Torrefaction of pine wood in a continuous system and optimization of torrefaction conditions

Red pine wood particles were torrefied in a screw conveyor reactor system continuously having a capacity of 5 kg/hour. During torrefaction, operating conditions were very important. Changes in the reactor temperature and the reactor residence times had large influences on product yields. With increasing torrefaction temperature, the volatile matter and oxygen content of biomass decreased, while fixed carbon content and heating value greatly increased. Design-Expert software package was used for the design of experiments (DOE) and to carry out the statistical analysis according to the experimental results. The optimum biocoal yield of 56.59%, energy yield of 47.49%, higher heating value of 26 761.9 kJ/kg, hardgrove grindability index of 91.76, H/C ratio of 0.099, and O/C ratio of 0.312 were obtained at 299.71 degrees C and 28.4 minutes (approximately 300 degrees C and 30 minutes). The biocoal prepared in this work exhibited similar properties to selected Turkish lignites. It suggests that the biocoal can be used as a supplementary fuel for production of energy in coal-fired combustion systems, especially as an auxiliary fuel for existing power plants.