Coal catalytic pyrolysis method

Abstract

The invention discloses a coal catalytic pyrolysis method, and particularly relates to the field of catalytic pyrolysis, the coal catalytic pyrolysis method comprises the following steps: S1, pulverized coal preparation: crushing raw material coal through a crusher to obtain pulverized coal; s2, drying treatment, wherein the pulverized coal is dried through airflow; s3, adding a catalyst: adding sunflower straw ash and nano calcium oxide into the pulverized coal to obtain a mixture; and S4, pyrolytic reaction: mixing the mixture with ceramic balls, and carrying out pyrolysis. The sunflower straw ash and the nano calcium oxide are used as catalysts for catalytic pyrolysis of the coal, and the sunflower straw ash contains rich alkali metal, so that the H2 yield can be remarkably increased, the reaction temperature zone is optimized, the activation energy is reduced, premature generation of CO is inhibited, and the coke deposition risk is reduced; alkali metal in the sunflower straw ash can reduce the coverage of pollutants on active sites by adsorbing or fixing sulfur and nitrogen compounds; as waste biomass, the sunflower straw ash is wide in source and low in cost, the requirement for resource recycling is met, and solid waste emission is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic pyrolysis, and specifically to a method for catalytic pyrolysis of coal. Background Art

[0002] Coal is a solid combustible organic rock formed by the complex geological action of ancient plant residues. Its main components are elements such as carbon, hydrogen, and oxygen, and it has a layered structure and flammability. As a fossil energy source, coal can be decomposed into coke, coal gas, tar and other products when heated under anaerobic conditions. Catalytic pyrolysis of coal is an important development direction of coal conversion technology.

[0003] Catalytic pyrolysis of coal is a chemical conversion process in which coal is decomposed into gaseous, liquid and solid products by heating under the action of a catalyst. Compared with conventional pyrolysis, catalytic pyrolysis significantly optimizes the product distribution and reaction efficiency by introducing a catalyst.

[0004] There are various catalysts used in the catalytic pyrolysis of coal, including metal oxide catalysts. For example, the metal oxide catalyst Fe3O4 used in a rotary bed coal catalytic pyrolysis method disclosed in Chinese Patent Application CN201510246846.8 is prone to phase change or oxidation in a high-temperature or reducing pyrolysis environment, resulting in the loss of active sites, limited cracking ability for heavy components in tar, and easy formation of carbon deposition or coke on the catalyst surface, covering the active sites and reducing the specific surface area, thereby reducing the catalytic performance. Moreover, Fe3O4 needs to be artificially synthesized or extracted from minerals, with a high cost.

[0005] Therefore, we make improvements and propose a method for catalytic pyrolysis of coal. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for catalytic pyrolysis of coal according to the present invention includes the following steps:

[0008] S1. Pulverized coal preparation: The raw coal is crushed to less than 200 mesh by a crusher to obtain pulverized coal;

[0009] S2. Drying treatment: The pulverized coal is dried by pneumatic drying so that the water content of the pulverized coal is less than 5%;

[0010] S3. Catalyst addition: Sunflower straw ash and nano-calcium oxide are added to the pulverized coal and mixed to obtain a mixture;

[0011] S4. Pyrolysis reaction: The mixture is mixed with ceramic balls according to a mass ratio of 2:1 and placed in a circulating fluidized bed reactor for pyrolysis. The obtained gaseous products are condensed to separate tar, and the semicoke is collected by a gas-solid separator.

[0012] As a preferred technical solution of the present invention, the addition amount of sunflower straw ash is 10-15% of the mass of coal ash, and the addition amount of nano-calcium oxide is 2-5% of the mass of coal ash.

[0013] As a preferred technical solution of the present invention, when preparing the sunflower straw ash, it needs to be burned at 600-700 °C for 40-100 minutes.

[0014] As a preferred technical solution of the present invention, after the raw coal is pulverized, it needs to be classified and screened, and the particle size distribution of the pulverized coal obtained is 150-200 mesh.

[0015] As a preferred technical solution of the present invention, when drying the pulverized coal, the drying temperature is 120-150 °C, the air flow velocity is 8-12 m / s, and a high-temperature flue gas circulation drying system is adopted to utilize the waste heat of the pyrolysis furnace to heat the drying air flow.

[0016] As a preferred technical solution of the present invention, the temperature control in the pyrolysis reaction stage needs to be divided into an initial stage, a main reaction period and a final stage. Among them, the temperature in the initial stage is controlled at 300-450 °C, the temperature in the main reaction period is controlled at 450-580 °C, and the temperature in the final stage is controlled at 580-650 °C.

