Is it worthwhile to Distill Bio-Ethanol as Fuel?

First published on Distillique's website in 2015 by GM Bosman

Since then, the principles stayed the same but the current price of diesel/petrol is in the region of R20/litre. Perhaps we should update the article with recent figures.

In 2015 we received a question from one of our customers who wanted to start distilling bio-ethanol on his farm to run his farm vehicles. Is it worthwhile?

Now ...

Is it worthwhile to distil ethanol for fuel purposes?

This question requires two answers:

1. Does it makes sense from an energy or technical point of view? and;
2. Does it make sense from a financial point of view?

In this article we will have a quick look at both of these answers.

First we can look at the feasibility from an energy or technical point of view:

We will make a few assumptions (such as that the reflux column still is 100% insulated and does not loose heat through the column) to simplify the calculations a bit, and so as not to over-complicate the calculations and in the process distract us from the basic principles:

Beer normally contains 4-6% alcohol (by volume), wine might contain up to 16% alcohol and some sugar washes might contain up to 20% alcohol.

The energy required to bring say, a 4% beer to the boil requires a heat (or energy source) to do two things:

1.    Bring the beer to the boiling temperature:  

Depending on your altitude, and the lowering of the boiling point of pure water due to the alcohol content, we can make an assumption that your beer will boil at about 95 Degree C.

If we start with beer at a temperature of say, 20 Degree C, it means that we have to increase the temperature of the beer about 75 Degree C (95 minus 20)

Water has a specific heat capacity of 4.2 kiloJoule per kilogram per Degree Kelvin, or 4.2 kJ/Liter/Degree C

Lets assume a beer volume of 100 Liters.

This means that we have to use 4.2 x 100 x 75 = 31500 kJ or 31.5 MJ of energy to bring the beer to a boiling temperature.

2.    Once at the boiling temperature, additional heat is required to evaporate (boil) the beer

To evaporate beer (that is already at the boiling temperature) additional heat is required (the latent heat of vaporization) and this is 336 kJ/kg for water. (which we will use to simplify calculations a bit)

That means that we have to add another 33600 kJ or 33.6MJ of heat (337 x 100) to vaporize/boil the beer.

If we add these two heat/energy requirements, we get a total energy requirement of 65.1MJ to bring 100 liters of beer to the boil and to evaporate it.

Now look at the energy of the distillate that we can "produce":

From 100 liters of beer with an alcohol content of say 4% abv, we can distill a maximum of about 4 liters of azeotrope (96.4%) alcohol

One liter of ethanol contains 22.8MJ energy

This means that we can expect about 91.2MJ energy from the 4 liters of ethanol that we distilled from the 100 liters of beer.

From a simplified point of view:

We would use 65.1MJ of energy to concentrate (from beer/wine to ethanol) 91.2MJ of energy. We could thus say that we achieved a 40% nett “increase” ((91.2-65.1)/65.1 x 100) in energy through the distillation of 4% beer. (technically we do not “increase the energy, but we rather “concentrate” it. More on this a bit later in the article)

If we use beer at 8% alcohol content, it would translate to a 176% net “increase” and with a 16% wine it would translate to a massive 453% net “increase” in energy

With a 16% wine we would still use only about 65.1MJ of energy to distill 100 liters of wine, but we will end up with about 16 liter azeotrope. (with about 360MJ of energy in it)

From technical point of view it is clear that it is definitely worthwhile to distill beers or wine to get a much more concentrated source of energy.

The following point is however important to remember:

Distillation does not actually increase the energy (in total) but it concentrates the energy. In 100 liters of 16% wine, there already is 360MJ of energy in the alcohol. This wine would have a volumetric energy density of 3.6MJ per liter. However, the same amount of energy (360MJ) in 16 liters of 96.4% alcohol would have a volumetric energy density of 22.5 MJ per liter.

Distillation actually only “concentrates” the energy.

