Fluidized bed combustion of solid lignin-rich residues from bioethanol production

Abstract

The behaviour of lignin-rich residues from a second generation bioethanol production plant has been investigated for fluidized bed combustion. The fuel has been characterized using lab-scale fluidized beds with the aid of different diagnostic and experimental protocols to investigate the devolatilization behaviour and rate, char burnout and fragmentation and attrition phenomena. The effect of bed temperature and fuel particle size onto the devolatilization rate was scrutinized, while the effect of the superficial gas velocity was studied onto the fragmentation and elutriation tendency during fluidized bed combustion experiments. A bimodal pattern in the time-resolved devolatilization rate was observed probably caused by the formation of a large-scale particle texture made of a macro-porous cortical region and of a core characterized by large voids. Devolatilization times were relatively long and increased when bed temperature was decreased. As regards fragmentation phenomena, primary fragmentation did not occur, while secondary fragmentation was active for large particles (>10 mm) at late conversion stage. Generation of fine carbonaceous particles by attrition was limited: it increased with the superficial gas velocity and it was more pronounced under inert than reactive conditions.