[Gasification] Gasifier design information

[drewrt]

The best place to start is probably Doug's simple little gasifier here

http://www.fluidynenz.250x.com/Fluidyne%20Special%20Project.pdf

Some things to keep in mind are that tar output from almost any imbert 
(funnel shaped downdraft system where the air is injected at the change 
in taper of the funnel) style gasifier can be minimal under *_just_ *the 
_*right*_ conditions.    The major variables are fuel size/shape 
(affects surface area to volume), fuel type(hard wood, softwood, etc.), 
moisture content, air injection temp and humidity (not in order of 
importance, as there is likely many opinions on what is most 
important).   All these factors interrelate in a fairly complex fashion.   

    So any fuel that is of the appropriate size shape to gravity feed 
and not too wet will likely allow you to produce clean gas at some flow 
velocity, but most likely not the perfect flow velocity for your needs, 
and not necessarily over much of a range of flow velocities (I know this 
will get me flak from a lot of directions).    The kiln dried 
construction scrap you are talking about might be an ideal fuel if you 
can size it right, remember it must gravity feed nicely (the most 
successful fuel seems to be small wood cubes, high surface area, high 
angle of repose, low potential for bridging, wood chips can be used but 
tricky to get good feeding).  

What you might do is build a little system like Doug describes at the 
link above, then add a system for measuring gas out, or air in then run 
it at a variety of flow rates until you find a flow rate that gives you 
a clean gas output for the fuel (type, shape, size, moisture) you 
have.   Then you can look at the engine you want to use, and figure out 
how much gas it's going to need and then build a gasifier based on that 
flow rate (or range of rates) using the ideal SV you found from your 
experiments (read Tom's paper on SV, it will help you gain an 
understanding of system dynamics).    One thing you have going for you 
is a source of nice dry wood, most successful imbert style systems 
operate best on dry wood, with a few of those systems using water/steam 
injection to cool the reaction to increase the turndown ratio (turndown 
ratio is ratio between highest clean gas production flow, to lowest 
clean gas production flow, very important in variable load systems like 
cars).  Scaling is tricky though, but if Dougs is close to what you need 
you might find that you can make it work by resizing your fuel, drying 
it further, preheating your air in.......
    Something to keep in mind about this forum is that it is 
continuously re inhabited in a wonder way by new members who are hoping 
that there is a simple answer out there to their energy needs.   The 
forum has no central briefing document that says "this is how to do it" 
or even "this is what we agree on".   In fact the core members of the 
forum are some very knowledgeable people, who like knowledgeable people 
in most places have a variety of opinions.   One issue is that new 
members tend to ask questions with such broad scope that to give a 
proper answer would require the writing of one of more books.    This 
tends to mean that specific detail oriented questions get answered (or 
opinioned) and broad questions get few replies.    Try reading the FAO 
document and the inspirational (though oversimplified) document on wood 
gasification on the journey to forever website.    They will help to get 
you up to speed so that you can ask questions that people can answer 
without writing new books.   Sorry I can't handily provide the links to 
those but perhaps someone else will be able, or you can search around.   
Perhaps others could recommend their favorite process overviews?   

Off Topic,    While I do miss Peter's interesting idea's I don't miss 
his vitriolic style of "debate".    I have no doubt he is a genius, but 
like so many he scatters his seeds in such a way that few will likely 
sprout.    To truly contribute to the huge mass of wisdom and 
information we have accumulated, it is not enough to shout your ideas at 
people.   You have to work with people, in teams and in ways that are 
tolerant of people and idea's of all types.   It may be too much to hope 
for but I hope that Peter loses some of his anger and is able to 
contribute in the future.

Best
Drew