Algal Greenhouse Gas Mitigation for Coal-Fired Flue Gas

Abstract

CO2 emissions from coal-fired power plants in the US accounted for approximately 30% of the overall national greenhouse gas emissions in 2008. Coal will continue to dominate the electric power industry in the near future. Carbon mitigation for coal-fired power plants is an indispensible element of the climate change strategy. Algae culture is one potential pathway to mitigate the CO2 emissions from fossil fuel fired flue gas. This master project investigates the performance of integrating an algae facility into a 500 MW coal-fired power plant in the US. The analysis presents two major indicators of the performance: the Emission Rate (the CO2 emissions related to the production of per kWh electricity) and the Energy Cost (energy used to reduce 1 kg CO2 emissions). This analysis concerns diverse operation methods and algae culture means. Two generic scenarios, a 50% CO2 emissions reduction and a 1000 ha algae facility, are assumed. The results suggest that the former scenario requires a large algae infrastructure and other inputs, while the latter has little impact on the overall CO2 emissions. Under each scenario, the system that employs flues gas direct injection, raceway pond culture facility and nutrient recycling is the most efficient in terms of reducing CO2 emissions at the lowest energy cost. This study also proposed an improved practice with higher algal productivity, energy efficiency, and carbon-neutral nutrient sources. Energy Return On Investment (EROI) is calculated for several conversion technologies. The EROI estimates show that co-firing of algal biomass with coal results in the highest net energy output.