Sunday, June 8, 2008

Woodgas Stove initial evaluation

You may recall I am advocating Energy Independence Week this 4th of July, which is observed by 1) Using no grid electricity, 2) Burning no fossil fuel, and 3) making no trips to the grocery store.

If you can pull this off for a week in July, maybe you learn enough to do a week in October, from which you learn enough to do a month in January.  Maybe not all in the same year but you get the idea.  Learning energy independence strengthens your household and America.

For this July I'm thinking of it as a staycation, like camping at home.  I need a way to cook without electricity, gas, propane, or even fossil-derived charcoal.  This means biomass, like wood and wood-derived charcoal.  I did get a charcoal grill, but for cooking on wood I liked the looks of the Woodgas Campstove XL from the Biomass Energy Foundation.  It's a small forced-air inverted downdraft gasifying stove which claims to burn wood and the like much more efficiently and cleanly than say, a regular open campfire.  

Last night and this morning I cooked two meals on it and did a couple of additional test burns.  I hereby report my findings:

Trial one:  Loaded the stove with chunks of wood about the size of hot dogs or dill pickles, and used flax straw for kindling.  I think the wood pieces were way too big as it took quite a while to get the stove burning cleanly - I had to add more tinder about seven or eight times.  I get the feeling the wood pieces should be more like the size of grapes or berries.  Once it did get going I sliced up a potato and made home fries.  This worked really well, the skillet was just the right temperature for browning the potatoes.

Trial two:  Test burn with flax straw as the only fuel.  I stuffed the stove really tight with it.  This got going smoothly but didn't burn as long.  The stove burns in two phases - the gasifying or smoke-burning phase, and then the charcoal-burning phase.  You can tell when it switches over because the flame goes out and the coals sit there and glow.  With the straw as the only fuel, the flaming phase lasted just seven minutes.  

Trial three:  I found some smaller wood about finger-sized to egg-sized.  I decided to get fancy and try to make strawberry pancakes.  This time it took maybe four or five additions of straw tinder to get the thing burning hot enough to stop smoking.  As with the first trial, even when burning with no visible smoke there was a kind of pitchy odor, maybe because most of my wood was pine, and not all that dry.  A bit of soot formed on the bottom of the skillet.  Even with the fan on low, the pan got way too hot and I scorched half my pancakes.  I should have brought out a trivet to set the pan down off the stove.

Trial four:  Another test burn with flax straw only.   I took a wad of it, bunched it up tight like this with the top looser, and stuffed it down into the stove.
Where's my aim'n'flame?  I might have to write an exception to the no-fossil-fuel rule to allow the use of butane lighters.

The reason I keep on about the flax straw is that we've got so much of it.  Here's that same blue wheelbarrow parked in front of the supply - enough to run the stove half a million times I guess, although it'll probably decompose first; there's already mushrooms growing on top.

Here it is burning nice and clean on the straw.  It didn't even burn as long as the earlier straw-only trial, maybe four minutes instead of seven for the flaming phase.  I'm not sure why, maybe the straw was more damp or I didn't pack it as tight.  The pile of char and ash there is from the Strawberry Pancake Trial.  I want to try saving the charcoal and running the stove on it later.

My beloved 8-inch iron skillet fits nicely on top of the stove.


This will do nicely for Energy Independence Week.  It basically works and is pretty okay for what it's trying to be, which is a portable camp stove.  I'm convinced it's vastly more efficient than a regular campfire; how else could you cook a batch of pancakes on one handful of wood?  

It's harder to get going than I expected maybe; I needed a lot of kindling, more than would fit in the stove at first.  It would take a lot of skill to be able to load it, light it with one match, and just have it come up without smoking.  In that respect it is similar to fire-making in general.  I think my Trial Two was beginner luck.  The manual says you may have to use commercial fire-starting sticks.  I vaguely recall reading somewhere else about this kindling-on-top technique, in the context of making an open fire or maybe it was a Rumford fireplace.  In that article they had four or five different sizes of fuel layered with the biggest on the bottom.  

When burning wood the stove did occasionally sort of sputter and let out a puff of smoke, I don't know why.  Might be wind, or maybe my wood chunks are still too big, or uneven, or damp.  When burning straw, it tended to puff out little bits of ash all the time - it's a forced-air stove and the straw burns to a very fine ash.

I mentioned earlier about saving the charcoal.  There are two reasons for doing this.  One is to save it as fuel for later, cleaner-burning fuel.  The other is to use it as a soil amendment in the garden, in which case you might as well save the ash too, as it will have calcium and suchlike mineral nutrients.

With this stove it's a little inconvenient to save the charcoal, basically you have to dump the coals out while the stove is hot - there's no damper to shut off the charcoal burning.  If you're saving it for the garden you could dump the char/ash into a pail of water.  To save the charcoal for later use as fuel, I dumped it into my wheelbarrow and spread out the coals so they'd stop burning. 

For the stay-at-home use I have in mind for it, I think it would be worth making some kind of stand or cart for it, to hold it securely at a convenient height, and with a side shelf or two.

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