Effect of Biomass Properties and System Configuration on the Operating Effectiveness of Biomass to Biofuel Systems

Operational inefficiencies due to wide variability in physical and compositional attributes characteristic of existing corn stover supply systems threaten the development of a sustainable bioeconomy. We utilized discrete event simulation to conduct stochastic feedstock property-dependent throughput analysis of a conventional corn stover supply logistics-preprocessing-conversion system. Pilot scale preprocessing equipment data and experiential information were used to inform failure frequency and down time. A new metric was introduced, “overall operating effectiveness” (OOE), which over a specified time period dynamically assesses the composite impacts of feedstock quality on the operational efficiency and productivity of the individual subsystems of the biomass to biofuel supply chain. For a 55% minimum carbohydrate specification at the entrance to conversion, the modeled OOE values for the supply logistics, preprocessing, and conversion subsystems were 56.9%, 24.4%, and 101%, respectively. The severity of throughput impacts depended primarily on moisture, while performance impacts depended on the range of corn stover compositional variability. Costs varied significantly as a function of assumed minimum acceptable carbohydrate contents from 45 to 59 wt % (proxy for conversion robustness), with a mean feedstock cost of $249.93/dry Mg (median of $146.39/dry Mg) for a 55% minimum carbohydrate content. As the floor was relaxed from an nth-plant specification of 59%, a higher proportion of the preprocessed feedstock was fed to conversion leading to feedstock contributions to biofuel costs ranging from $4.15 to $8.73/gge (2016$). We conclude that while conversion robustness can serve to minimize discarded feedstock, properties other than yield potential are more significant contributors to the feedstock contribution to biofuel cost.