Green Energy From Wood Based Fuels Using Foster Wheeler CFB Boilers

Abstract

Biomass fuels are one important way to meet the Kyoto requirements for the reduction of global CO2 emissions in power generation. For years, Foster Wheeler CFB-boilers have been used for combustion of waste wood and forest residues. The latest CFB-projects in Germany are utilizing demolition wood and production waste from wood-working industries. Compared to coal, wood-based fuels have some special characteristics. To ensure smooth fuel feeding, the wood fuels have to be carefully crushed and chipped. From demolition wood it is necessary to remove metals and other large uncombustible impurities. Moisture content of wood waste may vary in a wide range from 10–60%. To ensure steady heat input into the boiler using volumetric feeders, a good homogenization at fuel yard is required. Fuel ash contents are low and particle sizes are fine. Due to high potassium contents, ash melts at low temperature; hence, ashes have a tendency for fouling and slagging in boilers. Biomass fuels also contain some chlorine, which together with alkalies, induces aggressive corrosion. The demolition wood may contain additional heavy metals. Corrosion abatement is discussed and related to the novel INTREX superheater technology. In INTREX boilers, final superheater and reheater are placed in the hot solid return flow back from the cyclone to the combustion chamber, thus avoiding high temperature corrosion. This allows steam temperature after superheater in the flue gas channel to be kept below 400°C. The arrangement also prevents effective fouling of heating surfaces. The longtime experience of demolition wood-fired plants in Hornitex Beeskow, 86.3 MWt, 110 t/h, 480°C, 89 bar (startup 1996), Hornitex Horn 94 MWt, 120 t/h, 480°C, 89 bar (startup in 1999) is presented. Operational results from Ko¨hler Kehl 44 MWt, 59 t/h, 500, 90 bar (startup in 2002) are discussed. The used steam parameters allow an increase of power production efficiency from 25–30% to 33–35.5% using steam cycle without reheat and with reheat up to 36.4% (gross) in condensing operation.