Entrained flow gasification of torrefied wood residues

• The torrefaction pretreatment reduced the milling energy consumption.
• Torrefaction pretreatment contributed to increased gasification plant efficiency.
• The fuel carbon conversion efficiency was affected by torrefaction pretreatment.
• The CH4 yield from gasification was reduced for severely torrefied fuel.

In this work, four different fuels were gasified in a pressurized entrained flow pilot plant gasifier at approximately 270 kWth. The different fuels were; two torrefied wood residues, one raw wood residue and one torrefied stem wood. The system pressure and oxygen equivalence ratio (λ) were held constant for all four gasification experiments. It was found that the torrefaction pretreatment significantly reduced the milling energy consumption for fuel size reduction, which in turn contributed to increased gasification plant efficiency. Furthermore, the results indicate that the carbon conversion efficiency may be enhanced by an intermediate torrefaction pretreatment, whereas both less severe torrefaction and more severe torrefaction resulted in reduced carbon conversions. The results also indicate that the CH4 yield was significantly reduced for the most severely torrefied fuel.