Cement kiln

Cement kilns are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity usually define the capacity of the cement plant. As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture, improvement of their efficiency has been the central concern of cement manufacturing technology.

The objective of kiln operation is to make clinker with the required chemical and physical properties, at the maximum rate that the size of kiln will allow, while meeting environmental standards, at the lowest possible operating cost. The kiln is very sensitive to control strategies, and a poorly run kiln can easily double cement plant operating costs.

Portland cement clinker was first made (in 1842) in a modified form of the traditional static lime kiln. The basic, egg-cup shaped lime kiln was provided with a conical or beehive shaped extension to increase draught and thus obtain the higher temperature needed to make cement clinker. For nearly half a century, this design, and minor modifications, remained the only method of manufacture.

A kiln is basically an industrial oven, and although the term is generic, several quite distinctive designs have been used over the years. Although perhaps more normally associated with pottery making, both ‘Bottle’ and their very close relatives ‘Beehive’ kilns, were also the central feature of any cement works. Early designs tended to be updraft kilns, which were often built as a straight sided cone into which the flame was introduced at, or below, floor level.

 

Source: Wikipedia