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

Sun Oct 16 19:31:16 CDT 2011

Tom,

I found this which confirms what you are saying:

*The melting point of SiO2 is 1410–1610°C, while that of
K2O and Na2O is 350 and 1275°C respectively. It has
been suggested that at higher temperatures, the low-melting
oxides fuse with silica on the surface of the rice husk
char and form glassy or amorphous phases, preventing the
completion of reaction. This places an upper limit on local
temperature of the gasifier.
*
Thanks.
Paul

On Mon, Oct 17, 2011 at 5:36 AM, Paul Olivier <paul.olivier at esrla.com>wrote:

> Tom,
>
> The coffee husk is composed of several layers that are liberated from one
> another in the dry milling process.
> There are some thin soft layers and some thicker hard layers.
> It would be easy to take measurements with a caliper,
> and compare them to the thickness of the rice hull.
>
> If silica reacts with potassium, do we end up with potassium silicate ( K2
> SiO3)?
> Potassium Silicate
>
> A liquid source of potassium and silica. Silica is often a forgotten
> element and has many benefits in the plant including strengthening cell
> walls.
> Benefits
>
>    - Biological Farmers of Australia (BFA) Registered Product 456AI.
>    - Improves photosynthesis and raises brix in all plants.
>    - Reduces the negative effects of excess aluminum, sodium and
>    manganese.
>    Improves plant growth, lifting yield and quality.
>    - Enhances reproduction by improving pollination and increasing pollen
>    fertility.
>    - Produces an armour-like resilient layer in the outer cell wall
>    resulting in:
>    - Reduced lodging.
>    - Decreased plant palatability.
>    - Less fungal colonisation sites.
>
> Thanks.
> Paul
>
>
> On Mon, Oct 17, 2011 at 3:36 AM, Tom Miles <tmiles at trmiles.com> wrote:
>
>> 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****
>>
>> ** **
>>
>>
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>> ****
>>
>>
>>
>>
>> --
>> 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/****
>>
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>>
>
>
> --
> 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/
>

-- 
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/
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