Catalytic Combustor Questions

[Mike the heater]

Hi,
Did I ruin my Catalytic Combustor?
It's on a Country Flame E1-6 wood stove. Stove is probably 30+ years old. After cleaning the combustor with a shop vac. I re-installed the heat shield but left it about 1/2 inch below the combustor, leaving a gap between the shield and the combustor. The shield is 1/8 inch thick sheet of steel. It all was working fine for about 6 weeks, then when I got it good and hot, the combustor housing got glowing red and thick opaque grey smoke came out the chimney. I immediately pulled the lever to bypass the combustor and let the fire die. Now I've removed the combustor housing and combustor. The holes in the housing were very clogged with ash and what looks like powered grains of metal. The iron housing turned a rusty red.

Anyway, I've now ordered a new combustor. But hoping to learn what happened.

Should the heat shield have been installed right up against the combustor housing? What that the problem?

Can I use the stove without the combustor in place while I wait for the new combustor to arrive?

Thanks for any input.
Mike

 

[Mike the heater]

These photos go with my post above about the Catalytic Combustor.
1. The top of fire box with combustor and its housing removed.
2., 3., 4. The housing showing some holes clogged.
5. The combustor, some ash in holes. Possibly damaged.

Any comments much appreciated!

 

[Highbeam]

Nah, it's fine, dust it off and put it back in service.

 

[begreen]

I don't have the manual for the E1-6 but this is what the manual says for the BFF, B, R models.

 

[Mike the heater]

I don't have the manual for the E1-6 but this is what the manual says for the BFF, B, R models.

View attachment 305580

Thanks! That is nearly identical to my E1-6. Just the heat shield is slightly different. Curiously though, the diagram doesn't show any gasket between the catalyst holder and the top of the fire box. Mine had a gasket there when I moved into this house, so I put in a new one when I remove the catalyst. I was able to find the gasket material online. Thanks again.

 

[Mike the heater]

Nah, it's fine, dust it off and put it back in service.

Thanks.

 

[Woody Stover]

After cleaning the combustor with a shop vac. I re-installed the heat shield but left it about 1/2 inch below the combustor, leaving a gap between the shield and the combustor. The shield is 1/8 inch thick sheet of steel. It all was working fine for about 6 weeks, then when I got it good and hot, the combustor housing got glowing red and thick opaque grey smoke came out the chimney. I immediately pulled the lever to bypass the combustor and let the fire die. Now I've removed the combustor housing and combustor. The holes in the housing were very clogged with ash and what looks like powered grains of metal. The iron housing turned a rusty red.
Should the heat shield have been installed right up against the combustor housing?
Can I use the stove without the combustor in place while I wait for the new combustor to arrive?

It looks in the diagram like they have two nuts between the cat shield and the cat housing. You need space between the two to allow the smoke to enter the bottom of the cat.
How could you tell that the combustor was "working fine for 6 weeks?" Could you see it glowing, or did you see that the plume outside was clear, not smoky?
Have you run the stove a period of time before this episode, and you know how hot the stove has to be before you can close the bypass, get the cat burning, and get a clean plume outside? Or maybe it has a cat probe thermometer that you go by (my neighbor's BBF has one.)
You may need to keep some flame going in the box for a bit after you close the bypass, in order to kick off the cat burn. But once you get the cat burning, you'll generally cut the air back to get a moderate cat burn, either with no flame, or maybe a little lazy flame. I've found that with too much air, and big flame, sometimes the smoke can blow through the cat before it has enough time to burn it, and may exit the stack outside. Now, if you have big flame in the box after you've closed the bypass, flames could be sucking around the cat shield and directly heating the cat housing to a red glow..you never want any metal in your stove glowing! 😯
While you wait for the new cat, I would put the old one back in, even if it's not working. At least with the bypass closed, it will route the exhaust in a longer path through the stove, allowing it to extract more heat than if the bypass is open and the heat exits straight into the chimney.
Just gently dust the face of the cat with a soft brush, and blow through the cat either manually or with low-pressure air. No compressor full-blast air..you can peel the coating right off the substrate! 😖

 

[rijim]

Looks like a ceramic cat, I don’t see crack in it; is that correct?

 

[Woody Stover]

Looks like a ceramic cat, I don’t see crack in it; is that correct?

