The continuous development of the cement industry has put forward corresponding requirements for cement rotary kilns, and the choice of lining materials for rotary kilns has become particularly critical. Whether the selection of lining refractories is reasonable, the quality of refractory products, the design and correct construction of the kiln lining and the rational use of the kiln lining are the most direct factors affecting the operation of the rotary kiln. The following describes the use of refractory materials in various parts of the cement kiln. Claim:
(1) Kiln lining refractory materials for firing zone and transition zone
The kiln lining at the high temperature part of the firing zone and transition zone undergoes the comprehensive destruction effect of heat, mechanics and chemistry. 60-70% of the total consumption of refractories in the whole kiln system occurs in the firing zone and transition zone. The lining material must meet the following requirements:
①Sufficient mechanical strength at both ambient temperature and operating temperature: The metal shell of the kiln is not completely rigid, and the ellipse of the kiln is too large. The Large or small deformations cause compressive, tensile and shear stresses in the kiln lining, coupled with the continuous relative displacement and local stress between the refractory materials, resulting in material cracking, peeling and even falling off: the kiln lining is heated and cooled during the process The temperature difference stress can also lead to the cracking and peeling of the material: there is also chemical erosion to form some new minerals, resulting in volume changes, and new mechanical stresses in the material: the above conditions require refractory materials to have enough at room temperature and high temperature The strength can be used normally.
②Have sufficient resistance to chemical attack: the infiltration of clinker liquid phase, molten fuel ash and sulphuric acid and alkali chloride infiltrated with kiln gas have strong chemical attack ability on various refractory materials at high temperature. In the kiln where the oxidation-reduction atmosphere is frequently alternated, potassium iron sulfide is formed under the reducing atmosphere, which infiltrates and condenses in the bricks with the kiln gas, and turns into an oxidizing atmosphere when the kiln is stopped, and the sulfide is converted into sulfate with increasing volume. Circulation destroys the structure of the brick and causes the brick to crack.
③It is easy to hang and maintain the kiln skin: the flame temperature in a large kiln is above 1700℃. If there is no kiln skin protection, the refractory bricks are easy to explode and peel off due to the large temperature difference in the brick. The thermal conductivity of the kiln skin is 1.163W/MK, and the thermal conductivity of the alkaline brick is 2.67~2.79W/MK. If the kiln skin of about 150mm can be maintained regularly, the hot surface temperature of the alkaline brick can be maintained at 600~700 ℃, the thermal expansion rate of the hot surface layer is only 0.6~0.7%, while the thermal expansion rate of refractory bricks without kiln skin protection can reach 1.5%, causing the temperature difference stress in the kiln lining to reach 60~70MPa, which exceeds the strength of the brick, resulting in Cracking and peeling. To hang and maintain the kiln skin, it is necessary to work hard on the kiln material composition, refractory composition and performance, as well as the equipment conditions and calcination system of the kiln.
④Good thermal shock stability: The thermal shock stability of refractories increases with the increase of its thermal conductivity (λ) and mechanical strength (σ), and with the increase of thermal expansion coefficient (α), elastic modulus (Σ), specific heat (C) and bulk density (ρ) increase and decrease. The thermal expansion coefficient and elastic modulus of refractory materials are determined by the basic quality, so we must try to increase the strength of refractory materials to improve the thermal shock stability of the materials
(2) Preheating and decomposition zone kiln lining refractory materials
The preheating zone and decomposition zone of cement are volatilized in the form of alkali-RCL and R2SO4 from the raw fuel, and condensed and enriched in the kiln section at 800℃~1200℃. The amount of alkali circulating in the kiln system is higher than that in the raw fuel. The amount of alkali is much higher. Alkali is enriched on the surface of refractory material and penetrates its interior. Common clay system reacts with alkali to form potash nepheline and leucite, which causes swelling in the material and causes cracking and peeling of the material. Al2O3 25%~25% SiO2 65%~70% alkali-resistant material or alkali-resistant heat insulation material reacts with alkali at a certain temperature of use, forming a high-viscosity glaze layer on the surface, sealing the alkali The channel penetrating into the material prevents "alkaline cracking" and increases the resistance of the material surface to kiln material grinding. However, the use temperature of this refractory material must not exceed 1200°C, so it can only be used on parts with a surface temperature of 1150°C to 1200°C. Only high-aluminum refractory products can be used at a brick surface temperature of 1200°C to 1350°C.
(3) Kiln lining refractory materials for cooling zone and kiln mouth
The temperature of the kiln air at the cooling zone and the kiln mouth fluctuates between 1100℃~1400℃, whether the kiln skin is stabilized, the grinding of the clinker and the erosion of the air flow are serious, and the alkaline bricks with excellent thermal shock stability are suitable for the cooling zone. Inside: wear-resistant and heat-resistant high-alumina bricks or steel fiber reinforced castables and low-cement high-alumina castables are suitable for kiln mouths: but for large kilns with higher kiln mouth temperatures, ordinary or steel fiber should be used Enhanced corundum castable.
