Thermal Behavior of Coal and Biomass Blends in Inert and Oxidizing Gaseous Environments

Abstract

Oxy-fuel combustion and gasification (pre-combustion) may have potential for capturing carbon dioxide at lower costs for power generation. Oxy-co-firing and co-gasifying coal with biomass could further reduce effective CO 2 emissions and utilize renewable energy resources. A key feature of these two approaches is that they process fuel in concentrated CO 2 or O 2 /CO 2 instead of N 2 or O 2 /N 2 . Accurate predictive models of these processes using blends of coal and biomass can be used in process simulation and could aid in the development and implementation of these technologies. To de-velop these accurate predictive models, it is important to understand the conversion routes and thermal behavior of these fuels in appropriate gas environments. The objectives of this study are to investigate the impact of inert and oxida-tive gaseous environments on thermal behavior and reactivity of coal and biomass blends and to study the effect of bio-mass percentage on coal/biomass blend co-utilization. Fuel samples included a Powder River Basin (PRB) sub-bituminous coal, yellow pine wood sawdust pellets, and mixtures of 10 and 20 weight percent wood in coal. The samples were tested under N 2 , CO 2 , and 10% O 2 in CO 2 by volume using a non-isothermal thermogravimetric method for tempera-tures up to 1000˚C. Fuel weight losses of both coal and wood are essentially the same in CO 2 as in N 2 in the low tem-perature range, but higher in 10% O 2 in CO 2 compared to N 2 and CO 2 . However, total weight losses at 1000˚C under CO 2 and 10% O 2 in CO 2 are similar and higher than in N 2 due to char gasification by the CO 2 and combustion by O 2 . The char combustion in10% O 2 in CO 2 takes place at lower temperature than char gasification in CO 2 . Coal and wood blends have higher reactivity compared to coal alone in the lower temperature range due to the high volatile matter content of wood. Interactions of wood and coal in these gas environments and blend percentage are discussed.