Yep, ceramic. Like Highbeam said, it looks fine. You can even run a cracked one, as long as it's not falling apart.
This one might just be worn out. OP didn't say how long he's been running the stove. If it was there from a previous owner, he may not know how many hours it has on it. He said it was working OK for six weeks, then he saw smoke exiting; Coulda just been blowing through the cat due to an air setting that was too high, not giving the smoke necessary residence time in the cat.

 

[Ashful]

Looks like a ceramic cat...

 

[Mike the heater]

Nah, it's fine, dust it off and put it back in service.

Thanks.

It looks in the diagram like they have two nuts between the cat shield and the cat housing. You need space between the two to allow the smoke to enter the bottom of the cat.
How could you tell that the combustor was "working fine for 6 weeks?" Could you see it glowing, or did you see that the plume outside was clear, not smoky?
Have you run the stove a period of time before this episode, and you know how hot the stove has to be before you can close the bypass, get the cat burning, and get a clean plume outside? Or maybe it has a cat probe thermometer that you go by (my neighbor's BBF has one.)
You may need to keep some flame going in the box for a bit after you close the bypass, in order to kick off the cat burn. But once you get the cat burning, you'll generally cut the air back to get a moderate cat burn, either with no flame, or maybe a little lazy flame. I've found that with too much air, and big flame, sometimes the smoke can blow through the cat before it has enough time to burn it, and may exit the stack outside. Now, if you have big flame in the box after you've closed the bypass, flames could be sucking around the cat shield and directly heating the cat housing to a red glow..you never want any metal in your stove glowing! 😯
While you wait for the new cat, I would put the old one back in, even if it's not working. At least with the bypass closed, it will route the exhaust in a longer path through the stove, allowing it to extract more heat than if the bypass is open and the heat exits straight into the chimney.
Just gently dust the face of the cat with a soft brush, and blow through the cat either manually or with low-pressure air. No compressor full-blast air..you can peel the coating right off the substrate! 😖

I knew it was working well for 6 weeks because when the bypass was closed the smoke out the chimney was very clear. There was almost no visible smoke at all, more like just heat waves. I always got the stove up to about 600 or more degrees before closing the bypass. Yes, it has a probe thermometer that I go by. I used the stove all last winter too. It worked well then. But I had the heat shield closer to the Cat holder then. I carelessly left it too low this fall after cleaning the chimney ( that's what I think is the problem). I did have a big flame when the cat holder glowed and the exhaust smoke turned an ugly thick opaque grey, a color I had never seen before.

The stove is probably 30 years old. I've been in this house 5 years. So I know the Cat is at least 5 years old, but it's probably much older. In past years I could never see the cat holder because the shield was close up against it. The holder even has a protruding nub so the shield can be against the nub without being too close. So, you're probably right about the big flame hitting the Cat. I just wasn't thinking when I put the shield back on this fall and left that extra space.

It cost me my time of messing with the whole thing. The new Cat costs $230, not too bad, and it might've needed one anyway.

 

[Mike the heater]

Nah, it's fine, dust it off and put it back in service.

Thanks.

It looks in the diagram like they have two nuts between the cat shield and the cat housing. You need space between the two to allow the smoke to enter the bottom of the cat.
How could you tell that the combustor was "working fine for 6 weeks?" Could you see it glowing, or did you see that the plume outside was clear, not smoky?
Have you run the stove a period of time before this episode, and you know how hot the stove has to be before you can close the bypass, get the cat burning, and get a clean plume outside? Or maybe it has a cat probe thermometer that you go by (my neighbor's BBF has one.)
You may need to keep some flame going in the box for a bit after you close the bypass, in order to kick off the cat burn. But once you get the cat burning, you'll generally cut the air back to get a moderate cat burn, either with no flame, or maybe a little lazy flame. I've found that with too much air, and big flame, sometimes the smoke can blow through the cat before it has enough time to burn it, and may exit the stack outside. Now, if you have big flame in the box after you've closed the bypass, flames could be sucking around the cat shield and directly heating the cat housing to a red glow..you never want any metal in your stove glowing! 😯
While you wait for the new cat, I would put the old one back in, even if it's not working. At least with the bypass closed, it will route the exhaust in a longer path through the stove, allowing it to extract more heat than if the bypass is open and the heat exits straight into the chimney.
Just gently dust the face of the cat with a soft brush, and blow through the cat either manually or with low-pressure air. No compressor full-blast air..you can peel the coating right off the substrate! 😖

