Techno-Economic Analysis for the Production of Algal Biomass via Closed Photobioreactors: Future Cost Potential Evaluated Across a Range of Cultivation System Designs

Abstract

In this assessment, we have evaluated target minimum biomass selling prices (MBSPs) of algae biomass production for four photobioreactor (PBR) designs compared to a previous open pond target case. We utilized techno-economic assessment modeling to determine if the target PBR cases can compete with open ponds for low-cost commodity fuels in an 'nth-plant' scenario. In the process, algal biomass is produced in one of the five cultivation options, including: open ponds, horizontal tubes, helical tubes, and two vertical bag/panel designs termed 'GWP-II flat panels' and 'Leidos hanging bags.' The projected target cultivation productivity for each PBR design was estimated based on the most credible literature data presenting PBR and pond cultivation on a directly comparable basis, and then extrapolating out to the future. Resulting productivities on an aerial basis were estimated to range from 25 g/m2/day to 52.5 g/m2/day (cultivation area). CO2, nutrients, and algae inoculum are supplied to the production area. After cultivation, the biomass is dewatered to 20 wt% solids in three stages including in-ground gravity settling, membrane filtration, and centrifugation. CO2 piping, water piping, and storage are also included in the analysis. Based on our recently published 'algae farm' design report, the open pond cultivation benchmark was set at an MBSP of $494/ton ash-free dry weight (AFDW). The horizontal tubes are large volume reactors with productivity similar to that of open ponds, but result in an MBSP of $708/ton AFDW. The helical tubes are made from glass and have a high capital investment resulting in a MBSP of $1,737/ton AFDW. The GWP-II PBR is a vertical flexible plastic flat-panel system with an estimated MBSP of $1,793/ton AFDW. Finally, the Leidos hanging bag system, which derives cultivation cost values based on inputs furnished by Algenol, results in an estimated MBSP of $639/ton AFDW.