[Stoves] Ulaanbaatar Air Quality

Fri Nov 8 10:38:46 CST 2013

Dear Dean

The situation in China is interesting because it is so diverse.

>In China burning coal instead of wood was established by Mao and it
continues today. 

I was surprised to find that a company was manufacturing cast iron downdraft
stoves in Ulaanbaatar ins 1905. I think they have been burning coal for a
very long time but I was not aware of Mao's popularising it. Maybe there was
a transport issue from the places with and without coal.

>We looked at the honey combed briquette makers in Shengzhou, a town of
about 800,000, and about 185 tons per day of honey combed briquettes were
made daily and sold. 

There is a plant in Ulaanbaatar that can make 400,000 a day but it was
wrapped around a Korean stove that was a TLUD that could be refuelled.
Interesting, pretty clean but under-powered. It also relied on waste coal
from Nalaikh mine which is clearly a limited business model.

>As you point out, coal burns with very little PM once its lit. However, I
hear that there are other types of harmful pollution made by coal, like
heavy metals. And it smells bad.

The part about the 'metals' is highly variable, even controversially
promoted as part of the 'war on coal'. Metals that evaporate (if they are
present in the first place) are the problem and that is easy to check. Coals
vary enormously. Some even have fluorine and arsenic, if it is in the
groundwater. Western China has that problem. Smelling bad is totally the
result of bad combustion. H2S is the product of incompletely burning S. A
clean burning coal stove (which most people have never seen) doesn't smell
of anything at all. It just puts out water vapour and CO2, like a biomass
stove or a natural gas stove or ethanol and so on.

>Inexpensive electric lighters are sold in China to replace the starting
with wood although it's common to see incredible amounts of smoke in the
morning as the restaurants start up their coal cook stoves with wood. 

That is a terrible way to light coal! Wow. The smoke is unburned fuel so
imagine how much is lost before something gets hot enough to spontaneously
ignite! The best method is a small TLUD wood fire sitting on top of a bunch
of small coal, all slightly nestled into a shallow trench. This allows the
'side coal' to fall onto the wood as it burns away. We will explore a couple
of other ideas next week. Even for the TLUD's there can be a lot of smoke if
the ignition is not carried out well. It is always worse if there is a lot
of secondary air with no controller.

>Adding secondary air can burn up the CO and added 10% to thermal efficiency
because the burning CO no longer escaped unburned!

The problem exemplified in the chart from the TLUD I sent earlier is that
there is no secondary air at all. It works 'most of the time' but not all. I
agree the heat loss from CO is huge if the traditional stoves. The CO from
the TLUD's tends to concentrate on the end of pyrolysation because there is
quite a change in the power (gas generation rate) as it finalises the coking
process. 

I wonder if John Davies is still with us on this channel.  John, did you
notice a power increase in your heating stove when the pyrolysation was
completing?

I have seen the excess air level drop to zero. On one occasion we had a
CO(EF) of 130,00 ppm. 13% (undiluted).

>Like charcoal, once lit coal burns with very little PM. For some reason,
the theoretical ability of coal and charcoal to burn with very little PM is
often actively ignored and rejected. 

With important publications like the Berkeley stove comparison deliberately
omitting coal stoves, when millions, probably hundreds of millions of people
rely on them, we are failing in our basic mission of improving people's
lives, on which people like you and many other have spent so much effort.
Hyping negatives, especially blaming a fuel for the failure of the stoves
that burn it, is not helpful. The health problems created by burning coal
are largely from condensed volatiles which result from poor combustion
conditions, bad lighting and refuelling techniques. High carbon, low
moisture fuels require very little air supply. It is possible to get the
best burn on a downdraft stove with excess air of 30%. That is amazingly
low. Imagine a coal stove with an air hole entrance 1/20th of the size of a
comparably powered Rocket stove! Until people see real time measurements
they find it hard to accept.

>Perhaps it's good to concentrate on how to accomplish the clean burning of
wood. When we have stoves that can burn wood with very low PM we have added
another low PM resource for solid fuel users joining coal and charcoal. 

That is fine in places with biomass to burn. Personally I favour creating
the resource where it does not exist, but that takes decades. China is doing
a creditably job of getting pellets and briquettes to a lot more people, but
the overall numbers are still inadequate. It is a big investment of money
and energy to make them, and transport limits the radius of impact.
Cleaning up wood fuel emissions in a stove that is acceptable to cooks is a
big challenge. Getting it to work 'at all' is really different from getting
people to buy and use them because they like the performance. 

Frans says we should worry about dioxins, furans, naphthalene, benzene,
polycyclic aromatics and formaldehyde from biomass combustion. Right Frans?
Others things we inhale are listed by UC Davis here
<http://exposurescience.ucdavis.edu/Projects/cancer.php> .

Good (perfect) combustion defeats (almost) all of them.

Regards

Crispin

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