[Stoves] BIOMASS ENERGY VS COMPOSITION

[Thomas Reed]

Dear Frank:

I'm glad to see someone exploring alternate biomass fuels here. at 
STOVES and GASIFICATION.  Mother Nature produces  biomass in many forms 
beside  wood, and they are all potentially good for making energy or 
charcoal, each with some reservations. 

It is important to report both particle density and the buld density 
under various packing conditions.  Many of the measurements you project 
can be done with simple apparatus, but HHV and ultimate analysis will 
cost a bundle.  Fortunately, Mother Nature is quite conservative in 
building her various biomass forms and the variation is limited.  For a 
long time I have used the average formula

C H1.4 O0.6
The molecular weight for this formula is 23; the energy content is 21 
MJ/kg (high heating value, HHV, bone dry) or 19 MJ, (low heating value, 
LHV (liquid water not condensed) with  10% moisture (Denver dry).

This covers most structural biomass (wood, straw etc.)  You can see an 
extensive listing of properties at our WoodGas site, 
http://www.woodgas.com/proximat.htm  
<http://www.woodgas.com/proximat.htm>along with links to other listings. 
------------------------------------------------------------------------

However, I have discovered important exceptions in "reproductive" 
biomass (cobs, seeds, husks, shells, ....) which are also good fuels, 
particularly for our woodgas stoves.  Reproductive biomass could be over 
50% of the available biomass residues in the world, since in the past 
they have not found a use. 
Fortunately, there are corellations between the simple proximate 
analysis and the ultimate analysis. 

I discovered the importance of this second category when working with 
Acai pits from Brazil and Cherry pits (8 tons of each).  The proximate 
analysis of the Acai pits was very close to being pure starch with an 
energy content of 16 MJ/kg (HHV), while the cherry pits had 23 MJ/kg 
HHV, both outlyers of the above assumptions.  Reproductive biomass 
contains vey little lignin and lignin has an energy content of ~26 
MJ/kg.  Starch ((C6H10O5)n has an energy content of  ~17 MJ/kg.  
Triglycerides (vegetable oils) have an energy content of ~ 40 MJ/kg, so 
it doesn't take much oil tucked away in the seed to kick up the energy 
content.  

I hope you will continue your investigation and let us all know the results.

Yours truly,

TOM REED       THE BIOMASS ENERGY FOUNDATION

frank wrote:
> Stovers,
>
> The WBT relies on the energy (joules) used during the test. Determined 
> in the starting fuel energy and subtracting the fuel energy remaining.
> Because we may be using it with a mix of different woods, small fuels 
> like nuts and berries, leaves, dung and all types of organics we need a 
> good simple method of determine the energy output of any type of fuel.
>
> I am trying to come up with such a procedure.
>
> If one takes a block of wood 10 X 10 X 10 cm and drops it onto a fire it 
> does three things (as I understand it):
> 1) moisture goes off
> 2) turns to carbon
> 3) then, finally, the size is reduced as the carbon oxidizes until there 
> is only ash remaining.
>
> The particle density is reduced as the moisture and wood gases go off 
> and remains the same during the carbon to ash phase until the ash is 
> heavy enough to increase the density.
>
> If we know some things about a fuel at the start like:
> 1) moisture
> 2) ash content
> 3) joules per kg ash-free volatile solids
> 4) joules per kg ash-free charred
> 5) particle density ash-free volatile solids
> 6) particle density ash-free charred fuel
>
>
> Then when testing a stove we can start with a 1) known weight of fuel. 
> After the test at the end we 2) weight what is left and determine the 3) 
> particle density of the wood-char-ash mix.  We can then calculate the 
> Joules we started with and the joules left over at the end. 
>
> For my testing I have replaced the Joules with Carbon because I  have a 
> Leco carbon analyzer.
>
> If you wanted to test a stove using a type of fuel you would send in a 
> sample to a lab and have the following test done:
> Example:
>
> Moisture % 28.6
> Volatile solids dry wt 99.2%
> Ash dry wt 0.77%
> Particle Density of fuel (ash-free dry wt) g/cc 0.75
> Particle Density charred sample (ash-free) g/cc 0.61
> Carbon  in ash-free volatile solids g/cc 0.38
> Carbon in ash-free char g/cc 0.45
> (char is produced in preheated oven 400 deg. C sample covered for one hour)
>
> example as we go.....
> tare 153.25
> tare + sample wet 191.65
> tare + sample dry 180.68
> tare + sample charred 162.34
> tare + sample ashed 153.46
>
>
> For the stove tester using the above fuel:
> weigh the amount of fuel starting  2000g
> calculate volatile solids dry wt by subtracting water and ash. 1413 g
> weigh the wood-char-ash at the end. 400g
> determine particle density (easy test)  0.65
> calculate ash-free particle density and plot on the line between 
> (wood-carbon) and (char-carbon) from data received to get the carbon 
> (Joules) in the cubic centimeter.0.430 Carbon (g)/cc
> calculate total carbon left  1413/0.65 = 2173cc.     2173 X 0.43 = 934  
> grams carbon left.
> If the density of the remaining mix from the stove test is between the 
> wood - char density values above (a mixture of wood+char remain) use 
> that plotted value for the energy not burned. If the density of the 
> remaining material is at (or less) than the char density value use the 
> char value as the energy.
>
> I have been working on 6 samples:
> 1) Shredded bark
> 2) almond tree trimming
> 3) cow manure
> 4) Pellets of sewage
> 5) paper and fruit juices
> 6) wood chips
>
> Open to any help or suggestions.
>
> Getting a little 'burned out'!
>
> Frank
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