Homemade Catalytic Wood Boiler - Possible?

[Unhippy]

As the title says is it possible to make a catalytic wood boiler?

i'm in Southern New Zealand (Long time reader that didn't have any questions to ask until now so i signed up) and catalytic combusters are unheard of here on wood stoves and wood boilers are fairly rare to say the least...so i thought i would ask somewhere that people seem to know a fair bit about both

I was building a homemade underfeed stoker coal boiler but a little very reliable birdy told me that due to "clean air ideals" there are moves afoot in the local council to outlaw the not the coal boilers but the selling of coal to private individual's for home heating....commercial companies will still be able to buy coal for industrial use

I'm a Welder/Machinist by trade so building a boiler isn't a problem but making one that is not a smoke monster when its not running flatout is a little more challenging but necessary considering local regulations

i've seen clips on u-tube of outdoor wood boilers with aftermarket/add-on Cat's in the stack but that just seems stupid from a heating point of view as all the heat from the catalytic combuster is dumped straight to atmosphere, however considering the amount of smoke they normally seem to produce i can see why they have been installed.

So to the point....is a purpose built catalytic wood boiler feasible if it was sized to the approximate heat output of a wood stove?, 50,000BTU would be more than large enough for my little house (1000sq-ft) in the coldest part of winter.

From what i understand after doing a lot of reading on here the catalytic stoves can be "turned down" a lot further than a secondary burn type stove and still run clean...and by clean i mean very little to no visible smoke out the chimney....which would be good for any time that the boiler is up to temperature and the draught regulator has the draught flap closed(<which would have be open just enough to keep the cat lit).

for periods of "idle" would an adjustable closing stop on the draught flap and a barometric chimney damper be sufficient to maintain a catalytic combuster "lit" or would it be better to hook a thermostatic control up to an auxiliary air inlet to control the minimum heat required to keep the cat "lit"

i have valve with a capillary tube sensor that opens at 95C and closes at 91C to allow me an over temp control or heat dump circuit

I don't envisage it will idle very much of the time but it will spend most of its time running at less than 1/4 of its full capability which unless i missed something in all my reading is where the catalytic systems really shine.

i have a design in mind (shamelessly plagiarised from the only wood boiler that i have ever got to pull apart to repair) that is a crossdraught type deal and keeps a fairly constant amount of wood in the firebox with more waiting to be fed in by gravity as the wood in the combustion zone burns away....according to the guy who owned the thing it worked very well and didn't smoke as much as all the houses around him with wood stoves did

So is this something it would be worth me carrying on considering or is it flogging a dead horse?

Cheers
Callum

 

[webbie]

My opinion would that it would only be worth pursuing if that's something you fancy doing for your own education. There is quite a lot to it and just the inclusion of a catalytic converter isn't enough to mean it will burn efficiently.

Off the top of my head, I would approach such a design in this way. There is no need for a wet bottom (under the fire), since most heat would be radiated upward. Also, depending on the placement, you may be happy with some radiant heat from the boiler itself. In that case, a firetube heat exchanger located above the catalytic converter may be the best way to get the most heat out of the fire, because having water elsewhere will cool the temp of the fire.

 

[TCaldwell]

due to the low flue temps that boilers employ to maintain a high thermal efiency , and the pressure drop across the cat, it is not really a good match. you are better off to spend your time on the p/s air staging and hx design. a wood stove with a high flue temp and natural draft is a better fit for a cat.

 

[Unhippy]

Hmmmm sounds like it might not be as of an good idea as it seemed to be for a start....lol back to the head scratching stage

thanks for your advice

Cheers
Callum