KILOWATTS FROM CORNOBS

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SAME SONG, DIFFERENT VERSE

The technology necessary to make fuel from biomass dates from the nineteenth century, and was further refined during the Second World War ... when a shortage of petroleum encouraged the use of charcoal in gasification systems. Recently, there's been a renewed interest in wood-fueled gasifiers (we've reported the progress of MOTHER's researchers, among others, in past issues), and the availability of modem materials and components—along with a more complete understanding of how wood, rather than charcoal, can function within such a system—has done a lot to improve the performance of this type of equipment.

Odin Associates' goal, though, was to develop a working generator that would use as many off-the-shelf components as possible ... thus standardizing the construction of each unit and—by minimizing expensive "custom tailored" fabrications—keeping costs down.

The Odin units (two were developed, along with several different fuel conditioning systems) are similar indesign to those that utilize wood scraps as feedstock, with the exception that some features were included and a couple removed-to make the hardware compatible with corncob fuel. For example, because the shelled ears are considerably less dense than wood, and thus more porous (yet still offer a heating value of 7,700 BTU per pound, equivalent to that of the best oak), the moisture problem usually associated with wood gasification is virtually nonexistent when corncobs are used. Lumber scraps may be as much as one-third water by weight . . . but cobs—even those stored in open piles—retain only about 7 to 9% moisture, with 15% being the "worst case" limit.

This means that the corn-burners can get by without [1] double-walled fuel hoppers or internal condensate gutters, [2] exotic—and often costly—in-line moisture traps, or [3] prefeed fuel-drying bins ... and the elimination of these extras reduces both the necessary initial investment and the time that must be spent on periodic maintenance.

And, in the process of developing the costeffective gasifiers, Bob Haug and his associate, TorBjorn Haugen, made some other discoveries worth mentioning. They realized—from studying World War II—vintage European hardware and accounts of its performance-that the preheating of inlet air, and the even distribution and regulation of that atmosphere through "tuyeres" (or nozzles) within the combustion zone, had always been considered of utmost importance. But because they felt that they couldn't meet both criteria successfully, they opted to eliminate the preheating hardware in order to give full attention to combustion air distribution. The end result was a 12-nozzle arrangement that utilized short, valve-equipped pipes to deliver air—at ambient temperature—directly to the hearth area. Then, to enhance the overall burn pattern, they set up the tuyeres at two levels, with a three-inch space between, and staggered the alignment of the pipes in such a way that the upper six are offset from the entrance points of the lower six.

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