<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.6000.17093" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff background="">
<DIV><STRONG><FONT face=Arial size=2>Hi Tom,</FONT></STRONG></DIV><STRONG><FONT
face=Arial size=2></FONT></STRONG><STRONG><FONT face=Arial
size=2></FONT></STRONG>
<DIV><BR><FONT face=Arial size=2><STRONG>This reads like a trick question, as
you obviously have something specific in mind. <BR></STRONG><BR>To what extent
can you clean today's gas by passing it (cooled to about 150 C) through a barrel
of tomorrows REASONABLY DRY fuel, thus permitting you to burn all the tars
AND finish drying the fuel?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>Firstly, I wouldn't do it, as once gas is
made, I don't like to bring it anywhere near filter material that can
continue to discharge humidity into the gas, just to dry the next days fuel. Yes
the fuel might collect some of the tars, but how to keep the operational
temperatures of the filter mass stable, can be severely affected by
environmental and gas output conditions. Gas humidity also carries sub-micron
particulates, plus being inherently acetic in the presence of tar, the
condensate ingested into the engine will shorten the oil and engine
life.</STRONG></FONT></DIV>
<DIV><FONT face=Arial size=2><STRONG></STRONG></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>Of the gasifiers I have seen using incoming
fuel as the filter for dirty tar laden gas:</STRONG></FONT></DIV>
<DIV><STRONG><FONT face=Arial size=2></FONT></STRONG> </DIV>
<DIV><FONT face=Arial size=2><STRONG>1. Thailand using rice husk in large
tanks, needing to be dug out by hand.</STRONG></FONT></DIV>
<DIV><FONT face=Arial size=2><STRONG></STRONG></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>2. Wood blocks used to catch tars in
the first Biomass Engineering gasifier they inherited as a project in N.Ireland
as a first stage filter, but quickly replaced as their own engineering expertise
recognised it's short comings for later projects. </STRONG></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>3.Then one you already know,
wood chips are used as a filter for the FEMA emergency gasifier.
</STRONG></FONT></DIV>
<DIV><STRONG><FONT face=Arial size=2></FONT></STRONG> </DIV>
<DIV><STRONG><FONT face=Arial size=2>4. Fluidynes own early experimental
filtration systems used wood shavings and wood blocks, very nasty to clean out .
Good reason to learn how to make the gas tar free ):-)</FONT></STRONG></DIV>
<DIV><FONT face=Arial size=2><STRONG>-----------</STRONG></FONT></DIV>
<DIV><STRONG><FONT face=Arial size=2></FONT></STRONG> </DIV>
<DIV><FONT face=Arial size=2><STRONG>I don't recommend anything that filters
tar, which in any way might bring the operators into handling and
breathing vapours from tar contaminated wood. </STRONG></DIV>
<DIV><BR>While a moisture content less than 20% is desirable for gasifier fuel,
I suspect it should not be bone dry for long runs because it becomes
autopyrolytic and won't retain a level pyrolysis zone.</DIV>
<DIV> </DIV>
<DIV><STRONG>I will show my ignorance as never seen written or used the
term "autopyrolytic". All I can say is, that what ever it means to you, I have
never seen any evidence that oven dried fuel is detrimental to gas making in the
way that I understand in downdraft gasification. The fact that you refer to a
level pyrolisis zone, suggests that you are linking into either stoves or open
core gasifiers as the ones quoted affected by this terminology.</STRONG></DIV>
<DIV><STRONG></STRONG><STRONG></STRONG> </DIV>
<DIV><STRONG>The only thing that affects the zones in packed bed downdraft
gasifiers with fixed air nozzles using appropriately dried fuel,
is excessive gas output rate, which can see the pyrolysis zone shallow
out as more endothemic heat is consumed in reduction, and less radiant
exothermic heat/time is available to the incoming fuel for pyrolysis. Even
using oven dry, roughly 20% of the fuel weight is bound moisture, and H2 levels
remain fairly constant, but less or no condensate results.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Hope this may be of assistance, and look forward to any other
contributions on the subject as you describe.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Doug Williams.</STRONG></DIV>
<DIV><STRONG>Fluidyne.</STRONG></FONT></DIV></BODY></HTML>