Environmental Engineering Reference
In-Depth Information
• It generates a product that is easy and cheap to handle, transport, and store.
• Briquettes facilitate the optimization of combustion processes, resulting in
higher efficiency, lower emissions, and reduced ash production.
• Briquette combustion typically requires considerably less investment in fur-
naces and purification equipment than some alternatives.
Biomass briquetting can be performed using an exogenous binder or by direct com-
pacting with no added binder. One example from a pilot plant (Biofuel Technology
Centre, Sweden) is presented below. In this case, bales of raw material are put on a
conveyor and transported to a shredder. The shredded material is then stored in a
silo. The shredder cuts the material into particles with diameters ranging from the
microscopic to 15 mm. Briquette production is initiated by transporting the mate-
rial from the silos through a mixer and a separator to a buffer silo above the briquette
press. At the bottom of the buffer silo, an auger then transfers the material into the
press. The briquette press has a high production capacity of 450-500 kg h -1 . The
humidity of the raw material prior to pressing can be determined using a Haymatic
moisture meter, which measures the material's electrical conductivity and uses that
to roughly estimate the moisture content at the sample surface.
Several parameters affect the mechanical strength of the briquettes, including
the moisture content of the raw material and the pressure and temperature at
which they are formed. A wide range of raw materials have been used in briquette
production, including dry household waste fractions in combination with cellu-
lose-rich materials such as straw or reed canary grass. In general, the resulting
briquettes have favorable combustion properties and the incorporation of waste
into the biofuel does not increase the emissions of organic compounds formed
during combustion and heat production [3].
7.2.4
Pellet Production
Fuel pellets made from sawdust represent a renewable energy source for heat pro-
duction that has become increasingly popular in recent years. About 2.2 million
tons of wood pellets were manufactured in Sweden in 2010, making this country
the biggest fuel pellet producer in Europe. Moist solid biomass, such as sawdust
and other feedstocks used in pellet production, normally has a moisture content of
more than 50 wt%. It is often stored outdoors before being pelletized, in order to
ensure an adequate supply of fuel to sustain pellet production during winter time.
A wood pellet can be regarded as a small, round, hard unit of stored bioenergy.
They are typically cylindrical with diameters of 6-8 mm and variable lengths.
Over the last decade, softwood pellets have emerged as a leading source of renew-
able energy that is primarily used for heat and power production and which has
the potential to replace fossil fuels such as oil and natural gas in many applica-
tions. The energy value of 1 ton of pellets is about 5.0 MWh, which is equivalent
to that of 0.5 m 3 of oil.
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