Page 269 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Mechanical Separations 241

For an aqueous-hydrocarbon or organic solvent mixture: Optimum vessel diameter:
Assume 20% cross-sectional area is occupied by an
The top layer will be hydrocarbon, with the aqueous layer emulsion and is recognized as a ‘“dead volume.” This is
droplets settling through the hydrocarbon. The terminal actually the height over which the interface level will vary
velocity is: during normal operations L-261.

vhc = 12.86 (ASpGr)/phc, in./min (4-2 1) A, t Ab = 0.8 nD2/4 (4-24)

vhc = terminal settling velocity of aqueous droplets in
hydrocarbon phase in top of vessel, in./min
ASpGr = differences in specific gravity of the particle and sur-
rounding fluid
phc = viscosity of surrounding fluid, cp

The economical vessel ratio is L/D = r
Height of hydrocarbon layer to the interface:
Modified Method of Hagpel and Jordan E291

This method is a modification of the earlier method
h, = 38.4 A,/(aD) -t 1.2D (415A) [30] by Reference [26], as follows, and can be less con-
servative [26] than the original method [30]. A basic
ht = height of continuous hydrocarbon phase in the top of assumption is that particles must rise/fall through one-
vessel, in. half of the drum vertical cross-sectional area [26].

t = h/v

At = cross-sectional area at top of vessel occupied by the con- t = (1/2) (7.48) [0.8 nD2L/4]F, (428)
tinuous hydrocarbon phase, sq €t
f+, = cross-sectional area at bottom of vessel occupied by con- F, = flow rate of both phases
tinuous aqueous phase, sq f: vt = v = terminal settling velocity, in./min

For the bottom aqueous phase: This assumes 20% of the cross-sectional even as “dead vol-
ume.” The height from the interface can be determined
hydrocarbon droplets settle out of the continuous aque- by combining the above equations:
QUS phase. The terminal velocity is for hydrocarbon
droplets: h = (0.748)nD2Lv/F, (4-29)
The height for each interface is:
vas = 12.86 (ASpGr)/p,,, in./min (423)
h, = (0.748) TCD2Lhbc/Ft (430)
vaq = terminal settling velocity of hydrocarbon droplets in
aqueous phase in bottom of vessel, in./min
pa, = viscosity of aqueous phase, cp

Height of aqueous layer to the interface: Ab = [ (0.748) ED2LVas/F, - 1.2DI ~D/38.4 (433)

Example 43: Horizontal Gravity Settlers

h, = 38.4 Ab/TD + 1.2D (415A) Using the data from Sigales [31] and following the
design of [26] :
hb = height of continuous aqueous phase in bottom of vessel, Data for propane/caustic wash:
in. Fh, = 95 GPM
Ab = cross-sectional area at bottom of vessel occupied by con- Fa, = 39 GPM
tinuous aqueous phase, sq ft vaq = 5 in./min
vhc = 120 in./min
r = 3.4