Treatment and use of bottom bed waste in biomass fluidized bed combustors

Abstract

Bottom bed waste (BBW) from combustion of forest biomass residues was characterized aiming its use as partial substitute of fresh bed sand (FBS) in industrial bubbling fluidized bed combustors (BFBC). BBW partide size distribution, elemental composition (mainly Si, Ca, Al, Na, K, P and Mg) and mineralogy were evaluated considering also the influence of the characteristics of the biomass used as fuel. Biomass combustion experiments were developed using a pilot-scale bubbling fluidized bed combustor. The operating conditions during the experiments were monitored, namely the flue gas composition (CO2, O-2 and CO), temperature and pressure, and compared with data collected from BFBC located in two industrial biomass thermal power plants. Physical, chemical and mineralogical characteristics of the FBS and BBW revealed that practices related with biomass handling at the forest strongly influence the BBW properties, in terms of not only coarse soil particle addition (>1.0 mm) but also mineralogically. However, the results obtained here indicate that by sieving of BBW it is possible to recover almost 60% of the original BBW particles (size between 0.3 and 1.0 mm), which have properties that allow its reuse as substitute of FBS for bed make-up in industrial BFBC.