A method for improving the quality of low-rank coal pyrolysis products using a molten medium

Abstract

This invention proposes a method for improving the quality of pyrolysis products from low-rank coal using a molten medium, belonging to the field of coal chemical technology. The method includes: 1) mixing low-rank coal particles with a particle size of 2mm–10mm with low-melting-point alloy particles with a particle size of 3mm–5mm at a mass ratio of 1:10–30; 2) adding a binder to the mixture and preheating it to form a mixed raw material; 3) pyrolyzing the mixed raw material to obtain pyrolysis products. This invention utilizes a low-melting-point alloy as a hot melt agent to mix with low-rank coal particles, forming a liquid-solid contact heat transfer to pyrolyze the low-rank coal particles. This reduces the temperature transfer gradient, promotes exothermic reactions while the low-rank coal particles undergo endothermic decomposition, promotes the release of volatiles, and increases the yield of pyrolysis gas and tar.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology, and relates to pyrolysis technology in coal chemical industry, specifically a method for improving the quality of pyrolysis products of low-rank coal using a molten medium. Background Technology

[0002] Low- and medium-temperature pyrolysis is an efficient way to utilize coal resources. Low-rank coal pyrolysis is widely used to produce chemical products such as syngas, tar, and semi-coke. The distribution and quality of low-rank coal pyrolysis products are affected by many pyrolysis conditions, such as the final pyrolysis temperature, heating rate, coal particle size, pyrolysis atmosphere, and heat transfer medium.

[0003] Patent CN112625720B discloses a cross-flow mixed coal pyrolysis method and a pyrolysis device adapted to this method. It employs a special gas collection structure and a combination of gas-solid two-phase counter-flow and cross-flow, simultaneously achieving heat exchange and dust reduction, thereby improving pyrolysis stability and product quality. Patent application CN115106038A discloses a pulverized coal pyrolysis experimental platform utilizing infrared rapid heating. This platform improves heat transfer efficiency and reduces temperature gradients through infrared heating, minimizing secondary reactions during pyrolysis and improving tar yield and quality. Patent application CN114836231A discloses a device and method for conveniently converting coal pyrolysis to produce high-quality pyrolysis oil or syngas. By changing the gas channel and adjusting the degree of secondary reaction between high-temperature steam and high-temperature semi-coke, it regulates the main product oil / byproduct gas, adjusting the quality of tar or syngas according to the demand for main and byproducts. Patent CN109437227B discloses a method for preparing gallium-containing zeolite and its application in the upgrading of volatile matter from coal pyrolysis. Using gallium-containing zeolite with an MFI framework effectively reduces catalyst deactivation due to carbon deposition and synergistically catalyzes various structural components in coal pyrolysis volatiles, promoting macromolecular polymerization, removal, and aromatization reactions, thereby achieving the upgrading effect on coal pyrolysis volatiles. Therefore, existing methods, limited by heat source and heat transfer efficiency, still cannot effectively improve the distribution and quality of low-rank coal pyrolysis products. Summary of the Invention

[0004] To address the problem described above that traditional low-rank coal pyrolysis technology cannot effectively improve the distribution and quality of low-rank coal pyrolysis products, this invention proposes a method for optimizing low-rank coal pyrolysis products in a molten medium.

[0005] This invention mixes a hot melt flux composed of a low-melting-point alloy with low-rank coal particles and adds a binder. Utilizing the characteristics of low-melting-point alloys—low melting point, high heat capacity, and high thermal conductivity—the molten alloy is used as a liquid-phase heat transfer medium to achieve liquid-solid contact heat transfer. This satisfies the reaction requirements of coal pyrolysis, thereby regulating product quality and improving the quality of pyrolysis products. The specific technical solution is as follows:

[0006] A method for improving the quality of low-rank coal pyrolysis products using a molten medium includes the following steps:

[0007] 1) Mix low-rank coal particles with a particle size of 2mm to 10mm with low-melting-point alloy particles with a particle size of 3mm to 5mm at a mass ratio of 1:10 to 30 to obtain a mixture;

[0008] 2) Add a binder to the mixture and preheat to form a mixed raw material;

[0009] 3) Pyrolyze the mixed raw materials to obtain pyrolysis products.

[0010] Further specifying, the particle size of low-rank coal is 3mm to 8mm.