To achieve this higher energy concentration, we used 65MJ (for 100 litre 16% wine) to increase the volumetric energy density from 3.6MJ per litre to 22.5MJ per litre.

Apart from increasing the volumetric energy density, we also achieved another important characteristic. The flashpoint of the liquid was lowered dramatically:

The flashpoint of a liquid is defined as that temperature above which a liquid will burn if exposed to an open flame.

•    Beer at 5% alcohol has a flashpoint well above 60 degree C
•    Ordinary wine (at 12.5% abv) has a flashpoint of about 52 Degree C
•    Spirits (whisky, brandy, gin, vodka) at 43% abv has a flashpoint of about 25 Degree C
•    Mampoer at 70% abv has a flashpoint of about 21 degree C
•    Ethanol at 96.4% (azeotrope) has a flash point of almost 17 Degree C
•    Pure ethanol (100%) has a flashpoint of 16.5 degree C

Through distillation, we can lower the flashpoint for beer (above 60 degree C) and wine (about 52 degree C) to well below 20 degrees to make it an effective fuel source at relative high volumetric energy densities.

From the above, it is clear that distillation is definitely feasible from a technical point of view, to produce higher volumetric energy dense liquids (i.e. azeotrope ethanol) from low alcohol fermented products (i.e. beer and wine)

From a costing point of view, it however becomes much more complicated to perform the calculations to see if it would make sense to distill your own ethanol based fuel.

We have to add up all the costs involved in producing ethanol and translate that costs to an equivalent monetary value per MJ (mega joule) of energy and;

Compare this cost to the alternative energy sources available, before we can come to a conclusion whether it would make financial sense to distil our own ethanol based fuel.

The main factors involved in determining the cost of production would be:

•    Cost of feedstock to ferment to a low alcohol beer or wine
•    Cost of yeast/nutrients additionally required
•    Cost of energy required to distill the beer/wine
•    Cost of labor to oversee the distillation process.
•    Capital cost of equipment

One of the alternatives to ethanol fuel is off-course normal petrol or diesel:

In South Africa the prices for these energy sources varies widely from time to time but at the time of writing (September 2015) we could safely work on R12.32 per liter of petrol (Inland Price - Coastal Price being cheaper).

Petrol contains about 34.2 MJ energy per liter and diesel about 37.3 MJ per litre.

This translates to a value of about R0.36 (36 cent) per MJ energy.

Let’s compare this to “home distilling costs” of small quantities of ethanol fuel.
Assumptions:

        We ignore the costs of feedstock (as this might be fruit/potato/grain unsuitable for the market or consumption)
        We ignore the capital costs of our equipment
        We use municipal electricity as energy for our still.
        We ignore the costs of water and yeast (as it will be very little)
        We ignore the cost of your time and labor

To ferment 100 liters of over-ripe fruit to a 5% wine would be quite feasible without adding any sugar.

This will eventually distill to about 5 liters azeotrope in a reflux still and require about 31.5 MJ of energy (ignoring any inefficiencies and heat losses, from our previous example)

When we convert this 31.5 MJ of energy to kilowatt.hours (as we are billed for electricity) it translates into about 9kW.hr. Currently the rate per kW.hr is R1.36

This calculates to an electricity cost of about R12.24 to produce 5 litres of azeotrope ethanol.

When we again calculate the cost per MJ or energy, it turns out that it would cost us about R0.11 per MJ to produce (or rather concentrate) our own energy through distillation.

To summarise:

If you produce your own ethanol, as an energy source through fermentation and distillation, it might cost you as little as R0.11 (11 cent) per MegaJoule, compared to the R0.36 (36 cent) it would cost you to buy normal petrol or diesel!

In liter terms, it translates to the following:

• Buy petrol/diesel at R12.32 per liter, compared to
• Producing your own bio-ethanol (at 96.4% abv) at R2.50 per liter
   

Some food ... no fuel, for thought!