Techno-economic uncertainty quantification of algal-derived biocrude via hydrothermal liquefaction

Abstract

Using microalgae for fuel production via hydrothermal liquefaction (HTL) has received increasing attention in recent years because of its high biocrude productivity and quality, cultivation flexibility, and potential for large scale operation. Most of the current knowledge on algae HTL is based on laboratory benchtop findings and/or simulation models, while yield correlations or simplified kinetics models were usually developed based on small batch equipment. In this work, the lack of commercial experience and knowledge gaps of algae HTL process were addressed through techno-economic uncertainty quantification. Particularly, a “component additivity” model was developed to predict the yields and qualities of biocrude derived from a variety of algal biomass via HTL process with model uncertainty quantified based on the operating data of PNNL's continuous flow HTL system. Impacts of algae types on the biocrude yield and process economic were investigated by performing sensitivity analysis. Monte Carlo simulations were conducted using rigorous process and economic models developed in Aspen Plus and Excel to determine the process uncertainty. The results indicate that higher total lipid content (including membrane lipid) yields more biocrude, which directionally reduces biocrude production cost. For the base case scenario (Chlorella with 18.2 wt% lipid, capacity of 200 tpd daf algae, dewatered algae price of $1171/dry ton), the modeled biocrude production cost is approximately $11/gge, of which 90% is attributed to feedstock cost of dewatered algae. According to the Monte Carlo simulation, the modeled production cost for HTL biocrude production is between $5/gge and $16/gge when the algae price ranges from $400 to $1800/daf ton, of which an uncertainty (range between 10% and 90% percentiles) up to ±12% is observed. Tornado analysis suggested that the algae composition and capital investment are the two main contributors to the economic uncertainties of the algae conversion via HTL.