Process Optimization for the Hydrothermal Production of Algae Fuels

In this work, the production of liquid fuels from algae via hydrothermal liquefaction has been analyzed. The process consists of algae growing and harvesting, biomass liquefaction, hydrocracking of the biocrude, and the separation of the products into fuels. Surrogate models for all of the units are developed to evaluate the optimal operating conditions including the nutrient and light effects on algae growth rate. The yield and distribution of the products of hydrothermal liquefaction (HTL) and the hydrocracker are predicted using kinetic and yield data, and the operation of the column is determined using both rules of thumb and experimental data. The model is optimized aiming at selecting the algae composition, HTL, and hydrocracking product distribution. In particular, the algae should have 53% lipids, 30% proteins, and 15% carbohydrates for the production of a mass with 51% biocrude that is cracked into 18% kerosene, 24% gasoline, and 59% diesel. The estimated facility investment costs add up to 130 M€ with a production cost of 0.64 €/gal. These results are competitive with renewable-based Fischer–Tropsch (FT) fluids and biodiesel.