Fluidized Bed Combustion of Leached Rice Straw

Abstract

Leaching of inorganic constituents from biomass offers an approach to avoid extensive ash slagging, deposition, and bed agglomeration associated with many herbaceous materials including cereal straws. Leaching occurs naturally in the field when straw is exposed to rainfall, or it can be conducted under controlled conditions in industrial apparatus. Elemental composition and ash fusibility show that leaching can result in significant improvements in combustion characteristics of rice straw and other biomass. Bench-scale combustion in an atmospheric fluidized bed combustor confirms that the extensive bed agglomeration that occurs with combustion of untreated rice straw does not take place with naturally leached rice straw at combustion temperatures up to 900 °C. In addition, blending leached rice straw into a wood-based fuel blend does not increase but rather leads to a decline in ash deposit formation rate. The mechanism for a decline in deposition rate is not fully understood but may be related to the increased loading rate of ash in the furnace and possibly higher erosion rates of deposits that do form. Results confirm observations made during limited full-scale tests and further demonstrate that leached rice straw can be used as fuel without the rapid and undesirable ash deposition generally associated with untreated rice straw.