24-04-2014, 10:39 AM
UTILIZATION OF WASTE HEAT FROM EXHAUST OF CERAMIC KILN A PROJECT REPORT
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ABSTRACT
To develop a system which utilize the waste heat release from exhaust of
ceramic kiln. Kiln is used for final baking of ceramic in the unit. Coal is used as
a fuel in tunnel kiln.
Average monthly fuel consumption in ceramic industry is in term of lakes
depending on the size of the industry. In ceramic plants, about 50% of total
energy cost is required for kiln. Exhaust heat released from tunnel kiln by two
ways first one is flue gas released at a temperature of around 190 °C and
second one is hot air from final cooling zone at a temperature of around 120 °C
which is already used in drier. At present, exhaust heat from tunnel kiln sent to
atmosphere and combustion air use at an ambient temperature.
INTRODUCTION
Existing technology equipment
Description of existing/technology
Roller kiln is used for final firing of tiles to get the finished product. Natural gas is used as a
fuel in roller kiln. Tiles are fired up to a temperature of about 1200°C. There are two sources
of exhaust from the roller kiln. One is flue gas from the preheating zone of the roller kiln
which is at a temperature of about 249°C. The other exhaust is the hot air from the final
cooling zone which is at a temperature of about 250° to 300°C. This hot air is already utilized
in almost by all the ceramic unit owners for drying or heating purpose. But the waste heat of
flue gas is not utilized in any of the ceramic unit due to presence of sulphur in flue gas.
Utilization of flue gas for preheating of combustion air leads to saving in fuel consumption in
roller kiln.
Role in process
Roller kiln is used for final firing of the tiles to get the finish product. Natural gas is used as a
fuel in roller kiln. Ceramic tiles are fired up to a temperature of about 1200°C in the roller
kiln. It removes the moisture present in the product and also improves the strength of the
products by firing at higher temperature.
Skilled manpower
At Morbi ceramic cluster, the availability of skilled manpower is one of the limitations due to
more number of ceramic units. One local technical persons available at Morbi takes care of
about 5 - 10 ceramic units. For major equipments of ceramic units like kiln, Polishing
Machine etc maintenance or the repair work of these equipments will be taken by the
equipment suppliers itself even the suppliers like Sacmi, KEDA, Modena etc depute one of
their representative staying at Morbi for the maintenance work. Local technical persons of
Morbi takes care As not many experts/skilled persons are available in the cluster, one expert
takes care of all maintenance & operational problems of about 5 - 10 industries.
Heat Wheels:
A heat wheel is finding increasing applications in low to medium temperature waste heat
recovery systems. Figure 3.6 is a sketch illustrating the application of a heat wheel. It is a
sizable porous disk, fabricated with material having a fairly high heat capacity, which rotates
between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. The axis of the
disk is located parallel to, and on the partition between, the two ducts. As the disk slowly
rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot
air and, as the disk rotates, from the disk to the cold air. The overall efficiency of sensible
heat transfer for this kind of regenerator can be as high as 85 percent. Heat wheels have been
built as large as 21 metres in diameter with air capacities up to 1130 m3 / min. A variation of
the Heat Wheel is the rotary regenerator where the matrix is in a cylinder rotating across the
waste gas and air streams. The heat or energy recovery wheel is a rotary gas heat regenerator,
which can transfer heat from exhaust to incoming gases. Its main area of application is where
heat exchange between large masses of air having small temperature differences is required.
Heating and ventilation systems and recovery of heat from dryer exhaust air are typical
applications.
Shell and Tube Heat Exchanger:
When the medium containing waste heat is a liquid or a vapor which heats another liquid,
then the shell and tube heat exchanger must be used since both paths must be sealed to
contain the pressures of their respective fluids. The shell contains the tube bundle, and
usually internal baffles, to direct the fluid in the shell over the tubes in multiple passes. The
shell is inherently weaker than the tubes so that the higher-pressure fluid is circulated in the
tubes while the lower pressure fluid flows through the shell. When a vapor contains the waste
heat, it usually condenses, giving up its latent heat to the liquid being heated. In this
application, the vapor is almost invariably contained within the shell. If the reverse is
attempted, the condensation of vapors within small diameter parallel tubes causes flow
instabilities. Tube and shell heat exchangers are available in a wide range of standard sizes
with many combinations of materials for the tubes and shells. A shell and tube heat
exchanger is illustrated in Figure 3.9.