Commonly found in waste facilities in Nigeria are medium sized locally fabricated incinerators that work just as well compared to their much larger counterparts in the third world countries. The incinerators are locally fabricated to suit the nation's kind of waste and well working. They are usually made of Aluminum covering for better efficiency and insulation.
Of course, waste facilities have to make do with these incinerators because of the relative affordability of these equipment as compared to the large scale ones. These incinerators are limited in the tonnes of waste it can handle at a time, but it is just about sufficient for the amount of waste procured by these facilities in the country. If more waste management facilities, with two or more locally fabricated incinerators installed, could be established at various regions of the Country, then perhaps the rate of waste generation of the nation could be matched.
Wastes not of
economic value to the facility are usually disposed off into the incinerator for
complete disposal by combustion. For example, Oil Sludge (tank bottom) which are
sediments in oil tanks are normally incinerated. The incinerator has 2 chambers
and a chimney:
1. Primary Chamber: This
chamber has a door through which waste is loaded into the incinerator. The
chamber has a burner supplying heat of the range of 1800°C to 2100°C
2. Secondary Chamber: The
effluent gases moves from the primary chamber to the secondary chamber for complete
combustion. The burner in the secondary chamber burns up to 2200°C.
The time taken
for the loaded waste to pass through the primary chamber to the secondary
chamber to the expulsion of the gas through the chimney is known as the
Retention Time. It's advisable to increase the retention time to ensure total
breakdown and combustion of the waste.
Combustion Process: Combustion involves the breakdown of carbon molecules or chains by
the addition of oxygen. When there is less oxygen in supply, the toxic carbon
monoxide would be produced. But when there is much oxygen in supply, the
non-toxic carbon dioxide would be produced.
In the presence
of sulphides and nitrogen, sulphur oxides and nitrogen oxides would be produced
respectively.
3. Chimney: Dioxins and
furans, which are carcinogenic, may occur due to incomplete combustion (as in
the case of burning Plastics). Hence it's not advisable to burn plastic in an
open environment. These gases when formed in the incinerator gets to the
chimney, which has a scrubbing unit that scrubs off toxic compounds and gases
to a tank that feeds them back to the incinerator for proper combustion. The
scrubber main component is acidified water which is sprayed to reduce the
Kinetic energy of the heavy metals.
Other gases not
scrubbed off by the scrubbing unit (e.g. Ammonia, ozone, oxides of sulphur,
oxides of nitrogen,etc. goes out through the vent of the incinerator and is being
monitored for their SPM (suspended particulate matter) release rate.
Ashes formed during combustion are oxides
of heavy metals salts that are not able to move.
Waste burns at
different rate. So the amount of waste to be burnt by the incinerator with time
varies. But normal (soft) waste is estimated to be incinerated at about
900kg/hr.
As safety
precautionary measures, there are usually a lot of safety signs stamped on the body of the
incinerator such as Danger! keep off, authorized personnel only, etc. At the incinerator section, it is required for operators to wear respirators
while already kitted with other PPEs. Though the outer body of the incinerator doesn't get heated up by the rise in temperature within during operation, the door of the incinerator is expected
to be locked during an operation, and even for some time after the
operation to prevent direct exposure to the heat within.
The incinerator
has some safety components. For instance, it electrocutes anyone who touches it
in small amounts when in operation. It short circuits and shuts down and
request for password when the door is opened while in operation.
Photo source: flashpointnews.wordpress.com
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