Fly ash characteristics in co-combustion of wood with coal, oil or peat

Co-firing of bio fuels with fossil fuels is often applied for environmental , technical and economic reasons. The properties of the solid residues prod uced from such fuel combinations cannot be predicted based on the propertie s of the ash from each fuel. In this work, Ay ash materials from combustion of wood/oil, wood/coal and wood/peat combinations were characterized. Elem ental compositions, mineralogical speciation of major elements as well as l eaching properties are reported. The Ay ash materials from co-combustion ha d in many aspects similar properties to those from combustion of pure wood. The differences noted were lower calcium, potassium and chlorine contents and higher contents of aluminium, iron and sulphur when coal or peat was ad ded. The speciation of alkali metals in the ash materials studied here is s omewhat different from that of wood ash, which leads to lower salt levels i n leachates. The pH of these leachates was not as high as in leachates from pure wood ash because of a lower content of calcium oxide in the ash. Trac e metal levels and leaching rates were in the same range as for wood ash ma terials studied earlier. (C) 1999 Elsevier Science Ltd. All rights reserved .