Biomass-Based Energy Production - Introduction to Chemicals from Biomass - page 251

Processes Products

Drying Dry biomass

Physical upgrading
processes

Pulverization Powder

Briquetting Briquettes

Pelletizing Pellets

Torrefaction Torrefied biomass

Lignicellulosic
biomass
(Wood sawdust/chips, forest
residues, wood residues,
clearing and tinnings, short
rotation crops, agricultural
residues, agricultural crops,
straw, waste, peat)

Pretreatment, Hydrolysis
& Fermentation

Ethanol, Butanol &
Biogas, Hydrogen

Biological & chemical
processes

Esterification Biodiesel

Gasification Methanol/DME

Thermochemical
processes

Pyrolysis FT-diesel

Liquefaction Ethanol

Combustion Hydrogen

Figure 7.1 Different types of bioenergy production processes from biomass.

such as particle size distribution, particle shape, and moisture content. The pow-
der is usually handled in closed systems from milling to its storage in silos to
avoid the risk of dust explosions. The properties of the powder are determined by
the raw materials and type of mill used in its production [2].

7.2.3 Briquette Production

Briquettes are another type of upgraded biofuel. Agricultural and forestry residues
and other biological materials are often difficult to use as biofuels because they
are heterogeneous, uneven and bulky in nature, and awkward to handle. These
problems can be eliminated by densifying the material into compact, regular
shapes. This is done by forcing the biomass through a die at high pressure using a
screw or piston-press. The friction between the raw material and equipment
increases the temperature inside the press, softening the lignin present within the
materials, which then acts as a binder. Typical briquettes have diameters of
35-90 mm. The process has many advantages as follows.

• It increases the net calorific content of the material per unit volume. Briquettes
typically have densities of 800-1300 kg m -3 whereas the bulk density of loose
biomass is 10-20 kg m -3 and that of wood chips is about 300 kg m -3 .
• It generates a product of uniform size with a well-defined quality and moisture
content.