RE: OT(?) Catalytic converters re: N.A. heating stoves

["Bryan Willson" <Bryan.Willson@colostate.edu>]

I would like to support Dean's comments that "catalytic converters are not
always successful."  I don't have any experience with catalysts on stoves or
open fires, but lots of experience on engines - both automotive engines and
large industrial engines.  Generally, my comments come from research on
natural gas engines.

Below about 550 degrees F, sulfation can rapidly deactivate the performance
of most oxidation catalysts.  This is "quasi-permanent" degradation, but can
often be reduced somewhat by a high temperature cycle.  I don't know how
much sulfur is in wood, but even a few ppm can have a dramatic effect.  On
the other end, temperatures above about 1300 degrees F can produce sintering
of the catalyst washcoat which causes deactivation.  If significant unburned
gases are present (through pyrolysis perhaps?), they will release their
energy on the catalyst, which can dramatically raise temperature.  A few
misfires from an engine can melt a catalyst in very short order.

In addition to temperature effects any ash and tar can cause masking.  These
materials can also accumulate and then combust, causing thermal problems.
Masking is probably reduced as temperatures increases, but any fire goes
through a wide range of temperature regimes in its firing cycle.

- Bryan

 Dr. Bryan Willson
 Professor of Mechanical Engineering
 Research Director, Engines & Energy Conversion Laboratory
 Department of Mechanical Engineering
 Colorado State University
 Fort Collins, Colorado  80523-1374
 Phone:  (970)-491-4783
 Mobile: (970)-227-5164
 FAX:    (970)-491-4799
 EECL Web Site: www.engr.colostate.edu\EECL


> -----Original Message-----
> From: Dean Still [mailto:dstill@epud.net]
> Sent: Saturday, September 28, 2002 10:17 AM
> To: willing@mb.sympatico.ca; stoves@crest.org
> Subject: Re: OT(?) Catalytic converters re: N.A. heating stoves
>
>
> Dear Scott,
>
> In my own experience I have not found that catalytic converters are always
> successful. I was told by the manufacturer that the cat. needs to
> be 500F or
> above but not touched by flame which destroys the unit. Perhaps these
> conditions are not always met? I don't know. I just know that adding a cat
> to a cooking stove did not visibly reduce smoke.
>

>
> Dean-


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