Page 271 - 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. 111e terminal actually the height over which the interface level will vary
velocity is: during normal operations [26].

vhc = 12.86 (6SpGr)/µhc, in./min (4-21) (4-24)

vhc = terminal settling velocity of aqueous droplets in 0 = ± [a/2 ± (a 2 - 4b) 112 /2] 112, ft (4-25)
hydrocarbon phase in top of vessel, in./min
6SpGr = differences in specific gravity of the particle and sur- (4-26)
rounding fluid
(4-27)
µhe = viscosity of surrounding fluid, cp
The economical vessel ratio is L/D = r
Height of hydrocarbon layer to the interface:
Modified Method of Happel and Jordan [29]
(4-21A)
This method is a modification of the earlier method
h, = 38.4 A/ (rcO) + 1.20 (4-l5A) [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].

(4-22) t = h/v

A 1 = cross-sectional area at top of vessel occupied by the con- t = (1/2) (7.48) [0.8 1t0 2 L/4]F, (4-28)
tinuous hydrocarbon phase, sq ft
Ab = cross-sectional area at bottom of vessel occupied by con- F, = flow rate of both phases
tinuous aqueous phase, sq ft v, = v = terminal settling velocity, in./min

This assumes 20% of the cross-sectional even as "dead vol-
For the bottom aqueous phase:
ume." The height from the interface can be determined
hydrocarbon droplets settle out of the continuous aque- by combining the above equations:
ous phase. The terminal velocity is for hydrocarbon
droplets: h = (0.748)TC0 2 Lv/F, ( 4-29)
The height for each interface is:
"•q = 12.86 (6SpGr)/µ.iq, in./min (4-23)
(4-30)
Vaq = terminal settling velocity of hydrocarbon droplets in
aqueous phase in bottom of vessel, in./min hb = (0.748) TC0 Lvaq/F, ( 4-31)
2
µaq = viscosity of aqueous phase, cp
A,= [(0.748) TC0 2 Lvhc/F, - 1.20] TCD/38.4 ( 4-32)
Height of aqueous layer to the interface:
Ab= [(0.748) TC0 2 Lvaq/F, - l.20] TCD/38.4 (4-33)

(4-21A) Example 4-3: Horizontal Gravity Settlers

(4-15A) 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. Fhc = 95 GP:tv1
Ab = cross-sectional area al bottom of vessel occupied by con- Faq = 39 GPM
tinuous aqueous phase, sq ft
Vaq = 5 in./rnin
Vhc = 120 in./min
Ab= l.20[(7.48)Lvaq(f,gF,g) - 38.4/(TC0)]- 1 (4-22) r = 3.4