Cement Industry Overview

	Concrete is used as a material in quantities second only to our use of water.
	As much as 1.25 tonnes of CO2 is produced for every tonne of cement.
	Around 1600 kg of raw material is needed to produce 1000 kg cement.

Today’s cement industry

Portland cement, the basic ingredient in concrete, was first produced and patented in 1824 by a British stonemason. Today around 1700 million tonnes of cement are used every year, with different types manufactured to meet various chemical and physical requirements. To produce these requires a clear understanding and careful control of the manufacturing processes.

Detailed information about the history, manufacture and different types of Portland cement, including a virtual plant tour, is freely available on the website of the Portland Cement Association www.cement.org.

A recent report* concludes that global cement consumption rose an average 2.75% in the period 2000-2002 and at the end of 2002 there were an estimated 1447 integrated production facilities and a further 250 separate grinding installations world-wide.

Key stages in cement production

Cement production is one of the world’s most energy intensive industries. Key production stages can be summarized as:

1. Raw materials
These are generally combinations of limestone, shells or chalk, and shale, clay, sand or iron ore, usually mined from a quarry close to the plant where they undergo reduction using primary and secondary crushers. When the reduced materials reach the cement plant they are proportioned to create a cement of specific chemical composition. Much work is being done on the use of alternative raw materials – often the by-products of other industrial processes. These can minimize the effects of quarrying, reduce the impact of the cement plant on the local environment and enable the cement industry to become a major player in materials recycling.

There are two basic methods used in Portland cement production – wet and dry. In the dry process dry materials are proportioned, ground to a powder, blended and fed into the kiln dry. The wet process involves adding water to the proportioned raw materials and completing the grinding and blending operations in slurry form.

2. Pre-heater
To conserve energy, most modern cement plants pre-heat raw materials before they enter the kiln, using the hot exhaust gases from the kiln itself.

3. Kiln
The mixture of raw materials is fed into the upper end of a rotating, cylindrical kiln, which achieves temperatures in excess of 1000°C. It passes through at a rate controlled by the slope and rotational speed of the kiln. Chemical reaction inside the kiln leads to the fusion of the raw materials to produce clinker. Traditionally kiln fuels have been powdered coal or natural gas, but increasingly alternative fuels are being used. These include materials such as scrap tyres, processed sewage sludge and packaging waste.

4. Cooling/finish grinding
Clinker is discharged from the lower end of the kiln and transferred to various types of coolers. Cooled clinker is combined with gypsum and ground to a fine powder in a ballmill to produce the final grade cement.

Where is on-line particle sizing used?

Using real-time on-line particle size analysis in the finish mill to monitor the cement final grade translates directly into energy savings by reducing overgrinding and. It allows optimal use of the plant and generates sustainable improvements in product quality and consistency.

*Global Cement Report 5 (2003); International Cement Review