Page 246 - Separation process engineering

If xA < 0 Or xB < 0 Or xC < 0 Then
Cells(i + 13, 3) = "Feed stage too high"
Exit For
End If
i = i + 1
' Test for too many stages, which may mean reflux rate is too low.
If i > 100 Then
Cells(i + 12, 2).Value = "Too many stages"
Exit For

End If
yA = (LbaroverVbar * xA) - (LbaroverVbar - 1) * xAbot
yB = (LbaroverVbar * xB) - (LbaroverVbar - 1) * xBbot
yC = (LbaroverVbar * xC) - (LbaroverVbar - 1) * xCbot
' Test for calculations being done.
Loop While xC < xCbot
' Fractional recovery of A based on stage-by-stage calculation
with stage
' calculation using fractional stage, which is an approximate
calculation. With very
' few stages this can be inaccurate. In this case adjust L/D so
that frac is close
' either 0 or 1.0.

frac = (xCbot - xCold) / (xC - xCold)
xCcalc = xCbot
' Assume that frac calculate for C is also valid for A and B.
xAcalc = (xA - xAold) * frac + xAold
xBcalc = (xB - xBold) * frac + xBold
' Calculate new frac recovery of A in distillate from estimated
bottoms calculation.
' Calculation is damped to prevent excessive oscillation.
fracAdistcalc = 1 - (xAcalc * B) / (F * zA)
difference = fracAdist - fracAdistcalc
fracAdist = fracAdist + df * (fracAdistcalc - fracAdist)
' Test if have convergence of fractional recovery of A.
If Abs(difference) < epsilon Then Exit For
Next j
Cells(i + 14, 1).Value = "Calc frac recovery A in distillate"
Cells(i + 14, 5).Value = fracAdistcalc

Cells(i + 14, 6).Value = "j"
Cells(i + 14, 7).Value = j
' Calculate and record on spreadsheet mass balance results and
error in mass balance.
Cells(i + 15, 1).Value = "Mass bal: frac, A, B, C at bot, % error
B"
Cells(i + 16, 1).Value = frac
Cells(i + 16, 2).Value = xAcalc
Cells(i + 16, 4).Value = xBcalc