[Gasification] pre mixed boiler secrets?

[jim mason]

some new boilers drive premixed fuel/air into the combustion chamber
through a single blower.  this premixing of the charge improves the
combustion efficiency and cleanliness.  i've found similar benefits of
premixing fuel/air into the swirl burner on our gasifier.

however, things got more difficult recently when we started returning
to blowers.  with the ejector architecture, you have a very high
velocity section that the flame cannot back up through.  with a
premixed blower, the gas/air velocity is much slower and it is much
easier for the flame to back up into the blower.

which brings me to my question:  does anyone know how contemporary
premixed 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
2. keep the gas/air velocity faster than the flame front of the fuel
3. 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
flow rater lest your "constriction" size get out of spec.  also, when
you are working with blowers for a gasifier, the main problem is to
get to adequate pull vac, so canceling some of this by pushing through
a constriction is not attractive.

3 we have not played with much.  but it seems likely that a long
honeycomb section might give adequate heat dissipation to quench a
flame 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
already been well explored and solved in premixed boiler applications.
 anyone know how they do it?  any related prior art on flame arrestors
that we might consider?

j






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Jim Mason
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