Turbine Performance Assesment_bhel

•Assessment of true performance •Establishing Performance Bench Mark of the Unit •Computation of performance deterioration due to Ageing •Deterioration apportioning analysis •Cost effectiveness of suggested modification •Performance Optimized Operation of the set

Focus on 1. Reliability of available data 2. Consistency of operating parameters 3. Weeding out incorrect/ doubtful data 4. Stable and predictable TG Cycle 5. Accounting of leakages & passing 6. Adjustment in the performance for variation in terminal parameters & cycle configuration

Cylinder Internal Efficiency First Stage Pressure Vs Flow characteristic System Leakage Heatrate Auxiliary Power Consumption

Original HBDs are valid for brand new condition Cycle data in HBD’s are predicted based on design, though actual data may be different in some cases. Unit Specific conditions to be incorporated Actual Cycle conditions may differ from the design condition, like •Main steam Pressure/ Temperature •Reheat steam Temperature •Reheat Circuit Pressure Drop •Reheat/ Superheater spray •Cooling water inlet temperature/Condenser Vacuum •Regenerative Feedheater(s) out of service

How to workout predicted performance? •Tests to be preferably performed at full load or VWO condition. •Data can be obtained from plant instrumentation, with suitable corrections. •Performance data obtained from tests, to be corrected for actual cycle conditions. •Data to be compared with corrected HBD/ Last available test report. •Allowance to be made for performance deterioration due to ageing •Realistic assessment of unit performance can be done.

Calculation of performance deterioration due to ageing as per International standards AGEING OF STEAM TURBINES

1.6 1.4

PERCENTAGEPOINTS

1.2 1 0.8 0.6 0.4 0.2 0 0

5

10

15

20

-0.2 M ONTHS DIN

ASME

BS

25

Above Curves are prepared by ASME/DIN/BS based on feedback of large no of sample machines. Depends upon

• Grid healthiness • Operating Condition • Unit Size • Water/Fuel chemistry

Similar exercise needs to be carried out by Indian Utilities Actual feedback on ageing with the influence of

• Rapid Grid Fluctuations • Fluctuations in the terminal Parameters • Condenser Tube fouling • Higher leakages/ Passing

Compilation of performance data of similar machines will form back-bone to Bench Marking This data can be used to calculate actual Ageing of machine Leading to true assessment of performance. *********************************************

PRESENT POWER SECTOR SCENARIO MAJOR IMPETUS ON

•

EFFICIENCY

• RELIABILITY • AVAILABILITY • POLLUTION NORMS • COST

RESULTING IN ENHANCED EMPHASIS ON REDUCTION IN GENERATION COST BY HAVING LOWER EQUIPMENT COST HIGH EFFICIENCY OF TG CYCLE FUEL COST REDUCED O & M COSTS REDUCED FORCED OUTAGES

RESULTING IN ENHANCED EMPHASIS ON => INCREASED AVAILABILITY SHORTER GESTATION PERIOD REDUCED DOWNTIME UNIT CAPABILITY TO OPERATE AS BASE LOAD MACHINE FOR MAXIMUM TIME REDUCED PLANNED SHUTDOWN TIME ENHANCED SPAN BETWEEN TWO OVERHAUL

RESULTING IN ENHANCED EMPHASIS ON

RELIABILITY (CAPABILITY TO FULFILL) GRID REQUIREMENTS GRID FLUCTUATIONS SUDDEN LOAD THROW OFF HOUSE LOAD OPERATION COLD,WARM & HOT START

RESULTING IN ENHANCED EMPHASIS ON =>MINIMIZING ENVIRONMENTAL HAZARDS BETTER HEATRATE LEADS TO Reduced Green House Effects Lower Coal requirement Lower emissions of NOx, SO2, CO Reduction in quantity of ash disposal Less Air Pollution during coal transportation Reduction in Heat release to CW *****************************************************

IMPROVEMENT IN TG PERFORMANCE POSSIBLE THROUGH

• INCREASE IN TURBINE CYLINDER INTERNAL EFFICIENCY

• ENHANCING TERMINAL PARAMETERS • OPTIMISATION OF REGENERATIVE FEEDHEATING CYCLE

• IMPROVED O & M PRACTICES

O & M ISSUES INFLUENCING PERFORMANCE

1. Variation in terminal parameters from the design cycle 2. Deviation/ Malfunctioning of equipment 3. Passing of valves & system Leakages 4. Load fluctuations 5. Frequency variation 6. Higher Auxiliary Power Consumption

O & M ISSUES – Variation in terminal parameters Major factor affecting the performanceMain Steam Pressure Main Steam Temperature Hot Reheat Temperature Cooling Water Inlet Temperature Condenser Back Pressure Final Feed Water Temperature Reheater spray

