Effect of secondary gas injection on the peanut shell combustion and its pollutant emissions in a vortexing fluidized bed combustor.

Peanut shell is a common agricultural waste in Asia, and its high calorific value is suitable to be used as a fuel. In this study, a vortexing fluidized bed combustor (VFBC) with silica sand as the bed material was used for peanut shell combustion. There was no indication of bed agglomeration during combustions for as long as 12h. The temperatures and gas concentrations were measured along the axial direction at various operating conditions, including excess oxygen ratio and secondary gas flow rate. Results show that CO emission decreases with rising excess oxygen ratio and secondary gas flow rate, while NOx emissions show a reverse trend. To meet the minimum CO and NOx emission standards of Taiwan EPA, excess oxygen ratio ranging from 40% to 55% and secondary gas flow rate ranging from 1.56 to 2 Nm(3)/min are found optimal for crushed peanut shell combustion in a VFBC.