[Stoves] Dung Berry Fireballs and Indian chracoal

[Jeff Davis]

Dear Crispin,


Crispin wrote:
> Does it take more energy to compress light biomass into a pellet or log
> than
> it gives back in heat?  I presume not.  So...what is the return on energy
> investment?


We would have to know the method of pelleting. For example: the ring
pelleter people say that it only consumes 4% (if my memory is correct) of
the energy pelleted. But I look further than the electrical receptacle and
I see line, transformer, generator and prime-mover loss. My thinking is to
see how the efficiency stacks up in the field. In other words place the
prime mover and pelleter at the point of work and fuel it with your made
fuel. I gave the math (with my POOR math skills) a try, on my web page,
and I copied it below. My heat value is too high (I believe) for
switchgrass but you get the idea.






Copied from my web page:
********************************************************
I could not find the heat value for swichgrass but the above document
stated the swichgrass was made of 50% carbon, 43% oxygen and 6% hydrogen.
So in "Handbook of Biomass Downdraft Gasifier Engine Systems" on page 13,
I found a chart of many HHV and picked something close: maple at 19.9
kJ/g. Think I should use LHV?????


switchgrass = ~19.9 kJ/g  (I now think this should be lower)
hence 19900 kJ/kg

I assumed metric tons
1 ton of switchgrass = 19900kJ/kg x 1000 = 19900000kJ

Joules x (2.78 x 10-7) = kWh (Pocket Ref, Thomas J. Glover)
hence kJ x (2.78 x 10-4) = kWh
or kJ x 0.000278 = kWh

1 ton of switchgrass = 19900000 kJ x 0.000278 = 5532.2 kWh
hence switchgrass = 5532.2 kWh/ton

eff. = output / input



Let's give the ring pelleter a try.

50kWh for the pelleter (Tom Miles)
50kWh for conditioning (Tom Miles)
energy needed to ring pellet switchgrass = 100kWh

eff. = output / input

eff. = 5532.2 kWh / 100 kWh
eff. = 55.322
or
eff. = 5532%



Let's try this all over with a gasifier/engine system at combined
efficiency of 20%, powering the pelleter.

100kWh input needed
20% eff. prime mover/gasifier

20            100
----    =    -------
100            x

20x = 10000
x = 500

500 kWh needed to fuel our prime mover.


eff. = output / input

eff. = 5532.2 kWh / 500 kWh

eff. = 11.0644

or

eff. = 1106%




> Next, what is the return on energy investment (or loss) making charcoal
> out
> of the boimass instead, and extruding Sarai Cooker fuel?  It takes far
> less
> energy in the form of electricity, but more in the form of charred
> biomass.
> Having excess biomass and less electricity, perhaps the best solution then
> is to make charcoal with a low investment of high quality energy, rather
> than to make the same raw material into a high density, uncharred lump.


No idea what a Sarai Cooker is but when one makes charcoal you keep ABOUT
1/3 of the fuel value. But now if one uses the off gas, things look
better.

I do not believe there is a silver bullet! We need to use the correct
method for the situation.



Best regards,

Jeff




-- 
Jeff Davis

Some where 20 miles south of Lake Erie, USA