Efficient operation at part load – The need of hourSandeep Chittora, Power Generation Services, Siemens Limited
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Plant OptimizationFlexibility is the new efficiency
A Balance of Plant (BoP) Optimization makes a significant contribution to economic values
An improved efficiency leads to lower CO2
emissions!
Improved I&C and combustion for stable
operation at lower loads
Reduced startup-times and earlier power
productions by improved I&C and hardware
measures
Higher ramp rates up to 15MW/min
Reduced Electricity Production Cost and Increased Competitiveness *
3x higher
@ 75% load, including aging recovery effects by new hardware in HP and LP turbine at constant
coal consumption
Down to 30% 16 MW more Up to 5% lower >60min earlier
Improved Ramp Rates
Increasing Efficiency and
Performance (MW)
Reduced Costs for Starting and earlier Power Production
Reducing CO2Emissions
Reducing technical minimum plant
load
* Values are based on a 500 MW reference steam power plant
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Plant OptimizationTotal Plant Evaluation is key for successful operation in deep part load
Balance of Plant (BoP) Assessment for Boiler, Condenser, Steam Turbine & Auxiliaries
BoilerFuel SupplyInstrumentation & ControlsCombustion Concept & OperationThermal DesignFans and Pumps
Feed Water Heaters
Boiler Feed Pump (incl. Motor orturbine drive)
Turbine
Blading
Operation
Steam Seal
Drains
CondenserTerminal Temperature Difference (TTD)
Condensate Pump
Cooling Water System
Steam Piping System
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40% Technical Minimum is Possible – NTPC Dadri
0
50
100
150
200
250
300
350
400
450
500
550
3:00
3:30
4:00
4:30
5:00
5:30
6:00
6:30
7:00
7:30
8:00
8:30
9:00
9:30
10:0
010
:30
11:0
011
:30
12:0
012
:30
13:0
013
:30
14:0
014
:30
15:0
015
:30
16:0
016
:30
17:0
017
:30
18:0
018
:30
19:0
019
:30
UNIT LOAD
GCV (kcal/kg) VM% Ash %
3000 22% 35%
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Influence on Ramps on Temperature Transient
510
520
530
540
550
560
570
7:00
7:30
8:00
8:30
9:00
9:30
10:00
10:30
11:00
11:30
12:00
12:30
13:00
13:30
14:00
14:30
15:00
MS TEMP
500
510
520
530
540
550
560
570
7:00
7:30
8:00
8:30
9:00
9:30
10:00
10:30
11:00
11:30
12:00
12:30
13:00
13:30
14:00
14:30
15:00
HRH TEMP
DT = 1 K/min
DT = 1.5 K/min
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Lower technical minimum is better than two shift operation
Comparison of life consumption based on cold, warm and hot start
Start Life Consumption IEC 45 permissiveCold Start 23 – 75 hours 100Warm Start 15 -17 hours 700Hot Start 10 -12 hours 3000Load Change 3 hours -
140%155%
170%
100%120%140%160%180%
210 MW 500 MW 660 MW
Incremental O&M costs
Base Load Technical Minimum 2 shift
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Transient Operation (Ramp Up / Ramp Down)increased temperature gradient results increased life consumption
Crack depth: 50% wall thickness
Main steam valve
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Time for crack initiation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
100 1000 10000 100000
Tem
pera
ture
gra
dien
ts [K
]
Number of (thermal) cycles to crack initiation [cycles]
Pre-Damagee.g. due to starts Load changes with
DT=100 K
Load changes withDT=50 K
N (50K) >> N(100K)
Curve based on Manson-Coffin-Model(at 550°C)
Initiation of cracks
50
100
150
200
250
300
350
400
450
500 Operational Strategy
• Part load may lead to steam temperature changes, especially hot reheat temperature
• Thermal stresses due to temperature changes across thick wall components are detrimental to life consumption
• Careful analysis and suitable modification would lead to improved fatigue behavior and reduce maintenance requirements
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Power on DemandReduction of Wall Thickness to Improve Start Up & Cycling Capabilities
Example: Reduced Casing thickness & reduced thermal piston loading by HP bypass cooling
Significant improvement in LCF
coolingsteammixed steam main steam
0
20
40
60
80
100
Load
in %
Time
Design with internal bypass
cooling
Design without internal bypass
cooling
Interstage admission
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Performance at lower part load factor
210 MW modernization leads to 25 paisa savings in cost of generation with payback period of ~3 years
Zone of interest
660 MW supercritical unit
500 MW subcritical unit
500 MW modernized unit
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Part Load Efficiency: Turbine hardware upgradeHP Turbine
* Relative to aged condition (both in fixed pressure operation)
Load 50% 75% Full load
Savings (coal) * ≈ 1.3% ≈ 1.3% ≈ 1.5%
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Part Load Efficiency: Turbine hardware upgradeHP + LP Turbine
