[Gasification] Gasification Digest, Vol 6, Issue 35

[Laurence Stewart]

Sorry for my intemperate email.  The package arrived today.

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Today's Topics:

   1.  A) Merry Christmas B) Steve Redmond is onto (Steve Redmond)


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Message: 1
Date: Wed, 27 Dec 2006 12:33:37 -0500
From: "Steve Redmond" <skiprock at earthlink.net>
Subject: [Gasification]  A) Merry Christmas B) Steve Redmond is onto
To: <gasification at listserv.repp.org>
Message-ID: <000601c729dd$25583f00$6701a8c0 at desktop1>
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Greg,

Thanks for clarifying. I appreciate your positive comments now and in
earlier posts.

Just to give my own definitions, so that others will know what I'm talking
about, by green wood, I mean wood that has been cut but not dried in any
way. The wood I am cutting on my property consists primarily of Red Maple,
Beech, Black or Sweet Birch, Red Oak, Eastern Hemlock, Yellow Birch, Sugar
Maple, Eastern White Pine, and Eastern Cottonwood. I'm cutting them now and
chipping them with a tractor mounted Jin Ma 6" wood chipper. The tractor is
a small one - 18 hp 1951 John Deere Model M. I've chipped up to 6" limbs,
but 3-4 inch stock is preferred.

The moisture content of the chips is measured by oven drying samples for 4
hours. This probably gives a slightly conservative moisture content by
comparison with laboratory regimes that last 24 hours or more, but for the
purposes of establishing that high moisture fuels are a viable heating
source, a conservative estimate is certainly acceptable. The variability in
samples, bark content, species, effect of air moisture, etc. are far bigger
factors in the actual determined result than an extended drying
time. The chips from the chipper are small by comparison with commercial
chips, and dry in the oven more rapidly. Weights taken during the last hour
of drying show no measurable change on the scale I'm using.

I find that wood cut now (in late Fall/ Early winter) on my property varies
between 43 and 47% moisture content by oven dry test. During summer months
it may be higher, but that isn't proven. In fact because of the warm winter
so far here, I've noticed that on some days the sap is running, so moisture
content may be close to summer levels on those days. Leaves included in
chipped wood in summer would undoubtedly add to moisture content. In general
for calculation of heat capacity and sizing furnace components I use the
generally understandable and convenient figure of 50% moisture content for
describing green wood chips.

I do not define green chips as wet. To me wet means chips that have surface
water on them. In fact, a dry chip can be "wet" if it was say dipped in a
glass of water. Wood does not necessarily absorb surface moisture quickly.
Water vapor on the other hand permeates wood deeply over time and affects
the finished moisture content.

A green and wet chip to me at least, means a chip that was high in moisture
content as well as wetted by surface water. A wet chip pile typically
results if it is left uncovered in the rain. The chips may have been green
prior to the rain, and are both wet and green after the rain.

I find these distinctions useful and actually important to specify, because
they have different effects on the combustion, lighting, and burn stability
of a furnace, and would presumably on a gas generator as well..

I would classify wood that has been dried for awhile as semi-dry. Again this
would burn differently than green wood, and it is important to make the
distinction between 25-30% moisture content wood, and what I call green
wood.

I have burned wet wood, green wood, wet and green wood, and even composted
wood and wood mixed with snow in the VTHR furnace. They burn differently,
some start easier than others, and the heat released naturally varies. I
have purposely wet a high-heat chipped green fuel to slow combustion. I have
had a few materials fail to complete a burn. The point of experimenting with
a variety of fuels is to characterize this furnace. It has revealed some
surprising things, and I'm sure will continue to do so.

I do understand that because it is relatively counter-intuitive, it may be
difficult to accept initially.  It would be helpful if or when there is
skepticism to understand what in particular it centers around. One thing
however is certain to me. Every day I personally put green and sometimes wet
wood chips into it, record and study what I've done, and every day I, my
wife, my child, my house and even our 14 year old cat are warmed by it here
in Vermont.

-- Steve




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End of Gasification Digest, Vol 6, Issue 35
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