Green Waste/Wood Pellet Pyrolysis in a Pilot-Scale Rotary Kiln: Effect of Temperature on Product Distribution and Characteristics

In this study, a pilot-scale rotary kiln was used to perform the pyrolysis of garden green waste. The results are compared to wood pellets (a mixture of oak and beech sawdust). Both samples have similar organic composition and energy content except for ash content, which is around 3 times higher in the case of green waste. Pyrolysis tests were performed at different temperatures ranging from 700 to 900 °C. The study of the product yields as a function of temperature showed that above 700 °C, volatile matter (gas and bio-oil) yields were higher than 80 wt % and syngas (CO + H2) concentration was higher than 59 mol %. On the other hand, the char yield was below 20 wt % with a higher heating value (HHV) of 29 MJ/kg and an 80% carbon content. Tar quantitative gas chromatography/mass spectrometry (GC/MS) analysis showed the predominance of benzene and naphthalene. Hence, this work revealed and validated the relevance of green waste thermochemical conversion for syngas production. In addition, this investigation can support the optimization of operating parameters and energy efficiency of a two-staged gasification process where pyrolysis is a decisive initial step.