Co-pelletization of corn stover and plastic waste as an alternative fuel for cement industry

Haley Stockham
Graduate (MS)
Ajay Shah
Food, Agricultural and Biological Engineering

The cement industry has an established practice of substitution of fossil fuels with alternative fuels from non-hazardous wastes. Plastic films, including high-density polyethylene (HDPE) bags, are rejected by recyclers and waste-to-energy facilities due to processing constraints and primarily landfilled. Corn stover, an abundant agricultural residue, is left in the field post grain harvest due to low bulk density that negatively impacts the efficiency of its logistics, and thus limits application as a fuel in industrial settings. The objective of this study was to co-pelletize corn stover with HDPE bags, and evaluate the techno-economics of producing it as fuel source for cement industry. Different blends of HDPE bags (0-25% dry basis) and corn stover were co-pelletized using a flat ring pellet mill with die sizes of 6- and 8- mm. Pellets were cured for a minimum of one week at room temperature prior to determination of physico-thermal properties, including moisture content, bulk density, and durability. It was found that 6-mm 0-20% HDPE pellets had durability greater than 96.5%, which meets commercial standards for fuel pellets. Bulk density was in the range of 417-634 kg/m3. Specific energy consumption varied from 38-120 kWh/t. The operating cost ($/t pellets) for a pelletization plant producing 200,000 t/y was in the range $72-$105. Sensitivity analysis indicated that operating cost is most affected by the delivery price of corn stover. Such a system would create a commercial pathway for excess corn stover and divert non-recyclable plastic waste from landfills. Future work will evaluate the environmental impacts of stover-plastic pellets as an alternative fuel for cement production.