Hi Tom, Pleased that you are still able to contribute to these debates, and as you seek comment to your intentions to do some testing, here goes(:-)
Dear Doug and all: The Toplit Updraft gasifier produces a different gas (plus 20% charcoal, mostly from the lignin) than the downdraft gasifier. I believe it may be a cleaner gas, since cellulose (~ CH2O) vaporizes to produce a different gas (CO + H2 + ?) than the lignin. My understanding of these open core concepts of gas making, is that all the pyrolysis gases released at the descending flame front of the raw fuel, are combusted in and with a portion of the char on the upper gas outlet side of the flame front. Reduction would take place in this narrow band of high temperature to give us the CO, but I would expect to see the H2 start out low, and increase as the depth of char increases.(Needs longer dwell time). Question. Have you done continuous gas analysis from start-up to shut down? Your question mark in the equation suggests a combustible gas (~CH20), which would have to survive the combustion /oxidation phase, or does this vaporization take place as a portion of the char is consumed first in oxidation,then reduction? Looking at these gasifying stove rings burning as a blue gas, one might conclude that there is little if any condensable tars present. If CH20 survives to be measured as a gas, it's formation may be reflected in the H2 variation if present, depending on exactly where the H2 forms. Having said that, I have no experience to draw from, to know if there is enough thermal inertia after reduction to allow "other" reactions to take place. As soon as we get some warm weather, I'll try to measure the tar content from each, using my 2 kW generator and a 5 gal tar filter made from the charcoal. Comments, suggestions? As you expect to capture tars in charcoal, then I would want to have good control over the gas cooling/filter temperatures, as the dew points of the fuel moisture content are linked to carrying lighter pyrolysis gas/oils through filter media. I'd want to know, especially the downdraft gasifier, if it had a proven ability to make gas without or known condensing hydrocarbons, using the fuels of the test. You also have the engine to feed you lots of info as to gas condition, and I would use that as a pre-test before you add the charcoal filter. A quick look under the throttle butterfly could save you a lot of useless testing if you see the sticky stuff in there! I'm sure you know all these answers already Tom, but will watch for your postings of the results. Regards, Doug Williams, Fluidyne----
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