Energy performances of molded charcoals from bamboo and Chinese fir blends: influence of pyrolysis temperatures and residence times

To investigate the effect of pyrolysis temperatures and residence times on the fuel characteristics of mixed-biomass molded charcoals, the waste of bamboo and Chinese fir were uniformly mixed to briquettes, which were further carbonized to molded charcoals under various pyrolysis conditions. It was concluded that the molded charcoals demonstrated desirable properties of solid fuel, including a high heating value of 32.65–33.85 MJ/kg, an energy enrichment factor (EEF) of 1.65–1.71, a calorific value improvement (CVI) of 64.73–70.79%, an energy yield (EY) of 44.77–48.73% and a fuel ratio (FR) of 3.94–13.34. Pyrolysis temperatures had a more significant impact on fuel characteristics than residence times. The content of volatile matters, H/C, O/C, EEF, CVI, EY, and activation energy decreased as pyrolysis temperatures and residence times increased. In contrast, the content of fixed carbon (FC), carbon (C), ash, carbon densification factor (CDF), and fuel ratio (FR) increased. The combustion of molded charcoals mainly occurred at temperatures ranging from 300 °C to 550 °C. As pyrolysis temperatures increased, the combustion process shifted to the high-temperature zone, decreasing the combustion reaction. [Display omitted] •The mixed biomass molded charcoals had high-energy densification.•Pyrolysis temperatures impact the energy performance more significantly.•Pyrolysis increases carbon densification factor, fuel ratio and calorific value.•Pyrolysis decreases the H/C, O/C, energy enrichment factor and activation energy.•Pyrolysis can shift the combustion process to the high-temperature zone.