- Time:Sep 11, 2023
With the increase of the rotary kiln speed, the materials and gas components in the kiln are complex and will have complex chemical interactions with the surface of the refractory materials at high temperatures. In particular, the circulation and enrichment of harmful elements such as alkali, chlorine, and sulfur at the end of the kiln have intensified. Causes erosion and damage to refractory materials. These factors have put forward higher requirements for refractory materials used in rotary kilns.
一. Factors affecting the service life of refractory bricks in new dry process rotary kilns
1. Mechanical force effect
The rotary kiln is a horizontal rotating equipment with an inclination angle. This inclination angle causes the refractory bricks in the kiln to naturally squeeze toward the kiln head.
The compressive strength of refractory bricks at normal temperature is generally above 50MPa, which can resist the extrusion of refractory bricks. However, as the temperature in the kiln increases and is corroded by alkaline components in the kiln, the compressive strength of refractory bricks will decrease significantly. , once the pressure limit is exceeded, the refractory bricks will be damaged and fall off, causing red kiln accidents and seriously affecting production safety.
2. Thermal stress
During the heating process of the kiln, the refractory materials undergo thermal expansion due to the high temperature, causing adjacent refractory materials to squeeze each other. When a large amount of alkaline bricks are used in a rotary kiln, the expansion rate is very large. Therefore, in the early stage of ignition and drying of the rotary kiln, the temperature rise and insulation are carried out strictly according to the temperature rise system. If the temperature rises too fast, the temperature of the kiln barrel will not have time to rise and cannot compensate for the expansion of the refractory bricks, causing the compressive stress of the refractory bricks to rise sharply. In order to ensure the service life of refractory bricks, the temperature must be raised strictly according to the heating curve.
3. Chemical attack
Refractory materials will be penetrated and corroded by high-temperature liquid phase and harmful substances such as alkali salts and some harmful gases. At high temperatures, the clinker liquid phase will react chemically with the surface of the refractory bricks. If the calcination temperature is too high, the amount of clinker liquid phase will increase, and the chemical reaction between the clinker and the refractory material will intensify, resulting in a reaction between the clinker and the hot end of the refractory material. As the layer deepens, qualitative changes occur due to differences in the internal structures of the reaction layer and bricks.
These chemical attacks cause the bricks to lose their stability, making them brittle and prone to peeling, and the voids expand, making it easier for the bricks to absorb moisture. Chemical erosion substances may also produce deposits on the surface of the bricks, further affecting the performance of the bricks. Due to the combined effect of these factors, the compressive strength, heat resistance and dimensional stability of the refractory bricks are reduced, thereby shortening the life of the rotary kiln refractory bricks. service life.
二. Selection of commonly used refractory materials for rotary kilns
1. Castable material
Rotary kilns mostly use high-aluminum castables. High-aluminum refractory castables are made of high-aluminum raw materials as aggregates and powders, and added with binders. High-aluminum refractory castables have high mechanical strength and good thermal shock resistance and abrasion resistance. Depending on the resistance to high-temperature thermal stress and mechanical stress, the Al2O3 content of the refractory castable should be from 45% to 95%, and the construction methods include vibration, gravity flow and spraying. The castable is overall solid and operates stably.
2. Magnesia-aluminum and magnesia-iron spinel bricks
Modern cement rotary kilns are mainly dry process cement kilns, and magnesia alkaline refractory materials are used in dry process cement rotary kilns. Among them, magnesia-aluminum and mafic spinel bricks are used in the transition zone and firing zone of the cement kiln. The most extensive. Both magnesia-aluminum and magnesia-iron spinel bricks have low ASR, excellent alkali resistance, excellent resistance to alkali salt penetration, and are chromium-free and low-iron, making the products effective in solving common chemical damage in cement kilns and ensuring cement The kiln operates efficiently and safely to save energy and reduce consumption.
3. Silicon mullite bricks
Silicon mullite brick is a composite material with corundum, mullite and silicon carbide as the main crystal phases. It has good wear resistance, corrosion resistance and high temperature mechanical properties, and its service life is longer than that of magnesium aluminum spindle. Stone bricks are therefore also widely used in the transition zone of cement rotary kilns.
Due to the dense structure and strong crystal stability of silica molybdenum bricks, a continuous dense layer of silicon oxide will be formed on the surface of the scale bricks during use, which protects the brick surface. It also has high thermal conductivity, good wear resistance, and thermal expansion. Low coefficient, good thermal shock resistance, especially suitable for use in transition zones without kiln skin protection.
