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REGENERATOR&
RECUPERATOR
Presented by: Animesh Saha MEB11019
Kabyashree Bora MEB11021
Shuvanando Das MEB11022
Deepjyoti Das MEB11023
Himangshu Deori MEB11027
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INTRODUCTION
• A heat exchanger is a device that is used to transfer thermal energybetween two or more fluids, between a solid surface and a fluid or
between solid particulates and a fluid at different temperatures and
in thermal contact.
• Usually, there is no external heat and work interactions.
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CLASSIFICATION
Heat exchangers can be classified on the basis of...
NATURE OF HEAT EXCHANGE PROCESS
REGENERATOR RECUPERATOR
DIRECT CONTACT
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RELATIVE DIRECTION OF MOTION OF FLUID
COUNTER-CURRENT
OR COUNTER FLOW
CO-CURRENT ORPARALLEL FLOW
CROSS-FLOW
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MECHANICAL DESIGN OF HEAT EXCHANGE SURFACE
SHELL AND TUBE
CONCENTRIC
TUBES
MULTIPLE SHELL
AND TUBE PASSES
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REGENERATOR
Storage type heat exchanger.
The hot fluid is passes through a certain medium called matrix. The heat istransferred to the solid matrix and accumulates there; the operation iscalled heating period. The heat thus stored is subsequently transferred to
the cold fluid by allowing it to pass over the hot matrix.
Desired material properties - high volumetric heat capacity, low effectivethermal heat conductivity in the longitudinal (gas flow) direction.
Applications - gas turbines, open hearth and glass melting furnaces,etc.
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RECUPERATORS
Fluids flow simultaneously on either side of a separating wall; heat
transfer occurs between the fluid streams without mixing or physical
contact with each other.
Used when mixing of the two fluids is undesirable.
Applications - boilers, superheaters, automobile radiators, oil heaters for
an airplane,etc.
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REGENERATOR
Heat regenerator are oftenemployed when the use of heat
recuperators is either
uneconomical, because of the
enormous heat-transfer required, or
impractical, due to the likelihood of
surface fouling by particulatematters.
The use of regenerator has been
widespread for recovering heat
from exhaust gases and preheating
inlet air in commercial and
residential oil-and coal-fired
furnaces. [4]
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Heat is not exchanged directly
between hot and cold fluids across a
separation solid wall.
Hot and cold gas flow alternately
over solids with high heat capacity
per unit volume that periodically
absorb and release heat. A regenerator typically operates
cyclically.
Hot gas flows past the solids, it
heats them while being cooled. This
heating period is followed by flow
of cold gases over the hot solids i.e.,
the cooling period .
Principles of Operation
Fig: Rotary-bed regenerator [9]
[4]
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Heat regenerators can be used either continuously to heat a cold gas and recover
heat from a hot one, or to store thermal energy for use later on.
For continuous heating and cooling, the main task is to ensure maximum energy
recovery (the best thermal efficiency);for the other use, the job is to find the
fraction of energy that has been stored (heat storage factor) and predict heatleaks during storage.
For continuous operation, two or more regenerators are used in parallel. While hot
gas passes into one, cold gas flows through the other; and gas flows are switched at
appropriate times. This is called swing operation. The alternative is to rotate the
solids between the hot and cold gas streams, as is done in a rotary (Ljungstrom)
regenerator.
Fig : Fixed-bed swing regenerator
[10]
[4]
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Thermal Efficiency
(1)
[4]
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[4]
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[4]
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[4]
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ANALYSIS OF THE FUNCTION OF REGENERATOR IN A
GAS TURBINE POWER PLANT
Flue gas coming out of gas
turbine is fed into a regenerator.
The regenerator is placed
between the air compressor and
the combustion chamber. The regenerator pre heats the
compressed air going into the
combustion chamber.
This reduces the heat input
required thus increasing the
efficiency of the power plant.
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ANALYSIS OF THE FUNCTION OF A REGENERATOR IN
A STEAM TURBINE POWER PLANT
Steam coming out of the steam turbine is
bled to the liquid before entering the
boiler.
