Cori

CORIOLIS MASS FLOW METERS R. Mascomani Chief Research Engineer FCRI, PALAKKAD.

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MASS FLOW 

Determination of energy balances

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Measuring efficiency of Engines

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Energy content of natural gas/Crude

Mass is constant independent of pressure, temperature, gravity, viscosity, pressure, temperature, density  Mass Flow tops the list 

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MASS FLOW MEASUREMENT  Area

x velocity x density  True mass flow meters : Output is direct function of mass flow.

• Coriolis meters

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MASS FLOW MEASUREMENT  Inferential

mass flow meters : Employs simultaneous measurements of flowing volume and density.  Product gives mass flow.

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CORIOLIS MASS FLOWMETERS 

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Movement of particle across the surface of a rotating body Acceleration by a force called Coriolis force Normal to both particle direction axis of rotation of the body. Magnitude directly proportional to the product of the mass of the particle and Coriolis acceleration.

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Oscillating Flow Tube, No Flow

Outlet Inlet

Support Axis Outlet Side

Inlet Side

Outlet Side

Inlet Side

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Oscillating Flow Tube – Response to Flow Twist Axis

Inlet

Fluid Reactive Force (Outlet)

Outlet Support Axis Outlet Side

Inlet Side Fluid Reactive Force (Inlet)

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Dual-Tube Sensor

Fluid Reactive Force (Inlet)

Fluid Reactive Force (Outlet)

Inlet

Outlet

Fluid Reactive Force (Inlet)

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Fluid Reactive Force (Outlet)

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Oscillating Flow Tube, No Flow

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Dual-tube Sensor

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Mass Flow Measurement SENSOR SIGNAL , NO FLOW

Outlet Side C1

OutletSide C1

Inlet Side C2

Inlet Side C2

∆T

∆T

Time

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SENSOR SIGNAL , WITH FLOW

Time

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Flow Calibration Factor (FCF)

3.8552 5.13 Flow Factor (grams/sec/µ second of ∆ T)

Temperature Correction Factor (% / 100 oC)

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How Transmitter Computes Mass Flow-Calibration Constants 

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Flow Calibration Constant (determined during factory or field calibration) Zero Flow Offset (determined during field calibration) Flow Temperature Coefficient (specified for the sensor)

Flow rate in grams per second that produces 1 microsecond of ∆ t. Value of ∆ t when there is no flow through the sensor. Percent change in tube rigidity resulting from a change in temperature of 100 ºC.

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MECHANISM OF VIBRATION 

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Tube anchored at two points vibrate up&down Vibration at resonance Vibration at free end Forces operate in opposite directions and the tube twists Twist angle or change in phase between two transducers detecting the movement of legs is measured 17

m = K × ∆T / 8 / r K

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Constant for tube material ∆ T : Time interval  r: Tube radius

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MATERIAL OF CONSTRUCTION  Common

material SS316  Special materials such as Titanium, Hastelloy, Zirconium and tantalum for chemical compatibility

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PARALLEL TUBE CONSTRUCTION      

Two tubes vibrate in out of phase giving equal and opposite signal. Effect of vibration cancels out Drive coil an one tube and an opposing magnet on the other to vibrate the tube. Motion sensors electro magnetic types. Miniature temperature sensor on the surface of the tube. AC/DC powered versions and power consumption 10 W typically. Output pulsed /frequency/4-20 mA

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DESIGN MASS FLOWMETERS  Full

scale deflections less than 0.001”  Chemical compatibility and material.  Pressure Rating  Flow Range  Pressure Drop  Signal amplitude to noise ratio.  Electronics to resolve times in ns range.

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TUBE CONFIGURATIONS  Variety

of shapes  sensitivity  increase range  reduce stress  Straight tube reduced pressure drop

• Easier installation • Needs sensitive detectors

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PERFORMANCE Size : 1/16" up to 6"  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 

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Calibration with different fluids

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Effect of Pressure

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Effect of Temperature

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% erro r in indic a te d ma s s

C A L IBR A T IO N C UR VE (3 ") E& H Sl N o.99 08 -30 08 1-1-1 8

0 .60 0 0 .50 0 0 .40 0 0 .30 0 0 .20 0 0 .10 0 0 .00 0 -0 .10 0 -0 .20 0 -0 .30 0 -0 .40 0 -0 .50 0 -0 .60 0 0

