[Gasification] Wood Chip classificaton

Thu Apr 12 14:41:13 CDT 2012

Hello gents,
before making money got back in the way of gassing, I too made this benchmark.  
I built a few different rolling barrel shaped screens and made some pressure drop measurements with a mock hearth, knowing that the real thing in operation would be somewhat different. ending up with several different sized chips with different pressure drops per size.  It seemed to me that I came to the conclusion that since they are all about the same thickness that the “x” and “y” measure didn’t seem to make any real change in test or actual use.  the only important revalation  I remember is to screen to get the super fines out and not much changes after that.
I’m totally with you Pete, If I can’t use wood chips, I’m done, call me lazy that’s fine. But I still wonder how much energy a guy would spend in december here in the pacific northwest sifting the fines out and drying the rest to an accepable level  vs  the energy made from those now sifted and dry chips. 
It seems like you have to tumble those things to get them to dry out in a confined space, as they can sit wet forever in an open bucket and will never dry out.  The other option is spread them out thin over acerage on a nice day, and then gather them back up.
either way it kinda takes the thrill out of gassing.
I will take it one step further, than you Pete, if I can’t shovel wet/green chips into a hopper and make the thing work, then I’m checking out.  I plan on working on drying them on delivery from the hopper to the hearth as they flow between the two.  Next time I have some “free time”.
I suppose a guy could do a preliminary energy calculation just for fun.  
Energy required to bring “x”pounds of soaked and green wood chips at 60% water down to one pound of 20% water wood chips.   Vs the energy that can be made from that pound of dried wood chips.
Note,, vent the evaporated wood moisture outside, or everything in your shop will get wet and rust in a very quick manner.
Roger that,,,, “along way to go” 
Fuel prep sucks.
Luke

From: Kevin 
Sent: Wednesday, April 11, 2012 4:09 PM
To: Discussion of biomass pyrolysis and gasification 
Subject: Re: [Gasification] Wood Chip classificaton

Dear Pete

An "ideal situation" would be if you had a constant flow rate of air, which you then flowed through such chips screened to different sizes. Then you could measure the pressure drop across a length of the bed. This would tell you just how much pressure drop various sizes of chips would give you. Then you could decide how small a chip size you could consider using. 

"Too small a chip" will likely give tar, unless the gasifier is specifically designed to handle such fine chip sizes. However, this is a lesser concern for gasifiers producing "Heating Grade Gas."

Best wishes,

Kevin

  ----- Original Message ----- 
  From: Pete & Sheri 
  To: 'Discussion of biomass pyrolysis and gasification' 
  Sent: Wednesday, April 11, 2012 6:59 PM
  Subject: Re: [Gasification] Wood Chip classificaton

  Hi, Kevin.

  Thanks for the input.  I had better go out and check the sizes of my screens.  

    I realize that the APA gauge is focused on thin chips for pulping.  But you folks have been telling me that I need thicker chips (in relation to the length and height).  I have actually been using a 3 screen system, with a smaller screen (1/4” X ¼”) to get the dust out before I even think of saving anything.  

  But even with the 1X1 screen, I could get chips that are only 1/32” thick, and therefore, very light in weight.

  I am learning that those chips may be okay in some circumstances, but I want to be able to see the difference for myself.

  I still have a long way to go.

  Pete Stanaitis

  ----------------

  From: gasification-bounces at lists.bioenergylists.org [mailto:gasification-bounces at lists.bioenergylists.org] On Behalf Of Kevin
  Sent: Wednesday, April 11, 2012 2:47 PM
  To: Discussion of biomass pyrolysis and gasification
  Subject: Re: [Gasification] Wood Chip classificaton

  Dear Pete

  I would suggest that a simpler, and better way to evaluate wood chips is to use a  "Two Screen System." For example, if you used square mesh screen with 1/2"x1/2", and 1"x1" openings, you would end up with 3 products:

  1: +1"

  2: -1", + 1/2"

  3: -1/2"

  The APA Gage is intended for a different purpose... to give a reflection of wood fibre length, because that is what is important to Pulp Mills. For gasifier applications, uniformity of size, and the percentage of void space is what is important. The "two screen system" should give screened chips from "between the screen decks" that are much more uniform, and having much better gas flow characteristics.

  Best wishes,

  Kevin 

    ----- Original Message ----- 

    From: Pete & Sheri 

    To: Gasification at bioenergylists.org 

    Sent: Wednesday, April 11, 2012 3:37 PM

    Subject: [Gasification] Wood Chip classificaton

    My only interest for gasifier fuel is wood chips.  If I can’t understand them and  make them work well, I won’t be using a gasifier at all.

    I know this may be old news to many of you, but I recently found a couple of ways to characterize wood chips.  Although there are plenty of good systems out there the best ones are way to complex and expensive for me. 

    So,  I am using a simple gauge from the APA (American Pulpwood Association.

      My simple page to explain the process is at:

    http://www.spaco.org/Woodgas/WoodChipMeasurement.htm

    It has links to a couple of in-depth sources for understanding wood chips, too.

    Pete Stanaitis

    ----------------

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