CN113621832A - Preparation method of metal magnesium - Google Patents
Preparation method of metal magnesium Download PDFInfo
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- CN113621832A CN113621832A CN202110959296.XA CN202110959296A CN113621832A CN 113621832 A CN113621832 A CN 113621832A CN 202110959296 A CN202110959296 A CN 202110959296A CN 113621832 A CN113621832 A CN 113621832A
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
- C22B26/20—Obtaining alkaline earth metals or magnesium
- C22B26/22—Obtaining magnesium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
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- C22B1/14—Agglomerating; Briquetting; Binding; Granulating
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- C22B1/26—Cooling of roasted, sintered, or agglomerated ores
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B5/00—General methods of reducing to metals
- C22B5/02—Dry methods smelting of sulfides or formation of mattes
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Abstract
The invention discloses a preparation method of metal magnesium, which comprises the following steps: weighing dolomite, a reducing agent and fluorite according to a stoichiometric ratio; grinding the material obtained in the step one, and then drying; step three, sequentially suspending and preheating the materials obtained in the step two, suspending and calcining, suspending and cooling, calcining to obtain a calcined dolomite mixture with the amount of proper reduction being less than or equal to 0.5% and the hydration activity being more than or equal to 29%, and using waste heat generated by suspension calcination as a drying heat source in the step two; step four, mechanically pressing the mixture obtained in the step three to obtain material balls; and step five, heating the pellets obtained in the step four to 1100-1200 ℃, keeping for 8-10 hours under the vacuum condition of 0-14 Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain metal magnesium. The calcined dolomite has high production capacity, the maximum single-line production capacity can reach 10000t/d, and is 6-7 times of the maximum single-line production capacity (1200t/d) of a rotary kiln.
Description
Technical Field
The invention relates to a metal preparation method, in particular to a preparation method of metal magnesium.
Background
In the traditional silicothermic process (Pidgeon process) for producing magnesium metal, dolomite (20-40 mm) is calcined, mixed with ferrosilicon and fluorite, ball-milled and then prepared into pellets, heated in a vacuum furnace at 1100 ℃ for reduction, generated magnesium vapor is condensed and recovered, and then cast into magnesium ingots. The calcination section for producing the metal magnesium dolomite is an important part for preparing the raw materials for smelting magnesium, directly determines the yield of magnesium in the subsequent reduction section, and also influences the energy consumption index of magnesium per ton.
The mixing of the massive calcined dolomite, fluorite and ferrosilicon calcined by the traditional silicothermic method mainly has two modes: one way is to grind the three raw materials respectively and then mix them evenly; the other way is to add the three raw materials into a ball mill after proportioning for mixing and fine grinding. At present, enterprises mostly use the second mixing mode, but the two methods are easy to cause the problem of uneven mixing. There are studies showing fluorite (CaF)2) The existence of the dolomite can accelerate the decomposition of the dolomite, accelerate the calcining speed and shorten the calcining time. When the ferrosilicon powder is heated in the air, the oxidized silicon in the ferrosilicon is mainly simple substance silicon, and the alloy phase in the ferrosilicon does not obviously react with oxygen.
The existing dolomite calcining equipment comprises a rotary kiln, a shaft kiln, a tunnel kiln, a fluidized bed furnace and the like. Low shaft kiln output, uneven calcining zone temperature,The calcination temperature and time are difficult to control, the calcined material or the calcined material is contained, and the hydration activity of calcined dolomite is low; the energy-saving sleeve kiln has high calcined dolomite activity of more than 360ml, low over-calcination rate and low calcined dolomite residual CO2The content is less than 1.5 percent, but the investment is larger compared with the novel energy-saving rotary kiln, which is almost 2 times of that of the rotary kiln.
