[Stoves] Fan assisted stoves in Nepal

[Rajan Thapa]

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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