[Stoves] [Gasification] Grass Fireballs burn cleaner than wood

[Roger Samson]

Tom and all

My guess is that the loss of dry matter from jeffs retting/rotting process
is quite high (likely 50-75%). Here in Quebec when we overwinter our grass
for fuel pellet production the grass largely avoids any dry matter loss due
to decomposition. Most of our losses we have experienced are related to
breakage of leaves and seed heads, we largely retain all stem and leaf
sheath biomass. Now we believe we are best to late fall cut (overwintering
the material in the field in a swath) and subsequently spring harvest to
avoid the wind breakage during the Canadian winter.  We mostly get leaching
and a mild retting. Even this process seems to soften the fibre somewhat and
take the wax off the grass. It makes it easier to make a high quality fuel
pellet or cube if there is a delayed harvest. Getting the wax off the grass
is likely important to allow it to ball up as well. From our studies with
switchgrass here in Canada for the pulp and paper industry, we learned that
switchgrass has a relatively wide spectrum of lengths of fibre relative to
wood (it has both more long fibres and more fines than poplar trees). This
is likely one of the reasons it tends to ball up nicely and why a sheet of
paper made of wood and switchgrass fibre has superior printing quality (it
is smoother as the diverse fibre lengths fill out the paper sheet better). I
would assume many tropical grasses would behave similarly and will ball up
nicely like switchgrass. It may be in fact some tropical grasses may even
ball up better than switchgrass and these could be specifically cultivated
for this application.  
   
See the report on our web site on line library: "switchgrass: a potential
pulp fibre source" which describes the fibre attributes of switchgrass 
http://www.reap-canada.com/online_library/Reports%20and%20Newsletters/Agri-F
ibres/8%20Switchgrass,%20A.pdf


It may be that for grass fireballs in developing countries we can accept a
high dry matter loss in some areas where grass grows in abundance. However
we should likely try and avoid too much loss (for both energy recovery and
fuel quality reasons). I am not sure we need a binder. It may be all we need
to do is chop the fibre somewhat and use a good grinding/balling process. In
the pulping business they regularly regrind the stones to ensure they keep
their grinding stones effectively operating. I would assume we would need to
regularly regrind our cement mixer ball grinding stones as well (maybe we
could use steel balls even instead of stone).  

The other options to enhance the process would be to use a relatively low
cost starchy binder such as cassava. They are using cassava in briquette
production as a binder (google cassava as a binder) and you will see a
number of reports from the Philippines. It seems it is used at about 6-15%
of the dry matter being briquetted. See for example 
http://erdb.denr.gov.ph/denr_rec/vol10/denr_v10.pdf

There seems to be something about round objects tending to naturally form as
an entropy avoidance strategy (nice round planet we live on). We just need
to understand and nurture the process and we will create nice grass ball
fuel without a lot of expense or effort. 

Roger Samson
www.reap-canada.com

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Tom Miles
Sent: Friday, December 29, 2006 12:59 AM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] [Gasification] Grass Fireballs burn cleaner than wood

Jeff,

It would be interesting to measure the dry matter loss from your retting
process. 

Composting can work the other way - reducing the carbon increases the
relative ash which reduces the heating value.

Tom