Page 99 - Separation process engineering

3. K drum Calculation.

Calculation of flow parameter F :
lv

K drum from Eq. (2-65) gives K drum = 0.4433, which seems a bit high but agrees with Watkins’s

(1967) chart.
4.

5.

Use a 4.0 ft diameter drum or 4.5 ft to be safe.
6. If use h total /D = 4, h total = 4(4.5 ft) = 18.0 ft.

E. Check. This drum size is reasonable. Minimums for h and h are easily met. Note that units do
v
f
work out in all calculations; however, one must be careful with units, particularly calculating A c
and D.
F. Generalization. If the ideal gas law is not valid, a compressibility factor could be inserted in the
equation for ρ . Note that most of the work involved calculation of the physical properties. This is
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often true in designing equipment. In practice we pick a standard size drum (4.0 or 4.5 ft diameter)
instead of custom building the drum.

2.10 Using Existing Flash Drums

Individual pieces of equipment will often outlive the entire plant. This used equipment is then available
either in the plant’s salvage section or from used equipment dealers. As long as used equipment is clean
and structurally sound (it pays to have an expert check it), it can be used instead of designing and building
new equipment. Used equipment and off-the-shelf new equipment will often be cheaper and will have
faster delivery than custom-designed new equipment; however, it may have been designed for a different

separation. The challenge in using existing equipment is to adapt it with minimum cost to the new