CN112250323B - Method for preparing sintered magnesia from powdery magnesite by one-step method - Google Patents
Method for preparing sintered magnesia from powdery magnesite by one-step method Download PDFInfo
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- CN112250323B CN112250323B CN202011094774.7A CN202011094774A CN112250323B CN 112250323 B CN112250323 B CN 112250323B CN 202011094774 A CN202011094774 A CN 202011094774A CN 112250323 B CN112250323 B CN 112250323B
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- magnesite
- reburning
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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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- 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
- C04B2/12—Preheating, burning calcining or cooling in shaft or vertical furnaces
Abstract
A one-step process for preparing sintered magnesite from powdered magnesite includes such steps as pretreating magnesite, preheating, reburning, recovering heat, recovering CO2Trapping, flue gas purification and the like. The core of the methodThe idea is small particle size magnesite heat transfer and CO2The discharging is faster, and the problems that blocky magnesite used in the traditional shaft kiln and the electric melting furnace is difficult to transfer heat, the external temperature is higher than the internal temperature, so that the external crystal form is firstly converted into a compact structure, and the internal gas is difficult to discharge are solved. The method utilizes the characteristics of high heat exchange rate of the fluidized bed/moving bed, high yield, uniform heating of particles and the like, greatly reduces the reburning temperature and shortens the reburning time compared with the traditional reburning technology, thereby improving the treatment capacity of the system and reducing the production cost of the sintered magnesia. Moreover, the method also solves the problem that the powder magnesite cannot be used in the traditional shaft kiln and electric melting furnace process, and improves the utilization rate of magnesite resources.
Description
Technical Field
The invention relates to a method for preparing sintered magnesia, in particular to a method for preparing sintered magnesia from powder magnesite by a one-step method.
Background
Magnesite is a mineral resource composed of magnesium carbonate as a main mineral, the storage capacity of magnesite in China is about 30 hundred million tons, the magnesite is the first in the world and is mainly distributed in Liaoning and Shandong provinces, and Liaoning accounts for more than 90 percent. The products of magnesite after calcination and melting at different temperatures include light-burned magnesia, heavy-burned magnesia and electric-melted magnesia. Among them, dead burned magnesia (also called sintered magnesia) is an important refractory material raw material, widely used in high temperature industries such as ferrous metallurgy, building materials, non-ferrous metal metallurgy, etc., accounting for more than 40% of the whole magnesia refractory material, and the quality of the refractory material plays a key role in the technical development of the high temperature industries such as steel. Wherein the MgO mass fraction is more than 99 percent (domestic general means that the MgO mass fraction is more than 98 percent), and the volume density is more than 3.30g/cm3The sintered magnesia is also called high-purity magnesia.
The high-purity magnesite has a melting point as high as 2825 ℃, has good high temperature resistance, corrosion resistance and heat preservation characteristics, is a refractory material with excellent performance, and is widely applied to various fields and industries such as steel, metallurgy, building materials, national defense, medical appliances, cement, glass and the like. In recent years, with the progress of smelting technology in the steel and metallurgy industries, higher requirements on the yield and quality of high-purity magnesite are also put forward.
The high-purity magnesite can be produced by adopting a two-step calcining process of light burning, fine grinding, high-pressure ball pressing and dead burning of magnesite. At present, the production process of high-purity magnesite in China adopts high-quality magnesite as a raw material, after the magnesite is lightly burned by a reverberatory furnace taking coal gas as fuel, the lightly burned magnesite powder is finely ground into powder, the ball is pressed by a high-pressure ball press in a dry method, and finally the high-purity magnesite is calcined in a high-temperature shaft kiln taking heavy oil as fuel. The high-grade high-purity magnesite can be produced by improving the purity of magnesium oxide through a flotation process, lightly burning the magnesia by a multi-layer furnace and calcining the magnesia in a vertical kiln at high temperature by taking liquefied natural gas as fuel. However, the technology has high requirement on the quality of magnesite raw materials, only blocky high-quality raw materials can be used, a large amount of powdery and low-quality magnesite resources are wasted, the temperature required by the reburning in the shaft kiln is high, the time is long, the energy consumption is high, the yield of dry-method ball pressing equipment is low, and the dust pollution is serious.
Therefore, it is necessary to develop a preparation method of sintered magnesia with good raw material adaptability, environmental protection, low energy consumption and high reburning efficiency.
Disclosure of Invention
The invention aims to provide a method for preparing sintered magnesite by a one-step method from powdery magnesite, which solves the problem that the traditional sintered magnesite preparation method has strict requirements on the quality and granularity of magnesite, reduces the calcining temperature required by preparing the sintered magnesite from the magnesite, shortens the calcining time, and improves the calcining efficiency, thereby improving the resource utilization rate of the magnesite and promoting the technical upgrading of the magnesite industry in China. .
The purpose of the invention is realized by the following technical scheme:
a method for preparing sintered magnesite from powdered magnesite by a one-step method comprises the following preparation processes: the powder magnesite is sequentially subjected to preheating, reburning, heat recovery, separation and purification and flue gas purification treatment to prepare a sintered magnesite product in one step; the raw material is prepared by crushing natural powder or blocky magnesite, or magnesite light-burned powder is directly used as a heavy-burned raw material; the preheating is to preheat the magnesite raw material by using high-temperature flue gas after the reburning; the reburning is to use fluidized bed/moving bed to preheat the powder magnesiteRe-burning the ore to convert the crystal form of the ore so as to prepare high-purity sintered magnesia; the heat recovery is to cool the sintered magnesia in a high-temperature state by utilizing air, and the heated air is used as fluidized gas and combustion-supporting gas of the fluidized bed/moving bed; the separation and purification means that when pulverized coal is used as fuel in a reburning device, coal ash mixed in the sintered magnesia is removed by adopting devices such as particle size classification or gravity separation and the like according to the particle size and density difference between the coal ash and the magnesia; the flue gas purification is an environment-friendly means for desulfurizing, denitrating and dedusting flue gas generated by burning fuel in the burning process, so that the gas discharged into the atmosphere meets the environment-friendly requirement, and in addition, CO is generated by calcining magnesite in the process2Concentration and market demand vs. CO2Collected as a system byproduct.
The powder magnesite one-step method for preparing the sintered magnesite is characterized in that the powder magnesite is prepared by crushing natural powder or blocky magnesite, or magnesite light burning powder is directly used as a heavy burning raw material; the particle size of the raw material for re-burning is, for example, but not limited to, 0 to 3mm, preferably 0 to 1mm, more preferably 0 to 0.2mm, which is much smaller than 20 to 300mm used in conventional shaft furnaces and electric furnaces.
In the method for preparing sintered magnesite from powdered magnesite by one-step method, the powdered magnesite raw material is heated by hot flue gas discharged by a reburning device through a heat exchange device, and the temperature of the cooled flue gas is, for example but not limited to, less than 200 ℃; the heat exchange device is a plate-type or tubular non-contact heat exchanger, or a direct contact heat exchange device, such as a fluidized bed, a moving bed, a countercurrent transport bed, and preferably a moving bed.
In the method for preparing the sintered magnesite by the one-step method of the powdery and granular magnesite, the powdery and granular magnesite after being preheated is fed into a fluidized bed/moving bed calcining furnace for calcining, the heat in the furnace is provided by injected fuel, the fuel is gas or coal powder, preferably gas, and oxygen required by fuel combustion is provided by fluidizing gas entering from the bottom of the calcining furnace; the rapid heat transfer and crystal transformation of magnesite at a specific temperature are realized by adjusting the amounts of fluidized gas, fuel and magnesite raw materials; the re-burning temperature is lower than 1800 ℃ which is the minimum temperature required by the traditional shaft kiln and the electric melting furnace, such as but not limited to <1600 ℃, and the preferred temperature is 1400 ℃; the reburning time is for example, but not limited to <0.5 hour, preferably <5 minutes, more preferably <1 minute lower.
In the method for preparing the sintered magnesite by the one-step method of the powder-granular magnesite, the heat recovery is to cool the sintered magnesite in a high-temperature state by using air through a heat exchange device, and the temperature of the cooled magnesite is, for example and without limitation, less than 200 ℃; the heat exchange device is a plate-type, tubular non-contact heat exchanger, or a direct contact heat exchange device, such as a fluidized bed, a moving bed, a countercurrent transport bed, preferably a moving bed.
In the method for preparing the sintered magnesite by the one-step method of the powdery and granular magnesite, the separation and purification means that coal ash mixed in the magnesite is removed by adopting a particle size grading or gravity separation method according to the density/particle size difference between the coal ash and the sintered magnesite when fuel is pulverized coal in a re-combustion device, so that the purity of the magnesite is improved; this link is not required when the fuel is a gaseous fuel.
