The Incinerator Guidebook: A Practical Guide for Selecting ... - SSWM

Auto-combustion incinerators
In an auto-combustion system, the
incinerator is preheated using dry wood
and/or other agricultural residues (e.g.,
coconut shells, charcoal, etc.). At some
point, the waste itself generates the heat for
continued combustion during the waste
disposal process. Auto-combustion
incinerators are substantially cheaper to
operate than fuel-assisted incinerators,
however auto-combustion incinerators are
not suited to destroy placenta or anatomic
waste unless anatomic waste is interspersed
with safety boxes, dry wood, or charcoal in a
ratio of 1 kilogram of anatomic waste to 3
kilograms or more of plastic, wood or
charcoal.
Figure 1. Standard components of a small-scale incinerator.
Auto-combustion incinerators are able to
destroy non-sharps infectious waste if the
ratio by weight of safety boxes, wood, or
charcoal to non-sharps waste is 2:1 or
greater. In consideration of the amount of
plastic waste generated by injections, it is
important that incinerator technologies
which can destroy 50 to 100 percent plastic
in the waste load without causing damage to the refractory materials are selected. It is important
that metalwork in the incinerator is stainless steel or cast iron if incinerator equipment is expected
to be operational for more than three years without replacement.
Fuel-assisted incinerators
Fuel-assisted incinerators require a fossil fuel (diesel or gas) and a continuous electrical power
supply to operate. Fuel-assisted incinerators are sometimes prone to damage if an electrical power
failure occurs during operation.
The better-designed fuel-assisted incinerators control the fuel supply in order to maintain constant
combustion temperatures and to economize on fuel consumption. Fuel is injected into both the
primary and secondary chambers, along with auxiliary air through blowers.
Most fuel-assisted incinerators with a capacity to destroy 100 to 150 kilograms of waste per day
consume 5 to 8 liters per hour of fuel (4 to 6.5 kilograms of gas). It is important to note that some
fuel-assisted incinerators cannot destroy more than 15 to 25 percent of plastic per load because of
the high caloric value of plastics and the damage that can be caused to the refractory lining.
Temperature
An incinerator should operate in the temperature range of 800° to 1200°C when medical waste is
incinerated. Toxic fumes including furans and dioxins are emitted at temperatures below 600°C if
polyvinyl chloride or certain other materials are incinerated.
5