Processing tyres in cement kilns

Widely used process

The use of tyres as a cement kiln fuel in the manufacturing process is widely used across the world.

Tyres are used to maintain the high temperatures required within the cement kiln for the complex chemical reaction between raw materials to take place.

Depending upon the raw materials available, cement can be made in two different ways – the wet and dry process. The method employed at a particular plant has a bearing on the way tyres are used. In the dry process, tyres are cut into small chips before they are inserted into the kiln.

The diagram illustrates the dry cement making process from raw material stage (in this instance limestone and shale to the left of the diagram) to the bagging and distribution stage (to the right). In the pre-heater tower and kiln (centre), the raw materials react together to form clinker – the basic ingredient of cement. Before entering the kiln, the raw materials are heated to around 900°C by a kiln flame heated by coal and petroleum coke.

In this example, tyre chips are inserted into the bottom of the pre-heater tower to maintain the high temperatures of around 900°C. Due to the extremely high temperatures maintained at this stage of the process, the tyre chips are completely consumed with no residual waste, smell or smoke.

Using tyres as a cement kiln fuel in the wet process produces the same result. However the method used is slightly different: whole tyres are inserted into the middle of the kiln to maintain temperatures of around
1,450°C.