Waste Heat Recovery[1]

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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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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66 UNEP 2006

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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Introduction


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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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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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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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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1313 UNEP 2006



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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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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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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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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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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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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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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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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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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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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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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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Heat PumpTher

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Figure 13. Heat Pump Arrangement(SADC, 1999)

The vapourcompression cycle


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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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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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Introduction


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:

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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

UNEP 2006


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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:



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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



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3131

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

Waste Heat Recovery[1]

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