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

Tom Miles tmiles at trmiles.com
Sat Oct 15 21:00:53 PDT 2011

The actually exists as KOH and vaporize starting at about 350 and increasing
in greater proportions as you increase temperature. Once it vaporizes it
condenses quickly with chlorine or sulfur, if present. Only when it is hot
enough (750 C or higher) will it begin to melt, especially If it is present
with silica in a ratio of about 1:2. Husk silica is more resistant than
straw silica to alkali silicate formation. I would think the most of the K
will stay in the char. If you get K volatilization you will see it where you
burn the gas. Over time you’ll get agglomeration of very fine (submicron
like cigarette smoke) particles that we call an alkali fume. At such low
fuel rates you’re not likely to see anything for some time.    


Using the rice husk as a pilot fuel for the coffee husk makes a lot of
sense. You’ll get a clean gas and a rich husk char. 




From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul Olivier
Sent: Saturday, October 15, 2011 5:17 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] why does coffee husk biochar smell like urine?



When subjected to temperatures greater than 350 C, 
are you saying that K2O melts but does not vaporize?
Are you saying that we end up with melted K2O?
If the original coffee husks contains 36% to 38%
then the final biochar must contain at least twice that amount.
If this is correct, then coffee husk biochar must be quite valuable,
not only as a soil amendment but also as a fertilizer.
Surely this cannot be right.

The coffee husk contains some sort of oily substance
that begins to volatilize at temperatures as low as 170 C.
When gasified it produces a lot of black soot.
I tried many burner designs in the last few weeks to get rid of the soot and
to turn orange flames into blue.
Supplying hot premixed secondary air does not effectively consume this soot.
Sometimes it makes things worse.

A few days ago I cheated.
I mixed coffee husks and rice hulls in equal volumes.
(Note that the coffee husk has a bulk density of 180 kg/m3,
while the rice husk has a bulk density of about 100 kg/m3.)
The flame at the base was blue and white.
This is the first time I saw the color white in the gasification of coffee
As the flame rose, it split into two parts:
one part vertical and the other part more horizontal.
The vertical part was blue/white and the more horizontal part was orange.
But there were no streaks of black within the orange part of the flame and
no visible soot.

The gasifier that I used looked like this:
Note the burner design: 
it is a Belonio burner with two rings of burner holes, together with a
burner housing.
This burner design gives by far the best result.
Secondary air is sucked up between the housing and the burner.
It then moves from vertical to horizontal,
and from here it hits the two rings of holes that are offset from one

The best result, of course, is with 100% rice husks.
With the current burner design, the flame is totally blue right from the
very beginning.

When I mixed rice hulls with coffee husks (half/half by volume),
not only does most of the soot disappear, 
but the burn is quite consistent and steady from beginning to end.


On Sun, Oct 16, 2011 at 5:35 AM, Frans Peeters <peetersfrans at telenet.be>

Dear Paul ,


   I did many times fusions with pure KOH .

At 350° C it melts and is very aggesive to dissolve ceramics Al2O3 and SiC
powders . (Diamond recup. )

It is verry verry  hygroscopic and the hydroxyde airosols with water in the
air gives your nose sense alcalic .

Your brain makes the link to urine . but not the real potasium make it .

It goes not into gas  but sputers airosols has a special creep effect out of
a creuset .! Even after cooling .

Also a battery  and fuel cel with KOH . It creeps in a isolated conductor
for 20 cm after years ,and destroys manny apparati .

KOH Is colourless but Nickel gives  yellow.salts .

It does not become K2O2 becouse to destroy SiC we must ad Na2O2 to oxydize
the carbide .

Potasium is to measure with flame spectro 440 um purple colour in a hydrogen
flame . (Sodium =yellow . Cupper =green Sr =red

Sorry ,I drink no coffe !            But have a friend who drinks pee 







Van: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] Namens Paul Olivier
Verzonden: zaterdag 15 oktober 2011 9:07
Aan: Discussion of biomass cooking stoves
CC: Will Rutherford; loren cardeli; CHRISTA ROTH
Onderwerp: [Stoves] why does coffee husk biochar smell like urine?



Do you have any idea why coffee husk biochar smells like urine?

I just read that coffee husks contain 36% to 38% K2O.
This supposedly accounts for the low melting point of its ash.
That its ash has a low melting point makes sense to me,
since, if I leave the fan on a bit too long after the gasification cycle is
I see a stony yellowish/white ash at the bottom of the reactor.

How is this possible that coffee husks could have so much K2O?
What happens to the K2O when it is subjected to heat?
I see that K2O has a melting point > 350C.
If subjected to heat does it turn into K2O2 or even KO2?
At what point does it turn into a gas?

Does the presence of K2O account for its urine smell?
What does this urine smell mean with regard to the value of coffee husk
Would coffee husk biochar be rich in potassium?

Paul A. Olivier 
27C Pham Hong Thai Street

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