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Selection and Application of Light Burned Magnesium Powder for Refractories

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Selection and Application of Light Burned Magnesium Powder for Refractories

Date of release:2019-03-11 Author: Click:

Rotary kiln incinerator, also known as rotary kiln, is a slightly inclined hollow steel cylinder lined with refractory bricks. Most waste materials are heated by the gas generated during combustion and the heat transferred from the kiln wall. Solid waste is fed into kiln from the front end for incineration to rotate to achieve the purpose of mixing waste. It is necessary to keep a proper tilt when rotating in order to facilitate the decline of solid waste. In addition, waste liquor and gas can be fed from kiln head or secondary combustion chamber, and even whole barrel waste can be fed into rotary kiln incinerator for combustion. Rotary kiln incineration technology is the most mainstream technology in hazardous waste incineration technology. It is the most widely used type of furnace. It is a versatile incinerator that can incinerate a variety of solid, semi-solid, liquid and gas wastes. Combustible wastes of different shapes and shapes (granules, powders, lumps and barrels) can be sent to rotary kiln for incineration. Hazardous waste incineration in rotary kiln usually goes through several stages, such as drying, pyrolysis, combustion and burnout. After these stages, the harmful components in hazardous waste are fully decomposed and destroyed under the action of high temperature, forming high temperature flue gas and slag. These high temperature flue gas and slag will cause corrosive damage to refractories built in rotary kiln. (1) High temperature resistance. It can operate in high temperature environment above 800 C for a long time. (2) High strength and excellent wear resistance. The refractories in the light-burned magnesia powder rotary kiln need to have certain mechanical strength to withstand the expansion stress at high temperature and the stress formed by the deformation of the shell of the rotary kiln. (3) Good chemical and thermal stability to resist the corrosion of chemical substances in flue gas and to withstand the alternating thermal stress under incineration. (4) The stability of thermal expansion is good. Although the thermal expansion coefficient of the shell of rotary kiln is larger than that of the refractory of rotary kiln, the temperature of the shell is generally about 150-300 C, and the temperature of the refractory is generally above 800 C, which may cause the thermal expansion of the refractory to be larger than that of the shell of rotary kiln and easy to fall off. Because of the complex composition of incinerated waste, it has a strong erosion on refractories. The refractories of rotary kiln are prone to cracking, loosening of cracks, asynchronous displacement and shedding between rings after a period of operation. As the rotary kiln is the key equipment in this engineering technology, the life and falling off of refractories in the rotary kiln are the main problems that directly affect the reliable and safe operation of the system. Suggestions are as follows: (1) Selecting excellent refractory suppliers, refractories should adopt composite refractory castables or bricks with high strength, high temperature resistance and acid resistance, while avoiding glass and other low melting point materials adhering to kilns. For example, the refractory used in a hazardous waste incineration project is not less than 300 mm thick; the chrome corundum brick with Al2O3 composition not less than 80%; the apparent porosity is less than 20%; and the maximum service temperature is not less than 1700 C. (2) Selection of size of refractory bricks, according to the characteristics of hazardous waste provided by this project, special design, comprehensive consideration of the size. (3) A special location and anti-skid structure of refractories is set up inside the rotary kiln to keep the refractories in the rotary kiln in the optimal expansion balance and non-alignment of the refractories in the whole rotary kiln under the condition of repeated start-up and stop or abnormal operation, so as to prevent the abnormal longitudinal and radial sliding of refractories. (4) The unique advanced construction scheme is adopted to change the conventional rules of staggered joint masonry of refractory bricks. Each circle is self-made and does not overlap with the front and back circles, so as to ensure that the refractory bricks are not twisted when the rotary kiln starts and stops due to asynchronous displacement, so that the newly-made lining refractory bricks do not extrude the adjacent bricks when the front and rear displacements occur. (5) Carry out the oven drying strictly according to the oven curve, carry out strict management and monitoring on the actual oven curve, absolutely ensure that the actual oven curve meets the design requirements, and ensure that the oven is checked and accepted once, so as to ensure the quality of the oven. (6) Control of the thickness of the kiln skin attached to the refractory surface. Hazardous waste is fed into the rotary kiln body through feed structure for high-temperature incineration. After 60 minutes of high-temperature incineration, the material is thoroughly burned into high-temperature flue gas and residue, and a stable slag layer is formed, commonly known as "kiln skin" can play a role in protecting the refractory layer. If the thickness of kiln skin is controlled within 100 mm, the force on the kiln carcass will be uneven if the thickness exceeds 100 mm. Through the above five technical measures, the service life of refractories in rotary kiln is greatly prolonged, and the problem of refractories falling off in rotary kiln is effectively solved.

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