CN112939038A - Method for preparing aluminum oxide by using high-alumina fly ash based on chlorination-oxygen pressure conversion - Google Patents
Method for preparing aluminum oxide by using high-alumina fly ash based on chlorination-oxygen pressure conversion Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/30—Preparation of aluminium oxide or hydroxide by thermal decomposition or by hydrolysis or oxidation of aluminium compounds
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
- C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/08—Compounds containing halogen
- C01B33/107—Halogenated silanes
- C01B33/1071—Tetrachloride, trichlorosilane or silicochloroform, dichlorosilane, monochlorosilane or mixtures thereof
- C01B33/10715—Tetrachloride, trichlorosilane or silicochloroform, dichlorosilane, monochlorosilane or mixtures thereof prepared by reacting chlorine with silicon or a silicon-containing material
- C01B33/10721—Tetrachloride, trichlorosilane or silicochloroform, dichlorosilane, monochlorosilane or mixtures thereof prepared by reacting chlorine with silicon or a silicon-containing material with the preferential formation of tetrachloride
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/08—Compounds containing halogen
- C01B33/107—Halogenated silanes
- C01B33/10778—Purification
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/26—Magnesium halides
- C01F5/30—Chlorides
- C01F5/32—Preparation of anhydrous magnesium chloride by chlorinating magnesium compounds
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/48—Halides, with or without other cations besides aluminium
- C01F7/56—Chlorides
- C01F7/58—Preparation of anhydrous aluminium chloride
- C01F7/60—Preparation of anhydrous aluminium chloride from oxygen-containing aluminium compounds
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/48—Halides, with or without other cations besides aluminium
- C01F7/56—Chlorides
- C01F7/62—Purification
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K3/00—Materials not provided for elsewhere
- C09K3/18—Materials not provided for elsewhere for application to surfaces to minimize adherence of ice, mist or water thereto; Thawing or antifreeze materials for application to surfaces
- C09K3/185—Thawing materials
Abstract
The invention discloses a method for preparing alumina by using high-alumina fly ash based on chlorination-oxygen pressure conversion, which comprises the following steps: pressing high-alumina fly ash and coking coal into pellets according to a proportion, adding the pellets into a moving bed reactor, reacting mullite, alumina, silicon oxide and the like in the high-alumina fly ash with chlorine respectively to generate aluminum chloride, silicon chloride and the like, and reacting magnesium and the like in the high-alumina fly ash with the chlorine to generate magnesium chloride which enters slag; condensing the gas-phase product to obtain aluminum chloride and silicon chloride in turn, wherein the condensed tail gas is mainly unreacted chlorine gas, and compressing to obtain liquid chlorine which is returned to the chlorination process for recycling; introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, introducing oxygen into molten aluminum chloride under certain oxygen pressure to convert the aluminum chloride into aluminum oxide and chlorine, and returning chlorination to the chlorination process for recycling. According to the invention, the high-alumina fly ash is utilized to prepare products such as aluminum oxide, silicon tetrachloride and magnesium chloride slag in a chlorination mode, so that the cleaning treatment of the high-alumina fly ash is realized.
Description
The technical field is as follows:
the invention belongs to the technical field, and particularly relates to a method for preparing alumina by using high-alumina fly ash based on chlorination-oxygen pressure conversion.
Background art:
in China, coal consumption is high, 250-300 kg of fly ash and 20-30 kg of slag can be generated by burning 1t of coal, the total capacity of a thermal power generation machine in China at the end of 2014 reaches 9.16 hundred million kilowatts, and the generated energy reaches 5.78 million tons of fly ash when 41,731 million kilowatts are generated. In 2015, the thermal power generation amount of China accounts for about 73% of the total power generation amount, and the thermal power generation is still the most main power source of China. In 2015, the emission of the fly ash is 6.2 hundred million tons, and the production of the fly ash in China will be maintained at a higher level in the coming years, which is estimated to be 5.6-6.1 hundred million tons/year and is the first place in the world. In 2015, the annual emission amount of high-alumina fly ash (the content of alumina is more than 37%) in China exceeds 3000 million tons, and 140 million tons of high-alumina fly ash can be generated by taking 500 million tons of high-alumina coal resources as an important supplement of bauxite resources in China at present, and the utilization process of the high-alumina fly ash is widely concerned by related practitioners.