O & M ISSUES –

Variation in terminal parameters

TG Set performance will be optimum while operating the set at rated design condition. Any variation in the terminal parameters mentioned earlier may not result in better than optimum performance

O & M ISSUES-

Deviation from the design TG Cycle

Condition of Source of extraction for Deaerator/BFPT Alternate drain lines of HP/LP Heaters Passing of HP Bypass valves HP Heater FW Bypass valves Superheater /Reheater spray Vent lines of Deaerator/ HP/LP heaters Recirculation lines of CEP/BFP Air ingress in condenser

O & M ISSUES –

Malfunctioning of equipments

Major factors affecting the performance 1. Steam Turbine Worn-out Glands of HP/IP & LP Front & Rear shaft sealing Worn-out inter-stage sealing Higher balance piston leakage Variation in seal steam header set pressure

O & M ISSUES – Malfunctioning of equipments Major factors affecting the performance 1. Steam Turbine Steam leakage through parting plane, bellows, hoses Leakage through MAL Valves Poor cylinder internal efficiency Variation in First stage pressure characteristic

O & M ISSUES – Malfunctioning of equipments Major factors affecting the performance 2. Regenerative Feed Heating Cycle Level variation in heaters Improper cascading of drains HP/LP Bypass in operation Higher system leakage & Makeup Superheater & Reheater spray Poor efficiency of CEP/ BFP/ BFPT

O & M ISSUES – Malfunctioning of equipments Major factors affecting the performance 2. Regenerative Feed Heating Cycle • Higher air ingress leads to poorer vacuum • Cleanliness of condenser • HP/LP Heaters out of service • Poor TTD/DCA of heaters • Higher intake of steam for BFP drive Turbine

O & M ISSUESSystem Leakage Higher system leakage implies enhanced DM water requirement. It is generally 0.4 - 1.0 % of the MS Flow. As per international norms within 0.1 %. Leakage deteriorates the Unit performance. More in the High pressure region of BFP/HP Heaters & Boiler having high heat content.

O & M ISSUES-

Passing through valves

Internal leakage Affects the performance more Difficult to identify & quantify Being internal – gets low attention Damages the valve seat & other components Faster growth of damage if not arrested.

RECOMMENDED DIAGNOSTICS A. Turbine Cylinder Internal Efficiency • Most vital check • Any abnormality in the Steam Turbine will effect efficiency. • Can be done through plant instrumentation •

Should be carried out at regular interval

•

Ensure correctness of the data

RECOMMENDED DIAGNOSTICS

S1= f(P1,T1)

A. Turbine Cylinder Internal Efficiency

H2adia =f(P2,S1)

H1 =f(P1,T1)

H2 =f(P2,T2)

Efficiency (%) = (H1-H2) * 100/(H1-H2adia)

Cylinder Efficiency – Various Possibilities A. Gradual Deterioration Normal Ageing Process Wear & Tear of Sealing Fins Deterioration in steam flowpath Deposition in the steam flow path Erosion in the valve seat Erosion in the last stages

Cylinder Efficiency – Various Possibilities B. Abrupt deterioration in Efficiency Probable causes may be Blade failure Sealing fins Interstage sealing Internal mixing of steam at different temp. Foreign material in the steam path Water Ingress in the turbine

RECOMMENDED DIAGNOSTICS A. First Stage Pressure Characteristic • Most vital check

• Any abnormality in the Steam Turbine will effect Characteristic. Procedure •Main Steam Flow is derived by theoretical curve •Validate the characteristic by actual measured one Undertake measurement at regular intervals •Compare the characteristic with earlier data

RECOMMENDED DIAGNOSTICS B. First Stage Pressure -Flow Characteristic Procedure(contd)

• Analyse if variation is gradual or Abrupt

• If variation is gradual, whether synchronous with change in cylinder efficiency • Gradual variation can be permissible. •

If variation is abrupt, it is a serious issue

•

Analyse the possible reasons

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ACHIEVING OPTIMUM PERFORMANCE DURING OPERATION Throttle Control reaction turbine has best performance at higher load. It will always be advantageous to operate the set at higher load/ full load. During part load operation, running the set at pure sliding pressure operation mode will result in best performance .

ACHIEVING OPTIMUM PERFORMANCE DURING OPERATION But it will not have any margin for spinning reserve. Quick load increase under such condition not possible To overcome this shortcoming in case load fluctuations are expected, at part load, operate the set with modified sliding pressure with around 10% throttling.

CONCLUDING REMARKS 1. Operate the set near to the rated parameters 2. TG Cycle close to design 3. For Throttle Control Machine run as base load 4. Minimum system leakage 5. Reduced steam/ water passing 6. Minimum SH/RH Spray 7. Regular monitoring of Cylinder Internal Efficiency 8. Regular monitoring of First Stage Pressure

STEAM TURBINE ENGINEERING

BHEL, HARDWAR