Flexible Operation - Central Board Of Irrigation And...
Transcript of Flexible Operation - Central Board Of Irrigation And...
Flexible Operation
What kind of generation – load imbalances to compensate?Anticipated Indian Scenario in 2022 with 100 GW Solar & 60 GW Wind
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All India Demand (MW) June'22 Solar Wind Nuclear Others Coal
MW
15 Min Time block
289 GW Cap. Available-coal
146GWCoal Gen.
Ramp rates can be higher with sudden onset of
wind generation.Can change significantly
with seasonSolar with “must run” condition
46.3 GW
SOLAR
Flexibilization: The New Paradigm in Power Generation
• Defining from different perspectivesDefining
• Metrics• QuantifyingMeasuring
• Sources, options• Preparedness for Coal based plants
Operational-isation
• Regulatory framework• Market structure and mechanismsCompensation/Incent
ivisation
From the generator’s point of view, the metrics would be :Quantity (MW) which is required to
be kept in reservesTurndown
- Minimum boiler load:Cycling capability
( start-up to full load best achieved time taken) -Very hot start-up: <1h-Hot start-up: 1.5‒2.5 h-Warm start-up: 3-5 h-Cold start-up: 6-7 h
Ramp rate-30-50% load: %/min-50-90% load: %/min-90-100% load: %/min
We can assign a flexibility index for each unit based on the above parameters
IMPACT OF PART LOAD OPERATION
IMPACT OF PART LOAD OPERATION
STABILITY EFFICEINCY
Heat Rate
Aux. Power Consumption
Drum Level Stability
Flame Stability
At low load condition operator is often force to run following system/control loop is manual mode for stable operation. Few example are :-
Seal steam controller
Flame stability
Handling tube mill
SADC,
burner tilt
MS temperature,
Re-heater temperature
Oxygen trimming
Air flow of top most mill
Stalling of axial fan (ID/FD/PA)
Maintain chemistry parameter ( condensate DO, silica, etc)
Operational Challenges during part load cyclic operation
Effect of Part load cyclic operation onequipment
Thermal Fatigue : Fluctuation in temperature in cyclic manner
Thermal Expansion : With the large variation of load as per requirement of the grid the wear tear of equipments also increases which ultimately affect the reliability of the unit
Corrosion-Related issue :Cyclic operation challenges the ability of a plant tomaintain water chemistry, which lead to increased corrosion and accelerated component failure
Rotor Bore Cracking : When subjected to transients in the temperature of the admitted steam, the high-pressure and intermediate-pressure steam turbine rotors can suffer thermo-mechanical stress excursions, resulting in low-cycle fatigue damage
Impact on Reliability
Equipment Impact
Boiler
1. Thermal fatigue cracking in thick walled sections & valves 2. Increased BTL due to differential expansion 3.Thermal fatigue cracking in SH & RH ligaments 4. Corrosion & fatigue can combine to accelerate damage to WW Increased BTL
Deaerator 1. Stress corrosion cracking in weldments
Piping 1.Creep fatigue in MS & RH piping 2.Flow accelerated corrosion in steam piping
HPT & IPT1. Thermal fatigue cracking in thick section rotors casing valve bodies2. Erosion of valve components
LPT 1.Moisture erosion of blading
Generator1. Wear of copper insulation due differential expansion 2. Loosening of stator winding
Feedwater heaters 1.Thermal fatigue of thick sections of tube plates & end cover
Effect on Boiler Efficiency
BOILER EFFICIENCY VS LOAD
84.684.784.884.9
8585.185.285.385.4
60 80 100
% LOAD-TMCR
% B
OIL
ER E
FFIC
IENC
Y
From the tested data it is observed that for a 210 MW unit, boiler efficiency decreases by around 0.4 % with the reduction of 60 MW load
Effect on GTCHR
1940 1960 1980 2000 2020 2040 2060 2080 2100 2120
105 126 147 168 189 210
GTCHR (KCAL/KWHR)
LOAD (MW)
From the test data of Unchahar U#5 it was observed that with the reduction of 60 MW load, GTCHR decreases by 54 Kcal /Kwh.
GTCHR Vs Load
Effect on Auxiliary Power Consumption
SL NO EQUIPMENTPOWER CONSUMPTION IN KW
AT 220 MW AT 155 MW
1 ID FAN 1054.409 686.8071
2 FD FAN 170.9277 116.4406
3 PA FAN 1155.431 1111.326
4 BFP 2911.35 2295.582
THE CHANGE IN AUXILIARY POWER CONSUMPTION WITH DECREASE IN LOAD (100% to 75%) = 1.2%
Financial Implication of Low schedule
Schedule (%) Loading factor (%) Heat rate (Kcal/KWh) APC (%)
93.31 97.26 2405 8.32
79.66 79.11 2459 9.23
Revenue Loss : 13.65 % reduction in schedule result in revenue loss of 242.75 Cr
Loss in marginal contribution :Marginal contribution of station reduced by 97.24 % .
