Chapter 3: Gas Flow Measurement

1
Chapter 3 Gas Flow Measurement

• Introduction
• Measurements are needed by
• Gas production industry
• Gas transportation industry
• for
• Gas sales
• Reservoir engineering calculations
• For pipeline flows
• Plant applications

2
Chapter 3 Gas Flow Measurement

• Introduction
• Measurements are done at wellheads and testing
  facilities
• Classification of meters
• Volumetric flow meters
• Used for residential areas with low flow rates
• Dynamic flow meters
• For high flow applications like pipelines, fields
  and plants

3
Chapter 3 Gas Flow Measurement

• Types of Dynamic flow meters
• Orifice Meters
• Critical flow provers
• Choke nipples
• Pitot tubes

4
Chapter 3 Gas Flow Measurement

• Orifice Meters
• Most common in the gas industry because of
• Accuracy
• Simplicity
• Low cost

5
Chapter 3 Orifice Meters

• It has an interchangeable orifice plate with a
  small circular opening (orifice)
• Taps for pressure measurement either on pipe or
  flange.

6
Chapter 3 Orifice Meters

• It has a gauge that records the pressure and
  pressure difference

7
Chapter 3 Orifice Meters

• Operating principle
• The orifice meter operates on the principle that
  a change in the velocity of gas stream will
  result in a corresponding change in the pressure

8
Chapter 3 Orifice Meters

• Mathematical formulation
• Based on mechanical energy balance equation

9
Chapter 3 Orifice Meters

• Mathematical formulation
• Simplification for the case of gas flow through
  orifice plate
• No shaft work
• Same elevation (DZ0)

10
Chapter 3 Orifice Meters

• Assumptions to simplify
• First negligible friction loss (F0)
• Second constant specific volume vs simplify the
  integration procedure

11
Chapter 3 Orifice Meters

• Assumptions to simplify
• Third average velocity vq/A and vs(dP)h
• Fourth P1 measured at A1 unaffected by orifice
  and P2 at A2 at orifice plate

12
Chapter 3 Orifice Meters

• Operating principle
• The orifice meter operates on the principle that
  a change in the velocity of gas stream will
  result in a corresponding change in the pressure

13
Chapter 3 Orifice Meters

• Mathematical formulation
• Based on mechanical energy balance equation

14
Chapter 3 Orifice Meters

• Mathematical formulation
• Simplification for the case of gas flow through
  orifice plate
• No shaft work
• Same elevation (DZ0)

15
Chapter 3 Orifice Meters

• Assumptions to simplify
• First negligible friction loss (F0)
• Second constant specific volume vs simplyfies
  integration

16
Chapter 3 Orifice Meters

• Assumptions to simplify
• Third average vq/A and vs(dP)h
• Fourth P1 measured at A1 unaffected by orifice
  and P2 at A2 at orifice plate

17
Chapter 3 Orifice Meters

• Changing to a standard rate
• The equation simplifies to

18
Chapter 3 Orifice Meters

• After rearranging and substituting
• Where
• b is ratio of orifice and pipe diameters

19
Chapter 3 Orifice Meters

• After expanding and calculating at hourly rate

20
Chapter 3 Orifice Meters

• For a special case of
• gg 1
• Psc 14.73
• TfTsc520 R
• zf 1

21
Chapter 3 Orifice Meters

• The equation derived here contains the parameters
  affecting the measurement but is on a very
  idealized basis.
• For practical usage empirical factor have to be
  introduced

22
Chapter 3 Orifice Meters

• The equation with empirical factor is
• Where C is a combination of several factors