Uses of rotary kilns and required refractory materials

Uses of rotary kilns and required refractory materials

Common uses of rotary kilns:

Clinker production: In the cement production process, the raw material mixture is put into the rotary kiln and clinker is produced by high-temperature calcination.

Limestone slow burning: Rotary kilns are also used in the limestone burning process to convert limestone into lime. Lime is an important raw material in many industrial and agricultural applications, such as cement production, steel smelting, etc.

Metallurgical industry: Rotary kilns are used in the metallurgical industry for the reduction and purification of ore.

Chemical reaction: Rotary kilns are widely used in various chemical reactions, such as catalyst burning in the oil refining process, pyrolysis and incineration processes in solid waste treatment, etc.

Waste treatment: Rotary kilns can be used to treat various wastes, such as urban garbage, industrial waste, medical waste, etc., and waste can be treated and converted into energy or harmless substances.

The production characteristics of the rotary kiln are that the masonry of the kiln rotates with the kiln shell at high temperature, is in a state of vibration for a long time, and is also subject to the wear and impact of the charge. Therefore, the bricks used for kiln lining should have high strength and low porosity, the brick joints of the masonry should be tight and the staggered joints should be uniform, and the strength of the mud should be high to ensure that the masonry is firm and reliable.

Types of refractory materials commonly used in rotary kilns in my country:

Phosphate-bonded high-alumina lining bricks

Phosphate-bonded high-alumina lining bricks include phosphate-bonded high-alumina bricks (referred to as phosphate bricks) and phosphate-bonded high-alumina wear-resistant bricks (referred to as wear-resistant bricks).

Magnesia bricks

Magnesia bricks have a magnesium oxide content of not less than 91%, a calcium oxide content of not more than 3%, and are alkaline refractory products with periclase as the main mineral.

Magnesia-alumina spinel bricks

Magnesia-alumina spinel bricks are magnesia bricks with magnesium-alumina spinel as the main mineral produced by adding alumina to the ingredients in order to improve the thermal shock stability of magnesia bricks.

Directly bonded magnesia-chrome bricks

In large kilns, the kiln temperature is above 1700℃, and ordinary magnesia-chrome bricks are no longer competent. Directly bonded magnesia-chrome bricks are developed to adapt to large-scale cement production – high-quality magnesia-chrome refractory materials.

Ordinary magnesia-chrome bricks

Magnesia-chrome bricks contain MgO55%-80%, Cr2O3≥8%, the main minerals are periclase and chrome spinel, and the silicate phases are forsterite and calcium forsterite.

Sodium polyphosphate bonded magnesia bricks

This brick is a chemically bonded magnesia brick, which is composed of high-calcium synthetic magnesia sand as aggregate, sodium polyphosphate as binder, and pulp waste liquid as hydration inhibitor.

Alkali-resistant bricks

It is an alkali-resistant clay brick with an Al2O3 content of 25-28%. The alkali in the kiln gas condenses on the brick surface and then reacts chemically with the brick surface quickly to form a high-viscosity glaze layer, which closes the channel for the alkali to continue to erode the inside of the brick body, thereby preventing “alkali cracking”.

Insulation materials

Insulation materials are insulation products made of lightweight refractory materials. Its varieties include lightweight calcined bricks, refractory insulation concrete, insulation boards and ceramic refractory fiber products.

High-performance refractory castables

Due to the cyclic enrichment of harmful impurities such as alkali, chlorine and sulfur in cement raw materials, the cone, ascending flue, and material discharge slope of the preheater are prone to chemical reactions with raw materials, resulting in crust blockage, which hinders the flow of materials. It is very difficult to remove the crust blockage in these parts, affecting normal production. In response to this situation, China has developed high-performance refractory castables suitable for kiln mouths and coal injection pipes, as well as SiC anti-scaling and high-temperature alkali-resistant castables for kiln tails.

 

High-alumina bricks

High-alumina bricks are aluminum silicate refractory products with an alumina content of more than 48%.