Research Triangle Park

Steve Scavuzzo

Babcock & Wilcox Co.

Technical Consultant

• 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%

On the Steam Side

On the Boiler 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 Temperature

T1 = Temperature at which heat is added

• Increase T1 to improve efficiency

• Primary limiting factor is cost and availability of materials

Air Heater Performance Affects every air pollution control and combustion device in the plant

BURNERS

COMBUSTION

EMISSIONS

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

Penthouse Roof Seals

Access and Observation doors

Expansion Joints

Furnace Hopper Seal

Air Heater Performance Minimize Boiler Setting Air In-leakage

Setting Leakage

• Degrades Air Heater

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

• Degrades Combustion System

performance – Increases UBCL

and some emissions

• Requires operation at higher total

excess air – Increases stack

losses and ID/FD fan power

consumption

• Maintain boiler cleanliness

to minimize exit gas

temperature and stack

losses

A 30F Reduction in boiler

exit gas temperature

≈ 0.25% Heat Rate

• Implement Intelligent

sootblower control to

optimize absorption

distribution and heat rate

Air Heater Performance Operation and Maintenance of Boiler Cleaning Equipment

Air Heater Performance Operation and Maintenance of Coal Pulverizers

• Proper maintenance of pulverizer wear

parts will increase fineness and decrease

drive motor power consumption.

Increased fineness reduces unburned

carbon loss (UBCL) and possibly

emissions

• Upgrading to a dynamic classifier will

improve coal fineness and reduce UBCL

• Upgrading to an auto-loading system

optimizes primary air fan and pulverizer

motor power consumption, and coal

fineness

Ensure Proper O2 Measurement and Control

• Due to O2 Stratification at normal measurement locations, multiple instruments

should be installed in a grid arrangement

• Improper O2 measurement and control lead to off-design excess air, emissions

excursions, slagging and fouling, absorption maldistribution, and other problems

that degrade boiler and emissions performance, and heat rate

Turbine Steam Path Upgrades ≈ 4% improvement in NPHR

• Incorporate peak generating load increase

• Requires boiler heating surface modifications to match the boiler to the revised

turbine conditions

Heat rate degrades as load is reduced

• Split / Sliding Pressure Operation

• Allows the furnace to operate at full

pressure with turbine throttle valves

wide open - full steam temperature

to the 1st stage - at all loads

• Permits increased load change rate

capability

• Can be retrofitted onto drum or once-

through boilers

• Extends RH steam temperature control

range (better low load heat rate) Drum Boiler

Once Through Boiler

• Variable Frequency Drives for Large Fans and Pumps

• In a typical modern coal fired power plant, air and gas fans consume

2-3% of gross generator electric output

• VFDs allow fans to operate more efficiently over the range

of ambient conditions and fuel variations

• Most significant efficiency gains realized during reduced load operation

• Economizer resurfacing / heating

surface addition

• Air Heater Basket Upgrades

Not a Viable Option for all Units

• Lower economizer exit

temperature reduces SCR control

range

• Air heater exit gas temperature

may already be at the dew point

limit

Reduce Boiler Exit Gas Temperature

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

Combustion Efficiency

• Burners

• Overfire Air Systems

• Pulverizer Upgrades

Opportunities

New 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

Subcritical Supercritical (Both at 1000/1000F)

2750

2800

2850

2900

2950

Specif

ic C

oal C

onsum

pti

on (g/kW

h)

2.4%Heatrate

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

5.5%Heatrate

imprvm.

16% better heat rate and lower

CO2 emissions

@ nominal 600 MWNET

Average heat rate 8858 Btu/kWh

in 2013

US Fleet Average 10,555

Btu/kWh

* Power Engineering July 2014

+11% reduction in fuel consumption and CO2 emissions vs. 600C plant heat rate

+29% reduction vs. the current fleet average heat rate and CO2 emissions –

could replace existing units with new A-USC plants and meet EPA CO2 goal

without 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 CO2 emitted and auxiliary power consumption for capture

+$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)

• Opportunities to improve efficiency of existing fleet without significant capital

investment are incremental and unless the unit is ill-maintained, will not result

in large improvements to NPHR (<1.0 - 1.5%)

• Selected older units with original equipment -- turbine steam path upgrades

combined with boiler heating surface modifications are the most likely

opportunity to improve heat rate by multiple percentage points (≈4%)

• Opportunities are available to improve reduced load heat rate and load cycling

capability

• New ultra supercritical or advanced ultra-supercritical units offer the most

significant heat rate improvement opportunities (16-29%)