[Stoves] Retted Switchgrass Fireball Test

[Tom Miles]

Straw, even in he form of a fireball, seems to have just enough air to
support combustion in a smoulder but needs a pilot flame to burn the gas. A
combination of paper and switchgrass fireballs might work. 

Pictures of Jeff's switchgrass and paper fireballs that Paul brought to
Stoves camp can be found at
http://bioenergylists.org/en/fireballswg 

Tom Miles 

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Message: 4
Date: Sat, 02 Sep 2006 09:47:55 +0100
From: AJH <list at sylva.icuklive.co.uk>
Subject: Re: [Stoves] Retted Switchgrass Fireball Test
To: Jeff Davis <jeff0124 at velocity.net>
Cc: stoves at listserv.repp.org
Message-ID: <f2gif2hjc1v0dm23mpen16nrc0o9ctd197 at 4ax.com>
Content-Type: text/plain; charset=us-ascii

On Sat, 2 Sep 2006 00:27:51 -0400, Jeff Davis wrote:

>I had this evening to burn some of my small switchgrass fireballs. Big 
>disaster. They just made smoke.

I've had lots of poor experiences like this, I find adding a bit of
wood normally sustains a flame as does using a small amount of propane
as a support fuel.

My take is that despite perceived wisdom being that all biomass at the
same moisture content has the same calorific value there are
sufficient differences in pyrolysis products to change the flame
holding and ignition temperatures. If the flame cannot hold, for
instance because the offgas lacks a component with a high flame speed,
then the smoke billowing off is just wasted fuel, so there is no
feedback to keep the combustion above the spontaneous combustion
temperatures. The remaining char still burns at a fairly low
temperature but still high enough to continue pyrolysis of fresh fuel.

My guess is these types of fuel will need better insulation of the
combustion chamber and probably preheating of secondary air.

AJH