[Stoves] SEET Lab in Ulaanbaatar running again in its new home

[Crispin Pemberton-Pigott]

Dear Frank

 

>>
Generally speaking all stoves have chimneys that are too large in
diameter. That is interesting.

 

>You say to large in diameter. Based on the need for faster gas flow?

 

For any given quantum of heat you get more draft if the chimney has a
smaller total volume. Because of rapid cooling in the chimney (being thin
metal with a high emissivity) the draft is not as controllable if it is a
slow moving stream. Variations in the stove power make a large difference in
draft if the chimney is a major heat radiator (gives uneven performance).

 

>>The compressor compresses air. It is filtered to 0.01 µm and put through a
CO2 and water vapour adsorber, filtered again and then sued in the diluter.
It is very simple and effective. The dew point is -100 F. The CO2 is <1 ppm.
The O2 is much higher, about 33% which was interesting to see.

 

>All this seems unnecessary to me. The amount of CO2 in the room air must be
insignificant to what is going up the stack. Same as to moisture. Perhaps
particles are a problem so in-air should be filtered.   

 

The CO2-free air is used to calibrate the equipment (a zero-CO2 calibration)
without using any reference gas. A bottle of mixed gases from Japan (5 kg)
costs $19,000 delivered to Ulaanbaatar.  The entire adsorber system cost
less than $2000.

 

The dilution in the diluter can be quite high and the difference between the
CO2 measured and the background signal can be small. When zero-CO2 air is
used, the measurement is more precise. Moisture in the stack (and there is
plenty) can condense in the dilution tunnel (very easily) and is measured by
the particle counter as ‘particles’ but it is actually fog. This can give
the appearance of a stove being ‘dirty’ when it is not. Fog condensation is
a big problem in humid climates and where the fuel has a high moisture
content. 

 

I think it is a metal matrix of some kind. It does not get used up. There
are two units and they are cycled. One breathes with ‘wash air’ or ‘sweep
gas’ as it is termed. The other is under pressure for 30 seconds.

 

>Very interesting. I am thinking it may be a Teflon membrane where when the
gas is pressurized the CO2 goes through the membrane more than the O2 or
N2(?) and swept away on the other side. It would be interesting to know how
this works.  

 

It is an adsorber, rather than an absorber so it is easily flushed away when
not under pressure, using ordinary air.

 

>
Measure the CO2 before diluter in the stack and after the diluter in the
stack and you can get the dilution (mixing required I would think). 

 

It is not measured after the diluter ‘in the stack’, it is measured in the
stack and in the diluter. The ratio is the dilution factor, remembering
there is a small mathematical correction involve re ambient CO2.

 

>The CO2 concentration from combustion goes up and down a lot so the two
measurements before and after must be synchronized perfectly to determine
the dilution rate. 

 

Correct. In practice it changes very slowly. But change it we can, and do.

 

>It would seem that there is enough moisture in the outside air and the
combustion gas to create the fog. 

 

Yeas and it is a big problem for wet fuels. Lignite can have 33% moisture.
Imagine how much fog that creates if you collect it in a hood and cool it. I
don’t want to measure fog. It has to be sampled using dry air dilution to
keep the dew point below the ambient temperature. 

 

>That it is more the change in temperature (lowering) that creates the fog
than the moisture in the gas. Pre-heating the dilution air is the answer to
preventing fog and not dry air.  

 

That would create an additional problem which is that fires produce a lot of
condensable volatiles. If you do not cool the gases, they do not condense
and you get a dry dust measurement. This is very ‘EPA’. But it is the
condensable particles that are so harmful to health. If we do not condense
what we can of them, we will not know they are there. A dry dust measurement
of a stove is not very useful actually. It is quite common to have the PM be
50% condensable volatiles (tars and nasty liquids) so we do the best we can
to condense things without getting water vapour involved.

 

Regards

Crispin

 

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