[Stoves] Fan assisted stoves in Nepal

Mon Mar 5 10:10:55 CST 2007

Dear Rajan, Simon, and all,

Excellent reports and discussion.

I know Rajan from the ARECOP small gasifier workshop in Kunming last July.  I
hope that Rajan can come to the PCIA meeting on 20-24 March in Bangalore.  I
think that it is extremely important that he can come, and I hope funders will
assist him to get there.  RAJAN has some crucial hands-on experience.  By the
way, his ARECOP project is about a stove for making Lapsi candy using 
the Lapsi
fruit seeds as the main fuel in a TLUD design.  I am anxious to hear of your
experiences that I hope have been highly successful.

Note to all:  At the ARECOP workshop in China, Prof. Mukunda of IISc in
Bangalore was strongly advocating the TLUD technology in large sizes than the
residential cookstoves.  I hope information about those projects will also be
at the PCIA meeting.

Rajan, thank you for correctly using the terminology about the Nepal stoves:
> They are actually TLUD semi gasifier double wall metallic stove with 
> contineous feeding.

Only change that I would have said "...actually TLUD-inspired 
semi-gasifier..."

Simon observed that at a common characteristic of the fan-assisted stoves in
Nepal is:
> - A pattern of holes (approx 3/16th inch) all the way up the inside of the
> chamber.

That many holes is NOT a characteristic of a TRUE TLUD Top-Lit UpDraft 
gasifier.
Too much air coming in too low for it to be a true TLUD.

That many holes is consistent with the stoves I called "fan-blasters" or could
be called "fan-jet" or some other name, but not just a "fan stove" because
there are too many other stoves that can and could use a fan.  These "fan-jet"
stoves function very well because of the turbulence down inside the fuel
chamber.  An excellent example is the Philips stove (seen at ETHOS and on the
Internet.)  It is, in my opinion, a excellent "semi-gasifier" or
"quasi-gasifier."  Very clean burning.

These "fan-jet" stoves (derived from the earlier TLUDs) have the important
characteristic that Rajan described as "continuous feeding" of the fuel.  A
major "plus", except that (from the units that I have seen and tested) the
feeding must be done very very frequently (every 4 to 8 minutes??) in small
pieces of fuel.  I have only heard of the feeding being done manually, so that
is a negative aspect because of the need to attend to the stove so frequently.

Important note:  At all emissions tests (that I know of) conducted with 
the Reed
WoodGas Campstove (a true TLUD), the stove has ALWAYS been operated in the
"fan-jet" mode.  The WoodGas stove is NOT optimized for "fan-jet" combustion,
but it works very well that way and has inspired the development of the 
Philips
stove to make the air-flow changes to optimize the "fan-jet" mode of 
operation.

NOTE:  Part of the reason for the "fan-jet" usage in the Reed Campstove and in
the Philips stove is that they are designed for the cooking pot to sit 
directly
on the stove unit, making it very inconvenient to operate those stoves as true
TLUDs that use BATCHES of fuel and require the removal of the pot and
(preferably) the cooling down of the fuel chamber before reloading and
re-ignition.  As a consequence of USE, not of design, the original 
TLUDs by Tom
were found to function in the "fan-jet" mode, using "trickle-feeding" of fuel
that can be called "continuous feeding."

Comment:  We should distinguish between continuous/continual feeding of 
the fuel
and the much different feature of continuous/continual operation of the
combustion in the single stove unit that might need fuel added 
infrequently. Said differently, "continuous combustion without 
continuous/frequent fuel
feeding" is a goal for cookstoves.

To some of you, it might seem that I am "splitting hairs", but I assure 
you that
only by understanding these sometimes subtle differences can we truly 
understand
what is happening in combustion and inside our stoves.

So, from my vantage point half a world away, I feel that most (perhaps all) of
the fan-assisted Nepal stoves are probably "semi-TLUDS" or "fan-jet" or some
other name that does not confuse their technology with that of the true TLUDs
or with other stoves that might have fans.

I have worked on TLUD gasifiers for six years (since I met Tom Reed in 
2001).  I
have only seen natural draft versions that function well for respectable time
WHEN THEY HAVE DISTINCTIVE CHIMNEY-LIKE FEATURES ABOVE WHERE THE SECONDARY AIR
ENTERS INTO THE GASES.  And I believe this will apply to any "fan-jet" design
that is being used without the fan forcing the air.  It is true that you can
get some functioning some of the time with some fuel if you only have 
the lower
portion of the natural-draft TLUD gasifier.  The Karve updraft gasifier is of
that type, and it can make charcoal, as did Ron Larson's charcoal-making
updraft designs.  But they are not give strong flames.  "Chimney effect" is
essential if a TLUD or semi-TLUD is operated with natural draft.  Simon and
Rajan, please comment (or send photos) on the issue of anything that is
"chimney-like" associated with the Nepal stoves.

Must close.  I have another stove design (related to the above topics) waiting
for me in my frigid garage.  When (if) it works, I hope it is at PCIA with me.

Paul

-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson

Quoting Rajan Thapa <ics at crtnepal.org>:

> 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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