Ten residual biomass fuels for circulating fluidized-bed gasification

In co-operation with a Dutch company (NV Afvalzorg) and the Dutch agency fo r energy and environment (Novem), ECN has successfully tested 10 different biomass residues in its 500 kW(th), circulating fluidized-bed gasification facility. Among the fuels used are demolition wood (both pure and mixed wit h sewage sludge and paper sludge), verge grass, railroad ties, cacao shells and different woody fuels. Railroad ties turn out to contain very little ( heavy) metals. initially, fuel feeding problems often impeded smooth operat ion. Contrary to feeding systems, the circulating fluidized-bed gasificatio n process itself seems very flexible concerning the conversion of different kinds of biomass fuels. The fuel moisture content is one of the most impor tant fuel characteristics. More moisture means that more air is needed to m aintain the process temperature resulting in better carbon conversion and l ower tar emission but also lower product gas heating value and lower cold g as efficiency. So, for a good comparison of the gasification behaviour of d ifferent fuels, the moisture content should be similar. However, the moistu re content should be defined on an ash-free basis rather than on total mass (the usual way). Some of the ashes produced and retained in the second cyc lone were analysed both for elemental composition and leaching behaviour. I t turned out that the leaching rate of Mo and Br, elements only present in small concentrations, are preventing the ash to be considered as inert mate rial according to the Dutch legislation for dumping on landfill sites. (C) 2001 Elsevier Science Ltd. All rights reserved.