Henry Gomes

SGS Kuwait WLL

Aspects of Flow Control in

Metering

HENRY GOMES Metering Consultant SGS Kuwait

• Born on Aruba (Carribean) in 1963

• School and College in the Netherlands

• Resident in Romania - Bucharest

• Mechanical Engineer (3 years) at Stork

• Instrument Engineer (7 years) at MW Kellogg

• Metering Engineer (17 years) at Polar Systems

/ Imtech Systems

• Metering Consultant at SGS Kuwait

Aspects of Flow Control in Metering

Sharing experience regarding flow control:

• Valve capacity sizing

• Control valve type

• Characteristic / Rangeability

• Effects on metering applications

Theory

Principle of Daniel Bernoulli:

Liquid flowing through an orifice, the

square of the fluid velocity is directly

proportional to the pressure

differential across the orifice and

inversely proportional to the specific

gravity of the fluid.

Calculation

Calculation for liquid Q = Flow rate

Cv = Valve sizing Coeff. ΔP = diff. pressure G = Specific gravity

Cv:

• Valve sizing coefficient determined experimentally for each style

and size of valve using water

Beside the flow and differential pressure:

• Choking, Flashing and Cavitation for liquid applications

• Critical flow for gas applications

Rangeability / Characteristic Inherent rangeability

• Ratio of its maximum Cv to its minimum

controllable Cv

• Property of the control valve alone

Installed rangeability

• Ratio of its maximum controllable flow

to its minimum controllable flow

• Product from hydraulic calculations

Characteristic:

• Linear

• Equal percentage

• Quick opening

Effects on Flow metering Proper valve sizing can reduce cost and prevent inconvenience

• A control valve that is too small will not pass the required flow

• An oversized valve is expensive and could lead to instability

Cavitation caused by the control valve:

• Lifetime expectancy control valve

• Vibrations on the metering skid (negative effect on flow meter,

temperature elements, valves, actuators).

• Flow profile disturbance when upstream meter run

Noise cause by the control valve:

• Ultra-sonic noise from control valve can disturb the

measurement in ultra-sonic metering

Control Valve Types • Globe Control Valve

• Eccentric Rotary Plug

Valve

• Butterfly Valve

• Segmented Ball Valve

Application 1

• 24” stream butterfly control

valves

• Designed for flow balancing

during loading / proving

• Loading rate flow control by

control valve to vessel

Application 2

Coriolis meter trial proposed by metering supplier

• Higher pressure drop across Coriolis meter:

Coriolis meter pressure drop @ max. flow 33 psi

Turbine meter pressure drop @ max. flow 1 psi

• Cavitation expected at turbine run control valves while

proving Coriolis flow meter

• Poor rangeability of 24” butterfly control valves

Application 3

High pressure natural gas:

• Noise predicted across control valve

• Noise dampening with additional 90° elbows

• Control valve equipped with low-noise trim

• Integrator, flow meter manufacturer and control valve

supplier cooperation to prevent noise problems on metering.

12” Ultra-Sonic Natural

Gas Flow Meter

Application 4

Allocation Flow

Control with inlet

block valve of orifice

meter run

• Inlet gate valve was used for flow control

• Straight length upstream orifice not designed for partially

closed gate valve

• High pressure drop across gate valve caused cavitation:

• high vibration on the meter run

• noise

Conclusion Control Valves in Metering Applications must be ‘right sized’ for its

specific application.

Improper sizing, or just line size control valves will have negative

effects on the metering application when not done properly.

Close cooperation between integrator, flow meter manufacturer and

control valve manufacturer to achieve the best performance,

especially in new technology metering.

Questions ?