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Most of my earlier prototype gasifier/combustor systems were based on a rectilinear side-draft gasification flow through a narrow fuel column into a close-coupled combustor surrounded by a ceramic heat exchanger that preheated  gasification air, even using fuels with up to 2/3 their weight in water.  For more details on my previous work
http://www.fundamentalform.com/html/energy_from_waste.htm

OMNIFUELED GASIFIER

I have a design for a gasifier that I want to share with the world. It is the culmination of my 35 years of work in the field, and I think it will solve many of the problems that now plague those modeled after the old WWII Imbert gasifiers.

The design is based on the following observations and discoveries:

• Fuel in a hopper gasifies best and most evenly, without bridging, when it is vaporized/gasified evenly at the base of a vertical-sided hopper. Whenever there is constriction without size-reduction from burning or gasification, as is often the case in the upper throat of an Imbert or constricting throat gasifier, where combustion doesn’t consume the fuel to the contour of the throat, bridging and uneven gasification occurs.
• Whenever there is bridging of the fuel, air supports combustion beneath the bridge, creating hot flames and a spent gas with excess oxygen and little if any energy value.  Then the bridge collapses, quenching the flames and heat with cool damp fuel and steam, creating a burst of sooty gas, followed by diminished cool gas production.
• Providing the first feed conditions are addressed, preheating the incoming air can almost entirely solve this problem, if it is hot enough, because the endothermic gasification is sustained in a deeper coal bed by the heat of a lesser volume of air.  This is quite different from conditions created by a larger volume of cool air, with its oxygen content creating combustion to supply the heat along with lots of diluting nitrogen and CO2.
• Of the three fundamental thermodynamic ingredients of Time, Temperature and Turbulence, Time is too often neglected in favor of (old school) Turbulence, as in the jet of speedy air shooting from the tuyers of a downdraft gasifier. I have found it better to let the air slowly permeate the fuel, heating up a large mass of fuel slowly, evenly, creating a large hot coal-bed. letting the gas become saturated with CO and Hydrogen over time and temperature. I think we can forget turbulence for most applications, and instead rely on laminar mixing of self-propelled convection flow.  Steam and CO2 are primary combustion enhancers, speeding heat transfer significantly by their bipolar molecular property of absorbing and radiating radiant energy.  Radiation is the primary mode of heat transfer at the temperatures of gasification. N2, O2, CO and H2 do not absorb radiant energy, so heat transfer must come from neighboring bipolar molecules or be delayed.
• Contrary to expectations, adding all this heat and insulation does not deteriorate the materials of construction as much as allowing local hot spots of 2500F combustion, which is far above the required gasification temperatures of 1300 - 1600F. Temperatures above 1500F rapidly oxidize metals and thermal-shock ceramic when cool fuel suddenly lands on orange-hot refractory,