Biochar production from vineyard pruning waste by oxidative torrefaction

The torrefaction process for producing biochar from waste biomass has garnered significant attention in recent years. However, economic constraints hinder the broader adoption of this process. One such constraint is the requirement for an inert atmosphere during torrefaction. This study aimed to evaluate the feasibility of torrefying vineyard pruning waste in an oxygen-rich environment. Torrefaction of waste vine shoots was conducted in a fixed-bed reactor, utilizing a carrier gas medium with varying O2 concentrations (0% to 21%) at process temperatures of 220, 250, and 280ºC. Proximate and elemental analyses revealed that the torrefaction temperature is the key variable influencing biochar yield. Moreover, under mild torrefaction conditions, an increase in the carrier gas O2 concentration had a lesser impact on product yield compared to process temperature. Thus, it can be inferred that combustion gases and gases generated under mild torrefaction conditions could serve as carrier gases for a more cost-effective torrefaction process. Under oxidative conditions, the total biomass energy recovery was measured at 87.3 ± 1.7% for low temperatures and short torrefaction durations.