Effect of torrefaction atmospheres on the pyrolysis and combustion of torrefied municipal solid waste

Flue gas torrefaction (FGT) is a promising pretreatment to improve the fuel properties of municipal solid waste (MSW). Four torrefaction carrier gases (N2, flue gas, flue gas/air (1:1), and air) were employed for the comparative investigations. As expected, the higher heating value (HHV) of the oxygenated torrefied MSW was nearly twice as much as the raw MSW. In particular, the chlorine content in torrefied MSW decreased from 35.57 % in the N2 atmosphere to 14.50 %-9.37 % in oxidative torrefaction. Furthermore, the dominant form of chlorine was converted from organic to inorganic. TG-MS results envisaged that the thermodynamic properties of torrefied MSW were affected by the choice of carrier gases. Among them, oxygen carrier gas effectively improved the thermal stability and fuel properties of torrefied MSW. During pyrolysis, the release of H2 and CH4 was enhanced by flue gases (flue gas and flue gas/air). The release of H2O was reduced during combustion. The emissions of HCl and CH3Cl were inhibited. After FGT, 44 % of chlorine was present in torrefied MSW. Notably, torrefaction increased slagging and fouling inclination and was exacerbated with increasing oxygen content. This study provides a reference for further improving the theoretical system and application of flue gas torrefaction.