[Stoves] Mongolian traditional clay stove

Tue May 26 12:40:09 CDT 2020

Thanks for the additional input, Ron.

>[RWL1:  My guess is that Ag people almost everywhere have this dung-use concern. Dung use is seen all over the world’s most populous country - India.

In Tajikistan there is a fuel crisis (trees all cut down with no replanting effort of adequate size to compensate).  Fuel efficiency is very important to everyone, however cost dominates.  There is a lot of coppicing taking place – very common between fields. The remaining fuel is dung and the land is being deleted of some essentials due to the burning of what used to be applied annually from collected wastes.

[RWL2:  I wonder if the “tray" stove under question is felt to have those characteristics?   If not, why not?  The flame looked good enough.

The tray is a drying platform.  The fuel is fed in one piece at a time.  Based on observations, this would happened roughly every 10-15 minutes. The reason the flame is so clean is partly from burning dry dung and partly from being a tall “flame space”.  This vertical dimension is often missing from traditional stoves, especially India is an example of that.  The traditional stove is too short to burn biomass properly.  It takes a minimum of about 350mm to burn a complex biofuel cleanly (unless it is a downdraft combustor).
…Model 2 in later iterations during the Kyrgyz stove project. The final version for heating above 10,000 ft is the KG2.5. It is larger, the kind of stove that would be used in Pamir in Tajikistan.
                [RWL:  Can you give us a cite for both those stoves?

It is mentioned here<https://www.nature.com/articles/s41533-019-0144-8.epdf> but it is not a technical description. Full drawings are available here<http://www.newdawnengineering.com/website/library/Stoves/Kyrgyzstan/KG%20Model2/> for the Model 2 and here<http://www.newdawnengineering.com/website/library/Stoves/Kyrgyzstan/KG%20Model2.5/> for the Model 2.5.  The latter has a full set of cast iron tops and mould patterns etc.  The KG2.5 also gets a mention in the main technical document<https://openknowledge.worldbank.org/handle/10986/31282> previously referenced.

There is a large amount of char that goes to the fuel with the ash.
                [RWL:  This last sentence not clear.

There is a large amount of char that goes to the field with the ash.   I was surprised how much, actually. I took photos.  Carbonized dung is one way to get char to the field, but it is enormously wasteful as a processed fuel.  Somewhat less than half the energy is released in the stove meaning that more than twice as much dung has to be collected, processed into cakes, dried in the sun, collected, transported, and stored under shelter, then carried again into the house through the winter.  It is a terrible waste of human energy to “make char” from dung.

…the MM2 from Ulaanbaatar.
                [RWL:  another cite for the MM2 stove?

Modified Mongolian Traditional Stove version 2.0.  This has an end-lit crossdraft operating style (ELCD) with a flame tube mounted horizontally between the combustion chamber and the extended heat exchanger.

The main problem with the traditional stove converted from burning wood and dung to burning coal is the loss of thermal efficiency (and too much excess air at all times).  So the heat exchanger was enlarged to compensate based on some simple modeling of the heat losses to the room. The KG2 series is based on the MM2, with the KG2.5 including a higher level heat exchanger.  This allowed the tilting of the flame tube upwards at 20 degrees giving it superior ignition behavior.

An other significant change is that the chimney extends into the heat exchanger to near the bottom, creating a downdrafting heat exchanger, which is far superior particularly at lower power.  The flame tube is a generic improvement that can be added to any biomass burner that has a “smoky fuel” problem.  Adding a flame tube to the traditional stove (and nothing else) reduced emissions of PM2.5 by more than 80% and only cost $1.  It was rejected by the main sponsor of the stove replacement project on the basis that it was “too cheap”.  They had been instructed to spend a huge amount of money.  To this day, this locally-devised solution has not been incorporated into the traditional baseline stove design.

The result is a controllable flame, very much better combustion efficiency, higher temperatures and better CO combustion. The fuel saving is large - maybe 50%. The KG2.5 is about 88+90% efficient (LHV).
                [RWL:  Great news.  What portions of that efficiency number for cooking and heating?

That is the heating efficiency.  Cooking comes before the heat exchanger so whatever the cooking efficiency is (depends on the power setting) that is subtracted from the space heating efficiency.

I think the Ag people think that dung is a better offer.  If only half the work is needed for fuel preparation and it provides faster cooking, a more controllable fire, less chimney cleaning and less 50% transport, it is a good choice.
                [RWL:  Those of us in the biochar business hear a different story.  Will certainly depend on the increased NPP.  We hear of increased NPP factors like 2x, 3x, 4x with biochar.

Many this are said about biochar that are not fully descriptive of the exact circumstances in which this yield was determined.  Any such claims should be automatically greeted with measured skepticism.  The Japanese have been researching this for centuries and show that for particular fields with particular deficiencies that yields can be improved using a particular tree species prepared in a particular way applied in a particular dose.  Many of the claims for biochar improvement (char being almost entirely inert) can be replicated using vermiculite. I am sorry so many over-claims have been made for biochar because it is distracting from the scientific work that goes into understanding its potential.  The Cameroonian field tests (previously discussed here) are a particularly egregious example of such hubris.

Stay well, everyone
Crispin

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