On Sun, 08 Feb 2009 17:16:33 -0800, David Nebenzahl wrote:
On 2/7/2009 3:11 PM Willie The Wimp spake thus:
Natural gas is principally methane. Per "Combustion" at:
http://en.wikipedia.org/wiki/Methane
the methane combines with sufficient oxygen, producing carbon dioxide (CO2),
water, and heat.
Carbon monoxide (CO), a poison, is produced as a by-product but, given
sufficient oxygen, is almost instantaneously converted to harmless CO2.
If sufficient oxygen is not present, a certain amount of CO can be produced.
Where do you get this from?
So far as I know, methane *always* produces only carbon dioxide and
water vapor under ordinary combustion conditions. If there's a lack of
oxygen, wouldn't it simply result in more unburned fuel?
Depends. On lots of things.
I think the only things as a result of burning CH4, besides CO2 and H2O,
would be due to the additives (like the mercaptans for odor).
Then why do we spend lots of $ for inducer fans in standard furnaces?
Natural gas is principally methane. Per "Combustion" at:
http://en.wikipedia.org/wiki/Methane
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Combustion
In the combustion of methane, several steps are involved:
Methane is believed to form a formaldehyde (HCHO or H2CO). The formaldehyde
gives a formyl radical (HCO), which then forms carbon monoxide (CO). The
process is called oxidative pyrolysis:
CH4 + O2 --- CO + H2 + H2O ------------ Production of Carbon Monoxide
Following oxidative pyrolysis, the H2 oxidizes, forming H2O, replenishing the
active species,[clarification needed] and releasing heat. This occurs very
quickly, usually in significantly less than a millisecond.
2H2 + O2 ---2H2O
Finally, the CO oxidizes, forming CO2 and releasing more heat. This process is
generally slower than the other chemical steps, and typically requires a few
to several milliseconds to occur.
2CO + O2 ---2CO2
The result of the above is the following total equation:
CH4(g) + 2O2(g) --- CO2(g) + 2H2O(l) + 890 kJ/mol[3]
where bracketed "g" stands for gaseous form and bracketed "l" stands for liquid form.
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When we had power outages due to ice storms 2 winters ago, everyone was
warned NOT to run their gas ranges for heat. I believe this is because
they assume that improper venting could lead to CO poisoning. Likely
what they really needed to do is crack windows a little.
There are similar warnings about running space heaters in sealed-off
rooms.
It *is* possible to produce CO with incomplete/choked-off combustion
of nat. gas. I can't tell you the exact circumstances or how much. A chemistry
prof might be able to.
Care to venture an answer to the original question?
Willie