The cement industry is one glowing factor in the infrastructural and economical development of a nation. The clinker grinding process in cement manufacturing is one of the processes that factors in the effectiveness of the products and efficiency of the industry.
This article, therefore, aims to explain the need for a clinker grinding plant as well as insights into the process involved in clinker grinding in cement manufacturing processes.
Clinker Grinding
Coal grinding and burning is one of the most integral parts of cement manufacturing. The clinker (a hard mass of ash and fused coal which is a well-known residue of coal burning) is added to gypsum and mixed together in accurately known proportions. This becomes the feed of the grinding mills. Sometimes, chemical gypsum is used in place of the natural gypsum and this necessitates mechanical or natural drying process after which it can be used for the already cooled clinker and fed to the grinding mills.
It is noted that the gypsum is usually easy to be graded into fines compared to the clinker and since the strength of the cement is notable high when closely graded; there are improvements in tending to the clinker to achieve a specified product.
The Clinker Proportionate Grindability Index
The strength of the desired products of clinker grinding is due to the rate of hydration in the product. Therefore, the tendency of a clinker to be gradable into fines is dependent on the mineralogical composition as well as the time span of its production. It has been noted that the calcium silicate (C2S) content of the clinker is a prevailing factor that determines its capacity to be converted into the desired size of the fines. The higher the content, the more difficult it is to graded into the desired size.
In terms of its lifespan, it has been noted that the fresher the clinker, the harder it is. Therefore, in clinker grinding plants, the clinker is stored for about 2-3 weeks before use.
Clinker Grinding Systems and Processes
In most clinker grinding plants, factors that suit their prevailing conditions are considered before choosing a circuit system for clinker grinding. Open Circuit Mills or Closed Circuit Mills are quite effective in the process of clinker grinding but some conditions factor in its optimal use.
Open Circuit System for Mills
The operations of clinker grinding plants in open circuits are based on the offers of lower capital investment requirements, simplicity in operation and low maintenance costs, and better capacity to be handled under dusty conditions.
Closed Circuit System for Mills
Using the closed circuit system in clinker grinding plants is usually on an operational basis with an air separator. This circuit offers cement manufacturers:
- Lower power consumption, and the mills’ internals consumption is also lowered
- Higher strength and uniformity of the desired products as well as proper grinding of materials with different grindability indices
- In the grinding of clinkers, there are different grinding mechanisms applied to these circuit systems for optimal results depending on the desired products, the availability of the grinding system and the time limit for production.
The Operation of a Ball Mill, Bucket Elevator, Highly Efficient Air-Separator in a Closed Circuit System
The application of a roller press in the semi-finish mode and finish grinding in a ball mill using either an open or closed circuit system
- Mixed grinding in a roller press using a closed circuit system with an air-separator and successive finish grinding with a ball mill, BE and separator
- Grinding in a semi-finish mode with a roller press and completely finishing with a ball mill, BE, a separator in a closed circuit system
- Finish grinding with roller press with a de-agglomerator and air-separator in a closed system or using a vertical roller mill.
Finish Grinding and Grinding Aids
In any cement manufacturing plant, finish grinding is one of the processes applied to the materials before they are separated and bagged in silos. The application is based on the particle size specified for strength development and fineness quality and influence on the strength of the final products.
However, the facilitation of grinding of the clinkers is mostly done by aids such as Amine acetate, Ethylene glycol or Propylene glycol which, though have no effect on the final products, eases up the power and energy consumption of the plants. They help in optimising the materials used for finish grinding.
Atmospheric Conditions of Clinkerization Plants and the Cooling Procedures Used
A high rise in temperature is usually associated with the grinding of clinker and the heat is usually at 1200 C due to the gypsum in the mixture which on mixing forms a solidifying mass with the clinker.
The management of temperature is usually easier in closed circuits due to its higher temperature control, but the cooling can be done via the air separator by proper ventilation of the plant. This is done by water cooling procedures by using a sprinkler for the shell of the mills used or injecting water into the hot parts to cool them down.
