Goals for continuous distillation using the West column: 1. Determine the overall efficiency of the system by comparing the actual number of stages

with the theoretically calculated number using the experimental data. 2. Determine the local efficiency at certain plates. 3. Study the effect of reflux ratio on the concentration of the top and bottom product. 4. Operate of the continuous distillation column with a given reflux ratio and feed composition,

and predict the output concentration with the modified a McCabe-Thiele diagram. Week 1 Experiment: run the column with the total reflux condition and determine the overall and local efficiencies. Overall efficiency can be calculated by comparing the actual number of plates in the column with the number of plates obtained from McCabe-Thiele diagram when the column operated at total reflux. Local efficiencies can be calculated by measuring the compositions of the liquid streams corresponding to two successive plates. Week 2 Experiment: run the distillation column with two different reflux ratios. These two chosen refluxes have to be higher than the minimum reflux ratio, which can be calculated from the slope of the rectifying (enriching) line in the modified McCabe-Thiele diagram. After the steady state condition been established, the composition of feed tank and top condensor can be used to determine the appropriate position of the feed plate. Week 3 Experiment: run the distillation column with a feed rate and certain reflux ratio given by TA. Based on the characteristics of the column obtained in week 1 and 2, you need to predict the output concentrations using both modified McCabe-Thiele diagram and enthalpy verses x and y diagram.

General Operation Procedures Preparation for Start-up: Key purposes:

Get familiar with the system; locations of the valves and sample taps Check the liquid level in the reboiler Check the composition in the reboiler and feed tank Turn the Siemens system on Check the valves in the correct position

Preparation for Start-up 1. Ask the TA/Lab Assistant to turn on the computer system hooked to the West column. 2. Turn on the reboiler mixing pump. Let the contents of the reboiler mix through the recycle

line for at least 10 minutes. To turn on the reboiler mixing pump, use the computer system: click on the pump symbol near the bottom of the reboiler; a window will pop up; make sure the pump is in “Manual” mode—if not, click on “Manual”; click “Start” and close the window.

3. Close the valve above the bottoms rotameter (see Figure 6). 4. Check the reboiler level on the computer and on the sight-glass. Anything between 25 to 30 inches is fine for operation. If the level is too high or too low, seek assistance from the TA/Lab Assistant. 5. Checks that the green gate valve leading to the computer-linked steam pressure gauge is

fully open (see Figure 7 – it’s red in the picture…). 6. Take a sample from the reboiler.

a. Obtain a sample tube from the small ventilated area that you pass through to get to the control room.

b. Open sample tap on the bottoms line to take sample (see Figure 5). 7. Determine the composition of the reboiler using the GC. 8. Think about when and where you will want to take samples during operation. Sample taps

are available at the reboiler/bottoms line (Figure 5), reflux/distillate line (Figure 1), and at each tray.

Reflux Control valve

Reflux Manual bypass valve

Distillate Sample tap

Figure 1: West Column Reflux line

Red Valve on the Reboiler Recycle line ReboSight Glass

Steam Valve

Steam Bypass Manual Valve

Reboiler Recycle line Figure 4 – West Colum Reboiler

Start-up 1. Ensure that the reboiler has enough material and then turn on the air for the 1

st floor by

manually opening the air valve fully. The exact position of the valve is shown in Figure 7. Air is needed to operate pneumatic control valves.

2. Turn the water on for the 1st floor by manually opening the water valve fully. The exact

position of the valve is shown Figure 6. Water is needed for cooling purposes. Water valves by convention are blue in color.

3. Turn on the steam from the 1st floor by manually opening the steam valve fully and then turn a quarter back. The exact position of this valve is shown in Figure 8. Steam is required for heating purposes. Kindly note the sequence of turning on the utilities, it is air first (no cost) followed by water (somewhat expensive) followed by steam (highly expensive). The sequence will be exactly reversed while turning them off. The rationale is to cut-off the steam and save the operating cost as much as possible.

4. Ask the Lab Assistant/TA to purge the steam lines using the steam purge valve located on the 1st floor and shown in Figure 8. While the lines are being purged, the students should have fingers in their ears and should not be directly facing the outlet of the purge line. The Lab Assistant/TA should have ear plugs. The ear plugs should necessarily be discarded after one use.

Figure 8. Steam purge line.

5. Repeat steps 1 and 2 on 2nd floor. i.e. turn on the air for the 2nd

floor by manually opening the air valve fully. The exact position of the valve is shown in Figure 9. Also, turn on the water for the 2

nd floor by manually opening the water valve fully. This valve is a large

blue valve located at the base of the water rotameter. The exact location of the valve is shown in Figure 10. (But according to me, Figure 10 does not show the correct v10.

