Fireballs! Increasing volume energy density and porosity

[Reedtb2@cs.com]

Dear Biomessers:

SOME PROBLEMS:Assorted biomass is a great energy source - and an awful fuel,
with typically low mass and volume energy density.  We can fix the first with
torrefaction and the second with densification, but at a cost.  

Another important criterion is porosity.  There's lots of sawdust in the
world, but it is hard to burn because air won't easily pass through a bed of
sawdust.   Char dust is a great fuel, but again hard to burn.  If we are to
burn sawdust or other fine particles in stoves and gasifiers, we need to
increase porosity.

                                                ~~~~~~~~
SOME SOLUTIONS:  My friend John Tatom (working then at the Asian Institute of
Technology) told me about making charcoal "fireballs" and I still have a few
in my lab.  Start with a tumbling drum full of powdered sawdust and slowly
add a starch water solution.  As in making bread, you will pass through a
lumpy stage.  Stop!  You have fireballs which, dried in the sun will
withstand a drop from 3 feet.  There has been a lot of speculation about what
to do with charcoal fines here, and I believe Elsen Karsted is now marketing
something close to these fireballs.

Yesterday I got to wondering if you could make fireballs from sawdust or
coconut shell fines in a similar fashion.  Cows and children in India make
cowdung patties and dry them on the walls of houses.  Maybe other too-small
biomass forms can be treated similarly.  

I made a 250 ml of starch solution by adding 25 ml of corn starch to 260 ml
water and boiling.  I then added fine sawdust from my table saw until I got a
dry paste.  By hand I molded 3 cm diameter balls and put them on a cookie
sheet for drying in the oven, first at 80C, then at 110C.  (I could have sun
dried them here in Denver, but was in a hurry.)   Here are the densities I
measured:

Loose Dry Sawdust                           160 g/l
Packed Dry sawdust                          260 g/l
3 cm Sawdust fireballs                       260 g/l, but big pores

In making coconut shell fuel for our gasifier we get 10-20% fines, some dense
shell, but some coiry stuff.  I winnowed out the coir in a medium breeze and
mixed the rest with a cup of starch-water. It was hard to make balls, but I
made a patty 2 cm thick and oven dried it.  It broke up into discrete pieces
(like granola).  

Coconut shell fines                              160 g/l  (chaff winnowed out)
Coconut shell chunks                           195 g/l  but quite porous

I intend to run both of these fuels in a Turbo stove and believe they will
work fine.  



HINT:  The "1 lb coffee can" is a main tool in my lab (but seldom delivers a
lb of coffee - usually 10-13 oz).  It measured 9.8 cm diameter by 13.5 cm
high.  From this I calculate the volume as 1.017 LITERS ~

                                        1 lb coffee can  ~ 1 LITER.  

So, while I had such a handy measure, I weighed a bunch of other fuels.

Sawdust pellets ($3.00/20 kg bag)                 640 g/l
Peanut shell pellets ($35/ton)                           600 g/l

How many other too-fine fuels could be made into patties by the children?
I'll bet they'd like it better than dung!
(What's brown and sounds like a bell? *)

Onward,                                        TOM REED




* DUNG