The Mayon Turbo Stove

[RSamson@reap-canada.com]

Dear Stovers

You may be interested in an ongoing rice hull cooker stove improvement
program REAP has been involved in with partner organizations in the
Philippines.  Detailed information on how to use and build the Mayon
Turbo Stove is now on our WEB site at:

www.reap-canada.com

Please fund below a summary of the projects background and development.

Like many developing countries, the Philippines has a growing population
and increasing rural poverty, and cooking fuels are becoming
increasingly scarce. REAP recently completed a report for NREL on
“Strategies for Enhancing Biomass Energy Utilization in the Philippines”
and one of the most promising options identified was to utilize rice
hulls as a low cost domestic cooking fuel source. There are more than
1.5 million tonnes of recoverable rice hulls in the Philippines which
could be used as cooking fuel by more than 1 million families. Using
rice hull locally in low cost cookers seemed the ideal way to utilize
the resource as it is widely dispersed and of a bulky nature.  Rice hull
also has the natural advantage of being of a uniform and small size.
These characteristics make it relatively easy to design an efficient
combustion system for household cooking in comparison to burning with
wood or other crop residues.

In 2001, REAP acquired a 3 year funding program from the Canadian
International Development Agency to introduce an improved rice hull
stove into approximately 10,000 households in the Western Visayas region
of the Philippines. To improve the stove, we accessed all the major rice
hull stoves available in the Philippines including versions from the
International Rice Research Institute (IRRI), Philrice, the Central
Philippine University (CPU) and a version of the Lo-Trau model developed
in Vietnam. Some of these stoves were superior to others but all
suffered from  from one or several deficiencies including: incomplete
combustion, excess air, uncontrollable fuelbed fires, high rice hull
consumption and being overly expensive for rural peasants to purchase.
We needed to build a stove for under (US) $7.50, as this  represented
one weeks salary in rural areas of the Western Visayas. Peasants also
were  used to buying charcoal and firewood stoves made from clay that
sell for about (US)$ 0.50.

We decided to work with the Lo-Trau model because of its relatively low
cost and simple basic design. With our partner organizations, PDG and
MASIPAG, we streamlined production improvements to manufacture the stove
to get production costs down to  (US)$7 per stove. However, we observed
that the stoves we were introducing to communities were experiencing
problems of incomplete combustion and required constant maintenance and
tapping.  We made some initial combustion improvements to the stove by
lengthening the frustrum (the center cone) from 5 to 7 inches (which
also shrank the cone top and concentrated the flame under the pot). We
also drilled secondary air holes, 2 to 3 from the top of the cone. To
minimize fuelbed fires, we eliminated one of four rows of holes at the
base of the fuel bin to reduce upward airflow through the fuel bin.
These changes improved the stove, but the flame remained excessively
smoky and the stove required regular tapping (although this was reduced)
to maintain combustion. The CPU stove we tested had a single air vent
pipe through the bottom of the ashpan, which appeared to help reduce
smoke events. We decided to experiment with different sized pipes to
determine a level of air that would be adequate but not excessive. We
noticed that the single pipe caused a blue flame in the center of the
cone. However, surrounding this oxygen source, the flame was still an
orange-yellow colour. We realized we needed more air mixing in the cone
as we perceived there were still oxygen dead spots that led to
incomplete combustion of the gases. One option we tested was twin air
pipes of 1 inch diameter to increase turbulence inside the cone. They
ended up creating vortexes in the flames and appeared to slow the rate
of air flow out of the cone (which was excessive in the centre with the
single large air pipe). The result of the twin air injectors was that
after 3-5 minutes, a blue or nearly colourless flame was present
throughout the cone. Maintenance of the stove also was reduced, tapping
of the stove was only required after 10-12 minutes to maintain the stove
flame.  However, we still experienced some smoke events after ten
minutes of burning when the rice hull turned to ash and reduced airflow
from the holes at the base of the fuel bin. We decided to increase the
size of the 10 secondary air vents from ¼ to 3/8 inch. After this
modification, we experienced no more smoke events due to oxygen
problems. Smoke events only occurred when the flame was going out due to
lack of fuel. This occurred generally when the fuel bed turned grey from
the hulls being completely burnt out. Simply tapping to introduce more
fuel, about every 10 minutes maintained the flame.  The new model also
has been found to be easier to start, and produces less smoke upon
termination. Essentially we believe now the stove has a near perfect air
situation. There appears to be no excess air and no oxygen deficient
areas of the cone, or oxygen deficient periods during the entire burn
cycle. When new fuel is added, smoke infrequently occurs and a clean
burning flame returns rapidly. Clean combustion occurs as the new design
appears to increase the gases residence time in the inner cone and
exposes them to higher temperatures. The rice hull ash falling out is
now of a whitish grey colour. The changing nature of the airflow through
the fuel bed (as the relatively porous hull turns to ash) is dealt with
through the twin air pipes and secondary air at the top of the inner
cone. The most important new design improvement appears to be the twin
air injectors that create a swirling and mixing action. Older stoves in
communities are now being retrofitting with the twin pipes.

We have had favorable feedback thus far from communities using the
stove. Households are experiencing reductions in rice hull fuel
requirements, less maintenance and less smoke. The main activity we are
now examining is to build a smaller stove with a 6 inch diameter
fuelbed. The 7” diameter fuelbed model now appears to have excessive
heat output for smaller pots of rice because of more complete combustion
of the rice hulls and gases, and better control of the air flow. The
project is still in its first year and we are currently producing and
marketing approximately 350 stoves per month. Savings appear
considerable for low income rural families purchasing firewood, charcoal
and LPG. A user survey found cooking with the Mayon Turbo reduces the
annualized cooking cost (annual stove and purchased fuel cost) to only
(US) $5.20 per year in Negros, a  91-95% compared to purchasing the
aforementioned fuels.

A line drawing and instructions on how to build and use the Mayon Turbo
Stove can be found at www.reap-canada.com. We would be most willing to
work with other groups who are interested in building the improved stove
in other rice producing nations.

Good luck trying the stove and we look forward to your feedback.

Trevor Helwig, Claudia Ho Lem and Roger Samson

Resource Efficient Agricultural Production-Canada
Box 125, Maison Glenaladale,
Ste Anne de Bellevue,
Quebec, CANADA
H9X 3V9
WWW.REAP-CANADA.COM
Tel. (514) 398-7743
Fax (514) 398-7972

"Creating ecological energy, fibre and food production systems"






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