Description

Figures C-1 and C-2 present gas capacity charts for square-edge orifices of different sizes and allow the calculation of gas flow rates for different combinations of upstream and downstream pressures. Calculations are based on the following assumptions: Gas Sp. Gr. = 0.65; C _d = 0.865 ₁ T ₁ = 60 F. For other gas specific gravities, discharge coefficients and flowing temperatures, the gas rates found from these figures must be corrected according to Figure C-3.

Figure C-1

Figure C-2

Figure C-3

Example problem

Find the gas passage capacity of an 30/64 ? choke, if upstream and downstream pressures are 800 psig and 600 psig, respectively. Gas specific gravity is 0.7, flowing temperature is 100 F, and a discharge coefficient of 0.9 is to be used.

Solution

Based on the choke size, Figure C-2 is to be used. Start at an upstream pressure of 800 psig and go vertically until crossing the curve valid for a downstream pressure of 600 psia. From the intersection, draw a horizontal to the left to the proper choke size (30/64 ?). Drop a vertical from here to the upper scale to find the gas flow rate of 3,432 Mscf/d. Since actual flow conditions differ from chart base values, the correction as given in Figure C-3 must be applied. At a temperature of 100 F and a gas specific gravity of 0.7 the correction factor is read to be equal CF=1.072. Corrected gas volume is according to the formula in...