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

)

Stea

m T

empe

ratu

re (℃

)

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