[Stoves] benefits from reduced indoor air pollution.

Mon Oct 16 05:59:11 CDT 2017

Dear Tom

That is a very valuable contribution at this time. I attended a short conference on Wednesday and a presentation by a Professor from the Chinese Academy of Sciences who is researching 'Decoupled combustion". He has created a stove that is all but identical to the KG4 crossdraft gasifier being made in Bishkek. Quite astonishing. After years of investigation he came to the same architecture: a hopper without air moving through it, a pyrolysis zone under it, a coke bed blocking the gases from getting to the combustion chamber, and a gas burning area above the coke.

He said something I have never heard before which is that passing the fuel N through the semi-coking and coke burning zones reduced the NOx. He said it reduced the CO as well but I believe that less than the story about the NOx.

As I understand what you wrote below, the NOx precursors, held in the semi-coking and coke burning zones long enough would reduce to N2O if the conditions are right. Possible? The stoves are small, so it might be difficult, but relative to many other stoves, the combusting fuel mass is relatively large and the gas velocity slow. The temperature is adequate.

I doubt the temperature in the coke bed is high enough to split N2 but we can remain open minded on that. So is there a glimmer of truth to the idea that a horizontal coke bed could achieve a NOx reduction? That is really work checking out. Perhaps what we need is a target 'regular burn' NOx benchmark then compare that with the crossdraft gasifier burning the same fuel.

The modeling work being done at the CAS include NOx formation so I need to following this more closely, if they got that correct, at least under certain circumstances.

Incidentally, Prof Jinghai Li, Academician and Vice-Director of the Chinese Academy of Sciences (Institute of Process Engineering), Vice-President of the China Association for Science and Technology and the Vice-President of the International Council for Science, agrees enthusiastically with the proposition that there is no such thing as a “dirty fuel”.  He laughed heartily at the “dirty fuel” idea. At first he said that a stove can be dirty, but we agreed in the end that a stove+fuel+context is what determines actual performance. On top of being sensible, he is a very nice guy.

Regards

Crispin

Fuel bound nitrogen is usually the cause of NOx with biomass fuelas rather than thermal NOx. Grains, manures, and biosolids can all be high NOx fuels.  Grains and manures can generate abundant NOx. As others have commented it is difficult to get to high enough temperatures for thermal NOx except by burning charcoal. Pyrolysis and gasification  generate NOx precursors that can be "inerted" to N2O if held long enough at high enough temperatures (760C--980 C) in the absence of air. Unfortunately this is not practical in a stove. Catalysts are typically used to reduce NOx from wood gas in engine applications.

Tom

-----Original Message-----

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Andrew Heggie

Sent: Sunday, October 15, 2017 3:26 AM

To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org<mailto:stoves at lists.bioenergylists.org>>

Subject: Re: [Stoves] benefits from reduced indoor air pollution.

On 15 October 2017 at 00:43, Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:

> ‎Prof Stuart Piketh said last night that the conversion of N2 to NOx is copious above 1850 C which is easily reached in a power station with only 5-6% excess air.

...but wood is already partially oxidised so the adiabatic flame temperature is only around 1600C and I seldom see more than 1100C .

This of course is why charcoal was needed before iron could be smelted, even then it depended on the fact iron carbide formed a eutectic mixture that lowered the iron melting point.

P

>

> The only way to get really high temperatures, which I define as melting the ash (in the absence of significant quantities of fluxes), ‎is to blow on the fire.

Yes this is char burning

I

>

> There is a very practical side to this. Is it worth separately measuring NO and NO2 when testing a stove? Many emission standards mention pollutants and metrics that are copied straight from power stations where the combustion process and goals are very different.

I wouldn't have thought so but stand to be corrected. I worked most of my adult life  by the exhaust of two stroke engines and they are particularly bad for both particulates and NOx, especially when running lean which gave some extra revs. You soon notices the acridity  from NO2 if working in a poorly ventilated hollow.

>

> ‎So the question is, what are the appropriate measurements to make and what should be the reporting framework?

That's for someone better qualified than me to answer but black sooty particulates come high on my list and then CO if unvented.

Andrew

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