Technical Note SB24: Woody biomass fuel forced drying options

Advantages of pre-drying:

Pre-drying of wet woody biomass for fuel can provide the following advantages:

• improved energy conversion efficiency;
• more stable combustion;
• ability to utilise fuel too high in moisture for an existing combustor design;
• ability to use less expensive combustion systems for fuels of higher moisture content (but there is a trade-off here since drying the fuel can have a cost); and
• lower stack emissions.

Extracting useful heat energy from wood involves processing the wood in a combustor or a gasifier.  Prior to combustion it can be left to dry naturally or dried in a fuel dryer.  The amount of energy able to be extracted depends on the processing equipment design, the calorific value of the material, and its moisture content.

Many wood waste combustion units are designed to burn reasonably wet wood.  However, there is a practical limit on the moisture content of the fuel for each system.