Manufacturing improvements for Portland cement
Actions being taken by manufacturers to reduce environmental aspects include the reduction of primary raw material needs by increased use of by-products from other industries and the use of waste products as alternative fuels (oil, solvents, tyres). The production process is being improved by dust suppression measures and the use of grinding aids to reduce clinker milling time.
During the past 40 years, the amount of fuel used in cement manufacture has reduced by 35% per tonne, with a consequent reduction in atmospheric emissions. Many materials previously considered as waste, such as used tyres, solvents, paper and plastics, contain recoverable energy and can be used as fuel in cement kilns. These and other measures will allow the cement industry to improve primary energy efficiency by over 25% by 2010 (using a 1990 benchmark), under the terms of the UK Climate Change Levy scheme.
High kiln temperatures, rigorous filtration, and emission monitoring systems enable these materials to be used as a primary energy source. They would have previously been disposed of by incineration and landfill. Indeed, this is a particularly effective and safe way of disposing of these materials.
As cement clinker is produced in the kiln, roughly the same amount of carbon dioxide is produced from the limestone or chalk component as that produced by kiln fuel combustion. Carbon dioxide is one of the so-called ‘greenhouse’ gases. As carbon dioxide production is a fundamental emission associated with cement manufacture, there is little scope for its reduction using current technology.
Emissions are also being reduced by investment in new plant and emissions technology, including ´dry´ kilns, and pre-heaters.
For information see The World Business Council for Sustainable Development - Cement Sustainability Initiative at https://www.wbcsdcement.org/
For further information see 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.