[Stoves] Biomass stoves v. PV-induction cooking (re: Frank)

Wed Feb 1 12:37:06 CST 2017

> The maximum working temperature for PYREX glassware is 490°C. However, once the temperature exceeds 150°C, ensure that heating and cooling is achieved in a slow and uniform manner.

Norman,

I am wondering if bits of broken pyrex beakers could be mixed in with the fuel to help establish the temperatures at different locations. In a furnace that fails (temperature heading up) before I detected results in beakers in an assorted array of melt. Seems around the temperatures we are interested in. i have made many such art works.  

Soda-Lime Glass
Glass transition <https://en.wikipedia.org/wiki/Glass_transition_temperature>
temperature <https://en.wikipedia.org/wiki/Glass_transition_temperature>, Tg	573 °C (1,063 °F)	564 °C (1,047 °F)

Regards

Frank

> On Feb 1, 2017, at 10:10 AM, Norman Baker <ntbakerphd at gmail.com> wrote:
> 
> Andrew and guys;
> 
> I could be wrong and am willing to be in the face of new evidence. But I do not think it is a simple convection effect at the surface. Obviously it is a convection effect but not due, I think, to being at a cooler surface. First, we used a heat shield (closed at the top) and the the temps inside the heat shield were about 200 degrees C above ambient. Core was typically at 450 -500C. External surface at the pyrolysis front was typically at 350 C without the heat shield. Second, we observed the pyrogas moving in any direction you could imagine. That was a real surprise. In concert with this unexpected gas movement, we also observed (quite consistently I have to add) smaller pieces of pyrolyzing wood chips lose their mass and volume and then simply cascade down into between the larger wood chips for an average distance of about 20 cm below the pyrolysis front. Often, they would induce pyrolysis along their path and sometimes would fall fast enough to simple induce an area of pyrolysis at a greater depth. That phenomenon was amazingly consistent. The new area or path pf pyrolysis would create a small channel that would offer a more open less pressurized path for primary air to flow. Along with it, the pyrogas would be sucked along (in almost any direction) and create what we saw with the gas going in any direction as well as up as expected. I'm interpreting here because we did not actually see it internally but did see it at the periphery of the barrel. 
> 
> That said, we early on found that any long or unusually large wood chips would create bridging and air channels the pyrolysis would follow downward. We also soon figured out the woodchips needed to be "settled in" as we filled the barrel. Consequently we would put in a scoop of chips and shake the bejusus out of it to make them "settle in" for more consistency of burn. This is just another way of saying more consistency of porosity for airflow. We also did a few burns where we would put a handful of coarse sawdust in a spot to see how it inhibited the migration of the pyrolysis front. Of course, it would inhibit the pyrolysis front since primary air had trouble getting through the sawdust. 
> 
> Consistency of particle size is important and that is a parameter we could ask landscape bark suppliers to work on. If you have ever been to a lumber mill that has chipping operations, size consistency is simply a matter of putting in the appropriate screens to separate particle sizes. If however, we use woodchips where there is some inconsistency to particle sizes, and pyrolysis proceeds as we alluded to, we simply need to understand that and accommodate that in our analyses.
> 
> That phase of our research is almost a side issue that was easy to do for a quick and dirty experiment to understand what was happening. It could and should be repeated just to document what was happening. At the time, both Paul and I were on our knees with our faces close to the tempered glass in the heat shield. It was fascinating to watch something we did not expect. At one point Paul looked at me and said "Blimey!" I looked at him and said "What the hell!".
> 
> I too would expect this to happen in larger diameter TLUD's. But I think it is mostly a function of inconsistent particle sizes. 
> 
> Unfortunately, I was not able to snip the videos I had on hand in to 20 second quickies to show people what was going on at ethos. If I have the opportunity, this next year I think I will take some videos of the entire process. This will include falling of smaller particle sizes, development of the small channels of pyrolysis, the evolution of tars and water vapors inside the glass, the passage of the main pyrolysis front, and the combustion of the tars from the glass as the front proceeds past the Pyrex dish. Two things we found interesting were unusually large particle sizes created channels that were often visible in the finished biochar after a burn cooled. The small channels created by the cascading small woodchips were never visible after the burn cooled. It is tempting to create a TLUD and do a burn that would extend the main pyrolysis front to below the Pyrex glass, and then flood the TLUD from the bottom with water to capture the small channels that we saw. This would extinguish pyrolysis and show us if the small channels are a surface effect or extend throughout the feedstock. I suspect, at this point, the small channels are found throughout the diameter of the feedstock.
> 
> By the way, the temperature tolerances of the Pyrex dish are greatly exceeded when used in a TLUD. Simply avoid drastic temperature changes and let the temperatures build slowly and then cool slowly. Once, without thinking about it, we dropped the wet carpeting in on the biochar to stop pyrolysis. The wet carpeting hit the Pyrex glass and it shattered instantaneously.
> 
> Norm
> 
> On Wed, Feb 1, 2017 at 7:13 AM, Ronal W. Larson <rongretlarson at comcast.net <mailto:rongretlarson at comcast.net>> wrote:
> Andrew:  cc list and Norm
> 
>         As Norm and I talked, we came to the same conclusion.  But it is and was a remarkable video to see ANY downward flowing gases.  I’d like to know if anyone with computational fluid dynamic simulation capability can report on this being observed as well - and whether they can report any negative implications, etc.
> 
>         Presumably this could suggest that larger is either better or worse.
> 
>         Thanks for the feedback.   Your own char-making was with very large diameters.  Might you have seen anything similar?
> 
> Ron
> 
> 
> > On Feb 1, 2017, at 2:22 AM, Andrew Heggie <aj.heggie at gmail.com <mailto:aj.heggie at gmail.com>> wrote:
> >
> > On 31 January 2017 at 17:04, Ronal W. Larson <rongretlarson at comcast.net <mailto:rongretlarson at comcast.net>> wrote:
> >
> >> 2.   As an example of an unexpected unknown that I saw for the first time
> >> yesterday:  Norm Baker is doing some extremely strong work on very large
> >> TLUDs, and he gave an outstanding talk on his 16th model (called “Ring of
> >> Fire”).  He later showed me parts of a 1.5 hour run with a pyrex window
> >> inserted into the side of his barrel.  Neither of us know how to explain the
> >> clear picture of pyrolysis gases (smoke) traveling DOWN near this window
> >> (mostly - not periodically).  Anyone else seen this?  (pretty hard without a
> >> window). Clearly the overall gas flow is upward - as he produces plenty
> >> (35%) of high quality char.
> >
> > Is this not a simple convection effect, the  outside of the  barrel
> > being cooled by ambient air whilst the core is at ~600C?
> >
> > I would expect this effect to be more pronounced the  larger the diameter.
> >
> > I doubt it affects the burn much unless it causes a "fold" in the burning layer.
> >
> > Andrew
> >
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Thanks

Frank
Frank Shields
Gabilan Laboratory
Keith Day Company, Inc.
1091 Madison Lane
Salinas, CA  93907
(831) 246-0417 cell
(831) 771-0126 office
fShields at keithdaycompany.com

franke at cruzio.com

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