[0017] As a preferred technical solution of the present invention, the pyrolysis gas and char are separated by a cyclone separator. The char enters the combustion riser for recycling, and the gas products are passed through a ceramic filter to remove dust.

[0018] As a preferred technical solution of the present invention, the tar condensation is carried out by an air cooler and a water cooler. The working temperature of the air cooler is 50-80 °C, and the working temperature of the water cooler is 20-30 °C.

[0019] As a preferred technical solution of the present invention, the ceramic balls burn with air in the riser, the temperature rises to 650-870 °C, and they are returned to the reactor by pneumatic conveying.

[0020] The beneficial effects of the present invention are:

[0021] In the present invention, sunflower straw ash and nano-calcium oxide are used as catalysts for coal catalytic pyrolysis. The sunflower straw ash contains abundant alkali metals, which can significantly increase the H2 yield, optimize the reaction temperature range, reduce the activation energy, simultaneously inhibit the premature generation of CO, reduce the risk of coke deposition, and the alkali metals in the sunflower straw ash can adsorb or fix sulfur and nitrogen compounds, reducing the coverage of pollutants on the active sites; at the same time, the sunflower straw ash, as waste biomass, has a wide source and low cost, meets the requirements of resource recycling, and reduces solid waste emissions. Description of the Drawings

[0022] The accompanying drawings are used to provide a further understanding of the present invention and form a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the accompanying drawings:

[0023] Figure 1 It is a schematic flow structure diagram of a method for catalytic pyrolysis of coal according to the present invention. Detailed embodiments

[0024] The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0025] Embodiment: As Figure 1 shown, a method for catalytic pyrolysis of coal according to the present invention includes the following steps:

[0026] S1. Pulverized coal preparation: The raw coal is crushed to less than 200 mesh by a crusher to obtain pulverized coal; after the raw coal is crushed, it needs to be classified and screened, and the particle size distribution of the obtained pulverized coal is in the range of 150 - 200 mesh. Overly coarse particles will cause uneven pyrolysis reaction, and overly fine particles will increase the risk of dust explosion. The selected raw coal is a high-quality coal type with low ash content and low sulfur content, which can reduce the pollution control pressure of subsequent processes from the source.

[0027] S2. Drying treatment: The pulverized coal is dried by pneumatic drying so that the water content of the pulverized coal is less than 5%; the drying temperature during the drying of the pulverized coal is 120 - 150 °C, the air flow rate is 8 - 12 m / s, and a high-temperature flue gas circulation drying system is adopted to utilize the waste heat of the pyrolysis furnace to heat the drying air flow. When monitoring the moisture content of the pulverized coal, an on-line infrared sensor can be used.

[0028] S3. Catalyst addition: Sunflower straw ash and nano-calcium oxide are added to the pulverized coal and mixed to obtain a mixture;

[0029] S4. Pyrolysis reaction: The mixture is mixed with ceramic balls according to a mass ratio of 2:1 and put into a circulating fluidized bed reactor for pyrolysis. The obtained gaseous products are condensed to separate tar, and the char is collected by a gas-solid separator.

[0030] The addition amount of sunflower straw ash is 10 - 15% of the mass of coal ash, and the addition amount of nano-calcium oxide is 2 - 5% of the mass of coal ash. When preparing sunflower straw ash, it needs to be burned at 600 - 700 °C for 40 - 100 minutes.

[0031] At 600 - 700 °C, the cellulose and hemicellulose in sunflower straw are fully decomposed to generate highly active potassium salts (the KCO content reaches 51.97%), avoiding potassium volatilization loss caused by high temperature (>750 °C). The combustion time of 40 - 100 minutes can balance the pyrolysis efficiency and energy consumption, and the residual carbon content is controlled at 8% - 12% to ensure the catalytic activity of the ash.

[0032] The main components of sunflower straw ash are SiO (about 30%), KO (about 25%), and CaO (about 15%). When mixed with coal ash (SiO 48.8%, Al O 15% - 40%), it can form a eutectic, reducing the gasification temperature by 100 - 150°C.

[0033] The particle size of nano-calcium oxide is ≤50nm. It is uniformly dispersed in coal ash by mechanical mixing, covering the surface of coal char to form active sites, increasing the gasification reaction rate by 30% - 50%. Adding 5% nano-calcium oxide can reduce the ash viscosity to 10 - 50 Pa·s (the original coal ash is 100 - 300 Pa·s), effectively inhibiting slag formation in the gasifier.