[0011] Further specifying, the low-melting-point alloy particles in step 1) are formed by mixing two or more of the following: tin, bismuth, indium, and gallium.

[0012] Further specified, the low-melting-point alloy particles are formed by mixing gallium and indium in a mass ratio of 3:1, or tin and bismuth in a mass ratio of 42:58, or gallium, indium and tin in a mass ratio of 7:2:1.

[0013] Further specifying, in step 2), the mass ratio of binder to low-rank coal particles is 1:0.5 to 1.5.

[0014] Further specifying, the binder in step 2) is coal tar pitch at 1000℃, which is calcined at 450℃ for 3 hours to obtain a semi-coke product.

[0015] Further specifying, the preheating temperature in step 2) is 150℃~250℃.

[0016] Further specifying, the conditions for pyrolysis in step 3) are: pyrolysis temperature 650℃~850℃, pyrolysis time 30min~60min.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention utilizes a molten medium to improve the quality of low-rank coal pyrolysis products. It mainly involves mixing a low-melting-point alloy as a hot melt agent with low-rank coal particles and adding a binder. During the pyrolysis process, since the low-melting-point alloy is in a molten state, it can act as a liquid-phase heat transfer medium, forming a liquid-solid contact with the low-rank coal particles to pyrolyze them, reducing the temperature transfer gradient. While the low-rank coal particles undergo endothermic decomposition, the invention promotes exothermic reactions, facilitates the release of volatiles, and increases the yield of pyrolysis tar and pyrolysis gas.

[0019] 2. The method of the present invention can effectively reduce the content of carbon monoxide and carbon dioxide in pyrolysis gas, increase the content of hydrogen and methane, reduce the difficulty of subsequent processing of pyrolysis gas, and obtain semi-coke with a richer physical structure and significantly improved mechanical properties.

[0020] 3. This invention uses a molten low-metal alloy medium for heat transfer, which effectively improves the heat transfer efficiency of the medium, increases the temperature transfer rate, and greatly reduces the impact of heat transfer hysteresis. Attached Figure Description

[0021] Figure 1 The distribution diagrams are of the pyrolysis products obtained in Examples 1-6 and Comparative Examples 1-3;

[0022] Figure 2 The composition distribution diagrams of the synthesis gas obtained in Examples 1-6 and Comparative Examples 1-3 are shown.

[0023] Figure 3 The graphs show the temperature change curves of the raw materials in different heat transfer media for Examples 3 and 4 and Comparative Example 2. Detailed Implementation

[0024] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments described below.

[0025] Based on the characteristics of molten alloys—low melting point, high heat capacity, and high thermal conductivity—this invention utilizes a hot melt flux as a liquid-phase heat transfer medium to improve the quality of coal pyrolysis products. The invention mixes the hot melt flux with coal and adds a binder to form a liquid medium during pyrolysis, achieving liquid-solid contact heat transfer, reducing temperature transfer, and thus improving the quality of the pyrolysis products.

[0026] The present invention provides a method for improving the quality of low-rank coal pyrolysis products using a molten medium, comprising the following steps.

[0027] 1) Mix low-rank coal particles with a particle size of 2mm to 10mm with low-melting-point alloy particles with a particle size of 3mm to 5mm at a mass ratio of 1:10 to 30.

[0028] In this invention, the particle size of the low-rank coal particles is 3mm to 8mm.

[0029] In this invention, the low-melting-point alloy particles are formed by mixing two or more of the following: tin, bismuth, indium, and gallium.

[0030] Further optimization reveals that the low-melting-point alloy particles are a mixture of metallic gallium and metallic indium in a mass ratio of 3:1.

[0031] Low-melting-point alloy particles are made by mixing metallic tin and metallic bismuth in a mass ratio of 42:58.

[0032] The low-melting-point alloy particles are a mixture of gallium, indium, and tin in a mass ratio of 7:2:1.

[0033] 2) Add a binder to the mixture and preheat to form a mixed raw material.

[0034] In step 2), the mass ratio of binder to low-rank coal particles is 1:0.5 to 1.5.

[0035] In step 2), the binder is coal tar pitch at 1000℃, which is calcined at 450℃ for 3 hours to obtain a semi-coke product.

[0036] In step 2), the preheating temperature is 150℃~250℃.

[0037] 3) Pyrolyze the mixed raw materials to obtain pyrolysis products.

