Integrated Assessment of Solid, Liquid, and Gaseous Fuels Derived from Fixed-Bed Pyrolysis of Waste Tires

The improper disposal of end-of-life tires poses significant environmental challenges due to their petroleum-based composition and slow degradation, while simultaneously representing an underutilized energy resource. This study investigates the slow pyrolysis of shredded waste tires in a fixed-bed electrically heated reactor to evaluate the production and fuel properties of gaseous, liquid, and solid fractions. Experiments were conducted with 100 g samples under nitrogen at final temperatures of 400, 500, and 600 °C, with residence times of 40, 25, and 10 min, respectively. Higher temperatures promoted gas formation, increasing yields from 27% to 32% and achieving a maximum lower heating value of 30.54 MJ m−3 at 600 °C, with enhanced H2 and CH4 contents. Solid yields decreased slightly (41% to 37%), while char maintained stable heating values (~29 MJ kg−1). Liquid yields remained near 33% and showed high calorific values (~41 MJ kg−1), densities of 700–770 kg m−3, low acidity, low ash content, and increased viscosity at higher temperatures. Energy conversion efficiency reached 74.4% at 500 °C. The integrated evaluation of all fractions under identical conditions highlights fixed-bed pyrolysis as a promising pathway for waste-tire valorization and decentralized fuel production.