Prepare Mag: August 2018 - page 20

on a component level than to try to fix after the system is
Critical: Testing for Leaks as you build!
It cannot be emphasized enough that controlling the air and
gas flow through the system is crucial to a successful
operating wood gas generator. Failure to ensure that there
are no air leaks in the system can result in internal ignition of
the gas which can be any simple ‘pops and bangs’ or
something much more dangerous. Additionally, air leaks in
the system can render the system non-functional providing
syngas too diluted to ignite. One of the most common
questions asked by first-time wood gasifier builders is “why
won’t my gas ignite or stay lit?” While there are several
contributing factors to this, air leaks in the system are the
most common problem.
Since the design of the system is to have a suction blower
placed near the gas exit which essentially ‘pulls’ air into the
system and gas through the system, any air leaks in any of
the critical flow components will introduce more air into the
system. When doing leak testing it is recommended that you
put the blower at the air intake into the system to essentially
“push” air into the system and gas through the system. Using
a spray bottle with water and dishwashing soap sprayed on
each weld or joint will quickly and visibly show where there
are air leaks. These leaks can then more easily be corrected
at the component level before the system is completed. Leak
tests should be done at each phase of the build for each
component in the critical flow process; air intake, pyrolysis
layer, heat exchange, cooling and filtering.
A complete
system leak test should also be conducted after final
assembly and before functional testing to ensure the system
is airtight. Failure to ensure an air tight system for proper air
and gas flow can result in a non-functional system and leave
you with a very costly 500lb. paperweight.
System Testing
Once you have completed your build it is ready for some
system testing. Initial testing should be done to test the
basic operation of the system and as few variables as
possible. Start testing using charcoal only as your fuel.
Charcoal has the lowest moisture content and will provide
less condensate, tars and best gas. Once you have tested that
your system is functional in creating gas that ignites and
remains lit, you can begin to experiment with different fuel
mixtures; always use charcoal to start the ignition process
but then add small chunks of low moisture wood as fuel.
Note things like how long it takes to start making usable gas,
what color is the flame as the gas burns, how long does the
gas stay lit. You can make minor adjustments to the fuel and
airflow until you are able to create good quality gas in a
consistent and predictable manner. Once you are able to
generate syngas consistently on demand, you can then begin
to begin to utilize the gas in your heating, engine or power
generation configurations.
Troubleshooting note: When doing your first system testing,
if you experience gas that won’t ignite or stay lit after
lighting, you may have air leaks in your system. Try using the
blower at the air intake and rerun the test. If you have any
air leaks, by ‘pushing’ air into the system and pushing the
resulting syngas, you would be pushing air and gas out
through any leaks. The remaining gas coming out the exit
port should be less diluted and should ignite. If this is the
case, leaks should be identified and corrected if possible.
Wood Fuel
The primary fuel for the wood gas generator is small ‘chunks’
of charcoal and wood. Both hardwood and softwood may be
used. It is the charcoal that is actually combusted; the raw
wood chunks are converted internally to charcoal as the
burning process continues. You may experiment with the
uses of other type of fuel such as wood pellets, corn husks,
and other biodegradable material, however when trying
these different fuel types, try to keep the ratio of these other
fuel materials to less than 20%. The function of the system
will be affected by the type fuel used and fuel too small may
cause ‘bridging’, which causes fuel to lump together and
restrict the flow of fuel through the reduction tube.
Production Testing
Once you have completed system testing and are able to
create consistent, quality gas for your specific application,
you can move onto production testing, which includes
optimizing the system performance for your particular
application. Maximizing run times, how often you need to
run, creating a maintenance schedule for ash clean out and
changing filter media, fuel creation and storage, etc.
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