Cement Introduction: Cement is the world’s second largest consumed product next to water. It is a fine powdery, inorganic, hydrophilic material which forms a paste, sets and hardens due to hydraulic reaction when mixed with water. Cement is the important binding material which adheres to the other materials of construction and there by results in homogeneity of the resultant product.
Currently, India is second largest producer and consumer of cement after China. However, China’s production is nearly nine times higher than India.
Manufacturing process of cement
Manufacturing process of the cement involves the following stages
1 Stage 1:
Collection of raw materials: Raw materials, which are of mineralogical origin or industrial waste products can be used for cement production. Major components used for cement production are of calcareous and argillaceous materials. Calcareous materials are those containing maximum part of calcium based compounds in its composition. Whereas argillaceous materials are those containing fine grained alumina (clay) minerals in its composition. Some of the calcareous and argillaceous based rocks which are commonly used for cement production are listed in table 1 below
Table 1: list of Calcareous and argillaceous materials
Calcareous materials | Argillaceous materials | ||
Silicon based | Aluminum based | Iron based | |
Limestone | Sand stone | Fly ash | Blast furnace slag |
Marl | Fly ash | Aluminum ore refuse | Iron ore |
Calcite | Rick husk Ash | Shale | |
Aragonite | Slag | ||
Shale | |||
Sea shell | |||
Stage 2:
Grinding, Mixing and proportioning of the raw materials: The collected raw materials are crushed into small sizes and then stored in large tanks. Further, the raw materials are mixed and proportioned before feeding it into the rotary kiln. In order to obtain good quality of cement, the raw materials should be mixed and fed proportionately. The quantity of raw materials feeding into the kiln depends on the purity of the material. Generally, if the material is pure to its maximum extent, then lime stone is fed 80% and clay is taken as 20% of the total weight of raw material.
Stage 3:
Pre heating of the raw material: After final grinding, the material is ready to face the pre-heating chamber. Pre-heater chamber consists of series of vertical cyclone from where the raw material passes before facing the kiln. Pre-heating chamber utilizes the emitting hot gases from kiln. Pre-heating of the material saves the energy and make plant environmental friendly.
Stage 4:
Burning phase: In this phase the preheated raw materials are burned up to 1500oC in the huge rotating furnace called as kiln. At this temperature limestone releases huge amount of carbon di oxide, and the process is called decarbonation. Further due to the exposure of high temperature there will be series of chemical reaction between limestone (calcium carbonate) and clay (silicon di oxide) compounds to form primary constituents of cement. When the material reaches lower part of the kiln, it forms clinkers.
Stage 5:
Cooling and final grinding: The clinkers are finally cooled by lowering the temperature by means of forced air. After cooling the clinker, it is then passed to the horizontal rotating drum, filled with steel balls. Here, steel balls tumble and crush the clinker into a very fine powder. During grinding gypsum is also added to the mix in small percentage that controls the setting of cement.
Stage 6:
Packing
Material is directly conveyed to the silos (silos are the large storage tanks of cement) from the grinding mills. Further, it is packed to about 50 kg bags. Only a small percent of cement is packed in the bags only for those customers whom need is very small.
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