Combustion characteristics of torrefied biomass materials to generate power

Co-firing of biomass with coal for power generation is an effective way to lower the use of fossil fuels and to mitigate CO₂ emissions. However, high moisture content, high yields of volatiles, low density, and insufficient calorific value of biomass are the main challenges to burn them with coal in co-combustion systems. Also, co-firing systems usually suffer mainly from high volatile matter content of biomass that leads segregation of coal and biomass from each other during co-combustion. In this context, several woody biomass species such as olive milling residue (OMR), rhododendron (RH), and ash tree (AT) were subjected to torrefaction process at temperatures of 200, 250, and 300°C under nitrogen atmosphere to produce biochars that have lower content of volatiles and higher content of calorific value. The biochars were characterized by the proximate and ultimate analyses and the calorific value. It was found out that so significant improvements can be achieved in the calorific values that the biochars became almost comparable with sub-bituminous coals in terms of the calorific value. Besides, the burning reactivities of these biochars revealed that significant reductions took place in the burning reactivities through torrefaction. In addition, the burning characteristics of these biochars were investigated by thermal analysis methods.