CN111285628A - Comprehensive utilization method of low-grade magnesite - Google Patents
Comprehensive utilization method of low-grade magnesite Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2/00—Lime, magnesia or dolomite
- C04B2/10—Preheating, burning calcining or cooling
- C04B2/102—Preheating, burning calcining or cooling of magnesia, e.g. dead burning
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/50—Carbon dioxide
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- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D7/00—Carbonates of sodium, potassium or alkali metals in general
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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
- C01F5/24—Magnesium carbonates
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2/00—Lime, magnesia or dolomite
- C04B2/10—Preheating, burning calcining or cooling
- C04B2/108—Treatment or selection of the fuel therefor
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- C05—FERTILISERS; MANUFACTURE THEREOF
- C05D—INORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C; FERTILISERS PRODUCING CARBON DIOXIDE
- C05D7/00—Fertilisers producing carbon dioxide
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
- C10L3/06—Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04
- C10L3/08—Production of synthetic natural gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B1/00—Methods of steam generation characterised by form of heating method
- F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
- F22B1/18—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines
- F22B1/1807—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines using the exhaust gases of combustion engines
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/30—Technologies for a more efficient combustion or heat usage
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
Abstract
The invention provides a comprehensive utilization method of low-grade magnesite, which comprises the following steps: roasting the pretreated low-grade magnesite in a flash kiln; the high-temperature flue gas obtained by roasting is sent to a waste heat boiler to provide heat energy for power generation on one hand, and is used as a combustion improver raw material or other raw materials used by other processes on the other hand; the light calcined powder obtained by roasting is physically selected according to the content of magnesium oxide, and the light calcined powder after material selection and classification is conveyed to a middle-grade kiln, a soda ash process, a light magnesium carbonate manufacturing process and a magnesium wave plate process to be used as production raw materials; reducing carbon dioxide generated by the medium-grade kiln, and sending obtained coal gas to a waste heat boiler to provide heat energy for power generation. The low-grade magnesite comprehensive utilization method provided by the invention has the characteristics of high product quality, very low pollution, very high energy-saving degree, effective utilization of low-grade mineral resources, huge economic benefit and the like, and can be widely applied to the field of mineral products.
Description
Technical Field
The invention relates to the technical field of low-grade magnesite product utilization, in particular to a comprehensive utilization method of low-grade magnesite.
Background
At present, the storage amount of magnesite belonging to special mineral resources is greatly reduced after the magnesite is mined for a long time. Furthermore, for the processing of magnesite, the traditional way is to discard the poor and rich magnesite, which results in a large amount of low-grade magnesite being discarded. The tailings after mineral separation cause resource waste and new pollution, and even invade farmlands or mountain forests. In addition, the traditional process technology is relatively backward, so that the problems of uncontrollable product quality, high labor intensity of operators, poor energy-saving effect and the like exist in the processing process of magnesite.
In the Chinese invention patent with the application number of '201710584845.3' and the name of 'a comprehensive utilization method of low-grade magnesite', the low-grade magnesite crushed and screened by China is modified by adopting a surfactant, and then is directly subjected to chemical reaction with sulfuric acid or hydrochloric acid to prepare magnesium sulfate heptahydrate or magnesium chloride hexahydrate, and carbon dioxide is recycled. Then, coupling a part of carbon dioxide with a soda process to produce sodium bicarbonate and ammonium chloride; and introducing the other part of the carbon dioxide into a solution containing magnesium chloride and ammonia to generate basic magnesium carbonate and ammonium chloride. Reacting ammonium chloride with light calcined powder, and recycling the generated magnesium chloride and the evaporated ammonia gas. And reacting the filtered residue containing the calcium silicate and the light calcined powder with magnesium sulfate heptahydrate to prepare the magnesium oxysulfate cementing material. In a word, the low-grade magnesite comprehensive utilization method enables low-grade magnesite to be applied to a certain degree, but the utilization degree and the utilization rate are still lower; more importantly, the product quality vacancy rate is also lower.
Therefore, in the prior art, the problems of low product quality, serious pollution, large waste and the like exist in the processing process of low-grade magnesite.
Disclosure of Invention
In view of the above, the main object of the present invention is to provide a method for comprehensively utilizing low-grade magnesite, which has high product quality, very low pollution, very high energy saving degree, effective utilization of low-grade mineral resources, and great economic benefits.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a method for comprehensively utilizing low-grade magnesite comprises the following steps:
step 1, in a flash kiln, roasting low-grade magnesite which is subjected to coarse crushing, fine crushing and screening sequentially by using high-temperature coal gas from a reduction furnace as combustible gas and mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain light burning powder and high-temperature flue gas.
