The adoption of renewable energy standards aimed at reducing carbon dioxide emissions and the likelihood of a U.S. carbon cap and trade system are expected to have great impact on regions that are dependent upon coal for electricity generation. To meet renewable energy standards and eliminate CO2 emissions while minimizing costs to the consumer, new and retrofit technologies are needed for coal-fired power plants. This study addresses both of these issues by considering the cofiring of biomass with coal under both air-fired and oxy-combustion conditions. Co-firing biomass with coal in air will allow the renewable energy standards to be met while still supplying the bulk of the power from low-cost coal. Cofiring of coal and biomass in a system with carbon capture and storage is potentially a carbon negative technology, providing electrical power while removing CO2 from the atmosphere.
The costs of carbon capture and storage can be greatly reduced if the carbon dioxide in the flue gas is highly concentrated, thereby removing the need for a CO2 scrubbing system. This can be achieved by replacing combustion air with a mixture of oxygen and recycled flue gas (oxy-combustion). This work includes a study of oxy-coal and biomass combustion on two scales: laboratory (20-40 kW) and pilot (0.5 -1 MW). Pollutant formation (NOx, SO2, Hg, PM) resulting from oxy-combustion is compared to the tradition air-fired arrangement. In collaboration with Tsinghua University, the formation and properties of ultrafine ash particles are studied in order to evaluate the effects of both cofiring and oxy-combustion on ash deposition and fouling/slagging.