The energy-saving rotary kiln consists of a rotary kiln, a vertical preheater and a vertical cooler, the energy consumption is greatly improved, the heat consumption is 1300kcal/kg calcined dolomite, the single-line productivity can reach 1200t/d, the energy-saving rotary kiln is the current mainstream process, but due to the adoption of lump material calcination, under-calcination or over-calcination is difficult to avoid, and the control of the calcined dolomite activity is difficult.
In general, in the existing production method of metal magnesium, the mixing degree and the calcination activity of the calcination raw materials need to be further improved, the energy consumption is high, and the method is not beneficial to large-scale production.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention aims to provide the preparation method of the metal magnesium, which can improve the mixing degree of raw materials, improve the calcining activity and reduce the energy consumption of a system.
The technical scheme is as follows: the preparation method of the metal magnesium comprises the following steps:
step one, batching: weighing dolomite, a reducing agent and fluorite according to a stoichiometric ratio;
step two, grinding: feeding the material obtained in the step one into grinding equipment for grinding, and then drying;
step three, calcining: sequentially carrying out suspension preheating, suspension calcining and suspension cooling on the materials obtained in the step two at the temperature of 300-880 ℃, at the temperature of 900-1000 ℃, and calcining to obtain a calcined dolomite mixture with the proper reduction amount of less than or equal to 0.5% and the hydration activity of more than or equal to 29%, wherein waste heat of waste gas generated by suspension calcining is used as a drying heat source in the step two;
step four, pressing the ball: mechanically pressing the mixture obtained in the step three to obtain material balls;
step five, vacuum high-temperature reduction: and heating the pellets obtained in the step four to 1100-1200 ℃, keeping for 8-10 hours under the vacuum condition of 0-14 Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
Further, in the first step, the reducing agent is any one of ferrosilicon, aluminum silicon and silicon-calcium alloy, and since the reducing agent is required to have low oxidizing property at 1000 ℃ or lower by the mixed calcination process, the ferrosilicon is preferably ferrosilicon having a silicon content of 45% or less.
In the first step, the particle size of dolomite is 1-45 microns, the particle size of the reducing agent is 1-50 microns, and the particle size of fluorite is 1-40 microns. 77-83 parts of dolomite, 15-20 parts of reducing agent and 1-3 parts of fluorite.
Further, in the second step, the discharged material after grinding has a particle size of 80 μm and the screen residue is 5-15%. The drying temperature is 200-250 ℃. And the drying gas source is waste gas at a kiln tail waste heat power generation outlet of the calcining section. The waste gas at the outlet of the mill is discharged after dust removal reaches the standard, and the raw materials with good running-in quality are discharged and sent to a storage.
And in the second step, a final grinding system of a roller press is adopted for raw material grinding, the raw material grinding system utilizes waste gas at the outlet of the preheater as a drying heat source of the raw material, and the raw material prepared according to the control requirement is conveyed to a feeding port of the V-shaped powder concentrator by a belt conveyor to enter the system. And conveying the materials extruded by the roller press into a V-shaped powder concentrator through a bucket elevator for primary selection, and conveying the V-shaped selected large blocks and coarse-grained materials to the roller press through a bucket for extrusion and crushing again. The V-outlet separation airflow carries the crushed materials into a finished product powder separator, the separated coarse materials return to a roller press for circular extrusion crushing, and fine powder meeting the requirements of raw materials is carried into a cyclone cylinder along with the separation airflow for separation. Raw materials are collected by a cyclone and are conveyed to a raw material warehouse through an air conveying chute and a bucket elevator; and the waste gas from the cyclone cylinder is discharged by a grinding circulating fan, one part of the waste gas is circulated to a V-shaped air selecting inlet to supplement the sorting airflow, and the other part of the waste gas is purified by a kiln tail bag dust remover and then is discharged into the atmosphere by the fan.
