creosote with catalytic stove on low burns

If the wood is seasoned and the combustor is working you will
Produce very little creosote. The Fireview is one not the cleaner burning stoves.

We burn low most all the time but have no creosote problems. Of course we also have good dry wood. Nor do we clean the chimney very often as there just is nothing to clean.

Ironically, unlike non-cat EPA stoves that add secondary air to reburn the smoke, all the tests I've seen show that cat stoves actually burn their cleanest at the lowest burn rates. Here is a table that was complied by Chris Neufeld (Vice President Blaze King Industries, Inc.) for the Oregon HPBA Renewable Heating Symposium 2009.

Jags said:

Interesting BK - at the highest burn rate the cat stove produces 3 times the particulate matter (per btu) than it does at the lowest setting. It must have something to do with airflow and time spent going thru the cat.

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That's exactly what is going on. Longer smoke residence times within the combustor increase the amount of smoke reburned. The folks at Woodstock are adding a secondary combustion manifold to their new stove in addition to their time-tested cat design. Claims are they will achieve over 90% combustion efficiency in a cordwood heater.

Just musing, but I wonder how tough it would be to add a couple of secondary tubes to the BKK?

Me too. Probably have to have a serious pre-heat system, and a shut-off to the secondaries. Maybe only one or two tubes located near the back of the box. reduce the chance of shocking the cat.

I don't know. These are the trains of thought that keep me from getting a good nights rest.

Beetle-Kill said:

Just musing, but I wonder how tough it would be to add a couple of secondary tubes to the BKK?

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Most stove manufacturers who tried to modify existing designs by attaching something to it have fallen by the wayside. It is always many times better to design a new stove from the bottom up. That's what Woodstock did. It is actually a non-cat with a burn manifold in the box and a combustor added downstream of that. The combustor catches what the secondary misses, and that seems the only way to do it if you ask me.

Jags said:

Interesting BK - at the highest burn rate the cat stove produces 3 times the particulate matter (per btu) than it does at the lowest setting. It must have something to do with airflow and time spent going thru the cat.

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Yup it's all about hang time and that is why they add an cat air intake to supply extra air for the high demand periods to create a more complete combustion for these high burn periods.. I rarely crank this stove as it performs best during low to medium burns..

Ray

Re: burning on low in the Fireview

You just need to get the cat and the load of wood hot enough first, then you can shut it all the way down if your wood is dry. I just filled up with pine (hot reload), let it burn 5 minutes or so at 1.5, engaged the cat, let it continue at about 1 for another few minutes - then closed the air all the way off. Its good to go overnight.

Try checking the smoke coming out of the chimney, if its white or you can't see any then the cat is working fine. If black then you need to get it hotter, or need drier wood.

Battenkiller said:

Jags said:

Interesting BK - at the highest burn rate the cat stove produces 3 times the particulate matter (per btu) than it does at the lowest setting. It must have something to do with airflow and time spent going thru the cat.

Click to expand...

That's exactly what is going on. Longer smoke residence times within the combustor increase the amount of smoke reburned. The folks at Woodstock are adding a secondary combustion manifold to their new stove in addition to their time-tested cat design. Claims are they will achieve over 90% combustion efficiency in a cordwood heater.

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Thanks BK. For comparison, and since you can probably rattle this off the top of your head, what might the gm/hr emission rate of a big non-reburn stove (not even downdraft) be on efficient full burn?

I'm asking to get an idea how much junk a cat/thermal secondary typically burns, and comparing that with the 5 grams that sneaks through a cat stove on high burn. In other words, how much fuel remains for a re-reburn system?

When I used to run a VC Defiant Encore cat, once the combustor was more than 2 years old, it would often lose its ignition on a very slow burn, even if that burn started out quite hot with the cat really cooking. I could tell because there would be billowing black smoke coming out of the chimney. The older the cat was, the hotter I had to run it to keep it ignited.

(Curious) George said:

Thanks BK. For comparison, and since you can probably rattle this off the top of your head, what might the gm/hr emission rate of a big non-reburn stove (not even downdraft) be on efficient full burn?

I'm asking to get an idea how much junk a cat/thermal secondary typically burns, and comparing that with the 5 grams that sneaks through a cat stove on high burn. In other words, how much fuel remains for a re-reburn system?

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Personally, I don't have much regard for g/hr emission figures because they disregard the size of the heater. When is comes to determining combustion efficiency, what is most important is grams of unburned gases/kg fuel burned. These aren't just the things that the EPA is concerned about, you must account for CO, methane, etc, which are proper fuel gases in their own right. A cat stove handles all of these gases more effectively, so looking at your clean flue doesn't really tell you much at all about combustion efficiency. That's why we have labs to measure everything - incoming fuel, ash, water from combustion (very substantial), CO2, VOC, PM. Combustion water carries 100% of its latent heat of condensation away with it, so that has to be accounted for as well.

You also need to very seriously evaluate the performance of each appliance at specific moisture contents. For example, it has been experimentally determined in several published studies that wetter wood produces less PM than drier wood per kg burned in conventional airtight wood heaters, but with a loss in usable heat output. I don't believe this would be necessarily true in reburn appliances, but I know of no recent study which examines this is depth (except old studies that show a slightly opposite effect in cats stoves), so it is just an assumption for most of us, but likely true nonetheless. It will be interesting to see if Woodstock publishes their numbers on the new stove, which is supposed to handle wet wood a lot better. Bottom line, for each stove there is likely an ideal burn rate/moisture content/excess air/draft strength/load size/wood type/piece size/reload frequency, and then there are all of the situational factors, which can include everything from operator experience to lifestyle necessities (like being forced to load the stove only twice a day due to the demands of the job).

So, no, I can't rattle any hard numbers off the top of my head because I don't believe they exist. There are way too many variables. To me, operator skill is the single most important variable of all, so burn on brothers and sisters, but pay careful attention to what you see, and to what is actually going on behind why you are seeing it.

Battenkiller said:

So, no, I can't rattle any hard numbers off the top of my head because I don't believe they exist.

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As you wish. I was just considering the same sorts of numbers for non-EPA stoves as the chart you posted showed for EPA stoves, to get an idea how much fuel that 5gm/hour figure represents, and what percent of the emissions a cat stove eats on high burn. I remember seeing them in a comparison of pollution from various sources--cars, epa and non epa stoves, gas and oil furnaces, etc.

I bet it's 90% or better, which makes the economics of adding a second cat questionable, even if workable--it could be twice the cost for much less improvement. Come to think of it, that would be nearly the same thing as simply making a single cat deeper, and I imagine present cat sizes are selected with regard to many considerations--cost, emissions burned, durability, susceptibility to clogging, etc. So it's hard for a layman to second guess.

It will be interesting to see how Woodstock juggles those factors in their new hybrid stove. For example, if they operate cat and non-cat together, or if it's an either-or proposition--cat for low and slow, non-cat for faster burns.

BeGreen said:

+1 operator skills, dry wood and a well maintained stove are the stuff of clean burning.

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Yessir.