Manufacture of Portland cement-Basic Civil Engineering|Industries Extension Officer
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Manufacture of Portland cement |
There are three main operations involved in the manufacture of ordinary or Portland cement
1.Mixing of raw materials
2.Burning
3. Grinding.
1. Mixing of raw materials:
There are two methods in the mixing of raw materials of cement.
a. Dry Process:
In dry process, the calcareous materials such as limestone and argillaceous materials such as clay are separately ground in ball mills or jaw crushers.
This powder is then stored in silos or hoppers.
Then they are mixed in correct proportions.
This raw material is stored in storage tank
b. Wet process:
In wet process, calcareous materials are crushed and stored in silos or storage tanks.
Argillaceous material such as clay is washed and stored in basins.
The crushed limestone from silos and wet clay from basin are conveyed to ball mill or tube mill and ground to form slurry.
2. Burning:
The burning of the dry mixture or fine slurry is carried out in a long rotary kiln.
The rotary kiln consists of a steel tube steel tube of diameter varies
from 250 cm to 300 cm and of length from 60m to 120m.
It is laid with a slight inclination of 1 in 30 towards the down end.
the kiln rotates about its longitudinal axis at the rate of one revolution per minute.
From the storage tank the collected slurry is injected at the upper end of kiln.
The hot gases or flames are forced through the lower end in kiln.
Portion of the kiln near its upper end is known as dry zone and in this zone, the water from slurry is evaporated.
As the dried slurry descends towards the burning zone, carbon dioxide from the slurry is evaporated and it is converted into small lumps called nodules.
As the nodules are heated to the temperature of 1500°C to 1700 C, then clinkers are formed.
Cement is obtained by grinding these clinkers.
These hot clinkers are collected in containers of suitable size.
3. Grinding:
The grinding of the clinker is done in ball mills or tube mills.
A small quantity, about 2 to 4 percent of gypsum is added.
Gypsum controls the initial setting time of cement.
The finely ground cement is stored in silos.
It is then weighed and packed in bags.
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