Full list of Nuggets
Portland cement is manufactured by heating limestone or chalk with clay in a rotary kiln to a high temperature (about 1450°C) to produce hard nodules of clinker that are then ground with a little gypsum in a ball mill. The firing process consumes significant quantities of fuel, usually coal or petroleum coke. Reduced fuel use is a fundamental objective of the cement industry. The major environmental concerns of cement manufacture are outlined in the Table.
|Stages in the cement making process
|Major environmental concerns
|1 Quarrying and processing raw material
|Scarring of landscape, transport produces dust and noise
|2 Burning raw material to make cement clinker
|Carbon dioxide emission from heating limestone and burning fuel
|Gas emissions, such as nitrogen and sulfur oxides (NOx and SOx)
|High energy use
|3 Grinding clinker
|4 Delivery to mixing plant, precast works, builders merchants
|Fuel, noise and traffic
The manufacturers have taken steps to minimise the impacts by:
1 Reducing primary raw material needs by increasing the use of by-products from other industries, along with dust suppression measures and landscaping after quarrying.
2 Use of waste products as alternative fuels (oil, solvents, tyres) along with greater emissions control and investment in more efficient plant (heat exchangers, pre-heaters, insulation). Reducing cement clinker by replacing during the grinding process with cementitious materials from by-products of other industries e.g. fly ash, ground granulated blastfurnace slab
3 Use of grinding aids to reduce clinker milling time and improved equipment efficiency.
4 Overnight deliveries, increased rail use, fuel efficient vehicles, reduction of empty truck movements by making use of returned concrete loads instead of dumping on site.
For information see MPA Cement
Acknowledgement: Concrete Society
Other references:Concrete and the Environment, published in CONCRETE in September 2001, pp39–46. Copies are available as a free download from the Members Area of the Concrete Society web site.