[Gasification] filtration options and their varying discontents

Mark Ludlow mark at ludlow.com
Mon Dec 10 21:26:41 CST 2012


The issues here are similar to those experienced with any burner. The
majority of combustible gases have rather restricted behaviors when it comes
to flame propagation speed and pressure build-up (acetylene and a few others
are notable exceptions). Air and natural gas is mixed in a burner, but
rarely are there backfires (edging toward lean combustion) and if there are
the pressure rise is rarely precipitous.

 

Naturally, it pays to be cautious, so a determined set of tests at various
combustible ratios may be comforting. But this is the same fuel that we wish
to encourage to burn by compressing it 20-fold and advancing an ignition
spark 30-or-more degrees. If explosion or conflagration were really a risk,
then we should be so lucky!

 

Mark

 

From: Gasification [mailto:gasification-bounces at lists.bioenergylists.org] On
Behalf Of jim mason
Sent: Monday, December 10, 2012 12:45 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] filtration options and their varying discontents

 

 

On Mon, Dec 10, 2012 at 12:41 PM, David G. LeVine <dlevine at speakeasy.net>
wrote:

On 12/09/2012 10:34 PM, jim mason wrote:

other than the explosive risk


There is an interesting question here:

Is there an explosion risk if the gasses have not been diluted by the
atmosphere?

 

 

well, in principle, the gas should not be diluted with air during typical
operation, and thus no explosion problem.  you are correct.  

 

the problem is typical operation is variable.  during start up you always go
through a stoich point as you move air out of the system and progressively
make gas.  even if you leave the system full of gas on shut down, start up
in the reactor can pass lots of air until things get up to temp again.  this
can easily result in a combustible mixture in the system.

 

we've found this to be a fairly significant operational reality that needs
to be addressed for regular users.  similar for the impact of backfires from
the engine igniting the intake stream.  while things are "usually" ok, the
marginal events can be quite, umm, compelling . . .   we've started adding
more pressure relief points where typically not needed to cover these
outliers.  we're also looking to add a flame arrestor right  at the manifold
to prevent backfires propagating.

 

again, you never use these during typical operation.  somewhat like an ESP
shouldn't cause any problems during regular operation.  it is the outliers
that are of concern.  when you start running these systems regularly, you
tend to find all the outliers.  and the ones you don't find in house, those
out in the fields certainly will.

 

j

 

 

 

 

 

 

 

 

 

 

Let's start with gasoline, if we evacuate a bell jar and inject enough
gasoline so there is a layer of liquid gasoline on the floor or in a pan,
and we generate a hot arc 1/2" above the gasoline, will there be an
explosion?  The correct answer is "only if there is an air leak."  

Without an air leak, there will be no oxidizer, fire (or explosions) require
three things:  Fuel, Oxidizer and Ignition.  Fuel is gasoline (in this
case), Ignition is the spark, but where is the oxidizer?  

If woodgas has excess oxidizer as it exits the reaction zone, it simply
burns off the extra gas.  So, unless there is an air leak, the reaction can
not occur.  However, if there is an air leak in _any_ fuel system, there
will be severe problems.

Dave  8{)

-- 

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the men he has around him." 
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Jim Mason
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