Step 2, conveying the high-temperature flue gas to a waste heat boiler; and simultaneously, carrying out physical separation on the light calcined powder: conveying the light calcined powder which is pressed into a ball shape and contains 90 percent and 96 percent of magnesium oxide to a middle-grade kiln for calcination; conveying the light calcined powder with the magnesium oxide content of 85 percent and 90 percent to a soda process; conveying the light calcined powder with the magnesium oxide content of 70 percent and 85 percent to a light magnesium carbonate manufacturing process; and (3) conveying the light calcined powder with the magnesium oxide content of less than 70 percent to the magnesium board process as waste residues.
Step 3, in a middle-grade kiln, calcining light calcined powder which is pressed into a ball shape and has the magnesium oxide content of [ 90%, 96% ] by taking high-temperature coal gas from a reduction furnace as combustible gas and taking mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain high-temperature high-density magnesium oxide balls; introducing cooling flue gas from a carbon dioxide storage tank, cooling the high-temperature high-density magnesium oxide balls, and outputting the cooled high-density magnesium oxide balls; meanwhile, the carbon dioxide generated by the combustion of the cooling flue gas absorbing heat, the combustible gas and the combustion-supporting gas is conveyed to the reduction furnace.
Step 4, in a reduction furnace, carrying out reduction reaction on carbon dioxide from a middle-grade kiln, cooling flue gas absorbing heat and semi-coke, steam and oxygen sprayed into the reduction furnace to generate high-temperature coal gas; one part of high-temperature coal gas is conveyed to the middle-grade kiln and the flash kiln, and the other part of high-temperature coal gas is conveyed to the waste heat boiler.
And 5, respectively carrying out heat exchange on the high-temperature coal gas from the reduction furnace and the high-temperature flue gas from the flash kiln and water in the waste heat boiler, so that the water in the waste heat boiler is changed into high-pressure steam, the high-pressure steam drives a generator set to generate electricity, and the obtained electric energy is used by self or supplied to the outside.
Step 6, the high-temperature coal gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling coal gas; and then, the cooled coal gas is pressurized by a pressurizer and then is sent into a coal gas storage tank.
Step 7, the high-temperature flue gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling flue gas; then, the cooled flue gas is pressurized by a pressurizer and then sent into a carbon dioxide gas storage tank; and one part of the cooling flue gas in the carbon dioxide storage tank is also used as raw material gas for producing soda ash and light magnesium carbonate, one part of the cooling flue gas is conveyed to the flash kiln and the medium-grade kiln, and the other part of the cooling flue gas is supplied to a breeding base.
In summary, in the method for comprehensively utilizing low-grade magnesite, the low-grade magnesite with the magnesium oxide content of 40% -43% which is usually discarded is pretreated and then is conveyed to a flash kiln for roasting, and the obtained high-temperature flue gas is used as a combustion improver material of other process equipment such as a middle-grade kiln, the flash kiln and the like, is used as a production raw material of processes such as soda ash, light magnesium carbonate and the like, is used as a photosynthesis medium for feed planting, is also used as a heat source of a power generation system and the like; and meanwhile, carrying out physical beneficiation on the light calcined powder subjected to full self-decomposition, and respectively conveying the light calcined powder to different processes according to the content of magnesium oxide in the light calcined powder to be used as production raw materials of the different processes. In the method for comprehensively utilizing the low-grade magnesite, the carbon dioxide generated by the medium-grade kiln is reduced by the reduction furnace to generate the coal gas required by the whole system for comprehensively utilizing the low-grade magnesite. Further, in order to fully utilize the high-temperature coal gas obtained by reduction, the high-temperature coal gas and the high-temperature flue gas output by the flash kiln are respectively conveyed to a power generation system to be used as electric power heat sources, and power is generated through a steam turbine, so that the electric energy use in the production process of the whole low-grade magnesite comprehensive utilization system is completely met; meanwhile, the system is connected with the national power grid in a grid mode, the use of users except a low-grade magnesite comprehensive utilization system is met, and the system has great significance for energy conservation and efficiency creation. In practical application, on the basis of light-burned magnesite powder, the low-grade magnesite comprehensive utilization method can save 56 kilograms of standard coal per kilogram of light-burned magnesite powder, and has a huge economic effect. In conclusion, the low-grade magnesite comprehensive utilization method realizes the enrichment and purification of carbon dioxide in the flash kiln, the denitration in the middle-grade kiln, the physical mineral separation, the waste heat power generation, the reduction and reutilization of the carbon dioxide and the cyclic utilization of water, thereby not only ensuring the production and use of the low-grade magnesite comprehensive utilization system, but also being used by other equipment or systems outside the low-grade magnesite comprehensive utilization system; in addition, the comprehensive utilization method of the low-grade magnesite hardly causes gas emission and tailing generation, so that the environmental pollution is hardly caused. Therefore, the comprehensive utilization method of the low-grade magnesite opens up an effective way for effectively utilizing low-grade mineral resources, saving energy, reducing consumption, providing energy, having no environmental pollution and having huge economic benefits.
