(741e) Analysis of Supply Chain, Scale Factor, and Optimum Plant Capacity for the Production of Ethanol From Corn Stover

A detailed model is used to perform a thorough analysis on ethanol production from corn stover via the dilute acid process. The biomass supply chain cost model accounts for all the steps needed to source corn stover including collection, transportation, and storage. The production cost is modeled based on technological advances. The scaling parameters for the widely used exponential function to scale the capital investment are calculated for several large-size plant ranges; a scaling function that accounts for the scaling nature of biorefineries that use bio-reactors (such as saccharification vessels and fermentors) is proposed.

The capital investment scaling factors for the exponential function are dependent on plant capacity. For the Exponential scaling function, the optimum plant capacity decreases as scaling factors regressed from smaller plant data are used. The optimum plant capacity using the Exponential function with scaling factors regressed from the range of capacities under study is 6150 Mg d^–1. As scaling data for large biorefineries is lacking; more thorough analyses are required to determine the dependence of the scaling relationships on size. Care must be taken when determining the optimum plant capacity over a wide range of capacities when using scaling data from narrow ranges as it might lead to falsely large optimum plant capacities.

Bio-reactors (such as saccharification vessels and fermentors) in large size biorefineries scale linearly with plant capacity. A mathematical expression to scale capital investment for biorefineries is proposed; the function accounts for the linear scaling behavior of bio-reactors and the exponential nature of all other plant equipment. The use of the proposed Exponential/Linear function yields an optimum plant capacity of 5750 Mg d^–1. Ignoring the linear scaling behavior of bioreactors leads to artificially large optimum plant capacities.

Minimum production cost range from 789 $ m^–3 to 858 $ m^–3 and optimum plant capacity range from 5750 Mg d^–1 to 9850 Mg d^–1 of corn stover, significantly impacted by several key parameters. The sensitivity of the model results to key parameters in the biomass supply chain is investigated. The optimum plant capacity and production cost is highly sensitive to farmer participation for low participation rates.

It is likely that a small fraction of farmers will collect corn stover for the initial biorefineries as uncertainty exists regarding the sustainability and profitability. Farmer participation should increase as the second generation biofuel industry develops and collection process improves. Furthermore, the significant reduction in production cost due to the increase in farmer participation is a great incentive for biofuel producers to spur participation of farmers in the collection of agricultural residues. As more farmers collect corn stover the optimum plant capacity is shifted to larger capacities. A sub-optimal plant, at the time of construction and/or during the first few years of operation, could be constructed to target the optimal capacity in the future based on expected farmer participation in the area around the plant location.