36
2 Conventional Approaches for Waste Management …
thermal treatment, it is normally a need for pre-processing of the raw materials,
e.g., for removal of unacceptable material (non-combustibles, oversized material),
shredding and screening to create a uniform and homogenous mixture, or for separation of recyclables. Compared to the landfill disposal, thermal treatment significantly reduces the amount/volume of waste materials, and provides the benefits
to recover energy from waste in the forms of heat and electricity, which hence
reduces the amount of GHG emissions and reduces the contamination to surfaceand groundwater. However, compared to landfills it has two major disadvantages:
it generates more emissions of air contaminants, and its operation is more costly.
Common thermal treatment technologies include incineration and solid recovered
fuel system.
Incineration: Incineration is the second common method for solid waste disposal
in Canada. It is referred to a range of operations from open burning to controlled
combustion processes with mass burning systems as well as other types of modern
incinerators. The temperatures of incineration operations are usually between 900 to
1100 °C. In Canada, less than 5% of the municipal solid waste (MSW) is disposed of
through incineration, while European countries such as Germany, the Netherlands,
and Sweden treat 35–50% of their generated MSW thermally [4, 6] due to the benefits of incineration, such as reduction of the amount/volume of waste for disposal,
stabilization of the waste and recovery of potential energy. There are two basic types
of incinerators depending on the number of combustion chambers and the amount
of air provided to each chamber [23]:
– Dual-chamber starved air systems
– Single-chamber excess air systems.
The dual-chamber starved air system also known as controlled air incinerator is a
well-established, stable and reliable technology extensively used for waste incineration. It is composed of two stages of combustion including the primary combustion
chamber and secondary combustion chamber. The primary combustion chamber
operates as a gasifier to partially oxidize MSW at 450–850 °C on a stationary hearth
with less than the stoichiometric amount of air required for combustion to produce
combustible gases such as carbon monoxide. The volatile gases from the primary
chamber then enter the secondary chamber where they are completely oxidized in 1–
2 s in the presence of 150–200% excess air at a temperature as high as 1000–1200 °C.
After oxidization, the residues, generally referred to as bottom ash, are removed from
the furnace [19]. The dual-chamber starved air system is more suitable for small cities
with little population and can be operated in batch and semi-continuous modes [19].
In single-chamber excess air systems, however, complete combustion of the waste
occurs in a single burn chamber in the presence of excess air (as much as 50% more
than the amount of air needed) [23].
Both types of incinerators can be operated in continuous, semi-continuous or
batch mode. Continuous feed incinerators operate without interruption for hours or
are loaded periodically during operation (e.g., in every 10 min). Ash is removed from
the facilities after a cool-down phase. The continuous feed facilities are normally
comprised of 3–5 parallel units with a design capacity of 10–100 tonnes per day for
2 Conventional Approaches for Waste Management …
thermal treatment, it is normally a need for pre-processing of the raw materials,
e.g., for removal of unacceptable material (non-combustibles, oversized material),
shredding and screening to create a uniform and homogenous mixture, or for separation of recyclables. Compared to the landfill disposal, thermal treatment significantly reduces the amount/volume of waste materials, and provides the benefits
to recover energy from waste in the forms of heat and electricity, which hence
reduces the amount of GHG emissions and reduces the contamination to surfaceand groundwater. However, compared to landfills it has two major disadvantages:
it generates more emissions of air contaminants, and its operation is more costly.
Common thermal treatment technologies include incineration and solid recovered
fuel system.
Incineration: Incineration is the second common method for solid waste disposal
in Canada. It is referred to a range of operations from open burning to controlled
combustion processes with mass burning systems as well as other types of modern
incinerators. The temperatures of incineration operations are usually between 900 to
1100 °C. In Canada, less than 5% of the municipal solid waste (MSW) is disposed of
through incineration, while European countries such as Germany, the Netherlands,
and Sweden treat 35–50% of their generated MSW thermally [4, 6] due to the benefits of incineration, such as reduction of the amount/volume of waste for disposal,
stabilization of the waste and recovery of potential energy. There are two basic types
of incinerators depending on the number of combustion chambers and the amount
of air provided to each chamber [23]:
– Dual-chamber starved air systems
– Single-chamber excess air systems.
The dual-chamber starved air system also known as controlled air incinerator is a
well-established, stable and reliable technology extensively used for waste incineration. It is composed of two stages of combustion including the primary combustion
chamber and secondary combustion chamber. The primary combustion chamber
operates as a gasifier to partially oxidize MSW at 450–850 °C on a stationary hearth
with less than the stoichiometric amount of air required for combustion to produce
combustible gases such as carbon monoxide. The volatile gases from the primary
chamber then enter the secondary chamber where they are completely oxidized in 1–
2 s in the presence of 150–200% excess air at a temperature as high as 1000–1200 °C.
After oxidization, the residues, generally referred to as bottom ash, are removed from
the furnace [19]. The dual-chamber starved air system is more suitable for small cities
with little population and can be operated in batch and semi-continuous modes [19].
In single-chamber excess air systems, however, complete combustion of the waste
occurs in a single burn chamber in the presence of excess air (as much as 50% more
than the amount of air needed) [23].
Both types of incinerators can be operated in continuous, semi-continuous or
batch mode. Continuous feed incinerators operate without interruption for hours or
are loaded periodically during operation (e.g., in every 10 min). Ash is removed from
the facilities after a cool-down phase. The continuous feed facilities are normally
comprised of 3–5 parallel units with a design capacity of 10–100 tonnes per day for