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282 Chapter 6

volume of the dished heads is not considered in the procedure. Knock-out drums
are mostly installed in a vertical position. Younger [11] found that out of eleven
drums installed in several plants, nine were vertical.

Table 6.7 Summary of Equations for Sizing Knock-Out Drums_______

Subscripts: L = liquid — V = vapor
fp '-pv'Y /2
L
I————— I (6.7.1)
v v = k v
I Pv' >/
k v = 0.2 ft/s (0.061 m/s) — with no mist eliminator (6.7.2)
k v = 0.35 ft/s (0.107 m/s) — with a mist eliminator
V v '=v v A (6.7.3)

2
A = ?t D /4 (6.7.4)

L/D = 2 (6.7.5)

Variables
V y - k y - A - D - L

Table 6.8 Calculation Procedure for Sizing Knock-Out Drums_______

1. Select a value of k v from Equation 6.7.2.

2. Calculate a maximum gas velocity, v v, from Equations 6.7.1.

3. Calculate the cross-sectional area of the separator, A, from Equation 6.7.3.

4. Calculate the diameter, D, of the separator from Equation 6.7.4.

5. Round off D in 6 in (0.152 m) increments, starting at 30 in (0.762 m). If D is
less then 30 in (0.762 m), use standard pipe.

6. Calculate the length of the separator from Equation 6.7.5. Round off L in 3 in
(76.2 mm) increments, for example, 5.0, 5.25, 5.5, 5.75 ft, etc.

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