Drawings
Fig. 1 is a general flow diagram of the low-grade magnesite comprehensive utilization method of the invention.
Fig. 2 is a schematic diagram of a comprehensive utilization process framework of low-grade magnesite according to the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Fig. 1 is a general flow diagram of the low-grade magnesite comprehensive utilization method of the invention. Fig. 2 is a schematic diagram of a comprehensive utilization process framework of low-grade magnesite according to the invention. As shown in fig. 1 and fig. 2, the method for comprehensively utilizing low-grade magnesite according to the present invention includes the following steps:
step 1, in a flash kiln, roasting low-grade magnesite which is subjected to coarse crushing, fine crushing and screening sequentially by using high-temperature coal gas from a reduction furnace as combustible gas and mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain light burning powder and high-temperature flue gas.
In the invention, the low-grade magnesite contains 40-43% of magnesium oxide. The granularity of the screened low-grade magnesite is expressed as (0 mm, 0.5 mm) by a section method. The light calcined powder obtained by flash kiln roasting comprises: fully roasting the light calcined powder and insufficiently roasting the light calcined powder.
In the invention, the high-temperature flue gas discharged by the flash kiln contains carbon dioxide; wherein, the concentration of carbon dioxide in the high-temperature flue gas reaches 95 percent. It can be seen that the flash kiln achieves the enrichment of high concentration carbon dioxide. In practical application, the temperature of high-temperature flue gas discharged by the flash kiln is 900-950 ℃; the temperature of the fully burnt light burning powder discharged from the flash kiln is 800-850 ℃.
In practical application, flash kiln needs fuel for roasting material. The flash kiln has the function of purifying and enriching carbon dioxide on fuel combustion products so as to obtain high-concentration and high-quality carbon dioxide.
Step 2, conveying the high-temperature flue gas to a waste heat boiler; and simultaneously, carrying out physical separation on the light calcined powder: conveying the light calcined powder which is pressed into a ball shape and contains 90 percent and 96 percent of magnesium oxide to a middle-grade kiln for calcination; conveying the light calcined powder with the magnesium oxide content of 85 percent and 90 percent to a soda process; conveying the light calcined powder with the magnesium oxide content of 70 percent and 85 percent to a light magnesium carbonate manufacturing process; and (3) conveying the light calcined powder with the magnesium oxide content of less than 70 percent to the magnesium board process as waste residues.
And 2, performing physical beneficiation on the light calcined powder, and respectively conveying the light calcined powder to different processes according to the content of magnesium oxide in the light calcined powder to be used as production raw materials of the different processes. The method classifies the light calcined powder by adopting a physical ore dressing mode, avoids the procedure of processing ores to the granularity of hundreds of meshes, also avoids tailings caused by chemical ore dressing, and also lightens the ore dressing load. In practical application, tailings bring various defects, such as water consumption, pollution and the like.
Here, the conveying of the light calcined powder with a magnesium oxide content of [ 90%, 96% ] to the intermediate kiln for calcination is specifically: and pressing the part of the light calcined powder into balls, and then conveying the balls into a middle-grade kiln for calcination to generate middle-grade magnesia. The medium magnesia is high-density magnesia. The light calcined powder with the magnesia content of [ 85%, 90%) conveyed to the soda process is used as the raw material for producing soda. The light calcined powder with the magnesia content of 70 percent and 85 percent which is conveyed to the light magnesium carbonate manufacturing process is used as a raw material for producing light magnesium carbonate. The light-burned magnesium powder with the magnesium oxide content lower than 70 percent is taken as waste slag to be conveyed to a magnesium plate production process and taken as a raw material for producing the magnesium plate.