The heat and mass transfer efficiency of the fine powder is far better than that of lump material, and the fluorite (CaF)2) The existence of the dolomite can accelerate the decomposition of the dolomite, accelerate the calcining rate and shorten the calcining time, so that the mixed fine raw materials are beneficial to reducing the heat consumption of system sintering. Is different from the traditional silicon thermal methodAnd (3) calcining the marble lump material (20-50 mm) and then grinding the marble lump material together with the ferrosilicon and fluorite.
Further, in the third step, the suspension preheating is carried out through 3-5 cyclone preheaters, connecting air pipes and preheating pipes which are connected in series from top to bottom. The temperature of the last stage of the preheating pipe is 800-880 ℃. The pressure loss of suspension preheating is 3000 Pa-5000 Pa. The pressure loss of the suspension cooling is 2000-3000 Pa.
In the third step, the suspension preheating device is an N-stage heat exchange system consisting of N cyclone preheaters connected in series from top to bottom, a connecting air pipe, a material pipe and a spreading box. The mineral powder charging port is arranged on a gas inlet pipeline of the first cyclone, and a material outlet of the N-1 level cyclone is connected with a material inlet of the suspension calciner; and a gas outlet at the top of the calcining furnace is connected with a gas inlet of the Nth cyclone. N may be any of 2 to 4 stages. The outlet exhaust gas temperature can be adjusted by controlling the number of N.
The suspension calcining furnace in the third step is particularly suitable for calcining fine powder. Compared with the heat exchange rate of 5.8-45 ℃/min of the rotary kiln, the heat exchange rate of the suspension state can reach 1000 ℃/min. The calcining temperature is 1200 ℃ and the time is 20-40 min compared with the calcining temperature of the traditional rotary kiln process, and the calcining decomposition time of the raw material powder only needs 6-10 s when the temperature in the suspension furnace is 900-1000 ℃. The production capacity of the kiln can be 10000 t/d. A suspension calcining furnace is a spray-spinning combined pipeline type decomposing furnace. The calcining furnace adopts two-stage spray rotation, which is beneficial to improving the uniformity of the retention time of materials in the furnace and reducing the back mixing degree of the materials in the furnace. The calcining furnace adopts an online arrangement, and does not have thermal NO formed by high-temperature calcination in a rotary kilnxGas, and NO added to the furnace bottomxA reduction control zone of low NOxAnd (3) a calcination process.
In the third step, the suspension cooling device is an N-stage heat exchange system consisting of N cyclone coolers, connecting air pipes, material pipes and material scattering boxes which are connected in series from top to bottom. The feeding pipe of the Nth stage suspension preheater is connected with the gas inlet pipeline of the first stage suspension cooling cylinder, and the gas outlet of the first stage cyclone cooling cylinder is connected with the cone of the suspension calciner. And the outlet of the blanking pipe of the Nth-stage suspension cooler is connected with finished product conveying equipment. N may be any of 3 to 5 stages. The temperature of the waste gas at the outlet of the uppermost stage cyclone of the suspension cooling device is 550-700 ℃, and the waste gas is removed from the suspension calcining furnace to be used as combustion-supporting gas; the material discharging temperature of the last stage cyclone of the suspension cooling device is 50-150 ℃, and can be controlled according to requirements.
The preparation principle is as follows: after the raw materials are ground, the heat and mass transfer efficiency of the fine powder is far better than that of lump materials, and the existence of fluorite can accelerate the decomposition of dolomite, so that the calcination speed is accelerated, and the calcination time is shortened, therefore, the mixed fine raw materials are beneficial to reducing the heat consumption of system calcination. The suspension calcination adopts two-stage spray spinning, which is beneficial to improving the uniformity of the retention time of the materials in the furnace and reducing the back mixing degree of the materials in the furnace. Suspension preheating, suspension calcining and suspension cooling, and the conventional accumulation state of the materials is changed into the suspension state, so that the gas-solid contact area is obviously increased, the heat transfer process is obviously enhanced, and the reaction speed is accelerated.
