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

[Tom Miles]

Paul,

 

The structure and composition of rice husk ash make rice husks a unique fuel
and so they should not be compared to straws. We did a fair amount of work
with rice husk combustion after our work with alkali deposits. That work is
proprietary to our client. We included phase diagrams in our alkali study
that show the effect of K:Si composition and temperature on liquidus states.
http://www.trmiles.com/alkali/Alkali_Report.pdf In practice unground rice
husks are a very stable fuel for gasification. You need to burn out the
carbon and get to some pretty high temperatures to have problems. Even if
you have an excess of K relative to Si, which would be the case in adding
coffee husks, you dot; have the slagging problems you would have with rice
straw. 

 

While at the Asian Pacific Biochar Conference last month in Japan we visited
the  <http://www.kippo.or.jp/e/nature/environment/Picture/252012_e.pdf> Aito
Eco-plaza "Nanohana Kan". They use an updraft, stirred bed, gasifier
supplied by Kansai Corporation to convert rice husks to biochar (Kuntan) and
heat. They feed 150 kg/hr husk at 2000 kcal/kg and get 50 kg/hr char. It is
a stirred bed gasifier. They say that husks gasify in the bed at about 600C.
Air is added above the bed to burn the gases. Stack gas is 15% O2 so they
use lots of excess air. About 30% of the heat input is recovered as hot
water which is used in the bio oil process and in winter for heating. 

 

They pack the product in clear 10 kg bags. I was interested in the labeling
of the bags. They indicate 40% carbon and 50% silica. 

Their label indicates that in 1 kg biochar they have

   K   11000mg

   Ca   5700

   Na   1700

   Mn    790

  Fe    190

   Zn   110

Cu     a very small quantity

 

They provide separate instructions for use in gardens, horticultural crops,
row cropland tees.  

 

The numbers of units and actual use are still not clear. I heard that Kansai
Corp had installed 200 of these and made char from about 10% of their husk
production of 100,000 tpy. 

 

I would expect the traditional farm scale kuntan pyrolysis to be at a
similar low temperature. We were told that Kuntan is used in growing rice
plant seedlings because it is good for root development. 

 

Steve M Haefele et. al. (IRRI) have published research on rice husk char.
Carbon and potassium contents of the char are similar to the Aito label
above. K concentrations in the char is 2 x the untreated char. C and N are
in similar concentrations in the char as in the untreated husk. One furnace
was developed at IRRI in conjunction with Nong Lam University in Vietnam. 

All of this research is relevant to the use of char from carbonizing stoves.


 

Tom   

 

Haefele, S. M., Y. Konboon, et al. (2011). "Effects and fate of biochar from
rice residues in rice-based systems." Field Crops Research 121(3): 430-440.
http://www.sciencedirect.com/science/article/pii/S0378429011000402

 

                Although crop residues constitute an enormous resource,
actual residue management practices in rice-based systems have various
negative side effects and contribute to global warming. The concept of a
combined bioenergy/biochar system could tackle these problems in a new way.
Rice residues would be used for energy production, thereby reducing field
burning and the use of fossil fuels, and the biochar by-product could help
to improve soils, avoid methane emissions, and sequester carbon in soils. To
examine some of these promises, we conducted field experiments from 2005 to
2008 in three different rice production systems. Objectives were to study
the effect of biochar from rice husks on soil characteristics, assess the
stability of carbonized rice residues in these different systems, and
evaluate the agronomic effect of biochar applications. The results showed
that application of untreated and carbonized rice husks (RH and CRH)
increased total organic carbon, total soil N, the C/N ratio, and available P
and K. Not significant or small effects were observed for soil reaction,
exchangeable Ca, Mg, Na, and the CEC. On a fertile soil, the high C/N ratio
of CRH seemed to have limited N availability, thereby slightly reducing
grain yields in the first three seasons after application. On a poor soil,
where the crop also suffered from water stress, soil chemical and physical
improvements increased yields by 16-35%. Together with a parallel study
including methane and CO2 emission measurements at one site, the results
strongly suggest that CRH is very stable in various rice soils and systems,
possibly for thousands of years. However, the study also showed that CRH was
very mobile in some soils. Especially in poor sandy soil, about half of the
applied carbon seemed to have moved below 0.30&#xa0;m in the soil profile
within 4 years after application. We concluded that biochar from rice
residues can be beneficial in rice-based systems but that actual effects on
soil fertility, grain yield, and soil organic carbon will depend on
site-specific conditions. Long-term studies on biochar in field trials seem
essential to better understand biochar effects and to investigate its
behavior in soils.

 

 

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