Towards a better tinyhouse

Inventing to freedom?

Really easy to build waste vegetable oil heater.

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Just watched the video on the relaxshax blog about the vegetable oil heater, and it got me thinking and reading a bit about how practical waste vegetable oil might be for heating a tinyhouse.

Biomass is an even nicer idea in terms of the independence from fuel sources and environmental friendliness, but as far as I can tell, there are real issues with the combustion process efficiency, and the lower heat of combustion. Even worse, there is the safety problem: a large hopper of grass clippings is bound to be a real fire hazard, although there are certainly ways to mitigate the risk like making it into pellets or making the top of the hopper sealed shut to prevent ingress of air if it did ignite, an automatic feed mechanism would be a problem, since you have to reliably get the fuel from the hopper to the fire without letting the hopper ignite.

Vegetable oil is not easy to ignite, on the other hand, it has less ash, and is easier to burn efficiently, and it has a higher heating value 2.5 times as high as wood or so. From what I am reading here it is available at most restaurants free, but sometimes they want 25 cents or so a gallon, which is of course still very good, especially since unlike gas or heating oil it is not making the whole petroleum problem worse (or not inherently at least), and unlike used motor oil, will not have anything toxic in it.

After looking at some patents and thinking how to make it as cheap and easy to build as I could, here is what I landed on:

The oil level is of course equal in the float valve area and the funnel area, I messed the diagram up in that regard and didn’t want to fix it, so just mentally correct that if you don’t mind.

It is a so-called bowl burner. What happens is you put a piece of burning paper or something in the middle of the funnel to get it started. Or optionally there could be a fiberglass wick going up the middle of the funnel. After a while the vegetable oil around it, in the bowl (or funnel in this case) ignites, which for Deek was a problem, but here it is part of the solution. To control the combustion rate, you adjust the height of the vegetable oil in the furnace by adjusting the height of the float valve. When the vegetable oil level gets too low, the float valve opens, letting more oil in. The oil level would of course be equal in the float valve area and the funnel area, I just sort of messed the diagram up in that regard and didn’t want to fix it.

When the level of the veggie oil is higher in the funnel, a larger surface area is exposed to the air, and with a larger surface area, more combustion occurs.

The reason I decided against just using a wick alone, unless you want to replace it a couple times a day, is that the stuff in the veggie oil would clog the wick, apparently. Also, you need to connect it to the main reservoir anyway, and the siphon and float valve is an easy way to do it. If you took away the means to adjust the height of the float valve you would have a wick-based burner. Then there would be no point in making the burner part funnel shaped, either.

Still, if you made the wick turn upside down periodically, putting the part that has the particulates accumulated on it above the oil, and the clean part below, maybe the particulates would mostly burn off. Or the wick could be disk shaped… but then I wonder how often you would have to turn the wick, probably a couple times a day at least, or the furnace might go out. You could automate it, but that adds complexity.

Hm, if you could automate it though, you could have the wick be a continuous loop and just go through 2 long tubes, into the main fuel tank, then if the path was too long for capillary action, the wick could be moved around, into the tank, absorbs oil, then out to burn it off, and back…

Also, veggie oil leaves about 1% ash unlike, say, kerosene. So the ash needs somewhere to go, and here it can sink downwards. The ash box is otherwise filled with oil, which gets displaced by the ash. There would still be a lot of oil mixed in with the ash, it seems, which isn’t exactly perfect, but you could burn off the oil in some other way.

Another way to deal with the ash could maybe be to have a rotating disk or belt, part of which is submerged in the oil in the funnel area, and part is in the flame. Then as the disk rotates, oil+ash sticks to it, the oil burns off in the flame, and some of the ash is still stuck to the disk and could be scraped off, or better yet collect the stuff that falls off, eliminating the scraper, if that would work. It can’t turn too fast, though, or not all the oil would be gone, and some would get scraped in with the ash…

To turn it off, turn it down and then block the air intake, same as a wood burning stove.

A(n) anti-spill valve(s) might be a good idea if there was any possibility of it tipping over, and change the air intake so oil could not spill, although it still would be pretty dangerous… Maybe a rotating wick would be a better way to go there. You could use a curie effect engine as a cheap and easy way to provide the motive force for the wick movement…

The whole thing would be outside, with just the chimney going through the home to get the heat.

Edit: some more ideas:

Using a curie effect engine, you could have some basic movement without any electricity. A curie effect engine is really easy to make, too. Basically a piece of ferromagnetic stuff gets attracted to a magnet, which makes it get exposed to heat, then get heated up past it’s curie point, when it is no longer attracted to the magnet. Then another piece is attracted more, and takes it’s place.

So with some coat hangers and a magnet and a flame you can get some basic motorizing. To adjust the speed you adjust the rate at which the ferromagnetic piece heats up. The torque is of course limited by the magnetic attraction forces and geometry of the engine…

So with this, you could pump oil into a burner area, or could move a chain so that it dips into the oil, then some fo the oil sticks, the chain moves into the combustion zone, and oil burns off/drips off the chain.

I’m liking the chain (or belt) one because if all the oil burned off, some of the ash would be left stuck on the chain. Then the ash could be knocked off, into an ash container.

If not all the ash comes off, that is not a problem, some would then get transferred back to the main tank, but over time, it gets transferred to the ash tray. Eventually an equilibrium would probably be achieved with the amount of ash generated and the amount transferred to the ash tray.

You could also maybe pump with a threaded rod inside a tube like a fairly poor archimedes screw. Or maybe making it reciprocate would work.

Also, maybe the drip approach is worth considering again… but there is the potential safety problem of the float valve getting stuck open.

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Written by gregor

March 11, 2011 at 05:44

Posted in Uncategorized

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