2021-2022 BK everything thread

[stoveliker]

That was the hardest I've laughed on a message board in a long time.

I believe it was pointdexter who came up with this strategy.

 

[BKVP]

That was the hardest I've laughed on a message board in a long time.

Just read the post from our friend in Fairbanks about wife attire. That will bust you up. You could also remove the thermostat knob, but that would be a pain to reinstall each time. Yup, let her win.

 

[Highbeam]

Does that suggest that the cat should have been a bit bigger in order to eat all that is generated when running fast? After all, pine and fir is a "staple" food for BKs in some places, so it's not an exception in its use...

I think it is possible and well documented that you can overwhelm the catalyst with certain fuels and certain burn rates. However, as BKVP has stated and supported with documentation, the huge majority of burners spend the huge majority of the time burning at low burn rates so there is probably a tipping point or trade off. Certainly in cost for a bigger cat but when tuning a stove to burn clean at high rates you might lose some abilities on the more important bottom end. Like a hot cam in a car engine has a crappy idle.

 

[stoveliker]

I think it is possible and well documented that you can overwhelm the catalyst with certain fuels and certain burn rates. However, as BKVP has stated and supported with documentation, the huge majority of burners spend the huge majority of the time burning at low burn rates so there is probably a tipping point or trade off. Certainly in cost for a bigger cat but when tuning a stove to burn clean at high rates you might lose some abilities on the more important bottom end. Like a hot cam in a car engine has a crappy idle.

Most of those overwhelm situations are I think at low burn rates, generating lots of fuel, more than can be combusted.

I wonder if at the high rate end of the spectrum, the residence time of those gases inside the cat is not long enough for reaching a high fraction of cat-mediated oxidation of those gases. High rate is more flow, so things rush through the cat. - But indeed a thicker (longer channel, longer residence time) cat could be problematic at low rate/low draft situations.

 

[sacountry]

Most of those overwhelm situations are I think at low burn rates, generating lots of fuel, more than can be combusted.

I wonder if at the high rate end of the spectrum, the residence time of those gases inside the cat is not long enough for reaching a high fraction of cat-mediated oxidation of those gases. High rate is more flow, so things rush through the cat. - But indeed a thicker (longer channel, longer residence time) cat could be problematic at low rate/low draft situations.

This is good. You guys are helping me wrap my mind around the science of the heat and flow rate specific to the cat. I struggle with the cam analogy because we aren't talking about moving parts which obviously wear from friction. I also struggle with gas moving too fast through cat as an area for failure.....certainly an area for reduced efficiency, but I don't understand how that could result in increased wear.

 

[stoveliker]

We are speculating, having somewhat educated guesses... And analogies often work only up to a certain extent.

 

[Highbeam]

This is good. You guys are helping me wrap my mind around the science of the heat and flow rate specific to the cat. I struggle with the cam analogy because we aren't talking about moving parts which obviously wear from friction. I also struggle with gas moving too fast through cat as an area for failure.....certainly an area for reduced efficiency, but I don't understand how that could result in increased wear.

When we talk about overwhelming the cat we’re not talking about wear or damage but that too much fuel is passing through the catalyst unburned because flow rate is too high, residence time too low, or just too dang much fuel. Unburned fuel going up the chimney is wasted heat and ugly emissions so we want to keep it down.

Some of us older folks used to replace camshafts in car engines for performance. You could choose a camshaft optimized for high rpm with poor low rpm performance or get the opposite. It’s about trade offs. You could also buy a camshaft like the original that was pretty good at everything but sometimes left a little performance on the table at the low end and top end. That seems to be what Bk did with the stove. Optimized for low/medium output but still pretty good at high output.

I’ve never heard of a cat overwhelmed at low output. That’s where the BK is most efficient and has the lowest emissions.

The Bk design hasn’t changed much over the decades despite huge restrictions in emissions rates. Same cat has been used for decades in my princess. I just wish it would last longer.

 

[Nealm66]

I’m getting pretty consistent 24 hours and still plenty of coals to relight at current outside temp averages and I have a mark on my swoosh where this seems to happen. Would a failing cat start burning for less time and that would signal thinking about replacement?

 

[stoveliker]

I’ve never heard of a cat overwhelmed at low output. That’s where the BK is most efficient and has the lowest emissions.

