Civil Engineering Reference
In-Depth Information
types of fossil fuels that can be burned, generate heat and energy, and release CO 2 to
the air. On the other hand, biomass material is referred to live or recently dead plants,
vegetables or plant related material that can be either directly or indirectly (e.g.,
biofuel) used to provide heat and energy. Dedicated energy crops, agricultural crops
residues, aquatic crops, forestry residues, biomass processing residues, municipal
wastes, and animal wastes are common different types of biomass resources.
Dedicated energy crops are those plants such as Bamboo that offer the advantage
of being repeatedly regrown from the same roots in a relatively short time cycle.
These crops therefore reach their full productivity level in a few (usually 2-3) years
after being harvested and processed.
Another biomass type is agricultural crops residues that can further be subdivided
into two smaller categories of fi eld residues and process residues. The fi eld residues
are those left in the fi eld after harvesting the crops such as leaves and stems. Process
residues are what that have left after the crops are processed to fi nal usable resources
such as seeds and roots. The most important characteristics of residues of agricul-
tural crops is that they are biomass materials that usually other than capability of
being used as biomass resources have no other commercial application.
Two other main types of biomass resources are aquatic crops such as algae, and
forestry residues such as dead trees. Biomass processing residues are biomass
resources such as unused sawdust or branches of trees and municipal and animal
waste biomass resources are post-consumer wastes and animal-processing waste
respectively.
Different technologies can be utilized for breaking down biomass materials in
order to release the stored sun energy in them. The most important of them are bio-
fuel and bio-power.
12.4.2
Biofuels
Biofuels can be in either solid, gas, or liquid form. Ethanol and biodiesel are the
most common biofuels. In the USA generated ethanol is either fermentation ethanol
(bio-thermal) type (which is either corn base or cellulosic material base) and is
used as an additive to petroleum-based fuels, or synthetic ethanol type which is
produced from ethylene and it is mainly used for industrial applications. The most
signifi cant characteristic of ethanol are its capability to increase the octane of the
fuel and decrease its air pollution effects.
Biodiesel (ethyl or methyl ester) is generated through combining organic oils
with alcohol in presence of a catalyst. This product can be either used as pure bio-
diesel fuel or as an additive to regular diesel fuels with different percentages.
Another category of biofuels are known as Bio-Oils, which are produced
through the process of fast and fl ash pyrolysis. The generated fuel through this
process can be the source of energy for some boilers. In a fast and fl ash pyrolysis
process solid fuel is heated up to about 500 °C for a very short period of time to
generate bio-oil fuel.
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