Talk given at the ETHOS Conference 2011 about the latest developments in rice husk cook stove technology. Rice husk cook stoves are an interesting technology because of the amount of waste rice husk in developing countries worldwide.

1. State of the Art in Rice
Husk Cook Stoves
Marc Paré
Mechanical Engineering // Georgia Tech
Jan 2011 // ETHOS Conference
Saturday, January 29, 2011

2. Saturday, January 29, 2011

3. [Resource Opportunity]
[Properties of Rice Husk]
100 kW
($4000) [Resulting Notable Designs]
0.8 kW
($30) 0.3 kW
0.3 kW
($20)
($10)
Saturday, January 29, 2011

4. World Rice Consumption 2008 (USDA)
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6. How much energy is
out there?
432,039 metric tons of rice consumed / year
x 0.6 milling rate
x 12 GJ / metric ton
/ 1.3 MJ to cook a meal
2 billion meals / year
Saturday, January 29, 2011

7. Properties of Rice Husk
• Energy Content
• Chemical Composition
• Angle of Repose
• Thermal Conductivity
• Air Flow Resistance
Saturday, January 29, 2011

8. Properties of Rice Husk
or Understanding a Really Strange Fuel
• Energy Content Low
• Chemical Composition High in Silicates
• Angle of Repose Causes Bridging
• Thermal Conductivity Can Put Out Fires
• Air Flow Resistance Darn High
Saturday, January 29, 2011

9. Energy Content
Hull 3000 kcal / kg
Char
Ash
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11. Ash Chemical
Composition
Al2O3
6% MgO Losses
2% 9%
Fe2O3 CaO
1% 2%
SiO2
80%
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12. Angle of Repose
θ
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13. Thermal Conductivity
Test Results from ASTM testing by
R&D Services of Cookville,
Tennessee (Courtesy Dr. Paul
Olivier)
Saturday, January 29, 2011

14. Dr. Paul Olivier http://www.esrla.com/
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15. Resistance to Air Flow
• Pressure drop higher
than that generated by
stack effect in a natural
draft cook stove
Saturday, January 29, 2011

16. Summary, courtesy of
Eldon Beagle
“The high percentage of silica in rice hulls and the
peculiar silica-cellulose structure impede uniform
and thorough burning of the hulls in a combustion
process.”
“Eldon Beagle set a pile of rice hulls 300’x500’x50’ on fire
and they burned for six months.”
“However, husk cannot be burnt easily or cleanly with
excess air, and energy recovery is very low as the heat
produced cannot be utilized in a beneficial manner.”
Beagle (1978), p. 8. ,Velupillai (1996), p. 18., Ibid., p. 24. , Ibid., p. 25.
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17. It can’t be done?
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18. Gasification
• Two-stage
• Cleaner burn
• More fuels
• Air-controlled
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19. Power Generation
$34 / kW
30-300 kW
• Fluidised bed
• Projects around the
world
Dr. Alexis Belonio
Saturday, January 29, 2011

20. Forced Air Batch Gasification
$113
0.8 kW
• Requires a fan and
electricity
• Blue flame
• Easy to control
Dr. Alexis Belonio
• Batch operation
Saturday, January 29, 2011

21. Dr. Paul Oliver
Saturday, January 29, 2011

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23. Continuous Quasi-Gasification
$30
0.3 kW
• Requires tapping every
few minutes
• Continuous operation
• Easy to start
• Emissions?
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25. Natural Draft Batch Gasification
$20
0.3 kW
• Chimney provides
necessary draft
• Very little material
• Batch operation
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28. Future?
• TEG (or thermopile) to power fan
• More autonomous continuous stove
• Blue flame on natural draft stove
• More options for cooking surface
construction
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29. smallredtile.com
Saturday, January 29, 2011

30. Sources
• IRRI World Rice Statistics http://beta.irri.org/solutions/index.php?
option=com_content&task=view&id=250
• Chemical Analysis of Rice Husk Ash: http://www.scribd.com/doc/3085035/Chemical-Analysis-of-
Rice-Husk-Ash
• Rice and Straw Properties (Rice Knowledge Bank) http://www.knowledgebank.irri.org/rkb/
index.php/rice-milling/contributions-and-references-milling/further-information-byproducts/
husk-and-straw-properties
• “No other plant offal even approaches the amount of silica found in rice husks.” Beagle, E.C.
1978. FOA Agricultural Services Bulletin 31, p. 8.
• Kaupp, A. (1984). Gasification of Rice Hull: Theory and Praxix.
Federal Republic of Germany:
GATE/GTZ. 303pp.
• http://gasifiers.bioenergylists.org/content/continuous-flow-rice-husk-gasifier-thermal-application
• Sawdust stove image: http://www.motherearthnews.com/Do-It-Yourself/1974-11-01/How-To-
Sawdust-Stove.aspx
•
Saturday, January 29, 2011