Technology > Process

Manufacturing Clinker:

Stage 1

Limestone mining

Limestone mining involves benching, drilling and blasting. In limestone benching, the quality of the input is assessed and compared with benchmarks before the additives are mixed. The benched limestone is then drilled and blasted into small pieces. After blasting, the limestone is extracted and transported for crushing.


Here the limestone is crushed to make particles suitable for blending and storage. At the crushing plant, a series of crushers and screens reduce the limestone rocks to a size less than 10 mm. The crushed material is stored in linear stockpiles for further processing. Other additive materials like sand, shale, clay, and iron ore are crushed and stored in separate linear stockpiles for later use.

Stage 2

Raw mill grinding

Raw material grinding is carried out through a dry process, wherein, each of the raw materials is fed in the right proportion to attain the desired chemical composition before being fed to a rotating ball mill. The raw materials are then dried with waste process gases and ground to less than 90 microns in size. The resultant mixture of material is known as ‘raw meal’.

Blending and storage

The raw meal is stored in a vertical continuous blending cum storage silo where it is pneumatically blended to ensure a uniform chemical composition. The thoroughly homogenized mixture is then fed to the pre heater.

Coal Crushing and Grinding

Our Company procures coal from indigenous sources. In addition we also use coal that is imported from Australia, Indonesia, and South Africa. They are then blended together to achieve a uniform heat value. The coal mixture is then crushed and ground in a ball mill up to 75 microns in size and stored in fine coal hoppers.

Stage 3

Pre-heating stage and kiln

Pyroprocessing is carried out in a 5 stage preheater, calciner and rotary kiln with cooler. It takes place inside the pre-heater tower which is about 90 meters in height.

Raw meal from the storage silo is extracted at a defined rate and fed at the top of the pre-heater tower while being subjected to higher temperatures at every single stage of the 5 stages. High temperatures free the raw meal of all moisture and also do the preheating. After 4 stages, the raw meal enters the ‘calciner’ wherein calcium carbonate in the raw meal is decomposed into calcium oxide and carbon dioxide. The material is then fed to rotary kiln.

The pre-heater tower and rotary kiln are made of a steel casing and lined with special refractory materials to protect it from not only the high temperatures in the kiln but also from reactions with the raw meal and gases in the kiln, abrasion and mechanical stresses induced by deformation of the kiln shell as it rotates.

In the kiln, the calcination process is completed as the raw meal burns at 1,450 degree Celsius with fine coal fed through the kiln outlet and calciner. The raw material inside the kiln liquefies. During this heat treatment of raw meal, calcium oxide reacts with silica, alumina and iron oxides to form crystals of calcium silicates, calcium aluminates and calcium alumino ferrites etc. This process is called sintering. The reaction results in nodular product known as ‘clinker’ which has the desired hydraulic properties.

The heated clinker is discharged from the rotary kiln into a clinker cooler. Large cooling fans blow air through the heated clinker cooling it down on its way out. The hot kiln gases are filtered through the reverse air bag house and cooler hot gases are filtered through electrostatic precipitator. The clinker cooler is primarily meant to transfer heat from the clinker to the pyroprocessing system in the form of hot gases, optimizing the whole system by reducing fuel consumption and improving overall energy efficiency.

Clinker leaving the clinker cooler is at a temperature of 100 degree Celsius capable of being handled by standard conveying equipment. Clinker is then stored in well sheltered stock piles.

  Manufacturing Clinker to Cement:

Stage 4

Final Grinding and blending

The black, nodular clinker, gypsum and fly-ash are stored in separate hoppers ready to follow the course of final grinding. From the hoppers the clinker along with gypsum and fly-ash are ground together in ball mills in defined proportions to form the final cement products. Fineness of the final products, amount of gypsum added, and the percentage of fly-ash added are all varied to develop the product variants and different grades of cement.

Stage 5

Distribution and Dispatch system

Each product variant is stored in an individual bulk storage silo ready to be dispatched. Cement is packed in bags using auto roto packer to maintain accurate weight of the cement in the bag and is distributed by road. Customers may also demand cement to be dispatched in bulk tankers.