28-06-2013, 03:32 PM
Research Paper WASTE HEAT RECOVERY USING STIRLING ENGINE
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ABSTRACT
Waste heat is that heat which is generated in a process by way of fuel combustion or chemical reaction, and then dumped into the
environment even though it could still be reused for some useful and economic purpose. There exist today worldwide concerns
about the best ways of using the deployable sources of energy, and of developing techniques to reduce pollution. This interest has
encouraged research and development for re-use of the usually wasted forms of energy.
There are many methods through which waste heat energy can be recovered and utilized. Stirling engines are mechanical devices
working theoretically on the Stirling cycle. It uses air, hydrogen, helium, nitrogen or even vapors as working fluids. The Stirling
engine offers possibility for having high efficiency engine with less exhaust emissions in comparison with the internal
combustion engine. We had manufactured a gamma type sterling engine which operates at high temperature difference. Our
ultimate aim is to develop Low Temperature Difference (LTD) Stirling engine and for that modification in existing design is
going on.
INTRODUCTION
For any developing country energy acts as a catalyst in
the process of expansion and development of the
country. India ranks sixth in the world in total energy
consumption and needs to accelerate the development
of the sector to meet its growth aspirations.
Development of Stirling engines is preceding worldwide
in spite of their admittedly higher cost because of
their high efficiency, particularly at part load, their
ability to use any source of heat, their quiet operation,
their long life and their non-polluting character. They
were generally called air engines and were
characterized by high reliability and safety, but low
specific power. A great variety of experimental Stirling
engines have been built from the same general
principles to directly pump blood, generate electricity,
or directly generate hydraulic power. Many are used as
heat pumps and some can be used as both heat pumps
and heat engines depending upon the adjustment.
WASTE HEAT RECOVERY SYSTEMS
Depending upon the type of process, waste heat can be
rejected at virtually any temperature from that of
chilled cooling water to high temperature waste gases
from an industrial furnace or kiln. Usually higher the
temperature, higher the quality and more cost effective
is the heat recovery. In any study of waste heat
recovery, it is absolutely necessary that there should be
some use for the recovered heat. Typical examples of
use would be preheating of combustion air, space
heating, or pre-heating boiler feed water or process
water. With high temperature heat recovery, a cascade
system of waste heat recovery may be practiced to
ensure that the maximum amount of heat is recovered
at the highest potential. An example of this technique
of waste heat recovery would be where the high
temperature stage was used for air pre-heating and the
low temperature stage used for process feed water
heating or steam raising.
Indirect Benefits
• Reduction in pollution: A number of toxic
combustible wastes such as carbon monoxide gas,
sour gas, carbon black off gases, oil sludge,
acrylonitrile and other plastic chemicals etc,
releasing to atmosphere if/when burnt in the
incinerators serves dual purpose i.e. recovers heat
and reduces the environmental pollution levels.
• Reduction in equipment sizes: Waste heat
recovery reduces the fuel consumption, which
leads to reduction in the flue gas produced. This
results in reduction in equipment sizes of all flue
gas handling equipments such as fans, stacks,
ducts, burners, etc.
Stirling Engine in Brief[5]
A Stirling engine is a heat engine operating by cyclic
compression and expansion of air or other gas,
the working fluid, at different temperature levels such
that there is a net conversion of heat energy to
mechanical work. The engine resembles a steam engine
in having all heat transfer flowing through the engine
wall. This is traditionally designated an external
combustion engine in contrast with an internal
combustion engine where the heat is put in by
combustion of fuel within the body of the working
fluid. Unlike the steam engine's usage of water as the
working fluid in both its liquid and gaseous phases, the
Stirling engine encloses a fixed quantity of
permanently gaseous fluid such as air or helium.
Typical of heat engines, the general cycle consists of
compressing cool gas, heating the gas, expanding the
hot gas, and finally cooling the gas before repeating the
cycle.
Design of Power Piston and Cylinder
Power piston is the most important part of engine. It
produces power stroke from the expansion of air in
power piston. Power piston and cylinder must have
very low friction. From empirical relation power piston
expansion volume should be around 1/25 times swept
volume of displacer cylinder. And stroke of power
should be same as displacer stroke (slightly smaller
power piston stroke is also permissible). Co-efficient of
friction between piston and cylinder should be as low
as possible, so proper lubrication is also required to be
done.
CONCLUSION
Here we have selected materials and dimensions of our
model, according to materials and dimensions specified
by American Stirling Engine Company for their model
which is having efficiency of 17 %.
After making model heat is supplied from the heat
source of candle and kerosene burner. The engine was
working but didn’t give output as the amount of
supplied heat is less to conduct the experiment on our
model. So our main objective to find out optimum
temperature difference at which model would give
maximum thermal efficiency is in process.