6. Then go to the Control Room. One of the computer systems is hooked to the West Column. The system would have already been made on by the Lab Assistant/TA. The computer screen will indicate values of different process parameters like temperature, pressure and flow rates as well as the positioning of different valves. Note that the values of some of the parameters might not be correctly shown on the screen due to some or the other reason and typically such values will be grayed out. Set the “Steam/PID” on the screen to somewhere between 20 to 30%. Usually 25% is a good start. You will slowly see a rise in the temperature of the liquid in the reboiler and the pressure. You should see the boiling of the liquid in some time. Allow a stable level to be attained in the sight glass. Set the “Reflux/PID” to a 100%. Now, it essentially means that you are operating the column at total reflux. In case, you see the column flooding meaning the sight glass getting overfilled, turning on the “Reflux Pump” momentarily helps it to get stable. When the “Reflux Pump” turns on, it will be indicated in green. Reducing the % in the “Steam/PID” also helps to lower down the level of the material in the sight glass. The general start up procedure followed is the same during all the three weeks. However, from week 2 onwards, it is suggested to check if the feed tank located on the 3rd floor has enough material before starting the experiment. Also, collecting the feed sample from the feed tank and getting information on its composition upfront will be useful in deciding the appropriate plate on which feed should be introduced. 7. After the level of the material in the stand pipe is at a fairly stable for some time, check if the system has attained steady state or not. This can be done by measuring the composition of one of the streams (reflux is the easiest because it is located on the first floor) as a function of time. When the composition changes by less than 5% with time, the system can be considered in a steady state condition. The reflux sample port is located on the second floor. 8. From week 2 onwards, feed has to be introduced in the column. For this, it is important to measure the composition of the feed by drawing off the sample from the feed tank on the 3rd floor and thereby identify the appropriate feed plate. Once the feed plate is identified, turn on the feed pump located on the 3rd floor and position the valves such that feed is introduced. If feed is being introduced, the feed rotameter will indicate a value corresponding to the flow rate of the feed.

Notes: All composition measurements are done with a Perkin Elmer Gas Chromatography

instrument in the Lab. Get help from the lab assistant on using it.

Figure 9. 2nd floor air line.

Figure 10. 2nd floor water lines.

Drawing off Distillate Product 1. Check the levels in the two distillate tanks by checking the sight-glass on the tanks. Usually

they will be empty. In case, they are full or nearly full, seek assistance from the Lab Assistant/TA.

2. Make sure the red manual valves at the bottom of both tanks are closed (see Figure 2). 3. Select a tank for the distillate product. 4. Open the red manual valve at the top of the tank selected for distillate (see Figure 2). 5. Make sure the red manual valve at the top of the other tank is closed (see Figure 2). 6. Monitor distillate tank level visually using sight-glass (see Figure 2). 7. Open the distillate control valve (Distillate/PID) to 100% and slowly close the reflux control

valve (Reflux/PID) until flow is established in the distillate line, keeping an eye on the standpipe level.

8. Control distillate flow rate using distillate (Distillate/PID) and reflux (Reflux/PID) control valves.

Note: If both distillate tanks become full during operation, seek assistance

Drawing off Bottoms Product 1. Open and close the appropriate manual valves on the 3

rd floor (see Figures 8 and 12). (but

figure 8 does not show the correct valves. Figure 12 is where?) 2. Close the red valve on the reboiler recycle line (see Figure 5). 3. Open the manual valve above the bottoms rotameter (see Figure 6).

Note: Ensure that the level of the material in the reboiler does not get too low. The system will eventually turn itself off when the level in the reboiler goes below 6 inches or so.

Shutting Down 1. As mentioned before, the utilities will be turned off exactly in the reverse order meaning

steam first, then water and lastly air. 2. Set the “Steam/PID” on the computer screen to 0%. 3. Turn off the Steam valve on the 1st floor. 4. Turn off the water and air valves by manually turning them fully in the clockwise direction

on both floors. 5. Use the computer to turn feed pump off. 6. Use the computer to turn off the reboiler mixing pump 7. Close the manual valve above the bottoms rotameter. 8. Close all manual valves associated with feed (Figures 8 & 12), distillate (Figure 2), and

bottoms tanks (Figures 8 &12). 9. With the “Reflux/PID” at 100%, use the reflux pump to drain the standpipe. Turn pump off.