Download - B&W PGG Powerpoint Template
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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 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
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Air Heater Performance Affects every air pollution control and combustion device in the plant
BURNERS
COMBUSTION
EMISSIONS
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Air Heater Performance 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 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
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• 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
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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
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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
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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
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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 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
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• 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
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• 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
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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
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
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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.
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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
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+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
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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 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%)