HW 7 - p 9.18 - Distillation of Chlorination Reactor Effluent : Fenske-Underwood (class 2)-Gilliland - 10 pts
Please post all of your questions about this problem as comments on this post. I will respond with my own comments.
posted by Dr. B at 5:49 PM
6 Comments:
What should we put for the q value?
Va:
The feed is a saturated liquid, so q = 1.
I remember you said in class that N~8 and NR~5 and NS~3. However, there is an equation that is N = 2(part reboiler + part condenser) + 1(feed) + NR + NS. Are the part reb and cond and feed stage accounted for in the values you gave for NR and NS (5 & 3)?
If so, how do you determine if the feed is in the RS or in the SS?
Lastly, should you round N to the nearest stage (or higher stage?) before you calculate NR and NS or leave it as a decimal?
Thanks,
Karen
anon / Karen:
This can get confusing. As far as Kirkbride is concerned, a partial reboiler is part of the rectifying section and the reboiler is part of the stripping section. But when you build a column, the condenser and reboiler are NOT part of the column. See slide 18 in my powerpoint. The picture there is worth at least 1000 words here.
i got a different answer from yours for bC2H6 - i got 0.132 kmol/h.
i calculated this using b=Fz/(1+di/bi) where di/bi = 75. was this incorrect? I don't know how you got 0.516 kmol/ but my answers for Nmin, Rmin, and N at 1.5Rmin matched yours
anyways, this led to a different value for the feed stage because i got Nrs/Nss = 0.55 and the feed stage being 1.93 instead of 4 like in your notes.
pb&j:
I think you must have done something wrong. I think I know what, but I am not sure. Here is the problem. You say you used: b=Fz/(1+di/bi) where di/bi = 75 but I THINK you meant to type it Eqn 9-15 on pg 349, which is: b=Fz/(1+(di/bi)*alpha{i,HK}^Nmin)
But the HK is C2H5Cl and not C2H6.
Other students have told me they used this eqn and got slightly different answers than I did. BUT YOU CANNOT use eqn 9-15 here because d{HK} / b{HK) IS NOT = x{D,HK} / x{B,HK) because D IS NOT = B !
You cannot solve this part of the problem using just material balances as you seem to have done and you cannot solve eqns 9-15 and 9-16 without iterations (think solver or your calculator).
Best of luck,
Dr. B
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