I knew it was working well for 6 weeks because when the bypass was closed the smoke out the chimney was very clear. There was almost no visible smoke at all, more like just heat waves. I always got the stove up to about 600 or more degrees before closing the bypass. Yes, it has a probe thermometer that I go by. I used the stove all last winter too. It worked well then. But I had the heat shield closer to the Cat holder then. I carelessly left it too low this fall after cleaning the chimney ( that's what I think is the problem). I did have a big flame when the cat holder glowed and the exhaust smoke turned an ugly thick opaque grey, a color I had never seen before.

The stove is probably 30 years old. I've been in this house 5 years. So I know the Cat is at least 5 years old, but it's probably much older. In past years I could never see the cat holder because the shield was close up against it. The holder even has a protruding nub so the shield can be against the nub without being too close. So, you're probably right about the big flame hitting the Cat. I just wasn't thinking when I put the shield back on this fall and left that extra space.

It cost me my time of messing with the whole thing. The new Cat costs $230, not too bad, and it might've needed one anyway.

 

[Mike the heater]

Yep, ceramic. Like Highbeam said, it looks fine. You can even run a cracked one, as long as it's not falling apart.
This one might just be worn out. OP didn't say how long he's been running the stove. If it was there from a previous owner, he may not know how many hours it has on it. He said it was working OK for six weeks, then he saw smoke exiting; Coulda just been blowing through the cat due to an air setting that was too high, not giving the smoke necessary residence time in the cat.

Yes, it's a ceramic Cat. I don't know how old it is, but 5 years, minimum, probably much older. The residence time could've been an issue, but probably not the problem. Like you said, the Cat. holder shouldn't have been glowing. And the smoke was very thick, opaque grey. The holes in the holder were clogged with a mixture of ash and I-don't-know-what, grains of the metal from the holder itself I think. I cleaned the holes out with a small screw driver and pipe cleaners.

 

[Woody Stover]

Thanks.

I did have a big flame when the cat holder glowed and the exhaust smoke turned an ugly thick opaque grey, a color I had never seen before.
The new Cat costs $230, not too bad, and it might've needed one anyway.

Sometimes when things get hot in the top of the stove, some creosote that has been deposited in the area might be burning off. If you are downwind, it smells like creo smoke, not wood smoke. I haven't actually looked for smoke when I've stepped out and smelled creo, but I imagine it would look darker and heavier than regular wood smoke.
Is the cat size 6x2" or is it 8"? My Dutchwest uses a 6x2, and I've gotten a steel cat from Woodstock Soapstone, as well as a ceramic from firecatcombustors (Applied Ceramics.) Not sure if Woodstock is still making the round cats, now that they are making them in-house..

 

[Ashful]

Watch your smoke output when your cat probe indicates temperatures of 500 - 1100 °F. If you're seeing a lot of black smoke at those temperatures, the cat is due for replacement. Otherwise, keep running it.

If you run a lot of low burns on softwood, this might occur as soon as 10 - 12,000 hours of operation. But if you burn mostly higher rates on hardwood, you might go 2x - 3x longer before you notice a serious decrease in performance. Figure how many hours per year to run, to convert to years, but for most "full time" burners we're looking at 2 - 4 years. Part-time burners might go 20+ years on the same combustor, with no issue.

Oh, and why 500 - 1100 °F? Below 500°F the cat will not reburn the fuel it is receiving, it goes inactive. Above 1100°F you can achieve non-catalytic reburn, even with a depleted catalyst, such that your plume might be clean even when the cat is toast.

 

[Mike the heater]

Watch your smoke output when your cat probe indicates temperatures of 500 - 1100 °F. If you're seeing a lot of black smoke at those temperatures, the cat is due for replacement. Otherwise, keep running it.

If you run a lot of low burns on softwood, this might occur as soon as 10 - 12,000 hours of operation. But if you burn mostly higher rates on hardwood, you might go 2x - 3x longer before you notice a serious decrease in performance. Figure how many hours per year to run, to convert to years, but for most "full time" burners we're looking at 2 - 4 years. Part-time burners might go 20+ years on the same combustor, with no issue.

