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Pollution from woodburners
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tahir



Joined: 28 Oct 2004
Posts: 44283
Location: Essex
PostPosted: Mon Jul 04, 05 2:43 pm    Post subject: Pollution from woodburners  Reply with quote    

Wood burners fuelled by locally coppiced wood are being touted in some quarters as the perfect fuel source, carbon neutral and virtually infinitely renewable, the only thing is that we (mostly) stopped using solid fuels because of the pollution they generate....


Anyone got any facts or figures on emissions generated by burning wood?

sean
Downsizer Moderator


Joined: 28 Oct 2004
Posts: 41984
Location: North Devon
PostPosted: Mon Jul 04, 05 2:46 pm    Post subject: Reply with quote    

Clearview's stoves burn clean enough to be used in 'smoke-free' zones. There's a very good Canadian website about this, I'll try to find it again and post a link.

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Mon Jul 04, 05 2:51 pm    Post subject: Reply with quote    

The carbon in wood was recently fixed from the atmosphere; it's almost carbon neutral, except of course for the fuel used in processing and transporting it.

The problem arises when lots of people in an area are burning solid fuels, which is why a really good stove is a good idea. Whether they'd have any impact on air quality, I don't know.

Behemoth



Joined: 01 Dec 2004
Posts: 19023
Location: Leeds
PostPosted: Mon Jul 04, 05 2:52 pm    Post subject: Reply with quote    

I think that with wood burners the problem is particulate matter whereas 'old' pollution, smogs etc was due to burning coal and oil inefficiently. After all we only started digging coal out of the ground when we'd chopped all the trees down. Also coal and oil contain chemical compounds as a residual of the process that created them among these was suplhur etc.

tahir



Joined: 28 Oct 2004
Posts: 44283
Location: Essex
PostPosted: Mon Jul 04, 05 2:54 pm    Post subject: Reply with quote    

Obviously the wood has to be produced as locally as possible, it's more about how clean the combustion is from all theses new woodburning stoves and boliers and how it compares to a modern gas boiler.

Jonnyboy



Joined: 29 Oct 2004
Posts: 23924
Location: under some rain.
PostPosted: Mon Jul 04, 05 2:59 pm    Post subject: Reply with quote    

The quality of wood is a major part of it. Well seasoned wood will burn with very little smoke, smoke being after all unburnt fuel.

If you get your wood from FSC then it will be carbon neutral, but on top of that we have access to waste wood from joiners shops, window manufacturers etc. some of that is non fsc or even imported hard wood, the question is, do we use this wood and minimise the overall environmental impact and waste or make a principled stand?

Northern_Lad



Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere
PostPosted: Mon Jul 04, 05 3:01 pm    Post subject: Reply with quote    

tahir wrote:
Obviously the wood has to be produced as locally as possible, it's more about how clean the combustion is from all theses new woodburning stoves and boliers and how it compares to a modern gas boiler.


Interesting thought.
However, I would go for wood-burning over gas even if it was slightly less efficient.
Trees have many uses while they're around; not only are they a part of the carbon-cycle, they're also a big part of the water-cycle; they produce food and habitat for various creatures; and they look good.
Gas, on the other hand, tends to just lie about in big reserves underground not doing much except holding onto carbon.

Trees also have the ability to provide fuel forever. Once gas is gone, it's gone for the next few million years.

Behemoth: to an extent, yes, we turned to coal and oil once all the trees were gone, but we went through charcoal first suggesting that heat was the driver rather than other factors.

tahir



Joined: 28 Oct 2004
Posts: 44283
Location: Essex
PostPosted: Mon Jul 04, 05 3:01 pm    Post subject: Reply with quote    

Jonnyboy wrote:
do we use this wood and minimise the overall environmental impact and waste or make a principled stand?


That's a whole nother conundrum, innit?

Andy B



Joined: 12 Jan 2005
Posts: 3920
Location: Brum
PostPosted: Mon Jul 04, 05 3:12 pm    Post subject: Reply with quote    

http://www.clearviewstoves.com/
You should never mix fuel types, wood and coal, just one or the other at any one time. And they are not waste disposal units either so dont burn off cuts of wood covered in old paint.

Will



Joined: 30 Jun 2005
Posts: 571
Location: Grenoside, Sheffield
PostPosted: Mon Jul 04, 05 4:16 pm    Post subject: Reply with quote    

Tahir,

I'd suggest that off cuts are just that - off cuts. The same amount of wood will be cut for joinery whether these are burnt or landfilled, so it shouldn't make that much difference, and you get a warm "waste not want not" type glow (pun intended).

