Utilization of industrial by-products - Flyash - Origin, production and characteristics

Fly ash is the residue of coal combustion in thermal power plants.

Presentations on fly ash are the subject of three articles:

• the present article [C 5 373] which sets out the nature and properties of these industrial by-products with a view to their use, relevant, as well as data on production sites;

• article [C 5 374] to follow, which deals with the wide range of possible uses for these materials;

• article [C 5 375] , which will be devoted to technical reports and presentations on recently completed projects using fly ash.

Here, we first describe the processes involved in power plant operation and ash recovery, which determine the different categories of ash produced with a view to their use. We then turn to the production sites.

The scale of ash production depends on the energy policy of the country concerned. Industrial by-products, such as fly ash, are available in large quantities worldwide, but in much smaller proportions in France.

Worldwide, coal –, whose reserves are still extremely large –, is the main resource used to generate electricity.

In France, only around 4% of electricity is currently generated by coal-fired power plants. Since French resources have been depleted, coal has been imported from various countries to meet these needs.

The economic stakes must not, however, overshadow those of the environment, which are of paramount importance. The modernization of thermal power plants and new "clean coal" techniques are helping to reduce the polluting effects of coal combustion.

Fly ash has remarkable characteristics, such as its pozzolanic power, which we describe at the end of this article. These properties...