A comprehensive utilization method of coal gangue

Abstract

The present invention discloses a comprehensive utilization method of coal gangue, including processes such as coal gangue combustion power generation, combustion ash carbon thermal chlorination, gas-solid separation, solid waste utilization, gas phase condensation, condensate treatment and tail gas recovery. While fully utilizing the steam heat and electricity generated by the combustion of coal gangue, this method extracts the components of Si, Al, Fe, Ti, alkali metals and alkaline earth metals in the combustion ash of coal gangue, realizing the comprehensive and efficient resource utilization of coal gangue. And an improved carbon thermal chlorination process is adopted, adding a small amount of silicon powder and hydrogen chloride gas as additives to participate in the reaction to provide heat, thereby reducing the temperature required for the chlorination reaction and increasing the reaction conversion rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recycling, and particularly relates to a comprehensive utilization method of coal gangue. Background Art

[0002] Solid waste is generated during the process of coal mining and utilization. For example, coal gangue generated during coal mining, fly ash generated during coal combustion and utilization, and gasification ash residues generated during coal chemical conversion. These solid wastes are collectively referred to as coal-based solid wastes, and currently, their disposal mainly relies on landfill stacking.

[0003] There is a part of carbon remaining in the coal-based solid waste, and the ash is rich in aluminum-silicon-based compounds. The coal-based solid waste has fuel properties and raw material properties. The two main properties of the coal-based solid waste determine that its main disposal methods are carried out from two aspects: the combustion utilization of carbon and the materialization utilization of ash. The combustion utilization of the coal-based solid waste can realize the utilization of carbon, and can be used to generate steam or electricity to achieve coal substitution. However, current coal gangue power generation still faces many challenges: on the one hand, the economic benefits are not high; on the other hand, a large amount of fly ash is generated during coal gangue power generation and needs to be treated.

[0004] By mass percentage, the fly ash generated by burning coal gangue includes O 47.83%, Si 11.48% - 31.14%, Al 6.40% - 22.91%, Fe 1.90% - 18.51%, Ca 0.30% - 25.10%, K 0.22% - 3.10%, Mg 0.05% - 1.92%, Ti 0.40% - 1.80%, Na 0.05% - 1.40%, and others 0.50% - 29.12%. Each component exists mainly in the form of oxides, with complex components and extremely difficult to process. Currently, the processes for raw material recovery and utilization of fly ash mainly include sintering method, acid leaching method, alkali leaching method, acid-base combined method, and direct reduction method, etc. Among them, the sintering method involves a high-temperature sintering process, with high energy consumption and a large amount of slag that is difficult to digest; in the acid method and alkali method, impurity separation is difficult and equipment corrosion is serious. The above methods all have relatively high requirements for raw material components, complex process operations, cannot achieve comprehensive separation and utilization of each component of waste coal ash, have high costs, and basically do not have economic and environmental benefits.

[0005] Currently, a feasible process is the carbothermal chlorination reduction method, which can simply and quickly separate most components in fly ash through a simple chlorination - condensation step, and has obvious advantages in the field of fly ash comprehensive utilization.

[0006] Publication No. CN108217659A discloses a method for comprehensive utilization of fly ash, which comprises mixing fly ash and a carbon reducing agent, adding silicon carbide as an energy donor, passing chlorine gas for chlorination reaction, cooling twice to obtain aluminum chloride, a mixture of ferric chloride and silicon tetrachloride respectively, and separating aluminum chloride and ferric chloride by adding sodium hydroxide. The process recycles chlorine gas for recycling, recycles CO and CO2 for the preparation of methanol, and can realize the recycling of tail gas. However, the process has limited utilization of fly ash raw material components, the product purity is not high, and NaOH is used in the separation and purification process, which has high production costs and is not conducive to comprehensive resource utilization.

[0007] Publication No. CN102923747A discloses a method for producing aluminum chloride, silicon chloride and ferric chloride using coal gangue, wherein the coal gangue is mixed with a carbon reducing agent in a certain proportion, placed in a chlorination furnace, and chlorine gas is passed through at 800-1000°C for chlorination reaction. After the furnace gas is dusted, crude products AlCl3, FeCl3 and SiCl4 are obtained through three-stage condensation, which are distilled and purified, and AlCl3 is electrolyzed to obtain Al and Cl2. This process makes full use of the carbon in the coal gangue to supplement part of the carbon required for the reaction, and realizes the utilization of C, Al, Fe, and Si components in the coal gangue. However, the difference in carbon content in the coal gangue causes the process to be more volatile in actual application, which is not conducive to long-term stable production. In addition, the process needs to react at a higher temperature, has high requirements on the equipment environment, high energy consumption, and high production cost.

