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Details of aSteam Path Audit
Paul RoedigerEncotech, Inc.
Overview of Presentation:
Audit OverviewBenefitsChronologyMeasurementsCalculationsResults / ReportConclusion
Audit Overview :
Inspection of the steam path(Comparison to new & clean conditions)
Results: clear priority for maintenance decisions
Benefit: maintenance dollars used with the highest return
Verification of maintenance
Overview:
What: Inspection of the steam path (determined by VWO heat balance conditions)
When: Immediately after steam path is exposed and again after maintenance has been performed
BenefitsOPENING AUDITIdentification of degradationCost-effective maintenance actions
CLOSING AUDITQuality check on maintenance performed during the outagePerformance improvement resulting from individual maintenance actionsExpected return-to-service performance
Required ResourcesComputerLoss Calculation SoftwareOne or Two AuditorsMeasurement Tools
Radial Packing Gauge6” Digital CaliperTape measureBall GaugesSurface Roughness Comparator
Maintenance Action Itemsfor B/C > 3.5
Heat Rate Heat Rate Benefit Benefit Repair cost Action Item (Btu/kWh) ($1,000) ($1,000) Benefit/Cost ______________________________________________________________________________ Sharpen HP stg 6 interstage packing 3.1 9.3 0.3 31.0 Sharpen HP stg 4 interstage packing 2.8 8.4 0.3 28.0 Sharpen HP stg 5 interstage packing 2.6 7.8 0.3 25.0 Sharpen HP stg 2 interstage packing 2.5 7.5 0.3 25.0 Sharpen HP stg 3-6 interstage packing 7.0 21.0 1.2 17.5 Replace IP stg 1 tip spill strip 13.0 39.0 4.0 9.8 Polish HP nozzles 13.0 39.0 4.0 9.8 Replace IP stg 2 tip spill strips 9.0 27.0 4.0 6.8 Polish IP nozzles, exhaust side 8.0 24.0 4.0 6.0 Second reheat stage minor repairs 10.0 30.0 8.0 3.8 Replace top half snout rings 23.0 69.0 19.0 3.6 ______________________________________________________________________________
Maintenance Action Itemsfor B/C < 3.5
Sharpen stg 1 tip spill strip 0.3 0.9 0.3 3.0 Replace IP stg 3-6 tip spill strips 12.0 36.0 16.0 2.3 Sharpen stg 2 tip spill strip 0.2 0.6 0.3 2.0 Replace stg 2 interstage packing 4.0 12.0 7.5 1.6 Replace stg 6 interstage packing 3.5 10.5 7.5 1.4 Polish LP Nozzles, exhaust side 3.0 9.0 7.0 1.3 Replace stg 4 interstage packing 3.0 9.0 7.5 1.2 Replace stg 5 interstage packing 3.0 9.0 7.5 1.2 Second reheat stage major repairs 15.0 45.0 55.0 0.8 Replace bottom half snout rings 2.0 6.0 19.0 0.3 ______________________________________________________________________________ Total repair cost for B/C >3.5 45.4 Total repair cost for B/C < 3.5 127.6
Chronology
Model
On Site
Analysis / Report
Model
Create model using the Thermal Kit
Design heat balance (VWO)Turbine cross sectionClearance and steam seal diagramFirst stage shell pressure curve
SPA On-Site Time-Line
TURBINE O UTAG E
S h u t d ow n S t a rt u p
Pre-Outage Test Opening SteamPath A udit
Closing SteamPath A udit
Upgrade andMaintenanc e
Pos t-OutageTes t
Disassembly Reassembly
Measurements
GeometryClearancesSurface roughnessDamage
Solid Particle ErosionThroat OpeningsSteam Path Length
Clearance Measurements
What Tooth Throttles Steam?
