Page 215 - Separation process engineering

Range("A8", "G108").Clear
Dim i, feedstage As Integer
Dim D, B, xd, xb, F, z, q, LoverD, LoverV, x, y, xint, yint, yeq
As Single
Dim a6, a5, a4, a3, a2, a1, a0, L, V, LbaroverVbar As Single
' Input values from spread sheet
xd = Cells(1, 2).Value
xb = Cells(1, 4).Value
F = Cells(1, 6).Value

z = Cells(1, 8).Value
LoverD = Cells(2, 2).Value
q = Cells(2, 4).Value
feedstage = Cells(2, 8).Value
' Fit VLE data to 6th order polynomial to find y. a6 is
coefficient of x to the 6th.
a6 = Cells(5, 1).Value
a5 = Cells(5, 2).Value
a4 = Cells(5, 3).Value
a3 = Cells(5, 4).Value
a2 = Cells(5, 5).Value
a1 = Cells(5, 6).Value
a0 = Cells(5, 7).Value

' Calculate flow rates and ratios.
D = ((z - xb) / (xd - xb)) * F
L = LoverD * D
V = L + D
LoverV = LoverD / (1 + LoverD)
LbaroverVbar = (LoverV + (q * F / V)) / (1 - ((1 - q) * F /
V))
' Calculate intersection point of operating lines. If yeq < yint
reflux ratio too low.
xint = ((-(q - 1) * (1 - LoverV) * xd) - z) / (((q - 1) *
LoverV) - q)
x = xint
yint = LoverV * xint + (1 - LoverV) * xd
' Equilibrium y at value of x intersection. When yint=yeq, have
minimum L/D.
yeq = a6 * x ^ 6 + a5 * x ^ 5 + a4 * x ^ 4 + a3 * x ^ 3 + a2 *

x ^ 2 + a1 * x + a0
'Record intersection and equilibrium values on spreadsheet.
Cells(6, 2).Value = yeq
Cells(6, 4).Value = yint
Cells(6, 6).Value = xint
' Step off stages from bottom up. Stage 1 is partial
reboiler. Initialize
x = xb
i = 1