Flow meters for gas measurement

1,866 views

Published on

types of flow meters are used for gas measurement with details and images

Published in: Business, Technology

Flow meters for gas measurement

  1. 1. Ultrasonic meter : 12 ” Operating flow rate : 90 % Qmax Bais Error : 0.5 % $2500/day or $1000000/annum Loss can be avoided by calibration Cost due to Error of 0.25% is about Rs120 Crore/annum
  2. 2. Initial calibration by manufacturers For checking of accuracy by the user. After major repairs. Under Statutory Obligations Legal Disputes To improve accuracy
  3. 3. Orifice meters Turbine meters Ultrasonic gas meter Critical flow Venturi Coriolis mass meters Large volume Large volume Large volume Large volume CNG
  4. 4. Cheap, commonly used meters Reasonable performance, good reliability Moderate cost Pressure difference proportional to flow rate Sharp square edged cylindrical throat
  5. 5. Flange, corner, D and D/2, pipe taps Flange tap for Natural gas Diameter ratios ,0.1 – 0.75 Orifice diameters > 0.45” Cd depends on β, ReD and tap
  6. 6. Depends on Reynolds Number, diameter ratio For Cd, 0.4 – 1% Expansibility factor Geometrical measurements Flow parameters Overall uncertainty 1 – 2%
  7. 7. Cheap, good performance and reliability Moderate cost with Simple metrology Conform to AGA-3 standard No need for wet plate calibration Low flow range (1:3 Typical) Susceptible to erosion, damage Cost effective metering solution Overall uncertainty 1 – 2% (0.4-0.6% in Cd)
  8. 8. Flowing gas imparts force on rotor Actual rotational speed depend passage way size shape/ rotor design load due to internal mechanical friction fluid drag external loading gas density maximum velocity 50 m/s
  9. 9. Rotor End connection Mechanical or Electrical Readout Body 1 2 3 4 56 Inlet Annular Passage Nose cone Electronic Pickup Outlet Mechanism Houseing and Tail Cone
  10. 10. 1.25 1.00 Percent error ±1% for 0.2 Qmax - Qmax ±1.5% for Qmin 0.2 Qmax ±0.35% for 0.2 Qmax - Qmax Repeatability : ±0.2% Effect of swirl should be less than 1/3 of normal specifications 1.75 1.50 0.75 0.50 Repeatability +/-0.2% 0.25 Maximum peak-to-peak error 0.00 1.0% (Qi > Qt) 0.25 0.50 0.75 1.00 1.25 1.50 1.75 Q min Qt < 0 .2 Q Flow rate (Qi )
  11. 11. Frequency counters - for instantaneous flow rate Integrator - for totalized flow Transmitters - for control applications Flow computers - for billing purposes
  12. 12. The ability of the meter to duplicate a given output or performance for test runs with an identical set of flowing conditions. Under normal conditions +/-0.1% on successive short duration and +/-0.15-0.2% on day to day basis.
  13. 13. Designed for a maximum flow rate Fixed by rotor speed Normal pressure loss. Same irrespective of operating pressure. Lowest flow rate at which the meter will operate within specified accuracy limits (+/-1%). Depends on magnitude of non-fluid drag and the density Qmin ∝ ρ-0.5
  14. 14. SWIRL EFFECT  Rotor designed for axial flow at rotor inlet  Swirl affects the rotor speed  swirl increases or decreases the speed depending on the direction of swirl.  Tests at 0.25, 0.4, Qmax with atmospheric air.  Error shifts 1/3 of maximum permissible error.
  15. 15.     Low level perturbation tests Perturbation unit with double elbow out of plane. Resembles perturbations by bends, tees, convergent and divergent sections. High level perturbation tests Perturbation unit with double elbow out of plane with half area plate in between Resembles perturbations by regulators or throttling devices.
  16. 16. Recommended Installation
