2017 Algae Harmonization Study: Evaluating the Potential for Future Algal Biofuel Costs, Sustainability, and Resource Assessment from Harmonized Modeling

Abstract

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.NREL prints on paper that contains recycled content. ErrataThis report, originally published in August 2018, has been revised in September 2021 to correct life cycle assessment calculations applied to the biomass conversion via combined algae processing pathway analyses. The amended calculations and associated results were used to update Figures 22-28 and Tables 14 and A-1-A-4 in the Appendix. The changes to the results were not significant enough to impact any of the overall conclusions or trends outlined in the report, and did not impact resource assessment or techno-economic analysis metrics, nor life cycle assessment metrics for the hydrothermal liquefaction conversion pathway.iii This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. NomenclatureAD anaerobic digestion AFDW ash-free dry weight ANL Argonne National Laboratory BAT Biomass Assessment Tool BETO Bioenergy Technologies Office BGY billion gallons per year BGGE/yr billion gallons gasoline equivalent per year BT16 2016 Billion-Ton Report CAP combined algae processing CC carbon capture CHP combined heat and power CONUS conterminous United States DAP diammonium phosphate DOE U.S. Department of Energy FAME fatty acid methyl ester FFA free fatty acid FY fiscal year GAI Global Algae Innovations GHG greenhouse gas GREET Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation HCSD high-carbohydrate Scenedesmus

Conceptual Basis and Techno-Economic Modeling for Integrated Algal Biorefinery Conversion of Microalgae to Fuels and Products (2019 NREL TEA Update: Highlighting Paths to Future Cost Goals via a New Pathway for Combined Algal Processing)

“…The process begins with biomass delivered to the CAP conversion facility from upstream algae cultivation and dewatering (co-located at the same site). As discussed previously, the majority of the targeted cultivation and dewatering performance parameters implicit in the delivered MBSP remain consistent with NREL's 2016 algae farm design report, with the exception of added blowdown/salt disposal costs reflective of non-freshwater production, as well as associated evaporation rates tied to average Gulf Coast region figures [4,8]. Additionally, final-stage dewatering (centrifugation) is slightly relaxed from a prior target of 20 wt% solids to 18 wt% more suitable for this CAP schematic.…”

“…More details for this operation are discussed in Section 3.1. The targeted algal biomass composition delivered from the upstream algae farm is maintained consistently with prior recent NREL TEA efforts [4,8], reflecting a compositional profile exemplified by Scenedesmus acutus (LRB-AP 0401) based on biomass cultivated by Arizona State University. Specifically, the base case CAP model employed here reflects measured compositional data attributed to an early stage of nutrient deprivation for this species in moving between high-protein nutrient replete to low-protein/high-lipid nutrient deplete harvesting, historically termed "high-carbohydrate Scenedesmus" or HCSD [4,17].…”

“…Accordingly, over more recent years the TEA modeling and CAP research efforts have shifted in focus toward the inclusion of value-added coproducts which may be produced alongside fuels in a biorefinery configuration. Although this adds processing complexity relative to fuel-only configurations, TEA modeling has demonstrated that when constrained to future target biomass costs of nearly $500/ton, algal conversion processes focused on producing fuels alone cannot feasibly achieve MFSP levels below $3.5-$4.5/GGE, falling short of BETO algae platform goals of $2.5/GGE in the future unless higher-value coproducts are also produced [8,9]. Within NREL's CAP program, research and TEA modeling efforts have evaluated a number of algal coproduct opportunities to date, including succinic acid (from sugars), surfactants (from sterols), and initial investigations into bioplastics and mixotrophic algal biomass (from protein).…”

“…Instead, the CAP approach considered here utilizes flash hydrolysis pretreatment (more severe conditions but shorter residence time and without utilizing acid), lipid extraction and upgrading (with optional diversion of a fraction of lipids to polyols/polyurethanes, similar to the prior CAP schematic), and oxidative thermochemical treatment to upgrade both solubilized and solid carbohydrates and protein to fuel precursors. In the context of the present study, this new CAP approach is still considered for its application to a lower-protein/higher-carbohydrate harvested algae composition in keeping with prior TEA models [8], but is also anticipated to provide a basis framework for future work moving into more nutrient-replete/higher-protein algal compositions from upstream harvesting.…”

“…Similar to prior algae conversion designs [3,15], the scope of this analysis begins with harvested algal biomass feedstock delivered to the conversion facility after dewatering to a target solids content, thus upstream cultivation/processing logistics are outside the scope of this assessment. (See details documented in NREL's 2016 algae farm design report [4] and more recent 2017 harmonization report [8] for a description of the process reflected in NREL's algal biomass production models and associated TEA results.) In summary, the algae farm is based on 5,000 acres of production pond cultivation area (not including inoculum production), utilizing large 10acre ponds with minimal requirements for plastic liners aside from targeted areas for erosion control.…”