Bundling different residues into one use in Table 11.2 does not contradict our attention to detail in Table 11.1. The properties of individual combustion residues need to be taken into account even when considering the same use. All quantitative information on the properties of ash that has been determined in the Ash Programme as well as all information from Swedish R&D projects on ash is stored in a database, Allaska. It is available in Swedish and English at http://www. askprogrammet. com.1

11.2.4.1 Pulverised Fuel Furnaces

Pulverised fuel (PF) furnaces are often very large furnaces converted from furnaces for coal or oil to biomass. The fuel must be ground finely for it to be injected into the 1rThe Web site of the Ash Programme will soon be incorporated into that of Varmeforsk (http:// www. varmeforsk. se), but visitors will be redirected to the Varmeforsk Web site.

burners. This is not a very common type, as one usually prefers to retrofit such a furnace with a grate or to convert it to a fluidised bed furnace. However, when there are severe constraints on space in an existing combustion plant, a new PF furnace may be attractive.

The major part of the residues is fly ash. Having passed through high tempera­tures, 1,200°C and more, fly ash consists of small glassy particles that can yield pozzolanic reactions as in Portland cement. Biomass fly ash is not as good a binding material as coal fly ash, but it is very suitable for road building.

In converted coal or oil furnaces, the bottom ash usually has high contents of unburned carbon and it may be used as fuel in fluidised bed furnaces. It is a poor road building material because of its high water uptake. However, it may be used as low-quality filling material.