Technical and Environmental Feasibility of Co-firing Torrefied Biomass in a Coal-fired Power Plant

Biomass torrefaction is a thermochemical pretreatment process performed at a temperature range of 200
^o
C-300
^o
C in an inert environment. Moisture and part of the hemicellulose are released during the process resulting an energy densified solid fuel. In this study, rubberwood chips were torrefied at a temperature of 300
^o
C for 60 minutes. The results show that the lower heating value of biomass increase from 14.58 MJ/kg to 16.38 MJ/kg after torrefaction. Further, a 300MW
_e
coal-fired power plant was simulated using Aspen Plus software and co-firing possibilities of both raw and torrefied rubber wood were evaluated. The results reveal that up to 10% of thermal input can be substituted by raw rubberwood whereas torrefied rubberwood has the potential to substitute around 20% of thermal input without compromising the electrical efficiency. The total input mass flow rate is a crucial factor when co-firing is to be implemented in an existing plant even though it gives the expected energy output with a further increase of torrefied biomass share. With increasing co-firing ratio, it is observed that the total NO
_x
and SO
_x
emissions are reduced due to low N and S content of biomass. Further, combustion efficiency is increasing with increasing co-firing ratio of torrefied biomass.