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Separator Design 277

Table 6.6 Calculation Procedure for Sizing Accumulators_________

1. Select a residence or surge time, ts, from Equation 6.5.2.

2. Calculate the accumulator volume, V, from Equation 6.5.1

3. Select a vessel head. If the internal pressure is 150 psig (10.3 barg) or less,
select a torispherical head. If the internal pressure is above 150 psig (10.3 barg),
select a 2:1 ellipsoidal head.

4. Select the geometrical factor for the volume of the head, fnv, from Equation
6.5.5.

5. Substitute Equation 6.5.4 into Equation 6.5.3 and solve for the vessel diameter,
D.

6. Round off D in 6 in (.152 m) increments, starting with 30 in (0.762 m). If the di-
ameter is less than 30 in (0.762 m), use standard pipe.
7. Calculate the length, L, of the accumulator using Equation 6.5.4.

8. Round off L in 3 in (7.62 cm) increments, for example, 5.0, 5.25, 5.5, 5.75 ft, etc.

Example 6.1 Sizing a Reflux Drum_________________________

A fractionator separates dimethylformamide from water and acetic acid. The dis-
tillate contains a trace amount of acetic acid. Assuming that the fractionator uses a
total condenser, estimate the diameter, length, and wall thickness of the reflux
drum. Because the mixture contains acetic acid, use stainless steel (SS 316) for the
drum.

Data
Distillate flow rate 16,000 Ib/h (7,260 kg/h}
Acetic acid 20 ppm
Temperature 212°F(100°C)
Pressure 14.7 psia(l 1.013 bar)
3
Density 62.38 lb/ft 3 (9993 kg/m }
Follow the calculation procedure outlined in Table 6.6. First, calculate the
reflux-drum volume from Equations 6.5.1 and 6.5.2 in Table 6.5. From Equation
6.5.2, take the average of the surge times.

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