INGENIEUR
Table 3: Strengths and Weaknesses of Rotary-Kiln Incinerator
Strengths
Suitable for incineration of a variety of waste
streams; solid, liquid, sludge, gas
Readily controls residence time of solid in kiln
High turbulence and effective contact with air/gas
within the kiln
Availability of different feeding mechanisms (ram
feeder, screw feeder, direct injection) according to
needs
Weaknesses
Relatively high particulate carryover to the gas
stream
Requires a separate afterburner for destruction of
organics in the off gas
Relatively high amount of excess air is required
Difficulty in controlling oxygen level in the
incinerator due to air seal issue
Figure 7: Schematic Diagram of
Fluidised Bed Incinerator
kiln incinerators are used at Kualiti Alam and
Radicare for incineration of HW and clinical waste,
respectively.
Table 3 indicates strengths and weaknesses of
rotary-kiln incinerators.
Fluidised Bed Incinerator
Fluidised bed incinerators are used for both
industrial and sludge incineration processes.
There are two types of fluidised-bed incinerators,
namely bubbling and circulating beds. In a
fluidised-bed incinerator, waste is quickly and
uniformly incinerated due to high thermal capacity
of the hot fluidising bed. In its most basic form, fuel
particles are suspended in a hot, bubbling fluidised
bed of ash and other particulate materials (sand,
limestone etc.) where a strong air flow is forced
through a sand bed to provide the oxygen required
for incineration. Such air flow results in a fast and
intimate mixing of gas and solids, which promotes
rapid heat transfer and chemical reactions within
the bed. Figure 7 and Figure 8 show the schematic
diagram and a scaled-up fluidised bed incinerator
in the UTM laboratory respectively.
Fluidisation is the process where granular
materials in solid state are turned into a fluid-like
state by passing a fluid (liquid or gas) through it.
During the process, drag forces overcome the
gravity force, and the material expand as the
particles move away from each other. Eventually,
as the fluid and material spread farther apart,
the velocity decreases and the force of gravity
overcomes the drag forces, causing the particles
to fall onto the bed until they begin to fluidise
again. Given sufficient fluid velocity, the particles
will remain suspended or fluidised, and will exhibit
fluidic behaviour. The fluidised bed allows uniform
and homogeneous combustion inside the bed.
Table 4 indicates the strengths and weaknesses
of fluidised bed incinerator.
Ash Recovery
Cement production has been regarded as an
important process for recycling of ashes produced
from various processes in accordance with the
circular economy concept. According to the
32 VOL 82 APRIL-JUNE 2020