Page 234 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 223

Q = Liquid load, gpm = L w1 = Weir length, in.
Rh = Hydraulic radius for Loth cross flow, ft w, =Width of slot (rectangular), in.
& = Ratio of top to bottom widths of trapezoidal slot, z = Characteristic length in CCFL model, ft
bubble cap dimensions
&, = Vapor distribution ratio, dimensionless Greek Symbols
K7,. Ratio valve weight with legs/valve weight without
=
legs, dimensionless, see Table 8-22
Re], = Reynolds Number modulus a = Relative volatility, dimensionless
&I, = Reynolds modulus for friction cross-flow ad = Mean aeration factor of froth (dimensionless)
-
A’r = Liquid gradient per row of caps, uncorrected, in. a = Relative froth density, hI/hf
S‘ = Effective tray spacing, distance between top of f3 = Fraction perforated or open hole area in perforat-
foam, froth, or bubbles and tray above, in. Note: ed area of tray (not fraction hole area in tower
for Hunt’s relation, S’ = tray spacing minus 2.5 h, area); or
Sc = Schmidt number, dimensionless = Aeration factor, f, dimensionless
S” = Same as S’, except unit, ft h = Slope of equilibrium line/slope of operating line
St = S = Tray spacing (actual), in. ft, m A = Liquid gradient (corrected) for tray or tray section,
St, = Tray spacing, ft in.
s = Cap skirt clearance between cap and tray floor, in. A’ = Uncorrected liquid gradient for tray or tray sec-
T, = Metal thickness of valve, in. tion, in.
t,“ = Liquid throw over weir, in. AIr = Liquid gradient per row of caps, uncorrected, in.
U = Superficial vapor velocity, m/sec 4 = Relative froth density, ratio of froth density to clear
UN = Vapor linear velocity based on net area for de- liquid density
entrainment usually tower cross-section minus one E = Eddy kinematic viscosity, m2/sec (assumed equal to
downcomer, ft/sec eddy diffusivity; see Ref. 2
La = v, = Vapor velocity based on active area, A,, ft/sec 8 = Time to drain tower, min
V = Total vapor flow through tray or tower, ft3/sec ~r. = Viscosity of liquid at tower temperature,
V‘ = Internal vapor flow, lb/hr or lbs/sec, Equation centipoise, cp
8-297 1.11 = Viscosity of liquid, lb/ft-sec
VG = Superficial gas velocity in channel (not tower), JI = Pi = 3.14
ft/sec 9 = Entrainment expressed as fraction of gross down-
Vload = Vapor load corrected for density, ft/sec flow
V, = Maximum allowable vapor load per tray, ft3/sec p = Liquid density at tem erature of tower, gm/cc
17, = Superficial vapor velocity in tower, ft/sec (based on PL = Liquid density, lbs/ft s , or kg/m3
tower cross-section)
pv = Vapor density, lbs/ft3, or kg/m3
Vd = Design hole vapor velocity, ft/sec; or pm = Valve metal density, 1b/fr3
= Downcomer velocity, ft/sec
vdu = Velocity of liquid flowing between segmental down- o = Surface tension of liquid, dynes/cm
comer and inlet weir, ft/sec
vf = Vapor velocity through equivalent net tray area, Subscripts
based on tower area minus twice downcomer area,
ft/sec; also F = Flood = At flood point
= Velocity of froth cross flow, ft/sec g=G=Gas
v’f = Velocity of froth, ft/sec H20 = H = h = Water
Vflood = Gas superficial velocity based on tray net area, A,, L = 1 = Liquid
ft/sec OG = og = Overall (gas concentration basis)
vh = Vapor velocity through valve hole, ft/sec Vap = vap = Vapor
vPt = v, = Vapor velocity through holes, ft/sec
v,%. = U, = Linear velocity of gas based on window area,
ft/sec References
v,, = Minimum velocity through holes at weep point,
ft/sec 1. Akers, W. W. and D. E. Wade, “New Plate-to-Plate Method,”
W = Maximum allowable mass velocity through column Pet. Re? V. 36, p. 199 (1954).
using bubble cap trays, lb/(hr) (ft2 tower cross sec- 2. American Institute of Chemical Engineers, “Bubble Tray
tion) Design Manual, Prediction of Fractionation Efficiency,”
We = Liquid entrainment mass velocity, lb entrain- her. Inst. Chem. Engrs. (1958).
ment/(min) (ft2), based on net tray area of tower 3. Biggers, M. W., private communication.
minus twice downcomer area 4. Bogart, M. J. P., “The Design of Equipment for Fractional
W‘, = Assumed allowable liquid entrainment mass veloci- Batch Distillations,” Tram. A.1.Ch.E. \J. 33, p. 139 (1937).
ty derived from assumed allowable loss mols liq- 5. Bolles, W. L., “Optimum Bubblecay Tray Design,” Pet. fie
uid/mol vapor, Ib/hr (ft2), based on net tray areas cessing; Feb. through May 1956.
same as for We 6. Boston and Sullivan, Canadian Jou7: of Chem. Engx V. 50, Oct.
W*, = Liquid entrainment mass velocity corrected for liq- (1972).
uid properties and plate spacing, lb entrain- 7. Broaddus, J. E., A. J. Moose, R L. Huntington, “How to
ment/(hr) (ft2), based on net tray area as for We Drain Bubble Cap Columns” Pet. Re$, Feb. (1955).