[Stoves] EPA emissions units

[Andrew Heggie]

I've brought back Norbert's reply from the digest into this thread so
it flows onward more logically, some further comments below. It gets a
bit long-winded but reflects difficulties I am having coming to terms
with this subject.

On Mon, 9 Jul 2018 at 21:59, Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:
>
>
> There is something interesting emerging from the development of this new generation of coal-burners. It is that the emissions of PM are not substantially the result of incomplete combustion, but the lofting of fly-ash. I think this is significant. If fly-ash is an unimportant ambient air contaminant, it puts a creates different perspective on air pollution.

Yes fly ash from fan powered devices were part of a discussion I had
with Tami Bond on here some time back. Fly ash from the wood fired
boilers I used to deal with was classified as hazardous waste and was
not supposed to be disposed with the bottom ash.

This again brings up Nikhil's point about equitoxicity. I deduce that
black carbon particulates are more likely to be damaging than these
siliceous fly ash particles, even though we know siliceous particles
cause lung problems, and  asbestos fibres are siliceous.

Therein lies another quandary: PM10s are defined as particulates that
have the same aerodynamic characteristics as a spherical particle of
diameter 10 microns IIRC but a long thin or irregular particle  would
act like a much smaller spherical particle in air.


I'm thinking it's the small particles  that carry PAHs into the body
where they can disrupt DNA almost anywhere once in the blood stream.

>From what Crispin and Prof Lloyd have told us it's the particles from
4micron down to 0.6 micron that have the greater chance of passing
from the lungs into the bloodstream, the body's mucous membranes
trapping much of the the larger and boundary effects  inhibiting
absorption of smaller particles than this range.

>
>
>
> Having tested some of the high performance domestic products from Kyrgyzstan now for 18 months, it is clear that fly-ash I an on-going issue and that VOC’s, PIC’s, PM2,5 BC and OC are not.

What weighting are you using for that, if it's only the relative
quantities I find that hard to understand?
>
>
>
> The high velocity of air through the combustion zone (which is constricted in order to generate adequate turbulence and mixing) lofts fly-ash and gets it flying, No big surprise there.

None at all, as I say we saw it a lot in fan powered wood boilers an
that was just what was trapped in the fire tubes and flues, much must
have carried on to the atmosphere.
>
>
>
> Fan stoves like the Mimi Moto and others will have the same problem, save that wood ash is usually finer than coal ash. Dung ash can be very fine – to the point it is difficult to remove from the stove without creating a cloud of fine ash in the room. In fact, we had to add an ash drawer to the Model 2.5 heating and cooking stoves to address this problem. Never before had people seen a stove that completely burned the dung, and the pure white ash from such a fire is extremely fine. Sweeping it out of the stove from an ash collection area proved to be a major source of IAP. So we added a drawer at the request of the homeowners.  This allows the ash to be removed carefully without disturbing it until it is tossed into the field as mineral-fertiliser.

I can vouch for that from my own wood stove experience and  my little
particulate monitor warned of a many fold increase in the room  just
from opening the fire door and disturbing a bit of ash.
>
>
>
> If the mass permitted by the EPA is ‘bad combustion’ (up to 18 g/hr) that is going to be an air quality problem, whereas 18 g/hr of fly-ash is what, exactly? That is the sort of air pollution experienced in Beijing years ago – fly ash from boilers with strong fans pushing as much through the heat exchanger as possible.
>
>
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> We are going to need epidemiological studies on health impacts based on the PM2.5 composition to make valid claims.

Yes I definitley need a better understanding  of what the hazards are
from different types and sizes of particulates.


Norbert said:
>
> This is specifically for domestic wood fired boilers.
>
> It is part of a Federal Rule known as EPA NSPS (New Source Performance Standards).
>
> It also covers wood stoves and pellet stoves, although those are regulated in g/h.
>
> For boilers including those with storage, there is an additional upper limit of 18 g/h, no matter the size of the boiler.

Thanks Norbert

So US EPA acknowledges  domestic wood fired boilers will not  be as
clean as oil or gas fired domestic heaters and sets practicable
standards for manufacturers to meet.

In London UK we have a mayor who appears to have first hand experience
of breathing difficulties attributed to particulates and pollution and
seems to be advocating a clamp down on wood burning over and above the
current "clean air act" which exempted stoves that met a lesser
criteria.
>
>
>
> It would be a non-issue for gas or oil fired boilers, and I'm not aware of any domestic scale coal fired boilers
>
> for sale in the US.

A firm called Trianco used to make an underfed automated  domestic
coal boiler here, that I came across, if fired on anthracite "beans"
which were carefully graded for the feed mechanism.
>
> and the PM limit is 0.01 - 0.02 lb/MMBtu. (Compared to 0.32 lb/MMBtu for domestic wood)

Which 30 fold reduction is presumably achieved using wet scrubbers,
electrostatic precipitators etc. which would not be economic on the
domestic scale.

I would like to see a table of standards for various particulate
emissions by thermal plant, preferably referred back to  SI units.
Currently in Europe diesel cars (with their sophisticated particulate
filters) are required to meet a figure of ~0.2 grammes of particulates
emissions per kilometre travelled. With a diesel car typically
managing 7.2litres per 100km and fuel containing around 43ML kg and
34.5MJ/litre LHV that amounts to 1g of particulates for 2.4MJ of
combustion . I hope someone can look at my figures in case of
mistakes.

The EPA figure you used for domestic wood of 0.32lb  per million is
145g per 1055.87MJ or 1g per 7.3MJ so  better than a Euro 5 diesel car
which has only milliseconds to complete combustion. Mind prior to 1990
it looks like an unfiltered diesel was producing 8 times as much .

Unfortunately no weighting allowance seems to be available for sizes
of particulates.


>
> On Sat, 7 Jul 2018 at 19:48, Norbert Senf <norbert.senf at gmail.com> wrote:
>
> > Domestic boilers are regulated in terms of pounds of PM emissions per million BTU's of delivered heat. The limit is 0.32 lb/MMBtu. At 75% efficiency, this is equivalent of 1.7 g/kg.

So the EPA units relate to heat delivered into the building rather
than HHV or LHV of the fuel?

Working back to energy units and allowing 15MJ/kg for 20% dry 1.7g/kg
is  1g/8.8MJ so a small discrepancy but in the same ball park.

Twenty years ago I was happy I could produce a burner with only 35ppm
CO, now it looks like that was a wrong metric, is the EPA figure of
~1g pm per MJ a good target we should aim for in cook stoves? Should
we weight the size class of particulates measured  to favour stoves
that don't produce particulates in the pm 4 down to pm0.6  sizes?