Rocket Mass Heater Dioxin Emissions

I grew up with a wood stove, one of those hundred year old smoke belching, wood gobbling monsters that made far more chores than were necessary.  It had so many holes, it was tough to shut down at all.

So now I'm an adult and was wanting to get a wood stove for the house I'm trying to buy, but come to find out, RMHs may be a better option, and a big slow burning catalytic stove like a Blaze King probably belches out all sorts of dioxins anyway.

So I was wondering, has anyone tested the dioxin output of a RMH?  I know that different chemicals are produced at different temps, do RMHs produce less dioxin due to temps?

Also, I was amazed to see that the old 40 hour burning blaze king puts out 2500 ppm of CO, whereas a good burn on a RMH produces 10ish.  That's a lot of fuel up the chimney (having fun with a woodgas generator too, but that's a story for another day.)

People get far more dioxin from eating meat than from wood stoves, but I don't feel comfortable belching excessive amounts of carcinogens all over the neighborhood, know what I mean?

Thanks

Hi Solomon; Welcome to Permies!

We have folks here with Testo machines that measure air quality. Hopefully one of them can tell you exact numbers on Dioxin output.
It is my understanding that almost all nastys are burned up with the high temperatures.
Rest assured that a RMH J tube or batch box will outperform any conventional wood gobbler.

If you have not got a copy yet I highly recommend the RMH Builders guide as a must have book for any builder.

Dioxin hasn't been tested soo far. But i doubt it can be very high.



IIRC, Most of dioxins are burned above 800C° And all above 900C°

Not all Rocket Mass Heaters are built the same, so depending on build quality there may be different results based on how well the design of the RMH is made.

That said, many RMH include an outside air feed for the fuel box so that there is not an extreme input from indoor air.

Another factor is the "rocket"  effect of the RMH, as if you put a candle up to any crack while it is going in rocket mode it will actually draw the flame in so air is not escaping into the home when the fire is going in rocket mode.     But this is with a proper chimney and a well designed rocket mass heater.

Yes outside from the chimney I am sure there is dioxin being emitted, but  with far less creosote than with other stoves ( with a few exceptions ) because of the 2nd burn in the barrel.

I do believe several tests with meters have been done at permies central with testing equipment.

Was reading around looking for random info, I can confirm that dioxin is burned above 850C, according to what I read.  Other ingredients are Oxygen above 6% and around two seconds residence time.  So if I were to make a hypothesis, I would say a RMH would be much better on the dioxin emissions than a conventional wood stove and far better still than a catalytic stove.

I really like the concept of a cast batch rocket with a huge masonry bell and benches.  Whatever is necessary to get the insurance company cover the house.

I wasn't aware of the issue of dioxins and furans, and in googling stumbled upon this site https://woodsmokepollution.org/wood-stoves.html

"A recent study that compared emissions from different kinds of wood-burning appliances found that the “advanced” wood stoves emitted amounts of non-methane hydrocarbons, nitrogen oxides and PAHs that were similar to or higher than those from traditional wood stoves. In fact, the newer wood stoves were found to emit even more carcinogenic benzo(a)pyrene than the traditional stoves."

There are a lot of alarming evidenced based claims on that website like this one

"An animal study found that modern technology appliances (which included a newer wood stove as well as pellet-burning appliances) had lower PM1 emissions, “but they induced the highest inflammatory, cytotoxic and genotoxic activities” in the lungs. "

So, in the quest to reduce particulate pollution new higher efficiency stoves may be creating more potent carcinogenic compounds which we are inhaling! If there is data on the amount of dioxins produced by burning wood in a rocket stove I have yet to find it.

There certainly seems to be conflicting information about this problem.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.735.8004&rep=rep1&type=pdf

Polychlorinated dioxins and furans (PCDD/PCDF or PCDD/F) are a group of
highly toxic components. They are found to be a consequence of the de novo synthesis
in the temperature range within 180°C and 500°C [23]. Carbon, chlorine,
catalysts (Cu) and oxygen are necessary for the formation of PCDD/F, so PCDD/F
can be formed in very small amounts from all biomass fuels containing chlorine.
The emissions of PCDD/F are highly dependent on the conditions under which
combustion and flue gas cooling take place; therefore, wide variations are found
in practice. Although herbaceous biomass fuels have high chlorine contents, their
PCDD/F emissions are usually very low. This may be explained by their high
alkali content, which leads to the formation of salts (KCl, NaCl) and thus to a
lower level of gaseous chlorine for the de novo synthesis. Because of the many
factors influencing PCDD/F formation, wide variations may appear even within
the same biomass combustion installation, but in general, the PCDD/F emission
level from biomass combustion applications using virgin wood as a fuel is well
below the health risk limit.

The major factor here is the catalyst.  The dioxin study showed eight times higher emissions from the catalytic stoves.

Now, to be totally fair, wood smoke accounts for very little of people's exposure to dioxin.  And not eating beef will do way more on that front than stopping breathing (facetious here).  In fact, going vegetarian will do WAAAYYY more than eliminating all wood stoves. People get the vast majority of their dioxin from eating meat.

However, we are heading into a future in the US where all approved production stoves are catalytic (2020).  And I think less dioxin is better than more, since there is really no safe level as it is a potent carcinogen.

That's what brought me back to rocket mass heaters when the prospect of wood heating returned to my life. I'm not saying "yer gonna get cancer."  I'm saying, "I want to be a good neighbor and do what I can to spew LESS dioxin into the air."

What is the mechanism that causes catalytic stoves produce more dioxins?  I assumed it was because catalytic stoves allow the catalyst to burn off the hydrocarbons at lower temperatures so therefore they're less likely to incinerate the dioxins that appear to be formed de novo in every wood stove.

I believe that dioxins are formed more in the presence of the heavy metal catalysts like platinum and palladium that are used in stove catalysts.  The lower temperatures at which catalytic stoves burn also help to produce more.  Whether or not what is created by the wood burning gets destroyed, the study seems to show that cat stoves create eight times more  than a non-cat stove.

It seems the temperatures needed to incinerate dioxins are a bit beyond what a typical wood stove will create, but right in the range of what RMHs are said to create.  Plus there's the catalyst itself, which people would like to not have to replace.

Yes, that appears to be the conclusion of others

https://www.ncbi.nlm.nih.gov/pubmed/22397840

Platinum and palladium may catalyze chlorination of PCDD/Fs via the Deacon reaction or an oxidation process.

What a shame that such a good idea is shot down by flames.

So, the question to ask is, does this also occur in cars/diesel trucks which all use catalytic converters?

I would hypothesize that there would be much less dioxin produced in engines.  The main ingredient is the chlorine, which is not present in significant quantities in hydrocarbon fuels.  The combustion temps are also a bit higher than a wood stove.  You are going to find plenty of benzene though, it is actually disposed of in fuels as a waste product from industrial processes.  Optimally, all of it will be burned by the catalyst.

Also, I just remembered that the catalyst in a car has a much tighter matrix, I don't know how that would affect things.

At any rate, I'm not finding engines listed in any of the primary sources.