Non-electric heating for a processor

[russg]

I'm working with a small charity which is trying to re-activate a biodiesel operation in Sierra Leone - local people are making soap using oil from discarded palm kernels and using this for biodiesel would produce some fuel for farmers in the area. They do have one significant problem, which is a lack of electrical power. They have started to build a system with a 'paddle' stirrer powered by a small diesel engine which could also be used to operate a couple of pumps, but were going to heat the oil processor directly with a wood fire. I'm really not keen on this, and would prefer to start again with a GL processor and with indirect heating of the oil, perhaps by a hot-water coil connected to a wood-fired water heater. That way, the water heater could be a couple of meters away from the processor, oil drums etc. We could probably get the processor up to 80deg.C in this way, but not to the 90deg. mentioned in the GL design.

Getting to my questions at last - would 80 deg. or so be enough to adequately pre-dry the oil and after processing to drive off enough methanol to drop out all the soap and contaminants from the fuel? Has anyone used a water-coil or other indirect heater to heat a biodiesel processor?

[Tony]

Sounds like a very worthy cause

I know a guy that uses bottled gas and a gas fired boiler to heat the oil, though I think he heats the oil directly (rather than with a water loop and the boiler's heat exchanger).

There are a couple of people that heat indirectly using water jackets - so I see no reason why your plan of a coil in the processor wouldn't work.

It's that or directly heat the oil if you can get a cast iron heat exchanger from an old boiler - pump the oil through it over your heat source.

When demething I usually get most out by 85C anyway - and if you're having trouble getting the last bit of Meth out then maybe you could just air-bubble the mix to drive the rest off?

[K.H]

Ive got a cast iron heat exchanger sat here doing nothing,very heavy tho

[russg]

K.H thanks for the offer, but air-freighting it to West Africa is a bit too much for our budget! 

[Bio Dervotee]

is it air or water cooled engine?
if its water-cooled, use engine water through a heat exchanger.
give me a day or two, i'll think it out for you
Will
ps. tell me what engine.

[Bio Dervotee]

if engine is diesel water cooled, then it should run at 95degrees c
you still woont be able to boil water off
but should be good for what you want to do
Will

[russg]

Will,
Thanks very much for the suggestion. The diesel is water-cooled, so that's the way we're going to go, hoping the temperature is enough - the notes on the GL system suggest a temperature of 90 deg. is sufficient for oil drying and driving off methanol. Russ

[Tony]

The key to drying without boiling is surface area.

Like a sheet hung to dry in wind, the water doesn't boil of so much as evaporate off.

The theory behind the GL is that it keeps the air volume above the liquid dry, so there is no barrier to further evaporation - anything that can be done to improve the liquid surface area (EG diffusers) can only help.

[Ross.Dunmall]

They have started to build a system with a 'paddle' stirrer powered by a small diesel engine which could also be used to operate a couple of pumps, but were going to heat the oil processor directly with a wood fire. I'm really not keen on this, and would prefer to start again with a GL processor and with indirect heating of the oil, perhaps by a hot-water coil connected to a wood-fired water heater. That way, the water heater could be a couple of meters away from the processor, oil drums etc. We could probably get the processor up to 80deg.C in this way, but not to the 90deg. mentioned in the GL design.

I was going to suggest exactly the same more or less, but I think using fire will be a little problematic for control. A diesel Generator running on Bio they make, kept a "safe distance" away from the main processor. Then can use this generator to heat an electric heater in a water tank and then re-circulate this water by pumping it through pipes loacted in the Processor to heat the Oil to Temperature. This effectively turns the Processor into a reaction vessel /heat exchanger. If they also limit the temperature of the water being heated by way of a simple thermostat, they can ensure that the reactor vessel never goes above a certain temp. I can always draw a simple PFD (Process Flow Diagram) and send it to you illustrating exactly what I mean.

