Page 117 - Applied Process Design For Chemical And Petrochemical Plants Volume II

100 Applied Process Design for Chemical and Petrochemical Plants

V,in = Minimum fresh air flow based on slope of operat- XL = Mol fraction of feed as liquid, Scheibel-Montross
ing line, L/V, on x-y diagram xlo = Mol fraction light key in overhead expressed as
v = Vapor flowrate, mols/hr; or molar volume fraction of total keys in overhead, Scheibel-Mon-
W = Bottoms product, or still bottoms, or kettle bot- tross equation
toms, mols; also see B; or mols/hr bottoms prod- x, = Tray liquid mol fraction for start of calculations
uct; or mols of residue or bottoms/unit time (most volatile component)
(Ponchon heat balance) xo = Mol fraction of component, i, in bottoms B.ro at
W = Weight of material in vapor (steam distillation) start time, To; or VOC mol fraction
W1 = Mols final content in still x, = Mol fraction of feed as vapor, Scheibel-Montross
Wil = Contents of still pot or kettle at any point, 1, after equation
start for components, i, mols y = yi = Mol fraction of component in vapor phase, as
Wi, = Initial contents of kettle or still pot, mols, for may be feed, distillate, or bottoms; or Henry’s
component, i Law, yi = mol fraction solute in vapor
Wo = Mols liquid mixture originally charged to still pot yi = Mol fraction VOC component in the exiting
w = Pounds coolant per hour VOC contaminated air
= x = Mol fraction of component in liquid phase; y’ = Mol fraction of least volatile component
or mol fraction solute in solution (Henry’s Law) y* = Equilibrium value corresponding to xi
xf = xlF = Mol fraction of any component in feed, yn = Average light key mol fraction vapor leaving
vapor + liquid, F,; xf = Fxf/F, plate, n
x‘ = Mol fraction of least volatile component yn + 1 = Average light key mol fraction vapor entering
X‘I = XI - k plate, n + 1
= x - k
XI,, YN + 1 = Mol fraction VOC component in the incoming
x = dol fraction more volatile component in liquid fresh air (equals zero for fresh air)
XI = Mol fraction of component, i, in liquid mixtures yj = Mol fraction solvent component in vapor
as may be feed distillate or bottoms, ET, at any ys = Mol fraction steam in vapor
time, TI; or mol fraction more volatile in vapor Y~B = Percent recovery of, i, in the bottoms
entering column at any time (or in distillate) Yl~ Percent recovery of, i, in the distillate
=
Xit = Mol fraction liquid at intersection of operating Z = Compressibility factor
lines at minimum reflux, Scheibel-Montross Z~,F = Mol fraction component, i, in feed
equation zi,q = Mol fraction component, i, in feed, j
xhf = Mol fraction heavy key in feed zi,s = Mol fraction component, i, in sidestream
xn = Pinch composition any light component mol Zi,sk = Mol fraction component, i, in sidestream, k
fraction
XN = Mol fraction VOC component in the stripped
water exiting, usually targeted at meeting envi- Greek Symbols
ronmental regulations
Xl~ Mol fraction light key component in overhead a, a1 = Relative volatility of light key to heavy key compo-
=
product; or, any light component (Colburn) nent, or any component related to the heavy key
X~B = Mol fraction light key component in keys in origi- component, except Equation 8-65, ai is based on
nal charge heavy key
=
xio = Mol fraction light key in overhead expressed as aavg Average relative volatility between top and bot-
fraction of total keys in overhead tom sections of distillation tower/column
X1B = Mol fraction most volatile component in bottoms ai = Relative volatility of more volatile to each of
xhD = Overhead composition of heavy key component, other components (steam distillation)
mol fraction ai = Relative volatility of component, i
Xhn = Pinch composition of heavy key component, mol aH = Relative volatility of components heavier than
fraction heavy key, at feed tray temperature
xl = Mol fraction of component in liquid phase; or ai = Relative volatility of more volatile to each of
mol fraction more volatile component in vapor other components
entering column at any time aL = Relative volatility of components lighter than
xs = Mol fraction of a more volatile in kettle at time 0 light key at feed tray temperature
x,i = Value of x, when distillate receiver is first filled p = Constant of fixed pressure in Winn’s relative
xs0 = Mol fraction more volatile in kettle at time 0 volatility, Equation 8-43
x, = Mol fraction more volatile component in bottoms 0 = Time from start of distillation to fill receiver, or
residue (final); or, composition of liquid in still, value of relative volatility (Underwood Parame
mol fraction ter) to satisfy Underwood Algebraic Method
xwo = Initial mol fraction of more volatile component 01 = Time for filling distillate receiver, hrs
in liquid mixture 02 = Time for refluxed distillation (batch), hrs
XF = Mol fraction more volatile component in feed p =Viscosity, centipoise
XD = Mol fraction more volatile component in final u = Activity, coefficient
distillate = mol fraction in distillate leaving con- n; = total system pressure, absolute; atm, mm Hg, psia
denser at time 0 x = 3.14159
xp = Mol fraction of more volatile component in liq- Z = Sum
uid leaving column at any time I) = First derivative function