Oh, and why 500 - 1100 °F? Below 500°F the cat will not reburn the fuel it is receiving, it goes inactive. Above 1100°F you can achieve non-catalytic reburn, even with a depleted catalyst, such that your plume might be clean even when the cat is toast.

Thanks, good info. I ordered a new cat. Seems worth it.

There is a little fire damage on the heavy iron Cat holder (the housing in which cat sits, ) where that hot flame was hitting it. That's what likely caused the very thick smoke. I thinking that damage is insignificant, but not sure, still looking into it. I looks like small bits of the metal flaked off from the heat.

 

[Woody Stover]

There is a little fire damage on the heavy iron Cat holder (the housing in which cat sits, ) where that hot flame was hitting it. That's what likely caused the very thick smoke. I thinking that damage is insignificant, but not sure, still looking into it. I looks like small bits of the metal flaked off from the heat.

Did the flame heat warp the cat housing enough that smoke is now escaping through a gap between the cat housing and the top of the stove, where you said you put a gasket? The gasket you found online was just a high-temp fiber gasket, right, not interam gasket? Interam gasket expands with heat initially, closing any gaps. If the cat housing is warped to where smoke can now get past it, you could possibly use a piece of interam in there to close the gap. Or just get a new cat housing if that part is still available.
Is the cat housing made of cast iron? It's less prone to warping than plate steel would be, but it's still possible that it's warped...
If the cat housing is warped, and no longer available, maybe it's possible to grind the old one to be closer to flat, I'm not sure. That would weaken it, of course...

 

[Mike the heater]

Update to this thread:
I bought a new cat combustor unit, it's steel. I installed it. Everything's working EXCEPT when the stove is 1500 F or more. At that temp the cat housing glows and smoke gets darker. I didn't think a cat combustor could get too hot. The cat heat shield covers the combustor, I put it tight up against the cat housing. It has a nub that prevents the heat shield from getting too close and blocking the combustor. But flames could get around the shield a little. So I try to keep the temp between 1000 and 1500 F. Something's not right if I can't let it get hotter than that. It easily can get to 2000 F when I stuff it for the night.

Did the flame heat warp the cat housing enough that smoke is now escaping through a gap between the cat housing and the top of the stove, where you said you put a gasket? The gasket you found online was just a high-temp fiber gasket, right, not interam gasket? Interam gasket expands with heat initially, closing any gaps. If the cat housing is warped to where smoke can now get past it, you could possibly use a piece of interam in there to close the gap. Or just get a new cat housing if that part is still available.
Is the cat housing made of cast iron? It's less prone to warping than plate steel would be, but it's still possible that it's warped...
If the cat housing is warped, and no longer available, maybe it's possible to grind the old one to be closer to flat, I'm not sure. That would weaken it, of course...

Thanks for commenting. I didn't see your response til now. The cat housing is not warped. It's cast iron about 5/16" thick. It changed color a little, to a rusty red where the little bits of metal flaked off. The gasket I believe is called glassine. It feels like fabric, it's fibrous. About 1/8" thick. Anyway, there's no gap, so that's not a worry.

 

[Woody Stover]

I didn't think a cat combustor could get too hot.

I've read that you can damage the cat if it is run above 1500 for too long. The catalyst can apparently separate from the substrate. I really don't like to see it over 1400, myself.
But I wouldn't expect to see smoke getting by the cat at those temps--it should be burning everything, I'd have thought. 🤔

 

[Ashful]

I've always read more like 1800F - 2000F, for various stages of damage. Paging @stoveliker, I think he knows more about this than either of us.

 

[stoveliker]

What does the mfg say about max temps?

I always read that above 1600 f it gets dicey. But new cats often are very active (=hotter), and will settle down after some time. (Due to the changes resulting from that hyperactivity.)

Delamination of the coating depends on the stability of the coating (duh) and on the difference in thermal expansion coefficients between coating and substrate. I don't know what the latter would result in for a ceramic substrate and whether it would be different than a steel one.

I'd simply ask the vendor what they recommend if the documentation doesn't mention anything.

Regarding the thick smoke, I think you burned something in the top of the stove (or bottom of the chimney) when the old cat got hotter than before, possibly due to more flame impingement. Failing cats do not suddenly "switch on a smoke generator".