Step 3, in a middle-grade kiln, calcining light calcined powder which is pressed into a ball shape and has the magnesium oxide content of [ 90%, 96% ] by taking high-temperature coal gas from a reduction furnace as combustible gas and taking mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain high-temperature high-density magnesium oxide balls; introducing cooling flue gas from a carbon dioxide storage tank, cooling the high-temperature high-density magnesium oxide balls, and outputting the cooled high-density magnesium oxide balls; meanwhile, the carbon dioxide generated by the combustion of the cooling flue gas absorbing heat, the combustible gas and the combustion-supporting gas is conveyed to the reduction furnace.
In the present invention, the density of the high-density magnesium oxide spheres is 3.9 tons/cubic meter. In practical application, the cooled high-density magnesia ball is medium-grade magnesia.
In practical application, for the combustible gas and the combustion improver which are used as fuels for calcining the light calcined powder in the middle-grade kiln, the combustible gas and the combustion improver do not contain nitrogen, so that nitre which influences the quality of the middle-grade magnesite is not generated in the process of calcining the light calcined powder in the middle-grade kiln. Therefore, denitration in the kiln is realized in the middle-grade kiln in the process of calcining the light calcined powder, and the quality of high-density middle-grade magnesia generated by calcination is improved.
Step 4, in a reduction furnace, carrying out reduction reaction on carbon dioxide from a middle-grade kiln, cooling flue gas absorbing heat and semi-coke, steam and oxygen sprayed into the reduction furnace to generate high-temperature coal gas; one part of high-temperature coal gas is conveyed to the middle-grade kiln and the flash kiln, and the other part of high-temperature coal gas is conveyed to the waste heat boiler.
In the invention, the temperature of the high-temperature coal gas is 800-850 ℃.
In practical application, every 1 standard cubic meter of carbon dioxide is reduced by the reduction furnace, 2.03 standard cubic meters of carbon monoxide can be generated. The carbon monoxide is used as production fuel, so that the fuel required in the production process can be greatly saved.
And 5, respectively carrying out heat exchange on the high-temperature coal gas from the reduction furnace and the high-temperature flue gas from the flash kiln and water in the waste heat boiler, so that the water in the waste heat boiler is changed into high-pressure steam, the high-pressure steam drives a generator set to generate electricity, and the obtained electric energy is used by self or supplied to the outside.
In the invention, in a light-burned magnesia powder production system producing 10 ten thousand tons per year, the generating capacity of the generating set is 10000 kilowatt-hours.
In practical application, condensed water obtained after high-temperature steam is condensed is sent to a water replenishing system of the waste heat boiler for recycling.
Step 6, the high-temperature coal gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling coal gas; and then, the cooled coal gas is pressurized by a pressurizer and then is sent into a coal gas storage tank.
In the invention, the high-temperature coal gas and the cooling coal gas are mixed gas of carbon monoxide, carbon dioxide, hydrogen and impurity gas, and the volume content of the carbon monoxide is 55%, the volume content of the carbon dioxide is 29%, the volume content of the hydrogen is 13% and the volume content of the impurity gas is 3%.
In the invention, the temperature of the high-temperature coal gas flowing out of the waste heat boiler is 240-260 ℃; the temperature of the cooling coal gas is 60 ℃. The preheated hot water is used for the soda process.
In the present invention, other media include water source, air, etc.
Step 7, the high-temperature flue gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling flue gas; then, the cooled flue gas is pressurized by a pressurizer and then sent into a carbon dioxide gas storage tank; and one part of the cooling flue gas in the carbon dioxide storage tank is also used as raw material gas for producing soda ash and light magnesium carbonate, one part of the cooling flue gas is conveyed to the flash kiln and the medium-grade kiln, and the other part of the cooling flue gas is supplied to a breeding base.
In the invention, the combustion improver is carbon dioxide CO2With oxygen O2The mixed gas of (1).
In practical application, carbon dioxide in the cooling flue gas delivered to the breeding base is used as a photosynthesis medium for feed planting.
In the present invention, after step 1 and before step 2, the method further comprises the following steps:
and step A, the insufficiently roasted light calcined powder in the flash kiln falls into a storage bin at the bottom of the flash kiln, and is discharged after being continuously decomposed for 5 hours by utilizing the self waste heat.
