Portland Cement
Portland cement is an extreme ground material having adhesive and cohesive properties, which provide a binding medium for discrete ingredients. Portland cement is hydraulic cement made by finely pulverizing the clinker produced by calcining to incipient fusion a mixture of argillaceous and calcareous materials. Cement undergoes a chemical reaction with water and sets and hardens when in contact with air or underwater.
Portland cement is a general term used to describe hydraulic cement. The typical raw materials used for making cement are limestone (CaCo3), sand (Sio2), state clay (Sio2, Al2O3 or Fe2O3) and iron oxide (Fe2O3). Thus, the chemical components of cement are calcium (Ca), silicon (Si), aluminum (Al) and iron (Fe).
The manufacturing process of Portland cement
The raw materials required for the manufacture of Portland cement are calcareous materials, such as limestone or chalk and argillaceous materials, such as shale or clay. The process of manufacture of cement consists of grinding the raw materials, mixing them and then burning them in a kiln at a temperature of about 1300oC to 1500oC at, which temperature, the material sinters and partially fused to form nodular shaped clinker. The clinker is cooled sinters and partially fuses to form nodular shaped clinker. The clinker is cooled and ground to a fine powder with the addition of about 2 to 3% of gypsum. The product formed by using this procedure is Portland cement.
There are two processes, known as ‘wet’ or ‘dry’ processes depending upon whether the mixing and grinding of materials done in wet or dry conditions. A wet process was popular in the early years because of the possibility of more accurate control in the mixing of raw materials. The nowadays dry process is much popular because the dry process required less fuel than the wet process because in a wet process the slurry contains 35 to 50 percent water.
Manufacturing of Portland cement
Manufacturing of Portland cement
- The wet process of portland cement
- The dry process of portland cement
the wet process for the manufacturing of Portland cement
In the wet process, limestone is first crushed to smaller fragments. Then, it is taken to ball or tube mill where it is mixed with clay and finely ground. Then, water is added to it to make a slurry. Is pumped to slurry tanks, where it is kept in an agitated condition by means of rotating arm or by compressed air from the bottom to prevent settling of limestone and of the flexible chain, loses moisture and becomes flakes. These flakes are dropped reaction takes place and 20 to 30% materials get fused. Lime, silica, and alumina get recombined. The fused mass turns in to nodular from called clinker. The clinker drops into the rotary cooler where it is cooled under controlled conditions. The cooled clinker is then ground in a ball mill with the addition of 2 to 3% of gypsum.
In the ball mill, particles are crushed to fine powder and filled into bags. The following flow sheet shows the details of the wet process in the manufacture of cement –
The dry process for manufacturing of Portland cemen t
In this process, the raw materials are dried and ground to fine powder by grinding mill. The dry powder is then further blended and corrected for its right composition and mixed by means of compressed air. The blended powder is then stored in the storage silos from where. It is passed to the granulator comprising an inclined rotating drum or dish. A quantity of water about 12 percent by weight is then added to make the blended powder into nodules. These nodules are then dried by preheater and then entered to the rotary kiln from the upper end. These nodules are dropped to lower end where it subjected to the temperature about 1500oc Chemical reaction takes place and 20 to 30% material get fused. Lime silica and alumina get recombined. The fused mass turns into nodular from called clinker. The clinker drops into the rotary cooler, where it is cooled under controlled conditions. The cooled clinker is then ground in a ball mill with the addition of 2 to 3% of gypsum. In the ball mill, particles are crushed to fine powder and filled into bags.
The equipment used in the dry process in comparatively smaller. This process is economical than the wet process. The total consumption of coal in the dry process is only about 100 kg, as compared to the requirement of about 350 kg, for producing a tonne of cement in the wet process.