When the hot water temperature is lower than 90℃, the drying equipment automatically switches to auxiliary steam heating to ensure the drying effect of coal gangue.

[0040] Scenario 3: Application scenarios in areas rich in biomass resources

[0041] This scenario typically includes straw collection and baling equipment, a biomass pellet mill, and a small biomass pyrolysis furnace. The connection and installation of this invention with existing devices is as follows: the inlet of the agricultural and forestry waste crushing equipment in the raw material pretreatment unit is connected to the unpacking machine outlet of the existing straw collection and baling equipment via a conveyor belt; the biochar outlet of the existing biomass pyrolysis furnace is connected to the inlet of the composite carbon source mixer of this invention via a star-shaped discharge valve, forming a dual biochar supply channel; the finished product bin of the existing biomass pellet mill is connected to the charcoal storage tank of this invention via a pipeline, allowing excess biomass pellets to be crushed and used as supplementary raw material for charcoal.

[0042] Structural Usage: The unpacking machine of the straw collection and baling equipment operates synchronously with the crushing equipment of this invention. After the crushing equipment crushes the straw to 60-80 mesh, it is sent to the carbonization furnace via a bucket elevator. In the dual biochar supply channels, the carbonization furnace of this invention and the existing biomass pyrolysis furnace operate alternately. When the existing pyrolysis furnace is under maintenance, the carbonization furnace of this invention automatically increases the heating power to 500℃ to increase biochar production. A quality sensor is installed in the composite carbon source mixer to monitor the mixing ratio of biochar and charcoal in real time to ensure stable ratio.

[0043] Linkage details: The conveying speed of the existing straw collection and baling equipment is linked to the feeding speed of the crushing equipment of this invention via a frequency converter. When the material level in the crushing equipment is higher than 80%, the conveying speed of the existing equipment is automatically reduced by 20% to avoid material blockage. The biochar production signal of the existing biomass pyrolysis furnace is transmitted to the raw material pretreatment unit control system of this invention. When the biochar production of the existing equipment exceeds 50% of the demand, the carbonization furnace of this invention stops heating and relies solely on the existing equipment for feeding. The material level sensor of the charcoal storage tank is linked to the existing biomass pellet mill. When the charcoal storage is lower than 30%, the existing pellet mill automatically starts the crushing program to crush the biomass pellets to 60-100 mesh before replenishing them into the storage tank, ensuring a stable supply of composite carbon source.

[0044] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for synthesizing artificial coal based on coal gangue-charcoal and biochar activation and pyrolysis, characterized in that, Includes the following steps: 1) Raw material pretreatment: Crush coal gangue to 80-120 mesh size, dry at 105-120℃ for 4-6 hours to remove free water, and obtain dry coal gangue powder; crush agricultural and forestry waste to 60-80 mesh size, carbonize at 400-500℃ for 2-3 hours under an inert atmosphere to obtain biochar, and then mix biochar with charcoal at a mass ratio of 3:1-5:1 to obtain a composite carbon source; 2) Activation treatment: Dry coal gangue powder and composite carbon source are added to a mixer at a mass ratio of 2:1-3:1, and activator accounting for 5%-8% of the total raw material mass is added at the same time. Stir for 30-45 minutes until uniform to obtain a mixture. 3) Pyrolysis synthesis: The mixture is fed into an internally heated rotary kiln and heated to 650-750℃ at a heating rate of 5-8℃ / min under a nitrogen protective atmosphere. The mixture is then held at this temperature for 2-3 hours, during which the pressure inside the kiln is controlled at 0.15-0.2MPa. 4) Molding and Cooling: After pyrolysis, the product is quickly transferred to a hydraulic molding machine and molded under a pressure of 15-20MPa for 30-60s to obtain a block intermediate; the block intermediate is then naturally cooled to room temperature to obtain the finished artificial coal product.

2. The method according to claim 1, characterized in that, The agricultural and forestry waste mentioned in step 1 is a mixture of at least two of the following: straw, sawdust, walnut shells, or cottonseed hulls, with a mixing mass ratio of 1:1 to 2:

1.

3. The method according to claim 1, characterized in that, The charcoal mentioned in step 1 has a fixed carbon content of ≥85%, ash content of ≤5%, moisture content of ≤3%, and a particle size of 60-100 mesh.

4. The method according to claim 1, characterized in that, The activator mentioned in step 2 is a mixed aqueous solution of KOH and H3PO4, wherein the mass fraction of KOH is 10%-15%, the mass fraction of H3PO4 is 5%-8%, and the mass ratio of KOH to H3PO4 is 2:1-3:

1.

5. The method according to claim 1, characterized in that, The mixing speed of the mixer in step 2 is 200-300 r / min. During the mixing process, the material temperature is controlled at 40-50℃ by jacket heating. After the mixing is completed, the mixture is left to stand for 10-15 minutes for activator impregnation.

6. The method according to claim 1, characterized in that, In step 3, the kiln body rotation speed of the internally heated rotary kiln is 1-2 r / min, the oxygen content in the kiln is controlled at ≤0.5%, and the combustible gas generated by pyrolysis is purified by desulfurization and dust removal and then reused for kiln body heating through the burner.

7. The method according to claim 1, characterized in that, In step 4, the mold of the hydraulic forming machine is hexagonal or cylindrical, and the bulk density of the block intermediate after forming is 1.2-1.4 g / cm3.

8. The method according to claim 1, characterized in that, The calorific value of the artificial coal product is 22-26 MJ / kg, compressive strength ≥15 MPa, ash content ≤18%, sulfur content ≤0.8%, and thermal stability TS+6 ≥75%.

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