And step B, conveying the fully roasted light calcined powder and the high-temperature flue gas to a high-temperature cyclone separator together, and separating the fully roasted light calcined powder and the high-temperature flue gas by the high-temperature cyclone separator to obtain the fully roasted light calcined powder with the granularity of more than 200 meshes.
And C, the separated light calcined powder which is not fully calcined enters an intermediate storage tank, and then is discharged after being continuously decomposed for 4 hours by utilizing the self waste heat.
In practical application, the intermediate storage tank is provided with external heat preservation to ensure the self-decomposition of the light-burned magnesium powder with sufficient combustion.
In practical application, the light burning powder after the self-decomposition is discharged continuously or periodically by a discharging machine, so that the defect that the existing flash kiln needs to be stopped periodically or irregularly to clean accumulated materials in the kiln is overcome. Moreover, the transportation of the light-burned magnesium powder is carried out in a closed channel so as to avoid the pollution of external dust.
In a word, in the comprehensive utilization method of low-grade magnesite, the low-grade magnesite with the magnesium oxide content of 40% -43% which is usually discarded is pretreated and then is conveyed to a flash kiln for roasting, and the obtained high-temperature flue gas is used as a combustion improver material of other process equipment such as a middle-grade kiln, the flash kiln and the like, is used as a production raw material of processes such as soda ash, light magnesium carbonate and the like, is used as a photosynthesis medium for feed planting, is also used as a heat source of a power generation system and the like; and meanwhile, carrying out physical beneficiation on the light calcined powder subjected to full self-decomposition, and respectively conveying the light calcined powder to different processes according to the content of magnesium oxide in the light calcined powder to be used as production raw materials of the different processes. In the method for comprehensively utilizing the low-grade magnesite, the carbon dioxide generated by the medium-grade kiln is reduced by the reduction furnace to generate the coal gas required by the whole system for comprehensively utilizing the low-grade magnesite. Further, in order to fully utilize the high-temperature coal gas obtained by reduction, the high-temperature coal gas and the high-temperature flue gas output by the flash kiln are respectively conveyed to a power generation system to be used as electric power heat sources, and power is generated through a steam turbine, so that the electric energy use in the production process of the whole low-grade magnesite comprehensive utilization system is completely met; meanwhile, the system is connected with the national power grid in a grid mode, the use of users except a low-grade magnesite comprehensive utilization system is met, and the system has great significance for energy conservation and efficiency creation. In practical application, on the basis of light-burned magnesite powder, the low-grade magnesite comprehensive utilization method can save 56 kilograms of standard coal per kilogram of light-burned magnesite powder, and has a huge economic effect. In conclusion, the low-grade magnesite comprehensive utilization method realizes the enrichment and purification of carbon dioxide in the flash kiln, the denitration in the middle-grade kiln, the physical mineral separation, the waste heat power generation, the reduction and reutilization of the carbon dioxide and the cyclic utilization of water, thereby not only ensuring the production and use of the low-grade magnesite comprehensive utilization system, but also being used by other equipment or systems outside the low-grade magnesite comprehensive utilization system; in addition, the comprehensive utilization method of the low-grade magnesite hardly causes gas emission and tailing generation, so that the environmental pollution is hardly caused. Therefore, the comprehensive utilization method of the low-grade magnesite opens up an effective way for effectively utilizing low-grade mineral resources, saving energy, reducing consumption, providing energy, having no environmental pollution and having huge economic benefits.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A comprehensive utilization method of low-grade magnesite is characterized by comprising the following steps:
step 1, in a flash kiln, roasting low-grade magnesite which is subjected to coarse crushing, fine crushing and screening in sequence by taking high-temperature coal gas from a reduction furnace as combustible gas and taking mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain light burning powder and high-temperature flue gas;
step 2, conveying the high-temperature flue gas to a waste heat boiler; and simultaneously, carrying out physical separation on the light calcined powder: conveying the light calcined powder which is pressed into a ball shape and contains 90 percent and 96 percent of magnesium oxide to a middle-grade kiln for calcination; conveying the light calcined powder with the magnesium oxide content of 85 percent and 90 percent to a soda process; conveying the light calcined powder with the magnesium oxide content of 70 percent and 85 percent to a light magnesium carbonate manufacturing process; conveying light calcined powder with the magnesium oxide content of less than 70% to a magnesium board process as waste residues;
