Lime applications

Concepts for shaft kilns.

As opposed to rotary kilns, shaft kilns are static production systems in which the raw material (limestone in various particle sizes) is fed into the kiln from the top, from where it moves downwards through the kiln shaft purely by gravity. By introducing heat energy (fuel), a chemical reaction (dissociation) takes place, whereby the limestone (CaCO3) is split up into lime (CaO) and carbon dioxide (CO2).

Although shaft kilns in different versions and sizes are used in a wide range of industries (lime, sugar, soda, iron & steel, etc.), what they have in common is that their refractory linings always consist of several layers. Usually, these consist of several insulating layers, the permanent lining, and the wear lining. Similarly, the zones in a shaft kiln can generally be divided into the preheating, calcining, and cooling zones.

Tasks of the refractory lining in a shaft kiln
As the filled shaft kiln basically represents a column of limestone that reaches up to the feeding area and is permeated by a flow of hot combustion gases, the stresses of the refractory lining are somewhat different to those in a rotary kiln. Due to the heat transition through the different refractory layers, and the specific temperature limits of the insulating materials, the insulating layer is usually built up of one to three plies. The purpose of the insulating layer is to reduce the shell temperature to a specified maximum value.
The permanent lining is located between the wear lining and the insulating layer, and has the task of reducing the temperature on the insulating layer side, and also to act as an "emergency lining" in case of a fault in the wear lining.
Because the wear lining is in direct and continuous contact with the kiln charge and the hot gases, it must exhibit good thermal and chemical resistance as well as high strength against hot and cold mechanical abrasion. The mechanical flexibility required in a rotary kiln does not have much importance in a shaft kiln.
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