In the EN 14588 standard, biomass is defined as “material of biological origin excluding material embedded in geological formations and transformed to fossil”. When discuss­ing solid biofuels, one generally assumes that the fuel has to have 100% biological origin and that it is a virgin material, not a waste. A few points should be made here.

Peat is normally regarded as something between a renewable and a fossil solid biofuel. From our point of view, peat is a biomass because:

It agrees with the definition in the standard.

The annual formation of peat in Sweden and Finland is much larger than the yearly harvest.

Vast peat land areas have already been drained in Sweden and in Finland, and these areas now leak climate change gases; utilising the energy that the oxidation releases is much better than not using it at all.

Harvesting old peatlands increases the rate of growth of new peat.

This being said, peat is a minor fuel: woody biomass represents 48% of the fuel supplied to district heating systems in Sweden, on an energy basis. Peat represents only 5%, but it is often used for its comparatively high sulphur content as an auxiliary fuel to abate corrosion.

Unless the biomass is harvested solely for energy and used as is, most solid biofuels are actually wastes. For example, logging residues are considered as virgin biomass although technically they are residues from the conventional exploitation of forests. Analogously, residues from sawmills, board production, and pulp and paper mills combusted at the mills for the energy needs of the mills are somewhere between virgin biomass and wastes. Waste biomass is still biomass according to EN14588. For example, often 85% of the energy in MSW is biomass, and industrial biomass waste contains normally somewhat less than that.

Incineration is destruction of waste without utilisation of the energy produced. This does not occur in Sweden, where all waste-burning plants provide heat to district heating systems and most of them are cogeneration plants. The Swedish High Environmental Court wanted to regard all combustion of industrial or municipal waste as incineration. It has, however, been overruled by the Advocate General of the EU: if the main purpose is to generate energy, then this is co-combustion, even if all fuel fractions are wastes.

To keep within the purpose of this review of the Ash Programme, we will not consider residues from the combustion of MSW. The review deals with other non­fossil fuels, i. e. those originating from wood or peat. The properties of these residues are discussed in Sect. 11.2.4.