Densification (BEF, 2010) [WGT10010]

While biomass is a great renewable energy source, it is not a good fuel, because it typically contains more than 70% air and void space.  This low volumetric energy density makes it difficult to collect, ship, store and use.

Densification is a relatively new process in which the air is squeezed out at very high pressure to make pellets (using feed type machines), cubes (using alfalfa cuber) or logs (PrestoLog etc.). Best of all, for many applications almost any biomass can be used provided it is chopped fine: sawdust; agricultural residues and even municipal solid waste.

Once densified, the fuel has many uses.

Mass and Volume Energy Densities:  The High Heating Value (kJ/kg or Btu/lb) is a mass energy density of the fuel.  (See biomass table of HHV). However, for biomass a more important figure is the volume energy density, (kJ/liter, MJ/m³ , Btu/ft³).  Because most biomass is so light, weight is not nearly as much a factor as volume in collecting, shipping, storing and using.

The following table shows the dramatic difference between high density and low density biomass fuels.  The dense biomass fuels are a factor of 3 to 4 times heavier than wood chips, though not as dense as coal or diesel. 

                              
Mass and Volume Energy Densities of Some Fuels