Abstract
Recent techno-economic analysis (TEA) has underscored that for algal biofuels to be cost competitive with petroleum fuels, co-products are necessary to offset the cost of fuel production. The co-product suite must scale with fuel production while also maximizing value from the non-fuel precursor components. The co-product suite also depends on algal biomass composition, which is highly dynamic and depends on environmental conditions during cultivation. Intentional shifts in composition during cultivation are often associated with reduced biomass productivity, which can increase feedstock production costs for the algae-based biorefinery. The optimal algae-based biorefinery configuration is thus a function of many factors. We have found that comprehensive TEA, which requires the construction of process models with detailed mass and energy balances, along with a complete accounting of capital and operating expenditures for a commercial-scale production facility, provides invaluable insight into the viability of a proposed biorefinery configuration. This insight is reflected in improved viability for one biorefining approach that we have developed over the last 10 years, namely, the Combined Algal Processing (CAP) approach. This approach fractionates algal biomass into carbohydrate-, lipid-, and protein-rich fractions, and tailors upgrading chemistry to the composition of each fraction. In particular, transitioning from valorization of only the lipids to a co-product suite from multiple components of high-carbohydrate algal biomass can reduce the minimum fuel selling price (MFSP) from more than $8/gallon of gasoline equivalent (GGE) to $2.50/GGE. This paper summarizes that progress and discusses several surprising implications in this optimization approach.
Highlights
The production of economically competitive algal biofuels has been a goal of the algae community for decades
Combined Algal Processing provides a flexible framework for valorization of algae with varying composition
By producing an organic lipid phase, an aqueous hydrolysate phase, and a residual solids phase, the conversion of each phase can be optimally tuned to their individual chemistries to produce both fuels and co-products
Summary
The production of economically competitive algal biofuels has been a goal of the algae community for decades. Since 2014, research efforts by national laboratories in the United States to quantify algal biofuel production costs have resulted in annual “State-of-Technology” (SOT) and design reports summarizing the current status of each of these factors based on published literature, experimental results, and industry consultation These SOT reports describe detailed process models to quantify capital and operating costs, including mass and energy balances, for a model algae farm and biorefinery configuration (Davis et al, 2018). The organic lipid fraction can be upgraded to fuels, co-products, or both This flexibility in the CAP approach affords multiple options to achieve MFSP targets through the possibility to valorize one or more constituents of the algal biomass to either fuels or co-products as best suited for the incoming biomass cost and composition. This mini-review summarizes the key findings of the annual SOT reports that have led to the decrease in MFSP for the CAP approach to algae biorefining
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