GROUP B
FALL 2002
DISTILLATION STARTUP
Pre-Lab:
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Fill out paperwork for the lab-technicians to startup the distillation
column at total reflux for the day of experimentation.
Initial Checklist:
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Verify column is at steady state. The guidelines for steady state
are listed in Determination of Steady State.
Verify the reflux tank level exceeds 20% in Labview, or ¼ of the
reflux tank meter, otherwise see Reflux/Reboil Tank Level
Adjustments.
Verify the reboil tank level is within the designated “green” zone,
otherwise see Reflux/Reboil Tank Level Adjustments.
Verify the temperature profile of the column is similar to that
shown in Figure 1A, initial. If the reboiler temperature exceeds 91
ºC, It will be necessary to reduce the temperature of the reboiler.
Refer to Reboiler Temperature Reduction for instructions.
Select the 9th feed tray by turning the valve on. The valve handle
on the 9th tray must be horizontal. Verify that no other feed tray is
turned on, i.e. the other feed tray valve handles are vertical.
Turn the feed direction valve, located above the feed tank, to
“Feed”. Note: The feed direction valve usually set initially to
“Reboiler”.
After completion of the initial checklist proceed to the Start-up
Procedure.
Determining Steady State:
Total Reflux:
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Tray temperatures do not change more than 1 degrees in 5 minutes.
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Reflux tank level does not change more than 1% in 5 minutes.
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Reboil tank level does not change more than 1% in 5 minutes
Continuous:
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Conditions from Total Reflux must be satisfied.
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Feed, Distillate, and Bottoms streams must be balanced.
Reflux/Reboil Tank Level Adjustments:
Reflux Tank Level High:
Reflux Tank Level Low:
Reboil Tank Level High:
Reboil Tank Level Low:
Notes:
Increase distillate valve setting.
Decrease distillate/reflux valve setting.
Increase bottoms valve setting.
Decrease bottoms/steam valve setting.
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If both tanks are low or decreasing valve settings do not
significantly change the tank levels, a feed stream may be added to
increase the volume of liquid in the column.
If the reboiler needs additional liquid quickly, the feed direction
valve may be changed to send the feed directly into the reboiler.
Make sure that the feed valve is turned OFF while changing the
feed direction valve. This should only be done between runs
due to the drastic changes that will take place in the column.
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Reboiler Temperature Reduction:
1. Make sure that the feed and steam valves are set to 0.
2. Turn the feed direction valve, located above the feed tank, to
“Reboiler”. The feed will now be sent directly to the reboiler and
not to the feed tray.
3. Set the feed/bottoms valves to 50 and 25 respectively. Pay close
attention to the level in the reboiler. Adjustments may be
necessary if the level changes more than +/- 2% or approaches the
limits of the “green” zone. To raise/lower the amount of liquid in
the reboiler, decrease/increase the bottoms valve setting
respectively. The optimal reboiler level is approximately 39%.
The temperature of the reboiler will usually appear to fall below 85
ºC. This is a false reading due to insufficient mixing of the cold
feed and hot reboiler liquid.
4. After a couple of minutes set the feed and bottoms valves to 25 and
~10. Watch the temperature of the reboiler closely. If it should
begin to rise above 91 ºC, step 3 must be repeated.
5. Once the temperature of the reboiler begins to slow its approach to
steady state, set the feed and bottoms valves to 0.
6. If the temperature begins to approach a steady state temperature
lower than 91 ºC, let the column come to steady state according to
Determining Steady State, and return to the initial checklist.
Start-up Procedure:
Note:
The specific values in this manual, used to determine times at
which valve settings must be changed, pertain specifically to the
steady state achieved with final valve settings of:
Steam: 25
1.
Feed: 42
Distillate: 32
Bottoms: 25
The column should be in total reflux at steady state with the initial
valve settings of:
 Steam: 31.1
Feed: 0
2. Set steam valve to 100.
 Steam: 100
Feed: 0
3.
Reflux: 44
Reflux: 66
Distillate: 0
Bottoms: 0
Reflux: 66
Distillate: 0
Bottoms: 0
At ~90.5-91 ºC set the feed valve to 42, ~13 minutes to step 3.
 Steam: 100
4.
5.
Feed: 42
Reflux: 66
Distillate: 0
Wait for the temperature profile to be approximately that of the
steady state position, shown in Figure 1B, transition. This will
occur approximately when the reboiler temperature has reached its
steady state temperature, ~92.0-93.0 ºC. However it is necessary
to make sure that the rectifying section trays have surpassed their
respective steady state temperatures to create a convex curve
demonstrated in Figure 1B, transition. It is also necessary to
ensure that the stripping section trays have reached or are slightly
elevated from their respective steady state temperatures. The Tray
7 temperature is the decisive condition for the final transition.
Once the prior conditions are met, tray 7 will begin to increase
significantly past its steady state temperature, ~68.5-69.0 ºC. DO
NOT let the stripping section tray temperatures raise more than 1-2
ºC above their respective steady state temperatures. At this point
change the steam, reflux, distillate, and bottoms to the following,
~4 minutes from step 3 to step 4:
 Steam: 25
Feed: 42
Reflux: 44
Distillate: 33
Bottoms: 25
Let the system come to steady state, ~7 minutes from step 4 to step
5. Verify according to Determining Steady State.
A) Initial
B) Transition
C) Final
Temperature Profiles on Startup
100
o
Temperature ( C)
Bottoms: 0
90
80
70
60
50
0
2
4
6
8
10
12
14
Tray Number
Figure 1. Typical temperature profiles during startup with only steam or feed/steam together.
A) Initial profile at time 0. B) Transition profile at a t when the final valve settings are set. C)
The final steady state profile achieved when both the profile and the reflux/reboil tank levels
are constant.
Troubleshooting/Helpful Hints:
 If the initial reboiler temperature is above that of the steady state,
and specifically 91 ºC in this experiment, follow the steps outlined
in Reboiler Temperature Reduction.
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If the temperature profile is allowed to pass the transition profile
outline in Figure 1B, two possible solutions exist:
I If the temperature profile of the rectifying section appears
horizontal, then follow Reboiler Temperature Reduction. Instead
of aiming for a temperature lower than 91 ºC the target temperature
will be the steady state reboiler temperature of ~92.5 ºC.
II If the temperature profile is only slightly above the target
transition profile, then the column can be left to arrive at steady
state over a longer period or forced down by following the steps in
Reboiler Temperature Reduction with a target temperature of
~92.5 ºC.
Reflux/Reboil tank levels must be closely watched and may be
adjusted according to Reflux/Reboil Tank Level Adjustments.
BE SURE TO TURN ON THE DATA LOGGING SYSTEM.
Pay extreme attention to the profile changes early on. Experience
in determining transition times is critical to reducing the column
startup time.
G.C. Calibration
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Make up methanol/water solutions with concentrations of 5, 20, 40, 60, 80, and 95
mole percent methanol.
Run each solution through the G.C. noting the peak areas for water and methanol
(methanol will be the first peak).
Plot concentration versus peak area for both water and methanol.
Linearly regress the data and use the resulting equation to accurately determine
concentrations from future G.C. runs.