Regenerator & Recuperator

8/18/2019 Regenerator & Recuperator

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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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Regenerator & Recuperator