Example: Calculate the gas velocity for gas flow rate 100 MMscfd through 24 in. internal diameter gas pipe, the gas specific gravity is 0.7, pressure 500 psia, Temperature 100 0F, and assume compressibility factor 0.85.Fundamentals of Oil and Gas Processing Book

Basics of Gas Field Processing Book

Prediction and Inhibition of Gas Hydrates Book

Basics of Corrosion in Oil and Gas Industry Book

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Solution: Using Eq., PV=nzRT, and remember that n= V (ft3)/379.5).

n = 100 × 106/379.5

Gas volume at operating conditions V= 100 × 106 × 0.85 × 10.73 × 560 / (379.5 × 500)

= 2,695,000 ft3/day

Gas flow rate cubic foot per second = 2,695,000 / (24×60×60) = 31.2 ft3/sec

Area of flow = π r2 = 3.14 × 12 × 12 / (144) = 3.14 ft2

(144 to convert r2 from in. to ft2.)

Velocity of gas will be 31.2/3.14 = 9.9 ft/s

The gas velocity may be calculated directly from the following equation:

Velocity = 6 ZTQ/(100,000×Pd2) ft/s.

Where Q = Flow rate scfd, d = diameter in inches.

The maximum recommended velocity of dry gas in pipes is 100 ft/s, (60 ft/s for wet gas), and to be less than the erosional velocity which is defined as:

Erosional velocity: The erosional velocity represents the upper limit of gas velocity in a pipeline. As the gas velocity increases, vibration and noise result. Higher velocities also cause erosion of the pipe wall over a long time period. The erosional velocity Vmax may be calculated approximately as follows:

Vmax = 100 √(2&ZRT/29GP)

Where G= gas sp. Gt (air=1), P = pressure psia

For Example 1-12, the erosional velocity Vmax is:

Vmax = 100 √(2&0.85×10.73×560/(29×0.7× 500)) Vmax = 70.9 ft/s.

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