Co-Firing Cassava Rhizome and Eucalyptus Bark in a Fluidized-Bed Combustor Using Reburning: Combustor Performance and Time-Related Bed Behavior

Pelletized cassava rhizome (base fuel) and eucalyptus bark (reburn fuel) with elevated potassium content were co-fired in a conical fluidized-bed combustor using reburning to reduce NOx emissions. Long-term co-firing tests were performed with two alternative bed materials, pure alumina sand and a mixture of alumina sand and silica sand (in equal wt.%), to mitigate bed agglomeration. All experiments were performed with constant operating parameters (total heat input to the reactor, energy share of the reburn fuel, excess air, and secondary-to-total air ratio). Physical and chemical characteristics of the bed materials and particulate matter were quantified at different time instants. The study showed weak effects of the bed material type on combustion and emission performance of the combustor. When co-firing the selected biomass fuels, high (over 99%) combustion efficiency can be achieved at about 45% NO emission reduction, as compared to firing the base fuel alone. Using the selected bed materials, bed agglomeration can be prevented in the combustor for a relatively long operating time. However, the bed materials showed time-domain changes in physiochemical characteristics and a diminishing capability to resist bed agglomeration, particularly when using a mixture of alumina and silica sand.