CO2 recycling using microalgae for the production of fuels

Abstract

CO 2 capture and recycle using microalgae was demonstrated at a coal-fired power plant (Duke Energy's East Bend Station, Kentucky). Using an in-house designed closed loop, vertical tube photobioreactor, Scenedesmus acutus was cultured using flue gas as the CO 2 source. Algae productivity of 39 g/(m 2 day) in June-July was achieved at significant scale (18,000 L), while average daily productivity slightly in excess of 10 g/(m 2 day) was demonstrated in the month of December. A protocol for low-cost algae harvesting and dewatering was developed, and the conversion of algal lipids-extracted from the harvested biomassto diesel-range hydrocarbons via catalytic deoxygenation was demonstrated. Assuming an amortization period of 10 years, calculations suggest that the current cost of capturing and recycling CO 2 using this approach will fall close to $1,600/ton CO 2 , the main expense corresponding to the capital cost of the photobioreactor system and the associated installation cost. From this it follows that future cost reduction measures should focus on the design of a culturing system which is less expensive to build and install. In even the most optimistic scenario, the cost of algae-based CO 2 capture is unlikely to fall below $225/ton, corresponding to a production cost of *$400/ton biomass. Hence, the value of the algal biomass produced will be critical in determining the overall economics of CO 2 capture and recycle.

Capture and recycle of industrial CO2 emissions using microalgae

“…In our previous publication, the development of a continuously circulating closed-loop PBR was described [18]. As a result of operating experience gained in the field, the PBR was extensively redesigned, resulting in the next generation 'cyclic flow' PBR used in the present study.…”

“…We have previously reported the results of studies conducted at a coal-fired power plant (Duke Energy's East Bend Station, located in Boone County, KY, USA) [18]. Initial evaluations led to the conclusion that algae cultivation sized to reduce the CO 2 output of a power plant would need to be of an enormous scale.…”

“…Photobioreactors (PBRs) were, therefore, chosen as the cultivation system of choice on the basis of their higher areal productivities [19], as well as potential for higher CO 2 capture efficiencies and limited water loss due to evaporation [20]. Subsequently, a vertical tube PBR was designed, prototyped and refined, with emphasis placed on cost minimization [18]. Indeed, capital costs are critical because of the scale inherent in trying to capture large quantities of CO 2 .…”

“…Indeed, capital costs are critical because of the scale inherent in trying to capture large quantities of CO 2 . In tandem, a lowcost growth medium for algae cultivation was devised, based on ingredients available on the agricultural commodity market [21], and an inexpensive process for algae harvesting and dewatering was implemented based on sequential flocculation, sedimentation and gravity filtration [18,22]. These innovations culminated in the deployment of a pilot-scale (18,000 L) demonstration facility at East Bend Station, which was commissioned in December 2012.…”

“…Based on the data collected at East Bend, a technoeconomic analysis indicated that from a process perspective the largest sources of cost reside in the algae culturing stage, corresponding mainly to the capital cost of the photobioreactor system and the associated installation [18]. Subsequent work has, therefore, focused on the implementation of cost reduction measures to the PBR, resulting in a radically new PBR design.…”