Page 105 - Applied Process Design For Chemical And Petrochemical Plants Volume II

94 Applied Process Design for Chemical and Petrochemical Plants

Drickamer and Bradford curve, E, = 46% 1. Assume or set condenser liquid product temperature,
O’Connell curve, E, = 53.8% tD.
2. Calculate condensing pressure, with tD as bubble
In this case, recommend using: point (if subcooling exists, and tD is below bubble
point, use bubble point temperature for pressure cal-
E, e (46 + 53.8)/2 = 49.6% culation only).
3. Vi = L + D
Actual trays in column:
+
HlVl= [L h~ + D h~] (8-184)
Nact = 20/0.496 = 40.3 trays
-
From tray-by-tray calculations, feed tray is 10/0.496 = (8 185)
20.1 trays from bottom, use 20.
Generally, practice would be to select a column allowing
a few extra trays, making column total trays = 45.

No.
Rectifying trays = 22
Feed =1 4. Calculate tl and xi by dew point on vapor VI. Then
Stripping =22
45 determine HI, referring to top tray as number one in
this case.
Feed nozzles should be located on trays Nos. 21,23, and where HI= total vapor enthalpy above reference datum
25 counting up from the bottom tray as No. 1. for sum of all contributing percentages of
individual components, i, in stream, Btu/lb,
Heat Balan-Mjacent Key sgstems with Sharp or Btu/mol
Separations, Constant Molal Overflow hD = total liquid enthalpy above reference datum
for sum of all contributing percentages of
Total Conhser Duty individual components, i, in product stream.
(Also same as reflux), Btu/lb or Btu/mol.
Refer to Figure 8-53 (System (1)).
5. For partial condenser: replace DhD by DHD in Step 3.
A dew point on compositions of yD (vapor) give tD or
total pressure. Also get liquid composition XD (liquid
reflux in equilibrium with product vapor YD. Over-
head vapor is sum of compositions of n, and xp. A
dew point on this vapor (overhead from tray one
I------------- 1 top)) gives top tray temperature, tl.

Reboiler Duty

Refer to Figure 8-53 (System (2))

1. Determine bottoms temperature by bubble point on
liquid XB.
2. From feed condition determine enthalpy.

3. Solve for Qg, reboiler duty, Btu/hr
L ___---------- F hF + QJ = DhD + BhB + Qc (8 - 188)
J
where hn = total enthalpy of distillate product, Btu/mol
-
*.
Figure 8-53. Heat balance diagram. or Btu/lb