[Gasification] Help with Heating Gasifier design (Starting to getconfused)

[Steve Carroll]

I just posted them here: http://luxthreads.tripod.com/gasifier.html
   
  Sorry about the attachments.  I thought that attachments were allowed but I can't find anything on how to go about sharing pictures on the list or about general etiquette and rules.
   
  Thanks for your patience,
  Steve


  No drawings attached Steve, can you please resend with drawings so that I 
can have a look at your set up? Thanks.

Shaun.



> Hello List,
>
> I am about to build a wood gasifying furnace to be used for home heating. 
> Most of the information that I find is about power generating gasifiers or 
> small cookstoves. I keep thinking that I have a good design but I'm never 
> 100% sure that it will work the way I intend it to.
>
> I have attached 3 small drawings (about 6k each and scanned for viruses) 
> that show a basic design of what I am attempting. The only differences 
> between them is where the primary and secondary air is introduced. The 
> goal for this process is to create as much heat as possible and to burn 
> all of the wood, charcoal, tar, and gas before leaving the gasifier.
> In drawing 1, I imagine that the primary air will be sufficient for 
> pyrolysis to occur in the area above the burning char. The secondary air 
> should have enough flow to burn the charcoal, tars, and gasses. My 
> concern with this one is that the woodgas will ignite as soon as it 
> contacts the secondary air and somehow cause a dirty combustion of tars 
> and unpyrolysized wood.
>
> In drawing 2, primary air is introduced at the top again with enough 
> airflow to allow for pyrolysis, the burning of charcoal and tar. The 
> woodgas does not ignite until it comes in contact with sufficient 
> preheated secondary air. My fear here is that the charcoal and tars will 
> not burn completely and that it might be hard to preheat the secondary air 
> enough to ignite the woodgas.
>
> Drawing 3 is the same as drawing 2 but the primary air inlets are located 
> in the burning char zone. Perhaps this would ensure that the primary air 
> is mostly used to burn the charcoal so that the woodgas does not ignite 
> until being introduced to the secondary air stream. I am concerned about 
> having enough primary air for the pyrolysis area.
>
> Is it possible that I need a third air inlet?
>
> My design at this moment is a large box made of 1/4" plate steel and 
> lined with insulating refractory. It should put out about 50,000 BTUs and 
> burn 7.2 lbs of wood an hour. The primary air would be set to about 12 
> cfm and the secondary air to about 60 cfm. After reading a paper on 
> superficial velocity in downdraft gasifiers I sized the throat area to 
> give an air velocity of 86 fpm in hopes of achieving fast pyrolysis. I'm 
> probably making a terrible assumption that the superficial velocity will 
> be something close to the calculated air velocity so I made the throat 
> area adjustable.
>
> Would you all be kind enough to set me straight on where my inlets should 
> be and if there are any glaring mistakes in my overall plan?
>
> One more question that I have is how hot should my secondary air be? I 
> plan to use stainless heat exchanger tubing to preheat the secondary air 
> but how hot it needs to be can help me decide where to run it.
>
>
> Thanks,
> Steve
>
>
> ---------------------------------
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