Slant Tooth Packing
Honeycomb Packing
Mechanical Damage
Solid Particle Erosion
Throat Opening Measurements
Ball Gauge Measurement
Surface Roughness Measurement
Miscellaneous Leakage Measurements
Cover Deposits
Nozzle Repair
On Site - Day 1
After Top is Lifted
Inspect horizontal jointMeasure Stationary Blade GeometryMeasure top half tooth heightsMeasure packing clearancesInspect shell sealing surfaces
On Site - Day 2Rotor Removed
Measure solid particle erosion damageMeasure deposit thicknessMeasure stationary and rotating blading surface roughnessInspect for mechanical damage
On Site - Day 3
Measure bottom half tooth heightsMeasure trailing edge thicknessMeasure turbine geometryInspect snout rings
Analysis / Preliminary Report
Input data & analysisPrint Steam Path Audit reportsGive preliminary presentation on
site
Calculations
Martin’s Formula
General Flow Equation
Dollar Value of Heat Rate
Annual Fuel Cost Savings
Cost of Lost Capacity
Martin’s Formula Calculation
General Flow Equation
k
k
k
p
p
p
p
k
k
v
pKCAW
1
1
2
2
1
2
1
1 11
*5.2406
W = Flow (lb/h)K = Packing type constantC = Rubbed coefficientA = Area (sq in.)P1 = Upstream Pressure (psia)v1 = Upstream specific volume (ft 3/lb) P2 = Downstream Pressure (psia)k = Isentropic exponent (1.3 typical)2406.5 = Unit conversion constant
Common Tooth Types
coefficient:2 TEETH: 0.403 TEETH: 0.334 TEETH: 0.295 TEETH: 0.26
SINGLE – AXIALFlow Equation
coefficient: 0.57
ROTATINGBLADE
STATIONARYBLADE
SINGLE – RADIALFlow Equation
coefficient: 0.57
DOUBLE STRAIGHTFlow Equation
coefficient: 0.70
TWO SINGLEFlow Equation
coefficient: 0.46
DOUBLE & SINGLEFlow Equation
coefficient: 0.52
STEPFlow Equation
TIP SPILL STRIP CLEARANCE
Ken Cotton Chart – Reference Table [449]
kW loss per mil excess clearance per stage:7+ ((591.9 – 500) / (500 – 100)) x (7.0 -2.5) = 8.03 kW/mil
][ )t(C)tC(GAP L+L+R+R2
1=ave
C GAPave =1
8ave
ti
i 1
8
1-34
Dollar Value of Heat Rate Degradation(Based on G.T.H.R.)
610*
8760***
BE
CFGRFCHRDV
FC = Cost of fuel $/million BTU’sGR = Rating of turbine in KWCF = Turbine capacity factor in %8760 = Hours in a YearBE = Boiler Efficiency
000,000,1*82
8760*75*000,500*00.2HRDV
= $8,012.20 / year
1-35
Annual Fuel Savings - $ Year
000,000,000,10
*8760**** SHRHRFCFRAFS
R - Rating of turbine in KWCF - Turbine capacity factor in %F - Cost of fuel $/million BTU’sHR - Change in heat rate in %SHR - Station heat rate BTU’s/KW HR
Example:
000,000,000,10
9900*8760*0.1*00.2*75*000,500AFS
= $650,430/year
1-36
Cost of Lost Capacity
710
8760*D*R*M*KL
Where: L = lost revenue $/yearK = percentage of year at max. capacity (%)M = average wholesale price of power ($/(MWh))R = unit capacity (kW)D = degradation in performance (%)
For:K = 50%M = 45 $/(MWh)R = 600,000 kWD = 1%
L = 1,182,600 $/year
ResultsOPENING AUDITQuantification of losses measured in pre-outage testListed cost-effective maintenance actions
CLOSING AUDITQuality check on maintenance performed during the outagePerformance improvement resulting from individual maintenance actionsExpected return-to-service performance
Opening Audit LossHeat Rate Loss by Category
Opening Audit LossHeat Rate Loss by Casing
