Leucaena biochar produced by microwave torrefaction: Fuel properties and energy efficiency

This study carried out leucaena torrefaction by using microwave heating to investigate the fuel properties of biochar and the energy efficiency of the technique. Both maximum temperature and heating rate increased with increasing microwave power level. Processing time was also an important operational parameter, but its effect was weaker than that of microwave power. The heating value of torrefied product was higher at higher power level and longer processing time, but the mass and energy yields were lower due to higher energy input and thus more intense reaction. Heating value was approximately 30 MJ/kg at a microwave power level of 250 W for 30 min processing time. The fuel ratio of torrefied leucaena was up to 3.7, which is much higher than that of bituminous coal and thus can be regarded as an alternative fuel to replace coal or co-fire with it. The energy return on investment of microwave torrefaction of leucaena can be 1.4, 17, and 34 when the handling capacities are 8, 100, and 200 g, respectively. Therefore, microwave torrefaction of leucaena is a promising technique that can be feasible if deployed at industrial scale. Activation energy and pre-exponential factor were 24.46 kJ/mol and 9.66 1/s, respectively. © 2017 Elsevier Ltd