The active lime rotary kiln is mainly used for smelting active lime used in metallurgical units such as roasting steel plants and calcined magnesia in nonferrous metallurgy industry. The rotary kiln is a high-temperature calcination equipment. The life of the kiln lining will affect the production efficiency during use. The chemical influence factors of the kiln lining life are analyzed. The chemical damage of the kiln lining mainly includes the low-melting reaction leading to corrosion and alkali salt infiltration. And the reduction of the oxidation effect.
1. Low melting reflection leads to erosion
There are certain low-melting impurities in the fuels such as limestone raw materials, refractory bricks and pulverized coal, and the components thereof are mainly CaO-SiO2-A1203-Fe203. Under the influence of the difference in concentration and temperature between the kiln and the brick, the melt migrates from the hot end to the cold end of the brick mainly by ion migration.
The operating conditions of the rotary kiln, the location of the brick in the kiln, the condition of the kiln skin and the temperature difference in the brick determine the temperature and melt properties of the infiltration, thus determining the penetration depth of the melt in the brick, ie the metamorphic layer. The depth, in general, the worse the kiln skin condition, the deeper the infiltration of the metamorphic layer in the brick, the depth can be from thin to almost invisible up to 70mm. The melt fills the pores in the brick and cooperates with a part of the ions in the refractory material to densify and embrittle the brick layer, and then is easily cracked and peeled off under the action of thermal stress and mechanical stress.
2. Alkali salt penetration
In coal-fired rotary kiln, the volatile components of coal in the base of sulphate and kiln are greatly increased. The alkali salt penetrates into the brick layer deeply and is suspected to be deposited in the brick layer of 700-1000 °C, which makes the site highly densified, resulting in the thermal shock stability of the layer being significantly weakened, and then cracking under the combined action of thermal and mechanical stress. Peel off.
3. Reduction and reduction of oxidation
When coal or gas is incompletely burned, a reducing flame is prone to occur. The trivalent iron in the high-aluminum brick is reduced to divalent iron, and the volume shrinks. In FeO, the ferrous iron is easily released and produces refractory bricks with low-melting voids. The structure of the brick is weakened and the strength is reduced. The alternating change of the reduction and oxidation atmosphere in the rotary kiln gas causes the volume effect of the contraction and expansion phases to occur repeatedly, and the bricks are chemically fatigued. For chemically bonded phosphate bricks, the consequences of the reduction of the reduction reaction are more serious. When the sulfur content is excessive, under the action of reduction, various sulfides such as FeS and KFeS2 are formed in the bricks, which are converted into sulfates under subsequent oxidation conditions, and repeated volume effects are generated to damage the bricks.