Influence of biomass pretreatment on co-combustion characteristics with coal and biomass blends

Fuel blending is one of the most effective ways to use biomass to reduce the use of coal. In this study, co-combustion characteristics including NOx emissions, unburned carbon (UBC), and the char reactivity of coal, biomass, and pretreated biomass blends were investigated by using a lap scale drop tube furnace (DTF) and thermogravimetric analyzer (TGA) to evaluate the availability of pretreated biomass from torrefaction or ashless technology to a pulverized coal boiler. In addition, scanning electron microscopy (SEM) was used to analyze the morphology of biomass and pretreated biomass to observe the physical differences between raw samples and their chars. In the results, NOx showed a linear correlation with the content of inherent fuel-N of biomass except in blending cases with ashless biomass. This indicated that the yields of NOx in these cases were higher than both that of single coal and ashless biomass. In addition, UBC declined with increasing the biomass blending ratio for all blending cases, and this can be explained by examining the fuel ratio and SEM images of the fuel samples. Finally, blends with coal and torrefied biomass showed higher char reactivity and lower activation energy than that with ashless biomass as the blending ratio increased. Overall, this paper indicates that it is better to increase the blending ratio of pretreated biomass than raw biomass up to 30% for enhanced reactivity and reduced emissions.