Subject: Why does a propane torch in a cold furnace stink ?

From: C++ Freak <[email-masked]>
Date: 4 Jul 1996 08:16:32 GMT

When starting up a propane forge for metal melting, 
the first few minutes a bad smell
exists in the exhaust gases. When I remove the lid (there is a hole in it,
but presumeable too small during startup) it's gone.
It's cilindrical with a tangential hole where the torch enters the combustion
room in which a crucible is in the center. On top of it there is a lid
with a hole in the center. The diameter of the room is about 5-7 cm (2-3").
The smell is somewhat NOx like, but I am not sure. 
After a few minutes it's gone (it reaches 1100 C after 10 minutes and 1350 C 
after 15 minutes *inside* the crucible).

What are these smells at startup ? Are these noxious ?

Klaas

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From: Andrew Werby <[email-masked]>
Date: 4 Jul 1996 19:02:59 GMT

>but presumeable too small during startup) it's gone.

[This is called "reduction", an atmospheric effect caused by lack of 
oxygen or too much fuel in the combustion reaction. Try starting with 
less gas until the airflow gets established, then you can turn it up.]

Andrew Werby - United Artworks

http://users.lanminds.com/~drewid

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From: [email-masked] (J. Kimberlin)
Date: 4 Jul 1996 16:03:22 -0700

>What are these smells at startup ? Are these noxious ?

Most propane has an additive to provide an odor.  This lets you know that 
gas is present because propane itself has no odor.  The odor is usually 
methyl mercaptan and is in the propane at low concentrations.  It is not 
harmful but is certainly noxious.  It is present at startup because of 
incomplete oxidation.  When your air/propane ratio is not proper you will 
always smell the stuff.

JerryK

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From: [email-masked] (Jim Shockey)
Date: 5 Jul 1996 07:45:01 -0700

In article <[email-masked]> [email-masked] (J. Kimberlin) writes:

[delete]

>incomplete oxidation.  When your air/propane ratio is not proper you will 

It's no big deal, Jerry; but, I think you meant to 
use the term "obnoxious" which means "very 
offensive; unpleasant." The common definition 
of  "noxious" is "harmful to health or morals; 
injurious or unwholesome." Your sentence didn't 
quite make sense or convey what you intended. 

And, thanks for the info. I never knew what the 
name of that additive was. 

Not trying to be picky, just more precise,  8-)

--jim			<[email-masked]>

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From: [email-masked] (James Kirkpatrick)
Date: 5 Jul 96 15:59:55 MDT

In article <[email-masked]>, C++ Freak <[email-masked]> writes:
|>When starting up a propane forge for metal melting, 
|>the first few minutes a bad smell
|>exists in the exhaust gases. When I remove the lid (there is a hole in it,
|>but presumeable too small during startup) it's gone.
|>It's cilindrical with a tangential hole where the torch enters the combustion
|>room in which a crucible is in the center. On top of it there is a lid
|>with a hole in the center. The diameter of the room is about 5-7 cm (2-3").
|>The smell is somewhat NOx like, but I am not sure. 
|>After a few minutes it's gone (it reaches 1100 C after 10 minutes and 1350 C 
|>after 15 minutes *inside* the crucible).
|>
|>What are these smells at startup ? Are these noxious ?

Just an educated guess:  When you burn propane (or most any hydrocarbon
fuel) you are combining a hydrogen/carbon fuel with oxygen, producing
water vapor (Hydrogen + Oxygen) and Carbon Dioxide (and possibly other
things like pure carbon (soot) if poorly adjusted).  When the furnace is
cold, some of the water vapor condenses into water, along with the compounds
they add to give the gas a unique smell, and possibly trace contaminants.
This is probably what you smell.  Once the furnace warms up enough to
prevent condensation of the water vapor, the smell goes away because the
combustion is more complete.

Corrections welcome!

Jim

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From: John Newby <[email-masked]>
Date: Fri, 05 Jul 1996 18:31:07 -0400

> --jim                   <[email-masked]>

I suspect that the smell in not methyl mercaptan, but is, as the poster
suggests, products of incomplete combustion, namely aldehydes, which
will be found at low temperatures even when there is plenty of air to
complete combustion.  The aldehydes are produced because the environment
is too cold for their combustion reactions to proceed to completeness
and the "intermediate" product's reactions are frozen.

Aldehydes and CO may both be produced in highly oxidizing atmospheres
when combustion reactions are taking place in cold environments.

John N.

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From: [email-masked] (J. Kimberlin)
Date: 5 Jul 1996 18:31:46 -0700

In article <[email-masked]>,
>--jim			<[email-masked]>

Go ahead and be picky. I am certainly not offended.  The stuff sure 
stinks though.  I think the maximum amount put into propane is quite low; 
I've heard 15 ppm which seems high to me.  Gas delivered to a house via 
the utility company also has mercaptans added as an oderant, but maybe 
not methyl mercaptan.  Wait till you smell the sulfur compound that is 
fishy, a real gut churning experience at higher levels.

Cheers,

JerryK