50 0

1 00 0

1 50 0

2 00 0

2 50 0

A ctu al flow rate in kg /m in 30

CALIBR ATION C URV E 6",F R,M eter serial no .217458

% error in indicated mass

Before final adjustment of cal factor After final adjustment of cal fac tor 0.500 0.400 0.300 0.200 0.100 0.000 -0.100 -0.200 -0.300 -0.400 -0.500 0

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100

150

200

250

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Ac tual flow r ate in tons /hr

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350

C alibra tion curv e o f a ma ss flow m ete r 3",FR,M ete r S eria l n o.:3446 01

% Error in indicated m ass

0.40 0.30 0.20 0.10 0.00 -0.10 -0.20 -0.30 -0.40 0

1 00 2 00 3 00 400 5 00 600 7 00 800 900 10 00 1100 12 00 13 00 Actu al flo w rate kg /m in 32

ZERO STABILITY 

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Well balanced meter vibrates freely independent of external environment Minimum potential for zero error effects. Tube balance (Passing of energy to pipes) Stress affect fundamental oscillation of meter causing zero shift Errors highest at bottom range of the meter Importance for gas measurement due to low density

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OPERATIONAL SAFETY    

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Material compatibility Tube under continuous stress Stress corrosion cracking may result failure Residual liquid may be potentially corrosive if liquid carry over Secondary containment for hazardous/explosive gases

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POTENTIAL FLUID EFFECTS 

Quoted uncertainty accounts for fluid effects

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Certain tubes sensitive to pressure

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Bourdon effect due to pressure increase

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ADVANTAGES 

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A clear tube provides a fundamental means of measuring mass flow. No moving components and requires less maintenance. Corrosion resistant materials. Calibration independent of viscosity and flow profile. Immune to swirl and asymmetrical flows Output linear with mass flow. High turn down ratio Very repeatable 36

COST OF OWENERSHIP

(Comparison of Coriolis and inferential meters)

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Metering accuracy ( % of reading) Human intervention ( Number per year) Safety ( points of leakage) Recalibration frequency ( Times per year) Long-term drift ( % per year) System components ( number required for measurement) Turndown ratio Reliability 37

Comparison of meters

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DISADVANTAGES  Accuracy degraded at low flow rates due to zero        

shifts. Performance affected by air/gas pockets. Sensitive to vibration. Need careful installation Difficult to prove at site High pressure drop at full flow Bulky in some designs. Size limitation Expensive.

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SIZING  Flow

rate and line size.  Pressure and temperature ratings  Materials of construction.  Resistance to corrosion and pitting  Fatigue strength.  Pressure drop.  Liquids.  Gases, Flowing velocity

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FLUID VELOCITY   

Maximum flowrate 0.5 Mach For airflow 160 m/s Sonic effects at higher velocities

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CALIBRATION  Master

meter system  Gravimetric methods  Volumetric methods

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CALIBRATION

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With some meters , there are shifts between water calibration and site fluid Variation depends on design Site calibration with PD meters Compact provers may be used

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Calibration Schematic

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INSTALLATION        

Mechanical Installation, Vibration reduction For Liquid measurement,keeping out of gas For Gas Measurement,keeping out of particle Vertical pipe with flow upward preferred. No condensate or other liquids should be trapped in the flowmeter Adequate rigid pipe supports on either side,close to the meter By pass loop. Stress due to bolting will change calibration

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Use of antivibration mounts to reduce the effects of stress. Avoid vibration in the range of 40 - 200 Hz. ( Near pumps and motors ) Alignment of gaps to reduce stress Downstream shut off valve to zero the meter. No special up/down stream piping requirement. Flow meter size can be less than process piping for low density gases. 20 - 30 pipe diameters in between meters to avoid "Cross Talk".

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APPLICATIONS Batch production of chemicals  Blending systems  Truck loading  Food, drink industry.  Photographic emulsions, polypropylene  Dispensing of LPG ,GNG  Air,CO2, ,Nitrogen and Chlorine 

 Ethylene,Hydrogen

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ACCURACY OF INFERRED TECHNIQUES  Volume  Pressure  Temperature  Gas

Composition  Compressibility Factor and  Measurement to be made simultaneously.

