Production process of cement
In the times of Egypt and Greece, sintered and ground lime or plaster was used as cement for civil engineering and construction. In the 19th century, portland cement was produced in England. This manual covers energy conservation in portland cement production.
A cement production plant consists of the following three processes.
1. Raw material process
2. Clinker burning process
3. Finish grinding process
The raw material process and the clinker burning process are each classified into the wet process and the dry process.
In the wet process, raw materials other than plaster are crushed to a diameter of approximately 20 mm by a crusher and mixed in an appropriate ratio using an automatic weigher, as shown in Fig. 1. Then, with water added thereto, the mixture is further made finer by a combined tube mill with a diameter of 2 to 3.5 m and a length of 10 to 14 m into slurry with a water content of 35 to 40%. The slurry is put in a storage tank with a capacity of several hundred tons, mixed to be homogenized with the corrective materials, and is sent to a rotary kiln for clinker burning. In the wet process, the slurry can be easily mixed but a large amount of energy is consumed in clinker burning due to water evaporation.
In the dry process, crushed raw materials are dried in a cylindrical rotary drier having a diameter of 2 m and a length of about 20 m for example, mixed by an automatic weigher, ground and placed in storage tanks. The resultant mixture is further mixed to make the ingredients uniform, and sent to a rotary kiln for clinker burning.
These processes are selected with consideration given to properties of raw materials, costs of fuel, conditions of location and others. For the wet process, plant construction cost is rather low and high-quality products are manufactured easily. On the other hand, the dry process consumes less energy and its running cost is lower. quartz manufacturing industry
The progress of technology is, however, eliminating the differences in quality between products from the above processes, while needs for energy conservation are getting increasingly strong. In future, the wet process will not be employed positively.
Finish grinding process
The finish grinding process is roughly divided into an open circuit grinding system and a closed circuit grinding system. The mill used is a tube mill or ball mill. In Fig. 11, ��a�� shows a closed circuit
and ��b�� shows an open circuit. crusher for silica sand
In the open circuit mill, the mill shell has a length of about 4 to 5 times of its diameter to obtain a prescribed fineness, and the shell outer wall is sprayed with water to prevent the temperature of the product in the mill from rising. It is also possible to spray water into the mill interior but the closest attention has to be paid so as not to deteriorate the product quality.
In the closed circuit mill, the mill has a length of 3 times or below of its diameter so as to accelerate the passage of the product. The separator works as a cooler for the product in addition to its function as classifier for the product.