The manufacture of cement is generally operated in two process. Clinker is first produced in a kiln system from calcareous (limestone, chalk or marl) and argillaceous (clay or shale) materials, with addition, in some cases, of small amounts of corrective materials (sand, waste bauxite, iron ore). Various fossil fuels and waste fuels are used in this process to reach the reaction temperature of 1450 °C. Secondly, the clinker is ground with calcium sulphates and with industrial processes wastes such as blast furnace slag, limestone, natural pozzolana and industrial pozzolanic materials, e.g. fly ash, silica fume and burnt shale.
Typical Cement Production Plant Layout
Two basic types of clinker production processes exist, depending on the way the row materials are prepared before entering the kiln system: in the wet method, water is added to form a wet thick slurry whereas the dry process is based on drying the bulk materials to form a dry powdered meal. The choice of process depends on moisture content of the available raw material. When wet raw materials (moisture content over 20%) are available, the wet process can be preferred.
However, in Europe, today’s new cement plants are all based on the dry process as the wet process requires approximately 56 to 66% more energy. For dry processes, current state-of-the-art technologies are kiln systems with multistage cyclone preheaters and precalciner.
Cement Grinding Mill
The two basic methods to produce cement are the wet and dry manufacturing processes. The main difference between wet and dry process is the mix preparation method prior to burning clinker in the kiln. In the wet process water is added to the raw materials to form a raw thick slurry whereas the dry process is based on the preparation of a fine powdered raw meal by raw materials grinding and drying.
The choice of the process is mainly based on the nature of the available raw materials. When the moisture content in raw materials is more than 20% (and up to 45%), the wet method is preferred to the dry method. However, the wet process is more energy intensive and expensive than the dry process as it requires the wet slurry to be evaporated before calcination.