[Stoves] Stove testing in Mongolia continues

[Crispin Pemberton-Pigott]

Dear Nurhuda

>Three years ago, I developed a formula for coal briquettes and pellet that
are easy to light and provide good flame instead of radiant heat. 

The stoves being requested are primarily needed for space heating with
cooking as a secondary function. There are several stoves on the market
which cannot cook but they are not selected by the project for subsidised
roll-out as the subsidy is primarily aimed at low income people who will
also have to cook with the same stove. 

The number of stoves involve is quite large. To date the subsidy programme
has placed about 100,000 stoves at a cost of maybe $20m. Phase One is ending
and Phase Two will start immediately with a different funding source.

>The feedstock is low grade coal, which is abundant in Mongolia.

I am not so sure what you mean by low grade coal. The coal available in town
came from two sources, one of which has been forced to close by the
government. Both have a high hydrogen content because of the high volatiles
content (hydrocarbons). Both are easily lit and were available in the raw
state or as semi-coked briquettes. The history of semi-coked briquette
promotion is not very encouraging. They are hard to ignite. There has been a
JICA team here for years working on various aspects of fuelling (and
changing) the boilers in apartment buildings which were not designed for
high hydrocarbon fuel. 

The result of a mismatch between the burner and the fuel is usually high
emissions of unburned gases. This is pretty easy to demonstrate by putting
the same fuel (say, raw coal from Nalaikh Mine) into four different stoves
and seeing a 2000:1 difference in the PM 2.5 emissions. For many years
people blamed the emissions on the fuel, not the burner, or rather, the
fuel+burner combination. That old idea is no longer accepted. It is widely
realised that testing a stove means testing it with a particular fuel and
assisting the manufacturer to adapt the combustion conditions to the fuel.

As you have shown in your video, this can be done for any particular blend. 

The pinkish flame is, from my experience, hydrogen, or very high temperature
water vapour. The hydrogen is liberated from the fuel (if it is not fully
coked) or from the decomposition of water lower in the fire (water gas shift
reaction). The water vapour is from the fuel or from the combustion of the
hydrogen lower down. In any of these cases the result is still a pinkish
flame.

The hydrogen content of the fuel, being higher than regular 'hard coal'
makes it much easier ignite and hydrogen has 4 times the heat of carbon, per
kg.  In terms of desirable qualities from the perspective of both the home
owner and the manufacturer, the most useful fuel is a briquetted raw coal
pellet of about 10-20 g with a controlled moisture content - about 10-12%.
As briquetting involves a certain amount of drying (the raw coal Is quite
wet) there is some advantage to the briquettes over lump coal.

Prof Lloyd has reported that South African producers managed to get raw coal
to bind without any additives if it was high in volatiles. That makes the
product really cheap. Here in Ulaanbaatar, briquettes have been typically
lower in energy per kg, harder to light and three times the price. One
attempt was made to produce a 1/3 clay 'holey briquette' about 160mm tall
but it was reliant on waste Nalaikh 'duff coal' and there is only a limited
quantity of that. In other words the coal was free and sitting at ground
level. It was used to fuel a TLUD large briquette burner and it was pretty
good, as a stove. 

It is no longer on the market. I think the main reasons were the power was
too low and the extraction of heat was too high (leading to condensation and
corrosion). The CO/CO2 ratio was about 3.8% which is not great but better
than the baseline. It could easily have been improved with a better burner.

Regards
Crispin