Techno-economic and Lifecycle Evaluation of Optimized Photobioreactor- and Pond-based Microalgae Systems for CO2 Mitigation - Topic 1

Microalgae are the fastest growing photosynthetically active organisms and have the potential for higher oil content per mass than other renewable sources of oil. This coupling of fast growth rate and high oil content renders algae a potential means of capturing and recycling CO2. In 2008 the Commonwealth of Kentucky tasked the UK with evaluating the technological and economic feasibility of using microalgae to mitigate the carbon emissions from coal fired power stations. Our research has led to the development of a pilot-scale (18,000 L) demonstration facility at Duke Energy’s East Bend station which was commissioned in December 2012 and which remains the focus for our process development efforts. While significant progress has been made with respect to technology development and cost reduction, several challenges remain. We have identified four challenges which we consider critical and which form the basis of this project proposal: 1) Quantification of the actual greenhouse gas (GHG) emission reduction benefits that can be realized using this approach. Regardless of the economics, CO2 capture and recycle only makes sense from an environmental standpoint if real GHG benefits result. Previous studies have shown that the cultivation of microalgae can result in both N2O and CH4 emissions, chiefly as a result of anaerobic microbial processes. However, very few studies have reliably quantified the magnitude of these emissions. Hence, we propose to address this knowledge gap. 2) Plant heat integration. We propose to perform a heat integration study to assess the viability of heating the algae cultivation system in winter, thereby improving algae productivity and lowering the cost of CO2 capture. An inventory of waste heat streams at East Bend Station will be made, after which a modeling study will be conducted to determine the viability of heat integration with given streams. 3) Capital cost minimization. There are two basic types of algal growth systems: open ponds and closed photobioreactors (PBRs). Open ponds are less costly to construct and operate than closed PBRs but have lower CO2 capture efficiency. We propose to operate both pond and PBR cultivation systems at East Bend to facilitate a detailed comparison between these technologies in terms of the cost of CO2 capture and GHG emission reduction benefits. 4) Production of valuable algae-derived products to off-set the cost of CO2 capture and recycle. The overall economics of CO2 capture and recycle can be improved by the production of valuable algae-based products. Consequently, the need for proof-of-principle experiments is indicated, in which the cultivation and harvesting of appropriate candidate strains – suitable for production of high value products such as lutein and ù-3 unsaturated fatty acids – is demonstrated under real-world conditions, i.e., with flue gas. The proposed research is aligned with a total of five of the actions proposed in Kentucky’s 7-Point Strategy for Energy Independence. One of these actions pertains directly to the use of algae for CO2 capture from flue gases, while the remaining recommendations relate to the research and development of algae as a feedstock for biodiesel.