Burning methane in furnace

[Willie The Wimp]

Natural gas is principally methane. Per "Combustion" at:

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.

I have a garden-variety 3-yr-old updraft 80% furnace. It has 3 burners. As near as I can tell, the heat-exchanger consists of 1 unit with 3 tubular chambers which wind around and around, finally exhausting to a standard roof-vent.

Following is just a theoretical question: If I could "wire" my furnace such that everything save the inducer motor worked fine, given sufficient oxygen, ventilation, etc, should I expect my CO-detector to issue a warning?

Would appreciate responses from those who fully understand the process of methane oxidation or have non-sensationalized personal experience: anyone can read the warnings.

Willie

[Bob F]

I would think any CO would go up the chimney, unless the heat exchanger is shot.

[Don Young]

Maybe I don't fully understand your question. I don't see how you can have sufficient oxygen and ventilation without the inducer running, since producing a proper draft is what it does. If you provide proper draft without an inducer motor you either have basically the same thing as the older furnaces which depended on natural thermal draft or you have some other type of fan produced draft. Proper combustion of a given volume of gas requires a given volume of air regardless of how it is produced. Insufficient air produces increased CO along with other effects. I am sure others will have comments which may help more.

Don Young

[Ed Pawlowski]

I'll give you a theoretical answer to your theoretical question.

Theoretically, you re-wire the furnace to run without the induction motor. It is not in perfect condition, so it gives off some CO. Your CO detector malfunctions and your theoretical wife and six kids die. Then you call

1-800-sleazylaw and sue the guy on the newsgroup that said it would be OK to run that way. Theoretically, you can get him put in jail and you are awarded all his worldly possessions.

While I have my own theories as to how well it would run, I'm not going to publicly state them. The manufacturers have more lawyers and engineers than me.

[WhiteTea]

Have you submitted the poster for a future Darwin award ? :-)

[clare]

If the furnace is properly set up, none of the Co produced will get into the house, it will all go out the stack. More likely to get Co from natural gas than methane, if anything. If the inducer fan is not working, Co COULD leak into the house because stack temperature alone may not be adequate to produce the required draft in the stack, particularly on startup (which is why inductor motors generally run on "high" for a short time at ignition, then slow down when the stack temperature comes up.

[ransley]

Are you planning on tapping a garbage dump, where do you plan on getting Methane. I bet the house will smell real real good with unpurified land fill methane and possibly have dangerous impurities.

[HeyBub]

Methane itself is odorless. Harvesting Methane from raw sources will, of course, include various organic compounds from decomposing opossums, methamphetamine lab waste, and an occassional Mafia success.

[Bubba]

ransley, did you miss the part where the op said, "Would appreciate responses from those who FULLY understand the process of methand oxidation or have non-sensationalized personal experience" That is what leaves you out as you dont seem to fully understand anything. Always flapping your yapper. Bubba

[JohnR66]

Maybe he farts a lot.

[ransley]

Did you re-tard understand my question

[ransley]

Your so pathetic, your life is so depressing and empty your only joy is attacking my every post with stupid rants. Bubba the heat pro, wont help nobody on alt.home.repair because he dont get a nickle. Get a life.

[Bubba]

No one can understand your delirium. Bubba

[Bubba]

Im guessing its starting to get to you, eh you hack? Bubba

[clare]

An old college professor friend of mine developed a methane digester about 40-45 years ago at the University of Waterloo that was installed at several local farms to make methane from animal manure. It was used for heating and running a generator and other equipment. The methane was stored in a floating tank and disolved, under pressure, in Propane tanks for portable use.

No, or very little, smell from the methane when burned. He had some sort of a "scrubber" on it to remove sulphur comounds if I remember correctly. I used to have all the detailed documentation about it, but lost it in one of several moves over the ensuing decades.

[David Nebenzahl]

On 2/7/2009 3:11 PM Willie The Wimp spake thus:

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?

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).

[Willie The Wimp]

Depends. On lots of things.

Then why do we spend lots of $ for inducer fans in standard furnaces?

Natural gas is principally methane. Per "Combustion" at:

---------------------------------------------------------------- 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 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.

----------------------------------------------------------------

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

[David Nebenzahl]

On 2/8/2009 7:47 PM Willie The Wimp spake thus:

Sure; the original question being

If I could "wire" my furnace such that everything save the inducer motor worked fine, given sufficient oxygen, ventilation, etc, should I expect my CO-detector to issue a warning?

my answer would be "no".

[Willie The Wimp]

Consistent with my personal estimate.

Willie