Around 1975, magnesia spinel bricks began to be used in cement kilns. Japan was the first country to apply magnesia spinel bricks in cement kilns to deal with the chrome hazards caused by magnesia-chrome bricks. The magnesia spinel brick not only has excellent thermal shock stability, but also chemically reacts with the cement clinker, forming a protective film on the surface of the magnesia spinel brick, which can prevent the liquid phase from diffusing into the magnesia spinel brick. Therefore, the peeling resistance of magnesia spinel bricks is better than that of magnesia chrome bricks.
Although magnesia-chrome bricks can be replaced by magnesia spinel bricks in cement rotary kilns to a certain extent, there are still some problems in magnesia spinel bricks:
(1) The ability to hang the kiln skin is weak, and the refractory bricks will be severely chemically attacked, thereby reducing the application time of the brick body;
(2) The heat loss of the cement kiln body is increased, the heat consumption is increased, and the material is wasted;
(3) In the high temperature state, a low melting point mineral phase is generated inside the magnesia spinel brick, and the magnesia spinel brick is easily subjected to severe chemical erosion and then damaged.
(4) Magnesium spinel bricks can easily undergo hydration reaction. Therefore, in order to prolong the service time of refractory bricks, it can be improved from the two aspects of hanging kiln skin performance and anti-peeling performance.
Among them, the methods for improving magnesia spinel bricks include the following measures:
a. Add additives to the magnesium spinel, such as: TiO2, Fe2O3, ZrO2, etc. The addition of additives is very beneficial to the sintering of materials, the decrease of apparent porosity, the enhancement of chemical corrosion resistance, and the improvement of kiln skin ability;
b. Appropriately reduce the content of magnesium spinel, so that there are micro-cracks inside the brick, thereby reducing thermal conductivity and improving peeling resistance;
c. The study found that when the alumina content in the refractory brick is less than 10%, the kiln skin performance of the brick is better, so by reducing the alumina content in the magnesia spinel brick, the kiln skin ability of the material is improved.
In the application of cement rotary kilns, magnesia spinel bricks with high strength, excellent thermal shock stability and strong chemical erosion resistance are mainly used in the upper and lower transition zones of cement rotary kilns and thermal kilns that require high temperature resistance and thermal shock resistance. furnace equipment.
