[Stoves] Gas heater without flames

[Crispin Pemberton-Pigott]

Dear David

My knowledge of N2 reactions is limited.

First, stoves produce NO if the temperature of the flame is above 700 C, only randomly below that. They produce very little NO2. Some combustion analysers 'guess' that it is 10% of the NO value. It is difficult to get an undiluted NO emission factor of 300 ppm burning  ‎biomass from a small stove.

I have seen 850 ppm NO (EF, O2=0%) in a coal stove.

NO2 production is paltry and NO3 is basically zero because there is no pressurisation. ‎In other words stoves are not significant sources of NOx so there is nothing to 'fix'.

I don't recall the path of NO to N2 offhand.

The catalyst idea is related to the cost-benefit analysis‎: if it is worth it people will build it. Small cars sometimes have catalytic converters so it seems cost isn't really an issue in context.

Having a son who is a metallurgical engineer I have confidence that anything to do with catalysts will be solved eventually and it will probably be an exotic ceramic.

On another note I was at the SEET lab in Ulaanbaatar for a few days last week and met a Japanese team testing a catalytic converter for coal stoves. It was conventional in all respects save one which was that it had an electric preheater. ‎Huh. I got some photos.

It starts to work at about 200 C and seems to be recommended at 300. It was at the bottom of the chimney which on a traditional stove can reach seriously high temperatures during flaming pyrolysis. Well over 700. It looked good but I think the solution to coal smoke is not to produce it in the first place.

This year there are quite a number of submissions for testing. Think of it as Stove Camp for coal stoves with the prize being sales of thousands or tens of thousands of your product.

About 1/2 the stoves are likely to pass this year which is a big improvement in a single year. Maybe 1/3. The fuel is 'difficult' meaning very high volatiles lignite (over 50 per cent) so some of 'the regulars' may not make it. A catalytic converter might help some of them but the big problem is the major portion of the smoke is emitted before the stack is hot enough to keep the converter working (at all). Once they are running ‎a TLUD or cross-draft coal stove makes very little PM2.5.

One stove cruised through, not the best but pretty good, with 20 mg per delivered MegaJoule. There isn't much to clean up. The best ones will be below 5. The best ever was 0.6 mg as I recall (cross-draft stove). These are much cleaner than any converter can achieve.

There is a vague plan to offer a course to Chinese manufacturers in a couple of months on how to build a coal combustor that will meet the Mongolian coal stove project emission standard which is pretty demanding (90% reduction minimum).

If we can get raw coal pellets ‎(all the above is achieved with raw lump coal) I am betting there will be a natural draft net-negative coal stove available.  The reason I say that is the top stoves clean the air passing through them for most of the burn while creating no PM2.5 at all - at least not measurable with light scattering.

One day that may be possible with biomass too.

Regards
Crispin

BBM 2B567CC3
From: David Young
Sent: Monday, June 30, 2014 02:44
To: Discussion of biomass cooking stoves
Reply To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Gas heater without flames


On Tue, Jun 17, 2014 at 05:33:09PM -0400, Crispin Pemberton-Pigott wrote:
> Keeping an eye on trends:
>
> http://www.youtube.com/watch?v=yvqEFPPLh7Q
> <http://www.youtube.com/watch?v=yvqEFPPLh7Q&list=PL6ABEE1873667B871>
> &list=PL6ABEE1873667B871

Neat device.  I take it that one advantage to using a catalyst instead
of flame combustion is that you can use lower temperatures, and at
lower temperatures, there are fewer reactions of atmospheric N2 and O2
producing NOx?

The device seems to use a precious metal, platinum, for a catalyst.
Perhaps suppose it is a greater problem that the metal is hard to come
by than expensive, if the amounts are very small.  Is it possible to use
less expensive catalysts to bring the cost down?  For example, it's my
understanding that mild steel catalyzes CO combustion.

Dave

--
David Young
dyoung at pobox.com    Urbana, IL    (217) 721-9981

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