Opening Audit: Summary Change In Power Loss G.T.H.R. Audit Category kW Btu/kWh Interstage Packings 502.8 19.91 Tip Spill Strips 2333.2 81.87 Shaft End Packings 1166.2 34.44 Steam Seal System Loss 0.0 0.00 Miscellaneous Leakages 33.5 1.76 Flow Path Damages 149.8 4.36 Flow Change Impact 0.0 0.00 Surface Roughness 947.3 40.28 Trailing Edge Thickness 0.0 0.00 Cover Deposits 10.2 0.53 Hand Calculations 0.0 0.00 Turbine Total 5142.9 187.71
HP Casing - Loss Summary Change In Power Loss G.T.H.R. Audit Category kW Btu/kWh Interstage Packings 279.7 8.14 Tip Spill Strips 1787.1 52.55 Shaft End Packings 1096.4 30.73 Miscellaneous Leakages 0.0 0.00 Flow Path Damages 27.0 0.78 Surface Roughness 414.0 12.06 Trailing Edge Thickness 0.0 0.00 Cover Deposits 0.0 0.00 Hand Calculations 0.0 0.00 Total 3604.2 105.92 True Casing Efficiency Change 6.25 % True Casing Efficiency 82.84 % Apparent Casing Efficiency 82.84 %
HP Casing – Tip Spill StripsOpening Audit
Measured Design Eff Power Change In Clearance Wear Loss Loss G.T.H.R. in. in. in. % kW Btu/kWh Stage 1 0.081 0.060 0.021 1.69 84.9 2.47 Stage 2 0.063 0.040 0.023 2.91 127.3 3.70 Stage 3 0.063 0.040 0.023 3.15 143.3 4.17 Stage 4 0.136 0.040 0.096 10.68 505.5 14.74 Stage 5 0.110 0.040 0.070 7.20 352.4 10.26 Stage 6 0.106 0.040 0.066 5.02 258.7 7.53 Stage 7 0.082 0.040 0.042 2.94 159.2 4.63 Stage 8 0.077 0.040 0.037 2.73 155.7 4.53 Total 1787.1 52.55
HP Casing – Tip Spill StripsClosing Audit
Measured Design Eff Power Change In Clearance Wear Loss Loss G.T.H.R. in. in. in. % kW Btu/kWh Stage 1 0.070 0.060 0.010 2.07 104.5 3.04 Stage 2 0.031 0.040 -0.009 -0.97 -42.6 -1.24 Stage 3 0.034 0.040 -0.006 -1.51 -68.6 -1.99 Stage 4 0.029 0.040 -0.011 -1.87 -88.3 -2.57 Stage 5 0.033 0.040 -0.007 -1.37 -65.7 -1.91 Stage 6 0.042 0.040 0.002 0.13 6.8 0.20 Stage 7 0.039 0.040 -0.001 -0.06 -3.3 -0.10 Stage 8 0.087 0.040 0.047 3.90 222.3 6.47 Total 65.1 1.89
Tip Spill Strips - Opening Audit
Tip Spill Strips - Opening Audit
Tip Spill Strips - Closing Audit
Tip Spill Strips - Opening Audit
HP - Repair or Replacement Cost
Interstage Tip Spill Diaphragms / Total Packing Strips Buckets Cost
Stage 1 $3,000.00 $38,648.00 $41,648.00 Stage 2 $14,230.00 $2,915.00 $23,901.00 $41,046.00 Stage 3 $7,115.00 $2,915.00 $22,973.00 $33,003.00 Stage 4 $7,115.00 $3,115.00 $16,110.00 $26,340.00 Stage 5 $7,115.00 $2,415.00 $17,725.00 $27,255.00 Stage 6 $7,115.00 $2,815.00 $14,967.00 $24,897.00 Stage 7 $7,115.00 $1,715.00 $28,462.00 $37,292.00 Total $49,805.00 $18,890.00 $162,786.00 $231,481.00
Economic AssumptionsAssumption
Rating 320,000 kW Cap. =1 Exp. = 0 1
Capacity Factor 30 %
Fuel Cost 3.5 $/ 10 6 Btu
Fuel Cost Escalation 6 %
Discount Rate 12 %
Economic Life 4 Years
Capital Escalation Rate 5 %
Year of Expenditure 1 Year
P.V. Carrying charge 1.34
(from financial Analysis/treasurer)
ConclusionUsually not everything is worth replacing
or repairing The Opening Audit will identify
degradation and B/C ratioThe Closing Audit will quantify the
expected recovery
The audit results should be reconciled with the enthalpy drop tests.
ConclusionIt is a fair question to ask if the
degradation would have been identified and repaired without the use of an audit.
Some would. Some may not. And some repairs may take place that were not really necessary.
1-888-Encotech
((518) 374-0924)
Questions?