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ACCURACY OF INFERRED TECHNIQUES PV = n. R. T.Z. (real gas law relationship)  Z = 0.6 (for CNG at 2000 PSI and 50 deg.F with specific gravity of 0.7)  If compressibility is not accounted a correction of about 40% is required in mass flow.  Over 8000 meters for past 10 years 

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CRITERIA FOR GAS MEASUREMENT Zero stability  Operational safety  Fluid velocity  Meter Uncertainty  Precision losses  Potential fluid effects 

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ZERO STABILITY METER BALANCE / INSTALLATION         

Meters employ twin or dual tube Well-balanced tube vibrates freely Poorly balanced meter pass energy into the flange Stresses or pipe forces Zero drift and its associated errors Brackets de-couples meter Errors highest at bottom range Gas densities 30-40 times lower Physical checking of vibration

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FLUID VELOCITY – GAS PROPERTIES

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Maximum flowrate 0.5 MACH Air Velocity 160m/s Calculated in relation to the measuring tube diameter Flow velocity / the speed of sound in gas

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ACCEPTABLE PRESSURE LOSS

Low pressure gases due to high velocity  Fluid vapor pressure to ensure no condensate formation 

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OPERATIONAL SAFETY

Complete material compatibility  Vibrating under stress  Incompatibility causes stress corrosion cracking  Liquid “carry over” can occur due to failure of gas scrubber or dryer  Residual liquid potentially corrosive to the tubes  Range of wetted in 316, 904L stainless steel, Hasteloy C, Titanium, Zirconium 

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METER UNCERTAINTIES Performance better than 0.5% across a 20:1 turn down  Uncertainties for gas flow facilities range from +/-0.3% to 0.6%. 

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POTENTIAL FLUID EFFECTS Fluid effects taken into account normally  Certain tube designs sensitive to pressure  “Bourden”effect at high pressure  Predictable and results in a shift in the Kfactor  Compensated for continuous pressure  Optional pressure compensation with external pressure transducer 

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CORIOLIS METERS IN THE NATURAL GAS FIELD GPU Gasnet, Victoria, Australia  36 meters from 6mm upto 50mm with flows <4,000 scm/hr  High costs for removing and recalibration  Field proving techniques using portable meters  Metering facilities permit series flow testing and validation 

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CORIOLIS METERS IN THE NATURAL GAS FIELD Five reference meters (6mm to 75mm)  Calibrated on air and / or on natural gas at pressure and water calibration  The results of proving relies stability and repeatability  Coriolis meters “finger print” the field meters 

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METER PROVING OF CORIOLIS METERS      

Coriolis meters rarely require field calibration Water calibration meets specifications on natural gas Performance verification by gravimetric scales or fixed volume tank Proving on natural with sonic nozzles or piston provers Coriolis meters in-situ calibration Coriolis meters practical choice in quantifying orifice and turbine meter

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APPLICATION OF CORIOLIS METERS FOR NATURAL GAS Over 8,000 for CNG  Verified gravimetrically to ±0.3%  Local weights and Measures authorities 

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PRODUCTION 90M to 10MM scfd at a 550 psig and 150 deg.F  Factory calibration matched with multiple orifice run to within +/-1%  Density measurement detect periodic slight crude carry over  Additional 30 gas meters 

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COMPRESSION / TRANSPORTATION 120 Coriolis meter for compressor stations  More accurate mass fuel measurement  Non-mechanical design  No straight run requirements  Immunity to extensive vibration inherent to station design 

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COMPRESSION / TRANSPORTATION Improved accounting gas consigned for compression  Vibration testing and proving against sonic nozzles  On-shore and off-shore gas compression stations 

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TRANSMISSION / DISTRIBUTION A grid for remote region  To reduce the metering maintenance and proving  Multiple orifice run costly  Cost savings $100 K per skid for Coriolis in place of turbine 

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TRANSMISSION / DISTRIBUTION Coriolis eliminated the need for skids  No need for flow conditioning and filters  Conversion from mass to standard volume  Eliminates uncertainties related to temperature and pressure 

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CNG METER CALIBRATION       

Storage Banks (13.5 m3) High-precision weighing High pressure at 250 bar Flow rates up to 4500 kg/h Extensive instrumentation and remote operation Real time PC based process control and DAS DAS records temperatures, mass, pressures

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CORIOLIS METER AS A SIMPLE ENERGY METER Energy content of natural gas  Estimation of energy content of the natural gas  Coriolis measures the mass  Assumption of constant inert gas composition  Scaling the output for a fixed Btu/lbs (kJ/kg) 

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TESTING AND APPROVAL FOR CORIOLIS METERS      

Compressed air & natural gas, pipeline natural gas Against sonic nozzles, turbine master meters and bell provers Coriolis installation, application practices and accuracy specifications PTB & NMI approval for coriolis metering in NIST approved dispensers US (NIST), Canada, Mexico, Japan, Russia Argentina, S.Africa, Venezuela, Chile, Colombia

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