Notes from Windward: #66


Gasification at Windward

how we're going about converting woodwaste
into useable energy

     Now that the winter rains have arrived to stay, we're going to be shifting our focus onto other parts of our sustainability mission such our goal to use forest waste to provide power, heat and fuel.

     There's nothing new about using firewood to produce heat, but traditionally that's involved discarding a significant portion of the tree since branches and small limbs aren't generally considered worth bothering with. And so the first step involves running anything that's smaller than two inches in diameter through our big, tractor-mounted chipper.

feeding branches into the chipper

     Chipping reduces the awkward-to-handle branches down into something which is more uniform in size and shape, something which has greater density that a pile of brush, and which can be handled in bulk. Biomass is never going to be as easy to work with as a liquid fuel, but so long as we're not having to transport them any great distance, these chips will serve our purpose nicely.

wood chips ready for gasification

     And while this work is central to fulfilling our goal of demonstrating how to feed, fuel and clothe twenty people on our hundred acres, there's actually a lot of slash generated locally that could be converted into bio-fuel for local consumption as the interns observed this summer. For example, here's a pic of Sarah atop one of dozens of slash piles created at the logging site just down the road from Windward.

Sarah gives scale to a slash pile

     Those wood chips can be converted in turn into a number of useful forms such as heat, power and fuel, and we'll be using different forms of gasifiers to perform the various tasks need to support our community. The similiest gasifier is the "updraft" sort that we're building to fire up our outdoor traditional stone pizza oven, an applicaiton in which we just want combustible gas that we can pipe a few feet, mix with air and burn to heat the oven. We can get away with that level of design simplicity because that sort of application isn't bothered by the formation of wood tars in the gas since they'll be burnt up as soon as they hit the burner.

Tristan checking out our updraft gasifier

     But that's not good enough for power applications where we want to produce fuel for an internal combustion engine to drive a generator, a case in which included tars could condense on the inside of the engine and wreck it. For applications such as that, we'll be using a more sophisticated design known as a downdraft gasifier, a design that generates very little tar. The gas still needs to be cooled and filtered before it reaches the engine, but that's all fairly straightforward.

     Downdraft gasifiers are more complex, and correspondingly more difficult to explain which is why I'm inviting you to check out a page on Ankur Scientific Energy's website that offers as good a description of a down draft gasifier as I've come across.

Note: pyrolysis (from the Greek meaning " to cut with fire") is the process by which the complex components of wood are heated until they break down into simplier products such as carbon monoxide and hydrogen, but the process also produces a quantity of wood tar, the chemical that makes smoke "burn" your eyes. It's this acidic tar that you want to cover the outside of meat when it's being "smoked" because not only does it create a desirable flavor in the meat, it also creates a surface upon which fly eggs can not hatch thereby protecting the meat during storage.

Notes From Windward - Index - Vol. 66