[Gasification] Practical gasifier ideas

[Benjamin Domingo Bof]

Daniel;please look at FAO 72 "Wood gas as engine fuel"  Loma Plata electric generation plant in Paraguay using two Waukesha L 7042G twelve cylinders Spark Igniton. motor. There is an Menonites Colony giving electricity for an saw mill and dairy factory. His gasifier is an Imbert type using like one metric ton an hour of firewood.
  Regards; Benjamin

Daniel Chisholm <dmc at danielchisholm.com> escribió:
  Nice to see some good practical ideas and solutions being discussed
lately. I quite liked the thermocouples-in-a-pipe and also the rotating
vane methods of fuel level measurement and control, the automotive O2
sensor, and Andy's mentioning of monitoring the computer's PWM (pulse
width) signals to the injectors.

Here's a recent "McGyverism" idea I had. Comments on it would be
appreciated.

I am designing a ~1MWth experimental CFB gasifier (for producing hot
gas, for the purpose of close coupled combustion). I calculate that I
need about 1/6th of a cubic metre of air per second, which is about
360scfm. (Feel free to check my calcs; I've based it on a SWAG
equivalence ratio of about 0.4)

A CFB needs its gasification air supplied at relatively high pressures
(typically 1-3psi), which is somewhat of an awkward pressure. It is
much too high a pressure for typical fans or blowers. It is too low a
pressure to be suited to turbomachines, and much too low a pressure to
be a good match to positive displacement compressors. The only
well-fitting machine I've seen so far is a high-speed multi stage
centrifugal blower (2-8 stages, ~5000RPM). And when you are running a
machine with an electric motor, variable speed control is an expensive
option.

A further wrinkle is that I can't at this stage accurately predict the
pressure drop that my CFB design will produce, therefore I don't know
whether I need my airflow at 1.5psi or 5psi (or 10psi...!). While
centrifugal blowers are remarkably flexible, I think that this is asking
a bit too much, especially if it is to be driven by a constant speed
electric motor.

So here's my idea for a quick-n-dirty source of a 1-10psi source of
0.16Nm3/sec gasification air....

*** The exhaust flow from a ~130hp diesel engine, running under
no load. ***

A diesel engine's air flow rate is independent of its fuel flow rate
(OK, there's a bit of a wrinkle if its turbocharged, but even that ends
up sorting itself out OK). Under no load conditions, it is burning very
little fuel, and its exhaust temperature is quite moderate. It is
capable of pumping against several psi of backpressure without damage
(e.g. into a muffler and/or a turbocharger) at full load - so at no load
it will be even less damaging.

At no-load or low-load conditions, very little of the O2 is consumed
(i.e. the exhaust has nearly the same oxygen concentration as the
incoming air). And all of the exhaust heat ends up being usefully used
as preheat for the gasifier's intake air, since the gasifier's intake
air _is_ the diesel's exhaust.


I think I have solved my near-term blower requirements for this rig.
When I have a better idea of actual pressure drops, I can then select a
properly matched multi stage centrifugal blower. Since my application
is an off-grid one, i.e. electricity means diesel genset electricity,
selecting a diesel engine drive for the main air blower is a
possibility, especially if a bit of variability in in blower shaft speed
is required. And of course the most logical place for any diesel
exhaust is straight in to the gasification air manifold (might as well
get 100% utilization of the exhaust gas waste heat, and will probably
end up cleaning up the dirty diesel exhaust by passing it through the
gasifier and combustor!).



-- 
- Daniel
Fredericton, NB Canada


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