Core Raw Material—Cement - The Issues and Discussion of Modern Concrete Science - page 38

3.2 Overview of Cement Production Process

Manufactured process of cement can be simply summarized as “ two grinding and

one calcining, ” namely raw meal grinding, clinker calcining, and cement grinding.

1. Raw meal grinding
Raw materials of limestone, shale, and clay are carried into crusher. Having been
crushed or hammered into pieces, they will be grinded. This is called raw meal
grinding.

2. Clinker calcining

High-temperature sintering system includes three procedures, which are drying,
preheating, and sintering.
Sintering system is divided into vertical kiln and rotate kiln. Most of the demotic
shaft kiln is basically sifted out due to instable quality so far. Sintering system can
also be differentiated as dry method and wet method. Dry method is prohibited by
environment protection bureau as causing too many dusts, but its low costing. Wet
method is environment protecting, but the cost is relatively higher. In recent years,
many cement factories have installed dedusting equipment. Therefore, cement
production in our country has changed into dry method mainly so far.
Calcining is the core section of this process. Raw material is continuously
weighted and moved into cyclone separator which is located at the bottom of
preheater. Then, materials in preheater are heated by ascending hot air. In the huge
rotate kiln, raw material is transformed into clinker under the temperature of nearly
1,450

° C.

3. Cement grinding

Clinker is taken out from the bunker and mixed with gypsum and additives in
proportions before clinker grinding.
During the process of clinker grinding, clinker and other materials are grind into

fines together. As much as 5 % of gypsum and other admixtures are added so as to
control setting time and types of cement. All the materials will be fed into ball mill
to continue the remaining grind manufacturing.
Clinker grinding can be divided into open-circuit and close-circuit grinding. As
close-circuit grinding can boost 3- and 7-day strength of cement by decreasing the
content of coarse particle drastically, clinker grind technologies all over the world
mainly adopt close-circuit grinding at present.

4. Storage and transportation

Cement end products are reserved in huge concrete bunker. They will be
transported from the factory if the soundness and other indexes are quali

ed.