[Stoves] Reducing smoke with steam

[IPC]

Dear Crispin

Having looked at the photos of your Ulaanbaatar stove, I felt you had lots
of secondary air which would do a great job of burning things cleanly.  Yes,
a bit of moisture would help, but the sorts of levels you were talking about
would mean a rather low cv coal, and I think the secondary air is more
important than the moisture.  Your spreadsheet seemed to confirm a
reasonable excess of air.

If there is excess air, then you have little to worry about condensation -
to get a dew point over 100 deg C you need to control the air very
carefully, as in a power station.  I have run into condensation problems
with a "slow combustion stove", however, where you burn well
sub-stoichiometric.

Incidentally, a bit of lime added to keep sulphur in check shouldn't lead to
ash caking - even calcium sulphate is good to at least 1500 deg C.  Its the
alkalis (sodium, potassium)that worry you in a fire, not the alkaline earths
(calcium, magnesium).

Happy New Year

Philip



-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: 02 January 2008 10:07
To: 'Discussion of biomass cooking stoves'
Subject: Re: [Stoves] Reducing smoke with steam

Dear Philip

Taxing your free time for a moment...

The downdraft coal burner in Ulaanbaatar was extraordinarily clean by any
measure, especially for a small device.  I wonder if the naturally high
moisture content had something to do with it?

Would you be willing to take a guess and perhaps ruminate on where emissions
might change as the moisture content dropped? The H2O is about 1/3 of the
coal by weight. Some lignites in the area are 40%, some 30%. I was appalled
but then, if it is leading to an extremely high combustion efficiency (as
measured by the European approach calculated from CO content) then perhaps I
shouldn't worry so much.

I am happy to have the flame temperature brought down by evaporation because
the metal will last a lot longer, but there are condensation issues.  People
heat their homes by passing the hot gases through hollow brick walls which
distribute heat throughout the house.  I suspect that in many cases the exit
temperature is below 100 C especially when starting up. No one complained
about it, but I think there is a lot of moisture in there sometimes.

Regards
Crispin