[0008] Publication No. CN102502665A discloses a method for comprehensive recovery of valuable elements in fly ash, wherein the fly ash is separated by chlorination in one stage to obtain FeCl3 and TiCl4, and separated by chlorination in two stages to obtain FeCl3 and AlCl3, which are condensed to obtain TiCl4 and SiCl4, which are purified by rectification and oxidation to obtain TiO2 and SiO2, and the TiCl4 obtained by chlorination in one stage and the AlCl3 obtained by chlorination condensation in two stages are electrolyzed to prepare metal elements, and the chlorine is recycled. This process realizes the utilization of Al, Ti, Fe, and Si components in fly ash, but the process flow is long, the steps for separating the components and products are complicated, the temperature required for the two-stage chlorination reaction is high, and there is a small amount of gas waste and solid waste, which is not conducive to the comprehensive utilization of fly ash resources.

[0009] In summary, the existing comprehensive utilization technologies of coal gangue have many shortcomings such as low utilization efficiency of various components of coal gangue, incomplete utilization, high energy consumption, low environmental benefits and low economic benefits. Summary of the invention

[0010] In view of the above deficiencies in the prior art, the present invention provides a comprehensive utilization method for coal gangue. While fully utilizing the steam heat and electricity generated by the combustion of coal gangue, the improved carbothermal chlorination process is adopted to extract the main elements such as iron, aluminum, titanium, silicon, alkali metals, and alkaline earth metals from the combustion ash of coal gangue, which not only reduces the production cost but also realizes a more comprehensive and efficient comprehensive utilization of coal gangue.

[0011] To solve the above problems, the present invention is realized through the following process technical solutions:

[0012] (1) Coal gangue combustion power generation: Coal gangue is used as fuel and burned in a circulating fluidized bed boiler to generate superheated steam, and the superheated steam drives a steam turbine to rotate for power generation; the combustion ash obtained during the combustion process of coal gangue is collected, and the combustion ash includes coal cinder remaining at the bottom of the boiler and fly ash recovered from the flue gas.

[0013] (2) Carbothermal chlorination: The combustion ash, carbon reducing agent, and silicon powder obtained in step (1) are added to a chlorination reactor, and chlorine gas and hydrogen chloride gas are introduced for chlorination reaction. After the reaction, a mixed flue gas and chlorination residue are obtained.

[0014] (3) Gas-solid separation: A cooling device is provided at the top of the chlorination reactor. The mixed flue gas obtained in step (2) is cooled to 400 - 500 °C by the cooling device, and the flue gas outlet is connected to a cyclone separator and a dust collection device to collect the settled dust.

[0015] (4) Solid waste utilization: The chlorination residue obtained in step (2) is mixed with the dust collected in step (3), washed with water, the washing liquid is recrystallized, and alkali metal and / or alkaline earth metal chlorides are obtained by filtration and separation. The water-insoluble filter residue is dried, ground, and added as a raw material to the chlorination reactor for recycling.

[0016] (5) Gas phase condensation: After gas-solid separation in step (3), the obtained mixed gas A is introduced into a multi-stage condensation system, and crude products such as FeCl3, AlCl3, TiCl4, SiCl4, and SiHCl3 are obtained through multi-stage condensation respectively.

[0017] (6) Product treatment: Each of the crude products obtained in step (5) is refined and purified to obtain products with a purity higher than 99%. The purified AlCl3 is electrolyzed to obtain high-purity metallic aluminum and chlorine gas, and the chlorine gas is dried and introduced into the chlorination reactor for recycling; the purified TiCl4 is oxidized with oxygen to obtain TiO2 and chlorine gas, and the chlorine gas is dried and introduced into the chlorination reactor for recycling; the purified SiCl4 and SiHCl3 are used for the preparation of high-purity polysilicon.