I wonder if the old cat was working at all, if you got some significant volume of stuff burning off resulting in the thick smoke.

Hard to say something definitive about this.

Finally, my flame shield often glows. It even bent/sagged a bit. This is fine (for my stove according to the mfg, whom I asked). It's more important to have the right temps to run the cat properly than to avoid any glowing metal, imo.


I had an old ('82) Dutch West FA cat stove before. Similar set up as yours. The flame shield also glowed from time to time.

 

[Woody Stover]

Update to this thread:
I bought a new cat combustor unit, it's steel. I installed it. Everything's working EXCEPT when the stove is 1500 F or more. At that temp the cat housing glows and smoke gets darker. I didn't think a cat combustor could get too hot. The cat heat shield covers the combustor, I put it tight up against the cat housing. It has a nub that prevents the heat shield from getting too close and blocking the combustor. But flames could get around the shield a little. So I try to keep the temp between 1000 and 1500 F. Something's not right if I can't let it get hotter than that. It easily can get to 2000 F when I stuff it for the night.

Thanks for commenting. I didn't see your response til now. The cat housing is not warped. It's cast iron about 5/16" thick. It changed color a little, to a rusty red where the little bits of metal flaked off. The gasket I believe is called glassine. It feels like fabric, it's fibrous. About 1/8" thick. Anyway, there's no gap, so that's not a worry.

Only thing I can think is that when the cat housing glows, it distorts and opens up some leaks where smoke gets past the cat.
How active a burn do you usually keep going? Medium to large flame in the box?
I have a Dutchwest with a similar setup, cast iron cat flame shield below the cat, then the 8x2" round cat is wrapped in interam gasket and drops into a "cup" that holds it. To get that cast iron shield glowing, cat has to be orange and I'd have to have pretty strong flame going in the box. If I have a cat-only burn, no flame, the cat shield doesn't glow. I never saw any cat probe temp above 1200-1300. The Buck 91 would try to push above 1500 on occasion, no flame in the box, but I would nip that in the bud when it happened.
Do you need flame going in the box to be able to heat your place, or will a cat-only burn do the job?
What kind of wood do you generally burn? If it's lightweight wood that burns faster and feeds the cat more volatiles, quicker, that will cause the cat to burn hotter. Dense woods like White Oak or Black Locust burn and gas slower, so are less of a problem in that regard.
With your new cat, was there interam gasket supplied, that wrapped around the cat? Is it an OEM cat? Some cats are wrapped in interam, then a stainless band is wrapped on top to hold the interam gasket in place. I'd guess the cat was made by Firecat (Applied Ceramics)...?

I've always read more like 1800F - 2000F, for various stages of damage. Paging @stoveliker, I think he knows more about this than either of us.

What does the mfg say about max temps?

I always read that above 1600 f it gets dicey. But new cats often are very active (=hotter), and will settle down after some time. (Due to the changes resulting from that hyperactivity.)

Yeah, but you're BK guys. You're commanded to keep your hands off things like stove air control/cat temps (no numbers on the probe dial,) let the stove run itself, and not worry your pretty little heads about such things. 😏 Unless you have a probe in your stoves, cat temps are a moot point for you.

 

[stoveliker]

I have probed more places on and in my stove than most here.

And I ran a Dutch West before the BK.

So rather than commenting on what others can't or shouldn't do, I'd keep to the advice you can provide yourself. (As indeed that is often useful, contrasting with your comments about other people here.)

 

[Woody Stover]

Fair enough..kind of. Glad you put that "on and in my stove" rejoinder in there.
My comment was mainly to Ashful. We have a long-running tradition of ribbing each other. Plus I just like ribbing BK owners about their "unique" stoves, and the company's approach to stove operation. They offer a lot of latitude for commentary in that regard, that's why my take on them has also been a long-running tradition with me as well, in contrast to the endless hype and blather about how they are the greatest thing since sliced bread...maybe even greater, possibly rivaling the arrival of penicillin and the polio vaccine. 😝
The problem is when people start misinterpreting my comments an ad hominem attack.
Not sure if Ashful runs a cat probe, but I don't think so...?? You'd think he would, nerd that he is.. 🤓

 

[Woody Stover]

Now, I will ad hominem Highbeam from time to time, just to give him a taste of his own medicine. 😆