(332b) Feedstock-Driven Operational Challenges Facing Pioneer Biorefineries in the Emerging Biofuel Industry

Authors: 
Thompson, D. N., Idaho National Laboratory
Hartley, D., Idaho National Laboratory
Roni, M., Idaho National Laboratory
Hu, H., Idaho National Laboratory
Recent evidence indicates that the operational performance of DOE’s 1st-plant Integrated Biorefineries (IBRs) are significantly impacted by feedstock variability. This is a high impact problem because several have already failed due in part to these unexpected operational issues. The remaining IBRs are working to solve the issues, however, solving one invariably creates other issues because of interactions across the system.

Conventional feedstock supply systems (CFSS) provide biomass to existing markets that have less stringent quality requirements than do biorefineries. They are vertically integrated, designed around limited markets, single biomass types, single biorefineries and a limited supply radius. In contrast, an Advanced Feedstock Supply System (AFSS) dynamically would provide a “conversion-ready” engineered feedstock from a myriad of diverse raw biomass sources, decoupling the supply of this engineered feedstock from the biorefinery infeed. “Conversion-ready” implies that the engineered feedstock meets all requirements for the conversion process, including physical requirements such as flowability and particle size distribution, as well as more conventional specifications such as convertible composition, convertibility and ash content.

Typically CFSS and AFSS are compared on an nth-plant delivered feedstock cost, which ignores the operational impacts of constant variation in moisture, ash and composition of the biomass entering preprocessing for introduction to the conversion process. A discrete event simulation model was constructed to examine the impacts of reduced throughput and equipment downtime on feed handling and preprocessing systems, replicating the operations and flow of material to the reactor throat of the pretreatment reactor of an integrated corn stover-to-ethanol biorefinery. Results indicate that neither CFSS nor AFSS were capable of achieving design capacity, due primarily to moisture and fines generated during processing. A significant result was the identification of the plug screw feeder to the pretreatment reactor as the primary cause of down time in the modeled pioneer biorefinery scenario, specifically as a result of fines (60-70% of total down time). Moisture-caused failure of grinders far exceeded any other failure, but accounted for only 20-30% of total down time. Additionally, decoupling the feedstock supply from the reactor throat with a five day feedstock buffer only marginally improved minimum scale throughputs for both CFSS and AFSS.