Catalytic stoves v Secondary Air

[neiln]

I think the advantage is not from necessity to meet the regs but rather it separates the wood from much of the heat/'burning' and allows a really low and long burn.  The cat sits up above the baffle in the neck of the flue I think, some way from the load of wood.  Once lit and up to temp the cat is engaged (by pass closed) and a thermostatic air control set.  The stove can then close right down so the wood just smolders.  In a regular old stove that gives a long burn but very very little heat and a lot of smoke and creosote.  In a modern stove with excess secondary air it just can't be done, but in a cat stove the wood load smolders but the cat burns the smoke.  I've read loads of bk owners comments about how the heat comes mainly from the cat area, not the stove body. The result is a long smoldering burn that still gives much useful heat and doesn't create smoke.

 

As to does the cat allow graphite Like soot particles to burn, I've no idea on the mechanism but I'm pretty certain that the EPA tests are more stringent for cat stoves, as I said, to allow for cat degradation over a few years.

 

[Billhook]

What about these heat  recovery devices for the flues, have any of you had success with one or do they lower the temperature too much and cause condensation and tar build u inside the flue?

 

flue+heat+exchanger - Google Search

WWW.GOOGLE.COM

 

[neiln]

You've answered your question

[Woodworks]

23 minutes ago, neiln said:

You've answered your question

If you achieve a hi temp burn would there be much tar to gum up a flue? 

[openspaceman]

7 minutes ago, Woodworks said:

If you achieve a hi temp burn would there be much tar to gum up a flue? 

No but even with 20%mc wood you're chucking a fair amount of water up the flue so ideally want it to exit the top above the dew point. Every kilo of wood you burn at 20%mc means you're chucking 0.6 litres of water up there.

 

I haven't worked out the saturation of the  mixture of water, nitrogen, oxygen and carbon dioxide as there are a number of variables so safest to keep it above 100C

[neiln]

Exactly, the water in the wood and the water produced by burning the wood makes a lot of water in total.

 

How did we get from cats and secondary air to heat exchangers!?

[openspaceman]

10 hours ago, neiln said:

Exactly, the water in the wood and the water produced by burning the wood makes a lot of water in total.

 

How did we get from cats and secondary air to heat exchangers!?

Quite logical progression; a catalytic converter allegedly enables a clean burn of a smouldering log, i.e. no proper flame or secondary secondary combustion but a clean burn. Add a heat exchanger to the flue and you further cool the flue, this is what condensing gas boilers do, they have a drain.

 

I see it less now, maybe because of ss liners but one could often trace out the course of a flue up a brick chimney by brown staining of the mortar as the sooty condensation percolated through. It was also acidic so gradually leached out the lime in the mortar.

[Khriss]

Yrs the catalytic conversion only starts to work at high temperatures, dont work in cars until the engine heats it up. K

[Witterings]

2 minutes ago, Khriss said:

Yrs the catalytic conversion only starts to work at high temperatures, dont work in cars until the engine heats it up. K

 

Reminds me of a story, my boy's at Uni so no money, took his old Seat Ibiza in for an MOT a couple of years ago (couldn't get booked into the place I normally go to and trust) and the garage said it  had failed on emissions and would be £750 to repair.

I rang the place I normally go to for a comparative quote and they said drop the car into us ..... they took it for "An Italian Tune Up" just before another MOT and it passed and has done for the subsequent 2 years without having anything being done to it 🙂  .... the garage I trusted did make the comment "Kevin up to his old tricks again is he".

 

Back on topic .... if it produces heat from a smouldering log I'm guessing there's no real flame but is also what contributes teh long burn times ??

Personally whilst it's obviously used for heat I love the esthetics of a decent flame, wouldn't quite be the same without if the logs were just smoldering away n teh box but maybe I've misinterpreted it?

 

 

[Khriss]

@Witterings from memory, O level chemistry texts put the optimum temp at 900 degrees (  now thats a long time ago) for complete conversion. Yes yr mate thrashing his car fr half hour would improve emmission test as it does with diesel lorry particulate filters. Stoves may be more sedate, K