[Stoves] why does coffee husk biochar smell like urine?
tmiles at trmiles.com
Sun Oct 16 15:14:13 PDT 2011
If you can keep peak temperatures below about 750 C then you can keep a
larger fraction of the K in the char. We have done this with staged
combustion in a variety of straw burners. It is now done commercially in
large scale straw burning power plants in Denmark, Spain and the UK.
That's the beauty of biochar from crop residues - low peak temperature
conversion to retain nutrients - but we have a wide variety of reactors,
including stove types, to deal with. It would be interesting to see an
elemental analysis of the principal ash components of the fuel and char from
the TLUDs to see what elements are retained. I haven't seen a proximate,
ultimate, Btu (HHV) and ash elemental analysis of any TLUD fuel.
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin
Sent: Sunday, October 16, 2011 2:37 PM
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] why does coffee husk biochar smell like urine?
I am bringing to mind that these high temperatures and the presence of at
least two fluxes were discussed when we were looking at making ceramic stove
components. The same principles apply: if there are fluxes (CL, K) in the
clay (ash) Si melts at a lower temperature. Alex found to his dismay this is
pretty easy to do with a large scale grass burner.
Roger Samson, to his credit, found out how to get the Cl and K out of the
grass and dramatically reduce the problem. When we speak of 'char' and at
the same time 'biomass' and 'wood', it would do us well to keep in mind the
very different result obtained when heating them to 900-950 C. One is going
to produce fused ash immediately and the other is hardly going to produce
any at all.
With ceramics, it is common to add K to reduce the melting temperature. It
seems that with combustion, we want it out because of the problems caused.
Attached is minimalist, two points, graph showing potassium volatility
beginning at 400C with a ~37% loss at 800C.
Courtesy of Preto and Hrbek;
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