Green credentials of wood-burning stoves under attack

[BowlandStoves]

I have to say that Jotul have produced some stunning stoves over the years but they seem to be losing out in the modern era due to greater brand awareness of the likes of Morso, etc.

[neiln]

https://windfarmaction.wordpress.com/2013/03/10/energy-density-of-wood-v-coal/

 

Energy density means the wasted energy due to shipping mounts up I guess.  Compared to UK coal drax needs 12 X the volume, and is shipped what? 100 times further.  1200 times the shipping by volume mile, that mounts up.  The maths still aren't strong but there is my point, the op article needs to be stronger and then it can put a decent case against the anti-wood lobby. It's possible!  I do personally think biomass from local source is good, biomass from distance is not.

 

 

Oh and I believe wood stoves are written in to the UK carbon reduction strategy, so they are needed and won't be disappearing.

 

 

Dirty wood piles!?  25m3 stacked in my London zone 3 garden, swept and polished weekly, clean as a whistle.

 

[Stere]

Quote

There is some evidence that bone dry/oven dry wood burned in a natural draught burner has increased particulate emissions.

I read that  but can't find it now.

 

Have you got a link to it?

[openspaceman]

2 hours ago, Stere said:

I read that  but can't find it now.

 

Have you got a link to it?

Not to hand, I see it cited in a number of anti wood burning web pages but not the original evidence, I was told it in an online discussion with a combustion chemist from Colorado, Tom Reed. Their equilibrium moisture content year round is under 10%, he called it "Denver dry".

 

I can explain the phenomenon:

 

Take a cup of petrol and light it, as the petrol boils off the surface it burns with a smoky flame, this is a diffusion flame and the reason it has black smoke is that the carbon particles stripped from the hydrocarbon molecules don't immediately burn like the hydrogen does, they then have insufficient time to burn to CO2 before they exit the flame and are quenched in air. Take the same pool of petrol and entrain it through a jet like a carburettor and allow it to premix with the right amount of air before it is burned and you have a clean blue premixed flame as the petrol and air are intimately mixed.

 

A wood natural draught wood flame tends to be diffuse rather than premixed What happens once the fire is lit is that the primary air reaching the bottom of the burning wood first causes the freshly formed char to burn. This generates a lot of heat and the heat in turn causes the remaining wood to pyrolyse. The offgas of CO2, CO from burnt char plus the pyrolysis products (and inevitable nitrogen) rise where they meet the flame and  sufficient air to diffuse into the flame and consume all the fuel gases.

 

 

Most of the time the stove is designed that the mixture of gases rising entrains  the right amount of air to complete combustion plus enough excess air to ensure a fuel molecule meets an oxygen molecule.

 

Pyrolysis above 330C is reckoned to be mildly exothermic, so once it starts in a log it can continue in a chain reaction. If the wood has some moisture then the chain reaction is slowed because the moisture absorbs heat as it is vaporised. If there is little moisture the pyrolysis chain reaction results in more heat in the log and increased rate of evolution of pyrolysis offgas. Thus the gases rising from the primary combustion increase and are more fuel rich. Hence the secondary air entrained is insufficient to burn the carbon out within the flame.

 

Now this doesn’t happen in a pellet stove where the pellets are around 10% mc wwb because the pellets are trickled into the burn pot at the same rate as sufficient air is supplied by a fan, so the pellets char, pyrolyse and burn at a consistent rate.

[openspaceman]

12 hours ago, neiln said:

https://windfarmaction.wordpress.com/2013/03/10/energy-density-of-wood-v-coal/

Apart from the obvious mistakes in using the wrong units, pointed out in the comments, I think I see other bad logic , I'm off to be a log goblin now but if you want I can revert to it later.

12 hours ago, neiln said:

 

Energy density means the wasted energy due to shipping mounts up I guess.  Compared to UK coal drax needs 12 X the volume, and is shipped what? 100 times further.  1200 times the shipping by volume mile, that mounts up. 

I thought I showed that it was modest and I believe coal comes from equally long distances. While the energy density of coal is over 1.5 times better the actual weights will be similar, which is why the the wood is densified into pellets first, plus once at the power station they can be crushed and blown in much as coal was.

 

[Squaredy]

13 hours ago, neiln said:

I do personally think biomass from local source is good, biomass from distance is not.

Just to throw another fly into the ointment of Drax burning woodchip sourced from the USA, there is evidence that some of the woodchip is being sourced from clearfelling virgin forest.  It is meant to come from low grade material that is produced as a by-product of the huge logging industry in the USA but satellite imagery has given very strong evidence that some of it is actually causing de-forestation.  

 

This is a problem that the USA will have to fix of course, and our government won't care - the stats will still show an improvement in the carbon footprint of Drax.

[neiln]

I guess coal does come a long way too these days, since we've closed our own puts down.  I'd forgotten that.

[daveatdave]

1 hour ago, neiln said:

I guess coal does come a long way too these days, since we've closed our own puts down.  I'd forgotten that.

yes it used to come from the big k about 3 miles down the road till they shut it (the last deep mine pit)