The Cement Manufacturing Process
India is the second-largest producer of cement in the world producing 502 million tonnes of cement per year. There are 210 large cement plants producing 410 million tonnes of cement every year and 350 mini cement plants producing 92 million tonnes of cement per year. Thus, the cement manufacturing industries share a major part in the Indian economy.
There is a huge demand for cement in India ever since the government of India has declared their projects and schemes related to infrastructure development, housing societies, highway constructions, etc to boost the Indian economy. The real estate sector is also proving to be a major demand driver accountable for 65% of the total consumption in India.
Sighting this supply-demand ratio for the future back in 1962, Cement manufacturing association (CMA) was established with an aim to promote the growth of the cement industry, protecting consumer interest and identifying new usage of cement.
Cement Raw Materials
The Indian mining industry plays an important role in supplying the raw materials used in cement industry. The most important raw material used in the cement manufacturing process is the Limestone that is found in the sedimentary rock. Limestone rocks are changed by dynamic metamorphism to turn into marbles. Other varieties of Limestone are marl, lime shell, algal limestone, coral limestone, pisolite limestone, crinoidal limestone, travertine, onyx, hydraulic limestone, lithographic limestone, etc. The lime shell and marl are thick calcareous mud contain a variable amount of clay and slits. Limestone mining extracts 203,224 million tonnes of limestone that is majorly used in cement manufacturing industries. States like Andhra Pradesh, Karnataka, Madhya Pradesh, Rajasthan, Gujrat, Meghalaya, Telangana have a major reservoir of limestone.
Another important cement raw material is coal that acts as an energy source in the cement manufacturing process. For this purpose, the raw coal is also crushed and stocked in the longitudinal stockpiles and is taken out diagonally by the reclaimers before further grinding of fine coal. Jharkhand has the biggest coal mines in India followed by Orissa, Madhya Pradesh, Chhattisgarh, West Bengal, and Andhra Pradesh. Coal is used for heating the raw materials at 1450 degrees centigrade to turn into clinker. The grade of coal supplied in the cement manufacturing industry depends on the grade of limestone used in the cement manufacturing process. If the limestone used in the cement manufacturing process is of high grade then low-grade coal is used and vice versa.
Cement Manufacturing Process
The cement manufacturing process starts with the mining of limestone that is excavated from open cast mines. Then this limestone is crushed to -80 mm size and is loaded in longitudinal stockpiles. Limestone is taken out diagonally from these stockpiles for grinding in raw mill hoppers. As mentioned earlier coal is used as a fuel to heat the raw materials in the cement manufacturing process.
After receiving cement raw materials from the Indian mining industry, limestone is transferred in raw mill for grinding into a fine powder. This fine powder of limestone is then heated at a very high temperature of 1450 degrees centigrade for clinkerisation. To heat, this fine powder at such high-temperature coal is used in clinkerisation section. This clinkerised raw material is then fed into electrostatic precipitator to store it in the form of the concrete silo. This is called as kiln feed. Kiln feed is fed into preheater for pyro processing.
The pyro processing of kiln feed produces cement clinkers. The hot clinkers are then cooled down and bucketed to store in clinker stockpiles. After this stage, the clinker and gypsum are mixed together and sent to the mill inlet for the further grinding process to form a fine grey powder. This fine grey powder is cement which is then packed and dispatched in the market for sale.