[Stoves] Calc. void space and pellet particle density

[Dean Still]

Hi All,

I have turned to chipped wood in some TLUD designs thinking that the
embedded energy favors chipping rather than making sawdust and compressing.
Does anyone have thoughts on quantifying the difference?

A pick up load of chipped wood is about $30 in Oregon and I imagine that
amount of wood to last a winter of cooking. Aprovecho Research Center is
moving to a new 5 acre rural campus and eventually I'd like to see a TLUD
powered cabin using chipped home grown biomass, no electricity.

Best,

Dean


On Sun, Mar 9, 2014 at 7:06 AM, Richard Stanley <rstanley at legacyfound.org>wrote:

> Hi Frank / Tom / Andrew/ Crispin et al,
>
> My own observations about densities achieved with high compression, are
> limited to 2" --80 mm dia x 8" long sawdust fuel log making machinery of
> UK, Tiawan and Danish origins over the mid 90"s and early 2000's in east
> Africa.  To achieve the kind of density you are talking about in a fuel
> log, involves a lot more energy (motor dirces were 8 to 10 kw at least plus
> a few more Kws were needed  for the necessary pre drying of the bulk fuel.
> The product was bound by melting the lignin in the sawdust creating a kind
> of chipboard cylinder. It was hot enough to char the surface of the
> cylinder and often involved added heat jackets to achieve the 400 deg f
> cylinder temperatures. The augur drives I have seen were operating at 6000
> to 9000 psig.  400 - 600 grams per cm^2...MAybe my math is off but its a good
> deal higher than what your numbers indicate. Its also one heck of al ot
> more expensive toe capitalize and maintain the augurs had to be resurfaced
> and hardened every few weeks of operation..
>
> Add binders and the pressure drops dramatically.
>
> Add water and a fiber binder and you are down to 125 to 150 psi/  12 - 15
> grams per cm ^2 .
>
> Of course, you are densifying the inherent material above while we are
> attempting to densify the matrix with finer and more dense in fillers. we
> have gotten to --(and apologies for my former screw up of units ), 0.6
> grams per cc,  but normally run at 0.3 to 0.4 grams per cc
>
>
> Its about different fuels for different markets  industrial
> central-produced generally for industrial or dense population centers may
> justify the cost of the first option, esp with centralized management in
> the inventional business model. That, versus diversified locally produced
> for local markets which requires a lower tech higher training and initial
> management  input in the attempt to adapt the hardware for local
> production, the training necessary to assure a good product and the network
> of the local micro-entrepreneurs to assure local self sustaining support
> internal to their own realities.
>
> The confusion often arises, when one try to enter the other market without
> that end point in mind.
>
> Hasta,
> Richard
>
>
>
> On Mar 9, 2014, at 5:22 AM, ajheggie at gmail.com wrote:
>
> [Default] On Sat, 8 Mar 2014 14:53:30 -0800,"Frank Shields"
> <frank at compostlab.com> wrote:
>
> > This is a sample from a local US pellet source. The bulk density is
> 0.638 g/cc and the particle density of the pellets is 1.338 g/cc
> >
> > Void space for air movement in a TLUD filled with these pellets is 52.3%
>
> I haven't checked your maths but the numbers seem good, I wasn't
> expecting the pellets to be quite so dense, perceived wisdom is that
> the density of wood with no pores is 1.5g/cc so the press has got
> quite close to the theoretical maximum.
>
> If we consider a 6mm cylinder of dry wood 10mm long then to achieve
> this density it will have needed to be squeezed down to 3mm.
>
> Of course we are starting with sawdust which is 1/3 the bulk density
> of dry wood so in fact we have to squeeze a 30mm column of sawdust
> down to 3mm the average force times 27mm is the energy necessary to do
> that, neglecting friction, or are my numbers too far out? Tom Miles
> said the pressure necessary is 2000psi so that seems to be an average
> weight on the 6mm column of only 40kg (~400N) moved through 0.027m ??
> I make that ~11Joules. The pellet has a mass of 0.378 gramme and a
> calorific value of 7036 Joules so the which seems to give a very low
> figure of 0.16% of the heat energy  is required in motive energy to
> compress the sawdust. Unless my suppositions are wildly out the losses
> in the pellet making system are high as we worked on 2.5%.
>
> Also the air space being greater than the solid space is more than I
> expected.
>
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