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Main products and present situation of magnesia refractory materials

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Main products and present situation of magnesia refractory materials

Date of release:2018-07-12 Author: Click:

 

Light Magnesium Oxide. At present, brucite is used as raw material in China to produce light burned magnesia powder (CCM) by light burning in reverberatory furnace. Light burned magnesia powder is a very important basic raw material of magnesia. According to its different chemical composition, particle size and properties, which one of ordinary fused magnesia industry can be applied to: calcining various grades of sintered magnesia (DBM) by balls, and synthesizing magnesia-alumina spinel sand, magnesia-calcite sand and other composite materials with different content of Al2O3, CaO and other raw materials It is used to produce fused magnesia (FM, refractory grade or electrical grade), converter slag splashing, magnesia ball protection and so on. The above products are mainly used as raw materials for refractory products. In addition, these products are also raw materials for magnesium chemical products such as light MgO, light MgCO3, magnesium fertilizer, magnesium building materials, feed additives and so on.

The traditional light burned Magnesium Oxide is made from raw ore baked in a reverberatory furnace. After 70-80 years of existence and development, light-burning magnesia produced by reverberatory furnace has not been eliminated, because the furnace has its outstanding characteristics: simple and practical technology; less investment, fast start-up, easy operation; suitable for the characteristics of brucite in southern Liaoning. In recent years, the kiln type production technology has also been greatly improved, mainly in the following aspects: changing to clean fuel, burning bituminous coal directly instead of gas produced by a simple gas generator for fuel roasting, avoiding the pollution of fuel ash to light burning magnesium oxide, basically solving the environmental pollution caused by black smoke emission, and improving The thermal efficiency is improved, the kiln type is enlarged, the volume of the kiln is increased, the output is increased, and the fuel consumption is reduced.

However, the following problems still exist in the production of light magnesia powder by magnesite roasting in the reflex furnace in China: simple mining activities, artificial mining; manual operation of the kiln, poor temperature stability, high energy consumption; into the kiln lump ore, crushed ore discarded, high material consumption; flue gas untreated, pollution of the environment; open cooling, poor labor conditions. As a result, it is difficult to recruit, the grinding equipment is backward, the granularity control is poor, and the final product quality is low and fluctuates greatly.

Therefore, the production of light burning magnesia in China must be controlled from the whole process of mining-finished product-packaging, and advanced light burning magnesia roasting technology and kiln should be studied and popularized according to the requirements of users. Large suspension kiln and multi-layer furnace (MHK) should be recommended for light burning and high efficient light burning magnesia fine grinding equipment.

Sintered magnesia. GB / T2273 - 2007 stipulates the physical and chemical properties of various sintered magnesia with 83% - 98% MgO content suitable for refractory production. Historically, sintered magnesia is also known as metallurgical sand, reburned magnesia, intermediate magnesia, high-purity magnesia.

Metallurgical sand. During the first Five-Year Plan (1952-1957), the first alkaline refractory factory in China, Dashiqiao Magnesium Brick Plant of Anshan Iron and Steel Company, was built with the assistance of the former Soviet Union. The semi-dry process of fine grinding, pelletizing, grate and rotary kiln was adopted in the sand-making workshop to produce metallurgical sand. In the bottom of furnace and repair. With the steel-making open hearth converted to converter, the product was eliminated in the 90s of last century.

Reburning magnesia. At present, the total output of sintered magnesia in China is 4 million ~450 tons per year. Following the industrial practice, sintered magnesia can be classified into heavy magnesia, medium magnesia and high purity magnesia.

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Before the 1980s, the production of sintered magnesia in China was mainly undertaken by Dashiqiao Magnesium Mine, Anshan Iron and Steel Co., Ltd. for more than 30 years. The shaft kilns of 25 cubic metres, 32 cubic metres, 40 cubic metres, 47 cubic metres and 55 cubic metres were used successively, using coke as fuel and massive magnesite as raw material, and one-step calcination and manual production were carried out. It is used to produce magnesia with MgO content of 92%, which provides raw materials for brick making furnaces in China.

