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

Ping Wang, Sheila W. Hedges, Kent Casleton, Chris Guenther

Department of Energy (DOE), National Energy Technology Laboratory (NETL), Morgantown, USA.
Department of Energy (DOE), National Energy Technology Laboratory (NETL), Pittsburgh, USA.

DOI: 10.4236/ijcce.2012.13004                

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 CO₂ emissions and utilize renewable energy resources. A key feature of these two approaches is that they process fuel in concentrated CO₂ or O₂/CO₂ instead of N₂ or O₂/N₂. 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 develop 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 oxidative gaseous environments on thermal behavior and reactivity of coal and biomass blends and to study the effect of biomass 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 N₂, CO₂, and 10% O₂ in CO₂ by volume using a non-isothermal thermogravimetric method for temperatures up to 1000℃. Fuel weight losses of both coal and wood are essentially the same in CO₂ as in N₂ in the low temperature range, but higher in 10% O₂ in CO₂ compared to N₂ and CO₂. However, total weight losses at 1000℃ under CO₂ and 10% O₂ in CO₂ are similar and higher than in N₂ due to char gasification by the CO₂ and combustion by O₂. The char combustion in 10% O₂ in CO₂ takes place at lower temperature than char gasification in CO₂. 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.

Keywords

Pyrolysis; Gasification; Combustion; Coal-Biomass Blends

Conflicts of Interest

The authors declare no conflicts of interest.

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