[0034] Sunflower straw ash and nano-calcium oxide can be used as catalysts separately or mixed. When the two are mixed, the tar yield and gas yield can be significantly increased. The specific data can be referred to Table 1 below:

[0035]

[0036] As can be seen from the above table, adding 10% sunflower straw ash significantly increases the tar yield but reduces the char yield at the same time. The addition of 5% CaO has a relatively small impact on the tar yield but increases the gas yield. When 10% straw ash and 5% CaO are added simultaneously, both the tar and gas yields increase, while the char yield further decreases.

[0037] The temperature control in the pyrolysis reaction stage needs to be divided into the initial stage, main reaction stage, and final stage. The temperature in the initial stage is controlled at 300 - 450°C, the temperature in the main reaction stage is controlled at 450 - 580°C, and the temperature in the final stage is controlled at 580 - 650°C. The specific sectional parameters and reaction mechanism can be referred to Table 2 below:

[0038]

[0039] In the initial stage of the reaction (300 - 450°C), after the moisture in the material is completely evaporated, volatile organic compounds (such as cellulose and hemicellulose) begin to deoxygenate and decarboxylate, generating light hydrocarbons and oxygen-containing compounds. In coal materials, lignite and bituminous coal release initial volatiles (such as methane and tar precursors) at this stage, but the tar yield is relatively low.

[0040] When controlling the temperature, the heating rate needs to be controlled at 5 - 10°C / min to avoid the formation of a crust on the surface of the material, which hinders internal heat transfer.

[0041] During the main reaction period (450 - 580 °C), high molecular organic compounds such as plastics and rubbers undergo chain-breaking reactions, generating liquid tar (containing monocyclic aromatic hydrocarbons such as benzene and toluene) and gases such as H and CO. The pyrolysis of coal enters the active decomposition stage, where the tar yield reaches its peak at around 450 °C, and gases (such as CO and CH) are abundantly produced at 450 - 550 °C.

[0042] When controlling the temperature, maintain a constant temperature or slowly increase the temperature (2 - 5 °C / min) to extend the residence time of the tar and reduce recombination and cracking.

[0043] In the final reaction period (580 - 650 °C), polycyclic aromatic hydrocarbons in the residual tar further crack into small molecule gases (such as H and CO), and at the same time, the residual carbon undergoes a gasification reaction (C + H₂O → CO + H₂).

[0044] When controlling the temperature, quickly increase the temperature to the target temperature and shorten the residence time (<10 minutes) to reduce the risk of coking in the high-temperature zone.

[0045] The pyrolysis gas and semicoke are separated by a cyclone separator. It is necessary to adjust the inlet air velocity of the cyclone separator according to the particle size of the semicoke (usually <3 mm), keep the air velocity at 15 - 25 m / s, adjust the cone angle to 20° - 30°, ensure that the separation efficiency is ≥95%, and avoid the semicoke entering the gas phase system, which may cause pipeline wear or blockage of subsequent equipment. The temperature inside the separator should be maintained at 450 - 600 °C (corresponding to the temperature of the main pyrolysis period) to prevent the semicoke from agglomerating due to too low temperature or secondary cracking and gas production due to too high temperature, which may interfere with the separation. Spray a silicon carbide coating on the inner wall of the separator or use a high-temperature resistant alloy material to reduce the risk of semicoke adhesion and coking.

[0046] Regularly monitor the pressure difference of the separator. If the pressure difference abnormally increases (such as exceeding 10% of the design value), it may be due to coking on the inner wall or adhesion of the semicoke, resulting in a decrease in efficiency. It is necessary to clean or adjust the operating parameters in a timely manner. The semicoke enters the combustion riser for recycling, and the gas product removes dust through a ceramic filter.

[0047] Before the semicoke enters the combustion riser, it is necessary to control its volatile content <8% to avoid unstable combustion or fluctuations in flue gas composition caused by too high volatile content. And adopt a staged air distribution technology, with the primary air volume accounting for 60% - 70% to maintain the suspended combustion of the semicoke, and the secondary air supplements oxygen to ensure complete combustion and reduce CO generation.

[0048] Stably operate the coal catalytic pyrolysis process by optimizing parameters such as air velocity and temperature.

