Cement Manufacturing – A Wet Process with the Flow Diagram

Portland Cement Manufacturing:

The raw materials used for cement manufacturing are calcareous materials, such as limestone or chalk, and argillaceous material such as shale or clay. Cement factories are installed where this raw material available in abundant quantity. Cement manufacturing units are placed near the consumption are, eliminating the inconvenience of long-distance transportation of raw and finished materials.

The manufacturing process of cement consists of,

  • Raw materials grinding.
  • Mixing this material in certain proportions depending upon their purity and,
  • Preparing Composition.
  • Burning this composition in a kiln at a temperature of about 1300 to 1500°C,
  • The process out clinker is cooled and ground to a fine powder with the addition of about 3 to 5% of gypsum.
  • The material produced by this process known as Portland cement.  

The cement manufacturing is done by majorly by two methods known as wet process and dry process depending on their mixing is done with water or without water.

The wet process of cement manufacturing too popular for several decades because of the possibility of more accurate control while raw material mixing. After that, the dry process of raw material mixing gained momentum with the modem development of the technique of dry mixing of powdered materials using compressed air. The dry process consumes much less fuel as the materials are already in a dry state, whereas in the wet process the slurry contains about 35 to 50 percent water. In a recent trend, the majority of cement factories are using the dry process of cement manufacturing.

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CEMENT MANUFACTURING – A WET PROCESS WITH THE FLOW DIAGRAM

In the wet process,

1) The raw limestone from quarries is first crushed to small size fragments. Then it is mixed with clay or shale in ball or tube mill and ground to form a slurry of a fine consistency with the addition of water. (The slurry is prepared with a water content of about 35 to 50 percent, fine crushed particle are held in suspension.)

2) This slurry is taken to slurry tanks or basins by pumping, where it is kept in an agitated condition using rotating arms with chains. Also, blowing continuously compressed air from the bottom to prevent settling of limestone and clay particles.

3) Slurry composition in the tank is tested to give the required chemical composition and corrected periodically in the tube mill.

4) After that, the slurry is stored in the final storage tanks and to keep slurry inhomogeneous condition continuous the agitation is done in tank.

5) This homogeneous slurry is sprayed on to the upper end of a rotary kiln against hot heavy hanging chains.

cement manufacturing by wet process
Wet Process

(The rotary kiln is an essential and important component of a cement manufacturing factory. It is made of a thick steel cylinder of diameter anything from 3 meters to 8 meters, lined with refractory materials, mounted on roller bearings and capable of rotating about its axis at a specified speed. It may of any length from 30 meters to 200 meters. When the slurry is sprayed on the hot surface of the flexible chain loses moisture and becomes flakes. These flakes (fragments) cutout and fall on the floor.) The rotary kiln keeps rotating causes the flakes to move from the upper end towards the lower end of the kiln.

7) The rotary kiln is fired from the bottom end. The fuel is powered coal, oil or natural gas.

8) With time the material accumulated to the lower end of the rotary kiln, the dry material undergoes a series of chemical reactions, in the hottest part of the kiln. At this point, the temperature is highest in the order of 1500°C about 20 to 30 percent of the materials get fused.

9) At this stage, Lime, silica, and alumina get recombined.

10) The fused material turns into a nodular form of size 3 mm to 20 mm known as clinker. 

11) This nodular form clinker collected into a rotary cooler where it is cooled under controlled conditions the clinker is stored in silos or bins.

12) These clinkers have weights about 1100 to 1300- gms per liter. The weight of the particle indicates the quality of clinker.

 13) These cooled clinkers are then taken in a ball mill with the addition of 3 to 5 percent of gypsum to prevent flash-setting of the cement. 

14) For crushing the clinker a ball mill is used. It consists of numbers of compartments charged with progressively smaller hardened steel balls.

15) The particles are crushed to require fineness are separated by currents of air and taken to storage silos from where the cement is bagged or filled into barrels.

16) In the modern method of cement grading, the particle size distribution of cement particles is maintained in such a way as to give a desirable grading pattern. Same as the good grading of aggregates is essential for making good concrete, it is now recognized that good grading pattern of the cement particles is also important.

CEMENT MANUFACTURING – A WET PROCESS WITH THE FLOW DIAGRAM

Advantages:

  • Raw material can be mixed easily, so a better homogeneous material can be obtained.
  • Capital cost (Cost of establishment) is comparatively less.

Disadvantages:

  • Mixing of Raw materials in wash mill with 35 to 50% water.
  • Materials exiting the mill are called “slurry” and have flowability characteristics.
  • Size of the kiln needed for the manufacturing of cement is bigger.
  • Fuel consumption is high i.e., 350 kg of coal per tonne of cement produced.
  • Cost of production is high.

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