[0038] Step 3) The pyrolysis conditions are: pyrolysis temperature 650℃~850℃, pyrolysis time 30min~60min.

[0039] The pyrolysis products in step 3) include semi-coke products, tar products, and pyrolysis gas.

[0040] The advantages of the method of the present invention are illustrated below with several specific embodiments, but these should not be construed as limiting the protection of the present invention.

[0041] The low-rank coal used in this embodiment was mined in the Shenfu area of ​​northern Shaanxi. The results of its industrial analysis and elemental analysis are shown in Table 1.

[0042] Table 1. Industrial and elemental analysis of low-rank coal

[0043]

[0044] The low-melting-point alloy used in this embodiment is inert in terms of both the metal itself and its melt at temperatures below 1000°C.

[0045] Example 1

[0046] The method for improving the quality of low-rank coal pyrolysis products using a molten medium in this embodiment includes the following steps.

[0047] 1) Crush and screen low-rank coal to obtain low-rank coal particles with a particle size of 3±0.5mm, dry them at 120℃ for 12 hours, and weigh 15g of low-rank coal particles; also weigh 150g of low-melting-point alloy particles with a particle size of 5mm. The low-melting-point alloy particles are made by mixing gallium and indium in a mass ratio of 3:1, with gallium accounting for 75% of the total mass. Mix the low-rank coal particles and low-melting-point alloy particles thoroughly to form a mixture.

[0048] 2) Add 20g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0049] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes to obtain the pyrolysis products.

[0050] In this embodiment, the obtained pyrolysis products include semi-coke, tar, and pyrolysis gas.

[0051] Example 2

[0052] The method for improving the quality of low-rank coal pyrolysis products using a molten medium provided in this embodiment includes the following steps.

[0053] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 5±0.5mm, dry them at 120℃ for 12 hours, and weigh 15g of low-rank coal particles; then weigh 150g of low-melting-point alloy particles with a particle size of 3mm. The low-melting-point alloy particles are made by mixing metallic tin and metallic bismuth in a mass ratio of 58:42. Mix the low-rank coal particles and low-melting-point alloy particles thoroughly to form a mixture.

[0054] 2) Add 10g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0055] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0056] Example 3

[0057] This embodiment discloses a method for improving the quality of low-rank coal pyrolysis products using a molten medium, which includes the following steps.

[0058] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 5±0.5mm. Dry them at 120℃ for 12 hours. Weigh 15g of low-rank coal particles and weigh 300g of low-melting-point alloy particles with a particle size of 3mm. The low-melting-point alloy particles are made by mixing metallic tin and metallic bismuth in a mass ratio of 58:42. Mix the low-rank coal particles and low-melting-point alloy particles thoroughly to form a mixture.

[0059] 2) Add 15g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0060] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0061] Example 4

[0062] The method for improving the quality of low-rank coal pyrolysis products using a molten medium provided in this embodiment includes the following steps.

[0063] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 8±0.5mm. Dry them at 120℃ for 12 hours. Weigh 15g of low-rank coal particles and weigh 300g of low-melting-point alloy particles with a particle size of 5mm. The low-melting-point alloy particles are made by mixing gallium and indium in a mass ratio of 3:1, with gallium accounting for 75% of the total mass. Mix the low-rank coal particles and the low-melting-point alloy thoroughly to form a mixture.

[0064] 2) Add 15g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0065] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0066] Example 5

[0067] The method for improving the quality of low-rank coal pyrolysis products using a molten medium in this embodiment includes the following steps.

[0068] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 8±0.5mm. Dry the particles at 120℃ for 12 hours. Weigh 15g of low-rank coal particles and weigh 150g of low-melting-point alloy particles with a particle size of 3mm. The low-melting-point alloy particles are a mixture of gallium, indium, and tin in a mass ratio of 7:2:1, with the three metals accounting for 70%, 20%, and 10% of the weight, respectively. Thoroughly mix the low-rank coal particles and the low-melting-point alloy to form a mixture.

[0069] 2) Add 15g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0070] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0071] Example 6

[0072] The method for improving the quality of low-rank coal pyrolysis products using a molten medium provided in this embodiment includes the following steps.

[0073] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 8±0.5mm. Dry them at 120℃ for 12 hours. Weigh 15g of low-rank coal particles and weigh 300g of low-melting-point alloy particles with a particle size of 3mm. The low-melting-point alloy particles are made by mixing metallic tin and metallic bismuth in a mass ratio of 58:42. Mix the low-rank coal particles and low-melting-point alloy particles thoroughly to form a mixture.

