Microalgae production from power plant flue gas: environmental implications on a life cycle basis June 2001

CO2 is a major greenhouse gas (GHG), and its physical capture from fossil-fuel power-plants has been considered as a potential remediation option since Marchetti (1977) first proposed the disposal of the captured CO2 in the deep ocean. Several investigators have since studied a plethora of options for CO2 capture from power plants which are stationary, concentrated sources of the gas and its subsequent disposal or use. Thus, CO2 capture is a common step for most of the remediation options.
In a general assessment of alternative processes for capturing CO2 from existing coal-fired power plants, Herzog et al. (1991) concluded that capture is currently technically feasible, but that the most efficient available technology will reduce energy efficiency of utility steam plants by about 30% and will increase the price of electricity by 80%, even before disposal costs are added. These results are consistent with a study by the Electric Power Research Institute (EPRI) on CO2 capture and disposal (Booras and Smelser 1991). Emerging and future electricity generation technologies have the potential to significantly reduce these costs.
Besides disposal, another potential sequestration option is to find recycle opportunities for power plant CO2 as a feedstock for industrial products or processes or as a component of alternative fuels.
For CO2 recovery, the monoethanolamine (MEA) absorption process is commonly employed and is the heart of the steam host requirement. The two commercial U.S. CO2 recovery facilities use MEA absorption technologies and produce a food- and beverage-grade product. The total industrial utilization of CO2 today in the U.S. is about 2% of the CO2 generated from power plants. However, in about 80% of the applications, as in enhanced oil recovery (EOR) and the food industry, CO2 used is rapidly returned to the atmosphere. While niches may be found for some utilization, it is unlikely that industrial use can sequester more than a minor fraction of the emitted CO2 from power plants. Use in fuels is feasible, but external energy inputs required to synthesize the fuels can be much more efficiently used to serve energy markets directly. Conversion of CO2 to microalgae is also a sequestration option; however, as in any other option, efficient recovery and delivery of the CO2 are critical.
This study discusses the environmental implications of using power-plant flue gas as a source of CO2 for microalgae cultivation and cofiring the algae with coal for electricity production.

By: K. L. Kadam (NREL)