Page 29 - Materials Chemistry, Second Edition

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Sustainable Industrial Design and Waste Management
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chamber, where additional air and fuel are added, to complete destruction of
all toxic emissions.
Fluidized-bed incinerator
This type of incinerator is used for liquid, sludge, or uniformly sized solid
waste. The fluidized-bed incinerator utilizes a fluidized bed consisting of sand
or alumina on which combustion occurs. Air flow is applied from below
which has sufficient pressure to allow it to fluidize the bed of sand, or hold
it in suspension, as long as the velocity of the air is not so great that it trans-
ports the sand out of the system. This is a fluidized bed in which the parti-
cles of the bed are in suspension, but not in flow. Waste is added/injected into
this fluidized bed. The air with which the bed is fluidized is heated to at
least ignition temperature of the waste, and the waste begins to burn (oxi-
dize) within the bed. Most of the ash remains in the bed, and some exits the
incinerator into the air pollution control system. Heat also exits with the
flue gases and can be captured in a boiler or used to preheat combustion air.
In almost all types of waste incinerators, primary and secondary com-
bustion chambers are necessary to complete the combustion and oxidation
to achieve the required destruction and removal efficiency (DRE). The pri-
mary chamber’s function is to volatilize the organic fraction of the waste.
The secondary chamber’s function is to heat the vaporized organics to a tem-
perature where they will be completely oxidized.
Advantages of incineration:

• It is applicable to all kinds of waste.
• Incinerators are made to avoid air pollution through air pollution
control units.
• The ash resulting from the combustion occupies only around 10% of
the solid waste volume.
• Energy may be recovered from incineration through many ways, for
example gas to water heat exchange. The water is converted to steam,
which may then be used to generate electricity through steam turbines.

Disadvantages of incineration:

• Incinerator construction requires high capital cost.
• Incineration operation and management require high cost and
skilled workers.
• Wastes require energy to be burnt.
• The air pollution control systems are very expensive. On the other
hand, the emissions and the ash resulting from incineration are
extremely dangerous. If not properly controlled, they cause air pol-
lution which can have dangerous effects on human health.