Cement clinker is a solid material produced in the manufacture of Portland cement as an intermediary product. Clinker occurs as lumps or nodules, usually 3 millimeters (0.12 in) to 25 millimeters (0.98 in) in diameter. It is produced by sintering (fusing together without melting to the point of liquefaction) limestone and aluminosilicate materials such as clay during the cement kiln stage.
The production of cement clinker is a complex process that begins with mining of limestone, which is the main raw material used to make cement. Limestone is excavated from open cast mines after drilling and blasting and loaded onto dumpers which transport the material and unload into hoppers of the limestone crushers.
The limestone is then fed to the raw mill by conveyor belts where it is ground into fine powder. The resulting raw mix is heated in a rotary kiln at a temperature of about 1450 °C to form clinker. The clinker nodules are then cooled and ground to a fine powder in a tube mill.
The clinker is cooled and ground to a fine powder in a tube or ball mill. A ball mill is a horizontal cylinder partly filled with steel balls (or occasionally other shapes) that rotates on its axis, imparting a tumbling and cascading action to the balls. Material fed through the mill is crushed by impact and ground by attrition between the balls. The grinding is typically done in water with the resultant slurry called the raw feed or kiln feed.
Clinker production can be divided into three stages: raw feed preparation, clinker burning, and clinker cooling.
Raw feed preparation: The raw materials, limestone, clay, sand, and iron ore, are crushed and ground to a fine powder and mixed together. This mixture is then fed into the kiln where it is heated to a temperature of about 1450 °C.
Clinker burning: The raw mix is heated by a flame that can be as hot as 2000 °C. The flame causes the raw materials to react and form clinker. The clinker is formed by a chemical reaction between the limestone and the other materials in the raw mix. The clinker is then cooled and ground to a fine powder.
Clinker cooling: The clinker is cooled in a cooling tower or by air. The cooled clinker is then ground to a fine powder in a tube mill or ball mill.
The clinker is ground to a fine powder and mixed with gypsum to create cement. The cement is then packaged and transported to construction sites where it is used to make concrete.
In addition to limestone, other raw materials such as clay, sand, and iron ore can be used to make clinker. These materials are added to the limestone during the raw mix preparation stage. The mix of raw materials is carefully controlled to ensure that the correct proportions of calcium, silica, alumina, and iron are present in the final product.
The burning of the raw mix at a temperature of about 1450 °C is also critical to the production of clinker. The temperature must be high enough to cause the raw materials to react and form clinker, but not so high that the clinker is melted.
The production of cement clinker is a complex and energy-intensive process. It requires significant amounts of energy to heat the raw materials to the high temperatures needed to form clinker. This energy is typically supplied by burning fossil fuels such as coal, oil, or natural gas.
In conclusion, cement clinker is a solid material produced in the manufacture of Portland cement as an intermediary product.
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