The pyrolysis process of dolomite can be divided into five steps: four physical transfer processes, including heat transfer from the surrounding medium to the particle surface, heat conduction in the particle decomposition layer, decomposition reaction of the particle inner layer, diffusion of decomposed CO2 out of the decomposition layer, diffusion of CO2 on the particle surface to the gas stream, and a chemical kinetic process. The heat transfer rate of the materials preheated in the rotary kiln is 5.8 ℃/min, the heat transfer rate of the suspension preheating is about more than 1000 ℃/min, and the materials are subjected to suspension heat exchange in a suspension state for only 0.01-0.1 s. Namely, in a suspension state reaction state, the time required for decomposing dolomite mainly depends on the chemical reaction rate, namely, the chemical decomposition step process, and the chemical decomposition step process is in direct proportion to the particle size diameter.
And the fluorite and other additives are non-surface active substances, so that the reaction energy on the surface can be increased during the reaction, the reaction is easier to carry out, the decomposition of dolomite can be accelerated, and the decomposition temperature of the carbonate after the fluorite is added can be reduced by 45 ℃ compared with that when the fluorite is not added. The reduction of the calcination decomposition temperature and the reduction of the calcination time can effectively prevent the activity reduction caused by the overburning of the surface of the dolomite. Therefore, the time required for the product obtained by suspension calcination of the fine powder to reach the same amount of reduction and hydration activity is obviously shortened, the heat exchange efficiency is high, the production efficiency is improved, and the energy consumption is low.
Has the advantages that: compared with the prior art, the invention has the following remarkable characteristics:
1. the suspension preheating, suspension calcining and suspension cooling processes are adopted, the overall heat exchange efficiency is high, the energy consumption is low, the calcining heat consumption is 1100kcal/kg, and the energy is saved by 15 percent compared with that of the rotary kiln process;
2. the thermal regulation of mixed material grinding and suspension conveying is adopted to contribute to the mixing degree and uniformity of the three materials, ensure the uniformity of the mixed materials in the reduction furnace and ensure the reduction rate of magnesium;
3. the process of feeding fluorite and dolomite into a furnace together for calcination is beneficial to improving the decomposition speed of the dolomite and reducing the decomposition heat;
4. the method provided by the invention has the advantages that the system production capacity is large, the maximum single-line production capacity can reach 10000t/d, and is 6-7 times of the maximum single-line production capacity (1200t/d) of the rotary kiln.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a schematic structural diagram of the suspension preheating device of the present invention;
FIG. 3 is a schematic diagram of the structure of the suspension calciner of the invention;
fig. 4 is a schematic structural diagram of the suspension cooling device of the present invention.
Detailed Description
The raw materials and the apparatus used in the following examples were all available.
Example 1
Referring to fig. 1, a method for preparing magnesium metal comprises the following steps:
a. preparing materials: mixing materials according to the mol ratio of Si/2MgO to 1.2, weighing 77 parts of dolomite, 15 parts of reducing agent ferrosilicon and 1 part of fluorite, wherein the silicon content is less than 45%, the grain diameter of the dolomite is 1 micron, the grain diameter of the reducing agent is 1 micron, and the grain diameter of the fluorite is 1 micron;
b. grinding: b, feeding the material obtained in the step a into grinding equipment for grinding, drying at 200 ℃, discharging the material with the granularity of 80 mu m and the surplus of 5 percent after grinding, wherein a drying gas source is waste gas at a kiln tail waste heat power generation outlet of a calcination working section, the waste gas at the outlet of a grinding machine is discharged after dust removal reaches the standard, and the discharged grinding qualified raw material is fed into a storage;
