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Surely this must be the end of stove related legislation for now?

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1 hour ago, openspaceman said:

Drying does not increase the amount of heat from a given log, it has just  driven off the moisture and made it lighter but releases about the same energy. If the piece of wood had not been dried some of its energy would be used to volatilise the moisture first, so the heat is not available to the room but goes up the chimney as steam.

 

The more significant effect is than in turning the moisture to steam the fire gets cooler and burns less completely, hence more pollution.

 

The bit about burning too quickly is rather spurious because in burning quickly it gives out heat quicker, if it's giving out more heat than required it's normal to turn down the air control to compensate.

 

@Stere the late Tom Reed, a combustion chemist from america, produced similar results to that graph, I have tried to explain the reasons in the past. Firstly the flame on a wood fire is largely not premixed like petrol:air in a saw or gas:air in a gas burner, it is diffuse, the hot wood gases meet incoming air and diffuse into each other at the flame:air interface. The oxygen in the air reacts differentially to strip hydrogen from the gases and these carbon bearing remains glow yellow in the flame. If the conditions are good the hot carbon meets fresh air and burns out, if not it exits as soot.

 

A premixed fuel to air has the gases and air intimate and the burn is simultaneous so no carbon left to glow and the flame is blue, this is how a gasifier burns a flame.

 

We all know that if you throw petrol on a fire it doesn't burn blue and the carbon cannot burn out because the air is not able to supply  enough oxygen, so we get black sooty smoke aka particulates.

 

When air dry wood burns  the heat from the fire raises the surface temperature of the new log, firstly to 100C as any surface moisture is driven off and then the wood pyrolyses evolving the woodgas and leaving char on the surface, the woodgas burns higher in the fire and oxygen combines with the char, burning it away and the next layer in repeats the process.

 

You will see the moisture in the wood controls how the wood burns away. The less moisture the quicker the log can pyrolyse and burn because volatilising the moisture takes some energy which has to be supplied from the burning surface area

 

 

Pyrolysis is slightly exothermic above 330C and below 440C  so if there is little or no moisture present to rob heat a chain reaction can occur in the wood, the wood can quickly pyrolyse throughout with no extra energy from outside once the temperature is high enough to initiate pyrolysis. The wood then evolves more woodgas that oxygen can burn and like the petrol analogy soot is given off.

Thanks, I enjoyed reading that and learning a lot on the way.

 

Have you a view on burning naturally air dried firewood @ 25% MC versus kiln dried @ circa 20% MC and the trade off between the amount of additional particulates burning at 25% versus burning fuel to force dry and /or fuel to transport to achieve the 5% lower MC?

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1 hour ago, arboriculturist said:

 

 

Have you a view on burning naturally air dried firewood @ 25% MC versus kiln dried @ circa 20% MC and the trade off between the amount of additional particulates burning at 25% versus burning fuel to force dry and /or fuel to transport to achieve the 5% lower MC?

No

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2 hours ago, openspaceman said:

Drying does not increase the amount of heat from a given log, it has just  driven off the moisture and made it lighter but releases about the same energy. If the piece of wood had not been dried some of its energy would be used to volatilise the moisture first, so the heat is not available to the room but goes up the chimney as steam.

 

The more significant effect is than in turning the moisture to steam the fire gets cooler and burns less completely, hence more pollution.

 

The bit about burning too quickly is rather spurious because in burning quickly it gives out heat quicker, if it's giving out more heat than required it's normal to turn down the air control to compensate.

 

@Stere the late Tom Reed, a combustion chemist from america, produced similar results to that graph, I have tried to explain the reasons in the past. Firstly the flame on a wood fire is largely not premixed like petrol:air in a saw or gas:air in a gas burner, it is diffuse, the hot wood gases meet incoming air and diffuse into each other at the flame:air interface. The oxygen in the air reacts differentially to strip hydrogen from the gases and these carbon bearing remains glow yellow in the flame. If the conditions are good the hot carbon meets fresh air and burns out, if not it exits as soot.

 

A premixed fuel to air has the gases and air intimate and the burn is simultaneous so no carbon left to glow and the flame is blue, this is how a gasifier burns a flame.

