2. Procedure for Sizing Three-Phase Horizontal
Separators—Half-Full
1. The first step in sizing a horizontal separator is to establish the
design basis. This includes specifying the maximum and minimum
flow rates, operating pressure and temperature, droplet size to be
removed, and so on.
2. Select a (𝑡𝑟)𝑜and a (𝑡𝑟)𝑤
3. Calculate (ℎ𝑜)𝑚𝑎𝑥. Use a 500-µm droplet if no other information is
available.
(ℎ𝑜)𝑚𝑎𝑥 = 1.28 × 10−3 (𝑡𝑟)𝑜 ∆𝑆𝐺 𝑑𝑚
2
𝜇
(ℎ𝑜)𝑚𝑎𝑥 = 320
(𝑡𝑟)𝑜 ∆𝑆𝐺
𝜇
for 500−µm
6. Procedure for Sizing Three-Phase Horizontal
Separators—Half-Full
6. Calculate dmax
Note: dmax depends on Qo, Qw, (tr)o, and (tr)w.
7. Calculate combinations of d, Leff for d less than dmax that satisfy
the gas capacity constraint. Use 100-µm droplet if no other
information is available.
7. Procedure for Sizing Three-Phase Horizontal
Separators—Half-Full
8. Calculate combinations of d, Leff for d less than dmax that satisfy
the oil and water retention time constraints.
9. Estimate seam-to-seam length.
8. Procedure for Sizing Three-Phase Horizontal
Separators—Half-Full
10. Select a reasonable diameter and length. Slenderness ratios (12
Lss/d) on the order of 3–5 are common.
11. When making a final selection, it is always more economical to
select a standard vessel size. API sizes for small separators can be
found in API Spec. 12J. In larger sizes in most locations, heads come
in outside diameters, which are multiples of 6 in. (150 mm). The
width of steel sheets for the shells is usually 10 ft (3000 mm), thus
it’s common practice to specify Lss in multiples of five.
9.
10. Vertical Separators’ Sizing
1. Gas Capacity Constraint
2. Settling Water Droplets from Oil Phase
for dm = 100 µm
for dm = 500 µm
11. Vertical Separators’ Sizing
3. Settling Oil from Water Phase
4. Retention Time Constraint
• where ho ¼ height of oil pad, in. (mm), hw ¼ height from water outlet
to interface, in. (mm). (Note: this height must be adjusted for cone
bottom vessels.)
for dm = 200 µm
12. Vertical Separators’ Sizing
5. Seam-to-Seam Length
6. Check the slenderness ratios. Slenderness ratios between 1.5 and 3
are common. The following equations may be used:
