[Gasification] stratified downdraft pressure

Tue Feb 6 17:37:35 CST 2007

Dear Greg, John and All:

I have just spent 30 enjoyable virtual minutes with Greg's gasifier 
journey.  I can hardly wait to see how the 25 (?) kW engine performs on 
what LOOKS like good gas.  Disregard his warnings at your own peril (no 
trashy chips, no yellow gas in the engine).  I strongly recommend 
reading this in detail if you want to build a simple gasifier and avoid 
most of the problems. 

Greg's gasifier is a WWII (Imbert type) gasifier which has advantages 
and disadvantages.  John's gasifier is based on the "Stratified 
Downdraft Gasifier" that we developed at NREL (SERI) here in GOlden 
1980-88.  It has different advantages and disadvantages.  We are 
currently developing a hybrid that will have all the advantages and none 
of the disadvantages of each.

Here are a couple of problems to consider:

    * If the gasifier is too big for the engine's rating it will produce
      more tar, so size the gasifier correctly.  Harry LaFontaine built
      the unit shown in our book (Construction of a Simplified Wood Gas
      Generator....) # 14 on our book list or
      http://www.gengas.nu/byggbes/index.shtml for those who prefer to
      read it on a computer screen.  On page 52 Harry recommends fire
      tubes varying from 1" (for a 10 CI engine) to 14" (for a 320 CI
      engine).  He also has a footnote saying "A fire tube with an
      inside diameter of less than 6" would create bridging problems
      with wood chips and blocks."
    * Many of the startup problems for gasifiers can be bypassed
      initially by using wood pellets which have a bulk density 3-4
      times that of wood and are small enough and dense enough to feed
      in smaller tubes.
    * For starting the gasifier one only needs a small flare, but for
      testing it thoroughly you should use a big one like Greg's and
      don't bother connecting to an engine until you can produce gas
      with < 30 ppm (30 mg/m3) unless you like rebuilding  engines
    * For testing tar, see our books at www.woodgas.com
      /* REVISED*:/ /*CONTAMINANT TESTING FOR GASIFIER ENGINE SYSTEMS:*/
      A. Das (TIPI 1989, 1999). Test that gas for tar! Long engine life
      and reliable operation requires a gas with less than 30 mg of tar
      and particulates per cubic meter (30 ppm). The simplified test
      methods described here are adapted from standard ASTM and EPA test
      procedures for sampling and analyzing char, tar and ash in the
      gas. Suitable for raw and cleaned gas. New edition & figures.
      ISBN 1-890607-04-5                                        
      32pp                              $10

      *_Add item #3 to my shopping cart._*
      <http://ww9.aitsafe.com/cf/add.cfm?userid=B663412&product=Contaminant%20Testing%20for%20Gasifier%20Engine%20Systems&price=10&units=0.25>

      <http://www.woodgas.com/book3.htm>
      /*BIOMASS GASIFIER "TARS": THEIR NATURE, FORMATION, AND
      CONVERSION: */ T. Milne, N. Abatzoglou, & R. J. Evans. Tars are
      the Achilles Heel of gasification. This thorough work explores the
      chemical nature of tars, their generation, and methods for testing
      and destroying them.  (100 page bibliography also available for
      additional $10)
      ISBN 1-890607-14-2                                        
      80pp                               $25

    * For approximate, visual testing, but a Bacharach smoke tester at
      DWYERINSTRUMENTS.com (100 times more sensitive and less quantitative.

I hope that we can get more people building and running gasifiers and 
reporting their progress here and on a website, and less talk talk talk.

Yours truly,

TOM REED                Moderator                         BEF
------------------------------------------------------------------------

Greg Manning wrote:
> Greetings John, and list members.
>
> I'm somewhat confused, the suction fan is ONLY used for startup of a 
> gasifier, and can be even at the "low point" of gas production volume (an 
> old automotive heating blower or such) the fan is not used during the 
> operation of the engine, and is by-passed via valves.
>
> Yes the amount of tar is indicative of gasifier internal temperature 
> AND/OR... water content of feedstock AND/OR  hearth to pryolosis zone 
> placement ratio.
>
> My suggestions..
>
> Remove everything "Ancillary" to the gasifier itself except the fan and a 
> "test flare", install the fan at a distance from the gasifier (10-15 ft) 
> (3-5m) as to allow the steel tube to act as a cooler for the hot gas as to 
> not melt the fan.  install a "T trap" just ahead of the fan to collect 
> condensate and drain it to an appropriate container. NOW, get the gasifier 
> working correctly... Then with trial and error, you can one at a time add 
> the other stuff back into the system.
>
> See my page on downdraft gasification:
> http://www.inetlink.ca/a31ford/cgcmb/
>
> Greg Manning,
> Brandon, Manitoba, Canada
>
>
>
> ----- Original Message ----- 
> From: "JOHN GOODWIN" <john.goodwin1 at btconnect.com>
> To: <gasification at listserv.repp.org>
> Sent: Tuesday, February 06, 2007 6:12 AM
> Subject: [Gasification] stratified downdraft pressure
>
>
>   
>> Dear list,
>>
>> I have made a stratified downdraft gasifier as described by Dr Reed at 
>> http://www.gengas.nu/byggbes/intro.shtml. Using a small blower, it works, 
>> and I have large quantities of flammable gas. I unfortunatley also have 
>> quantities of tar and steam coming through the filter, using wood chip of 
>> about 10% moisture.
>>
>> Being new to this, please feel free to correct me at any point. Please 
>> also excuse my mixing units.
>>
>> I assume that the tar and steam are present because the temperatures in 
>> the reduction tube are too low for the water gas reaction to fully 
>> complete, and too low for the tar to crack. From this I assume I need more 
>> suction from my fan.
>>
>> I have used a 10" reduction tube. From table 2.2, 
>> http://www.gengas.nu/byggbes/52.shtml this is suited to a 160 cubic inch 
>> engine (2.6 litre). At 2000 RPM, a 2.6l engine is drawing 5200 litres per 
>> minute. I understand that producer gas and air need mixing at 
>> approximatley 50:50, so would be drawing 2600 litres (91 cubic feet) per 
>> minute from the gasifier.
>>
>> So therefore, I am looking for a 100 cubic feet/min suction fan. How many 
>> inches water suction does this fan need to generate in order to achieve 
>> the neccessary temperatures in the reduction tube? Does anyone have any 
>> good sources of cheap fans (UK 240v, 50Hz).
>>
>> One more beginners question, when using a simple U bend to measure water 
>> guage, is the suction the difference between the gasifier side and 
>> atmospheric side levels of water, or the difference between the gasifier 
>> side and the starting level of water?
>>
>> Many thanks,
>>
>> John
>>
>>
>>
>>
>>
>>
>>
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>>
>>     
>
>
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>   