[0018] (7) Tail gas recovery and treatment: After multi-stage condensation in step (5), a mixed gas B with a lower boiling point is obtained. After water washing and desorption, Cl2 and HCl are absorbed, and after drying, it is introduced into the chlorination reactor for recycling. The remaining mixed gas C is used to prepare methanol by adding an appropriate amount of H2.

[0019] Preferably, in step (2), the combustion ash, carbon reducing agent, and silicon powder are ground to 80 - 200 mesh, mixed and pelletized in a certain proportion, and then added to the chlorination reactor after drying at 100 - 300 °C for 5 - 10 h.

[0020] Preferably, the raw materials in step (2) are mixed according to a molar ratio of SiO2 to carbon of 1:(1.5 - 2.5). Here, SiO2 is the total amount of SiO2 in the combustion ash and carbon reducing agent, and carbon is the total amount of carbon in the combustion ash and carbon reducing agent.

[0021] Preferably, the carbon reducing agent in step (2) is selected from one or more of activated carbon, petroleum coke, clean coal, and charcoal.

[0022] Preferably, the carbothermal chlorination reaction in step (2) is obtained by improving the traditional carbothermal chlorination process. That is, a small amount of silicon powder is added to the solid-phase raw materials, and a small amount of hydrogen chloride gas is mixed into the introduced chlorine gas. The silicon powder and hydrogen chloride gas together serve as energy donors, and the reactions of silicon with chlorine and hydrogen chloride release a large amount of heat, thereby reducing the temperature required for the chlorination reaction and increasing the conversion rate of each component in the raw materials. The related reaction equations are as follows:

[0023] SiO2 + 2C + 2Cl2 = SiCl4 + 2CO (1) Endothermic reaction

[0024] SiO2 + C + 2Cl2 = SiCl4 + CO2 (2) Slight exothermic reaction

[0025] Fe2O3 + 3C + 3Cl2 = 2FeCl3 + 3CO (3) Slight exothermic reaction

[0026] 2Fe2O3 + 3C + 6Cl2 = 4FeCl3 + 3CO2 (4) Exothermic reaction

[0027] Al2O3 + 3C + 3Cl2 = 2AlCl3 + 3CO (5) Endothermic reaction

[0028] 2Al2O3 + 3C + 6Cl2 = 4AlCl3 + 3CO2 (6) Slight exothermic reaction

[0029] TiO2 + 2C + 2Cl2 = TiCl4 + 2CO (7) Slight exothermic reaction

[0030] TiO2 + C + 2Cl2 = TiCl4 + CO2 (8) Slight exothermic reaction

[0031] Si + 2Cl₂ = SiCl₄ (9) A highly exothermic reaction

[0032] Si + 3HCl → SiHCl₃ + H₂ (10) A highly exothermic reaction

[0033] Specifically, in traditional carbothermal chlorination, only a carbon reducing agent and chlorine gas are added to the silicon-containing raw material for reaction, without adding other additives. The main reactions are those shown in formulas (1) to (8). Since the proportion of SiO₂ and Al₂O₃ in the combustion ash is higher than 80%, the overall reaction is an endothermic reaction, and the temperature required for the reaction is above 1200°C, with very high energy consumption.

[0034] Based on the traditional carbothermal chlorination reaction, the present invention adds a small amount of silicon powder and hydrogen chloride gas, and reactions shown in (9) and (10) also occur on the basis of the reactions shown in formulas (1) to (8). These two reactions are highly exothermic and will reduce the temperature required for the reaction.

[0035] Preferably, in step (2), the amount of silicon powder used is 5 - 20 wt% of the total amount of the solid raw material mixture, and the molar ratio of the hydrogen chloride gas to the amount of silicon powder used is (2 - 4):1. The solid raw material mixture includes combustion ash, a carbon reducing agent, and silicon powder. The amount of silicon powder used is related to the cost and the energy generated. Too low an amount will result in less energy provided and an insignificant effect on reducing the temperature required for the reaction, while too high an amount will increase the cost. The applicant hopes to minimize the amount of silicon powder used while ensuring a low reaction temperature and high chlorination efficiency, so 5 - 20 wt% is selected. To ensure complete reaction, the amount of chlorine gas used is 1.2 - 2 times the amount of chlorine gas required for the main components (SiO₂, Fe₂O₃, Al₂O₃, TiO₂, alkali metal / alkaline earth metal oxides) in the combustion ash to be completely converted into chlorides.

