Torrefied plastic-fiber fuel pellets as a replacement for fossil fuels — a case study life cycle assessment for Green Bay, Wisconsin, USA

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Department of Mechanical Engineering-Engineering Mechanics


Purpose: The commercial-scale production of torrefied plastic-fiber fuel pellets from waste plastics and waste fibers may offer a viable alternative to fossil fuel–based energy. In this study, the environmental impact of fuel pellets produced and consumed in Green Bay, Wisconsin, USA is evaluated and compared to the status quo of grid energy production from fossil fuels (i.e., coal or natural gas). Methods: A cradle-to-grave life cycle assessment was conducted using a functional unit of 1 kWh of energy produced using torrefied plastic-fiber fuel pellets versus production of energy from coal or natural gas. Regional data along with relevant manufacturing data was used to inform the inventory of the production of the torrefied fuel pellets, which are manufactured using waste fibers and waste plastics sourced from within 5 km of the torrefaction facility and consumed within 50 km of the facility. Since fuel pellets are produced from waste inputs and contain biogenic carbon sources, impacts were assessed with/without credit for biogenic carbon and with/without the burden of the torrefaction inputs. Results and discussion: The production of 1 kWh of energy using torrefied plastic-fiber fuel pellets was determined to produce between 0.303 and 0.757 kg CO2 eq emissions due to combustion and between 0.062 and 1.105 kg CO2 eq additional emissions as a result of the manufacturing process, with the ranges dependent upon the allocation method selected. Under a burden-free allocation due to waste materials used as inputs, along with a credit for biogenic carbon emissions, the system produces 0.365 kg CO2 eq per 1 kWh of energy; however, under a full-burden allocation with no credit for biogenic carbon emissions, 1.862 kg CO2 eq per 1 kWh of energy is produced. This highlights the differences between allocation scenarios and role of credits for biogenic carbon emissions when evaluating systems. Conclusions: The usage of torrefied plastic-fiber fuel pellets produced using waste plastics and fibers is a reasonable alternative to the status quo of waste disposal coupled with the production of grid energy from fossil fuels. In addition to the reduction in GHG emissions, the use of the process would also help to alleviate the environmental burden of waste plastics.

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International Journal of Life Cycle Assessment