Manufacturing of Cement By Dry and Wet Process
Manufacturing of Cement
In the manufacturing of cement, the following three important and distinct operations occur :-
- Mixing of Raw materials.
The process, by which cement is manufactured, depends upon the technique adopted in the mixing of raw materials. Therefore, on the basis of mixing the raw materials, the processes may be classified as:-
- WET PROCESS
- DRY PROCESS
Out of these wet process is generally used.
The Raw material, which is used for manufacturing of cement, contains the following materials :-
- CALCAREOUS (i.e. chalk consists of limestone.)
- ARGILLACEOUS (i.e. clay consists of silicates of alumina.)
Here is manufacturing of cement by wet process
When the raw materials are soft , then wet process is preferably to be used. The cement is manufactured by the following procedure:-
Mixing of Raw Materials:
- In wet process, there are two raw materials e. calcareous and argillaceous. Initially Calcareous materials are crushed using crushers and argillaceous material are washed With water in container.
- After crossing the line stones are stored in silos similarly after washing the clay is stored in basins.
- The crushed materials from different silos and basins are drawn in correct proportions in a channel called wet grinding mills. Both the materials are intimately mixed in the presence of water and to form a fine thin paste known as slurry
- Slurry is then stored in another silo may be called as slurry silo where it is constantly stirred. The composition of raw materials is checked again and, if required, corrected by adding clay or chalk materials as desires.
Burning : In this operation, the slurry is directly fed into a long inclined steel cylinder called Rotary kiln. Inthis kiln there are 3 different zones shown in fig. below
Cement Manufacturing Process Flow Chart
(i) Drying Zones : In wet process, the drying zone is comparatively larger than dry process. In is because the raw material in slurry form is directly fed into kiln which have more amount of water. As shown in figure it is the upper portion of the kiln . In this zone, water is evaporated at temperature 100-400°C.
(ii) Formations of modules: As the slurry gradually descends in the kiln , the carbon di oxide from slurry evaporates and small lumps formed which may be called as modules.
(iii) Burning Zone:- The modules enter in this zone where temperatures is kept about 1400-1500° C. The modules are converted into dark greenish balls and the product obtained in kiln , known as clinker, is of varying size 5 to 20 mm. The clinkers are very hot when come out from this zone.
(iv) Cooling of Clinkers:- As shown in figure another rotary kiln is provided in opposite direction which is also inclined. It is used for cool down the clinkers up to about 90°C.
Grinding: The cooled clinkers are finally ground in ball mills or tube mills.
Also the gypsum is added during grinding about 2-4% . The gypsum acts as retarder and so allows the cement to mix with sand or aggregate and to be placed in postion. i.e. it increases the initial setting time of cement.
Storage and Packing : As cement comes out from grinding mills, it is collected in a hopper and taken in bucket elevator for storages in silos.
The cement from silos is packed by machines in bags. Each bag of cement contains 50 kg or 0.035 m3 of cement.
Now let’s know manufacturing of cement by dry process
When the available raw materials are quite hard, then this process is used . The cement by this process can be prepared by using following operations:-
- Mixing of raw materials
- Burning and Grinding
Mixing of Raw Materials : The raw materials i.e. argillaceous and calcareous materials are undergo the following stages :-
- Crushing : The raw materials , first of all , are broken in crushers to small fragments that vary in size.
- Drying: The crushed materials are dried by heating at sufficiently high temperature. It may be done in drying kilns.
- Reduction of size: The drying materials are then grind by using ball mills and tube mills to reduce the size of materials to find powder.
- Mixing in correct proportion : The finely dried materials are mixed in exact proportions . The mixing may be done either mechanically or by pneumatic methods(e. pumped under pressure).
Burning and Grinding: These operations are same as for wet process. Except the mixing of raw materials. In dry process the raw materials mixed,fined and then fed into kiln whereas in wet process, the raw materials are crushed separately and then directly mixed in correct proportion in the presence of water to make a fine thin paste known as Slurry.