[0036] Preferably, in step (2), the temperature of the chlorination reaction is 500 - 1000°C, the pressure inside the chlorination reactor is 0.05 - 1 MPa, the flow rate of the mixed gas is 0.01 - 0.5 m / s, and the reaction time is 10 min - 10 h.

[0037] Preferably, in step (2), the carbothermal chlorination reaction converts oxides into chlorides. Chlorides with low boiling points such as FeCl₃, AlCl₃, TiCl₄, SiCl₄, SiHCl₃, etc. enter the gas phase, and chlorides with high boiling points such as CaCl₂, KCl, MgCl₂, NaCl, etc. remain in the solid phase. In addition, some unreacted components such as Si, SiO₂, C, etc. together form the chlorination residue. After the chlorination residue and soot are mixed and washed with water in step (4), CaCl₂, KCl, MgCl₂, NaCl dissolve in water and enter the washing liquid, while Si, SiO₂, C are insoluble in water and are separated by filtration to obtain the water-insoluble filter residue.

[0038] Preferably, the multi-stage condensation system in step (5) includes at least the following five stages but is not limited thereto. The condensation temperature range can be changed according to the raw material components, and the number of condensation stages can be increased or decreased. Among them, the first-stage condensation temperature is 200 - 280 °C, and FeCl3 is separated; the second-stage condensation temperature is 150 - 180 °C, and AlCl3 is separated; the third-stage condensation temperature is 80 - 130 °C, and TiCl4 is separated; the fourth-stage condensation temperature is 35 - 55 °C, and SiCl4 is separated; the fifth-stage condensation temperature is 0 - 30 °C, and SiHCl3 is separated.

[0039] Preferably, in step (6), the products obtained from the multi-stage condensation system are purified by distillation, and the heat required for distillation can be provided by the steam generated from the combustion of coal gangue.

[0040] Preferably, the electricity required for the electrolysis of AlCl3 in step (6) can be provided by the power generation from the combustion of coal gangue; the heat required for the oxidation of TiCl4 can be provided by the steam generated from the combustion of coal gangue.

[0041] Preferably, the main components of the mixed gas A in step (5) are FeCl3, AlCl3, TiCl4, SiCl4, SiHCl3, CO, CO2, Cl2, HCl, and H2. The main components of the mixed gas B in step (7) are CO, CO2, Cl2, HCl, and H2. The main components of the mixed gas C in step (7) are CO, CO2, and H2.

[0042] Preferably, the heat required for the preparation of methanol by adding H2 to the mixed gas C in step (7) can be provided by the steam generated from the combustion of coal gangue.

[0043] Preferably, the absorption solvents for Cl2 and HCl in step (7) are water, and the solvents after absorbing Cl2 and HCl are desorbed of Cl2 and HCl by heating.

[0044] A comprehensive utilization method of coal gangue in the present invention makes full use of the fuel property and raw material property of coal gangue, and realizes the comprehensive and efficient recovery and utilization of each component in coal gangue. Compared with the prior art, it has the following obvious advantages and remarkable effects:

[0045] 1. By adopting the improved carbon thermal chlorination process, adding a small amount of silicon powder and hydrogen chloride gas can effectively reduce the temperature required for the chlorination reaction, improve the conversion rate of each component in the raw material, and improve the utilization rate of coal gangue;

[0046] 2. Recycling the residues and dust from the chlorination reaction, and recycling the products CO, CO2, H2, and excessive Cl2 and HCl, without generating solid waste and gas waste, having good environmental benefits;

[0047] 3. The chlorine gas generated by electrolyzing AlCl3, the chlorine gas generated by oxidizing TiCl4, and the Cl2 and HCl obtained from the recycled tail gas are dried and then introduced into the chlorination reactor for recycling, reducing production costs and having good economic benefits;

[0048] 4. The electricity generated by burning coal gangue powers AlCl3, and the heat generated by burning coal gangue provides heat for reactions such as rectifying and purifying the condensed crude product, oxidizing TiCl4, and preparing methanol, reducing production costs and having good economic benefits;

[0049] 5. High-purity metallic aluminum, TiO2, FeCl3, SiCl4, SiHCl3, and methanol are finally prepared, and the added value of the products is high. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0051] Figure 1 It is a process flow diagram of the comprehensive utilization method of coal gangue provided by the present invention. Detailed Embodiments

[0052] The technical solutions and the technical problems to be solved in the embodiments of the present invention will be described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention patent, rather than all the embodiments.

