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Separator Design 299

3. Also, solve Equations 6.15.15, 6.15.17, 6.15.19, 6.15.21, and 6.15.23 for D H,
the inside diameter of the decanter, assuming that the heavy phase flow determines
the diameter.

4. The decanter diameter is the larger of the diameters calculated in Steps 2 and 3.

5. Round off D in six-inch (0.152 m) increments starting with 30 in (0.762 m).
Below 30 in (0.762 m) use standard pipe.

6. Calculate v d, the droplet velocity, from Equations 6.15.7 and 6.15.4 to 6.15.6

7. Calculate to, the dispersed-phase settling time, from Equation 6.15.8.

8. Calculate L$, the decanter length required for settling of the dispersed phase
from Equation 6.15.9.

9. Calculate HD, the dispersion-zone height, from Equation 6.15.10.

10. Calculate Aj, the interfacial area required for coalescing the dispersed phase
from Equation 6.15.11.

12. Calculate L, the decanter length required for coalescing the dispersed phase
D
from Equation 6.15.12.
13. Calculate L, the total length of the decanter, from Equation 6.15.13. Round off
L in 3 in (0.0762 m) increments, for example, 5.0, 5.25, 5.5, 5.75 ft, etc.

Example 6.4 Sizing a Liquid-Liquid Separator__________________

An oil-water mixture is separated in a decanter. The properties of oil and water
from an example by Hooper and Jacobs [22] are summarized in Table 6.4.1. If the
residence time required for coalescence is 5.0 min, obtained from experiments,
find the dimensions of the decanter.

The volumetric flow rates of both phases are
1.26 kg 1 m 3
m L
3
3
3
V L = —— = ———— ———— = 1.405xlO~ m /s (0.0356 ft /s)
1 s 897 kg
p L
and

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