The method for preparing the sintered magnesite by the one-step method of the powder magnesite is characterized in that flue gas generated by fuel combustion is subjected to desulfurization, denitrification and dedusting in the flue gas purification process, so that gas discharged into the atmosphere meets the environmental protection requirement, and in addition, CO is generated by calcining the magnesite in the process2Concentration and market demand vs. CO2Collecting the obtained product as a system byproduct; gas emission indicators such as, but not limited to: concentration of nitrogen oxide (NOx) emissions<50mg/Nm3（6%O2) (ii) a Sulfur dioxide (SO)2) Concentration of emissions<30mg/Nm3（6%O2) (ii) a Dust emission concentration<20mg/Nm3（6%O2）。
The invention has the beneficial effects that:
firstly, a method for preparing sintered magnesia by reburning powdery magnesite is provided, so that the restriction that powdery materials cannot be used in the traditional technology is solved, and the utilization rate of magnesite resources is improved;
secondly, the calcination temperature is reduced, and the calcination time is shortened, so that the system processing capacity is greatly improved, and the production cost is reduced;
thirdly, the concept of re-burning the materials by utilizing the fluidized bed/moving bed is provided, and the material is expected to replace a shaft kiln to become a main calcining device of future magnesite or other materials.
Drawings
FIG. 1 provides a model of the sintering mechanism of macroparticle magnesite, which illustrates both the source of the inventive concept and the underlying reason for the advantages of the present invention over conventional devices;
figure 2 shows a flow diagram for the preparation of sintered magnesite from magnesite according to an embodiment of the invention;
figure 3 shows a process flow diagram according to the invention (abstract figure).
Detailed Description
The present invention will be described in detail with reference to the embodiments shown in the drawings.
The preparation of high-density sintered magnesite by magnesite reburning is based on crystal transformation, but the internal of the bottom particles is not the CO generated by magnesite thermal decomposition2The density can be increased by exhausting gas or gas in crystal gaps, so that the applicant believes that the main reason for the slow reburning (including electric smelting) rate of magnesite is due to the difference between the temperature inside and outside the particles. As is known, magnesite light-burned powder and magnesite heavy-burned powder are both refractory materials and have excellent heat insulation performance, which means that heat is very difficult to transfer to the inside of particles through the outer layer of the particles, resulting in large temperature difference between the inside and the outside of the particles, or the inside of the particles reaches a target temperature after being out of the particles. The outermost layer, which reaches the target temperature first, the crystals are first converted into a dense structure, resulting in a particle layer relatively closer to the center of the particle, which also makes it difficult to vent the gas in the pores through the dense outer layer crystals after reaching the target temperature later. In order to achieve a compact structure inside, the conventional technology is to prolong the time or increase the temperature and increase the opportunity of gas exhaust. However, when the temperature is increased, the surface layer of the particles is melted, resulting in that the particles show channels through which no gas passes, and when the amount of the gas inside is sufficiently small, the particles cannot provide channels through which no gas passesThe exhaust stops with enough power to penetrate the blend-in layer and the crystal transformation is declared to be complete. The main problems of magnesite reburning are summarized as follows: 1) heat is difficult to transfer in the particles, and the target temperature is reached after the interior of the particles is more external; 2) the inside of the particles reaches a compact crystal form after being outside; 3) the gas in the pore canal in the particle passes through the outer dense crystal layer and the outer melting layer of the particle.
Therefore, the invention adopts the high-temperature fluidized bed/moving bed to carry out magnesite reburning, uses fine-grained magnesite as a sintering raw material, keeps the temperature inside and outside the grains consistent or slightly different to a great extent, and basically discharges the pore passage gas of the inner layer and the gas of the outer layer at the same time, and greatly shortens the discharge path of the internal gas, thereby quickly realizing the aim of crystal form transformation of the magnesium oxide without high temperature.
