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April 2006




Making your own reflux column from a piece of old irrigation pipe or some tin cans

By Dr Garth Cambray

In the first article in this series we saw how to ferment fruit using yeast, converting the fruit sugars to low grade fuel ethanol. In the second article  we saw how to make a solar still to concentrate the fuel ethanol. This article shows you how to concentrate the fuel and use it to run a 4 stroke and 2 stroke petrol (gasoline) engine.

To produce fuel grade ethanol, it is necessary to concentrate as much alcohol as is theoretically possible from the ethanol/water mixture that you get from the solar still. To do this, one needs a reflux column. What a reflux column does is allows you to perform a huge number of redistillations all in one go, thus using as little energy as possible and giving you the highest possible quality fuel. After refluxing, your ethanol fuel mixture will be about 94% Ethanol. To remove the last little bit of water, some plaster of Paris is added. But more about that later.

The parts needed to make the column. Pipe and fittings and stainless steel pot scourers. Make sure they are stainless steel as normal steel scourers will rust.

To make a very simple, yet highly effective reflux column, you will need a 750mm length of black pvc irrigation pipe and fittings for each end to connect it to your boiler on one end and the condenser on the other. A small layer of silicon rubber can be placed around each join when assembling. This will protect against leaks.

Pack the reflux column with stainless steel pot scrubbers. I used the 3M brand scrubbers from the local grocery store.

Alternatively, you can use 5 tin cans (the type that stack into each other). Attach plumbing fittings to the tin can at the base of the column, that will

The assembled boiler, reflux column and condenser in operation.

connect to the boiler, and to the can that will make up the top of the column connecting to the condenser. The cans in the middle should have small holes drilled in them as shown in the picture. The column is packed with stainless steel pot scourers. I stuck the whole thing together with silicon sealant and packing tape.

In the system I use, my boiler consists of an old 45l stainless steel urn. Essentially any heating system that can boil water will work as a boiler for a reflux column. (It is important to ensure that no alcohol vapour can exit the boiler through leaks – so called fugitive emissions as this is a fire hazard and will affect your ability to think clearly near the still).

Attach the boiler with crude alcohol fuel mixture in it, to the reflux column. Attach the reflux column to the condenser. Attach the condenser cooling system to your cold water source.

An alternative reflux column made from old tin cans.

Once the boiler begins boiling, vapour will pass slowly up the reflux column. This vapour will consist of a mixture of alcohol and water. The alcohol and water will condense at different rates as they contact the surface of the packing material in the reflux column. Because alcohol evaporates more easily than water, more vapour entering the column will transfer its heat to the condensed alcohol re-evaporating it, and a little less water, that will then go slightly further up the column, re-condense and be re-evaporated and so this process continues until very clean pure, near fuel grade alcohol comes out the top of the reflux column and enters the condenser, where the alcohol vapour condenses and runs out into your collection vessel.

As time progresses, and the concentration of ethanol in the boiler decreases, the concentration of ethanol vapour entering the reflux column will decrease too. Hence, again, it is important to separate your first cut of fuel from your second, which can go back to the solar still for further concentration.

Your first cut that came from the reflux column, contains a very high concentration of ethanol and some contaminant alcohols and ketones – all of which make good fuel. There is also a small amount of water. This can be removed with plaster of Paris – a powder formed by the heating of gypsum in the following reaction:

CaSO4•2H2O + heat -> CaSO4•½H2O + 1½H2O (steam)

An old Stihl chainsaw running on ethanol fuel. This chainsaw was actually manufactured in Brazil when this country was the worlds largest ethanol powered nation and is perfectly suited to ethanol fuel (gasohol). Note the cloud of pineapple and two stroke oil tainted smoke in the picture.

As you can see from the above equation, heat drove water out of the chemical matrix of the salt. When plaster of Paris is added back to a solution with some water in it, the water immediately reacts with the partially dehydrated CaSO4•½H2O to return the compound to its hydrated state of CaSO4•2H2O. After this happens it sediments to the bottom of your mixing vessel, and the clear liquid above is fuel grade ethanol.

I mix this with 5% unleaded petrol making the fuel something which only an engine can consume – just in case anybody gets worried about that.

To run your 4 stroke lawnmower engine on ethanol, fill the tank. Start the engine – it will sound a bit different to when it ran on petrol, and will not accelerate properly as the fuel air mixture provided by the carburettor, which is set for petrol, will be a bit lean, as ethanol has less energy in it than the same volume of petrol. You can modify your carburettor to overcome this problem, but then your engine will have the disadvantage of being only alcohol fuel compliant – which if you get bored with making your own fuel could be a problem. I just fiddle with the choke settings on our engines to get it to a point where the engine runs smoothly and accelerates properly.

A two stroke engine, such as that in a weedeater or chainsaw is far easier to run on ethanol than a 4 stoke engine. In our case, for the chainsaw, we just mixed the ethanol and two stroke oil as we would for petrol and then added 5% more chainsaw oil just for good measure as ethanol is a slightly worse lubricant than petrol, hence a little more lubrication is needed for the same volume of fuel.

Making your own fuel gives one a great feeling of independence, and nothing beats the faint smell of pineapple and two stroke oil coming out of the exhaust of a chainsaw!

You may wonder why we don’t show a picture of our lawnmower – well that's because they look like this. But if you don’t have some of these to mow your lawn, make your lawnmower sustainable at least!

More information:

Related articles:

Solar Cells take Stellar leap

Off the grid for 5 years

Fermenting waste fruit to fuel ethanol

Separating your alcohol from your fermented fruit



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