  17. 17. Less sensitive to upstream disturbances Output digital, linear, electronics Compact with moderate head loss More expensive (larger sizes) Gradual wear and fouling of surfaces Periodical recalibration Performance of smaller turbine meters
  18. 18. AGA Report No.9 Multipath ultrasonic meters for custody transfer of natural gas Dutch Ministry of Economic Affairs PTB, Germany Uncertainty in line with Turbine meter Production facilities, transmission pipelines Storage facilities, distribution systems
  19. 19. Bi directional capability No additional pressure drop Measurement of pulsating flows Wide rangeability No moving parts Less weight and space No drift due to no wear off Insensitive to asymmetrical , pulsating, rotating flows and wet/untreated gas
  20. 20. 18 Path USFM for liquids : 0.15
  21. 21. Measurement of spool diameter Acoustic path L and X Dry calibration accuracy 1% or better Performance depends on signal processing / path configurations Measurement of delays for electronics / transducers Measurement of sound velocity in pressurized test all.
  22. 22. L2x(tu - tD)  Flow Velocity, v = -----------2 x tu x tD Lx(tu + tD)  Sound Velocity, v = ----------- 2 x tu x tD  L : Straight length of acoustic path  X : Axial distance  tu, tD : Transit times
  23. 23. ACCURACY Precise Geometry of body and transducer location Inherent integration techniques Quality of profile, pulsation, gas uniformity Electronic clock stability Consistent detection of pulse Compensation for signal delays Parallel paths Direct or reflected paths along 2 or more tilted chords Weighting factors for each path
  24. 24. ACCURACY Average ID, Acoustic Path Length, Axial distance between transducer pair Average ID from 12 measurements Vertical(1), Horizontal(1) and 45o from vertical (2) Near upstream, near downstream and half way between transducer Calculation by trigonometry Body temperature at the time of measurement Correction to 20oC and to 0.01 mm
  25. 25. Zero Test Meter purged of air with pure test gas or gas mixture Properties of test gas must be known Sound velocities for each acoustic path recorded for 30s Mean and standard deviation Adjustments for compliance to performance Theoretical speed of sound from composition, pressure and temperature Document all relevant parameters Zero flow offset factor in +/- m/s
  26. 26. Zero Test
  27. 27. Flow Test qmin, 0.1 qmax, 0.25 qmax, 0.4qmax, 0.7 qmax and qmax At expected average operating conditions Specific piping configuration and / or flow conditioner Diameters of flanges /connecting pipes to match (±1%) Traceable flow calibration facility Properties AGA Report No.8 “Detail Characterization Method”
  28. 28. Size : 1/16" up to 10" Flow Range : g/h - 10 t/m Range : 25 : 1 (Typical) and 100 : 1 in some application. Accuracy : ±0.15% - ± 0.25% R+ Zero shift error. ±0.5% R for gases Uncertainty of measurement facilities ±0.3% - ± 0.6% R
  29. 29. Repeatability : +/-0.5% (qt<qi <qmax) Max Peak to peak error : +/-1%(qt<qi <qmax) Max mean error : +/-1% (qt < qi < qmax) 1.75 Repeatability ±1.0% (Qi < Qt) 0.75 Percent error 1.25 Repeatability ±0.5% (Qi > Qt) Max Peak to Peak spread 1.0% (Qi > Qt) 0.25 0.00 -0.25 -0.75 -1.25 -1.75 Qmin Qt Flow Rate (Qi) Qmax
  30. 30. Critical velocity at the throat Mass flow rate maximum for the existing upstream conditions ISO 9300 Throat Reynolds Number 2.1 x 104 - 3.2 x 107 Relative uncertainty in Cd 0.3% - 0.2% Gas pressure and the gas temperature at upstream Pressure ratios of 0.75 - 0.95
  31. 31. 0.9D to 1.1D _ >d Ød 2.5d ±0.1d _ ØD>4d 6.0° 2.5 ° r = 1.8d to 2.2d c

×