The Basics of the Column Still
From Yahoo Alcohol Fuel Group files
The column still has been used in industry for a number of years but is quite different than what the hobbyist distiller actually uses.
Commercial size stills of which we are copping the design of do not use boilers. Instead of boilers, steam is pumped into the bottom of the column and in our case beer would be fed into the column from about ½ ways up.
The steam would strip out the volatile organic compounds (including alcohol) and by the time the feed reached the bottom it would be waste water. The rising steam which would now be between 25 and 40% alcohol would rise in the column where it could be further stripped of waste water.
With the constant rise of chemical rich steam coming in contact with the cooler parts of the column, the water which has a higher boiling point than alcohol would drop out of the steam, leaving the lighter chemicals to continue to rise in the column.
With this basic knowledge the engineers began to develop improvements to help improve the use of the column and make it function to their own advantage.
The engineers who experimented with columns discovered that they could place collecting plates within the column at spaced intervals and as long as the steam which was fed into the column at the bottom remained a constant temperature, the purity of each plate would remain constant.
So a plate which tested to be 60% would always be 60% and a plate which tested 80% would always be 80%. That is as long as the steam was always the same temperature. If the temperature of the steam changed so would the % in each plate.
Plates, Marbles and Packing
Plates which includes some quite ingenious designs including bubblers, cascades and waterfalls were and are used today in commercial operations where it is important to separate different compounds such as Oil, Gas, and tar out of one column, but since we are concerned with just alcohol and the products that we can put into our gas tanks we are not impressed with or have the need for these plates. BUT in addition to being resting places for compounds these plates served another purpose.
As steam rises and carries with it our desired alcohol, it comes to a point where it begins to cool, condense and thus separate out some of the water and alcohol. By supplying a matrix inside the column which will absorb some heat and force the vapors to liquefy we get a rain inside the column which becomes richer in alcohol as the vapors go up.
In the Charles 803 still Marbles were used due to their compact size and cost. In the larger FFS still I used expanded copper mesh but stainless mesh would do the same thing.
Because our stills are not super heated with steam and are not connected directly above our boilers we must supply a reservoir at the bottom of the column which is kept well above the boiling point of an alcohol/water mixture. The condensing mixture raining down will contain a lot of alcohol for a good portion of the beginnings of the run and we want these alcohols to re-evaporate before they can be flushed out the overflow drain. So a bubbler section was designed in, In addition to keeping the alcohol hot the bubbler section has the additional feature of pulling some water out of the incoming vapors from the still.
The bubbler section should be preheated, as should the entire column prior to introducing the vapors from the still.
A still column that is attached directly to the top of a boiler would not want to include the bubbler but a still that is located above the level of the boiler and not attached to the boiler would want to have the bubbler section empty and the waste directed back into the boiler in order to take advantage of being able to utilize 100% of the alcohol produced in the brewing stage of production.
If we were only producing a gallon of alcohol at a time we could build a column of 2 or 3 inch copper only a couple of feet tall, fill it with packing, attach it to a 10 gallon boiler and then condense off the final vapors at the top, ending up with high quality alcohol. But we are not moon shiners looking to make our own drinking alcohol; we want to produce enough alcohol to fuel our machines and cars.
If we were producing hundreds of gallons of alcohol per day, the cost of cooling a tower would not be cost effective, so tall 4 and 5 story columns are used to concentrate the alcohol. But for the small producer the cost of a tall column is offset by the cost of cooling a shorter column.
A column must have enough internal volume to get the job done but can be larger than needed when sufficient heat is available to maintain the equilibrium of the column.
Equilibrium is the name for maintaining the different levels of purity that I spoke of above. When the column is in Equilibrium there is an un-interrupted flow of purity up the column. When this equilibrium is interrupted by a shock of extra heat in the column the purity of the finished product will go down, and if it is interrupted by a shock of cold in the column the alcohol will rain out prematurely and no alcohol will be produced at all.
Maintaining a constant temperature throughout the column means that the column is cooler at the top (ideally 173 F. and warmer at the bottom (no ideal temperature but I try for about 200 F) these temperatures are at sea level, they will change with altitude.
By running a controlled stream of cooled water through a cooling coil from top to bottom, the matrix can be kept at an ideal temperature range within the column due to the fact that the water will transfer heat from the matrix into the water. The water coming out at the bottom will be very hot because it now contains the heat it took from the matrix.
Controlling the Variables
If it were possible to control the temperature of the boiler throughout the whole distilling process and the water temperature flowing into the cooling coils was kept constant then there would be no need to control the water flow through the cooling coils, but with so many variables we must maintain a way to control the equilibrium of the column and still keep the column an economical size.
Among the designers of the Charles 803 included a plumber knowledgeable in commercial boiler operations. He passed on the information about a valve which was controlled by temperature and could open and close in small amounts depending on how much heat was delivered to the controlling bulb. We refer to it as the "Johnson Valve" which is simply the company that makes it, but the valve has the ability to maintain the top of the column at 173 F to within a fraction of a degree by controlling the amount of cooling water it lets through the valve.
If the temperature at the top of the still is above 173 F then the alcohol will be a lower percentage than 197 proof. If however the temperature at the top of the still drops below 173 F then there will be no alcohol produced at all.
The vapors coming out the top of the distilling column are as stated before 173 F. That's only 39 degrease below the boiling point of water and easily hot enough to produce bad scalding.
The condenser on the top of the Charles 803 is adequate for the amount of alcohol it produces however with larger amounts it is important to have a condenser that can handle the volume of alcohol we are producing.
The condenser on the FFS is pulled away from the column in order for the heat rising from the column to be trapped at the top and not influence the cooling of the vapors beyond that.
The condenser, just like the column has a cooling coil and is filled with a matrix. The difference here being that the matrix is to hold back the cooling liquids and not let them fall through the condenser too fast.
In the Column the cold water is introduced at the top, but in the condenser it is introduced at the bottom. As the vapors are cooled they are gradually transformed into liquid and then cooled down before leaving the bottom rather than be quickly liquefied and the hot liquids be allowed to drop through and out of the condenser. This gradual cooling helps prevent evaporation of the final product into the atmosphere when it is not directly stored in sealed containers upon exit from the still.
Source: Yahoo Alcohol Fuel Group files