Life Cycle Assessment of Cogeneration Systems Using Raw and Torrefied Dichrostachys Cinerea (L.) Wight & Arm. (Marabou).

Abstract

Purpose This study aims to assess environmentally three different alternatives related to the valorization of Dichrostachys cinerea (L.) Wight & Arm. (marabou), identified as an invasive tree, as a feedstock for cogeneration facilities installed in the sugarcane industry in Cuba. The alternatives are (A-1) Electricity generation from marabou in a conventional back-pressure steam turbine cycle, (A-2) Electricity generation from torrefied marabou in a back-pressure steam turbine cycle, and (A-3) Electricity generation from torrefied marabou using extraction-condensing turbines.Methods SimaPro 9.0.0.35 software was used for the modeling of the inventory, based on different operational parameters. The ReCiPe environmental impact assessment method was used in the hierarchical perspective, assessing 18 impact categories (midpoint), and 3 damage categories (endpoint).Results and discussion The results demonstrated that A-3 shows the lower environmental impacts (Fine Particulate Matter Formation, Terrestrial Acidification, and Water Consumption) as compared to A-2 and A-1. This performance is explained by a lower normalized marabou consumption (1.85 kg marabou/kWh generated), and lower emissions associated with marabou harvesting, transportation, and processing. The cogeneration stage was the main contributor to the environmental burdens in Water Consumption (100% in A-1; 87% in A-2 and A-3). Marine Ecotoxicity was the impact category with better environmental performance due to the substitution of synthetic mineral fertilizers by ashes produced during combustion. The human health damage category reached the higher impacts on the torrefaction subsystem in the A-3 scenario, representing over 94% of the total environmental burden of the process. PM<10, NO2, and SO2 contributed the most over this damage category, mainly in marabou combustion, causing injuries in respiratory systems by aspiration of organic compounds.Conclusions The use of more efficient technology (extraction-condensing steam turbine), using torrefied marabou as feedstock, compared with the previous alternatives, impacts beneficially on the environment. Thus, a combination of marabou torrefaction with cogeneration facilities in sugarcane industries can be considered as an environmental-friendly technology in the Cuban context. The current study results will help decision-makers implement more sustainable policies in the Cuban energy sector, using marabou as feedstock as an attractive bioenergy route pathway.