8/9/2019 Presentation on Heat Rate Improvement

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Research Triangle Park

Steve Scavuzzo

Babcock & Wilcox Co.

Technical Consultant

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• Plant Efficiency = Net Plant Heat Rate (NPHR)

• HHV or LHV >4% Difference by definition

• NPHR = (Fuel Input) / (KWGROSS

– KWAUX

), btu/kWh

• Generating Efficiency = (Turbine Eff.) (Boiler Eff.)

• Combined =

~36-42% ~ 84-90%

30-38%

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On the Steam Side

On the Bo i ler Side

Efficiency is a Function of:• Gas Temp Leaving the air heater • Ambient Temp• Excess Air • Unburned Combustibles• Fuel Properties

Cycles and the Second Law In 1823 Carnot Said: Max Efficiency = ≈ 65% for typical rankine cycles

T0 = Heat Sink TemperatureT1 = Temperature at which heat is added

• Increase T1

to improve efficiency• Primary limiting factor is cost and availability of materials

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A ir Heater Perfor m ance

Affects every air pollution control and combustion device in the plant

BURNERS

COMBUSTION

EMISSIONS

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A ir Heater Perform ance

Poorly maintained Air Heaters could degrade plant heat rate by 0.7 to 0.9%.

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Penthouse Roof Seals Access and Observation doorsExpansion JointsFurnace Hopper Seal

A ir Heater Perform anceMinimize Boiler Setting Air In-leakage

Setting Leakage• Degrades Air Heater

Performance3% air leakage ≈ +10F ≈ - 0.25% Eff

• Degrades Combustion Systemperformance – Increases UBCL

and some emissions

• Requires operation at higher totalexcess air – Increases stacklosses and ID/FD fan powerconsumption

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• Maintain boiler cleanlinessto minimize exit gastemperature and stacklosses

A 30F Reduction in boilerexit gas temperature≈ 0.25% Heat Rate

• Implement Intelligentsootblower control tooptimize absorptiondistribution and heat rate

Air Heater Perform anceOperation and Maintenance of Boiler Cleaning Equipment

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A ir Heater Perform anceOperation and Maintenance of Coal Pulverizers

• Proper maintenance of pulverizer wearparts will increase fineness and decreasedrive motor power consumption.Increased fineness reduces unburned

carbon loss (UBCL) and possiblyemissions

• Upgrading to a dynamic classifier willimprove coal fineness and reduce UBCL

• Upgrading to an auto-loading systemoptimizes primary air fan and pulverizermotor power consumption, and coalfineness

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Ensu re Prop er O2 Measurement and Con trol

• Due to O2 Stratification at normal measurement locations, multiple instrumentsshould be installed in a grid arrangement

• Improper O2 measurement and control lead to off-design excess air, emissionsexcursions, slagging and fouling, absorption maldistribution, and other problems

that degrade boiler and emissions performance, and heat rate

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Turbine Steam Path Upg rades ≈ 4 % imp rovement in NPHR

• Incorporate peak generating load increase

• Requires boiler heating surface modifications to match the boiler to the revisedturbine conditions

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Heat rate degrades as load is reduced

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• Split / Sliding Pressure Operation

• Allows the furnace to operate at fullpressure with turbine throttle valveswide open - full steam temperature

to the 1 st stage - at all loads

• Permits increased load change ratecapability

• Can be retrofitted onto drum or once-through boilers

• Extends RH steam temperature controlrange (better low load heat rate) Drum Boiler

Once Through Boiler

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• Variable Frequency Drives for Large Fans and Pumps

• In a typical modern coal fired power plant, air and gas fans consume2-3% of gross generator electric output

• VFDs allow fans to operate more efficiently over the rangeof ambient conditions and fuel variations

• Most significant efficiency gains realized during reduced load operation

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• Economizer resurfacing / heatingsurface addition

• Air Heater Basket Upgrades

Not a Viable Option for all Units

• Lower economizer exittemperature reduces SCR controlrange

• Air heater exit gas temperaturemay already be at the dew pointlimit

Reduce Boiler Exit Gas Temperature

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Condensing Heat Exchanger • Water vapor formed during the combustion process results in

a large stack heat loss≈4% for a typical coal fired unit – about 1/3 of the total losses≈10% for a typical Nat. Gas fired unit – about 2/3 of the total losses

• Most of the lost energy is due to latent heat of vaporization

Opportunity• Condensing heat exchanges could be used to reclaim a large

percentage of this lost energy

Why it isn’t already a routine practice• Heat exchangers are large and expensive• Corrosion is a problem to address• What to do with the low grade energy

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Combustion Efficiency• Burners• Overfire Air Systems• Pulverizer Upgrades

OpportunitiesNew burners and OFA systems optimized with CFD• Reduce total excess air: 5% reduction ≈0.2%

NPHR• Reduce UBCL

• Maintain or reduce NOx and CO emissions

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Su b c r i t ic al Su p erc r i t ic al (B o th at 1000/1000F

2750

2800

2850

2900

2950

S p e c i

f i c

C o a

l C o n s u m p

t i o n

( g / k W h )

2.4Heatrate

imprvm.

Steam pressure @ Turbine Inlet (psig)Source: Siemens,KWU FTP2/Ka/Gs

30.6.1997

Data based on:2 x 660 MW units

6500 hr/aLHV = 25MJ/kg

2400 psigSubcritical

3600 psigSupercritical

5.5Heat

rateimprvm.

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16% better heat rate and lowerCO

2emissions

@ nominal 600 MW NETAverage heat rate 8858 Btu/kWhin 2013

US Fleet Average 10,555Btu/kWh

* Power Engineering July 2014

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+11% reduction in fuel consumption and CO 2 emissions vs. 600C plant heat rate+29% reduction vs. the current fleet average heat rate and CO 2 emissions –could replace existing units with new A-USC plants and meet EPA CO 2 goalwithout carbon capture

• Lower flue gas handling equipment size and fan power • Lower plant fuel handling• Lower fuel transportation system impact• Lower water consumption and condenser heat duty

Lower CO 2 emitted and auxiliary power consumption for capture

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+$15.2 million by B&W in previous 12 years for A-USC

• Fireside Corrosion and Coatings

• Steam Side Oxidation

• Welding and Manufacturing Development

• Conceptual Design Studies

• Header Design 600C and 700+C (B&W projects)

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• Opportunities to improve efficiency of existing fleet without significant capitalinvestment are incremental and unless the unit is ill-maintained, will not resultin large improvements to NPHR (