Cleaning a catalytic combustor with vinegar bath

[Highbeam]

So as mentioned above my 2 year old steel cat stopped working earlier this year. I tried to tell myself that the white smoke was just steam but 14%MC wood and the dripping tar on my chimney cap told me otherwise. So did the constant smoke, reduced burn times, stalling cat, and low output. My cat was not doing its job and the BK design depends on a functioning cat to create low emissions, long burns, adequate draft, and heat output. The cat is the heart of this stove. The wood makes smoke, the cat eats the smoke to heat your home.

This is my second cat. The first one was the OEM ceramic and died in a less dramatic way after almost three years, replaced under warranty by BK with no hassle. That cat was just starting to let blue smoke by so the ceramic lasted longer in the same stove before failing. I burn 8-9 months of the year. Well over 5000 hours per year in my climate which is wet, dark, drizzly, cloudy, and muddy for most of the months. This amount of use will rack up the hours on a cat and cat life is rated by the manufacturers in hours. So if you are comparing, be sure to realize that my year is probably double your year based on hours.

So with this dead steelcat I first cleaned it in place per the manual and found that even with clear cells it was dead. Second step, really a last ditch effort, I decided to remove the cat and try the vinegar bath to clean, dissolve, melt off any junk that had deposited onto the cat cells and covered up the catalyst. The theory is that the precious metals that create the catalytic reaction with smoke are still there but are just being blocked by the hard remnants of previously burned smoke. You can't blow these deposits off. They are hard, thin, and preventing the cat from working. The deposits can be dissolved by acid and vinegar is acetic acid. Several different stove makers, catalyst makers, catalyst resellers, and even BK at one time have described the exact process of the acid bath. Each of the sources describes the same method so I felt like there was an agreed upon process and that's what I did exactly.

What follows are the photos of the acid bath process. I spent about 20$ on materials and about 4 hours of precious time. It was fun and I can probably do it faster next time. A new cat can be delivered to your home for 186$ in two days so if you value your time highly then you might be wise to just swap a new one in instead of the acid bath. I hate wasting stuff and want to revive the dead cat if possible and also as a learning experience for me and you folks. One gallon of distilled vinegar (used almost all of it) and 4 gallons of distilled water.

So I pulled the cat out with my fingers. Easy. The cat gasket is not reusable and fell out onto the firebox floor. I found a really wide 12" diameter, stainless steel, 5 quart pan in the kitchen with 3" tall sides to do the work. Make sure it fits. Once the cat is out of the stove you are kinda dead in the water. Make sure you have 36" of new cat gasket. That gasket is like 2$ per foot plus shipping. Note that I have a weird steel curtain behind my cat, supposedly this curtain is not present in all stoves. Looks to be just a baffle to prevent exhaust from shooting straight into the flue.

I fashioned a little handle out of some 14 gauge coated wire. You will use these handles a lot. I also installed a wire around the cat to keep it off of the bottom of the pot which will allow a flow of acid through the catalyst. If it just sits on the bottom then less acid will be able to flow through and remove deposits.

Getting long. To be continued.

 

[Highbeam]

The last two photos in this post are the revacuumed "cleaned" cat front and back. Notice the rear has fuzzy white stuff. Weird.

So here is my work station. First thing to do is get a fire going in the non-cat NC30. The NC30 was laughing about the vinegar to clean cat, it must be a girl situation. Ha! Note that from a distance the cat looks totally invisible, a really odd effect.

I didn't know how much headspace to leave in the pan but I was ready to top off the pan after the cat was dropped in. The instructions specified dropping the cat into the hot vinegar and so I didn't drop it in until the vinegar was boiling. Then I had to top it up. I kept the pan full for maximum coverage and simmering so you can see bubbling.

 

[Highbeam]

Here she is boiling in the acid. Yes it stinks, yes you will lose a lot to evaporation, and yes there is a brownish mud that is coloring the acid. Something is being removed from the cat. The stainless steel pan did not discolor or become damaged. The wife will never know.

Lots of dunking during all stages. You want maximum exposure of the cells to the liquid. If you are dealing with ceramic, no banging. Just lift it up and down every couple of minutes.

 

[Highbeam]

Dump the vinegar and then soap and water wash the pan. Dry with a paper towel, no smell remains, pan looks new. Distilled water bath twice. At this point there was snow on the ground and I needed to get the stove running. I don't know if there is any reason to dry a steel cat but I dried the cat on the NC30 for over an hour. Note how the cat cells dry out and lighten. Also notice that the white fuzz on the back dissolved! Pretty clean looking now. It was very apparent that water had soaked into the coating of the cat and that you should dry your cat whether it is ceramic or steel.

