Optimizing the operating parameters of torrefaction process on the combustion enhancement of coal/biochar blended fuels

Although the biomass is regarded as a suitable alternative fuel, its fuel properity and combustion characteristics are much different from fossil fuel. In order to make the properties of biomass more similar to coal, torrefaction was used to improve these disadvantages of biomass. However, operating parameters of torrefaction process are associated with the fuel property of biochar and coal/biochar co-combustion. Therefore, the Taguchi method was utilized to reduce the experimental runs and search for the optimum condition of torrefaction process. The produced biochar would blend with pulverized coal at 50% on gravimetric basis. Comparing the combustion behavior among the pulverized coal, biochar, and blended fuels, a thermogravimetric analyzer was used to observe weight loss of fuel from ambient temperature to high temperatures at fixed heating rate. The results showed the ignition temperature and burnout temperature of blended fuel would occur earlier than pulverized coal. In addition, the fuels were compressed as pellets and carried out combustion experiment in a practical system. The blended fuel has longer volatile combustion due to more volatile matter contained, while pulverized coal contained more fixed carbon results in persisting longer time during char combustion. The results showed that the coal/biochar blended fuel can effectively enhance the fuel conversion rate and combustion characteristic index. Furthermore, the results can be applied to co-firing in large scale boilers in the future.