[Gasification] [Stoves] Tar in P-Gas

Tue Dec 13 06:40:11 CST 2011

Dear Dean,  Ron and all

To clarify my tar collecting experiment, since I wasn't planning on burning the gas I did not have any secondary air holes, just the primary air the bottom, and only four of these, so you could call this a minimal smoke generator.  It was only half filled with oven dried wood chips.   The beaker was only 2/3 the size of the can, so with a pliers, I held the beaker of water Flush with the top of the can and about an inch above the gasifying chips.  It burned at ~ 2 g/ min.  

<><><>

Here's a suggestion relative to char burning for all TLUDS, if you don't want to fertilize a small pot of flowers.  

The air/fuel ratio for gasification varies from 1-1.5, depending on moisture content and intensity of flame.  So my ratio of size of  secondary to primary air holes is typically 5.  

But once you have burned the pyrolysis gas and only charcoal if left, it takes 6/1 Air/fuel to gasify charcoal, and 12/1 to burn it completely, so we need a LOT more air at the end of the TLUD burn to continue to provide heat. 

So if you want a stove that will have the right ratio (5/1) to first burn the cellulose gas and then 5/5 to burn the charcoal, you need to vastly increase air supply at the end of the burn.  

<><><><>

So drill a big 1/2" Hole in the bottom inch of the can surface and cover with duct aluminum tape.  When the fire reaches the bottom of the can, the tape will fall off and give the burst of air needed for a good charcoal fire.  If the sum of secondary air holes adds to that of the new big holes, you will have sufficient air to burn the CO from the charcoal.  

<><><><>

That sounded so good that I went down to my lab and drilled out to 11 - 3/32 inch primary holes near the bottom of the stove, and one 1/2" hole which I covered with aluminum duct tape to provide extra air when the P-gas (pyrolysis gas) has been consumed toward the end of the run.  

So, I'll send the pictures I took from my IPhone, since the Cloud doesn't seem to be transferring them here tommy IPad.

Onward to better cooking.  

Tom Reed

Akal

Dr Thomas B Reed 
The Biomass Energy Foundation
www.Woodgas.com

On Dec 12, 2011, at 12:33 PM, rongretlarson at comcast.net wrote:

> Dean,  Tom,  List:
> 
>        See few inserts below  - in both Dean and Tom's notes..
> 
> From: "Dean Still" <deankstill at gmail.com>
> To: "Thomas Reed" <tombreed2010 at gmail.com>, "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
> Sent: Saturday, December 10, 2011 12:51:06 PM
> Subject: Re: [Stoves] Tar in P-Gas
> 
> Hi Tom!
> 
> Miss you. Your experiment with tar brings up a question.
> 
> So far I've been trying to get as clean as possible and as efficient heat transfer as possible in TLUDs tuned under the emission hood. So we add just enough secondary air for clean but not too much that cools gases contacting the pot. We add a lot of primary air to have the made charcoal burn hot enough to keep the pot simmering above 93C so all fuel is useful in the cooking task. That means we can see 50% heat transfer and clean combustion with a variety of fuels.
> 
>     [RWL:  I hope also to hear something about saving of the char for application to soils.    
> 
>      How are you determining the optimum amount of secondary air?  Peak temperatures?
> 
>      It is not clear from this whether you have the ability to control (during a run) the primary air. I would guess that if you have enough primary air to ensure satisfactory combustion of the resultant char - that that amount of air is excessive during the char-making phase.  True?
> 
>     Re the 50% value - can you provide more details?  In particular are you doing this with or without a pot lid?   What sort of efficiency number might be obtained if the produced char was combusted in a separate device?]
> 
> I remember your experiments with taking made gas and burning in a separate burner. A team at Stove Camp got a continual flame for about an hour but we have a long way to go to get this kind of stove to really work. Lots of tar!
> 
>    [RWL:   What would be the rationale for this mode?    I am thinking of a few reports for partitioning off some gas for a lantern (maybe electrical production) - but it is not clear why one would do this for a stove. ]
> 
> Do you think we should we continue or concentrate on a TLUD approach? Larry has found the made gas to burner to be too persnickety for home cooking.
> 
>     [RWL:  I would certainly hope that you and Aprovecho continue work on TLUDs.  The justification of course is your highest-ranking results reported by EPA (Jim Jetter) recently for your version of a TLUD.
> 
>     Does Larry's comment refer to the immediately preceding paragraph and a separate burner?  Can you explain the geometry some more?   (Why "persnickety"?)     I am hoping this is not a comment for all your TLUD operations.  (As one of the main advantages of any TLUD would seem to be the constancy of the flame.]
> 
>   More below on Tom's note.     Ron
> Best,
> 
> Dean
> 
> On Sat, Dec 10, 2011 at 9:00 AM, Thomas Reed <tombreed2010 at gmail.com> wrote:
> Dear Pyrolysers (P-Guys)
> 
> Having defined the difference between Woodgas and pyrolysis gas this morning, I was inspired to measure the tar content of the gas.
>         [RWL:  I wll comment separately next on that (excellent) note.
> 
> In a 3 1/4 D X 5 1/2 High can, I drilled only four 3/32" primary air holes 1/2" above the bottom.  I half filled it with dry wood chips which I then lit, giving a modest generation of P-gas, burning about 2.0 g/ min.
> 
> I then held a weighed 200 ml Pyrex Becker filled with 150 ml of water down in the smoke for one minute.  It collected 63 mg of yellow, sticky, smelly tar.  This is 3.1% of the wood that burned during the minute.  The tar level may be higher, since probably not all of the tar condensed.
> 
> The P-Gasifier was operated at a low superficial velocity to avoid asphyxiation.  It may well be that levels are lower in % at higher operating levels, though the magnitude will only increase.
> 
>      [RWL:   Tom, can you clarify the phrase  "in the smoke".   Was the beaker above the flames or in them?   We have lots of YouTube showing little smoke for TLUDs.   Would you say this was a non-standard TLUD test?
>     
>       Since you haven't described any secondary air holes, can you describe the flame more?  Was there any attachment of flames to the topmost layer of char (with secondary air traveling downward inside the can?)  How high were the flames?  Might we expect something different in tar-collection in a more usual TLUD geometry, where the cookpot is above the flames/smoke?   
> 
> Ron
> 
> 
> Not much speculation here.
> 
> Tom Reed
> 
> Aka
> 
> 
> Dr Thomas B Reed
> The Biomass Energy Foundation
> www.Woodgas.co
> 
> 
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