[0074] 2) Add 15g of binder to the mixture and preheat to 200℃ to form a mixed raw material.

[0075] 3) Place the preheated mixed raw materials into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 1 is that no low-melting-point alloy particles or binders are added, and the low-rank coal particles are directly pyrolyzed.

[0078] The method for producing low-rank coal pyrolysis products provided in this comparative example includes the following steps.

[0079] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 3±0.5mm, dry them at 120℃ for 12 hours, and weigh 15g of low-rank coal particles as pyrolysis material.

[0080] 2) Place the pyrolysis material into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0081] Comparative Example 2

[0082] The difference between this comparative example and Example 3 is that low-melting-point alloy particles are not added; instead, a binder is added to the low-rank coal particles and then pyrolysis is carried out directly.

[0083] The method for improving the quality of low-rank coal pyrolysis products provided in this comparative example includes the following steps.

[0084] 1) Crush and screen the low-rank coal to obtain low-rank coal particles with a particle size of 5±0.5mm, dry them at 120℃ for 12 hours, and weigh out 15g of low-rank coal particles.

[0085] 2) Add 15g of binder to the low-rank coal particles in 1) to obtain pyrolysis feedstock.

[0086] 3) Place the pyrolysis raw material into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0087] Comparative Example 3

[0088] The difference in this comparative example is that low-melting-point alloy particles are not added; only a binder is added and the mixture is preheated before pyrolysis.

[0089] The method for improving the quality of low-rank coal pyrolysis products using a molten medium provided in this comparative example includes the following steps.

[0090] 1) Dry low-rank coal particles with a particle size of 5±0.5mm at 120℃ for 12 hours, and weigh 15g of low-rank coal particles.

[0091] 2) Add 15g of binder to the low-rank coal particles in step 1) and preheat to 100℃ to obtain pyrolysis raw material.

[0092] 3) Place the pyrolysis raw material into a pyrolysis furnace at 750℃ and pyrolyze for 50 minutes.

[0093] Furthermore, in order to demonstrate the superiority of the method of the present invention for improving the quality of low-rank coal pyrolysis products, the performance of the pyrolysis products prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was measured.

[0094] Distribution of pyrolysis products in Experiment 1

[0095] Based on the principle of conservation of mass, the distribution of pyrolysis products prepared in Examples 1-12 and Comparative Examples 1-3 was determined, and the results are as follows: Figure 1 As shown.

[0096] See Figure 1 Compared with the results of Examples 1 to 6 and Comparative Examples 1 to 3, the yields of tar and pyrolysis gas in the pyrolysis products prepared in Examples 1 to 6 were significantly improved. In particular, the yield of tar in Example 3 increased from 9.39% to 13.29% compared with Comparative Example 3.

[0097] Experiment 2: Determination of Pyrolysis Gas Components

[0098] Based on the principle of conservation of mass, the gaseous components of the pyrolysis gases prepared in Examples 1-6 and Comparative Examples 1-3 were determined, and the results are as follows: Figure 2 As shown.

[0099] See Figure 2 Comparing the results of Examples 1 to 6 and Comparative Examples 1 to 3, the yields of H2 and CH4 increased significantly. In particular, compared with Comparative Example 3, the yield of H2 in Example 3 increased from 60.81% to 68.48%, the yield of CO decreased from 19.28% to 13.69%, and the yield of CO2 decreased from 3.98% to 2.09%. This indicates that by using binders and low-melting-point alloy particles, the content of carbon monoxide and carbon dioxide in low-rank coal pyrolysis gas can be effectively reduced, while the content of hydrogen and methane can be increased, thus reducing the difficulty of subsequent processing of pyrolysis gas.

[0100] Experiment 3 Physical properties of semi-coke

[0101] The physical parameters of the semi-cokes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were determined using conventional standard methods, and the specific results are shown in Table 2.

