In the dry process, the raw materials are crushed dry, and the correct proportion of the materials is fed into a grinding mill. In the grinding mill, they are dried and finely powdered. The dry powder is then blended and corrected for its right composition and then mixed again by means of compressed air. The aerated powder behaves similar to that of a liquid. The blended mixture is sieved further and passed through a rotating disc called a granulator. In order to make the mixture as pellets, a small amount of water (about 12%) is added.
A small kiln is sufficient for the dry process. This process consumes less quantities of coal and is hence economical.
The pellets are passed through the kiln and form flakes after undergoing a series of chemical reactions and get fused. The fused material turns into nodular form of size 3–20 mm, known as clinker.
Then the clinker is cooled and ground in a ball mill with the addition of 2–3% of gypsum. The stages in the manufacture of cement by the dry process are shown in the flowchart (Fig. 6.5).
Figure 6.5 Flowchart for dry process
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