Wood burning stoves - what is the state of the art?



It could be that there is a confusion between Elder and Alder, totally different trees. Elder (usually only a small bush, biggest logs you'll get are only three or four inches diameter) really doesn't burn very well.

It needs a good hot fire to burn well but that's all.
--
Chris Green

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On 15 Aug 2006 08:02:36 GMT, snipped-for-privacy@isbd.co.uk wrote:

Yes, that sounds likely. Similarly, but not a problem in the UK, we have locust bean trees on our farmland. The logs from that won't burn at all, even if baked in the sun until they are bone dry. All they do is smoulder and stink.
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snipped-for-privacy@isbd.co.uk wrote:

Indeed. I so burn it, but mostly its really crap.

Its one of the best for stoves. #
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Tim wrote:

It's also bollocks..to generate any sort of heat is about a cubic meter of ash a month, in my experience.
I

Not a lot wrong with that - we use a couple of open fires and a 'highwayman' stove here..only one open fire is used consistently though.
The highwayman is definitely less draught inducing and more efficient than the open fire..we have it in our bedroom for days when we have the 'flu...its brilliant.
A good wood burner kicks out an easy kilowatt, and can be persuaded up to about 2-3. Our huge open fire is about 10KW, but a lot goes up the chimney..it takes ages to warm the room as mostly the first three hours its warming the brickwork around it. However it keeps the room hot all night afterwards. We tend to light it about 2pm in the winter, so that by 5pm its really well set up. It dies around 11pm which is a couple of hours before we hit the sack.

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The Natural Philosopher wrote: >

There is something seriously flawed with your stove or more likely the way you use it. Mine has a plastic shopping bag full of ash which will have become almost rigid and that is about once a month with a fire on day and night. Perhaps you are burning fresh timber or more likely you have a grate. Its best to burn the fire on the floor of the stove with no grate. That way you always have a hot bed of ash under it.

you use the traditional fireplace for your living room so perhaps you should not talk so knowledgably about wood burning stoves when you clearly have limited experience of them. That scenario would be much improved if you installed a wood burning stove in your living room. You could get 10 kw and lose very little up the chimney if you did what I said earlier. You would probably burn much less timber in the stove and get far better heat output and therefore put less of those pollutants you refer to into the atmosphere. You dont know what you are missing.
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Our good woodburner kicks out about 8KW according to the specs. It's Stovax unit, and although it's relatively new to us (and therefore we haven't use it that much - it's still summertime in Devon ;-) when we have run it up, we've been more than impressed with it.
http://www.stovax.com/products.htm?cid=4&sid=9&pid !6
Gordon
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I have looked at those ranges. Does anybody else have any other suggestions forparticularly efficient woodburning stoves that I should be exploring?
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Tim wrote:

Dunno. But fan blown furnaces fed on sawdust and chippings are supposed to be ultra low pollution.
The more oxcygen you get in the less carbon monoxide, and the higher the combustion temp, and the greater chance of breaking all organics down into simple stuff like H20, CO2 and SOx. And possibly NOx. AFAICR thats pretty much what wood is made from by and large..the trace stuff tends to stay in the ash.
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No, generally NOx level rise as combustion temperature rises and free oxygen in the flame increases. This is why diesels have exhaust gas recirculation - to reduce the amount of available oxygen when there isn't a full fuel charge.
--
Skipweasel
Pay no attention to that man behind the curtain.
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Guy King wrote:

I had a notion of that - which is why I said 'possibly' NOx...thanks for clearing that one up.
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wrote:

Yes broadly I think so but generally you need to limit excess air as this cools combustion. The thing is the dryer the wood the less excess air needed for a good burn.

True but you're talking about a fuel with a much higher cv and flame temperature. Generally wood burners don't get to the high temperatures where NOx would be formed in any quantities because of the lower calorific value and the latent heat of steam from moisture in the wood. Oven dry wood may be a different matter but even then we're only talking about maximum temperatures of 1600C.
AJH
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Given all this is there no stove maker that has a design with sensors on the flue and a control loop to regulate the inflow of air via a blower or actuated vent?
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wrote:

The pellet stoves often have closed loop and the higher tech (industrial looking) boilers for both woodchip and logs do but the cost is quite high. I saw a recent quote for a logwood installation, with closed loop, that was GBP11k compared with a similar spec oil install, with tank, of GBP4.5k.
Having said that it's fairly straight forward to build a small, blown, stove that has CO<100ppm, I've not been able to measure much else, with no feedback and simple air control for limited modulation. The crux is not attempting to burn wet wood.
The old National Coal Board licensed their design for a understoked, anthracite bean, domestic boiler to two companies. I have seen the poorly made model but not the better made one, I doubt they remain in production. I think these would burn woodchip with a bit of modification.
IMO forced air is the single most effective way to clean up woodburner emissions. BTW if you can see *any* smoke you must have fairly high, say 500+ ppm, CO.
AJH
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Tim wrote: > Given all this is there no stove maker that has a design with sensors

Yes it is a sweet dream but dont believe them. It all depends on how much wood you burn, how big the logs are, how you control the doors or air intake and the quality of the timber you burn. Not to mention the size of room, the temperature, the wind chill and how cold a person your wife is and many other variable factors. There is no pie in the sky answer. Some people never get warm.
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This may all be true but the job I am looking for is, I would hope, the advantageous and efficient wood burn and minimisation of emissions. I do not think we should be sidetracked by expecting a heating system to address the other aspects you mention as they would affect ANY heating system. The optimal combustion can be addressed however.
I am starting to wonder that if this product does not exist then I should seriously look into its development as a product since I have a background in analogue sensing, DSP and manufacturing design. However, with the development that companies like Tarm (www.woodboilers.com) have carried out then there is likely another manufacturer that has addressed, or is developing room stove designs.
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wrote:

Tarm is a Baxi made imported to the US. Kob and Kuenzel make similar crossdraught gasifying close coupled combustors.
AJH
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Thanks again AJH.
I found this from a mail list on the subject of gasification. I now need to explore the particular difficulties Gavin (the author) presented with small scale designs. I may be able to contribute to the control loop, if this is indeed the obstacle in small-scale designs
=========Small wood burners do not run as cleanly and efficiently as gasifiers because to control gasification you need controlled air supplies and consequently some sort of feedback . Gasification boilers like Kuenzel, tarm and Kob are much more expensive than a "conventional" boiler because of this control and feedback loop however they can achieve much higher efficiencies and clean combustion
source: http://www.repp.org/discussion/gasification/200209/msg00011.html
=========
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wrote:

You're getting too close to home there Tim ;-). Gav may rule the roost but he'll not readily argue the toss with me on technicalities!
AJH
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Tim wrote:

One place I would see potential to develop further in a wood burner is by utilising the waste heat going up the flue so that it heats a water jacket which need not be attached to the stove. that would take some of the heat going to waste and if a round or even a square jacket of water say about one yard long was inserted just up the chimney I think it would produce a good supply of hot water from heat that would otherwise just go up the chimney. I am averse to putting a water jacket in the stove as you neither have a fire nor hot water unless you really put on a good fire. What do you think of this idea Tim?
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snipped-for-privacy@hotmail.com wrote:

Cue condensation of the tars and acids, a chimney fire and a rusted-out flue.
Take heat out of the firebox if you want, where it's big and there's plenty of airflow. But leave the flue gas alone, lest you annoy it. Although we'd love to have the flue gas leave the terminal at a nice efficicent barely-above-room-temperature, it just isn't practical to do this on a workable system. You need to keep that gas hot, and you need to keep it moving.
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