Effects of carbonization conditions on the yield and fixed carbon content of biochar from pruned apple tree branches

Abstract Pruned apple tree branches are abundant and ideal raw material for biomass carbonization due to less ash. It would provide valuable guide to study the effect of carbonization conditions on the biochar characteristics for high-efficiency energy utilization of pruned branches. In this study, we systematically investigated the effects of carbonization conditions on yield and fixed carbon content by using the reaction temperature, heating rate, and holding time as factors in an experiment. The results were evaluated through a single-factor test and response surface analysis. Based on the results of single-factor experiments, the following conditions were determined to be appropriate for the carbonization of pruned apple tree branches: a temperature of 500°C, heating rate of 4°C/min, and holding time of 120 min. According to the central composite design test of the response surface methodology, the temperature, heating rate, and holding time had an extremely significant effect on yield and fixed carbon content. The effects of the main factors influencing yield decreased in the order temperature> holding time> heating rate, whereas that on the fixed carbon content was temperature> heating rate> holding time. In the range of the factor levels studied, the interaction between temperature and holding time has a significant effect on yield and an extremely significant effect on the fixed carbon content. The interactions between pairs of the other factors did not significantly affect the yield or fixed carbon content.