[Stoves] Dung Rocket Stove - Failed Test

Sun Jan 15 19:09:52 CST 2023

Dear Kevin

I was so impressed with your attempts earlier to try this that I saved a stash of corn stove/stalks from the garden intending to try it.

I have almost completed by emissions evacuation system in the workshop and will at some point try it out.

I have some ideas about how it might work well.  I like the idea of using a band to hold low density fuels which are tedious to burn otherwise. Too much fiddling to push them in.  I saw this sort of cooking in Eastern Niger with millet stalks - the dominant fuel there.   If it is worked out well, you should be able to promote it in the Sahel.  There are lots of people who can work with metal (forgerons).

Regards
Crispin

From: Stoves <stoves-bounces at lists.bioenergylists.org> On Behalf Of Kevin McLean
Sent: Sunday, January 15, 2023 17:44
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Dung Rocket Stove - Failed Test

Also, Crispin.  Have you tested anything related to top-lit bundles in bands?

On Sun, Jan 15, 2023 at 4:49 PM Kevin McLean <kevin at sun24.org<mailto:kevin at sun24.org>> wrote:
Crispin,

In high Mongolia, no crops or vegetables are grown so there is no need for fertilizer or biochar as a soil amendment, correct?

On Sun, Jan 15, 2023 at 4:13 PM Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Dear Ron and All

I will consolidate several message responses.

> a.  We'd rather not cook with dung at all  (agreeing with Paul Olivier below).

There are a number of places where dung is used because it can he accessed "in house" for example in a crowded urban area without access to purchased fuels.  The cow does the energy collection during the day and provides it free to the family.  It is not only where alternative fuels are absent.  If it is free and convenient, people use it.

Just because fuel is free doesn't mean it has to be burned badly.  Just because a fuel is burned badly doesn't mean it cannot be burned cleanly.  Just because a fuel could make biochar doesn't mean it is wise to do so.

> b.  We think making char apt to be cleaner and good for soil, but carbon dioxide removal (CDR) may also mean one can make money while cooking.  Might also save time for the cooks.

Many people have no soil, and cannot grow anything in the soil they have access to.  This is generally true for all high altitude locations where dung burning in a rural area is widespread. Such areas include the whole of the northern and southern Himalayas.  In the Pamir of Tajikistan, if you do not burn dung, you die.

> c.   We are unaware of any char-making stoves using dung (because dung is so non-dense - need a lot more volume.)

This is a good point. If you have to collect and (usually) process the dung, the resulting fuel is not very energy dense, meaning available MJ/kg.  Plus it is not dense kg/m3.  If you are creating char from a low energy fuel, it is not wise in terms of effort.  If you only get 1/3 of the available energy because the rest is tied up in char, you will have to collect 3 times are much fuel.  Who is going to do that?!  People are not crazy.

> 5.  Other:
                   a.  Anyone think that the present users of dung-burning stoves in Mongolia and similar would surely or not-at-all welcome such a stove?

The photo Paul sent of a "dung burning stove" shown a box with a chimney - typical of all Mongolian local baseline products.  There is nothing "dung-burning" about the design.  They are typically made from 2mm steel sheet and are good space heaters - with wood or dung.  As wood burners they tend to be pretty good, but they are terrible coal stoves which is the preferred urban fuel.

A reasonably designed dung-burning stove such as the KG2.5<mailto:http://www.newdawnengineering.com/website/library/Stoves/Kyrgyzstan/KG%20Model2.5/> produced in Bishkek has staged combustion and the ability to cook at least two pots - water heating being a major need.  Stoves, when not cooking, are often heating 3 containers of water.

> Anyone able to confirm those are from horses?  Maybe Yaks?   If guaranteed to be horse dung, then we don't need zoos.

Dung source depends of geography and climate.   Yaks can live on very poor grasses (like bison) and excrete modestly sized pellets. Bigger than a horse ("road apples") and much smaller than cattle.  In the high cold regions, dung dries rapidly however it is often collected, wetted, and mixed with chopped grass, for instance in southern Tibet.  The reason is an absolute scarcity of fuel.  If they were to make char, they would freeze due to lack of energy.

> There is not much wood to burn in Mongolia.

There is a massive amount of wood to burn in Mongolia, depending on where you are of course.  North of Ulaanbaatar there are huge forests.  The sawmills create enormous piles of sawdust which, when the market conditions are right, is made into wood pellets or briquettes.  But only some.  Most is too far away to complete with chopped and split wood.  I estimate thar the population of UB burns more than 100,000 tons of wood each winter.  It is a preferred summer time fuel, where the stove is removed to be used outdoors (because it overheats the yurt).

