Row materials and fuels

In the production of cement large amounts of mineral raw materials and large amounts of fuels are used as sources of thermal energy for clinker production. Cement plants can use natural resources but the process allows the use of different type of wastes, both to replace mineral resources as well as for replacement fuels. Such use is in environmentally sustainable direction, because it signifies the replacement of natural resources, solving a significant proportion of wastes and, globally speaking, reducing CO2 without negative effects on the environment or the quality of product.

Mineral raw materials

The basic raw material for preparation of the mixture for clinker production is obtained from quarries and it is mainly composed of limestone and clay in smaller shares. In the next stage of the production process the chemical composition of clinker must be regulated, possible solutions are: materials with iron or alumina or siliceous, such as iron ore, bauxite, silica sand, or other similar natural materials that can be replaced by different types of wastes that also contain significant proportion of elements necessary for regulation of the process. The most commonly used alternative raw materials are pyrite ashes, scales (wastes from steel manufacturing) and wastes from other industries. If the wastes partly replace limestone or clay, the result of such replacement can be the reduction of CO2 emissions.

Fuels and alternative fuels

Cement industry is energy-intensive process because large amounts of thermal energy are required to achieve the conditions in the rotary kiln. This energy could be obtained from natural sources, such as natural gas, fuel oil, hard coal or petroleum coke. The conditions in the kiln, such as high temperature of material and gas phase, the long time of material resistance and flue gases at high temperatures, high capacity enabling dosage in small portions and the obligatory oxidative atmosphere, which provide good combustion condition of organic matters allow the usage of different wastes as alternative fuels. Moreover, the process of cement production must be permanently placed under a very strict supervision in order to ensure adequate quality of final products, which also signifies a well-supervised and controlled process of co-incineration of wastes. Finally, emission values of flue gases are relevant and they must be within the formally determined limits.   The most commonly used alternative energy sources are: waste oils, waste tiers, sludge from sewage treatment plants and solid recovered fuels, prepared as a mixture of waste plastics, textile fibres, paper and wood wastes.  

Besides their primary activity, which is cement production, cement plants can also contribute significantly to the optimal use of relevant quantities of certain types of waste. Otherwise this kind of wastes could pose a great threat to the environment.

Links:

Uporaba alternativnih goriv in surovin v LAFARGE CEMENT d.d. TRBOVLJE.pdf

SALONIT ANHOVO Alternativna goriva v cementni industriji - možnosti in omejitve .pdf