[Stoves] burning woodgas

[Harris, Kirk]

All,

I believe Julien is correct about how clean stoves can be dangerous.  
They seem harmless since there is not smoke or smell, and so might be 
brought inside with no ventilation.  They still produce CO2, no matter 
how clean they are, and could cause asphyxiation.  I have given that 
warning to those who have looked into my designs.  It may seem harmless, 
but can be harmful if used improperly.

I was told early on in my efforts that TLUDs are good at burning smaller 
particulates.  This would make sense because the particulate would burn 
from the surface to the center, and in a small particulate that is not 
very far.  I can see two sources for small particulates; particulates 
which are not sufficiently mixed, and large particulates which burn from 
the surface too the center and don't quite finish burning.  These would 
result from inadequate mixing and inadequate dwell time.

The study of pressure variations in TLUDs seems not to have occurred 
substantially.  My efforts are perhaps a humble beginning on this 
topic.  The initial pressure variation in a TLUD is created by the 
density and weight of the gasses inside the stove vs. the density and 
weight of the gasses outside the stove.  The lower density, lighter 
weight hot gasses inside the stove are displaced upward by the higher 
density, heavier cool atmospheric air.  This is called draft, or more 
generally, buoyancy.  Once the gasses are moving, they display the 
Venturi effect, the exchange of energy between pressure and velocity.  
The higher velocity gasses have increased kinetic energy, and lower 
potential energy stored in pressure.  I visualize it in my mind as being 
like cars stopped at a red light, they are close together.  Once the 
light turns green the first car goes before the second which goes before 
the third.  As they accelerate they separate, having more space 
between.  I see the particles of gas in the same way, and so by this 
mechanism pressure and velocity can exchange energy.  In the burning 
concept I am working on, the lower pressure wood gas is accelerated 
(lowering its pressure still further) and the higher pressure secondary 
air is slowed (increasing its pressure), and so the pressure difference 
and pressure driven injection of one gas into the other is increased.  
In a stove that accelerates the secondary air, such as the common design 
that uses holes to jet streams of air into the column of wood gas, the 
increased velocity of the secondary air lowers its pressure, and the 
pressure difference between the gasses is decreased.  It may even be 
possible to lower the pressure of the secondary air to or even below 
that of the wood gas.  This loss of pressure difference will hinder 
pressure driven injection.  Such a system is relying more on surface 
contact and diffusion to mix, and will work, but wastes much of the 
pressure driven injection.  It will not have the range of clean burning 
power levels of a system that takes into account the pressure variations.

Kirk H.


On 8/1/2021 9:45 AM, Crispin Pemberton-Pigott wrote:
> Dear Julien
>
> You are on the right track with the ventilation, in my opinion,  
> however, there misinformation about regarding nanoparticles. (Real ones)
>
> Below a certain size nanoparticles and inhaled and expelled again. 
> They pass into the cell walls by diffusion, not by being trapped in 
> the usual manner. The particles of concern are between 0.1 and 4.0 
> microns. It is true that the 0.01 micron particles are emitted when 
> the combustion is very clean, however their role in disease is not at 
> all clear, compared with the larger "respirable" set. It is a very 
> active topic of interest.
>
> My caution is not to take every alarming claim at face value. There 
> are so many vested interests seeking funds. If all combustion was 
> totally clean, there would be nearly no rain. Think about it.
>
> Best regards
> Crispin heading to Val Quentin
>
> *From:* winter.julien at gmail.com
> *Sent:* August 1, 2021 6:34 AM
> *To:* stoves at lists.bioenergylists.org
> *Reply to:* stoves at lists.bioenergylists.org
> *Subject:* [Stoves] burning woodgas
>
>
> Hi folks;
>
> The emission of nano particulate matter from open-mouth TLUDs has 
> always been a big ethical bother for me.  The 'cleaner' we make TLUDs, 
> the more dangerous they become if they are treated as 'safe' by the 
> users.  In that respect, emission of some smoke from a TLUD at startup 
> and flameout could be a good thing if it discourages stove users from 
> cooking in poorly ventilated conditions.   In Bangladesh, I have been 
> encouraging the development of fume hoods and the incorporation of 
> TLUDs into chimney stoves.
>
> Cheers,
> Julien
>
> -- 
> Julien Winter
> Cobourg, ON, CANADA
>
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