2.2 Conventional Approaches for Non-hazardous Solid Waste Disposal
37
each individual unit [19]. A batch feed incinerators mean one-time feeding of the
waste to the unit in operation. Typical batch feed incinerators have a much smaller
capacity (1–20 tonnes per day) if compared with continuous systems. Whereas, batch
incinerators have the advantages of slow and silent incineration, simple operation,
good ash quality and relatively lower amounts of particulate emissions.
If classified based on the reactor types, there are three types of incinerators:
– Grate furnace,
– Fluidized bed combustor,
– Rotary kiln.
Grate furnace incineration, also called mass burning incineration, is a wellestablished technology developed over 100 years ago. The systems typically have
large capacities, composed of a single-stage or two-stage combustion. Thus, they are
often used in large cities with over 1 million populations [19]. In a basic combustion
process, solid waste is fed to the system as received and it is dried on the initial grate
section (in multi-grate systems) or in the single combustion chamber with underfire air and radiant heat from the furnace. Then the primary burning occurs and
more readily combustible materials are oxidized followed by the last burning phase,
which includes the oxidization of fixed carbons [19]. Combustion of waste could
be either a single-stage or a two-stage process. A two-stage process consists of a
pyrolysis/gasification stage that partially oxidizes dried waste on the grates with less
than the stoichiometric amount of oxygen required for combustion (30–80%) and
the complete-oxidization stage at which the pyrolysis gases or flue gases from the
previous stage are combusted in excess air [19, 40, 45]. Grate furnace incinerators
are capable of disposing of all types of MSW for steam or electricity production. The
capacity of grate furnace incinerators ranges from 200 to 1000 tonnes per unit per
day. In Canada, typical grate furnace incinerators have a capacity of 400–850 tonnes
per day [19].
Fluidized bed combustor (FBC) is an advanced combustion technology for
combusting solid wastes such as sewage sludge, petroleum waste, paper industry
waste and MSW, however, by far there is no fluidized bed incinerator in Canada
[19]. In a fluidized bed combustion chamber, the waste is partially gasified at 850 °C
in the lower section of the chamber to produce carbon monoxide and other volatiles,
and the resulting gases are subsequently combusted completely in the upper section
of the chamber. FBC has the advantage of low capital cost, long service life and low
maintenance cost as well as lower trace organic emissions (dioxins and furans) due to
extensive turbulence and long residence time in the combustion chamber. The disadvantage of fluidized bed incinerators is the carry-over of the fly ash to the flue gases
requiring more efficient dust emission control. They also require pre-processing of the
waste for particle size-reduction. Other operating problems include bed agglomeration and de-fluidization due to the deposition of low-melting-point alkali compounds
or the formation of eutectic mixtures. FBC incinerators usually have a capacity in
the range of 50–200 tonnes per unit per day [19].
Rotary kiln incineration systems are ideal for processing mixed industrial and
hazardous wastes such as infectious and medical waste, chemical, pharmaceutical
37
each individual unit [19]. A batch feed incinerators mean one-time feeding of the
waste to the unit in operation. Typical batch feed incinerators have a much smaller
capacity (1–20 tonnes per day) if compared with continuous systems. Whereas, batch
incinerators have the advantages of slow and silent incineration, simple operation,
good ash quality and relatively lower amounts of particulate emissions.
If classified based on the reactor types, there are three types of incinerators:
– Grate furnace,
– Fluidized bed combustor,
– Rotary kiln.
Grate furnace incineration, also called mass burning incineration, is a wellestablished technology developed over 100 years ago. The systems typically have
large capacities, composed of a single-stage or two-stage combustion. Thus, they are
often used in large cities with over 1 million populations [19]. In a basic combustion
process, solid waste is fed to the system as received and it is dried on the initial grate
section (in multi-grate systems) or in the single combustion chamber with underfire air and radiant heat from the furnace. Then the primary burning occurs and
more readily combustible materials are oxidized followed by the last burning phase,
which includes the oxidization of fixed carbons [19]. Combustion of waste could
be either a single-stage or a two-stage process. A two-stage process consists of a
pyrolysis/gasification stage that partially oxidizes dried waste on the grates with less
than the stoichiometric amount of oxygen required for combustion (30–80%) and
the complete-oxidization stage at which the pyrolysis gases or flue gases from the
previous stage are combusted in excess air [19, 40, 45]. Grate furnace incinerators
are capable of disposing of all types of MSW for steam or electricity production. The
capacity of grate furnace incinerators ranges from 200 to 1000 tonnes per unit per
day. In Canada, typical grate furnace incinerators have a capacity of 400–850 tonnes
per day [19].
Fluidized bed combustor (FBC) is an advanced combustion technology for
combusting solid wastes such as sewage sludge, petroleum waste, paper industry
waste and MSW, however, by far there is no fluidized bed incinerator in Canada
[19]. In a fluidized bed combustion chamber, the waste is partially gasified at 850 °C
in the lower section of the chamber to produce carbon monoxide and other volatiles,
and the resulting gases are subsequently combusted completely in the upper section
of the chamber. FBC has the advantage of low capital cost, long service life and low
maintenance cost as well as lower trace organic emissions (dioxins and furans) due to
extensive turbulence and long residence time in the combustion chamber. The disadvantage of fluidized bed incinerators is the carry-over of the fly ash to the flue gases
requiring more efficient dust emission control. They also require pre-processing of the
waste for particle size-reduction. Other operating problems include bed agglomeration and de-fluidization due to the deposition of low-melting-point alkali compounds
or the formation of eutectic mixtures. FBC incinerators usually have a capacity in
the range of 50–200 tonnes per unit per day [19].
Rotary kiln incineration systems are ideal for processing mixed industrial and
hazardous wastes such as infectious and medical waste, chemical, pharmaceutical