What I meant was if you char on high, and too suddenly go all the way to your lowest setting, the cat can stall at that low setting. I think because of too much fuel. (Hence the "decrease in steps" instructions in the manual.)

 

[sacountry]

Coming back to my original question. Doesn't appear as though my wife can overburn/harm the BK King, but I do need to highlight to her the wasted gas/fuel that goes out the stack when burning on high....not to mentioned that she remain comfortably dressed all winter long in the 3:00-3:30 position on the tstat.

I have to admit I really like the control the stove has over the flame. I can dial right down to a flicker of a slow flame further yet to just keeping the coals hot, "black in the box" as I'm learning you guys like to say. I never imagined that kind of control in a stove. With propane prices set to spike by 40% in my area, I'm really hoping our 8 cord wood supply is enough. Might have to go harvest a couple more logs just to make sure.

 

[circle_burner]

What I meant was if you char on high, and too suddenly go all the way to your lowest setting, the cat can stall at that low setting. I think because of too much fuel. (Hence the "decrease in steps" instructions in the manual.)

When I turn down too fast my cat temp spikes on the stock thermometer.

 

[stoveliker]

When I turn down too fast my cat temp spikes on the stock thermometer.

Sometimes it does, and sometimes it essentially stalls for me.

 

[stoveliker]

Coming back to my original question. Doesn't appear as though my wife can overburn/harm the BK King, but I do need to highlight to her the wasted gas/fuel that goes out the stack when burning on high....not to mentioned that she remain comfortably dressed all winter long in the 3:00-3:30 position on the tstat.

I have to admit I really like the control the stove has over the flame. I can dial right down to a flicker of a slow flame further yet to just keeping the coals hot, "black in the box" as I'm learning you guys like to say. I never imagined that kind of control in a stove. With propane prices set to spike by 40% in my area, I'm really hoping our 8 cord wood supply is enough. Might have to go harvest a couple more logs just to make sure.

Even running on high, the efficiency is still way, way better than the pre-EPA stoves. Don't worry about wasted energy. Yes, on high your flue will be a bit warmer. But if it's -10 F (or for some other unmentionable reason) you need the heat so you run on high.

Check what's coming out of your chimney every now and then. Learn to see when it's steam (white, and dissolving in a couple of feet) versus smoke (bluish, grey, not dissolving, but diluting in air). The latter means your (new, so good) cat is not doing what it's supposed to do.

 

[sacountry]

Even running on high, the efficiency is still way, way better than the pre-EPA stoves. Don't worry about wasted energy. Yes, on high your flue will be a bit warmer. But if it's -10 F (or for some other unmentionable reason) you need the heat so you run on high.

Check what's coming out of your chimney every now and then. Learn to see when it's steam (white, and dissolving in a couple of feet) versus smoke (bluish, grey, not dissolving, but diluting in air). The latter means your (new, so good) cat is not doing what it's supposed to do.

That's an interesting data point to check out. Never thought about seeing the effects of the cat by looking at what evacuates the pipe.

 

[Diabel]

I’m getting pretty consistent 24 hours and still plenty of coals to relight at current outside temp averages and I have a mark on my swoosh where this seems to happen. Would a failing cat start burning for less time and that would signal thinking about replacement?

Failing “cat” less heat into the house, smoke out the pipe. I believe your stove is relatively new 1 or 2 winter seasons . I think you are ok, the cat is still good.

 

[Highbeam]

That's an interesting data point to check out. Never thought about seeing the effects of the cat by looking at what evacuates the pipe.

Visible emissions during the burn even though the cat temp indicates active is probably the best signal that your cat has worn out and will soon need to be replaced. I need to replace mine every 18 months of burning which takes about 2 years since I heat 100% with wood. The king has a bigger cat and maybe lasts a little bit longer but start paying attention after 10,000 hours.

 

[Highbeam]

I’m getting pretty consistent 24 hours and still plenty of coals to relight at current outside temp averages and I have a mark on my swoosh where this seems to happen. Would a failing cat start burning for less time and that would signal thinking about replacement?

The beauty of a thermostatic air control. Since the worn catalyst is not burning all the fuel it is making less heat, the thermostat responds by feeding the fire more air, house stays warm but fuel burns faster. That’s what happens at medium and higher settings. At low output settings, the worn cat will stall easier so you need to turn up the thermostat or you will get a dripping tar mess out of your chimney cap.

