Study on one-dimensional steady combustion of highly densified biomass briquette (bio-coke) in air flow

Abstract

Combustion experiments on cylindrical bio-coke (BIC), a highly densified biomass briquette, have been conducted to observe whether quasi-one-dimensional steady combustion can be attained in room temperature air flow. In the experiments, the air flow velocity was the main test condition and the fuel consumption rate when the bottom surface of the BIC sample burned was evaluated as the regression rate of the combustion zone at the bottom surface. In addition, one-dimensional calculations based on an energy equation at the combustion zone were conducted to understand the mechanism that results in steady combustion and predict the effect of water and volatile matter content in BIC on the extinction limit. The results showed that steady combustion of the BIC sample could be attained in 4.67m/s or more, and, in contrast, extinction was observed in 3.82m/s or less. The critical regression rate explained by the combustion zone temperature was shown, and the reason combustion becomes unsteady could be explained by the energy balance at the combustion zone. Though the main reason for extinction was radiation heat loss, the heat loss by water and volatile matter was not negligible. Therefore, the effect of water and volatile matter content on steady combustion must be considered.