Production Process

The main raw material required for cement manufacturing is Limestone. Limestone is mining from the Aruwakkalu quarry, which is located 40km away from the Puttalam plant, using blasting explosives.

Extracted limestone is transported to the plant by railway wagons for the crushing operation. Limestone is initially fed into a primary hopper from which limestone boulders are fed to the crusher (Impact hammer crusher) through the material conveyor. The crushed limestone pieces are discharged through the screen and are transported by belt conveyors to the stacking and storage process.

Limestone from the crusher is transported to the storage yard by belt conveyors. In order to increase the uniformity of the material, limestone is been stacked in the heap in a longitudinal manner with one layer on top of the other. Limestone is retrieved as a cross-section from the stockpile to reduce material variation which more homogeneous mixture can be obtained. The ultimate objective of Pre- blending raw material is to consume uniform thermal load in the pyro operation which reduces the quality variations of the final product and achieves optimum energy efficiency in the process.

In addition to raw material (limestone) from the quarry, minor additives are fed to the system to correct oxides of Silica, Alumina, and Iron in the raw material mixture. This additive is mainly contributing from laterite. There are other minerals such as slag, industrial sludge, and bottom ash used in minor quantities.
Limestone and additive (laterite) are feeding to the feeding hoppers from the storage yard. Ball mills are used to grind raw materials.Ball mill is a rotating drum-shaped chamber with wear-resistant liners mounted inside. Exhaust gas from the kiln is used as an energy source for material drying in the grinding operation and carrier gas for ground material transportation.

The pulverized raw material is called raw meal. The raw meal, next transported to the raw material silo after separating using the classifier.

The pyro operation consists of a 4 stages of cyclone separators and a Rotary Kiln. There are two cyclones in the stage 01 and whereas from stage 02,03 and 04 consisted with single cyclone. The discharge stream of the 4th cyclone is directed to the Rotary Kiln and followed by a clinker cooler. Kiln is a hollow cylindrical tube with refractory lining inside to withstand for the high temperature. The discharge end of the Kiln is connected to the cooler operated by grates.

Raw meal from the storage silo is initially fed to the top stage of the cyclone and transported to subsequent stages via pneumatic transport. Cyclone geometry with pneumatic air transport is caused to absorb heat from the gas to raw material and subjected to different physical and chemical reactions on it.

The main energy source for the pyro processing is coal which the material is pulverized by coal mill. Raw coal is grinded and finely grinded coal is stored in a silo and is fed to kilns via pneumatic transport. The flame propagates and the main burner which in Palavi operation it is used only single burner in the whole process. The burner is positioned along the kiln axis from the kiln outlet side making countercurrent flow of material and exhaust air. Temperature of the flame is approximately yield up to 2000 degrees of Celsius to heat up material up to 1450 degrees of Celsius.

The material at the kiln feed is around 90 degrees of Celsius would reach up to 850 degrees of Celsius when it discharges to the kiln m after passing through cyclone stages of the preheater. The feed that entered the Kiln at the inlet is gradually travelled towards the outlet with to the rotation of the Kiln and kiln inclination of 2-3 degrees. The feed is entered to the kiln at the temperature of 850oC and at the burning zone it is required to heat up to 1450 degrees of Celsius to generate C3S (Alite) which is the main mineral component of the clinker. Partially calcined material at the kiln inlet is undergone with calcinations liberating carbon dioxide (CO2) to form (CaO) during the motion through kiln at the temperature gradient of low temperature to high temperature. The major oxide in the process is CaO is subjected to react with other oxides as silica, alumina and iron oxide presented in the Raw Meal, at elevated temperatures forming the clinker compounds, namely Di-calcium Silicate or Belite (C2S), Tri- calcium Silicate or Alite(C3S), Tri-calcium Aluminate or Aluminate (C3A) and Tetra Calcium Alumino-Ferrite (C4AF). This process within the preheater and the kiln is called calcination and mineralization yield in the product of clinker.

At the elevated temperature of 1450 degrees of Celsius Alite formation was occurred and to retain the mineral structure of clinker it is required to cool it at a rapid rate. The hot clinker from the Kiln is cooled with the help of atmospheric air in the grate cooler. Inside the cooler, fixed and movable rows of plates with air flow nozzles are arranged. The atmospheric air is blown through the air nozzles of the cooler plates, and cools the hot clinker passing over the plates. Required air for the operation was delivered by five cooler fans operated centrifugally. Movements of the cooler plates could push material to the discharge end and cooled clinker is discharged to the apron conveyor after a clinker breaker operated by hammers. Part of the air, used to cool the clinker is absorbed to kiln in terms of secondary air for the burning operation through the draft of preheater fan. The remaining excess air was absorbed by cooler ID fan through heat exchanger and bag filter.

Manufactured clinker is stored in the clinker yard for the cement grinding purpose.

Clinker stored in the clinker yard is fed to Roller press unit with combination of gypsum and mineral component mixture (MIC). This MIC is a combination of limestone and fly ash and feeding proportions are defined depending on type of the cement produced. After the material is been fed to roller press unit portion of the coarse particles were transferred to cement mills which are horizontal ball mills. Roller press is performed as a pre- grinder for cement mills which reduces the particle size feeding to cement mills.

Cement from silo is extracted and fed to the rotary screen/vibration screen through of air slides/screw conveyors and bucket elevators. Manufactured cement in silos is dispatched in two forms which bulk tankers and cement bags. Those bags were packed in two packers and palletizer warehouse also setup to set pack of bags in a palette to cater for the peak demand. Cement is packed in 50 kg bags with the capacity of dispatch cement at 40 bags per minute.