On the other hand, we got more than a winter's burning for 35 from www.conservationcrafts.com in Matlock - they still use horses for clearing and biofuels in their vehicles and saws and supply chopped into convenient stove size lengths.

Will

tahir



Joined: 28 Oct 2004
Posts: 44283
Location: Essex
PostPosted: Mon Jul 04, 05 4:17 pm    Post subject: Reply with quote    

That link didn't work for me Will

Treacodactyl
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PostPosted: Mon Jul 04, 05 5:56 pm    Post subject: Reply with quote    

A few facts from the small woods association ( www.smallwoods.org.uk ). Air dried wood burns at 70% efficiency in free standing stoves, 60% efficient in built in stoves and 35% efficient in open fires.

IMHO if some of the funding that goes to nuclear power, coal & gas power stations and boiler design was channelled into wood stoves I bet it would only take a few years to over come any of the problems.

Depending on the method of growing the wood I actually thought coppice was carbon negative as the roots of the tree lock away carbon from the atmosphere and as they are not harvested the carbon stays locked away.

tahir



Joined: 28 Oct 2004
Posts: 44283
Location: Essex
PostPosted: Mon Jul 04, 05 5:59 pm    Post subject: Reply with quote    

Treacodactyl wrote:
Depending on the method of growing the wood I actually thought coppice was carbon negative as the roots of the tree lock away carbon from the atmosphere and as they are not harvested the carbon stays locked away.


Must be quite marginal over the life of a coppice I'd have thought.

Treacodactyl
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Joined: 28 Oct 2004
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PostPosted: Mon Jul 04, 05 6:05 pm    Post subject: Reply with quote    

tahir wrote:
Treacodactyl wrote:
Depending on the method of growing the wood I actually thought coppice was carbon negative as the roots of the tree lock away carbon from the atmosphere and as they are not harvested the carbon stays locked away.


Must be quite marginal over the life of a coppice I'd have thought.

Depends, I've always been taught that the roots of a tree are the same size as the top. So assuming the trunk is about a third then the roots would be about a third. When a tree is cut down if it's coppiced then that third will carry on living and the carbon locked away for a few thousand years and if the stool is allowed to die then as the roots decompose I would think most of the carbon stays in the soil.

Either way, it's still better than digging up coal or extracting gas.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Mon Jul 04, 05 7:04 pm    Post subject: Reply with quote    

tahir wrote:
it's more about how clean the combustion is from all theses new woodburning stoves and boliers and how it compares to a modern gas boiler.
Modern boiler inovations are more about collecting more energy than further reducing pollutants. More energy efficiency of course means less CO2 for a given amount of heat. A gas boiler produces very little indeed apart from CO2 and water. There's very little NOx produced, the temperature being much lower than the combustion in a car engine. And the "Natural Gas" fuel is very (chemically) pure Methane, (which is a very simple compound, CH4). There's precious little sulphur - even the famous smell is a deliberate trace addition. There's practically no particulates. The purpose of annual "servicing" is largely to ensure that combustion is 'complete' and as little CO as possible is produced.
Its *very* clean-burning.
But mains gas supplies are fossil carbon.
However, it is perfectly possible (if not entirely practical for most folk) to bio-generate your own Methane, from renewable sources. Judyofthewoods has already provided pointers to the french guru Jean Pain.

In contrast, woodburners have a much more chemically complex fuel, with a variety of long-chain carbohydrates and some "aromatics" with ring-based structures. Consequently, combustion is much more difficult to complete.
When smoking food we are trying to use the active chemical products of very incomplete combustion. And those same chemical products of incomplete combustion are the "dangerous" pollutants!
Slightly more complete combustion gives sooty deposits. But, IIRC, wood gives larger (and so less harmful) sooty particles than coal.

Fossil fuels are essentially the remains of prehistoric vegetation. The sulphur in coal (and that extracted from liquid and gas petrochemicals) originated in the vegetation.
Modern wood is going to contain sulphur, but its not as concentrated as it becomes in coal.

We know that excessive use of raw coal produced fearsome pollution - the London "peasoupers" from Dickens to the 1950's. And ISTR that woodsmoke produces similar problems in some "third world" cities.
However, I would expect a modern, controlled domestic burner (especially those using chipped fuel) to be able to burn much more completely than those open fires, but never as cleanly as a gas boiler.
Apart from air pollution, the ash, in quantity would also be of concern.

The energy used in creating the stove wouldn't be massive, and the product lifetime should be very long.

One catch is "locally produced" fuel. The energy density is relatively low, so transport cost is relatively high...


So, while avoiding fossil carbon usage, with woodburning there is some price to pay in terms of pollution. I think the real question becomes whether that is a price worth paying.

So, not quite perfect, and not for everyone, but with local access to fuel, much better than most.

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