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8/6/2019 Waste Heat Recovery[1]
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Training Session on EnergyEquipment
Waste Heat
Recovery
Presentation from theEnergy Efficiency Guide for Industry in Asia
www.energyefficiencyasia.org
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Training Agenda: Waste
Introduction
Type of waste heat recovery
Assessment of waste heat recovery
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Introduction
Dumped heat that can still be
reused Value (quality) more important than
quantity
Waste heat recovery saves fuel
What is Waste Heat?Ther
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44 UNEP 2006
Introduction
Source and QualityTher
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Table: Waste heat source and quality
S. No Source of Waste Heat Quality of Waste Heat
1 Heat in flue gases The higher the temperature, the greater the
potential value for heat recovery
2 Heat in vapour streams As above but when condensed, latent heat alsorecoverable
3 Convective & radiant heat lostfrom exterior of equipment
Low grade if collected may be used for spaceheating or air preheats
4 Heat losses in cooling water Low grade useful gains if heat is exchangedwith incoming fresh water
5 Heat losses in providing chilledwater or in the disposal ofchilled water
1.High grade if it can be utilized to reducedemand for refrigeration2.Low grade if refrigeration unit used as a formof Heat pump
6 Heat stored in products leavingthe process
Quality depends upon temperature
7 Heat in gaseous & liquid
effluents leaving process
Poor if heavily contaminated & thus requiring
alloy heat exchanger
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55 UNEP 2006
Introduction
High Temperature Heat RecoveryTher
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Table: Typical waste heat temperature at high temperaturerange from various sources
Types of Devices Temperature (0C)
Nickel refining furnace 1370 1650
Aluminium refining furnace 650 760
Zinc refining furnace 760 1100
Copper refining furnace 760 815
Steel heating furnace 925 1050
Copper reverberatory furnace 900 1100
Open hearth furnace 650 700
Cement kiln (Dry process) 620 730
Glass melting furnace 1000 1550
Hydrogen plants 650 1000
Solid waste incinerators 650 1000
Fume incinerators 650 1450
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Introduction
Medium Temperature HeatRecovery
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Table: Typical waste heat temperature at medium temperature range
from various sources
Types of Devices Temperature (0C)
Steam boiler exhaust 230 480
Gas turbine exhaust 370 540
Reciprocating engine exhaust 315 600
Reciprocating engine exhaust (turbo
charged)
230 370
Heat treatment furnace 425 650
Drying & baking ovens 230 600
Catalytic crackers 425 650
Annealing furnace cooling systems 425 650
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Training Agenda: Waste
Introduction
Type of waste heat recovery
Performance evaluation
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Type of Waste Heat Recovery
Commercial Waste Heat RecoveryTher
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Recuperators
Heat exchangebetween flue gases andthe air throughmetallic/ceramic walls
Ducts/tubes carry
combustion air forpreheating
Waste heatstream on other side
Inlet air fromatmosphere
Outsideducting
Tune plate
Preheatedair
Centre tube plate
Exhaust gasfrom process
Figure 1 : Waste heat recoveryusing recuperator, Source: SEAV
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1010 UNEP 2006
Type of Waste Heat Recovery
Commercial WasteHeat Recovery
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Metallic radiationrecuperators
Figure2.Metallic
Radiati
on
Recuperator(H
ardtechGroup)
Simplest recuperator
Two metal tubes
Less fuel is burned perfurnace load
Heat transfer mosly byradiation
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1111 UNEP 2006
Type of Waste Heat Recovery
Commercial Waste Heat RecoveryTher
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Convective
recuperators
Figure 3. ConvectiveRecuperator(Reay, D.A., 1996)
Hot gas throughparallel small diametertubes
Tubes can be baffled
to allow gas to passover them again
Baffling increases heatexchange but moreexpensive exchanger
is needed
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Type of Waste Heat Recovery
Commercial Waste Heat RecoveryTher
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Radiation/convectivehybrid recuperators
Figure 4. Hybrid Recuperator(Reay, D.A., 1996)
Combinations ofradiation & convection
More effective heattransfer
More expensive but lessbulky than simplemetallic radiationrecuperators
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Type of Waste Heat Recovery
Commercial Waste Heat RecoveryTher
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Ceramic recuperators
Less temperature limitations: Operation on gas side up to 1550 C
Operation on preheated air side to 815 C
New designs
Last two years Air preheat temperatures
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Type of Waste Heat Recovery
RegeneratorTher
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Figure 5. Regenerator(Department of Coal, India, 1985)
Large capacities
Glass and steel meltingfurnaces
Time between thereversals important toreduce costs
Heat transfer in oldregenerators reduced by
Dust & slagging onsurfaces
heat losses from thewalls
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Type of Waste Heat Recovery
Heat WheelsTher
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Figure 6. Heat Wheel(SADC, 1999)
Porous disk rotatingbetween two side-by-
side ducts Low to medium
temperature wasteheat recoverysystems
Heat transferefficiency up to 85 %
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Type of Waste Heat Recovery
Heat PipeTher
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Figure 7. Heat Pipe(SADC, 1999)
Transfer up to 100times more thermal
energy than copper Three elements:
- sealed container- capillary wickstructure -working fluid
Works withevaporation andcondensation
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Type of Waste Heat Recovery
Heat PipeTher