[0049] Tar condensation is carried out by an air cooler and a water cooler. The operating temperature of the air cooler is 50 - 80°C, and the operating temperature of the water cooler is 20 - 30°C. The condensation efficiency of the air cooler for tar is 60% - 75%, and the pressure drop range is 0.5 - 1.2 kPa, which can reduce the adhesion of viscous tar; the condensation efficiency of the water cooler for tar is 85% - 95%, and the pressure drop range is 2.0 - 4.0 kPa. When cooling, the flow rate of the cooling water is controlled at 0.8 - 1.5 m / s to avoid low-temperature coking.

[0050] The temperature of the gas at the inlet of the air cooler needs to be quickly reduced from the pyrolysis gas outlet to 50 - 80°C. By combining natural convection and forced air cooling, the volatilization loss of light tar is reduced. In this temperature range, low-boiling components such as benzene and toluene are preferentially condensed, and the particle size of the condensate droplets is 50 - 200 μm. A cyclone separator is configured to assist in collection.

[0051] The water cooler further cools the gas to 20 - 30°C through circulating cooling water, and high-boiling tars such as naphthalene and anthracene (boiling point > 200°C) are liquefied and precipitated at this stage.

[0052] The ceramic balls burn with air in the riser, heating up to 650 - 870°C, and are returned to the reactor by pneumatic conveying. The ceramic balls use high-aluminum ceramic heat storage balls.

[0053] In the present invention, sunflower straw ash and nano-calcium oxide are used as catalysts for coal catalytic pyrolysis. Sunflower straw ash contains abundant alkali metals, which can significantly increase the H2 yield, optimize the reaction temperature range, reduce the activation energy, simultaneously inhibit the premature generation of CO, reduce the risk of coke deposition, and the alkali metals in sunflower straw ash can adsorb or fix sulfur and nitrogen compounds, reducing the coverage of pollutants on the active sites; at the same time, sunflower straw ash, as waste biomass, has a wide source and low cost, meeting the requirements of resource recycling and reducing solid waste emissions.

[0054] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A catalytic pyrolysis method of coal, characterized in that, It includes the following steps: S1. Pulverized coal preparation: The raw coal is pulverized to less than 200 mesh by a crusher to obtain pulverized coal; S2. Drying treatment: The pulverized coal is dried by air flow to make the water content of the pulverized coal less than 5%; S3. Catalyst addition: Sunflower straw ash and nano calcium oxide are added to the pulverized coal and mixed to obtain a mixture; S4. Pyrolysis reaction: The mixture and ceramic balls are mixed according to a mass ratio of 2:1 and put into a circulating fluidized bed reactor for pyrolysis. The obtained gaseous product is condensed to separate tar, and the semicoke is collected by a gas-solid separator.

2. The coal catalytic pyrolysis method according to claim 1, wherein The addition amount of the sunflower straw ash is 10-15% of the mass of the coal ash, and the addition amount of the nano calcium oxide is 2-5% of the mass of the coal ash.

3. A coal catalytic pyrolysis method according to claim 1, characterized in that When preparing the sunflower straw ash, it needs to be burned at 600-700 °C for 40-100 minutes.

4. The coal catalytic pyrolysis method according to claim 1, characterized in that, After the raw coal is pulverized, it needs to be classified and screened, and the particle size distribution of the obtained pulverized coal is in the range of 150-200 mesh.

5. A coal catalytic pyrolysis method according to claim 1, characterized in that, When drying the pulverized coal, the drying temperature is 120-150 °C, the air flow velocity is 8-12 m / s, and a high-temperature flue gas circulation drying system is adopted to utilize the waste heat of the pyrolysis furnace to heat the drying air flow.

6. The coal catalytic pyrolysis method according to claim 1, characterized in that, In the pyrolysis reaction stage, temperature control needs to be carried out in the initial stage, main reaction period and final stage. Among them, the temperature in the initial stage is controlled at 300-450 °C, the temperature in the main reaction period is controlled at 450-580 °C, and the temperature in the final stage is controlled at 580-650 °C.

7. A method for catalytic pyrolysis of coal according to claim 1, characterized in that, The pyrolysis gas and the semicoke are separated by a cyclone separator. The semicoke enters the combustion riser for recycling, and the gas product removes dust through a ceramic filter.

8. A catalytic pyrolysis method of coal according to claim 1, characterized in that, The tar condensation is carried out by an air cooler and a water cooler. The working temperature of the air cooler is 50-80 °C, and the working temperature of the water cooler is 20-30 °C.

9. A method for catalytic pyrolysis of coal according to claim 1, characterized in that, The ceramic balls burn with air in the riser, the temperature rises to 650-870 °C, and they are returned to the reactor by pneumatic conveying.

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