[0053] Example 1

[0054] A comparative experiment between the improved carbothermal chlorination process of the present invention and the traditional carbothermal chlorination process.

[0055] Improved carbothermal chlorination process: Using coal gangue combustion ash (Al2O3 38%, SiO2 45%, Fe2O3 4.5%, TiO2 2.0%) as raw material, mix it with activated carbon (purity > 99%) according to the molar ratio of SiO2:C being 1:2, add silicon powder (purity > 99%) accounting for 10wt% of the total solid amount, crush and grind it to 120 mesh, mix evenly, make pellets, dry to constant weight, and continuously introduce chlorine gas and hydrogen chloride gas (both gas purities > 99%) for 30 min in a small fluidized chlorination furnace for chlorination reaction. The amount of hydrogen chloride is 3 times the amount of silicon powder in terms of molar amount, the reaction temperature is 600 °C, and the gas flow rate is 0.01 m / s. After the reaction, gas-solid separation is carried out to remove dust, and the flue gas enters a multi-stage condensation device for condensation to obtain crude products AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3. Finally, the chlorination rates of Al2O3, SiO2, Fe2O3, and TiO2 in the raw material are 92.2%, 86.5%, 93.6%, and 95.2% respectively.

[0056] Traditional carbothermal chlorination process: Using coal gangue combustion ash (Al2O3 38%, SiO2 45%, Fe2O3 4.5%, TiO2 2.0%) as raw material, mix it with activated carbon (purity > 99%) according to the molar ratio of SiO2:C being 1:2, crush and grind it to 120 mesh, mix evenly, make pellets, dry to constant weight, and continuously introduce chlorine gas for 30 min in the same small fluidized chlorination furnace for chlorination reaction. The reaction temperature is 600 °C, and the gas flow rate is 0.01 m / s. After the reaction, gas-solid separation is carried out to remove dust, and the flue gas enters a multi-stage condensation device for condensation to obtain crude products AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3. Finally, the chlorination rates of Al2O3, SiO2, Fe2O3, and TiO2 in the raw material are 58.5%, 60.5%, 64.6%, and 53.2% respectively.

[0057] Compared with the traditional carbothermal chlorination process, when the process of the present invention reacts at the same relatively low temperature as the traditional carbothermal chlorination process, the reaction of this application is more complete, manifested as a higher chlorination rate of coal gangue combustion ash, that is, the chlorination rates of Al2O3, SiO2, Fe2O3, and TiO2 are significantly improved. Further, the present invention effectively reduces the reaction energy consumption while ensuring the raw material utilization rate, reduces the production cost, and has obvious economic benefits.

[0058] Example 2

[0059] Using coal gangue combustion ash (Al2O3 40%, SiO2 44%, Fe2O3 6%, TiO2 1.5%) as raw material, it is mixed with activated carbon (purity > 99%) according to the molar ratio of SiO2:C being 1:2, and 10 wt% of silicon powder (purity > 99%) based on the total solid amount is added. It is crushed and ground to 120 mesh, mixed evenly, pelletized, dried to constant weight, and chlorine gas and hydrogen chloride gas (both gas purities > 99%) are continuously introduced into a fluidized chlorination furnace for 30 minutes for chlorination reaction. The gas flow rate is 0.05 m / s, the reaction temperature is 600 °C, to obtain chlorination residue and flue gas. The flue gas enters a gas-solid separation system to be cooled to obtain dust and mixed gas A. The dust is mixed with the chlorination residue and washed with water, and the washing liquid is recrystallized and filtered to obtain crude products of KCl, NaCl, CaCl2, and MgCl2. Mixed gas A is subjected to multi-stage condensation to separately obtain crude products of AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3. Finally, the chlorination rates of Al2O3, SiO2, Fe2O3, and TiO2 in the raw material are 94.2%, 89.5%, 96.6%, and 97.2% respectively, and the purities of the condensed crude products of AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3 are all greater than 96%. After being refined and purified by a distillation column respectively, the purities of AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3 all reach 99.9%. The condensed mixed gas B is absorbed with an aqueous solution, heated and desorbed at 80 °C to obtain a Cl2 and HCl mixed gas, and the purity of Cl2 in the mixed gas is higher than 95% for recycling.