 

[Highbeam]

At this point I gasket the cat. I used webby3650's method of overlapping the gasket and then cutting for a perfect butt joint. No overlap, the cat is a tight fit. The tape keeps the gasket from sliding off as you work it into the tight hole. Just work it into the hole slowly, a little on each side. It squeaks but you don't want to dislodge the gasket. I did cut off the tape from in front of the cat after installation but the rear tape just burns off. The 36" of cat gasket leaves you with the pictured remainder so don't cut it any closer when ordering gasket.

A tasty beverage to consume while the new fire starts.

So It's working great. The decline in cat performance was gradual and then near the end was rapid, a snowball effect. The wife asked, "has it ever worked this well?" There is no smoke at all after the initial warm up. It's only been three days but I removed the flame shield and find that the whole cat is staying grey now and not that brown color, also no deposits are accumulating on the cat face as they were before.

The drawback is that my window is now dirtier and less flames since I am able to run the stat much lower while the flue temps are up above condensing and stove output is higher. It seems I have been wasting a lot of unburned fuel just trying to stay warm.

Did I do okay? You'll notice that the durafoil cat block has buckled a little bit and come apart near the bottom. It is pushed in towards the cat chamber by under 1/8" and not welded there. No big deal in my opinion. It's not loose.

 

[Highbeam]

Thank you mods for creating a new thread with this info. For an update, the cat did great for the remainder of last season which was 3-4 months of burning. I will be using it this season until it dies again which might be a few months or might be two more years. Folks that have done the vinegar bath with other brands have noticed that the time between the first vinegar bath and the second failure is much shorter than the time from new cat to first failure. In other words, I'm not getting another 12000 hours! At the first sign of a failing cat I will be ordering a new ceramic cat. They just aren't that expensive and the fresh catalyst will reward me with like-new performance.

 

[begreen]

I figured that if it took me 10 minutes to find it buried deep in the bowels of the BK2016 thread that a newcomer would have no chance. It's good info and can now be more easily discoverable with a searchable title.

 

[jetsam]

Those threads are big. This was a good bit. (Yay for pictures!)

Highbeam, your process was vastly less rednecky than mine. Gas burners, proper pans... walls....

Can we have a new thread for The Dreaded Swoosh Sticker Wars too?

 

[ohiojoe13]

When you did the acid bath was it straight vinegar?

 

[Highbeam]

When you did the acid bath was it straight vinegar?

Yes, but to be fair "straight" vinegar is already very diluted with water. There is a vinegar factory in my town and the straighter stuff is very dangerous. I used straight distilled white vinegar from the home depot for the acid boil.

 

[WoodyIsGoody]

I would like to see instructions for achieving the same thing using muriatic acid. That's what I use in my hot tub to maintain optimum pH so I always have it around (and I imagine it is has less impurities than vinegar). Of course proper acid handling procedures need to be followed (which is why manufacturers probably recommend vinegar). Also, some "Muriatic Acid" is not pure but formulated for specific tasks. I always buy the pure stuff (diluted to 31.45%). I imagine a further dilution would be recommended.

 

[redktmrider]

I would cation against using Muratic acid to clean a cat.
Vinegar is diluted acetic acid, which is organic in composition and not a very strong acid. Muratic acid is diluted hydrochloric acid, a very strong acid which is likely to attack the metal plating on the cat. I worked in a metals laboratory for a number of years and Hydrochloric acid was one the acids we used to dissolve metal into water solutions.

 

[Highbeam]

I would like to see instructions for achieving the same thing using muriatic acid. That's what I use in my hot tub to maintain optimum pH so I always have it around (and I imagine it is has less impurities than vinegar). Of course proper acid handling procedures need to be followed (which is why manufacturers probably recommend vinegar). Also, some "Muriatic Acid" is not pure but formulated for specific tasks. I always buy the pure stuff (diluted to 31.45%). I imagine a further dilution would be recommended.

I'm also a hot tub operator, was a pool operator in a commercial setting in my teen years, and I found that I never needed to add acid to lower pH unless I screwed up and added too much pH increaser. To this day I only keep sodium carbonate (pH increaser, soda ash) around for hot tub maintenance.

 

[WoodyIsGoody]

I would cation against using Muratic acid to clean a cat.
Vinegar is diluted acetic acid, which is organic in composition and not a very strong acid. Muratic acid is diluted hydrochloric acid, a very strong acid which is likely to attack the metal plating on the cat. I worked in a metals laboratory for a number of years and Hydrochloric acid was one the acids we used to dissolve metal into water solutions.

What I know about acids is the metal can't tell if it's "organic in composition" or not. With acid it's all about time, temperature and dilution. I can make that muriatic acid weaker than white wine vinegar more quickly than you can say "I'm not so sure about that".

