The Impact of Biomass Availability and Processing Cost on Optimum Size and Processing Technology Selection

Biomass processing plants have a trade-off between two competing cost factors: as size increases, the economy of scale reduces per unit processing cost, while a longer biomass transportation distance increases the delivered cost of biomass. The competition between these cost factors leads to an optimum size at which the cost of energy produced from biomass is minimized. Four processing options are evaluated: power production via direct combustion and via biomass integrated gasification and combined cycle (BIGCC), ethanol production via fermentation, and syndiesel via Fischer Tropsch. The optimum size is calculated as a function of biomass gross yield (the biomass available to the processing plant from the total surrounding area) and processing cost (capital recovery and operating costs). Higher biomass gross yield and higher processing cost each lead to a higher optimum size. For most cases, a small relaxation in the objective of minimum cost, 3%, leads to a halving of plant size. Direct combustion and BIGCC each produce power, with BIGCC having a higher capital cost and conversion efficiency. When the delivered cost of biomass is high, BIGCC produces power at a lower cost than direct combustion. The crossover point at which this occurs is calculated as a function of the purchase cost of biomass and the biomass gross yield.