In recent years, a great deal of research work is carried out by related practitioners aiming at the efficient and high-value utilization of high-alumina fly ash, and various processes for extracting alumina from fly ash, such as a soda lime sintering method, a limestone sintering method, an acid leaching method, an acid-base combination method and the like, are proposed. But the domestic fly ash aluminum extraction technology has a major breakthrough until 2006. The process for producing cement by limestone sintering developed by Mongolian West high and new technology group company and the process route for extracting alumina and co-producing active calcium silicate by pre-desilication-soda lime sintering developed by China Datang group company aiming at the characteristics of high-alumina fly ash of power plants both enter the industrial or industrial test stage in 2006.
The existing method mostly adopts acid or alkali to extract alumina in the high-alumina fly ash, can generate a large amount of acid and alkaline slag, and has the problem of secondary pollution.
The invention content is as follows:
the invention aims to overcome the defects in the prior art and provide a method for preparing alumina by using high-alumina fly ash based on chlorination-oxygen pressure conversion.
The method for preparing the alumina by utilizing the high-alumina fly ash based on the chlorination-oxygen pressure conversion comprises the following steps:
step 1, mixing materials:
(1) respectively taking high-alumina fly ash and coking coal, wherein the coking coal comprises C and silicon oxide, the high-alumina fly ash comprises aluminum oxide and silicon oxide, and the molar ratio of C: (alumina in the high-alumina fly ash, silicon oxide in the high-alumina fly ash and silicon oxide in the coking coal): 1.5-4
(2) Mixing high-alumina fly ash and coking coal to prepare pellets;
step 2, chlorination reaction:
adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor to perform chlorination reaction to obtain a solid-phase product and a gas-phase product; wherein the chlorine gas introduction amount is theoretical to completely convert aluminum in the high-alumina fly ash into AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl4The amount of the substance is 1.1-2 times of that of the substance, the chlorination reaction temperature is 600-1400 ℃, and the reaction time is 30-150 min; in the chlorination reaction process:
mullite in the high-alumina fly ash reacts with chlorine to generate aluminum chloride, silicon chloride and the like, and magnesium and the like in the high-alumina fly ash react with chlorine to generate magnesium chloride which enters the slag;
step 3, condensation:
firstly, cooling a gas-phase product obtained by chlorination to below 180 ℃ to obtain aluminum chloride; further cooling to below 56 ℃ to obtain a silicon tetrachloride product, pressurizing tail gas to obtain chlorine, compressing the chlorine into liquid chlorine, and returning to the chlorination process for recycling;
step 4, oxygen pressure conversion:
and (2) introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, keeping the oxygen partial pressure in a gas phase at 0.2-5 MPa, keeping the aluminum chloride in a molten state for oxidation reaction, wherein the reaction temperature is 200-1000 ℃, the reaction time is 15-90 min, introducing oxygen into the molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling.
In the step 1(1), the high-alumina fly ash comprises components and Al in percentage by mass2O3 37-52％，MgO≤10％，SiO2 25-60％，Fe2O3Less than or equal to 10 percent, and the balance being impurities.
In the step 1(1), the coking coal comprises 83.6% of C, 4.3% of silicon oxide and the balance of impurities by mass.
In the step 2, the reaction of mullite in the high-alumina fly ash and the like with chlorine in the chlorination process is as follows:
Al6Si2O13+13C+13Cl2＝6AlCl3+2SiCl4+13CO
or Al6Si2O13+6.5C+13Cl2＝6AlCl3+2SiCl4+6.5CO2
In addition, fly ash also contains a portion of alumina and silica, which react with chlorine as follows:
Al2O3+1.5C+3Cl2＝2AlCl3+1.5CO2
Al2O3+3C+3Cl2＝2AlCl3+3CO
SiO2+C+2Cl2＝SiCl4+CO2
SiO2+2C+2Cl2＝SiCl4+2CO
in the step 2, the obtained magnesium chloride slag can be used as a raw material of a snow remover.
In the step 3, the obtained silicon tetrachloride is used as a raw material for producing polycrystalline silicon or high-purity silicon dioxide.
In the step 3, more than 75% of silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride through detection.
In the step 4, the oxygen pressure conversion process is reacted as follows:
4AlCl3+3O2＝2Al2O3+6Cl2
in the step 4, the aluminum chloride is completely converted into aluminum oxide.
