Feedstock size
The size and density of the biomass is also important
because they affect the rate of heating and drying
during the process (Ciolkosz, 2010). Large particles
heat up more slowly than smaller ones, resulting in
larger particles producing more char and less tar
(Sadaka, 2010). In fixed bed gasifiers, fine-grained
and/or fluffy feedstock may cause flow problems
in the bunker section, resulting in an unacceptable
pressure drop in the reduction zone and a high
proportion of dust particles in the gas. In downdraft
gasifiers, the large pressure drop can also reduce the
gas load, resulting in low temperatures and higher tar
production.