[q]Have you noticed that when you drill some woods with a power drill, that the wood dust from the hole often binds up into little helical strips under the action of heat and pressure? I guess that this is attributed to the natural resins – particularly in pines and coniferous woods. I still think, however, that this level of materials processing should be left to those who wish to add value to their saw mill or carpentry factory, where tons of dust are produced each day, and pelletising is a good way to put it into a stable form. I recently did some research into the problems of sawdust waste for small sawmills, and the key thing is that the stuff is just not worth transporting in dust form. Once pelletised into a convenient form, it then takes on real fuel value, and this helps offset the costs of bulk road transport. For the small scale domestic use, the burner/gasifier needs to be able to handle whatever comes it’s way- truly omnivorous! I think some sort of cyclone burner where raw dust is transferred into the combustion zone in a stream of hot flue gas would be the way to handle small quantities of sawdust. Imagine a multi-fuel stove which burns different sizes of wood waste in different zones, analagous to the way that a modern printer or copier has drawers and a separate sheet feeding system for different sizes of paper. It might have a top hopper that would take either pellets, chips or sawdust directly – blown into the combustion zone in a swirling blast of hot gas, (vacuum cleaner technology re-applied) whilst another hatch would handle blocks, small branches (2″ round say) or logs, burnt on a more traditional grate, or side tray like the Rocket Stoves featured last night. [/q]
[a]
Colour me stupid possibly, but could you use a jet of air to blow the sawdust powder into a combustion zone? Like a Babington burner, but with the wood dust in a hopper above? [/a]
[a]
That’s exactly what I am hinting at. There is a bit of pneumatic equipment called an air/material transfer nozzle, which is used to blow materials (like plastic granules for injection moulding machines) between the bulk container and where they are needed. It works a little like the venturi which used to be used to draw liquids up from a can and then atomise them into a fine spray. The perfume sprayer was an example of this. They also produce up to 10″ Hg vacuum, and this is what provides the “suction” for transferring granular materials. This is the principle of the ejector, where a high pressure blast of air from a nozzle is used to drag along a significant volume of low pressure air and produce “suction” perhaps this is partly the effect on the babington burner air jet.[/a]
[a]
My thought was that it’s such a nuisance and expense (time + money) to have to convert a potential fuel to another ‘structure’ as it were. If wood dust is a worthless waste product, they might even pay you to take it away. [/a]
[a]
Well, actually, I’m not really interested in processing wood waste. As I said before, I’m looking at other types of biomass, which is a lot more plentiful — crop residues like corn cobs, marsh hay, cattail leaves, tree leaves in the Fall. I was also thinking of scrap paper, but I found out that’s bringing $100 a ton now, more than you could get for pellets wholesale. But you could go around with a truck the night before trash pickup and get tons of paper and cardboard — it’s set aside for recycling in most cities now. Run it through a hammermill (shredder/chipper) and pelletize it. Wouldn’t be too good to grill over tho. [/a]
[a]
Have you ever heard of Fire Cookies? I knew this crazy guy in Colorado who was making these things. Used them on his grille for cooking hamburgers, etc. Take strips of non-glossy newspaper. Put in blender with water. Turn into a paper pulp again. Press this fluid / mass in a potato ricer to get the water out. Set the “cookies” out in the sun to dry the rest of the way. Arid in Colorado. Take a handful of these fire cookies and place in the grille. Light them with a match. Notice that I DID NOT say use charcoal lighter fluid. Stand back and in about 5 minutes you are ready to grille your hamburgers. Objection number one: Oh those nasty inks will give you cancer! Not!…soy inks are used now. Objection number two: It will stink. Not! Objection number three: These are too much trouble and are too hard to dry out. Not! The list goes on. I made a few of these myself and they do work pretty damn well. Try it, it’s easy. You could dry them with a Babington burner set up for the task. [/a]
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