Valorization of organic municipal solid waste to enhanced solid biofuel: torrefaction kinetics, torrefied solid fuel performance, and fuel properties

Abstract

ABSTRACT The kinetics of the torrefaction process have been studied in various reactors. However, no study reported the torrefaction kinetics of organic municipal solid waste (OMSW) in a helical screw rotation-induced (HSRI) fluidized bed reactor. This study produced torrefied solid fuel, and the kinetic parameters of the OMSW torrefaction process were determined. The results showed that increasing temperature and residence time from 200 to 300°C and 0 to 40 minutes increased mass loss, calorific value, ash content, fixed carbon, energy density, and carbon content. Conversely, mass yield, volatile matter, energy yields, oxygen-to-carbon, and hydrogen-to-carbon ratios decreased. The calorific value experienced notable growth, varying from 17.80 to 26.18 MJ/kg, with increased residence time and temperature. The one-step kinetic model using a first-order reaction accurately predicts reaction data for long residence times with a maximum error of 2.42% at 300°C and 10 minutes and is useful for designing and scaling up the HSRI fluidized bed reactor within the temperature and mass loss ranges of 220–300°C and 2.61–47.38%. The OMSW torrefaction frequency factor and activation energy were 0.2036 s−1 and 24.46 kJ/mol, respectively. The findings of this study showed that residence time has less effect on the torrefaction process than temperature.