Insulation: good or bad?
Posted 16 May 2009 - 04:02 AM
i personally have argued that we want as full of insulation as possible around reduction, combustion and pyrolysis, but drying uninsulated so that we can have a cold wall to run a monorator type condenser.
certainly combustion is our heat source and we want the most of its thermall results go to reduction as possible. but in downdraft, we have a very non-ideal method of getting heat to pyrolysis. pyrolysis is not generating heat in any meaningful way. it is working mostly on the radiant heat coming upwards from the combustion zone. however, it is doing so poorly, which is why the pyro zone is often only a couple inches thick on top of the nozzles, and often pyrolysis is not complete by the time chunks fall into the heath. various add-ons can get the heat from output gas back to where it contributes to pyrolysis, but such is not a given with a downdraft architecture.
forcing this heat return to pyrolysis is part of the point of the heated fuel intake and internal tar recirculation systems we are working on for the GEK. the result is a longer pyrolysis time, at lower temps, and increased likelihood pyrolysis will finish before the chunks fall into combustion and reduction.
however, the other rough way to contribute heat back to pyrolysis is how the original imbert did it. in gek terms, the imbert was a tall reactor insert in a gas cowling, with zero insulation around the reactor walls. see here for the specifics: http://www.allpowerl....ertgeneral.jpg
the original imbert ran zero insulation around combustion, reduction and pyrolysis. this was often claimed to keep the hearth metal cool and non-destructing, given metals of the time. the downside of this was that heat was wicked away from the combustion and reduction zones given the cooler surrounding gasses. however, it also allowed some of the heat in the rising gasses to return to the relatively cool pyrolysis and drying zones, as these zones where cooler than the surrounding output gasses. the design of the gek and many other well insulated reactors prevents this from happening.
we can argue that the hot gas around the drying in the imbert is non-ideal, as it does not give us a place to run a monorator and remove moisture. this was the origin of the monorator designs back in the day.
however, it seems we can mix and match these concerns in a more optimal manner. a tall reactor like the gek, split from the hopper, gives one the ability to do a tall gas rise zone, extending along the outside of the pyrolysis zone, but breaking before the hopper starts, and thus allowing a monorator for moisture removal. the gek type reactor length might be considered a short imbert, or a tall fluidyne.
inside this reactor, i am currently insulting from top to bottom. full and robust insulation around the bottom combustion and reduction areas is still desired. but it seems we should try cutting off the insulation tube around the pyrolysis area, so we get some heat returning from the rising gases in the gas cowling. the exact place to cut should be determined via temp meaurement, but my guess is we might cut the insulation tube about 3" above the top of the nozzles. this gives 8" left to the top of the reactor.
this also widens the pyrolysis fuel stack, which lengthens its residence time. there may also be improved internal convection flow circulation given better delta Ts across the reactor.
no idea if any of this is true in operation. but in principle, it seems the insulation question is more complicated than first appearance.
Posted 16 May 2009 - 07:54 AM
sorry the previous link was in error. here is the link to the graphic where the basic imbert heat exchange particulars can be considered.
Posted 16 May 2009 - 03:12 PM
Posted 17 May 2009 - 11:39 PM
I was just rereading the Lutz Gasifier improvement paper and the following comment (rebuttal) paper.
These are available at:
Lutz postulated a 20% improvement in gas out energy by using selective unit insulation, active fuel moister condensating out and supplementary engine exhaust heat input. This was in the forties.
We need to start immediately using these strategies to get back even to what they were able to do back then, and then springboard forward using what we have now that they didn't have then.
such as Electronics, ceramics, Inconel metals, a few hundred million fractional HP motors, ect. ect.
Cheer up. The way forward is through today with a foundation in the past.
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