[Stoves] why does coffee husk biochar smell like urine?

[Tom Miles]

Paul,

 

The coffee husks I have seen are paper thin. Is your fuel like that or
thicker? If it is think then it will "flash" pyrolyze.  The rice husks would
provide structure and could dampen the evolution or loss of nutrients. We
have seen silica absorb potassium in the gas stream. So I don't think that
you can assume that you will lose it all even if your raw fuel reaches peak
temperatures of 800-1000 C. The char probablu sees 800-900C. 

 

Tom

 

From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul Olivier
Sent: Sunday, October 16, 2011 1:23 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] why does coffee husk biochar smell like urine?

 

Alex,

Thanks so much for this graph.

Alexis Belonio says that the temperature within his gasifiers on rice hulls
reaches 1,000 C.
If this is true in the case of rice hulls, 
then the temperature within the reactor in the case of coffee husks is a
good deal higher.
If this is true, a lot of the K is lost in the coffee husk gas.

Coffee husks biochar has a moment at which it swells or expands during
gasification.
The volume of char actually increases within the reactor.
But if I shake the reactor during the process, the volume of char decreases
enormously.
If left unshaken, large cracks appear in the char, and the char forms
clumps.

When I added rice hulls to the coffee husks on the one occasion,
cracks did not appear in the biochar within the reactor, and the burn was
far more uniform.
The production of soot decreased a lot.

A few months ago, I put coffee husks in a large pan and attempted to torrefy
them using gasifier heat.
During this process, a lot of fumes were produced, and the coffee husks lost
their oily aspect.
When I gasified these "torrefied" husks, the flame shifted from orange to a
color in between orange and blue.

This opens up the possibility of torrefying the coffee husks to produce
acetic acid and other compounds.
Just as we torrefy the coffee bean, we would torrefy the husk.
This would leave behind a solid that would no longer absorb water,
as well as a solid that would thermally decompose at high temperatures in a
superior manner.
I have no idea if this makes sense.

Thanks.
Paul



On Sun, Oct 16, 2011 at 7:58 PM, Alex English <english at kingston.net> wrote:

Paul,
 Attached is minimalist, two points, graph showing potassium volatility
beginning at 400C with a ~37% loss at 800C.
Courtesy of Preto and Hrbek;
http://www.biochar.ca/files/Can%20Biochar%20Initiative%20Preto%20Dec08.pdf

Alex




On 16/10/2011 2:25 AM, Paul Olivier wrote:

Tom,

But the temperature in the reactor is much higher than 350 C.
I have seen a sort of clinker in the biochar if I do not turn the fan off at
the end of a batch.
At what temperature does the vaporization of K take place?

Paul

 


_______________________________________________
Stoves mailing list

to Send a Message to the list, use the email address
stoves at lists.bioenergylists.org

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists
.org

for more Biomass Cooking Stoves,  News and Information see our web site:
http://www.bioenergylists.org/






-- 
Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam

Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20111016/a3ddbebe/attachment.html>