Quantifying Cycle Isolation Losses and Integration with On Line Systems Feedwater System Reliability...
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Transcript of Quantifying Cycle Isolation Losses and Integration with On Line Systems Feedwater System Reliability...
Quantifying Cycle Isolation Losses and Integration with On Line Systems
Feedwater System Feedwater System Reliability Users GroupReliability Users Group
2015 Meeting2015 Meeting
San Antonio San Antonio
Ken PorterKen Porter
Rich DugganRich Duggan
Frank ToddFrank Todd
Condenser
Leakage Flow
LeakingValve
High Pressure High Temperature
Agenda Introduction - Why Bother? Approach Calculation Program Process Application of Program Output to Plant Computer Example of Results Case Study
Introduction – Why Bother? Generating plants often suffer
from power losses due to leakages through valves that are faulty and/or do not seat correctly.
Often these losses are significant but have been difficult to quantify.
Many of the existing methods over predict the flow or can only generally predict (high medium or low flow)
High Pressure/High Temperature
Leaking Valve
Condenser
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Value of Leaking Valves
How Much is 1 MW of electricity worth? Revenue
If the plant can’t make it, they can’t sell it (Combined Cycle, Nuclear, Fossil plants operation at their boiler thermal limits)
Hrs/Year * Capacity Factor * Replacement Cost = Cost per Year 8760 MWh/Yr * 0.92 * $50/MWh = $402,960 (not small change)
Value of Leaking Valves
Data Source: Data Source: US Energy Information AdministrationUS Energy Information Administration
http://www.eia.gov/
$-
$50,000
$100,000
$150,000
$200,000
$250,000
$300,000
$350,000
$400,000
1 2 3 4 5 6 7 8 9 10 11 12
Months with leak in place
Total Additional Fuel Cost Lost Revenue
1 MW lost1 MW lost
Value of Leaking Valves
Typically plants have between 2-6 MW of lost generation from leaking valves
For a plant that can not make up this loss, this represents $800,000 - $2,400,000 annual lost revenue.
For a plant that can make it up, it represents additional fuel costs of $500,000-$1,500,000
The longer the leak the more extensive the damage It is often difficult to figure out which valves to fix
HP TURBINE
LP TURBINE
MSR
FEEDWATER HEATERS
GENERATOR
COOLING TOWER
CONDENSER
REACTOR COOLANT
PUMP
FEED PUMP
CIRCPUMPBLOW-
DOWN
MAINSTEAM
FEED WATER
COOLING WATER SYSTEMTURBINE CYCLE
NUCLEAR STEAM SUPPLY SYSTEM
STEAM GENERATOR
REACTOR VESSEL
CORE
Qr
Prioritization-Value of Leaking Valves
Source: Source: Evaluating Steam Turbine PerformanceEvaluating Steam Turbine Performance by K.C. Cotton by K.C. Cotton
Data from Ken Cotton Book page 303
A Solution Estimating losses from
these leaking valves can be done with advanced leakage calculations expect accuracy +/- 10%
to +/- 30% depending on conditions.
Every valve is different and needs to be modeled individually
High Pressure/High Temperature
Leaking Valve
Condenser
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Approach
Develop model for each valve Calculate flow rates and heat rate effect using TP-Plus
CIM software Develop equations for leakage and heat rate effects based
on software results.
Implement equations using OSIsoft® PI or other on-line software
Calculation Program Process
Uses temperature downstream of valve to determine pressure. Actual method is based on steam conditions (saturated vs
superheated) Calculates flow based on a series of equations
Grashofs ASME Figure 14 Darcy-Weisbach equation Sonic Flow Equation Choke Flow Equation
(Plant Engineering: Heat Cycle Isolation Valve Leakage Identification and Quantification [1025264 ])
Calculation Program Process Correct for equivalent length (including elbows and other
restrictions)
Account for problematic areas
Valve too close to sink
Valve discharges into a header
Valve has other heat sources downstream Bypass around air, hydraulic motor operated valve
Steam trap bypass
Other valves discharge into downstream of valve
Bound maximum flow based on valve/pipe size
High Pressure/High Temperature
Leaking Valve
Condenser
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TL
P
Difficult Areas to MonitorDifficult Areas to Monitor
Difficult Areas to MonitorDifficult Areas to Monitor
Calculation Program Process Model leakages in thermodynamic modeling software to calculate
Loss Factor (LF) Loss Factor will account for the overall effect of the leakage flow on the
cycle. Convert leak rate to Heat Rate or effect on Electrical Output
Calculate generation lost due to leak:
LFhh
QMW condenserupstreamloss
3412140
The Heat rate effect can be determined by converting the lost generation (LG) to heat rate using the Nominal heat rate and the nominal gross generation.
kwhbtuMWGen
HRHRE loss /
MW / BTU Constant
Plant Computer Process Establish temperature limit based on evaluation of
temperature measurement location. Using TP Plus CIM model the valve leakages across the
range of expected temperatures Condenser saturation temperature through upstream temperature
Develop polynomial equation from temperature to leakage relationship (Q)
Program polynomial in monitoring center or data historian If Td > Tlimit, then Q = A Td
3 + B Td2 + C Td + D
If Q > Qmax, then set Q = Qmax
Plant Computer Process Develop polynomial equation from leakage to heat rate
relationship Or using equations calculate the heat rate effect based on
polynomial results for leakage (more accurate for off load conditions and changes in condenser pressure)
Program polynomial for heat rate or program equations for calculating the effect from the determined leakage
Program special cases, e.g., in the case of two valves discharging to the same pipe - where the calculation is initiated based on a temperature near the valve but is based on a temperature further down stream.
