[Gasification] pre mixed boiler secrets?

[GF]

How does the Davy Safety lamp actually work? I thought a fine mesh gauze arrested the flame.

GF










-----Original Message-----
From: jim mason <jim at allpowerlabs.org>
To: Discussion of biomass pyrolysis and gasification <gasification at lists.bioenergylists.org>
Sent: Mon, May 16, 2011 2:08 am
Subject: [Gasification] pre mixed boiler secrets?


some new boilers drive premixed fuel/air into the combustion chamber
hrough a single blower.  this premixing of the charge improves the
ombustion efficiency and cleanliness.  i've found similar benefits of
remixing fuel/air into the swirl burner on our gasifier.
however, things got more difficult recently when we started returning
o blowers.  with the ejector architecture, you have a very high
elocity section that the flame cannot back up through.  with a
remixed blower, the gas/air velocity is much slower and it is much
asier for the flame to back up into the blower.
which brings me to my question:  does anyone know how contemporary
remixed boilers are keeping the flame out of blower?
in principle, it seems you have three methods to chose from
1. keep the mixture outside the flammability limits of the fuel
. keep the gas/air velocity faster than the flame front of the fuel
. keep the temp below the autoignition pint of the fuel
1 is unattractive as it requires a multistage mixing solution.
2 we've made work, but it is fussy, and requires a rather consistent
low rater lest your "constriction" size get out of spec.  also, when
ou are working with blowers for a gasifier, the main problem is to
et to adequate pull vac, so canceling some of this by pushing through
 constriction is not attractive.
3 we have not played with much.  but it seems likely that a long
oneycomb section might give adequate heat dissipation to quench a
lame pass through.  or maybe just a steel wool packed in the tube.
we can of course go design this from scratch, but it likely has
lready been well explored and solved in premixed boiler applications.
anyone know how they do it?  any related prior art on flame arrestors
hat we might consider?
j



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