[Gasification] Fuel, sizes........ And sensitivity to...
tombreed2010 at gmail.com
Sun Nov 28 16:32:59 CST 2010
Dear Greg and all
Very interesting and useful information.
Is this an open top gasifier (TBR, 1980) or is it the top closed with air nozzles and a bustle(Imbert). The open top gasifier has more resistance to airflow than the nozzles, but compensates by the large cross section area of the magazine.
I suppose that your observation that small chips contaminated with even smaller stuff gasifies well is due in part to the fact that most of the resistance to airflow is in the reaction and not the fuel bed
I have always been surprised that the main pressure drop through the bed is in the reaction zone and not the denser and longer unburned fuel zone. This is due in part to the fact that the viscosity of hot gas is higher than that of colder gas (explained by Knudsen). I've never seen a good measurement of the axial temperatures in a functioning gasifier, though it would be easy to measure with a draft meter and thermocouple.
Keep up the good observations.
Tom Reed THE BIOMASS ENERGY FOUNDATION
Sent from Tom Reed's Ipad
On Nov 28, 2010, at 10:09 AM, "Greg Manning" <a31ford at gmail.com> wrote:
> OK, First off, Greetings List(s)!
> Since my accidental discovery of smaller feedstock sizes about a week ago, I've been doing some tests (ok, mad scientist stuff), to the acceptable "Minimum" size level in my downdraft units.
> For those that do not know me, briefly, I build smaller downdraft gasifiers (under 250KwT) I do NOT go bigger than that, I have my reasons.
> I've been using a "standard" sized woodchip, typical of most small industrial units (NOT your home "shredder/mulchers") generally 15-30 hp units.
> These chippers produce, for the most part, chips about 3 x 3 x 0.25 cm chips (3/4 x 3/4 x 3/16") and down to the point of dirt, or mash.
> 6 - 7 years ago, I had settled on a rotary screen design using a "fines" screen of 0.63 x 0.63 cm (1/4 x 1/4") square openings. this has been my "smaller" size since then. (Until this week, we have always discarded anything that was considered "fines", used these as mulch or horse bedding).
> Upon the somewhat accidental use of a fines pile as feedstock, much to my surprise, the unit accepted the fines for the most part, for about 8 hours of operation, (these where raw fines, directly from under the rotary drum), Yes the gasifier did eventually plug up and shut down BUT, not knowing what was going on at the time (I did NOT know the unit was running on fines) I was perplexed as to what had caused the problem, upon investigation, and finding that the worker had inadvertently used this pile, instead of the correct one, and finding out the length of the time the unit had ran on them, I undertook the new question of "how small I can go" in feedstock sizes.
> As it turns out, the unit will run consistently on a much smaller chip size than originally thought. We have since changed the fines screen in the rotary screener to 3/16" round holes (punched panel) on an offset pattern (68% opening) the ratio change is as follows:
> Original 1/4 x 14" square openings, ratio of fines to acceptable feedstock 30% fines, 70% feedstock
> New 3/16" round openings, 10 - 13% fines, 87 - 90% acceptable.
> Hoping that this information is useful to someone.
> Kindest regards:
> Greg Manning,
> Canadian Gasifier Ltd. (www.cangas.ca)
> Building Hi-Performance Gasifiers, Since 2001
> Brandon, Manitoba, Canada
> 1 (204) 726-1851
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