c. and (3) calcining: b, sequentially carrying out suspension preheating on the materials obtained in the step b at 300 ℃, wherein the last stage of the material pipe temperature is 850 ℃, the pressure loss is 3000Pa, the suspension calcination is carried out for 8s at 900 ℃, the suspension cooling is carried out at 50 ℃, the temperature of the waste gas at the outlet of the uppermost stage cyclone cylinder of the suspension cooling device is 550 ℃, the waste gas removed from the suspension calciner is used as combustion-supporting gas, the pressure loss is 2000Pa, the blanking temperature of the last stage cyclone cylinder of the suspension cooling device is 50 ℃, the calcined mixture with the appropriate reduction amount of less than or equal to 0.5 percent and the hydration activity degree of more than or equal to 29 percent is obtained by calcination, the waste gas waste heat (320 ℃) generated by the suspension calcination is sent to waste heat power generation equipment to be used for reducing the waste gas to 250 ℃, and is conveyed to the step b by a pipeline to be used as a drying heat source; by controlling the admission of NOxRaw fuel proportion control decomposition furnace outlet NO of control areaxConcentration;
d. pressing the ball: c, conveying the mixture obtained in the step c into ball pressing equipment for mechanical ball pressing to obtain material balls;
e. vacuum high-temperature reduction: and d, heating the material balls obtained in the step d to 1100 ℃, keeping for 8 hours under the vacuum condition of 0Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
Example 2
A preparation method of metal magnesium comprises the following steps:
a. preparing materials: preparing materials according to the mol ratio of Si/2MgO to 1.2, weighing 83 parts of dolomite, 20 parts of aluminum silicon serving as a reducing agent and 3 parts of fluorite, wherein the silicon content is below 45 percent, the grain diameter of the dolomite is 45 microns, the grain diameter of the reducing agent is 50 microns, and the grain diameter of the fluorite is 40 microns;
b. grinding: b, feeding the material obtained in the step a into grinding equipment for grinding, drying at 250 ℃, discharging the material with the granularity of 80 mu m and the screen residue of 15 percent after grinding, wherein a drying gas source is waste gas at a kiln tail waste heat power generation outlet of a calcination working section, the waste gas at the outlet of a grinding machine is discharged after dust removal reaches the standard, and the discharged grinding qualified raw material is fed into a storage;
c. and (3) calcining: b, suspension preheating the materials obtained in the step b at 880 ℃, wherein the last stage of the material pipe temperature is 880 ℃, the pressure loss is 5000Pa, the suspension calcination is carried out at 1000 ℃ for 8s, the suspension cooling is carried out at 700 ℃, and a suspension cooling deviceThe temperature of the waste gas at the outlet of the uppermost stage cyclone is 700 ℃, the waste gas is taken as combustion-supporting gas by a suspension calciner, the pressure loss is 3000Pa, the blanking temperature of the last stage cyclone of the suspension cooling device is 150 ℃, calcined mixture with the proper decrement of less than or equal to 0.5 percent and the hydration activity of more than or equal to 29 percent is obtained by calcination, the waste gas waste heat (320 ℃) generated by suspension calcination enters waste heat power generation equipment and is utilized and reduced to 250 ℃, and the waste gas waste heat is conveyed to the step b by a pipeline to be used as a drying heat source; by controlling the admission of NOxRaw fuel proportion control decomposition furnace outlet NO of control areaxConcentration;
d. pressing the ball: c, conveying the mixture obtained in the step c into ball pressing equipment for mechanical ball pressing to obtain material balls;
e. vacuum high-temperature reduction: and d, heating the material balls obtained in the step d to 1200 ℃, keeping for 10 hours under the vacuum condition of 14Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
Example 3
A preparation method of metal magnesium comprises the following steps:
a. preparing materials: proportioning according to the mol ratio of Si/2MgO to 1.2, weighing 80 parts of dolomite, 17 parts of reducing agent silicon calcium and 2 parts of fluorite, wherein the silicon content is below 45 percent, the grain diameter of the dolomite is 23 microns, the grain diameter of the reducing agent is 25 microns, and the grain diameter of the fluorite is 20 microns;
