Page 232 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 221

Some of this condition can be attributed to surging or A’, = Total reversal area per tra ft2
“burping” inside and creating pressure surges under a, = Annular area per cap, in. ?
increased pressure. Other conditions of mechanical dam- a, = Inside cross-section area of cap, in.2
age include nuts coming off bolts, and tray metal and welds = Cross-section flow area, minimum, of down-pipe
clearance area between tray floor and down-pipe
cracking at or near supports, corrosion of tray sections and bottom edge, or up-flow area between outer cir-
welds is often caused by pressure pulsations from the tray cumference down-pipe and any inlet tray weir, in.2
action creating vibration and “autepulsations” of the trays a, = Individual hole area per hole on sieve tray, in.2
producing resonant or near resonant conditions at or near a, = Riser inside cross-section area per riser, in.2
a,‘ = Reversal area per cap assembly, in.*
the tray’s first or second natural frequencies [214]. Winter a,, = Riser outside cross-section area, based on O.D., in.2
[ 2141 presents rough estimating correlations for predict- per riser
ing natural frequencies and deflection of trays. a, = Slot area per cap, in.2
At = Total tower crosssectional area, ft2
Troubleshooting DistjJlation Columns ALM = Maximum valve open area, ft2
a, = Smaller area value, a, or a,, for use in Equation
8-231 or 8-233
To respond to difficulties during operation of distilla- B, = Dimensionless group identifier
tion columns a very careful and itemized analysis must be C = Factor for Souders-Brown maximum entrainment
made of (a) the process, (b) the mechanical details of the relation; or
column, and (c) the instrumentation for operation and = Empirical constant in CCFL correlation
control. A good column performance designer is general- Cd = Liquid gradient factor
ly in an excellent position to examine the operating per- C, = Specific heat, Btu/lb-”F
CF = Flooding capacity factor, ft/sec
formance and diagnose the nature and specific location of C1 = Constant in heat transfer Equation 8-328 = 0.0025
the conditions that may be preventing or contributing to CL = Liquid phase loading factor, ft/sec, Equation 8-282
good column performance. This often may involve C, = Orifice (vapor discharge) coefficient for dry tray,
detailed computer studies of data compared to tray-by-tray Figure 8-128, or 8-129, respectively
performance. CSB = GFactor at flood (Souders-Brown coefficient),
ft/sec (or, m/sec); or
It is beyond the scope of this text to thoroughly exam- = Souders-Brown flooding constant defined by Equa-
ine this subject; however, there are several good references tion 8-286
(but not all inclusive) including Hasbrouck, et al. [215] C, = Capacity factor based on tower area, ft/sec
and Kister [117]. CT,flood = Capacity factor at flood, ft/sec
C, = Liquid gradient vapor load correction factor; or
= Discharge coefficient (see accompanying table); or
Nomenclature for Part 3: Tray Hydraulics Design = Gas phase loading factor, ft/sec, Equation 8-281
C,v = Eddy loss coefficient, dimensionless, Table 8-22
A = AT = Total cross-sectional area of tower diameter, C, = Wet cap pressure drop correction factor, Figure
ft“ 8-115
Ad = Total annular cap area per tray, ft2; or c = Hole spacing center to center, in.
= Active or “bubbling” area of tray, generally (At - D = DT = Tower inside diameter, ft
2&), ft2 see Figures 8-1 19 and 8-129 Df = Total flow width across tray, normal to flow, ft
AB = Bubbling area; column area minus total of down- DH = Hole diameter, in.
comer and downcomer seal areas, ft2 or m2 DHE = Equivalent hole diameter, in.
4 = Total cap area inside cross section area per tray, ft2 DV = Valve diameter, in.
= Downcomer area, crosssectional area for total liq- d = Column diameter, (m)
uid down-flow, ft2; or, d, = Inside diameter of cap, in.
= Ytinimum flow area at bottom (under) of down- dh = Diameter of weep hole, in. Note that this is the
comer per tray, ft2 diameter equivalent to area of all weep holes per
Af = Fractional hole area (actual hole area/bubbling tray; or
area, AB) = Hole diameter, in. (or mm)
Ah = Net perforated area of tray, ft2 do = Hole diameter, in.
AH = Total hole area, ft2 d, = Inside diameter of riser, in.
An = Net open liquid area of one tray, equal to total dv = Diameter of valve unit at narrowest opening, mm
tower section minus area occupied by caps and ris d, = Diameter of circular weir, in.
ers and minus area of se mental or other down- Ed = Dry tray efficiency, fraction
8
comer at outlet of tray, ft ; or Ev,~ =Wet tray efficiency, fraction
= Net area, column area minus area at top of the e,$ = Weight of liquid entrained per unit weight of vapor
d,wncorners, m2 flowing, lb/lb
bp Open area of tray, ft2 f = Aeration factor (usually = 1.0); or
=
= Total slot area per tray, ft2 = Friction factor for froth cross flow, Equation 8-253
= ~otal tower cross-section area, ft2 fhg = Friction factor for liquid gradient, cross-flow for
A, = Total riser inside area per tray, ft2 sieve trays