 

[WoodyIsGoody]

I'm also a hot tub operator, was a pool operator in a commercial setting in my teen years, and I found that I never needed to add acid to lower pH unless I screwed up and added too much pH increaser. To this day I only keep sodium carbonate (pH increaser, soda ash) around for hot tub maintenance.

I maintained swimming pools for a homeowners association with over 5000 residents while I was in college. I learned the method from an expert pool guy although I didn't fully understand the chemistry until years later.

I'm fortunate to have almost ideal water for a hot tub/swimming pool right out of the tap. It has a very nice calcium hardness balance, no chlorine and is sourced from melting glaciers. This means much of it fell as snow over 10,000 years ago. I change it once every 12-18 months. Everyone who uses it comments on how nice it is on their skin and how it doesn't smell like typical "spa water". One of the secrets (besides the wonderful fill water) is borates (20 Mule Team Borax), about 1/2 box to a fresh fill. Then I need to add around 8 oz. of muriatic acid to make the pH ideal. The pH hardly fluctuates at all after that although I might add about 1 oz. of muriatic acid every 4-6 weeks if the aeration jets have been used a lot (I'm not gonna go into the chemistry involved).

I NEVER add "pH increaser" (which is soda ash) because it really depends upon the composition of your fill water. All water is not the same, obviously. The periodic addition of acid is not because I screwed up, it has to do with the minerals in the initial fill.

Do you use a salt water spa system? Because I notice you didn't list a sanitizer.

 

[Highbeam]

I maintained swimming pools for a homeowners association with over 5000 residents while I was in college. I learned the method from an expert pool guy although I didn't fully understand the chemistry until years later.

I'm fortunate to have almost ideal water for a hot tub/swimming pool right out of the tap. It has a very nice calcium hardness balance, no chlorine and is sourced from melting glaciers. This means much of it fell as snow over 10,000 years ago. I change it once every 12-18 months. Everyone who uses it comments on how nice it is on their skin and how it doesn't smell like typical "spa water". One of the secrets (besides the wonderful fill water) is borates (20 Mule Team Borax), about 1/2 box to a fresh fill. Then I need to add around 8 oz. of muriatic acid to make the pH ideal. The pH hardly fluctuates at all after that although I might add about 1 oz. of muriatic acid every 4-6 weeks if the aeration jets have been used a lot (I'm not gonna go into the chemistry involved).

I NEVER add "pH increaser" (which is soda ash) because it really depends upon the composition of your fill water. All water is not the same, obviously. The periodic addition of acid is not because I screwed up, it has to do with the minerals in the initial fill.

Do you use a salt water spa system? Because I notice you didn't list a sanitizer.

I'm a sodium dichlor guy. A little polymer if needed, and sodium carb for pH. It's so easy.

 

[begreen]

This is a good chat topic for the DIY forum or the Inglenook, but way off topic here. Can we keep the focus on cat cleaning? That's why this thread was created.

 

[redktmrider]

I have a BS in chemistry and 20 years of lab experience, I would NOT put a cat in any ionic acid (HCL, H2SO4, HNO3). pH is only one part of the acids chemistry.

 

[Highbeam]

Okay, vinegar it is! Cheap, available everywhere, and recommended by all cat manufacturers and stove manufacturers that provide cat cleaning instructions.

Plain old off the shelf distilled white vinegar. I'd better not hear about anybody using apple cider vinegar!

 

[WoodyIsGoody]

I have a BS in chemistry and 20 years of lab experience, I would NOT put a cat in any ionic acid (HCL, H2SO4, HNO3). pH is only one part of the acids chemistry.

OK, maybe citric acid would be better for catalytic converters?

 

[jetsam]

I used balsalmic. Tangy!

 

[ohiojoe13]

I tried the vinegar bath and I can still see some stuff in the cells. Did I do it wrong or is that normal to still see some stuff.

 

[jetsam]

You should be able to see catalyst adhering to the ceramic substrate, but no calcification/soot/ash.

 

[ohiojoe13]

You should be able to see catalyst adhering to the ceramic substrate, but no calcification/soot/ash.

Ok thank you.

 

[SCOTT S.]

Dump the vinegar and then soap and water wash the pan. Dry with a paper towel, no smell remains, pan looks new. Distilled water bath twice. At this point there was snow on the ground and I needed to get the stove running. I don't know if there is any reason to dry a steel cat but I dried the cat on the NC30 for over an hour. Note how the cat cells dry out and lighten. Also notice that the white fuzz on the back dissolved! Pretty clean looking now. It was very apparent that water had soaked into the coating of the cat and that you should dry your cat whether it is ceramic or steel.
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Where did you buy your gasket?