[Stoves] Fan assisted stoves in Nepal

Tue Mar 6 21:14:00 CST 2007

I'm pleased the CRT fan stove has been further developed, I think Paul
probably rightly describes the combustion system as 'fan blaster'. I fear it
will take some time for your improved design to become widely available,
simply due to the inertia of changing the design in dozens of small
workshops, clearing existing stock in small shops etc.

The culture here is definitely 'see a good idea, copy it' the possible
effect of this philosophy should not be underestimated and it is important
that any designs that make it from the workshop, through pilot studies and
into the market really are the best we can possibly do.

Designs need to be fully developed before they are released into wider
society, otherwise we will either be stuck with them for years to come, or,
just as bad, people will start to lose faith in this 'new' technology which
is always releasing a better version.

The ICS (mud stove) program concerns me almost more than the fan stoves, is
the design being disseminated in Nepal really the best one out there? (I
know you still have a smoke blowback problem due to short chimneys on the
downwind side of houses) Are all implementers using the same design (there
seem to be lots of NGOs involved in ICS)?

On a more affirmative note, Rajan I wholeheartedly agree with you on radiant
heat, I fitted one of my stoves with 1 inch of glass wool (under a sheet
metal casing) around the outside and it made a big difference, particularly
to the boiling time (heat into the pan), the stove has other problems but it
certainly helped with this aspect. My feeling is that double walled stoves
with larger spacing between inner & outer walls suffer much less from this
radiant heat problem, I guess the thick air layer helps reduce heat loss
this way.

I also agree that natural draft is much preferable, the less moving parts
the better.

Also on your list though surely there should be something about fuel size.
In much of Nepal wood is gathered green from 2-3 inch branches, although
this can be relatively easily split to reduce the diameter I just cannot see
anyone (particularly after spending hours cutting & carrying the wood)
spending further hours chopping it into the small pieces required for the
current
fan stoves.

(For those less familiar with this style of wood gathering check out the
photo on the billion stove website , the wood will normally be burnt just as
you see it there, in 2-3 foot lengths).
http://ww1.prweb.com/prfiles/2007/02/25/507518/Nepalwoodgathering.jpg

Is anyone working on side feeding stoves for this length of wood, or is it
back to the rocket stove? (I'd love to see some more information on the side
feeding designs already out there, I think at CSU, can I see some anywhere
on the web?)

Apologies I never introduced myself, I'm originally from Britain, Mechanical
Engineer by training (plus MSc in Combustion & Energy), have been in Nepal
for 3 years working initially in a training institute and latterly at an NGO
working mostly with Hydro-power. In a previous life I worked purely on
combustion systems where we refined the art of burning 50mg of diesel in a
few milliseconds 2000 times a minute as cleanly and efficiently as we
possibly could, we spent thousands of hours developing these systems before
they were let out of the door.

----- Original Message -----
From: "Rajan Thapa" <ics at crtnepal.org>
To: "Simon and Zoe" <simonandzoe at yakpost.net>; "Discussion of biomass
cooking stoves" <stoves at listserv.repp.org>
Sent: Monday, March 05, 2007 5:09 PM
Subject: Re: [Stoves] Fan assisted stoves in Nepal

