(526b) Preliminary Economic Assessment of Microalgae Via Hydrothermal Liquefaction with Co-Production of Protein Concentrates

The present study investigates a process that utilizes microalgae to produce a protein concentrate and generate biofuel through hydrothermal liquefaction (HTL). A preliminary economic analysis was conducted using high-protein algal feedstock to evaluate the benefits and risks of co-producing protein with biofuel, including sustainable aviation fuel (SAF).

Microalgae have been demonstrated to be a promising renewable feedstock for biofuel production. Currently, the high cost of algal feedstock leads to a high production cost for fuels, making it less competitive to other sources. Incorporating a high value co-product is one way to reduce the fuel cost. Microalgae protein is a promising co-product as an alternative protein source (Soto-Sierra et al. 2018). Using microalgae to produce protein-based food/feed augments current supplies for protein products, such as soy and pea. Furthermore, extracting protein from algae prior to HTL offers additional benefits since most of the nitrogen content in the resulting biocrude comes from the protein, which is unwanted in the final jet fuel product. Extracting protein can reduce the nitrogen content in HTL biocrude and thus lowering the hydrogen demand and cost for biocrude upgrading. Therefore, investigating the potential for such protein co-production in the algae-to-fuel process is worthwhile.

In this study, the algae feedstock is extracted to produce protein concentrate and then the protein-extracted algal residue is converted into biocrude through the HTL process. Finally, the biocrude is hydrotreated, hydrocracked, distilled and denitrogenated to produce naphtha, diesel, and SAF range fuels. For the baseline case, the algae feedstock is assumed to be from a 3400-acre open-pond farm, producing algae at a cost of 1,000 $/ton on an ash-free dry weight (AFDW) basis. With protein extraction and HTL conversion, the modeled fuel yield is approximately 49 gasoline gallon equivalents (GGE) per ton algae on AFDW basis. The produced fuel products were composed of 60% SAF and a balance of diesel and naphtha fractions. Results show that in the baseline case, the minimal fuel selling price (MFSP) can be lowered below $4/GGE if the selling price of protein concentrate is above $1.4/lb. A sensitivity analysis shows that algae feedstock prices and plant scale have the most influence on the MFSP, which can vary from $0.5/GGE to $25/GGE. Alternative case studies, including algae conversion to fuel only (without protein extraction) and algae/wood blended feedstock to fuel only, are also evaluated and compared to the baseline case.

Reference:

Soto-Sierra, L., P. Stoykova, and Z.L. Nikolov, Extraction and fractionation of microalgae-based protein products. Algal Research, 36, 2018; 175-192