step 3, in a middle-grade kiln, calcining light calcined powder which is pressed into a ball shape and has the magnesium oxide content of [ 90%, 96% ] by taking high-temperature coal gas from a reduction furnace as combustible gas and taking mixed gas of cooling flue gas from a carbon dioxide storage tank and oxygen as a combustion improver to obtain high-temperature high-density magnesium oxide balls; introducing cooling flue gas from a carbon dioxide storage tank, cooling the high-temperature high-density magnesium oxide balls, and outputting the cooled high-density magnesium oxide balls; meanwhile, carbon dioxide generated by combustion of the cooling flue gas absorbing heat, combustible gas and combustion-supporting gas is conveyed to a reduction furnace;
step 4, in a reduction furnace, carrying out reduction reaction on carbon dioxide from a middle-grade kiln, cooling flue gas absorbing heat and semi-coke, steam and oxygen sprayed into the reduction furnace to generate high-temperature coal gas; one part of high-temperature coal gas is conveyed to a middle-grade kiln and a flash kiln, and the other part of high-temperature coal gas is conveyed to a waste heat boiler;
step 5, respectively carrying out heat exchange on high-temperature coal gas from the reduction furnace and high-temperature flue gas from the flash kiln and water in the waste heat boiler, so that the water in the waste heat boiler is changed into high-pressure steam, the high-pressure steam drives a generator set to generate electricity, and the obtained electric energy is self-used or supplied outwards;
step 6, the high-temperature coal gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling coal gas; then, the cooled coal gas is pressurized by a pressurizer and then is sent into a coal gas storage tank;
step 7, the high-temperature flue gas flows out of the waste heat boiler after exchanging heat with water in the waste heat boiler, and continuously exchanges heat with other media to obtain cooling flue gas; then, the cooled flue gas is pressurized by a pressurizer and then sent into a carbon dioxide gas storage tank; and one part of the cooling flue gas in the carbon dioxide storage tank is also used as raw material gas for producing soda ash and light magnesium carbonate, one part of the cooling flue gas is conveyed to the flash kiln and the medium-grade kiln, and the other part of the cooling flue gas is supplied to a breeding base.
2. The comprehensive utilization method of low-grade magnesite according to claim 1, wherein the light calcined powder obtained by flash kiln roasting comprises: fully roasting the light calcined powder and insufficiently roasting the light calcined powder.
3. The method for comprehensively utilizing low-grade magnesite according to claim 1, wherein the high-temperature coal gas and the cooling coal gas are mixed gas of carbon monoxide, carbon dioxide, hydrogen and impurity gas, and the volume content of the carbon monoxide is 55%, the volume content of the carbon dioxide is 29%, the volume content of the hydrogen is 13%, and the volume content of the impurity gas is 3%; the temperature of the high-temperature coal gas is 800-850 ℃; the temperature of the high-temperature coal gas flowing out of the waste heat boiler is 240-260 ℃, and the temperature of the cooling coal gas is 60 ℃;
the high-temperature flue gas and the cooling flue gas are mixed gas of carbon dioxide and impurity gas, and the volume content of the carbon dioxide is up to more than 95%;
the combustion improver is a mixed gas of carbon dioxide and oxygen.
4. The method for comprehensively utilizing low-grade magnesite according to claim 2, wherein the temperature of high-temperature flue gas discharged by the flash kiln is 900-950 ℃; the temperature of the fully burnt light burning powder discharged from the flash kiln is 800-850 ℃.
5. The comprehensive utilization method of low-grade magnesite according to claim 1, wherein the particle size of the screened low-grade magnesite is (0 mm, 0.5 mm).
6. The method for comprehensively utilizing low-grade magnesite according to claim 2, wherein after the step 1 and before the step 2, the method further comprises the following steps:
step A, the insufficiently roasted light burning powder in the flash kiln falls into a storage bin at the bottom of the flash kiln, and is discharged after being continuously decomposed for 5 hours by utilizing the self waste heat;
b, conveying the fully roasted light burning powder and the high-temperature flue gas to a high-temperature cyclone separator together, and separating the fully roasted light burning powder and the high-temperature flue gas by the high-temperature cyclone separator to obtain the fully roasted light burning powder with the granularity of more than 200 meshes;
and C, the separated light calcined powder which is not fully calcined enters an intermediate storage tank, and then is discharged after being continuously decomposed for 4 hours by utilizing the self waste heat.
7. The method for comprehensively utilizing low-grade magnesite according to claim 1, wherein in the step 3, the density of the high-density magnesia balls is 3.9 tons/cubic meter.
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