[Gasification] wood moisture meters?

[Mark Ludlow]

The alternative to microwave is a simple loss-on-drying technique tailored
to your individual material. Typically, a convection oven (or your kitchen
oven) is set to about 105C and a disposable/reusable weigh boat of heavy
aluminum foil is tared and then re-weighed with an arbitrary amount of what
you want material you want to analyze. (You also need a cheap electronic
analytical scale for this.) The weight of the boat is subtracted from the
gross weight (boat plus sample) and placed in the oven. At regular intervals
the boat with contents are weighed, the moisture loss is recorded and the %
moisture is calculated. I assume that you are interested in a 1% or so
accuracy. In this case, a few weighings will allow an nth-order polynomial
to be fit to the time v. moisture % (I use Excel) relationship, so there is
no need to dry to bone-dryness to get useful results. Each material has it's
own characteristic curve; for some materials, free water is the issue; for
others, interstitial and bound (hydrated) water is most problematic.

The simple resistance meters work well within their limitations. The best
application technique for wood, as an example, is inserting the electrodes
into a fresh end-grain cut. Bales of hay are a different animal; there is no
surface phenomenon that is an accurate map of interior moisture conditions;
electrodes must be inserted into the interior of the bale.

The point I would like to make is that it's not necessary to spend a bundle
to do this determination. It can be done quickly, easily and accurately on
analytical-sized samples that are presumed to be homogeneous. If, on the
other hand, the desire is to measure the moisture in a dump-truck load of
fuel, then the protocol of sampling becomes important. For those who feel
the need for self punishment, the ANSI Z3 1993 Sampling Standard (95 pages)
should satisfy. Contact me off-line for more info on this one.

Ho, ho, ho!
Mark

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Sunday, December 23, 2007 4:37 PM
To: 'Discussion of biomass pyrolysis and gasification'
Subject: Re: [Gasification] wood moisture meters?

The Ligno meter cited works fine. Notice the short pins. Hopefully you have
chunks that are big enough for the pins. Delmhorst
(http://www.delmhorst.com/) meters are probably the most used in lumber and
hay applications. They're not cheap. 

Tom 
 

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of jim mason
Sent: Sunday, December 23, 2007 3:46 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] wood moisture meters?

this has all been very helpful.  both on real time moisture meters as
well as the microwave method.  thank you.

here is a short review on one of the cheaper moisture meters.
http://www.rockler.com/product.cfm?Offerings_ID=11447&TabSelect=Reviews&cook
ietest=1

as for specific ones, do people have suggestions for models they've
used and found impressive/adequate?  ones to avoid?

jim





On Dec 23, 2007 1:27 PM, andrew <list at sylva.icuklive.co.uk> wrote:
> On Sunday 23 December 2007 16:58, Tom Miles wrote:
>
> > Microwave on High
> > Place 50 gm sample on 3 paper towels (industrial towels work fine.
> > They are about 3 gm per towel.)
> > There are different drying schedules for hog fuel, chips or
> > sawdust. I think the standard calls for 1600 W microwave. All
> > heating on high. In general for fine wet fuel:
> > 1 min on high. Stop weigh and fluff,
> > 1 min on high. Stop weigh and fluff
> > 1 min on high. Stop weigh and fluff
> > 30 sec on high. Stop weigh and fluff.
> > Repeat until weight is stable.
>
> Thanks for that
>
> This is similar to what I've been doing except my microwave is 600W
> and I use the defrost setting for 20 minutes.
> >
> > I was running about 10-15 min per sample total. The stirring is
> > important because it releases moisture. As with any material it is
> > easy t overcook the sample.
>
> Yes the steam leaving the sample can easily be hot enough to pyrolyse
> the sample and that constitutes a loss of dry matter, the vinegary
> smell is the first sign you get.
> >
> > Moisture meters measure electrical resistance. They are fine when
> > the probe is sticking in the same chunk of wood, or in hay bales
> > that are reasonably packed (10 lb/ft3, 160 kg/m3). They are now
> > accurate up to about 40% MC. They are no good for loose materials
> > like straw, chips or hog fuel.
>
> And as I said they are only any good on homogeneous samples as they
> only measure the path between the probes, so a wet bit in the middle
> of a log will not be measured.
>
>
> AJH
>
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-- 
----------------------------------------------------------------------------
----
jim mason
website: www.whatiamupto.com
current project: mechabolic (http://www.mechabolic.org)
announce list: http://lists.spaceship.com/listinfo.cgi/icp-spaceship.com

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