Calculated Main Steam Valve Leakage
0
5000
10000
15000
20000
25000
30000
100 200 300 400 500 600 700 800 900
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r) Method 1
Method 2
Method 3
Method 4
Method 5
y
ExamplesParameter Value Unit
Pipe ID 1.5 in
Limit Temp 200 deg F
Upstream Pressure 2415 psia
Upstream Temp 1000 deg F
Condenser Pressure 3.5 in Hg
Upstream Enthalpy (calculated) 1460.4 btu/lbm
Main Steam Valve
ExamplesPolynomial for Main Steam Valve Leakage
y = 0.00024x3 - 0.26283x2 + 115.02241x - 14947.39271
R2 = 0.99725
0
5000
10000
15000
20000
25000
30000
100 200 300 400 500 600 700 800 900
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r)
y
Calculated HP Exhaust Valve Leakage
0
1000
2000
3000
4000
5000
6000
100 200 300 400 500 600 700
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r) Method 1
Method 2
Method 3
Method 4
Method 5
y
ExamplesParameter Value Unit
Pipe ID 1.5 in
Limit Temp 205 deg F
Upstream Pressure 440 Psia
Upstream Temp 647 deg F
Condenser Pressure 3.5 in Hg
Upstream Enthalpy (calculated) 1331.5 btu/lbm
HP Exhaust Valve
Polynomial for HP Exhaust Valve Leakage
y = 0.00006x3 - 0.05040x2 + 26.17907x - 3728.01050
R2 = 0.99992
0
1000
2000
3000
4000
5000
6000
100 150 200 250 300 350 400 450 500 550
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r)
y
Examples
Calculated IP Exhaust Valve Leakage
0
100
200
300
400
500
600
700
800
100 150 200 250 300 350 400 450 500 550
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r) Method 1
Method 2
Method 3
Method 4
Method 5
y
ExamplesParameter Value Unit
Pipe ID 1.5 in
Limit Temp 150 deg F
Upstream Pressure 68 Psia
Upstream Temp 579 deg F
Condenser Pressure 3.5 in Hg
Upstream Enthalpy (calculated) 1321.4 btu/lbm
IP Exhaust Valve
ExamplesPolynomial for IP Exhaust Valve Leakage
y = -0.00001x3 + 0.01364x2 - 2.97839x + 188.83734
R2 = 0.99824
0
100
200
300
400
500
600
700
800
100 150 200 250 300 350 400 450 500
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r)
y
Calculated 1st LP Extraction Valve Leakage
0
50
100
150
200
250
300
350
100 150 200 250 300 350 400 450
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r) Method 1
Method 2
Method 3
Method 4
Method 5
y
ExamplesParameter Value Unit
Pipe ID 1.5 in
Limit Temp 150 deg F
Upstream Pressure 37.6 Psia
Upstream Temp 462.7 deg F
Condenser Pressure 3.5 in Hg
Upstream Enthalpy (calculated) 1267.2 btu/lbm
First LP Extraction Valve
ExamplesPolynomial for 1st LP Extraction Valve Leakage
y = -0.00002x3 + 0.01734x2 - 3.64652x + 217.45892
R2 = 0.99966
0
50
100
150
200
250
300
350
100 150 200 250 300 350 400
Downstream Temperature (deg F)
Lea
kag
e F
low
(lb
m/h
r)
y
Case Study Conditions
Continuous Blowdown Line to Condenser 4 Inch pipe diameter, 1000 psi, saturated liquid (~ 10%
steam) Temperature decreases along pipe as location moves
away from valve Design Flow is 300,000 lbm/hr; Low Value is 209,000
lbm/hr Goals
Verify that calculation of flow is within the high and low value.
Verify that correction for measurement location is valid.
359°F
351°F
351°F
349°F
342°F
342°F
Flow Resistance Bernoulli:
Solving for V2 (“a” accounts for the other terms in the Bernoulli equation).
The separated term accounts for the flow resistance. Because it is proportional to velocity and flow it can be applied as a correction factor to the velocity and flow results of the basic flow equations which do not account for flow resistance.
5.0
2 21
KaV
g
VKz
g
V
g
Pz
g
V
g
P
222
22
2
222
1
211
5.0
21
K
Distance to Condenser By applying a correction to the calculated flow, a more
accurate estimate for the flow can be calculated “Distance to Condenser” applies this correction in the
TP-Plus software. This value is the equivalent hydraulic distance, based on
actual linear distance and the number of elbows, tees, valves, and other flow disturbances in the leakage path.’
Protects against over-promising the savings to be realized by repairing the leaking valve(s)
Valve Information Sheet
Continuous Blow Down Without Correcting FlowContinuous Blow Down Without Correcting Flow
180000
200000
220000
240000
260000
280000
300000
330
335
340
345
350
355
360
365
17.0 144.3 202.0 229.4 252.1 285.9
lbm
/hr
°F
Distance from Condenser
Comparison of Temperature and Flows
Pipe Temperature Calculated Flow Actual Flow (Design)
Continuous Blow Down With Corrected FlowContinuous Blow Down With Corrected Flow
Conclusion Cycle Isolation Monitoring can provide significant savings
The process can be utilized with an on-line monitoring system
Proper modeling can have a significant effect on reliability of results
Questions