[Stoves] venturi system -ratios of air and gas?

[Jock Gill]

Friends and cooperators,

In all of this conversation, where is the consideration of the residence time of the combustible products in the combustion zone?  As you may remember, I use a large washer to cover about ⅔s of the cross section of the TLUD above the fuel chamber and three smaller washers some distance above the this to create a combustion chamber or zone.  Three factors are important: residence time in the combustion chamber, turbulence of the burning gases in the chamber, and temperature in the chamber.

This suggests that TLUD designs that actually accelerate the rate at which the combustible gases exit the TLUD may be sub optimal.  My guess is that, for example, plates with central holes, concentrators, actually act to accelerated the exhaust gases. This may in part also explain why central spires of yellow/orange flame are also indicators of sub optimal TLUD operation.

It would be interesting to learn the optimal residence time + turbulence + temperature mix.  Further, it would be good to learn how best to achieve this mix, especially in a natural draft TLUD. 

Very curious.

Best regards,

Jock

PS: I now prefer to start with the idea of the essential requirement for CO2 Drawdown and then to use the idea of maximizing the residence time of the harvested carbon in soil. Carbon is too valuable to discard.




Jock Gill
P. O. Box 3
Peacham, VT 05862

google.com/+JockGill

Extract CO2 from the atmosphere!

> On Jan 9, 2016, at 7:05 AM, Julien Winter <winter.julien at gmail.com> wrote:
> 
> Hi folks;
> 
> I believe that thorough mixing of secondary air with somewhat (don't know how much yet) more than the stoichiochmetric requirement for oxygen is important for clean-burning wood gas in natural draft burners.  This is because the wood gas is very complex containing fast-reacting H2, CO, CH4 and slower reacting tars.  If oxygen is sufficient, then the fast gases, slow gases, suspended droplets and particles, and secondary products like soot, will oxidize in close proximity.  If oxyen is limited, then fast gases will react, and we loose heat from the site of reaction; heat that would have provide activation energy, and accelerated the reaction rates of the slower species.  
> 
> Conservng the heat is important for people who design gas burners that add air in stages.  It is also why I am cautious about adding secondary air through the side-walls of ND-TLUD reactors.  If this isn't done carefully, we end up with unburnt wood gas and products of incomplete combustion that we can't ignite because the reactants are too cold and too dilute. 
> 
> For a TLUD, the stoichiometric requirement for secondary air will depend inversely on the rate of primary air, where the combustion begins.  I recall that Mukunda lab in India reported that the ratio of secondary to primary air changed from 6:1 to 3:1 as the rate of forced draft gasification of pellets increased.
> 
> Cheers,
> Julien
> 
> 
> -- 
> Julien Winter
> Cobourg, ON, CANADA
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