Energy recovery from wood pellets and waste mulching film with minimization of harmful byproducts via thermochemical conversion with CO2 agent

Abstract

The additive and kind of thermochemical agent can greatly affect the thermochemical conversion process. In this study, the influences of Waste mulching film (WMF) as the additive and CO2 as the thermochemical agent on the characteristics of thermochemical products of Wood pellets (WP) were studied. With increasing temperature, the total non-condensable gas yields in N2 and CO2 atmospheres increased. The thermochemical conversion of WP in CO2 led to a higher total non-condensable gas yield than the conversion in N2 because the thermal cracking of volatile species was promoted in the former case. Above 700 °C in the CO2 environment, the dehydrogenation of volatiles and hydrogenation of the CO2 agent greatly increased the CO and CH4 yields. In addition, the yields of polycyclic aromatic compounds, phenolic compounds, and benzene derivatives obtained in CO2 were lower than those obtained in N2 at all tested temperatures. The CO2 agent significantly decreased the yield of WP-derived char at > 700 °C; this was likely because it expedites the evolution of volatile species from WP during thermochemical conversion. The addition of WMF to the thermochemical conversion of WP decreased the CO and CO2 yields by lowering the oxygen content of the feedstock, the CH4 yield by suppressing the methanation reaction in the CO2 environment, and the yields of harmful aromatic compounds by lowering the overall lignin content of the feedstock; by contrast, the addition increased the yield of fuel-range hydrocarbons. The higher content of volatile matter in WMF compared with that of WP decreased the char yield compared with the case in which the thermochemical conversion of WP was performed without the additive.