[0060] Example 3

[0061] Using coal gangue combustion ash (Al2O3 40%, SiO2 44%, Fe2O3 6%, TiO2 1.5%) as raw material, it is mixed with petroleum coke according to the molar ratio of SiO2:C being 1:2, and 10 wt% of silicon powder (purity > 99%) based on the total solid amount is added. It is crushed and ground to 120 mesh, mixed evenly, pelletized, dried, and chlorine gas and hydrogen chloride gas (both gas purities > 99%) are continuously introduced into a fluidized chlorination furnace for chlorination reaction. The gas flow rate is 0.05 m / s, the reaction temperature is 700 °C, and the reaction time is 60 minutes, to obtain chlorination residue and flue gas. The flue gas undergoes gas-solid separation and condensation to obtain crude products of AlCl3, TiCl4, FeCl3, SiCl4, and SiHCl3, and high-purity products with a purity higher than 99.9% are obtained after refined purification. Among them, high-purity AlCl3 is electrolyzed in molten salt to precipitate high-purity metallic aluminum, and the Cl2 produced at the anode is dried and recycled; high-purity TiCl4 reacts with excessive oxygen at high temperature to prepare products such as titanium dioxide, and the by-product Cl2 is dried and recycled; high-purity SiCl4 and SiHCl3 are used to prepare high-purity polysilicon by the improved Siemens method; FeCl3 is directly sold.

[0062] Comparative Example 1

[0063] Other steps and process parameters are the same as those in Example 2, except that hydrogen chloride gas is not added, and silicon powder is replaced with silicon carbide powder of equal mass and equal particle size. The chlorination rates of Al2O3, SiO2, Fe2O3, and TiO2 in the final raw materials are 64.2%, 59.5%, 76.6%, and 77.2% respectively, which are significantly lower than those in Example 2.

[0064] Comparative Example 2

[0065] CN107673359B discloses a method for preparing silicon tetrachloride and a method for controlling the reaction temperature. Using silicon dioxide and silicon carbide as silicon sources, chlorine gas is introduced, and the reaction is carried out in a reactor at a temperature controlled at 800 - 1500 °C. The reaction mechanism is as follows:

[0066] 2SiC + SiO2 + 6Cl2 = 3SiCl4 + 2CO (1)

[0067] SiC + SiO2 + 4Cl2 = 2SiCl4 + CO2 (2)

[0068] Both of the above reaction formulas (1) and (2) are exothermic reactions, but the reaction temperature still needs to be maintained at 800 - 1500 °C, preferably 1000 - 1400 °C, which is significantly higher than that in Example 2.

[0069] Analyzing the main performance indicators of SiC, its melting point is 2700 °C, the Si - C bond energy is about 62.8 kJ / mol, and the energy required to break the bond is high. Below 1500 °C, SiC hardly reacts. It can be considered that the strategy of using SiC to participate in the reaction as an energy donor is only applicable to reaction systems above 1000 °C, otherwise SiC cannot play its full role.

[0070] Comparing with the strategy of adding silicon powder and hydrogen chloride in Example 2, the following reactions occur:

[0071] Si + 2Cl2 = SiCl4 (3)

[0072] Si + 3HCl → SiHCl3 + H2 (4)

[0073] Reaction formula (3) occurs at about 500 °C, and reaction formula (4) occurs at about 400 °C, which can fully play the role of providing energy to reduce the chlorination reaction temperature. Its applicable range is wider, and the requirements for equipment and the environment are lower, having obvious advantages.

