Operation

That's it! Operation is equally simple. Close the gate valve and follow exactly the same procedure as for any other type of compound still (Chapter 5). When the time comes to draw off the heads, open the gate valve slowly until you are collecting distillate at the rate we recommend at this stage, which is about 1 or 2 drops per second. You may notice the only drawback of this system at this point - there is a lag of around 10 seconds after adjusting the valve before you see any change in the amount of distillate coming out of the product condenser. You will soon get used to this and find the still very easy to adjust. The gate valve allows you to make fine adjustments in the reflux ratio with coarse adjustments of the valve. One full turn of the valve wheel represents only about 2 or 3% change to the reflux ratio, and delicate control is much easier to achieve than with the small needle valve used with the liquid sampling method. Fig. A6-3

In fact, because the reflux ratio is not affected by vapor composition or production rate, you can easily calibrate the still by observing how your still operates at a known power with water. For each turn of the valve handle, collect product for 10 minutes and measure the quantity. You can calculate the % reflux for each valve setting by comparing the collected distillate to the amount of water being vaporized in the boiler. Because this design directly partitions the vapor, the reflux ratio at a particular setting will remain constant regardless of boiler power or the composition of the liquid in the boiler

Once the heads have been removed, then you can open up the gate valve even more and collect at whatever rate you choose. Because the two vapor paths and the valve are all the same size (1"), the minimum reflux ratio you can achieve is 50%. You will have full and complete control from 50% through 100% reflux.

At the end of the run, you will notice the temperature at the top of the column rises and the rate of collection drops off. This is because the volume of the distillate decreases as its percentage of water rises.

This gives you an independent test for the end of the main run, but slows down the collection of tails for future reprocessing. Fortunately, you can simply open the gate valve all the way and collect the tails quickly.

The vapor management head also works as an excellent stripper if you operate it with the gate valve fully open and collect raw material at a reflux ratio of around 50% with the boiler on full power. Due to the reflux action, the stripping run will produce a higher percentage product than a simple pot still, and this will save time later during the purification run.

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