The steam pre heats the air thus reducingthe heat input to convert the liquid to
steam.
Thus, the efficiency of the power plant
increases.
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TYPES OF REGENERATOR
FIXED BED REGENERATORS
ROTARY REGENERATORS
ROTHEMULE REGENERATORS
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FIXED BED REGENERATOR
Fixed bed regenerators use two or more
regenerators operating out of phase with respect to
one another so that while one regenerator is
supplying heated fluid, the other regenerator(s) is
storing heat from the heating fluid.
As one set of valves close, at a reversal, so another set open.
Hence , when one regenerator draws in heating
fluid, the valves of the other regenerator is closed
and the heat of the heating fluid is stored in the
regenerator.
In the next cycle, when the cold fluid is drawn in,
the regenerator draws heat from the already heated
regenerator and heats the cold fluid.
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ROTARY REGENERATOR
In a rotary regenerator, a porous packing is
rotated around an axis. In its simplest form,
the packing is divided into two gas tight
sections and the hot and cold gases flowsimultaneously in a direction parallel to this
axis.
As the packing rotates through the hot gas
stream, it stores heat, as in the hot period of
a fixed bed regenerator. This thermal energy
is literally transported into the cold gasstream as the packing is rotated
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ROTHEMULE REGENERATOR
It is also known as stationary plateregenerator.
The heat absorbing element in this type
of regenerative air preheater is stationary
rather than rotating.
Instead, the air ducts in the preheater are
rotated so as to alternately expose
sections of the heating absorbing element
to the up flowing air.
The hot flue gas enters at the top of the
preheater and flows down through those
exposed sections of the stationary heat-absorbing element that are not blocked
by the rotating air outlet ducts, thus
heating those sections of the stationary
element
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What is Recuperator ?
Def nA Recuperator is a type of counter-flow energy recovery heat
exchanger positioned within the supply and exhaust air streams of anair handling system, or in the exhaust gases of an industrial process,
in order to recover the waste heat. [5]
Description :
It is the most important type of heatexchanger in which the flowing fluids exchanging
heat are on either side of dividing wall (in the
form of pipes or tubes generally). These heat
exchangers are used when two fluids cannot be
allowed to mix i.e., when the mixing is
undesirable.In a recuperator the only fundamental loss is
the heat conduction through the wall in the flow
direction, which however can be reduced to less
than a per mille by using material with low heat
conductivity like plastics. [5]Fig.1 Types of recuperator profile
[5]
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Recuperator in gas turbine engine
Air is compressed, mixed with fuel, which is
then burned and used to drive a turbine.
The recuperator transfers some of the waste
heat in the exhaust to the compressed air,
thus preheating it before entering the fuel
burner stage
Since the gases have been pre-heated, less
fuel is needed to heat the gases up to the
turbine inlet temperature
By recovering some of the energy usually lost
as waste heat, the recuperator can make a
heat engine or gas turbine significantly more
efficient. [5]
Fig.2 Recuperator in gas turbine engine[6]
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Recuperator in HVAC systems
Recuperators are commonly used to re-use waste
heat from exhaust air normally expelled toatmosphere
Devices typically comprises a series of parallel plates
of aluminium, plastic, stainless steel, or synthetic
fibre, alternate pairs of which are enclosed on two
sides to form twin sets of ducts at right angles toeach other, and which contain the supply and extract
air streams. In this manner heat from the exhaust air
stream is transferred through the separating plates,
and into the supply air stream
Recuperator selected for a pressure drop of between 150 and 250Pa will have a good efficiency
[5]
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Recuperator in Microturbine
Recuperator can be used to increase the efficiency of
gas turbines for power generation, provided the exhaust
gas is hotter than the compressor outlet temperature.
The exhaust heat from the turbine is used to pre-heat
the air from the compressor before further heating in
the combustor, reducing the fuel input required.
The larger the temperature difference between turbine
out and compressor out, the greater the benefit from
the recuperator.