The defects of this process are: low utilization rate of ore, fine-grained ore can not be used; high impurity content, ash content in Coke will cause pollution to magnesia, so that the content of SiO2 and Al2O3 in magnesia increases, the maximum MgO content can only be guaranteed at 92%; poor continuous operation, large magnesite thermal decomposition produces small particles of ore adhere to the wall of the kiln The material in the kiln is prone to "caking", which results in frequent changes of material flow and thermal system in the kiln, resulting in failure of mechanized operation due to shutdown accidents; the low density of magnesite, the decomposition of magnesite in the preheating zone in the kiln, releasing CO2 into light burned MgO, but the "mother salt illusion" of MgCO3 still exists, which is not conducive to the entry of magnesite. One step densification, the volume density of sintered magnesia is only between 3.0 g and 3.1 g per cubic centimeter; the pollution environment is serious, magnesite decomposes a large number of CO2 and burning flue gas mixed with fine coke particles and light burning dust fly out of the kiln, polluting the environment, high temperature flue gas control is difficult.

At present, magnesia is still calcined in solid fuel shaft kiln with secondary and tertiary ores in China. The magnesia contains 90%~92% MgO and its bulk density is more than 3.10 grams per cubic centimeter. Reburned magnesia is the main raw material for producing ordinary magnesia fired bricks and amorphous refractories. The annual output of Liaoning Province is estimated to be 2.5 million tons.

Medium magnesia. In order to improve the density and purity of magnesia, two-step calcination of magnesia has been carried out in the refractory industry in China. Adopting the new technology and new process suited to the national conditions, the technological progress of sintering magnesia production has been promoted. In the early 1980s, Haicheng Magnesium Mine made use of high quality magnesite to burn lightly in a reflex furnace, with Raymond grinding, semi-dry two-stage ball pressing and coke shaft kiln calcination, and produced medium grade magnesia with MgO content (> 95%) and bulk density (> 3.20g) per cubic centimeter. This achievement has been rapidly promoted to form an annual production of hundreds of thousands of tons of scale benefit. Since then, the technology has been applied to the production of synthetic magnesia calcium sand and other synthetic sand products.

High purity magnesia. In 1980, the Mining Department of the former Ministry of Metallurgy organized and implemented the project of "new technology and high-temperature shaft kiln for producing high-quality and high-purity magnesite from natural magnesite". In Haicheng Magnesium Mine, a pilot production line with an annual output of 0.7 million tons of high-purity magnesite was built. In view of the characteristics of refractory sintering of large crystalline magnesite, brucite was developed for light burning, fine grinding, high-pressure balling and dead burning. The new two-step calcination process has been tackled for several years, and has reached the target of high purity magnesia MgO content (> 98%) and volume density (> 3.30 g) per cubic centimeter. Based on the utilization of fine ore, they adopted flotation technology, and imported from Europe the key equipment of the production line of high-purity magnesia with an annual output of 50,000 tons: suspension roaster, roller mill, high-pressure ball press, high-temperature oil shaft kiln and so on.

Based on China's national conditions, the production process of high-purity magnesia is mostly: select high-quality magnesite, light burning in the gas-fired reflex kiln, fine grinding of light burning powder with Raymond machine, dry ball pressing by high-pressure machine, and finally calcination in high-temperature oil shaft kiln, producing magnesia content of 97%, volume density of 3.25 per cubic centimeter. Gram ~3.30 grams of high purity magnesia. The process equipment is completely localized, and the products meet the requirements of magnesia for most of the high-grade magnesia refractories in China, and have a certain amount of export.

Fused magnesia. The development of fused magnesia is developing rapidly along with the development of MgO-C brick production technology. High quality MgO-C bricks require magnesia not only to have high purity and density, but also to have a large grain size, which is usually obtained by electrofusion process. The fused magnesia is prepared by melting and slowly cooling in an electric furnace with magnesite (to prepare ordinary fused magnesia) or light burned MgO (to prepare large crystalline fused magnesia).  Among them, low iron (Fe2O3) large crystalline fused magnesia is also a good filler material for electrical components. However, the production of fused magnesia consumes a large amount of electricity, which is an industry restricted by the national energy policy. Its development will be impacted by the implementation of the classified electricity price policy.

Nowadays, the emphases of technological development of fused magnesite production enterprises are energy saving, comprehensive utilization of magnesite resources and smoke control. The main technical measures are as follows: to carry out comprehensive energy-saving technology research on preparing fused magnesia and dust control, waste heat recovery and so on. Liaoning Province is taking corresponding control measures to sum up experience to solve the fume pollution and waste heat recovery of magnesia ballast cooling produced by electric smelting furnace.

At the same time, facing the problem of magnesite grade decreasing (MgO 98 grade fused magnesia MgO content is only 97.2%), some enterprises adopt flotation technology, using concentrate powder and light burned magnesia pressure ball to blend ore into the furnace for electric melting, which not only greatly reduces the unit power consumption of fused magnesia, but also increases the yield of high grade fused magnesia.


 


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