FIGURE 3-9 Chart showing the general power law dependence of a materials cost with production scale.
NOTES: As scale increases, price generally decreases. This is true both for fuel components and coproducts. The dotted line shows Szmant’s original curve and the solid line is inflation corrected to 2010.
SOURCE: Adapted from Szmant (1989).
plus return on capital. This is frequently overlooked as coproducts are touted as a significant source of additional revenues for an economically suspect fuel production process. The correlation is somewhat poor across different products, but for a single product, scale and price are related by a power law (Figure 3-9). This means that doubling scale reduces price more than double. For materials intended to be sold into the massive fuels market, coproduct volumes swell rapidly with the scaling of fuel production unless a wide variety of coproducts for different markets are produced. From a resource sustainability perspective, the reference pathway described earlier closely represents the economic analyses and LCAs that have been completed. The use of anaerobic digestion to return nutrients to the algae cultivation and electrical power to the algal biofuel production system is a key component of alternative pathway #1. Removing the residual biomass as a coproduct, therefore, affects the energy balance of fuel production and the required nutrient load.
Most of the reports on algal biofuels assume that FAME is produced. FAME is not a hydrocarbon fuel, but an ester made by transesterification of the triacylglycerol. This pathway most closely approximates conventional biodiesel in the way that crude bio-oil is converted to a transportation fuel (Figure 3-10). Algal triacylglycerol are reacted with methanol to form FAME or so-called biodiesel (Figure 3-11; Van Gerpen, 2005). FAME