Advanced Biorefinery Feedstocks from Waste Biomass: Technoeconomic Assessment of Integrated Air Classification-Hydrothermal Carbonization-Pelletization Processes

Corn stover is one of the most abundant agronomic resources in the U.S., however, those are either incinerated or unprocessed in the field to avoid high logistical cost, economic forfeiture, and environmental complications. Air classification has been proposed to separate clean corn stover from waste corn stover. Waste corn stover can be hydrothermally carbonized (HTC) into solid binder called hydrochar. Clean corn stover from air classification can be pelletized with hydrochar in a high moisture pelleting process (HMPP). The final product of the integrated process, pelletized corn stover, is a conversion-ready biorefinery feedstock. The aim of this study is to investigate economic feasibility of integrated air classification-HTC-HMPP process. Different scenarios were considered for technoeconomic analysis to convert 100 tonne/day corn stover into HMPP pellets. While, optimized air classification and HMPPP process parameters are obtained from our prior studies, HTC process was optimized using two cases. Case I assumed a batch HTC process and case II assumed a continuous HTC process in the integration system. Results show that both cases are economically feasible, where case I reached its break-even years earlier than case II. Additionally, despite the greater capital investment requirement for case I, there was also a greater return on investment (ROI) compared to case II. A sensitivity analysis was also performed which revealed that the effect of solid content in air classified waste corn stover or reactor’s feed, feedstock pumping cost, and total equipment cost were the influential parameters on breakeven selling price of the hydrochar.