EFFECT OF COCOMBUSTION OF BIOMASS ON EMISSIONS IN PULVERIZED FUEL FURNACES

Biomass not only has a considerable potential as an additional fuel so urce but it also shows a reasonable cast level in comparison to other renewable energies. The practicable fuel types are both residual mater ial from forestry and agriculture, such as wood or straw, and especial ly cultivated reproducible feedstock such as Miscanthus Sinensis, whol e cereal plants, poplars, or willows. Besides, as single fuel, it is a lso considered to be sensible to utilize biomass in co-combustion in e xisting firing systems, such as pc-fired power stations. In order to p romote the employment of biogenetic fuels, the European Union, within the framework of the APAS Clean Coal Technology Programme, initiated a research project concerning the co-combustion of biomass in existing firing systems. The focus of the investigations in experimental and in dustrial-scale plants was to establish the impact of co-combusting bio mass and sewage sludge in coal-fired systems with regard to combustion behaviour and pollutant formation. The investigations were carried ou t on laboratory scale and pilot scale, as well as in large-scale plant s. The task of the Institut fur Verfahrenstechnik und Dampfkesselwesen (IVD), University of Stuttgart, within the EU clean coal technology p rogramme, was to investigate the effects of co-combustion of solid bio mass (Miscanthus, straw) and municipal sewage sludge together with the primary fuel hard coal. The experimental plant used was a semi-indust rial pulverized fuel test rig (0.5 MW). Within the scope of this publi cation, a synopsis shall be given of the outcome of the project, with special regard to the effect of co-combustion;on emissions. The invest igations reveal that biomass addition has a positive effect on emissio ns. Since biomass in most cases contains considerably less sulphur tha n coal, an increasing biomass share in the thermal output makes the SO 2 emissions decrease proportionally. In addition, SO2 can partly be ca ptured in the ash by the alkaline-earth fractions of the biomass ash, As for sewage sludge, the emissions of SO2 correlate with the sulphur content of the fuel and, hence, rise with an increasing share of this biomass. Due to the high volatile content of the biomass, low NOx emis sions can be achieved both by air staging and by reburning. (C) 1998 E lsevier Science B.V.