I still have some of the tar drips. They are very hard to clean. Cats don’t last forever!

 

[begreen]

I still have some of the tar drips. They are very hard to clean.

Try taking a portable torch to them to soften, then scrape.

 

[ratsrepus]

First fire of the season in the Ashford, 3 small splits 78 in house door walls open.

 

[Poindexter]

I don't put a sap ball bigger than a golf ball, or a sapsicle with about golf ball of sap into mine for cold starts, and tend to put those in the middle or the back.

For baseball sized globules, I want a significant bed of hot coals and a combustor in the active zone for a hot reload. For big sap globs I want a raging active hungry combustor, not a tarry mess to clean up.

In the kind of weather where I am looking for baseball sized chunks of sap it is too cold to be walking around the yard looking at the stack plume. If I wasn't getting a noticeable heat spike out of them wouldn't burn sap globs and sapsicles.

I will say don't put more than one baseball size chunk of sap into your BK at a time. And it needs to be dry, with sharp corners on it that are biting into your skin, not putty.

When it is cold enough for my oil burning boiler to be pushing 70% duty cycle on backup duty, that is when I look for sap globs.

 

[Poindexter]

Looking for my second and third hot reload of the season this weekend, forecast high isn't above freezing again until Sunday afternoon.

Running a bit late this year, but not late enough to put on sack cloth and ashes to prostelytize in the streets. The squirrels are acting like snow bound freeze up is near, more or less on time.

 

[BKVP]

Looking for my second and third hot reload of the season this weekend, forecast high isn't above freezing again until Sunday afternoon.

Running a bit late this year, but not late enough to put on sack cloth and ashes to prostelytize in the streets. The squirrels are acting like snow bound freeze up is near, more or less on time.

What's current heating oil price up there?

 

[ABMax24]

I find that it smokes a lot more with the high pitch at higher settings too. Blue to black emissions. Honestly the noncat does it too with pitch. Some pieces have surface pitch and some are soaked all the way through. On lower burn rates, once at steady state, the Bk cat system is able to eat the pitch smoke.

I’m talking real pitch. What some folks would call fat wood. I burn a lot of logging waste which often includes the butts.

I believe this to be a function of the terpenes within the resins of many softwoods causing this. I have noticed the same in my tube stove where the resins partially burn and produce soot that can escape up the flue. Terpenes usually contain 5-20 carbon atoms per molecule and just like the hydrocarbons found in gasoline in diesel can be difficult to burn completely in open air without left over hydrocarbons or soot.

Comparably many of the other products of wood smoke are easy to completely combust; CO, methane, alcohols, acetic acid, etc. Both tube stoves and catalysts can readily oxidize these products completely.

From my understanding the cats in a BK are similar to the old 2-way cats used in gasoline vehicles prior to '81 or the diesel oxidizing catalysts used on diesel engines. These catalysts are efficient at converting most components of wood gas to CO2 and water vapour, I believe they could even completely combust terpenes if they were fed into the catalyst as a gas, much in the same way a DOC can clean up unburnt diesel from a diesel engine. The issue comes when these terpenes are partially burnt within the stove and produce carbon soot prior to reaching the cat, these catalysts are very inefficient at decomposing this soot to CO2 and the majority will pass through unchanged and exit the flue as black smoke. This was also in issue with diesel engines and resulted in the implementation of exhaust filters back in 2008. I believe this is what you see with your stove, at low output the terpenes are vaporized and sent into the catalyst for combustion, at higher output the heat of the firebox is greater and these terpenes partially combust within the firebox and the catalyst can't clean up the resulting compounds.

 

[stoveliker]

Given that graphite (as the too idealized and more inert model for soot) combusts at about 750-800 F and the cat should be able to do that, I think this is a matter of particle size rather than chemistry. Too big particles don't have enough surface to finish the combustion reaction in the short time they spend in the cat channels.

 

[kennyp2339]

I can dial right down to a flicker of a slow flame further yet to just keeping the coals hot,

The small candle like flames with secondary vapor blasts is my go to spot when it get cold, in the princess when I turn the T-stat down to that setting means a 12hr burn.