Station profit has reduced by 14.76% due to loss in marginal contribution
Effect on Performance Parameter
Unit heat rate is defined as ratio of GTCHR to Boiler Efficiency
.GTCHR
Unit Heat rate = ------------------------------------X 100BOILER EFFICIENCY
Description Unit At 160 MW At 220 MW Difference
Boiler efficiency
% 85.27 85.65 0.38
GTCHR Kcal/Kwh 2049 1995 54
Unit Heat Rate Kcal/Kwh 2403 2329 73
Operational Practices Improvement
Optimization of processes and parameter for better efficiency APC & stabilityof unit at cyclic part load operation to use total available margin in the equipments
Single BFP operation: At full load two BFP kept in service but at part load one BFP stopped, result is saving of 1100 KW.
Single mill operation with tube mill: Two Mill kept in service but at part load single mill operation is being done; result is saving of 1250 KW.
Mill optimization with bowl mills: With bowl mill 04 mill are in service at full load, at part load 03 mill in Stg-I & 02 mill in Stg-III are kept in service, result in power saving of 250 KW.
Oxygen optimization: Oxygen was being maintained around 4.5-5 % during part load, now oxygen is maintained at 3.5-4% at part load, result in saving of 200 KW in draft power & 10 Kcal in Heat rate.
Selective LRSB operation with cost benefit analysis to maintain Super heat & Reheat temperature.
Installation of VFD : VFD installed to reduce throttling losses.
Burner tilt modulation
Control loop tuning for low load operation
R&M of control system for better control
Additional sensor/probe for close process monitoring
Fuel supply control logic upgrade
Operational Practices Improvement Cont..
Integration of updated technology for rigorous process monitoring to analyze the actual real time condition of system. Few systems are:
Turbine Stress Controller (TSC)
Boiler Stress Monitoring System (BOSMON)
Blade Vibration Monitoring System (BVMS)
Stator End Winding Vibration Monitoring
Rotor Flux Monitoring
Partial Discharge Monitoring
Additional sensors for health monitoring
Reliability Improvement
Opportunities are being fully utilized for carrying out maintenance jobs. Currently weare doing following jobs during overhaul of the units which supports the stability & performance of unit at cyclic operation:-Complete replacement of coal burner assembly
Time based replacement of expansion bellow of heaters
Thickness measurements & maintenance of high energy drain lines
Boiler tube replacement on the basis of Boiler Thickness survey
Regenerative heaters parting plate inspection & its replacement.
Inspection of last stage blades of LP turbine.
Turbine bearing inspection
Although above activity is being carried out in every overhauling, but they also support us in mitiga
ting the effects of cyclic operation.
Maintenance Strategies
We have to bring about a paradigm shift in OH/maintenancestrategy from time based to condition based. It should be based on wear & tear, vibration,
temperature & performance.
Design Modifications/ System Updation (Contn..)
More efficient equipment in a wide range of operation is to incorporated during R&M and replacement of equipment. Following Modification and Retrofit can be done in existing system for cost effective load cycling:--
Improved Instrumentation & automation
Increased Drainage
Sliding pressure control
Economizer re-circulation
Improved oil burner reliability ,stability and turndown
Advanced flame scanners
New, more reliable pulverizes
Additional oil burners at upper levels
• Improvement of Burning CharacteristicsVertical Pulverizer
• Improvement of Steam Temperature ControllabilityThree-stage of SH SprayRH Inlet Spray, or Intermediate SprayRH Bypass Steam Spray
• Appropriate Capacity of AccessoriesPulverizer, Fan, Pump, Valve, etc.
• Advancement of Control EquipmentControl deviation of steam temperature within ± 8 ° CEliminate sudden change of environmental value (NOx )
Loading rate Improvement
Load change rate ( High Load Range )1 ~ 2 %/min. ⇒ 3 ~ 5 %/min.
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負荷変化特性
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MWD(M
W) 燃料・給水流
量(t/h)
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蒸気温度(℃)
MWD
主給水流量
燃料流量
主蒸気温度
再熱蒸気温度
Load change characteristics 1
Reheat Steam Temp.
Main Steam Temp.
Feed Water Flow Rate
Generator Output command
Fuel flow rateOut
put (
MW
), Fl
ow R
ate
(t / h
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m T
empe
ratu
re (℃
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100% L ⇔ 50% L : 3%/min.
Source: JPOWER, IHI19
Loading rate Improvement
Load
Flow
Rat
e, A
ir/C
oal R
atio
Air Flow
Fuel Flow
Air/Coal Ratio
Stable Combustion
Unstable Combustion
Without Oil SupportWith Oil Support
Min. Vel.
At low load of the mill,pulverized coal at the outlet of the mill is in a lean condition with high Air/Coal Ratio of primary air, and oil support is required.
The minimum load of coal-firing without oil support limited to 30 ~40% load.
Optimization of minimum load
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In order to reduce the minimum load of coal firing (without oil support), it is necessary to increase the pulverized coal concentration of primary air in the burner.
By adding a primary air concentration function to the burner (Wide range burner), stable combustion becomes possible, making it possible to reduce the minimum load of coal firing (without oil support) to 15 ~ 25% load.
A/C Ratio at Burner(Concentrated)
Expanded
Optimization of minimum load
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In order to shorten the startup time, it is important to raise the turbine inlet steam temperature quickly.To that end, installing the following startup bypass system• SH Bypass System• HP / LP Turbine Bypass System (RH
Cooling)or Turbine Bypass System
Start-up time reduction
Startup Time of Hot Start ( DSS )120 ~ 180 min. ( Ignittion ~ 100%L ) 22