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CEMENT MANUFACTURING PROCESS: MATERIAL PREPARATION TECHNOLOGY

We were discussing “Cements and its types” and " Raw materials for manufacturing of cements” and “pyroprocessing in cement industry” in our previous posts. We have also see the concept of cement manufacturing process and its selection in our recent post.

Today we are going to start here one very important topic i.e. process technology of cement manufacturing. We will understand the various terminologies and engineering concepts used in cement technology with the help of this category.

Further we will go for discussion of properties of burning technology, firing technology, clinker cooling and grinding, cement packing and dispatch, pollution control and much more facts about cement technology in our next post in this category of cement technology.

Let us see here the process technology of cement manufacturing

Material preparation technology

The purpose of the preparatory processing of raw materials is to convert these chemically and mineralogically different materials, usually supplied to the plant in form of coarse lumps, into raw meal or slurry of homogenized composition.

The principal processing stages are

Primary crushing
Pre-blending
Drying and Grinding
Homogenization

Screening and classifying are separation methods used to carry out size reduction with greater economy.

Reducing the raw material to a fine powder - conventionally called ‘meal’, is necessary in order to produce a homogenous mixture which will quickly be converted in the kiln into a homogenized clinker.

Size reduction is effected in at least two main stages
 Crushing (Primary reduction)
 Grinding (Fine reduction)

Crushing:

Crushing of raw materials is a must to suit subsequent milling operations.
There are two distinct crushing systems: Open circuit and Closed circuit. Out of the two, open - circuit system with one pass is widely used.

The selection of crusher type depends upon the abrasiveness and stickiness (moisture content) of the raw materials. Most raw materials are non- abrasive and Hammer- crusher with outlet grates is employed. It can crush limestone from a lump size of 1- 2 m down to 35 mm. Fineness of this degree is necessary if the subsequent raw mill is a ball mill, a high pressure roller press or a combination of the two.

An Impact crusher for these raw mills would be unsuitable since it usually gives product with bigger lump size (100 mm or larger). Such large lumps cannot be ground in a ball mill and may cause damage to the hard facing of the roller press. For such applications, an impact crusher must operate in closed circuit with a sieve.

For abrasive materials, Impact crushers and Hammer crushers are unsuitable as the downtime and maintenance cost will be too high. Hence Gyratory crushers (compression type) are used which are simple and sturdy and well suited for large feed sizes. The reduction ratio is lower and hence these crushers are used as primary crushers followed by a subsequent secondary crusher.

For sticky materials such as clay, Roll crushers with single or double rolls are most suitable.

Mobile Crushing Plants:

Because of the coarse grading of the fragmented rock pile produced by blasting in the quarry, this material cannot be directly handled by belt conveyors. In order to be able to use belt conveying from a point as close to the quarry face as possible, the rock pile will have to be crushed to ‘belt conveyable’ size, ~ 200 - 400 mm. 

The need for crushing at the quarry face and for moving the crusher along with the site of quarrying operation has led to the development of Mobile crushing plants ranging in capacity up to the highest throughput required.

Depending upon the method of moving the crushing plants from one place to another, a distinction can be made between the truly mobile (self - propelled and having their own integrated travelling machinery) and semi - mobile plants. Crushing plants may be wheel mounted, crawler mounted or rail mounted. There are also reloadable plants which are skid mounted and moving them requires powerful tractors.

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We will see other topic i.e. “Process technology of cement manufacturing: Storage and Pre-blending” in our next post in the category of Steel and cement technology. 

I am very thankful to Mr. Subrata Bhaumik, Independent cement consultant, for providing such beautiful information and contents about cement technology. 

Mr. Subrata Bhaumik has more than 50 (Fifty) Years (1965 - 2016) of Experience in Cement and other related Industry covering more than 100 assignments in cement plants with capacities ranging from 100 tpd to 10,000 tpd in India and abroad involving visit to 25 countries overseas in connection with work.

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