[Stoves] benefits from reduced indoor air pollution.

Tue Oct 17 23:24:51 CDT 2017

As far as I know NOx is not regulated for biomass burning heating or cooking appliances anywhere in the US. The EPA threshold for regulation for biomass is typically 10 MMBtuh (10 GJ/hr) before emissions of criteria pollutants (NOx, CO) kick in. There are particulate standards for heating appliances. The thresholds are regulated by each state. The appliances are tested and permitted in independent laboratories so a supplier will have each model tested and certified. I’d have to check but I don’t think NOx is tested, except for academic purposes, not regulation. 

NOx is tested where wood gas is burned in a stationary engine to generate electricity. There are special standards for stationary generators. Emissions are usually met by putting a three-way catalyst on the engine.      

Tom

From: Nikhil Desai [mailto:pienergy2008 at gmail.com] 
Sent: Tuesday, October 17, 2017 6:29 PM
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>; Tom Miles <tmiles at trmiles.com>
Subject: Re: [Stoves] benefits from reduced indoor air pollution.

Tom: 

Were the emission standards for co-firing (industrial or power plant boiler fuel, I imagine) and gas engines the same? And if so, did they apply equally to urban and rural areas in the US? 

It may be counter-productive to apply the same NOx emission standards to cookstoves as for big sources unless the ambient NOx levels and ozone levels were much higher in that air basin than the national standards. Cookstoves being intermittently used and not moved across large distances during the course of their operation, I fail to see the rationale for NOx standards for biomass cookstoves.  

Nikhil

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On Mon, Oct 16, 2017 at 12:04 PM, <tmiles at trmiles.com <mailto:tmiles at trmiles.com> > wrote:

Crispin,

Thaksf or the comments. 

In 1990 and later we designed some burners for producer gas that held the gas to between 760C--980 C for at least ¼ second. We reduced NOX when burning high N fuels by about 40%. This was on fixed and fluidized bed gasifiers, and staged combustors,  from 10 GJ/hr to 90 GJ/hr. We use partial oxidation to reach the temperature and chamber design and gas flow to get the residence time. It still didn’t meet regulatory requirements but it did reduce the amount of urea/ammonia used for deNOx in the boilers. We also piloted the use of producer gas as a “reburn” fuel in a coal boiler. Producer gas was overfired in a coal boiler to “reburn” the combustion gases and reduce NOx. We again were able to reduce NOx by about 40%. The idea was to use a gasifier to convert agricultural residues and other biomass to gas for co-firing with coal. Energy prices fell so full scale industrial cofiring was not implemented. NOx control alone didn’t justify the investment in a biomass gasifier since there are cheaper alternatives. 

The challenge of using this strategy at any scale is the geometry to hold the gas at temperature in the sub-stoichiometric conditions. 

I agree that you are not likely to reduce or reform CO at these temperatures. If you don’t cool producer gas quickly you can get reversion to soot which would theoretically reduce CO. 

In my experience NOX generation is pretty consistent as long as you have a consistent fuel composition so it’s realistic to think about a baseline NOx range.  

When they add odorants to natural gas and LPG are they making “clean fuels” dirty? : - ) 

Tom    

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org <mailto:stoves-bounces at lists.bioenergylists.org> ] On Behalf Of Crispin Pemberton-Pigott
Sent: Monday, October 16, 2017 3:59 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.

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  

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