> Wow. 2 billion dung-stove  users!.  I had not been paying attention to the large number combusting dung  -  and do agree we should be trying to improve its combustion in cookstoves.   It might even be possible to make them fairly clean.

Of course it is.  Burning low density fuels (not only dung) requires particular air control and grate bar spacing.  It has very light ash so if the fuel is burned completely, it has rather a lot of fine white ash which can be lofted easily.  That needs consideration.

>But I think it much better to promote a switch to charcoal-making stoves.   Not just for dung, but for every fuel.

It is OK to think that, just don't expect people to act on it.  Doing so for most dung burning region would impose a huge additional labour-burden on women, in particular.  Gender rights advocates should rise up as One to protest any plan to enforce dung-burning char-making stoves on anyone.

>And we need urgently to be practicing carbon dioxide removal (CDR).

You want the energy-poorest people in the world to get involved in CO2 removal?  How more anti-poor can a policy possibly be?

> 3.   Re TLUDs and dung, I found TLIUD support in this 2014 non-fee paper:    A Biochar-producing, Dung-burning Cookstove for Humanitarian Purposes

"Humanitarian"? How more anti-poor could a proposal be?  Go to southern Tibet.  Altitude, 16,000 ft.  Nothing except grass and the occasional rhododendron can grow there. Either you live on animal products, or imported food, or you die.  No one is going to waste 2/3 of their available energy supply to appease rich, Western climate fanatics.

> Cooking with dung is exceptionally dirty.
Nonsense.  Cooking with a stove not designed for dung is "dirty".

> I'm working with a group that is trying to slow glacial melt in the Himalayas.

Then develop a clear burning stove combustor, and while you are at it, make it more thermally efficient so the mass needed per winter is reduced by, say, 50%.

>And I agree that it would be best if everyone used cooking methods that are cleaner than burning dung.

I pressure you have never seen a good dung burning stoves.  There is no "dirt" in dung. There is no "smoke".  Smoke is produced by stoves not burning it properly.

>Dung is not a good fuel.

Second opinion: Dung is a good fuel. Most stoves that burn it (not all) are absolute crap.

>Today we tested a dung rocket stove.  I'm a little surprised that the test was a failure.  Can anyone suggest changes?

This is a big ask. An whole theory of combustion is needed to address the matter.  The consolidation of the dung into a large single mass cause a lot of the problems. That is not how to prepare dung.  A great deal can be learned by observing people who use it.  Here is a Tajik dung burning stove loaded before ignition:

[cid:image001.png at 01D9290C.64834090]

Note the large pieces of wood used to establish a hot coal bed.  Once it is going well, the fire will be pushed to the far end of the chamber and new fuel added at the door. No fuel is placed on top of a going fire.  This arrangement is very clean burning.

This lady was involved in stove promotion for three years before seeing this simple, locally designed dung burning stove.  She tried it and said it was the first time in three years of promoting ISC that the "was excited" about a stove.

[cid:image002.png at 01D9290C.64834090]

The combustion is at the back under the big pot.  The water warming is at the front, not at the back, and it was very clean burning - even though at this time the design was primitive.  The KG2.5 came after 3 years of further development and is significantly more efficient, cleaner burning and burns for far longer on a load of fuel.

This is dung preparation in rural Tajikistan:
[cid:image003.png at 01D9290C.64834090]

This is one of several typical preparations. The diameter is about 5 inches.  The format suits poorly designed stoves with high excess air.

This is Umedjani Kurbon, aged 12, who is the operator of the CNC plasma cutter.  He got the responsibility because he could read and do simple arithmetic.  He had never received any instructions on how to use it properly.  If you zoom the screen, you can see the standard shapes from which to select a cut.  They owned no computer on which they could to prepare whole parts. This gives you an idea of the conditions in which producers live.

>The fire was never strong and there was a lot of smoke.

This is not surprising because, with good intentions, you were guessing. Now you know several things not to do. It might have done better if it have been dried at 105 C for a couple of days.  But I doubt it. It has to have a certain surface-to-volume ratio and controlled primary air to burn cleanly.  The total surface burning at any one time sets the firepower.  If you break each piece of fuel in half, it will increase the gasification (devolatilisation) rate.  A certain primary air flow is required for each surface area burn, and a separate secondary air flow is needed that relates to that gasification rate. You should aim for an oxygen concentration of 10% in the exhaust.

Good luck!
Crispin

Crispin Pemberton-Pigott

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