Dear Simon and Zoe,
Thanks for the information regarding fan assisted stoves in Nepal. They are
actually TLUD semi gasifier double wall metallic stove with contineous
feeding. Approximately~ more than 50,000 such stoves have been sold in the
market in the last 3-4 years.The first generation of these stoves had the
features exactly as you have mentioned and most of the fabricators are still
following the same design using 12 volt dc  computer fans with adaptors.
>From last year there has been some improvements like instead of pattern of
holes there are two rows of  3-16 inch holes for primary and secondary
burning (combustion and gasification),still not the blue flame but bright
yellowish flame and less emission.The fan has a control knob  like in the
table fan which controls the air and hence flame.The stoves are available in
2-3 sizes: the family sizes(4-5 inches) or for hostels, hotels and
restaurants they are larger than this. They can be used with contineous fuel
feeding with but smaller peices of wood. There is a grate which holds the
fuel and drops the ash in the bottom of stove which can be taken out from
the small opening. This  opening  also serves as an inlet for natural draft
both for combustion and gasification and works well even if there is no
electricity but of course there is a little more soot.
We have tried to disseminate this knowhow of improved version which is
better than the earlier version but  this has still not reached to many
local workshops in who fabricate fan assisted stoves in different parts of
the country.It's nice to hear that you have tested a couple of stoves and
made one your own design.We have also improved the design with more control
of primary and secondary air so that there is  cleaner combustion and flame
control. Our organisation Centre for Rural Technology, Nepal (CRT/N) an NGO
engaged in disseminating stoves in Nepal and have promoted more than150,000
sun dried mud brick (adobe)stoves in Nepal particularly in hills and mostly
the two pot hole with short chimney for reducing indoor air pollution
besides fuelwood saving. As  a promoting organisation of improved stoves in
Nepal we are also very much   interested to further improve these fan driven
stoves and share/disseminate the information with as many people.We have
made some improvements based on the information gained from stove list serve
and the knowledge gained from the Asia Regional Cookstove Program(ARECOP)
hosted Kunming workshop in  China last year. Some important issues we feel
are:
1.reduce soot by regulating actual amount of air flow both on top and the
bottom of the chamber with calculated  required no of air holes to different
volume of reactor/combustion chamber.
2. reduce the radiant heat loss.
3.reduce the ignition time which is now 2-3 minutes for constant and good
flame.
4. increase the durability of the inner metal wall which has a life of  6
months to 1 year for restaurants use and about a year and half for
households use when 16 -gauge mild steel sheet is used.
5.  have  reasonably better combustion even with the natural draft when
there is no electricity as  mentioned  6 hrs a day load shedding in the dry
season.
6. And most importantly have a household natural draft semi-gasifier without
fan (user friendly wood gas stove) because  60% -70% of 2.5 millions rural
households  have no electricity.
Regards,
Rajan Thapa
Centre for Rural Technology, Nepal.
Tripureshwor, Kathmandu.Tel 977-1-4256819,4260165
www.crtnepal.org

From: "Simon and Zoe" <simonandzoe at yakpost.net>
To: <stoves at listserv.repp.org>
Sent: Monday, March 05, 2007 7:45 AM
Subject: [Stoves] Fan assisted stoves in Nepal

Dear all,

Here's the good news: fan assisted stoves have taken off over here. It has
taken some time, I saw my first one at an industry fair this time two years
ago but recently they have become available all over the bazar here in
Kathmandu.

The bad news is that they don't seem to be anything like the kind of stoves
you guys are talking about! OK they burn pretty hot, but I've yet to see a
blue flame from one.

There are lots of variations on the design too, let me try and summarise:

All stoves have these features:

- internal diameter approx. 5 inches.
- depth of combustion chamber 4-5 inches.
- A pattern of holes (approx 3/16th inch) all the way up the inside of the
chamber.
- 12v fans of approx. 3 inch diameter attached normally very crudely.
- Fans on tube to one side (well away from the heat).
- Constructed of relatively thick mild steel sheet.
- Cost is 15 - 20 USD (including mains adaptor, not very useful at the
moment with 6hrs a day of load shedding!).

Some stoves:
- have a plain sheet floor (ie. no air holes).
- have quite a clever design which allows ash to be removed from below (not
that there is much ash).

I've tested a couple of these stoves (and one made to my own design) and am
getting wood consumption at best of 100g/litre (to bring 2L of water to boil
from around 20°C in 10-12 mins with no simmer time). Smoke is low enough to
be invisible after the first couple of minutes.

It is probably too late now that the stoves are all over the market, but it
would be great to demonstrate a really good fan assisted stove here. Can
someone point me in the direction of a really good design that works well
(most common fuel here is wood)? I can't get onto the 'bioenergylists.org'
site at the moment, is this the one which is mentioned as being down?

I have a few other points to add about fan assisted stoves but that's enough
for now!

thanks

Simon
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