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Performance and advantage
Lightweight and compact No need for mechanical maintenance, input power,
cooling water and lubrication systems
Lowers the fan horsepower requirement andincreases the overall thermal efficiency of the
system Can operate at 315 C with 60% to 80% heat
recovery
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Type of Waste Heat Recovery
Heat PipeTher
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Typical application
Process to space heating Transfers thermal energy from process
exhaust for building heating
Process to process Transfers recovered waste thermal energy
from the process to the incomingprocess air
HVAC applications Cooling and heating by recovering thermal
energy
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Type of Waste Heat Recovery
EconomizerTher
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Figure 8. Economizer(Bureau of Energy Efficiency,
2004)
Utilize the flue gas heat for pre-heating the boilerfeed water
1% fuel savings if 60 C rise of feed
water
200 C rise incombustion air temp
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Type of Waste Heat Recovery
EconomizerTher
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Shell and tube heat exchanger Used when the medium containing waste heat
is a liquid or a vapor that heats another liquid
Figure 9. Shell & Tube Heat Exchanger(King Fahad University of Petroleum & Minerals,
2003)
Shellcontains the tubebundle, andusually internal
baffles to directthe fluid
Vapor containedwithin the
shell
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Type of Waste Heat Recovery
Plate Heat ExchangerTher
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Figure 10. Plate Heat Exchanger
(Canada Agriculture and Agri-Food)
Parallel plates forming a thin flow pass
Avoids high cost of heat exchange surfaces
Corrugatedplates toimprove heattransfer
When directions
of hot and coldfluids areopposite, thearrangement iscounter current
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Type of Waste Heat Recovery
Plate Heat ExchangerTher
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Run around coil exchanger
Figure 11. Run Around Coil Exchanger(SADC , 1999)
Heat transferfrom hot tocolder fluid viaheat transferfluid
One coil in hotstream
One coil in coldstream
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Type of Waste Heat Recovery
Plate Heat ExchangerTher
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Waste heat boiler
Figure 12. Two-Pass Water Tube WasteHeat Recovery Boiler
(Canada Agriculture and Agri-Food)
Water tube boiler: hot
exhaust gases passover parallel tubeswith water
Capacities: 25 m3 to30,000 m3 /min ofexhaust gas
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Type of Waste Heat Recovery
Heat PumpTher
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Figure 13. Heat Pump Arrangement(SADC, 1999)
The vapourcompression cycle
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Type of Waste Heat Recovery
Heat PumpTher
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Developed as a space heating system
Can upgrade heat >2X the energyconsumed by the device
Most promising when heating and coolingcapabilities are combined
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Type of Waste Heat Recovery
Heat PumpTher
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Thermo compressor Compress low-pressure steam by very high-
pressure steam and reuse as medium pressuresteam
Nozzle for acceleration of HP steam to a highvelocity fluid.
Figure: Thermo compressor
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Training Agenda: Waste
Introduction
Type of waste heat recovery
Assessment of waste heat recovery
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Assessment of waste heatrecovery
Quality: Higher temperatures = Higher quality = Lower heat
recovery costs
Quantity: The amount of recoverable heat can be calculated as:
Heat LossesTher
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Q = heat content in kCalV = the flow rate of the substance in m3/hr
= density of the flue gas in kg/m3Cp = the specific heat of the substance inkCal/kg oC
T = the temperature difference in oCCp (Specific heat of flue gas) = 0.24
kCal/kg/oC
Q = V x x Cp x T
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Heat Saving Calculation ExampleTher
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Saving money by recovering heat from hot wastewater:
Q = m x Cp x T x
Discharge of the waste water is 10000 kg/hr at 75C
Preheat 10000 kg/hr of cold inlet water of 20C
A heat recovery factor of 58%
An operation of 5000 hours per year
The annual heat saving (Q) is:
Assessment of waste heatrecovery
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Heat Saving Calculation ExampleTher m
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m = 1000 kg/hr = 10000 x 5000 kg/yr = 50000000 kg/year
Cp = 1 kCal/kg C
T = (75 20) C = 55 C= Heat Recovery Factor = 58% or 0.58
GCV of Oil = 10,200 kCal/kg
Equivalent Oil Savings = 159500000 / 10200 = 156372 L
Cost of Oil = 0.35 USD/L
Monetary Savings = 54730 USD/Annum
Q= 50000000 x 1 x 55 x 0.58= 1595000000 kCal/year
Assessment of waste heatrecovery
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Training Session on EnergyEquipment
Waste Heat
Recovery
THANK YOU
FOR YOUR ATTENTION
UNEP
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Disclaimer and References
This PowerPoint training session was prepared as part ofthe project Greenhouse Gas Emission Reduction from
Industry in Asia and the Pacific (GERIAP). Whilereasonable efforts have been made to ensure that thecontents of this publication are factually correct and
properly referenced, UNEP does not accept responsibilityfor the accuracy or completeness of the contents, and shallnot be liable for any loss or damage that may be occasioneddirectly or indirectly through the use of, or reliance on, thecontents of this publication. UNEP, 2006.
The GERIAP project was funded by the SwedishInternational Development Cooperation Agency (Sida)
Full references are included in the textbook chapter that isavailable on www.energyefficiencyasia.org
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