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Automation Totalflow Measurement & Control Systems AGA3 Equations Design Considerations

Automation Totalflow Measurement & Control Systems AGA3 Equations Design Considerations. New AGA3 Equation - Implications for Electronic Flow Computers. Which Algorithm? Not Just One (Part 1, Part 3 main body, Part 3 Appendix, Part 4) Part 4 serves as guide for implementers

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Automation Totalflow Measurement & Control Systems AGA3 Equations Design Considerations

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  1. Automation Totalflow Measurement & Control Systems AGA3 Equations Design Considerations

  2. New AGA3 Equation - Implications forElectronic Flow Computers • Which Algorithm? • Not Just One (Part 1, Part 3 main body, Part 3 Appendix, Part 4) • Part 4 serves as guide for implementers • Part 4 most likely choice • Should There be Any “Factors” • Factors exist, just not same as old ones. (e.g. more fundamental) • Ev - Velocity of Approach • Y - Expansion • Nc - Numeric & Units based Constant • Cd - Coefficient of Discharge • d2 - diameter squared • - Density at Flowing Conditions • - Density at Base Conditions • - Differential Pressure

  3. New AGA3 Equation - Implications forElectronic Flow Computers • Should There be Any Other “Factors” • What About Fpv? • Actually Part of the density equations, but.... • Users want to choose method (or if used at all) • Many standards and documentation refer to Fpv as a factor • Probably need to arrange equation to support Fpv factor • What about In-Situ Calibration? Couple of possible approaches.... • Separate “auxiliary factor” Faux • Multiplier for biasing fundamental equation by a know percent • Percent determined from In-Situ test • User entered Cd • Option to disable Flow Computer Cd calculation • User enters Cd resulting from In-Situ test

  4. New AGA3 Equation - Implications forElectronic Flow Computers • What About Expansion Factor? • To avert need to perform a second supercompressibility calculation will likely use up-stream configuration of equation in all cases • If Pf measured downstream then, upstream must be calculated as:This must be used for all instances of Pf in the equation • What about Pipe Taps? • Pipe Taps Not Supported by AGA3-92 • Standard reverts to AGA3-85 for Pipe Taps • To Support User Selection of Pipe Taps Flow Computer mustsupport both AGA3-92 and AGA3-85

  5. New AGA3 Equation - Implications forElectronic Flow Computers • Integration and Time Related Issues • Fundamental Equation is a Rate Equation • Rate Equation must be integrated over time to produce quantity (e.g. volume or mass) • AGA-3 / API 14.3 does not specify integration requirements

  6. New AGA3 Equation - Implications forElectronic Flow Computers • Integration and Time Related Issues • API 21.1 tries to deal with these issues when they relate to measuring gas. It allows dividing (factoring) the equation into two components • Integral í Portion to be computed and integrated at least once per second. Must include at least SQRT (Hw * PF) • Integral Multiplier í Portion to be computed at least once per hour. Rest of equation not included in the Integral. • Volume í Result of combining the two components at least once per hour.

  7. New AGA3 Equation - Implications forElectronic Flow Computers • Possible Computation Time Domains • CONST í Constant, Computed Once, Never Change • SEC í Second, Computed Once Per Second • VOLP í Vol Period, Computed Once Per Volume Calc Period • NEW_CONST í Computed When Static (Config) Values Changed • NEW_COMP í Computed When New Composition Data Received

  8. New AGA3 Equation - Implications forElectronic Flow Computers • Considering Factor and Integration/Time Issues, an equation form based on the fundamental equation: Fundamental Equation(showing an Fip Term whichis used to include ...... from fundamental equation where, Fip Term showing(Fpv Factor and Integral Term) where, Integral (“Extension”) Term

  9. See API 14.3 Part 4 VOLP NEW_VOL_CONST & NEW_CONST VOLP but portions are computed on different time periods as shown in following three table entries CONST VOLP SEC computed and integrated until VOLP when used to compute Fip and Cd New AGA3 Equation - Implications forElectronic Flow Computers Summary of Calculation Time Periods

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