Therefore, microturbine (
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Heat Recuperator
The main aim is to transfer the heat contained in the dryer exhaust air to preheat the
drying air. It is also possible to use the recuperated heat to heat water for cleaning purposes
or air for heating rooms.
In principle, there are two different recuperating systems:1) Air-to-Air
2) Air-Liquid-Air [1]
Air-to-Air Heat Recuperator
In Air-to-Air Heat Recupeartor as shown in the
figure, the drying air is preheated by means of
the outgoing air passing counter-currently over
the heat surface of the recuperator. [1]
This surface is formed as a number of tubes,inside of which the outgoing warm air is
passing while the cold air is passing on the
outside. [1]
Fig.3 Air-to-Air Heat Recuperator set-up
[1]
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Air-Liquid-Air Heat Recuperator
More flexible regarding the installation
Divided into two heat exchangers, in between
which a heat transfer liquid is circulated
If, due to low air temperature during winter, it
may be expected that the temperature of the
water gets below zero, an anti-freeze agent isadded to the water.
As the heat transfer coefficient is higher for
Air-Liquid than for Air-Air, this system is
more efficient than the Air-to-Air heat
recuperator despite the fact that two heat
surfaces are needed. [1]
Fig.4 Air-Liquid-Air heat recuperatorset-up [1]
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Classification of recuperators
Recuperators
Ceramic Conventional
Radiation Convection Combined
Recuperativeburner
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Convection recuperator
Convection recuperators are generally
deployed with flue gases having temperatures 700-1100°C.They utilize convection heat transfer to preheat
combustion air or gas for the purpose of saving fuel.
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Radiation recuperators-
The design of radiation recuperators is based on thethermal radiation of non-luminous gases contained in the
products of combustion. Waste gas temperatures entering
radiation recuperators are usually in the 1090°C to 1371°C
range, and combustion air preheat temperatures areusually in the 426°C to 760°C range.
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Combined recuperators
When the flue gas temperature gets below 600-
650°C the emission from the gas becomes so weak
that the heating surface is not used economically.
One consequent solution is to introduce convection
sections after the radiation recuperator.
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Advantages of recuperators
1. Passive heat recovery unlike rotating wheels
2. Very reliable & low maintenance.
3. No leakage between airflows.
4. Suitable in high humidity environments
5. Aluminium and resistant to corrosion.
6.Double recuperators available for efficiency up
to 90%
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Limitations
1. Supply and exhaust airflows have to beadjacent.
2. No transfer of moisture, which can also be an
advantage ie pools3. Single recuperator efficienciy tends to be
slightly lower than aheivable than wheels.
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References
[1] Çengel, Yunus A.; Boles, Michael (1994). Thermodynamics: An Engineering Approach
[2] Rajput, R.K., (2014). Heat and Mass transfer. New Delhi: S.Chand & company Pvt. Ltd
[3] Nag, P.K., (2010). Basic and Applied Thermodynamics. New Delhi: Tata McGraw Hill
[4] Dudokovic, M.P. ; Ramachandran, P.A (1992). Heat Regenerators: Design and Evaluation
[5] Recuperator. (2015, March 18). In Wikipedia, The Free Encyclopedia. Retrieved March
19, 2015 from http://en.wikipedia.org/wiki/Recuperator
[6] Recuperated Gas turbine. ALENTEC. Retrieved March 19, 2015 from
http://www.alentecinc.com/power.htm
[7] Regenerator. (2015, February 17). In Wikipedia, The Free Encyclopedia. Retrieved
March 19, 2015 from http://en.wikipedia.org/wiki/Recuperator
[8] Recupearted Microturbine. WBDG. Retrieved March 19, 2015 from
http://www.wbdg.org/resources/microturbines.php
[9] Fluid bed regenerator. Industrial Heating. Retrieved March 20, 2015 fromhttp://www.industrialheating.com/
[10] Fixed bed regenerator. Theermopedia. Retrieved March 20, 2015 from
http://www.thermopedia.com/content/1087/
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