Why doesn't my biodiesel dry?

[Ivan]

I water-wash my biodiesel to get rid of soap. The biodiesel ends up quite wet (looks like orange juice), so I need to dry it before filtering and using it.

I usually dry by heating to around 80C and spraying at the top of my reactor for around 10hours, but this is quite expensive on electric- using around 12kWh. I make the biodiesel in a shed, so air circulation may not be ideal. I get around this by using a shower extractor fan to expel the moist air from the shed (air taken from near the reactor). I've been old you can dry in 2 hours at 55C using this method.

I made a batch over the weekend, but there's a problem with the main heater relay, so I can't do the usual process. I spoke to 24/7 at the Navitron Party, and he suggested drying by bubbling air through the fuel with an aquarium pump. I've read up on this, and it certainly seems preferable - 24hours of a few watts rather than 10hours of over a kW.

I heated the biodiesel to 65C for a couple of hours using the auxillary heater and drained a small amount of water from the bottom. I then started bubbling, and  turned off the heat. It's certainly a little clearer, but still very murky after 56hours.

Why doesn't my biodiesel want to dry?!

[frotter]

I used to air dry mine with a wee aquarium pump - BUT i used to just leave it bubbling until completely dry. It would even work at ambient temps but it sometimes took 2-3 days to be all super clear and shiny. Cheap but tedious, much like My Good Self.... ahem.

X

[martin]

somewhere I've got a hefty Hailea air pump you could try - something like 80w or so - bloody noisy, but don't 'arf bubble!

[oliver90owner]

Ivan,

Centrifuge it.  Only heat required is to make it about gas oil viscosity.

Regards, RAB

[Ivan]

Thanks for all the replies. I've been going for almost three days now. I'll try a bit of heat and spraying it as well - see if that speeds things up.

Centrifuge sounds an interesting approach. Any cheap and cheerful ways to centrifuge 130litres?

[PEMTEK]

A friend of mine in Scotland is pumping his biodiesel through hardwood shavings instead of washing. Claims it works really well.

He was using ion exchange resin but likes the shavings as he uses it on his woodstove after its spent!

Phil

[Ivan]

I wonder how the hardwood shavings works? I'm not a convert to the ion exchange resins - they will remove ionic impurities but I can't see how they'll absorb much soap - probably one of the reasons why commercial biodiesel can be very poor quality. If the wood shavings absorbs soap, it would be a very viable alternative (I especially like the disposal route!), as it doesn't cost £250 that ion exchange resins cost to replemish. I've seen manufacturer data suggesting that ion exchange resins contribute 10p or more cost to each litre of biodiesel produced.

[Twenty4Seven]

Ivan

Have you tried a 3/27 test to see if you have well converted fuel? If you've not come across the 3/27, it's 27ml of methanol and 3ml of fuel you're testing. Shake it up and leave it to settle. If you get ANY fallout, you have poorly conveted fuel and that may be responsible for the lack of clarity. Really well converted fuel will dissolve completely to give a single phase, clear yellow liquid. If it's cloudy but with no actual fallout, it is borderline but should be useable. BTW, you need to do the test at 20*C..... Have a go and let us know the result....

Cheers

Nick

[oliver90owner]

Ivan,

Centrifuge is 125 quid from Stationary Engine Parts and you need a suitable pump of about 4 litres per minute at around 6 bar.  A car-type power steering pump should suffice, belted to a motor, and ideally with an appropriate pressure limiting valve.

Centrifuge will collect about 60cm cubed of water before it needs stopping to collect the water, as it drains off, and then continuing.

Not tried it, but reports are good.  I would go a cheaper way.....

Also a toilet roll filter would remove moisture in a similar way to the wood shavings and is another alternative.  Softwood might be near as good as hardwood if it is dried thoroughly before use?

Regards, RAB

[longstroke]

Ivan,
Are you on the vegetable oil forum?

There is all sorts of advice, but also some good sources for Resin at prices that sound very reasonable compared to the £250 mentioned, unless you've an enormous drying tower?!

That centrifuge is a reasonable price, most places are after a lot more. Presumably when you stop the supply pump you would need to change the drain to another container as the water would drain down?

Ideally one could do with a pair of radio controlled water/sludge outlet valves on the periphery of the centrifuge to allow the water to be discharged without stopping the pump.
But then we're redesigning a self sludging purifier, although they are vastly expensive, and even the spares kits of sealing rings cost ridiculous amounts.

For heat you could put a set of your tubes on the shed roof and pump the oil through them - although from what I've read about the temperatures you may be risking causing the oil to carbonise onto the really hot surfaces?
How about some flat plates? 12 KwH is a lot of leccy which is a shame really whilst using a waste to make fuel.

I suppose we're back to the how much is it worth spending for a saving of fossil energy debate. But thats up to the individual.

[Ivan]

the centrifuge looks a really good idea - I've never heard of doing this before, and ironically, I ordered from that supplier earlier this week.

I've been thinking of using solar panel to heat the oil, although I was thinking of lowering a coil into the reactor to do this. Yes, 12kWh seems a lot of electricity to waste on heating. Chug tells me that some people he knows burn waste glycerine to provide some of the heat. Having said that, my 125litre or so batch is equivalent to 1100kWh of fuel energy, so it's only 1%. Still, it would be nice if I could reduce it...