Experimental study on the ash behaviour in combustion of pelletized residual agricultural biomass

Abstract

Agricultural residual biomass presents a high potential for energy use around the world, often not utilized to a large extent due to its significant differences with respect to other biomass types, such as the one of forest origin. These differences are mainly related to the characteristics of its ashes (quantity and composition) which increase certain problematic phenomena during combustion, among them bottom ash sintering and fly ash deposition. The main goal of this paper is the experimental study of these issues for four different agropellets made of residual agricultural biomass (one woody -vineyard pruning- and three blended with an herbaceous component -corn stover and/or barley straw-) and a forest wood pellet (used as a reference), evaluated under different operating conditions in a laboratory fixed bed reactor. The influence of inlet air flow and temperature on the sintering degree and deposition ratio has been analyzed in a systematic way. For the five biofuels, under tested conditions, a clear relation inversely proportional between air excess ratio and deposition ratio has been determined. Deposition was more substantial for the four agropellets; meanwhile the sintering degree was more important for the three with an herbaceous component. The information obtained in this research work is intended to help researchers and technologists to make choices regarding the design and operation of conversion systems adapted for agricultural residual biomass, enhancing its market penetration.