 

We all know that if you throw petrol on a fire it doesn't burn blue and the carbon cannot burn out because the air is not able to supply  enough oxygen, so we get black sooty smoke aka particulates.

 

When air dry wood burns  the heat from the fire raises the surface temperature of the new log, firstly to 100C as any surface moisture is driven off and then the wood pyrolyses evolving the woodgas and leaving char on the surface, the woodgas burns higher in the fire and oxygen combines with the char, burning it away and the next layer in repeats the process.

 

You will see the moisture in the wood controls how the wood burns away. The less moisture the quicker the log can pyrolyse and burn because volatilising the moisture takes some energy which has to be supplied from the burning surface area

 

 

Pyrolysis is slightly exothermic above 330C and below 440C  so if there is little or no moisture present to rob heat a chain reaction can occur in the wood, the wood can quickly pyrolyse throughout with no extra energy from outside once the temperature is high enough to initiate pyrolysis. The wood then evolves more woodgas that oxygen can burn and like the petrol analogy soot is given off.

How did you manage to get the bit that starts " however what is never mentioned ......." ,  (that was typed by arboriculturist ) and put it as a quote by me ?  No biggie but is it some sort of wizardry ?  😊

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2 hours ago, Stubby said:

I suppose the act of getting up of the sofa every 5 mins to chuck another bit of kiln dried on the stove would keep you warm anyway 👍

My apologies I snipped badly and somehow it mixed up the attribution, I don't know exactly how but it is something to do with the quote selection feature when I highlight the specific bit I am replying to.

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39 minutes ago, openspaceman said:

My apologies I snipped badly and somehow it mixed up the attribution, I don't know exactly how but it is something to do with the quote selection feature when I highlight the specific bit I am replying to.

No problem , just curious . I don't " snip" anything  just click the  Quote tab at the bottom of the post you want to quote . ( as I have done here )

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9 hours ago, Stere said:

Remember this graph

 

WOODSURE.CO.UK

Ready to Burn - Providing a solution to improve air quality The Ready to Burn scheme has had some great success but...

 

Very dry wood is worse for particulates?

 

(maybe only marginally but it shows 20% wood as good as 10% wood)

 

Is this correct info I wonder as don't get why very dry wood is worse?

 

 

 

image.png.72daa72b44b9d2e1a102a7eee6698db7.png

Yes it is correct, research by one of the UKs leading stove builders three years ago proved this.

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10 hours ago, Philip Anderson said:

I think if you add in all the emissions involved in transportation from Lithuania you may well have a low MC but a significant green footprint.

it seems crazy to me to transport firewood so far.

Agreed but thsts the wsy of the world. 

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20 minutes ago, Alycidon said:

Agreed but thsts the wsy of the world. 

Possibly not for much longer people might be looking to source all goods a little 

closer to home .

MC wise I have 3 wood burners all working well on barn stored air dried the same as I supply with no issues .

Its the crap that’s supplied at the garages that wet and rubbish.

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The customers I speak to about kiln dried wood say that it is very expensive and burns away far to quickly.
 
I do everything in my power to promote naturally air dried firewood and vise versa dissuading the public to avoid forced dried firewood and I will continue to actively do so.
 
The average homeowner with a woodburner is not so unintelligent that they can't work out for themselves that they do not wish to personally subside a business via the RHI scheme to force dry firewood, that they then have to pay a premium to buy back to burn themselves.
 
Stating the truth about force drying firewood does not make you popular with those that sell it, but it is a shameful practice that continues to exist at present and the planned legislation merely adds fuel to the fire. 
 
Any one else with me on this ?




I’m with you 100%. The only benefit of kiln dried wood is to the supplier. RHI and the ability to turn a load of green timber into a ready product in a short turn around. I’ve pulled plenty of air dried logs out my barn at 15% and lower. The perception that “kiln dried” is better is a load of BS. As soon as the customer stacks their kiln dried logs in their outdoor log store they suck up the moisture in the air regardless.
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Furthermore, most the so called “kiln dried” logs I’ve seen or checked is over 20% and even advertised as such. They it’s for the better for the environment but all this is going to result in is people imported kiln dried from Eastern Europe, what about that carbon footprint and for what imagine the majority of which is unsustainably sourced.

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