[0074] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A comprehensive utilization method of coal gangue, characterized in that, It includes the following steps: (1) Coal gangue combustion power generation: Using coal gangue as fuel, it burns in a circulating fluidized bed boiler to generate superheated steam, and the superheated steam drives the steam turbine to rotate for power generation; collecting the combustion ash obtained during the coal gangue combustion process, and the combustion ash includes coal cinder remaining at the bottom of the boiler and fly ash recovered from the flue gas; (2) Carbothermal chlorination: Adding the combustion ash, carbon reducing agent and silicon powder obtained in step (1) into a chlorination reactor, and introducing chlorine gas and hydrogen chloride gas for chlorination reaction. After the reaction, a mixed flue gas and chlorination residue are obtained; (3) Gas-solid separation: A cooling device is provided at the top of the chlorination reactor. The mixed flue gas obtained in step (2) is cooled to 400 - 500 °C by the cooling device, and the flue gas outlet is connected to a cyclone separator and a dust collection device to collect the settled dust; (4) Solid waste utilization: Mixing the chlorination residue obtained in step (2) with the dust collected in step (3), washing with water, recrystallizing the washing solution, and filtering and separating to obtain alkali metal and / or alkaline earth metal chlorides. The water-insoluble filter residue is dried and ground and then added as a raw material into the chlorination reactor for recycling; (5) Gas phase condensation: After gas-solid separation in step (3), the obtained mixed gas A is introduced into a multi-stage condensation system, and through multi-stage condensation, crude products of FeCl3, AlCl3, TiCl4, SiCl4 and SiHCl3 are respectively obtained; (6) Product treatment: Refining and purifying each of the crude products obtained in step (5) to obtain products with a purity higher than 99%. The purified AlCl3 is electrolyzed to obtain high-purity metallic aluminum and chlorine gas, and after drying, the chlorine gas is introduced into the chlorination reactor for recycling; The purified TiCl4 is oxidized with oxygen to obtain TiO2 and chlorine gas, and after drying, the chlorine gas is introduced into the chlorination reactor for recycling; The purified SiCl4 and SiHCl3 are used for preparing high-purity polysilicon; (7) Tail gas recovery and treatment: After multi-stage condensation in step (5), a mixed gas B with a lower boiling point is obtained. After water washing and desorption, Cl2 and HCl are absorbed, and after drying, they are introduced into the chlorination reactor for recycling. The remaining mixed gas C is used for preparing methanol by adding an appropriate amount of H2; 2. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (2), the combustion ash, carbon reducing agent and silicon powder are mixed according to the molar ratio of SiO2 to carbon of 1:(1.5 - 2.5), where SiO2 is the total amount of SiO2 in the combustion ash and carbon reducing agent, and carbon is the total amount of carbon in the combustion ash and carbon reducing agent.

3. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (2), the carbon reducing agent is selected from one or more of activated carbon, petroleum coke, clean coal, and charcoal.

4. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (2), the dosage of silicon powder is 5 - 20 wt% of the total amount of the solid raw material mixture, and the molar ratio of the hydrogen chloride gas to the dosage of silicon powder is (2 - 4):

1.

5. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (2), the chlorination reaction temperature is 500 - 1000 °C, the pressure inside the chlorination reactor is 0.05 - 1 MPa, the flow rate of the mixed gas is 0.01 - 0.5 m / s, and the reaction time is 10 min - 10 h.

6. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, Step (5) The multi-stage condensation system includes the following five stages: the first-stage condensation temperature is 200 - 280 °C, and FeCl3 is separated; the second-stage condensation temperature is 150 - 180 °C, and AlCl3 is separated; the third-stage condensation temperature is 80 - 130 °C, and TiCl4 is separated; the fourth-stage condensation temperature is 35 - 55 °C, and SiCl4 is separated; the fifth-stage condensation temperature is 0 - 30 °C, and SiHCl3 is separated.

7. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (6), the products obtained from the multi-stage condensation system are purified by distillation, and the heat required for distillation can be provided by the steam generated from the combustion of coal gangue.

8. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (6), the electricity required for the electrolysis of AlCl3 can be provided by the electricity generated from the combustion of coal gangue; the heat required for the oxidation of TiCl4 can be provided by the steam generated from the combustion of coal gangue.

9. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (7), the heat required for the preparation of methanol by adding H2 to the mixed gas C can be provided by the steam generated from the combustion of coal gangue.

10. The comprehensive utilization method of coal gangue according to claim 1, characterized in that, In step (7), the absorption solvent for Cl2 and HCl is water, and the solvent after absorbing Cl2 and HCl realizes the desorption of Cl2 and HCl by heating.

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