Quantifying Cycle Isolation Losses and Integration with On Line Systems Feedwater System Reliability Users Group 2015 Meeting San Antonio Ken Porter Rich Duggan Frank Todd Condenser Leakage Flow Leaking Valve 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)

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: US Energy Information Administration 1 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

Prioritization-Value of Leaking Valves Source: Evaluating Steam Turbine Performance 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

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 [ ])

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 T L P

Difficult 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: 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. 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 T d > T limit, then Q = A T d 3 + B T d 2 + C T d + D If Q > Q max, then set Q = Q max

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.

Examples ParameterValueUnit Pipe ID1.5in Limit Temp200deg F Upstream Pressure2415psia Upstream Temp1000deg F Condenser Pressure3.5in Hg Upstream Enthalpy (calculated)1460.4btu/lbm Main Steam Valve

Examples

ParameterValueUnit Pipe ID1.5in Limit Temp205deg F Upstream Pressure440Psia Upstream Temp647deg F Condenser Pressure3.5in Hg Upstream Enthalpy (calculated)1331.5btu/lbm HP Exhaust Valve

Examples

ParameterValueUnit Pipe ID1.5in Limit Temp150deg F Upstream Pressure68Psia Upstream Temp579deg F Condenser Pressure3.5in Hg Upstream Enthalpy (calculated)1321.4btu/lbm IP Exhaust Valve

Examples

ParameterValueUnit Pipe ID1.5in Limit Temp150deg F Upstream Pressure37.6Psia Upstream Temp462.7deg F Condenser Pressure3.5in Hg Upstream Enthalpy (calculated)1267.2btu/lbm First LP Extraction Valve

Examples

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.

Flow Resistance Bernoulli: Solving for V 2 (“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.

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 Flow

Continuous 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