A preferred embodiment of the invention will now be described in more detail, see fig. 2. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Preheating: 10t/h of magnesite raw material with the granularity of 0-1mm is heated to about 300 ℃ by hot flue gas in a moving bed, and the temperature of the hot flue gas is reduced to about 200 ℃;
re-burning: the preheated magnesite enters a fluidized bed reburning device, hot air and natural gas for recovering heat of high-temperature sintered magnesite enter the fluidized bed reburning device at the same time, the natural gas is combusted to provide heat required by magnesite calcination, and the amount of the natural gas and the air is controlled to control the temperature in the reburning device to 1400 ℃, wherein the amount of the natural gas is about 1000m3H, air volume of about 10000m3H is the ratio of the total weight of the catalyst to the total weight of the catalyst. Calcining for 10 minutes to form the ideal sintered magnesia (MgO content)>98% bulk density>3.3g/cm3）；
And (3) waste heat utilization: heat exchange is carried out between the high-temperature sintered magnesia at 1400 ℃ and air in the moving bed, and the temperature is reduced to 200 ℃ and is discharged to form a final product; the air temperature absorbing the heat of the sintered magnesia is increased from 20 ℃ to about 800 ℃ and enters a fluidized bed reburning device to be used as the fluidizing gas and the combustion-supporting gas of natural gas;
flue gas purification: the temperature of the flue gas cooled by the magnesite raw material is about 200 ℃, and the flue gas enters a flue gas purification device for denitration, desulfurization and dust removal and then is discharged into the atmosphere.
Claims (1)
1. A method for preparing sintered magnesite from powdered magnesite by a one-step method is characterized by comprising the following preparation processes: powdery magnesite is sequentially subjected to preheating, reburning, heat recovery, separation and purification and flue gas purification treatment to prepare a sintered magnesite product in one step; the powdery magnesite is prepared by crushing natural powder or blocky magnesite, the preheating is to preheat the powdery magnesite by using high-temperature flue gas after reburning through a first heat exchange device, the temperature of the flue gas after cooling is less than 200 ℃, and the first heat exchange device is a plate-type or tubular non-contact heat exchanger or a direct contact heat exchange device;
in the reburning, the preheated powdery and granular magnesite is reburned by using a reburning device fluidized bed calcining furnace, so that the crystal form of the powdery and granular magnesite is changed, and high-purity sintered magnesite is prepared; the heat recovery is to cool the sintered magnesite in a high-temperature state by utilizing air, and the heated air is used as fluidizing gas and combustion-supporting gas of the fluidized bed calcining furnace; the flue gas purification is an environment-friendly means for desulfurizing, denitrating and dedusting flue gas generated by burning fuel in the burning process, so that the gas discharged into the atmosphere meets the environment-friendly requirement, and in addition, CO is generated by calcining magnesite in the process2Concentration and market demand vs. CO2Collecting the obtained product as a system byproduct;
the granularity of the powdery magnesite is 0-0.2 mm;
in the reburning step, preheated powdery and granular magnesite is fed into a fluidized bed calcining furnace for calcining, the heat in the furnace is provided by injected fuel, the fuel is gas or coal powder, and oxygen required by fuel combustion is provided by fluidizing gas entering from the bottom of the fluidized bed calcining furnace; the rapid heat transfer and crystal transformation of magnesite at a specific temperature are realized by adjusting the amounts of fluidizing gas, fuel and powdered magnesite; the reburning temperature is lower than 1800 ℃, and the reburning time is less than 1 minute;
the heat recovery is to cool the sintered magnesite in a high-temperature state by using air through a second heat exchange device, the temperature of the cooled sintered magnesite is less than 200 ℃, and the second heat exchange device is a plate-type or tubular non-contact heat exchanger or a direct contact heat exchange device;
the separation and purification means that when the fuel in the reburning device is coal powder, the coal ash mixed in the sintered magnesia is removed by adopting a particle size grading or gravity separation method according to the density/particle size difference between the coal ash and the sintered magnesia, so that the purity of the sintered magnesia is improved; when the fuel is fuel gas, the separation and purification link is not needed.
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| CA1152294A (en) * | 1980-10-08 | 1983-08-23 | Xuan T. Nguyen | Fluidized bed sulfur dioxide removal |
| CN1281912C (en) * | 2004-12-23 | 2006-10-25 | 中国科学院过程工程研究所 | Blaze insulating fluidized forge furnace |
| CN104098280A (en) * | 2013-04-12 | 2014-10-15 | 沈阳铝镁设计研究院有限公司 | Low-grade magnesite light roasting technology |
| CN205443069U (en) * | 2015-12-25 | 2016-08-10 | 辽宁东和新材料股份有限公司 | Adopt magnesite ore crushing production magnesite clinker's device |
| CN108863114B (en) * | 2018-07-06 | 2021-09-21 | 沈阳化工大学 | Method for recycling waste heat in magnesite light burning process |
| CN111646711A (en) * | 2020-05-26 | 2020-09-11 | 浙江招通高温材料有限公司 | Production device and preparation method for synthetic dead-burned magnesia |
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