b. grinding: b, feeding the material obtained in the step a into grinding equipment for grinding, drying at 225 ℃, discharging the material with the granularity of 80 mu m and the surplus of 10 percent after grinding, wherein a drying gas source is waste gas at a kiln tail waste heat power generation outlet of a calcination working section, the waste gas at the outlet of a grinding machine is discharged after dust removal reaches the standard, and the discharged grinding qualified raw material is fed into a storage;
c. and (3) calcining: b, suspension preheating the materials obtained in the step b at 600 ℃, wherein the last stage of the material pipe temperature is 800 ℃, the pressure loss is 4000Pa, the suspension calcination is carried out for 8s at 950 ℃, the suspension cooling is carried out at 350 ℃, the temperature of the waste gas at the outlet of the uppermost stage cyclone cylinder of the suspension cooling device is 600 ℃, the de-suspension calciner is used as combustion-supporting gas, the pressure loss is 2500Pa, the blanking temperature of the last stage cyclone cylinder of the suspension cooling device is 100 ℃, the calcination is carried out to obtain calcined lime mixture with the appropriate reduction amount of less than or equal to 0.5 percent and the hydration activity of more than or equal to 29 percent, and the waste heat (320 ℃) generated by the suspension calcination is fed into a waste heat power generation deviceC, reducing the temperature to 250 ℃ for standby application, and conveying the obtained product to the step b by using a pipeline to be used as a drying heat source; by controlling the admission of NOxRaw fuel proportion control decomposition furnace outlet NO of control areaxConcentration;
d. pressing the ball: c, conveying the mixture obtained in the step c into ball pressing equipment for mechanical ball pressing to obtain material balls;
e. vacuum high-temperature reduction: and d, heating the material balls obtained in the step d to 1150 ℃, keeping for 9 hours under the vacuum condition of 7Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
Example 4
A preparation method of metal magnesium comprises the following steps:
a. preparing materials: mixing according to the mol ratio of Si/2MgO to 1.2, weighing 78 parts of dolomite, 18 parts of reducing agent ferrosilicon and 2 parts of fluorite, wherein the silicon content is below 45 percent, the grain diameter of the dolomite is 15 microns, the grain diameter of the reducing agent is 15 microns, and the grain diameter of the fluorite is 10 microns;
b. grinding: b, feeding the material obtained in the step a into grinding equipment for grinding, drying at 210 ℃, discharging the material with the granularity of 80 mu m and the oversize residue of 7 percent after grinding, wherein a drying gas source is waste gas at a kiln tail waste heat power generation outlet of a calcination working section, the waste gas at the outlet of a grinding machine is discharged after dust removal reaches the standard, and the discharged grinding qualified raw material is fed into a storage warehouse;
c. and (3) calcining: b, sequentially carrying out suspension preheating on the materials obtained in the step b at 500 ℃, wherein the last stage of the material pipe temperature is 870 ℃, the pressure loss is 3500Pa, the suspension calcination is carried out for 8s at 970 ℃, the suspension cooling is carried out at 200 ℃, the temperature of the waste gas at the outlet of the uppermost stage cyclone cylinder of the suspension cooling device is 650 ℃, the de-suspension calciner is used as combustion-supporting gas, the pressure loss is 2200Pa, the blanking temperature of the last stage cyclone cylinder of the suspension cooling device is 120 ℃, the calcined mixture is calcined to obtain calcined white mixture with the appropriate reduction amount of less than or equal to 0.5 percent and the hydration activity of more than or equal to 29 percent, the waste gas waste heat (320 ℃) generated by the suspension calcination is sent to waste heat power generation equipment to be utilized and reduced to 250 ℃, and is conveyed to the step b by a pipeline to be used as a drying heat source; by controlling the admission of NOxRaw fuel proportion control decomposition furnace outlet NO of control areaxConcentration;
d. pressing the ball: c, conveying the mixture obtained in the step c into ball pressing equipment for mechanical ball pressing to obtain material balls;
e. vacuum high-temperature reduction: and d, heating the material balls obtained in the step d to 1130 ℃, keeping the temperature for 8.5 hours under the vacuum condition of 3Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
Example 5
A preparation method of metal magnesium comprises the following steps:
