Cement production involves raw materials being dried, ground, proportioned and homogenized before being transferred to rotary kilns to be burned. The resulting material, known as clinker, is pulverized with gypsum at the cement grinding mill to make OPC or mixed with other additives to make other types of cement. On average, approximately 960kg of clinker is used to make one ton of OPC.

The following diagram shows the production of dry-process cement:

Quarrying

The main raw materials used in cement production are limestone, silica sand, clay, iron sand and gypsum. Limestone, clay and silica sand are quarried by drilling and blasting and then brought to the crushing plants located adjacent to the quarries. Crushed limestone, clay and silica sand are then delivered by means of conveyor belt system or by truck.

In wet-process system, raw materials are ground wet and fed to the kiln in slurry form, which results in relatively high rates of heat consumption. In dry-process system, raw materials are ground dry and fed to the kiln in powder form. Given this advantage, dry-process kilns have been used by modern cement producers. Indocement uses the dry-process kilns, which consume less heat and are more efficient than wet-process kilns.

Drying and Raw Grinding

Raw materials are dried in rotary dryers using waste heat from the kiln . The moisture content is greatly reduced to improve quality control and handling. The dried materials are mixed and fed to raw grinding mills to produce "raw meal". During the process of grinding, samples are tested half-hourly through X-ray analyzers to ensure consistent raw meal quality. The blended raw meal is delivered into storage silos.

Kiln Burning and Cooling

Blended raw meal is transported by pneumatic conveyors to the kiln's suspension pre-heaters where it is preheated to achieve a high degree of calcination (oxidization of the calcium carbonate) before the raw meal enters the rotary kiln. In the rotary kiln, the preheated raw meal is completely calcined and finally sintered at 1,450 C to form clinker.

Hot clinker from the rotary kiln is discharged onto coolers where it is quenched and cooled by fresh air from high capacity fans. The air that passes through the clinker layer is thereby heated and is subsequently used as combustion air in the kiln. Cooled clinker is delivered to clinker silos

Finish Grinding

From clinker silos, the cooled clinker is mixed with gypsum and fed into the grinding mill to produce cement. The finished cement is then pumped into cement silos.

Packing

Cement is transferred from the storage silos to the packing plant for bag and bulk loading. Bagging is done by high speed in line and rotary packing machines. Filled bags are automatically weighed, sealed and loaded onto trucks by conveyor belt. The total combined rated capacity of all Indocement's packing machines is 5,000 tons per hour. Bulk cement is loaded into special tank trucks for delivery to customers' portable silos at construction sites or is trucked to Indocement's port facilities.