[0102] Table 2 Physical parameters of semi-coke

[0103] Aperture structure parameters <![CDATA[Surface area / (m 2 / g)]]> <![CDATA[Pore volume / (cm 3 / g)]]> Average pore size / nm Comparative Example 1 1.86 <![CDATA[6.72×10 -3 ]]> 7.34 Comparative Example 2 1.89 <![CDATA[7.81×10 -3 ]]> 7.71 Comparative Example 3 1.92 <![CDATA[8.03×10 -3 ]]> 7.73 Example 1 1.99 <![CDATA[9.16×10 -3 ]]> 8.24 Example 2 2.16 <![CDATA[9.28×10 -3 ]]> 8.49 Example 3 8.11 <![CDATA[12.10×10 -3 ]]> 16.61 Example 4 6.46 <![CDATA[11.05×10 -3 ]]> 12.73 Example 5 5.23 <![CDATA[10.24×10 -3 ]]> 11.28 Example 6 3.79 <![CDATA[10.10×10 -3 ]]> 13.85

[0104] Referring to Table 2, the pore size structure parameters of the semi-coke in the pyrolysis products obtained in Examples 1 to 6 are all better than those of the semi-coke in the pyrolysis products obtained in Comparative Examples 1 to 3, especially the semi-coke obtained in Example 3, which has a richer pore structure than that obtained in Comparative Examples 2 and 3.

[0105] Test 4 Mechanical Properties

[0106] The Hastings grindability index of the semi-cokes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 was determined using conventional standard methods. The specific results are shown in Table 3.

[0107] Table 3. Hastelloy Grindability Index of Semi-coke

[0108]

[0109] Referring to Table 3, the Hasher Grindability Index of the pyrolytic semi-coke obtained in Examples 1 to 6 is higher than that of the pyrolytic semi-coke obtained in Comparative Examples 1 to 3. In particular, the Hasher Grindability Index of the semi-coke obtained in Example 3 is more significantly improved compared with that in Comparative Example 2, indicating that the pyrolytic semi-coke prepared in Example 3 has higher mechanical strength.

[0110] Temperature curve of Experiment 5

[0111] Using conventional standard methods, the temperature curves of the raw materials used in the pyrolysis process of Examples 3, 4, and Comparative Example 2 in different heat transfer media were measured. Specific results are as follows: Figure 3 As shown.

[0112] See Figure 3 The temperature curve of Comparative Example 2 changes more slowly, and the temperature rises more slowly under the same pyrolysis time. The temperature rise rates of Examples 3 and 4 are both faster, indicating that when a low melting point alloy is used, the molten medium generated by the low melting point alloy at the pyrolysis temperature makes the heat transfer efficiency of the low-rank coal raw material higher, which can reduce the temperature transfer gradient, promote the release of volatiles, and thus increase the yield of volatiles.

Claims

1. A method for improving the quality of low-rank coal pyrolysis products using a molten medium, characterized in that, Includes the following steps: 1) Mix low-rank coal particles with a particle size of 2mm~10mm with low-melting-point alloy particles with a particle size of 3mm~5mm at a mass ratio of 1:10~30 to obtain a mixture; 2) Add a binder to the mixture, the mass ratio of the binder to the low-rank coal particles is 1:0.5~1.5, and preheat to form a mixed raw material. The preheating temperature is 150℃~250℃, and the binder is coal tar pitch at 1000℃. The semi-coke product is obtained by calcining at 450℃ for 3 hours. 3) The mixed raw materials are pyrolyzed to obtain pyrolysis products. During the pyrolysis process, since the low melting point alloy is in a molten state, it can act as a liquid phase heat transfer medium and form a liquid-solid contact with the low-rank coal particles to pyrolyze the low-rank coal particles.

2. The method for improving the quality of low-rank coal pyrolysis products using a molten medium as described in claim 1, characterized in that, In step 1), the particle size of the low-rank coal particles is 3mm to 8mm.

3. The method for improving the quality of low-rank coal pyrolysis products using a molten medium as described in claim 2, characterized in that, The low-melting-point alloy particles in step 1) are formed by mixing two or more of the following: tin, bismuth, indium, and gallium.

4. The method for improving the quality of low-rank coal pyrolysis products using a molten medium as described in claim 3, characterized in that, The low-melting-point alloy particles are formed by mixing gallium and indium in a mass ratio of 3:1, or tin and bismuth in a mass ratio of 42:58, or gallium, indium and tin in a mass ratio of 7:2:

1.

5. The method for improving the quality of low-rank coal pyrolysis products using a molten medium as described in claim 1, characterized in that, The conditions for pyrolysis in step 3) are: pyrolysis temperature 650℃~850℃, pyrolysis time 30min~60min.

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