BIOMASS ENERGY FOUNDATION Inc. 1810 Smith Rd. - Box 1392 Golden, CO 80401 303-278 0558; 303-273 3730 FAX; E-Mail - 73002,1213
THOMAS B. REED - PRESIDENT
CURRENT STATUS OF THE "INVERTED DOWNDRAFT GASIFIER"
I invented the "Inverted Downdraft Gasifier" cooking stove on a trip to South Africa in 198fs5 when I became acutely aware of the terrible cooking conditions in the tribal homelands. In conventional downdraft gasifiers air passes down through the biomass, and so requires a blower or suction (usually provided by an engine). In the inverted downdraft mode air passes up through the biomass charge, meeting a combustion-pyrolysis zone at the top. Combustible gases then pass out the top and can be mixed with air and burned in a suitable burner. It can be operated with either natural or forced convection. It is particularly suitable for cooking with biomass. I have since met a Mr. Tom Taylor of Albuquerque who makes a large commercial gasifier operating on a similar principle. I returned to the Solar Energy Research Institute (SERI, now the National Renewable Energy Laboratory, NREL) in the Fall of 1985 and built and tested the first model of the inverted downdraft gasifier in my laboratory there from coffee cans and refractory cements. The stove gave an intense blue cooking flame that would be satisfactory for "modern" clean, efficient cooking anywhere in Third World countries. This work would be remembered by Jim Diebold and John Scahill, still there and working on fast pyrolysis. Unfortunately, this laboratory model used compressed air to achieve sufficient mixing of secondary air with the gas. I then set myself to build a model based on natural convection, since Third World homes do not typically have compressed air. I worked on inverted downdraft stoves in my spare time at my home in Golden after I left SERI and joined the Chemical Engineering Department at the Colorado School of Mines. In 1988 I visited a Mr. Fred Hottenroth (10806 Kaylor St. Los Alamitos, CA 90720). I (My son lives nearby in Long Beach). Fred is a maker of innovative biomass stoves and is also very concerned with Third World problems. I discussed the inverted downdraft principle with Fred at that time. I purchased several of his improved woodburning stoves. When I returned to my laboratory, I modified one of the wood stoves made by Fred to operate in the "inverted downdraft mode. It burned very steadily and cleanly, but not with a blue flame, my target of excellence. Later that year on a trip to Florida with a Mr. Art Krenzel I demonstrated a smaller stove to my friend and colleague, Dr. Harry LaFontaine, at his home in Miami Florida. I explained the principles of operation to him and said that we needed to improve the secondary air mixing for "blue flame" combustion. He didn't think it was possible. I bet him $1,000 that I could produce a blue flame with natural convection. At that time he said that he wished to leave the Biomass Energy Foundation to me, but did nothing about it. Harry began work on the inverted downdraft gasifier (and even tried to patent it) without consulting me. He visited me in Golden in 1989 and showed me a new model he had made. We made tests (with Agua Das), and were very impressed with the potential of the wood gas stove. I told him about the stoves of Fred Hottenroth and he then drove his motor home out to Los Alamitos to talk to Fred. He entered into some business arrangements with Fred that I was not aware of. Fred now markets a "Gas-I-Fire" stove along with his other excellent stoves. It is much superior to conventional wood stoves. In 1991 Harry sent me a paper on the inverted downdraft gasifier. I was not happy with the paper. It rambled on at great length about the nature of the cooking problems in Third World countries. It said almost nothing about the stove and how it worked. It also made efficiency claims which are probably overly optimistic. I corrected the paper as much as I could and Harry presented it at IGT "Biomass Symposium" in Washington, D. C. in March 28, 1991. Harry is a showman - he once owned a circus. He put on a demonstration at that meeting that was only partially successful and I was somewhat embarrassed because I did not feel the stove was fully developed and I still do not think so. Harry died in Spring 1994 and left the biomass Energy Foundation (a 501-c-3 not for profit corporation) to me. I am continuing the work to develop a "blue flame" stove, but If I win the bet, I doubt if Harry will be able to pay up. In 1994 Dr. Ronal Larson of Golden called me and asked if it were possible to make charcoal in such a way that the pyrolysis gases could be used for cooking. One characteristic of the inverted downdraft gasifier is that it produces 20-30% yield of charcoal which I have always considered a drawback. He argued that the charcoal could be made and sold by families while doing their cooking. He and I began work in my laboratory and at his home to develop improved cooking stoves. We have built a dozen different models and are still working on further improvements. I am currently building a "research stove" in which I can measure the air and gas flows and take the scientific data needed to design an optimum cooking stove. I believe this is a true summary of the developments in this field. Prof. Thomas B. Reed, Dept. of Chemical Engineering, The Colorado School of Mines, Golden, CO. 80401. 19 March, 1995