Load 50% 75% Full load
Savings (coal) * ≈ 2.7% ≈ 2.7% ≈ 2.9%
* Relative to aged condition (both in fixed pressure operation)
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Part Load Efficiency: Turbine hardware upgradeHP Turbine with control stage
Load 50% 75% Full load
Savings (coal) * ≈ 3.5% ≈ 2.9% ≈ 1.0%
* Relative to aged condition (both in fixed pressure operation)
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Part Load Efficiency: Turbine hardware upgrade with control stageHP + LP Turbine with control stage
Load 50% 75% Full load
Savings (coal) * ≈ 4.7% ≈ 4.1% ≈ 2.2%
Savings (coal) ** ≈ 2.7% ≈ 3.2% ≈ 1.3%
* Relative to aged condition (both in fixed pressure operation)** Relative to new and clean conditions
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Part Load Efficiency: Turbine hardware upgrade with control stageHP + LP Turbine with control stage
* Aging applied to HP/IP&LP-section** Aging applied to IP/LP-section*** Aging applied to IP-section
8300
8500
8700
8900
9100
9300
9500
40 60 80 100
Pla
nt
He
at R
ate
[kJ
/kW
h]
Plant Load [%]
Base - T2 - Fixed Pressure *
Base - T2 - Sliding Pressure *
HP-CS/3DS - Fixed pressure **
HP-CS/3DS_LP 3DS - Fixed Pr. ***
0
5
10
15
20
25
40 60 80 100
DP
to
Bas
e (
T2-F
ixe
d p
ress
ure
) ["g
ree
n"
MW
]
Plant Load [%]
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Return on investment with hardware upgradePotential Benefits
0 1 2 3 4 5 6 7 8 9years
HP-CS & LP
HP-CS only
typical I&C-measure
Initial IncrementalInvestment *
Investment Break Even Point *
* This example is based on a modernization of a 500MW-coal-fired power plant in India (KWU-design)
For the corresponding 500MW steam power plant the modernization of the Turbine
Hardware (new HP module with control stage / new LP rotor and inner casing) would
result in significant savings for coal.
Taking this into account, the return of invest period accounts to 4 - 5 years. Additional
benefits like the avoided CO2 and the enhanced ability for fast load changes are not
even considered here.
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Reduced Startup-times: Heating blanketsST Warm Standby Operation to prepare for fast start-up
Technology
• Electrical heating system for ST in turning gear
• Maintains rotor shaft temperature at warm startup conditions
Benefit
• Significant reduction of startup time
• > 60 min. earlier power production
• Reduction of EOH consumption per start
• Less energy is bypassed to condenser
• Reduced costs per start up
Electric heating coils to keep HP/ IP Turbine casing and shaft in warm start conditions
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Key Takeaway
• Lower Technical Minimum is better operation than two shift
operation
• Subcritical fleet is more suitable for flexible operation with respect
to loss in performance
• Lower Technical Minimum with part load performance
improvement is possible, unit specific changes needs to be applied
• Means of improving part load efficiency by upto 4% are available
• Need based R&M is the approach for part load performance
improvement
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Contact information
Sandeep ChittoraHead – Portfolio ConsultingSiemens Limited, IndiaPhone: +91 124 2842650Mobile: +91 9971170337
E-mail: [email protected]
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Power on DemandMonitoring of flexibility consequences: steam turbine EOH counter 4.0
Solution• Evaluation of operational history• Implementation of a state of the art EOH counter considering
load changes
Benefits• More accurate EOH counting• Improved outage planning• Enhanced operational flexibility
Task• Part load may lead to steam temperature changes,
especially hot reheat temperature• Thermal stresses during operation are not considered in
standard counting of equivalent operating hours (EOH counter)
• Maintenance needs may not be recognized
I. Generation
II. Generation
III. Generation
IV. Generation
Introduction of three start-up modes with fixed EOH consumption
Maintenance interval defined by operating hours and number of starts
EOH consumption is a function of actual thermal stress
EOH counting also considering load changes
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Maintenance FlexibilityFatigue Monitoring System
Don’t Guess when you can actually measure it
How much fatigue is it?
Old minimum sustainable load
NEW, minimum sustainable load
Load
Time
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Maintenance FlexibilityFatigue Monitoring System
Online calculation of Boiler Fatigue Components is possible
Both Creep Fatigue and Low cycle fatigue calculated
Depending upon the actual operating mode, residual life of critical components is determined