a. preparing materials: proportioning according to the molar ratio of Si/2MgO to 1.2, weighing 81 parts of dolomite, 16 parts of reducing agent silico-calcium and 3 parts of fluorite, wherein the silicon content is below 45%, the grain diameter of the dolomite is 32 microns, the grain diameter of the reducing agent is 35 microns, and the grain diameter of the fluorite is 30 microns;
b. grinding: b, feeding the material obtained in the step a into grinding equipment for grinding, drying at 240 ℃, discharging the material with the granularity of 80 mu m and the surplus of 13 percent after grinding, wherein a drying gas source is waste gas at a kiln tail waste heat power generation outlet of a calcination working section, the waste gas at the outlet of a grinding machine is discharged after dust removal reaches the standard, and the discharged grinding qualified raw material is fed into a storage;
c. and (3) calcining: b, sequentially carrying out suspension preheating on the materials obtained in the step b at 700 ℃, wherein the last stage of the temperature of a material pipe is 820 ℃, the pressure loss is 4500Pa, the suspension calcination is carried out for 8s at 920 ℃, the suspension cooling is carried out at 500 ℃, the temperature of the waste gas at the outlet of the uppermost stage cyclone cylinder of the suspension cooling device is 570 ℃, the defluxing calciner is used as combustion-supporting gas, the pressure loss is 2700Pa, the blanking temperature of the last stage cyclone cylinder of the suspension cooling device is 80 ℃, the calcined mixture with the appropriate decrement of less than or equal to 0.5 percent and the hydration activity of more than or equal to 29 percent is obtained, the waste heat (320 ℃) generated by the suspension calcination is sent to a waste heat power generation device to be used for reducing the waste heat to 250 ℃, and is conveyed to the step b by a pipeline to be used as a drying heat source; by controlling the admission of NOxRaw fuel proportion control decomposition furnace outlet NO of control areaxConcentration;
d. pressing the ball: c, conveying the mixture obtained in the step c into ball pressing equipment for mechanical ball pressing to obtain material balls;
e. vacuum high-temperature reduction: and d, heating the material balls obtained in the step d to 1170 ℃, keeping for 9.5 hours under the vacuum condition of 11Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain the metal magnesium.
The maximum single line production capacity can reach 10000t/d, which is 6-7 times of the maximum single line production capacity (1200t/d) of the rotary kiln.
In the step b, the raw material grinding system utilizes waste gas at the outlet of the preheater as a drying heat source of the raw material, and the raw material prepared according to the control requirement is conveyed to a feeding port of the V-shaped powder concentrator by a belt conveyor to enter the system. And conveying the materials extruded by the roller press into a V-shaped powder concentrator through a bucket elevator for primary selection, and conveying the V-shaped selected large blocks and coarse-grained materials to the roller press through a bucket for extrusion and crushing again. The V-outlet separation airflow carries the crushed materials into a finished product powder separator, the separated coarse materials return to a roller press for circular extrusion crushing, and fine powder meeting the requirements of raw materials is carried into a cyclone cylinder along with the separation airflow for separation. Raw materials are collected by a cyclone and are conveyed to a raw material warehouse through an air conveying chute and a bucket elevator; and the waste gas from the cyclone cylinder is discharged by a grinding circulating fan, one part of the waste gas is circulated to a V-shaped air selecting inlet to supplement the sorting airflow, and the other part of the waste gas is purified by a kiln tail bag dust remover and then is discharged into the atmosphere by the fan.
Referring to fig. 2, the suspension preheating device in step c is an N-stage heat exchange system composed of N cyclone preheaters, connecting air pipes, material pipes and spreading boxes connected in series from top to bottom. The mineral powder charging port is arranged on a gas inlet pipeline of the first cyclone, and a material outlet of the N-1 level cyclone is connected with a material inlet of the suspension calciner; and a gas outlet at the top of the calcining furnace is connected with a gas inlet of the Nth cyclone. N may be any of 2 to 4 stages. The outlet exhaust gas temperature can be adjusted by controlling the number of N.
