[Stoves] The PROTOS Plant Oil Cooker

[Keith Addison]

Hello A.D., Peter

>Dear Peter,
>In Indian cookery, deep-frying in boiling vegetable oil is quite common. The
>temperature of boiling oil is 250 C. I have never observed the oil getting
>pyrolysed into carbon and volatile matter at that temperature, even when the
>same oil is used again and again, as is often done here.  However, your
>suggestion of using a water-oil emulsion is interesting and worth trying.
>Have you any suggestions as to how one forms a stable emulsion of water and
>oil?

If you talk about water in diesel fuel all the diesel buffs yell 
"Aarghh!" But addition of water to the diesel process decreases 
combustion temperatures and lowers NOx emissions, and a lot of work 
is being done with water-fuel emulsions, with some big names 
involved..

What works with emulsifying petroleum diesel fuel might also work 
with vegetable oil, or at least indicate a direction

Try a search for "Fuel Emulsions" here, to give you an idea (though 
technical information requires a subscription):
http://www.dieselnet.com/search
Site Search

There's also this:
http://www.epa.gov/otaq/models/analysis/emulsion/emulbibl.pdf
Bibliography of Water-Fuel Emulsions Studies, October 11, 2001, U.S. 
Environmental Protection Agency, Office of Transportation and Air 
Quality. Following is a list of studies that are being considered for 
inclusion in work being done by EPA to assess the effects of 
water-fuel emulsions on emissions of oxides of nitrogen (NOx), 
hydrocarbons (HC), and particulate matter (PM).

This is from dieselnet.com:

"In emulsion systems, water is mixed with diesel fuel and the mixture 
is supplied through one injection nozzle. Depending on the method of 
mixing, either phase can be dispersed in the other. As mentioned 
before, in order to minimize water contact with internal engine 
surfaces, diesel fuel should form the continuous phase in which water 
should be dispersed in the form of small droplets. Water-in-fuel 
emulsions will also minimize the potential corrosion problems in the 
fuel system. Due to the differences in density and other physical 
properties, water-fuel emulsions are not stable. ... Unstabilized 
emulsions separate quickly and must be prepared on-line in the engine 
fuel injection system immediately before the injection. This type of 
system involves two tanks, one for fuel, another for water, followed 
by two pumps and a mixing device. In one laboratory study, mixing was 
carried out as a two stage process [De Vita 1989]. First, the liquids 
were mixed in a premixer, where the internal phase (water) was 
injected through nozzles into the continuous phase (fuel) swirling 
through a cylindrical chamber. The mixture was then fed, through a 
gear pump, to an emulsifier. The emulsifier was a static mixing 
device featuring a system of nozzles and channels, where the blend 
drops dimensions were decreased due to jet diffraction, impact, 
friction, and high pressure rates. The homogeneous emulsion was fed 
to the engine fuel injector. ... Stabilized emulsions involve mixing 
of fuel and water with the addition of small quantities (typically 
1-3% of the fuel) of chemicals which facilitate the formation of 
emulsion (emulsifiers) and prevent or delay separation once the 
emulsion is prepared (stabilizers). ... Emulsions must remain stable 
for a sufficient period of time to prevent separation in the fuel 
tank. In practical terms the required stability period must be at 
least several days, preferably several weeks."

Companies like Lubrizol, Caterpillar, Aquazole, Clean Fuels 
Technology, A-55 et al probably have more stable solutions than that.

Biodiesel brewers using used cooking oil as a feedstock find that the 
longer the oil has been cooked, and the higher the cooking 
temperatures, the higher the level of Free Fatty Acids will be, and, 
almost certainly, the higher the water content of the oil, which is 
of concern because water interferes with the biodiesel process and 
should be removed first.

This is what one Biofuel mailing list member said about water removal:

>Water in vegetable oil can exist as free water, which will 
>eventually settle to the bottom of a vessel; as suspended droplets, 
>which may settle if the oil is heated, or the droplets are 
>coalesced; and as water in solution with other impurities in the 
>oil. Free water is the easiest to remove. The droplets are removed 
>most efficiently by coalescing and draining. Suspended droplets that 
>cannot be coalesced and water in solution are more problematic.
>
>Boiling off the water is more difficult than it appears on the 
>surface. Colligative properties of solutions (and some mixtures) can 
>make removal of the last traces of water almost impossible. Water 
>mixed with oil will not boil at the same temperature and pressure as 
>pure water. As water is removed, more heat or lower pressure will be 
>required to remove more water. If the oil contains salts or 
>semi-soluble fatty acids, distillation is even more difficult.
>
>As the percentage of water in the solution decreases (its molar 
>fraction) its vapor pressure will continue to drop. Lowering 
>pressure in the system alone may be insufficient to sustain 
>vaporization when the solution becomes concentrated (the molar 
>fraction of the solute greatly exceeds that of the solvent). Results 
>will vary depending upon the nature of the water-soluble impurities 
>in the oil. Few solutions are ideal, in terms of Raoult's law, and 
>in used vegetable oil, there is no way to know what solutes are in 
>the oil.

Sorry, that's not exactly a how-to, is it? Hope it helps though.

Best wishes

Keith Addison
Journey to Forever
KYOTO Pref., Japan
http://journeytoforever.org/

 


>Yours
>A.D.Karve
>
>----- Original Message -----
>From: Peter Verhaart <pverhaart at iprimus.com.au>
>To: Discussion of biomass cooking stoves <stoves at listserv.repp.org>
>Sent: Monday, April 30, 2007 4:08 PM
>Subject: Re: [Stoves] The PROTOS Plant Oil Cooker
>
>
> > I still believe all vegetable oils will decompose thermally, into carbon
> > and vapours, making them unsuitable for pressurised burners such as
> > Primus. The temperature would be in excess of 200 C.
> > It would be nice if these oils could be emulsified with a tiny amount of
> > water. The steam resulting from heating the emulsion in the burner could
> > form a spray of small droplets that burn completely. In this way the
> > oils would not be exposed to temperatures causing decomposition inside
> > the burner.
> >
> > Peter Verhaart