Page 116 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 105

L = Liquid flowrate return to tower as reflux, lb ps = Partial pressure of steam, mm Hg
mols/hr, mols component in liquid phase; or, LI, QB = Net heat in through reboiler, reboiler duty,
L2 = Latent heat of vaporization; or, volumetric Btu/hr; or heat added in still or bottoms
flowrate for incoming contaminated water (strip- Qc = Net heat out of overhead condenser, Btu/hr, =
ping VOC with air) ; or mols liquid produced w cp (ti - to)
from F per unit time, leaving flash zone q = qF = Thermal condition of feed, approximately
L, = Liquid flowrate down rectifylng section of distilla- amount of heat to vaporize one mol of feed at
tion tower, lb mols/hr feed tray conditions divided by latent heat of
L, = Liquid flowrate down stripping section of distilla- vaporization of feed
tion tower, lb mols/hr q, = Thermal condition of sidestream (s)
LK = Light key component in volatile mixture R = Reflux ratio = External reflux ratio for a given
L/V = Internal reflux ratio separation, = L/D, L = liquid rectifylng column
L/D = Actual external reflux ratio R = Actual reflux ratio, O/D
d/D)min = Minimum external reflux ratio R, = Minimum reflux ratio, O/D
M = Molecular weight of compound R = Pseudo minimum reflux ratio
M, = Total mols steam required Rmin = Minimum external reflux ratio for a given
m = Number of sidestreams above feed, n separation
N = Number of theoretical trays in distillation tower RF = Feed component of minimum reflux
(not including reboiler) at operating finite RF, , = Feed component of minimum reflux for feed, n
reflux. For partial condenser system N includes ROF = Other feed components of minimum reflux
condenser; or number theoretical trays or trans- & = Sidestream component of minimum reflux
fer units for a packed tower (VOC calculations) rps = Ratio of light to heavy keys, stripping pinch
NB = Number of trays from tray, m, to bottom tray, but rpr = Ratio of light to heavy keys, rectifylng pinch
not including still or reboiler
Nmin = Minimum number of theoretical trays in distilla- rf = Ratio mol fraction light key to healy key in feed
tion tower (not including reboiler) at total or S = Steam flowrate, lb/hr or lb mols/hr; or theoreti-
cal stages at actual reflux (Figure 8-24) including
infinite reflux. For partial condenser system, reboiler and partial condenser, if any; or batch,
Nmin includes condenser; also, minimum value of
N mols in mixture in still kettle at time 0
N, = Number of theoretical trays above feed, or refer- S, = Theoretical stages at minimum reflux
ence plate, n, but not including n SM = Minimum theoretical stages at total reflux from
Nm = Number of theoretical trays before feed tray bottoms composition through overhead product
Nim = Mols of immiscible liquid composition, including reboiler and any partial
No = Mols of non-volatile material present; or, number condenser (if used); or minimum stripping fac-
tor at minimum flowrate of air
of theoretical trays/stages in column only, not Sk = Flowrate of sidestream, k, mols/hr
reboiler or condenser
N, = Mols of steam So = Theoretical stages at a finite operating reflux; or
n = Number of theoretical trays in rectifylng section batch, mols originally charged to kettle
or number of components, or minimum number S, = Theoretical stages in total rectifylng section,
of equilibrium trays including partial condenser, if used
nf = Number of feeds S, = Theoretical stages in total stripping section,
n, = Number of sidestreams including reboiler
P = Pressure, atmospheres; or, vapor pressure of com- St = Theoretical trays/stages at actual reflux, L/D,
ponent, am.; or, P = number of phases; or, P = including reboiler and total condenser
for batch operations, percentage draw-off Sopt = Optimum stripping factor
Pi = Vapor pressure of each component (SR)i = Separation factor
P, = Vapor pressure of steam, absolute s = Pounds (or mols) steam per pound (or mol) of
Pb = Vapor pressure of reference more volatile compe bottoms; or flowate of sidestream, mols/hr
nent, b T = Temperature, "Abs R
p = pi = Partial pressure of one compound in liquid, tB = Bottoms temperature, "F
absolute units, or, ratio r /r also, pi = partial ti = Temperature in, "F
ps
pressure of solute (Henry s I%) to = Temperature out, "F; or overhead temperature,
p = Total pressure of system = TC "F
p' = Number of trays below feed where introduction V = Vt = Total vapor leaving flash zone/unit time at
of light components should begin, Akers-Wade specific temperature and pressure; or total over-
calculation method head npor from tower, mols/hr; or mols of com-
pi* = Vapor pressure component, i, in pure state at ponent in vapor phase; or volumetric flowrate for
temperature - incoming fresh air
pii* = Similar to above by analogy V = Quantity of vapor, mols
p" = Number of trays above feed where introduction V, = Vapor flowrate up rectifymg section of tower, lb
of heavy components should begin. hers-Wade mols/hr
calculation V, = Vapor flowrate up stripping section of tower, Ib
pim = Pure component vapor pressure of immiscible mols/hr; or mols non-condensable gases entering
liquid, mm Hg with feed, F, and leaving with vapor, V/time