Referring to FIG. 3, the suspension calciner in step c is a jet-swirl combined duct type decomposing furnace. The suspension calcining furnace adopts two-stage spray rotation, is favorable for improving the uniformity of the retention time of materials in the furnace and reducing the back mixing degree of the materials in the furnace. The calcining furnace adopts an online arrangement, and does not have thermal NO formed by high-temperature calcination in a rotary kilnxGas, and NO added to the furnace bottomxThe reduction control zone is a low NOx calcination process.
As shown in fig. 4, the suspension cooling device is an N-stage heat exchange system composed of N cyclone coolers, connecting air pipes, material pipes and spreading boxes connected in series from top to bottom. The feeding pipe of the Nth stage suspension preheater is connected with the gas inlet pipeline of the first stage suspension cooling cylinder, and the gas outlet of the first stage cyclone cooling cylinder is connected with the cone of the suspension calciner. And the outlet of the blanking pipe of the Nth-stage suspension cooler is connected with finished product conveying equipment. N may be any of 3 to 5 stages.
Claims (10)
1. The preparation method of the metal magnesium is characterized by comprising the following steps:
weighing dolomite, a reducing agent and fluorite according to a stoichiometric ratio;
grinding the material obtained in the step one, and then drying;
step three, sequentially carrying out suspension preheating, suspension calcining and suspension cooling on the materials obtained in the step two at the temperature of 300-880 ℃, at the temperature of 900-1000 ℃, and at the temperature of 50-700 ℃, calcining to obtain a calcined dolomite mixture with the proper reduction amount of less than or equal to 0.5% and the hydration activity of more than or equal to 29%, wherein waste heat of waste gas generated by suspension calcining is used as a drying heat source in the step two;
step four, mechanically pressing the mixture obtained in the step three to obtain material balls;
and step five, heating the pellets obtained in the step four to 1100-1200 ℃, keeping for 8-10 hours under the vacuum condition of 0-14 Pa, reducing magnesium oxide into magnesium vapor, and condensing to obtain metal magnesium.
2. The method for preparing metallic magnesium according to claim 1, wherein: in the first step, the reducing agent is any one of ferrosilicon, aluminum silicon and silicon-calcium alloy.
3. The method for preparing metallic magnesium according to claim 1, wherein: in the first step, the particle size of dolomite is 1-45 microns, the particle size of the reducing agent is 1-50 microns, and the particle size of fluorite is 1-40 microns.
4. The method for preparing metallic magnesium according to claim 1, wherein: in the first step, the dolomite is 77-83 parts by weight, the reducing agent is 15-20 parts by weight, and the fluorite is 1-3 parts by weight.
5. The method for preparing metallic magnesium according to claim 1, wherein: in the second step, the discharged material after grinding has a particle size of 80 μm and the screen residue is 5-15%.
6. The method for preparing metallic magnesium according to claim 1, wherein: in the second step, the drying temperature is 200-250 ℃.
7. The method for preparing metallic magnesium according to claim 1, wherein: and in the third step, suspension preheating is carried out through 3-5 cyclone preheaters, connecting air pipes and preheating pipes which are connected in series from top to bottom.
8. The method for preparing magnesium metal according to claim 7, wherein: in the third step, the temperature of the last stage of the material pipe is 800-880 ℃.
9. The method for preparing metallic magnesium according to claim 1, wherein: in the third step, the pressure loss of suspension preheating is 3000 Pa-5000 Pa.
10. The method for preparing metallic magnesium according to claim 1, wherein: and in the third step, the pressure loss of the suspension cooling is 2000-3000 Pa.
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Application publication date: 20211109 |