[Stoves] Practical Stoves- Introducing The Versatile Stove

[kgharris]

AJH, Dale, and All,

Thank you, this is good to know.  The problems that you point out make good
sense.

Dale appears to have found a way to dry the wood in the fire, I think by
keeping the overall fire large (a benefit of the large combustion chamber),
compared with the evaporating water (the larger dry wood compared to the
smaller wet wood).  Thus the water is evaporated at a slower rate that the 
fire is able
to handle.  Under stressed circumstances this would make wet wood available
to burn right away, though the emissions may suffer.  I am looking forward
to hearing more about this stove as it progresses.  Versatility seems like a 
good approach.

Kirk H.



----- Original Message ----- 
From: <ajheggie at gmail.com>
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
Sent: Friday, November 04, 2016 4:20 PM
Subject: Re: [Stoves] Practical Stoves- Introducing The Versatile Stove


> [Default] On Thu, 3 Nov 2016 01:48:20 -0700,kgharris
> <kgharris at sonic.net> wrote:
>
>> I will have to think about the wet wood.  It might be using more energy
>> to evaporate the water then there is energy in the wood.  The Prime stove
>> has a nice design which holds wet wood to the outside of the stove so
>> that waste heat will dry it.  Making provisions to dry it before burning
>> it might be better then burning it wet.
>
> Hi Kirk
>
> I agree that we should  quantify the cost of burning wet wood but I
> think the problem is more to do with the way it affects combustion
> than the energy loss, though the effects are intimately interrelated.
>
> I generally use a figure of 2.7MJ per litre or kg of water evaporated
> and exhausted with the other flue gases so it's energy "cost" in
> burning a 1kg log at 50% moisture content is 2/7*.5 =1.35MJ. The log
> contains about 18.6MJ/kg so burned perfectly it would release 9.3 MJ
> so the cost in burning the log is about 15% of the gross heat from the
> log.
>
> Consider the three Ts advocated for good combustion, Time  for the
> gases to burn out, Temperature  for them not to be  quenched before
> they burn out and Turbulence to ensure good mixing increases the
> ability for a fuel gas to meet an oxygen molecule.
>
> The more significant effect to my mind is that this heat loss both
> lowers the Temperature, increases the mass flow and  dilutes the
> woodgas given off such that it is unlikely to complete combustion, so
> it is vented as un burnt gases and vapours as smoke, robbing the fire
> of some of the otherwise available chemical energy.
>
> Worse still is the problem that the wet log  has to give up it's water
> vapour before it can itself pyrolyse and burn, so it is still
> smouldering long after its heat was needed.
>
> AJH
>
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