The invention has the beneficial effects that:
(1) the process flow is short, and various components such as aluminum, silicon and the like in the high-alumina fly ash are extracted by adopting a direct pellet chlorination mode to obtain aluminum chloride and obtain an aluminum oxide product by direct oxygen pressure conversion;
(2) the method is environment-friendly, acid and alkali are not adopted in the process, and acid-alkali waste residue is not generated;
(3) the conversion efficiency is high, most of mullite alumina in the high-alumina fly ash can be converted into aluminum chloride by adopting a chlorination method, and the extraction efficiency of aluminum is higher than that of methods such as wet extraction;
(4) the comprehensive utilization of the high-alumina fly ash is realized, aluminum and silicon in the high-alumina fly ash enter a gas phase through chlorination, then aluminum chloride and silicon chloride are respectively obtained through condensation and separation, and the silicon chloride can be used as a raw material for preparing polycrystalline silicon or high-purity silicon dioxide; the slag amount of the method is less than 20% of the high-alumina fly ash amount, and the slag mainly contains magnesium chloride and the like, and can be used as a raw material of a snow remover.
Detailed Description
The high-alumina fly ash adopted by the embodiment of the invention mainly contains Al2O3-47.8％，SiO2-42.3％，MgO-1.21％，Fe2O3-3.51% and the balance impurity components;
the coke coal adopted by the embodiment of the invention contains 83.6 percent of C, 4.3 percent of silicon oxide and the balance of impurities;
the embodiment of the invention adopts the high-alumina fly ash, the production content of the invention is not limited to the adoption of the raw materials, and any raw material taking aluminum as a main component can be produced by adopting the technology.
In the following examples, it was determined that 85-95.4% of the aluminum in the high alumina fly ash was converted to aluminum chloride and 75-95% of the silica in the high alumina fly ash and coke was converted to silicon tetrachloride. The process is also suitable for other types of high-alumina fly ash raw materials, and correspondingly can realize the conversion of less than 85% of aluminum into aluminum chloride.
Example 1
Mixing the high-alumina fly ash and the coking coal according to a certain proportion to prepare pellets, wherein the total molar ratio of C in the coking coal to alumina in the high-alumina fly ash and silica in the high-alumina fly ash and the coking coal is 1.5: 1. Adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor, wherein the chlorine introduction amount is theoretical to enable aluminum in the high-alumina fly ash to be completely converted into AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl41.5 times of the amount of the substance(s) in the high-alumina fly ash, at a chlorination temperature of 600 ℃ for 150minThe mullite, the alumina, the silicon oxide and the like respectively react with chlorine to generate aluminum chloride, silicon chloride and the like, and the magnesium and the like in the high-alumina fly ash react with the chlorine to generate magnesium chloride to enter the slag. And (3) cooling a gas-phase product obtained by chlorination to below 180 ℃ to obtain an aluminum chloride product, further cooling to below 56 ℃ to obtain a silicon tetrachloride product, and pressurizing tail gas to obtain chlorine and returning the chlorine to the chlorination process for recycling. Through detection, 85% of aluminum in the high-alumina fly ash is converted into aluminum chloride, and 75% of silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride.
Introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, wherein the oxygen partial pressure in a gas phase is 5MPa, the reaction temperature is 200 ℃, the reaction time is 90min, introducing oxygen into molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling. After the treatment by the method, the aluminum chloride is completely converted into aluminum oxide.
Example 2
Mixing the high-alumina fly ash and the coking coal according to a certain proportion to prepare pellets, wherein the total molar ratio of C in the coking coal to alumina in the high-alumina fly ash and silica in the high-alumina fly ash and the coking coal is 4: 1. Adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor, wherein the chlorine introduction amount is theoretical to enable aluminum in the high-alumina fly ash to be completely converted into AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl4The amount of the substances is 1.2 times of the amount of the substances, the reaction is carried out for 30min at the chlorination temperature of 1400 ℃, mullite, alumina, silicon oxide and the like in the high-alumina fly ash respectively react with chlorine to generate aluminum chloride, silicon chloride and the like, and magnesium and the like in the high-alumina fly ash react with chlorine to generate magnesium chloride which enters the slag. And (3) cooling the gas-phase product obtained by chlorination to below 180 ℃ to obtain an aluminum chloride product, and further cooling to below 56 ℃ to obtain a silicon tetrachloride product. The tail gas is pressurized to obtain chlorine gas, and the chlorine gas is returned to the chlorination process for recycling. After the treatment by the method, 95.6 percent of aluminum in the high-alumina fly ash is converted into aluminum chloride, and 95 percent of silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride.
Introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, wherein the oxygen partial pressure in a gas phase is 0.2MPa, the reaction temperature is 1000 ℃, the reaction time is 15min, introducing oxygen into molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling. After the treatment by the method, the aluminum chloride is completely converted into aluminum oxide.
Example 3
Mixing the high-alumina fly ash and the coking coal according to a certain proportion to prepare pellets, wherein the total molar ratio of C in the coking coal to alumina in the high-alumina fly ash and silica in the high-alumina fly ash and the coking coal is 3: 1. Adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor, wherein the chlorine introduction amount is theoretical to enable aluminum in the high-alumina fly ash to be completely converted into AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl41.4 times of the amount of the substances, reacting at the chlorination temperature of 1000 ℃ for 60min, respectively reacting mullite, alumina, silicon oxide and the like in the high-alumina fly ash with chlorine to generate aluminum chloride, silicon chloride and the like, and reacting magnesium and the like in the high-alumina fly ash with chlorine to generate magnesium chloride to enter the slag. And (3) cooling the gas-phase product obtained by chlorination to below 180 ℃ to obtain an aluminum chloride product, and further cooling to below 56 ℃ to obtain a silicon tetrachloride product. The tail gas is pressurized to obtain chlorine gas, and the chlorine gas is returned to the chlorination process for recycling. After the treatment by the method, 90.2% of aluminum in the high-alumina fly ash is converted into aluminum chloride, and 85.2% of silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride.
Introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, wherein the oxygen partial pressure in a gas phase is 1.5MPa, the reaction temperature is 500 ℃, the reaction time is 30min, introducing oxygen into molten aluminum chloride in the system to convert the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling. After the treatment by the method, the aluminum chloride is completely converted into aluminum oxide.
Example 4
Mixing the high-alumina fly ash and the coking coal according to a certain proportion to prepare pellets, wherein the total molar ratio of C in the coking coal to alumina in the high-alumina fly ash and silica in the high-alumina fly ash and the coking coal is 3.5: 1. Adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor, wherein the introduction amount of the chlorine is theoretical to enable the high-alumina coal to be highComplete conversion of aluminum in ash to AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl4The amount of the substances is 1.4 times of the amount of the substances, the reaction is carried out for 75min at the chlorination temperature of 500 ℃, mullite, alumina, silicon oxide and the like in the high-alumina fly ash are respectively reacted with chlorine to generate aluminum chloride, silicon chloride and the like, and magnesium and the like in the high-alumina fly ash are reacted with chlorine to generate magnesium chloride which enters the slag. And (3) cooling the gas-phase product obtained by chlorination to below 180 ℃ to obtain an aluminum chloride product, and further cooling to below 56 ℃ to obtain a silicon tetrachloride product. The tail gas is pressurized to obtain chlorine gas, and the chlorine gas is returned to the chlorination process for recycling. After the treatment by the method, 88.2% of aluminum in the high-alumina fly ash is converted into aluminum chloride, and 82.0% of silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride.
Introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, wherein the oxygen partial pressure in a gas phase is 2.0MPa, the reaction temperature is 300 ℃, the reaction time is 60min, introducing oxygen into molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling. After the treatment by the method, the aluminum chloride is completely converted into aluminum oxide.
