[Gasification] Updraft, Downdraft, Stratified and inverted gasifiers and stoves terminology

[Tom Reed]

Dear GASIFICATION and STOVES:
              ESTES PARK, CO; 3 AM

I came across this old note from Doug Williams and thought it worth
rereading.  Doug is certainly one of our long time supporters and we are
so glad to have him and all his comments here.  Doug's note of 12/12/05
below predicts that the time is coming, as oil/gas prices increase
exponentially, when the whole world will need to return more to solid
fuels and gasification.  Many of us are pioneering the improved
combustion and gasification in preparation for that time.
------------------------------------------------------------------------
One caveat: Doug said...

Top lit gasifiers for instance, have gas out the bottom, air
in the top, but this is probably caused by studying top lit stoves, not open
core gasifiers, or stratified downdraft gasifiers as Tom Reed has named
these types.

There has been a lot of confusion caused by the terms "updraft" and
"downdraft" gasifiers.  I like to invent new gasifiers, so think in
other, less limiting  terms.  (Updraft and downdraft are fixed 
(actually, slowly moving) bed gasifiers. There are also fluidized bed 
and entrained flow gasifiers, typically much larger with more complex 
controls and generating much higher tar levels.)

The conventional "updraft gasifier" is widely used for coal gasification
with South Africa leading the field.  Fuel is introduced at the top and
air at the bottom.  As the fuel passes down it dries, pyrolyses,
gasifies and eventually becomes charcoal above the grate.  As the air
passes up, it first burns the charcoal on the grate to CO2 in the first
3 particle diameters, then the remaining charcoal reduces the CO2 back
to CO (about 1400 C, too hot, so steam is introduced to cool); then the
rising hot gases pyrolyse the falling fuel, generating more CO, H2, CH4
and lots of volatiles (tars, condensibles); then these hot vapaors dry
the incoming fuel.  These gasifiers are also called "countercurrent"
gasifiers.  I also call them "Char-burning - Tar making" gasifiers
because the char is burned to white ash and the volatiles are preserved
(10-20% for biomass).

The conventional downdraft (WWII, Imbert, stratified downdraft, suction,
....) power gasifiers have air flowing DOWN along with the fuel.  When
the air reaches the "flaming pyrolysis" zone,  the heat from below 
produces pyrolysis of the fuel and the air reacts with the pyrolysis 
gases to make Char (C), CO, CO2, H2, H2O, CH4 at about 1000 C.  These 
hot gases then pass DOWN through the resulting charcoal, further 
reducing the CO2 and H2O to the final gas at about 750C to be used in an 
engine for power.

The engine intake draws the air through the gasifier.  These are also
called "cocurrent" gasifiers.  I call them "Tar-burning, Char making"
gasifiers and at low intensity they can produce >20% charcoal.  At low
intensity or with improper air distribution they can leave 0.1% of the
volatiles unconverted.  With proper air distribution they can make less
than 0.01% unburned volatiles in the gas.

In 1985 I was wondering about how to make this useful for cooking.
Those who need WoodGas stoves the most don't have convenient suction
devices.  So I turned it upside down to make the "inverted downdraft
gasifier", with air entering a fixed bed of charcoal at the bottom and
rising by natural or forced convection.  I apologize for the confusing
terminology, easily understood by gasifier people and no one else.  Paul
Anderson has recenly called this the "TopLit Updraft Gasifier" (TLUD)
and this is more easily understood and instructs people how to light it.

I hope this illuminates the terminology of downdraft and "upside 
downdraft" (aka top lit updraft) gasifiers.

Yours truly,

TOM REED           THE BIOMASS ENERGY FOUNDATION
Doug Williams wrote:

>Hi Drew and Gasification Colleagues,
>
>I have no intention of entertaining you with deep thought discussion fuelled
>with jungle juice, and no time for arguing about commercially proven
>technology. I discuss what I can within the constraints that commercial
>licensing imposes, but that is clearly something that you have missed in my
>contributions to this forum.
>
>There are trade secrets, and that is why you have to pay if you want to go
>straight to the start line, and then add your innovative capability to what
>already has been done. I have the highest regard for talented enthusiasm,
>but not without supervision, as too often seen with gasification projects.
>On last rough tote-up of our costs, more than $4.5 million has been invested
>to develop the understanding of the processes to bring gasification
>technology up to the level that is GOING to be required. Our work has
>provided a large number of people to experience gasified power generation
>through out the world, and provided a measure of how these technologies can
>supply energy from local resources.
>
>Because the gasification market has never existed since WW2, except in wide
>spread one off projects,    IF it stands up, we MIGHT get some money back,
>and that is a BIG if.  One thing is for sure, the future after oil needs
>something, and it isn't Wally's.
>
>. Nothing will stop you from thinking that your new gas making principle is
>better, but by describing how you perceive both Imbert style, and top lit
>gasifiers work, it is clear that you are seriously off track. I am not
>criticising you, just pointing out you have missed the important things of
>how they work. Top lit gasifiers for instance, have gas out the bottom, air
>in the top, but this is probably caused by studying top lit stoves, not open
>core gasifiers, or stratified downdraft gasifiers as Tom Reed has named
>these types.
>
>Don't expect me, Tom Reed, or any other people with experience to provide
>you with a correspondence course to correct your gasification knowledge.
>Questions about engine gasification are rarely answered by anyone other than
>me on this forum, and you might ponder why.
> .
>By the way, this is not personal, if you can make it work, I will support
>you to the hilt.
>
>Regards,
>Doug Williams.
>
>
>
>
>
>_______________________________________________
>Gasification mailing list
>Gasification at listserv.repp.org
>http://listserv.repp.org/mailman/listinfo/gasification
>
>  
>