Another key issue to remember is that the local people that will be operating this bio-diesel system do not have the same awareness of health and safety that we have here in the UK. We are dealing with one highly toxic and another extremely caustic material. I foresee their operator not bothering to put on gloves to weight the hydroxide and not using a mask while loading the methanol or hydroxide into the methoxide tank.

Getting to my questions at last - would 80 deg. or so be enough to adequately pre-dry the oil and after processing to drive off enough methanol to drop out all the soap and contaminants from the fuel? Has anyone used a water-coil or other indirect heater to heat a biodiesel processor?

For methanol 65C would actually be enough it's boiling point is 64.7C. Can say go to 70C to remove it faster.

As for Pre-heating the oil, the higher you heat the oil the more FFA's are produced and the harder it becomes to make bio from this oil. I've read places that you shouldn't heat more than 65C but I have no evidence for or contrary to this, so cannot back up the statement. If I find something will let you know.

[Tony]

Very good points regarding operator safety.

Regarding removing Methanol and temperature, pure Methanol's boil point is 64.7C at atmospheric pressure, but mixed with biodiesel it is higher.  As the concentration of Methanol reduces in the mix, the higher the boil point, so typically we see mixes being heated to 90-95C to recover the Methanol, or, to save electricity cost, air bubbled in the open at lower temperatures (evaporation rather than boiling).

Interesting the comment on FFAs over 65C.  I've not tried titrating my oil before and after dewatering (typically I take it up to 105C).  The problem with the titration before is that water present may throw the titration result out.

I just work on the premise that it has been much hotter and for much longer in the fryer it came from, therefore some additional heating isn't going to make it much worse - but it would be very interesting to know if there are any figures for FFA formation vs heat with water present.

[Julian]

I was under the impression that oil didn't start to break down until it reached it's smoke point, which varies according to feed stock and level of refinement.  I think this is how recommended maximum cooking temperatures are reached.

examples:

Canola 190-232°C
Refined sunflower 227°C

info here ... http://en.wikipedia.org/wiki/Smoke_point

In fact a summery of this page could be a good addition to our wiki.

[Tony]

That might be the point where breakdown to FFAs occur without the presence of water - maybe water has an effect at lower temperatures.

[Ross.Dunmall]

As said I can't find anything to qualify the statement, just that I think I read somewhere about not heating the oil to too high a temperature. Might just be me confusing the vast amount of information I've read in the last 2-3 weeks.

Saying that I've also read in many different places yesterday that heating to 100C and then pushing to 130C is common practice.

[Julian]

I've recently added a sintered brass exhaust fitting inside my processor, through which I blow low volume compressed air.  I can now pretty much dry oil completely at 70°C where as I used to take it to 90+°C.

Similarly when demething, it's cut my slow demeth times almost in half using the current twin tube condenser.  If I have any thing more than a minimal flow, the condenser is overwhelmed and I get massive amounts of carry over.  With a multi tube condenser and a SHHE plumbed into the circuit, I recon demething will be very quick.

The draw back to demething with compressed air is that I believe you create an explosive atmosphere within the processor along with the possibilities of static if the air flow is to great.  Demething with a venturi most likely results in a safer, over rich atmosphere.  I have an oxygen analyser with which I intend to test this theory, but need a gas to zero it for any meaningful results.  Anyone know a cheap source of zero or low, known % O2 gas?

[countrypaul]

The rate of reaction is roughly doubled every 10C increase in temperature. Some in warmer climates therefore process without any external heat on the processor, it takes a little longer but costs less.

If the oil cannot be heated that easily and safely, then spraying the oil whilst blowing air through it might serve to remove most of the water. The other way might be to use a glycerol wash and not bother with heating the oil to dry it.

Two other sources of heat that you may want to consider and have not been mentioned are 1) Solar thermal - it should be possible to create some sort of solar panel out there to harvest the heat, and it may be that heating the oil directly would be feasible. 2) Exhaust gas heat exchanger for the diesel engine - again something that could be knocked up out there I'm sure.

Paul