Technoeconomic Analysis of Torrefied Pellets Produced from Municipal Solid Wastes

The U.S. Department of Energy promotes the production of advanced biofuels through support for fundamental and applied research pertaining to feedstock logistics and preprocessing. The disposal of municipal solid wastes (MSW) presents a growing challenge for municipalities and similar entities and transforming these waste streams to higher-value products presents both an economic opportunity and a sustainable solution by diverting materials away from landfills. Furthermore, identifying and developing advanced preprocessing systems is also imperative for MSW resources to be utilized at scale. This research evaluates the production of torrefied pellets from waste plastic, fiber and biomass residues, which can be utilized as fuel to produce electricity, from a technoeconomic standpoint. The major benefit of the studied preprocessing train is the elimination of bound chlorine, increased energy density during densification to a storage fuel pellet and increase in product uniformity (physical and chemical) at both the macro- and sub-millimeter scale. The system boundary for this analysis encompasses processes and equipment beginning from delivery of waste materials, size reduction using a three-stage shredding process, torrefaction in a reactor-extruder, and cooling of processes materials to produce 100,000 dry tons of torrefied materials annually. The technoeconomic analysis estimated the costs and energy consumption for the MSW torrefaction and pelleting operations. The analysis indicated that the baseline cost of processing sorted MSW material into uniform pellets is about $50.15/dry ton (2020$), which includes preprocessing costs at the equipment-level and other plant-level costs comprising of installation, labor, and maintenance. The most important preprocessing costs are attributable to the crammer and torrefier ($9.14/dry ton) and the three-stage shredder ($12.66/dry ton). At the plant-level annual labor costs ($15.07/dry ton) and installation costs ($8.62/dry ton) are the largest contributors to total costs. The system is designed to be self-sustaining whereby the gas stream from the torrefaction process is utilized in the heat management system with minimal usage of natural gas in the start-up phase. This study contributes to the growing body of research in the areas of waste utilization and management, energy recovery, and sustainability by evaluating novel production pathways for biopower application and to improve the economic potential of biopower production and use.