Example 5
Mixing the high-alumina fly ash and the coking coal according to a certain proportion to prepare pellets, wherein the total molar ratio of C in the coking coal to alumina in the high-alumina fly ash and silica in the high-alumina fly ash and the coking coal is 2.5: 1. Adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor, wherein the chlorine introduction amount is theoretical to enable aluminum in the high-alumina fly ash to be completely converted into AlCl3The silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl4The amount of the substances is 1.4 times of the amount of the substances, the reaction is carried out for 45min at the chlorination temperature of 800 ℃, mullite, alumina, silicon oxide and the like in the high-alumina fly ash are respectively reacted with chlorine to generate aluminum chloride, silicon chloride and the like, and magnesium and the like in the high-alumina fly ash are reacted with chlorine to generate magnesium chloride which enters the slag. And (3) cooling the gas-phase product obtained by chlorination to below 180 ℃ to obtain an aluminum chloride product, and further cooling to below 56 ℃ to obtain a silicon tetrachloride product. The tail gas is pressurized to obtain chlorine gas, and the chlorine gas is returned to the chlorination process for recycling. After being treated by the method, 9 in the high-alumina fly ash2.4% of the aluminum is converted into aluminum chloride, and 89.0% of the silicon oxide in the high-alumina fly ash and the coking coal is converted into silicon tetrachloride.
Introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, wherein the oxygen partial pressure in a gas phase is 0.8MPa, the reaction temperature is 800 ℃, the reaction time is 25min, introducing oxygen into molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling. After the treatment by the method, the aluminum chloride is completely converted into aluminum oxide.
Claims (7)
1. The method for preparing the alumina by utilizing the high-alumina fly ash based on the chlorination-oxygen pressure conversion is characterized by comprising the following steps of:
step 1, mixing materials:
(1) respectively taking high-alumina fly ash and coking coal, wherein the coking coal comprises C and silicon oxide, the high-alumina fly ash comprises aluminum oxide and silicon oxide, and the molar ratio of C: (alumina in the high-alumina fly ash, silicon oxide in the high-alumina fly ash and silicon oxide in the coking coal): 1.5-4
(2) Mixing high-alumina fly ash and coking coal to prepare pellets;
step 2, chlorination reaction:
adding the pellets into a moving bed reactor, and introducing chlorine into the moving bed reactor to perform chlorination reaction to obtain a solid-phase product and a gas-phase product; wherein the chlorine gas introduction amount is theoretical to completely convert aluminum in the high-alumina fly ash into AlCl3And the silicon oxide in the high-alumina fly ash and the silicon oxide in the coking coal are completely converted into SiCl4The amount of the substance is 1.1-2 times of that of the substance, the chlorination reaction temperature is 600-1400 ℃, and the reaction time is 30-150 min; in the chlorination reaction process:
the mullite in the high-alumina fly ash reacts with chlorine to generate aluminum chloride and silicon chloride, and the magnesium in the high-alumina fly ash reacts with the chlorine to generate magnesium chloride which enters the slag;
step 3, condensation:
firstly, cooling a gas-phase product obtained by chlorination to below 180 ℃ to obtain aluminum chloride; further cooling to below 56 ℃ to obtain a silicon tetrachloride product, pressurizing tail gas to obtain chlorine, compressing the chlorine into liquid chlorine, and returning to the chlorination process for recycling;
step 4, oxygen pressure conversion:
and (2) introducing aluminum chloride into a pressurized oxygen pressure conversion furnace, keeping the oxygen partial pressure in a gas phase at 0.2-5 MPa, keeping the aluminum chloride in a molten state for oxidation reaction, wherein the reaction temperature is 200-1000 ℃, the reaction time is 15-90 min, introducing oxygen into the molten aluminum chloride in the system, converting the aluminum chloride into aluminum oxide and chlorine, and returning the chlorine to the chlorination process for recycling.
2. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion according to claim 1, wherein in the step 1(1), the high-alumina fly ash comprises components and Al in percentage by mass2O3 37-52％，MgO≤10％，SiO2 25-60％，Fe2O3Less than or equal to 10 percent, and the balance being impurities.
3. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion according to claim 1, wherein in step 1(1), the coking coal comprises C83.6% by weight, 4.3% by weight of silicon oxide and the balance of impurities.
4. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion according to claim 1, wherein the magnesium chloride slag obtained in the step 2 is used as a raw material of a snow removing agent.
5. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion as claimed in claim 1, wherein the silicon tetrachloride obtained in step 3 is used as a raw material for producing polysilicon or high-purity silica.
6. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion as claimed in claim 1, wherein in the step 3, more than 75% of silica in the high-alumina fly ash and the coking coal is detected to be converted into silicon tetrachloride.
7. The method for preparing alumina by using high-alumina fly ash based on chloridization-oxygen pressure conversion according to claim 1, wherein in the step 4, aluminum chloride is completely converted into alumina.
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