Environmental Engineering Reference
In-Depth Information
Briefly, the process consists in a chemical splitting up of complex organic molecules into
simpler ones through thermal gasification at low temperature (T = 400°-500°C) performed in
controlled conditions of warmth and oxygen availability (max. 3-4% of O
2
) inside a locked
cell. Here, carbon chemical links are broken and simpler molecules take origin, thanks to
warmth effect during starting phases of fuel use (i.e., methane gas). The process is very slow
and the whole cycle lasts 24 hours; furthermore, the reduced turbulence and the flames
absence lessen the powder presence in smokes.
After breakdown, carbon matrix changes from
a solid condition into a gas one, by producing a synthesized gas (syngas) with good
combustible characteristics. The synthetic gas after depuration stage can be burnt in the
presence of air (T≈1100°C) in a following stage, where there are thermodynamic cycles, like
co-generator cycle. The systems can use several thermodynamic cycles, consequently they are
more flexible in regulation between heat and electricity production. The remaining waste is
composed of ash, inert and non toxic, and it can be disposed of in a dump or used for tiles
construction or mixed with asphalt.
2.3. Gasifier Licensed in Italy - System
c
A gasifier with a new technology was licensed in Italy. It is different from the traditional
gasifier and the molecular dissociation thanks to the gasification reactor and to different
conditions of management and control.
Gasification is a chemical decomposition produced by thermal energy. Without a surplus
of air and oxygen, gasification produces thermo chemical decomposition of waste's organic
matter and change this matter into
syngas
[11].
The system which produces the above-mentioned process involves a lot of sections, that
can be listed according to their functions:
•
materials preparation
section
: this involves the storage building and machinery
where wastes are treated and stored (raw materials for the plant) in order to make
their size suitable for feeding the reactor where the gasification process takes place.
These treatments are usually meant to transform the waste into waste fuels (dry and
crushed municipal solid waste).
•
gasification
section
: this is the technological heart of the system. Thanks to the
technology licensed in Italy, a specific reactor has been designed (with new
characteristics), with vertical development, descending flow and best temperature of
process at 1200°C. The waste is fed at the top of reactor and by falling down from
top to bottom (as a fluid bed) is covered by flames come out from thermic lances
which are tangentially in reactor. These lances produce high turbulences which create
an immediate gasification. Thermic lances fed by pure methane and oxygen
characterize this process which grant high ecological and energetic results. Another
peculiarity of this reactor is that it can be fed continuously, wih all the wastes
categories independently from their calorific value and chemical composition.
•
energy generation
section: it is the final step where the syngas is used. Nowadays the
groups with endothermic/alternator engine are more used thanks to their high electric
(about 38% compared to the fuel input) and global efficiency. Thermal recovery
