Re: GAS-L: Fireballs! Increasing volume energy density and porosity

["Peter M. Davies" <p.m.davies@bigpond.com.au>]

Tom,

 

Interesting line of thought.  I was recently offered plans for a small granulator (couple of hundred kg/hr but scaleble).  I was wondering whether such equipment might not have application with the charcoal and sawdust fines probem, then your message arrived.......

 

Might have to take up the offer and carry out some tests.

 

Cheers,

Peter Davies

----- Original Message -----

From: Reedtb2@cs.com

To: stoves@crest.org

Cc: gasification@crest.org

Sent: Monday, February 26, 2001 1:24 AM

Subject: GAS-L: Fireballs! Increasing volume energy density and porosity

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