GAS-L: Drying Hog Fuel

["Graeme Williams" <graeme@powerlink.co.nz>]

Hello Phil,

I can understand your quandary of producing mountains of chip in minutes,
and then trying to dry them to stop the problems of rapid decay.  No matter
what you end up doing, it will cost money, but it has to be considered as an
investment that will not only improve the quality of your gas, but possibly
solve some of your tar problems at the same time.

Because we have resolved the wet chip problem for both coppice willow and
wood chip fuel piles in a fairly simple way, the size of your storage area
can be increased depending on what sort of seasonal buffer you may need.

The fuel is stored in bunkers to a depth of 8 - 9 feet, with box channels
across the bunker with grill tops that blow air up through the fuel pile.
The channels pass through the wall where a continuous phlenum chamber right
down the side wall brings in the air (and heat if you have some) from a
large paddle fan.

The holes through the wall (about 2 foot centres) have a hinged board cover
that can be opened from the phlenum side so you can close the channels as
the bunker is emptied or divert it to the next bunker.

At Rural Generation in Northern Ireland, they actually use their grain
drying bunkers and I have some photos of the piles just after being cut.  We
had a similar system at Long Ashton Research Station in the UK but smaller,
so can say for sure it does a good job, even with just air blown through.
Ideally you need the moisture down to about 15% but the rule has to be, the
drier you get, the better the gas.

There is however a very important point to consider and it's the fines.  The
fines work their way to the bottom of these piles and when you scoop them
out with the loader, there is a big slug of fines in the bucket.  When you
dump this into the fuel hopper, they can upset the gasification process.

As you say that your gasifier is a stratified down draught, the drier fuel
should be excellent, but why are you collecting tar in the wash water?  My
understanding about these systems is they consume the tar by what Tom Reed
refers to as flaming pyrolysis.  Have you asked Tom for any advice on this
problem, or is it from some other technical source?

The photographs of the bunker dryers are posted on the Fluidyne Archive -
www.fluidynenz.250x.com and if you have a question, get it in fast as I'm in
Australia from 03 - 22 July.

Regards,

Doug Williams
FLUIDYNE GASIFICATION



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