[Stoves] re-kindling stoves

[ajheggie at gmail.com]

On Thursday 23 December 2010 04:38:25 Crispin Pemberton-Pigott wrote:

>
> the effect. What if the secondary air were preheated to >800C?
>
> Exactly - a most relevant question. What I have done is make most of
> the air pass through the lowest part of the grate where the coal has
> difficulty falling in (it is angled 15 degrees to assist coverage not
> but to completely choke the grate). Then I have 2 x 12mm secondary air
> holes supplying preheated air into the flame as it passes into the
> combustion chamber lined with 4 ceramic flat plates.
>
> The preheating is large, as the grate is really hot, and the preheating
> effect of the ceramic plates (about 20mm thick) is good.
>
> The next issue is the excess air quantity.

Yes I know you preheat secondary air but I was wondering what the effect 
would be on preheating as a test. Generally excess air acts to quench and 
dilute the reaction. I was just wondering if an experimental external 
heating element for the secondary air supply would make any changes to 
the pm. It's really only spark ignition reciprocating engines that need 
air:fuel close to stoichiometric most other combustion processes trade 
off the extra air massflow with the better chance of a fuel, or Product 
of Incomplete Combustion, particle meeting an oxygen molecule.

In fact I imagine the pm rate would drop dramatically if the secondary air 
were enhanced with O2, though of course the increased temperatures may 
have a non intuitive effect.

There will be a compromise to be made because the graphs of lambda, CO, 
PICs and pm will not all map to a single point.

<snipped>

>
> The flip side of no PM is that they are there, but that they are really
> really small and can't be seen by the instrument. That is pretty much
> the history of particle measurement.

Is there evidence that these smaller than pm2.5 particles are as or more 
dangerous? My understanding of another lung disease, from asbestos fibres 
( long silica crystals) is they are just small enough to incite damaging 
immune response or mutation but too awkward shaped to be engulfed by 
white blood  corpuscles and excreted.


>
> A chemical analogy is the popular belief that there are 'low SO2
> emission' stoves. What people are measuring is SO2 and when they don't
> find it, they think it is 'not being produced'. Well, that is sort of
> true, but if S is in the coal, it is going to be H2S instead of SO2
> which far worse! SO2 is the desired product.

Yes what goes in must come out either as ash or flue gas
>
> We have a long way to go...

Yes but your recent pictures of the modification to an existing, in use, 
stoves show there are big improvements to be made which should be readily 
accepted. Eliminating PMs will reach a limit below which we will struggle 
and we're not near yet
>
> It was -31 C this morning and it is very tough on the poor who have to
> choose between food or heat. 

I have never experienced cold like that

> The brutal winters the UK is feeling are 
> also affecting us. Three in a row. Last year 12 C below normal. Eight
> million animals froze last winter and this year it came early....

We need to put this in perspective, UK dipped down to -18 in one place 
and -8 in the south but the average has been hovering at 0C. The snow 
that arrived early was what the infrastructure couldn't deal with, simply 
because the trade off between expense of readiness verses disruption had 
resulted in most people not being prepared. The ground is still not 
frozen here, if it did there would be far more longer term problems.

What it is showing up is an over dependence on grid electricity for 
maintaining comfort. An interesting boiler related problem, that has 
shown up laxness in installation, is that most urban dwellers have 
heating by gas condensing boilers which require a condensate drain. Where 
this drain has been poorly installed in an exposed position, and the 
acidic condensate frozen, it has caused the boiler to cut out.

Merry Xmas everyone

AJH