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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.
Highlights
Coal is the dominant energy resource for electricity generation in the US because coal is abundant and less expensive than other options
The tests were conducted by a using non-isothermal method in a PerkinElmer Pyris 1 thermogravimetric analyzer (TGA)
The present study investigates the impact of biomass percentage on the thermal behavior of coal and biomass blends in inert (N2) and oxidizing gases (CO2 and 10% O2/CO2)
Summary
Coal is the dominant energy resource for electricity generation in the US because coal is abundant and less expensive than other options. Co-firing technology simultaneously fires coals with biomass in a coal-fired boiler. It generates “green” power by utilizing renewable energy resources and reduces coal CO2 emission since biomass is renewable and carbon neutral [1,2]. Most biomass has little or no sulfur or nitrogen, co-firing could lower SO2 and NOx levels. These co-firing advantages were demonstrated in most of the co-firing tests in Europe and the United States (depending on biomass used) [3,4,5,6]. The tests were at low biomass fraction (typically 20% or less) [3,4], and wood was the predominant biomass compo-
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