[palmtreepathos]

Hey neighbor!
Yes indeed on the protective eyewear! My parabolic is inherently more dangerous to the eyes since is reflects the sun up at you rather than directing it down toward the object of experiment. You, though, could vaporize things in a serious way with that fresnel lens and need some nice long tongs, gloves, etc...
(This is an interesting story about how to undo burns if or when the need arises, is AMAZING and I have tried it and proved to myself at least for some burns this will work! )
The President's Sphere - The Superdome -- "fighting fire with fire"

As for the dutch oven I tend to be a resale and estate sales shopper. You have a Goodwill on 41 north of Barret Pkwy, family style garage sales and army/navy stores might be a thought too. Mine is someone's "family heirloom" and quite the rust bucket from sitting out at an estate sale but a grinding disk on a drill will knock it off.

[Turtle]

Originally Posted by freeztar

I'm in Marietta, which is basically north metro (kinda NW).
I definitely have a very shady yard which is even shadier in the winter. And a dutch oven you say?! Where would you recommend getting one around here?

I think you can find the Dutch ovens in at least 2 different sizes from the kitchen utensil section of any well-stocked department store. I sorta remember that I paid less than $25 for the smaller size a few years back. If it's not already seasoned, it has instructions and you will need to season it if you're going to camp-cook in it.

I saw a piece on PBS tonight on solar power and they showed the world's largest solar parabbolic trough generating plant. The manager said they heat the sythetic oil in the receiver tubes to around 700F and the reflectors looked between 12 and 16 feet across.

You could spread your heat from your Fresnels using oil in coils, but you would have to add a powered pump to circulate the fluid. So much for "the Sun did it!"

[Nitack]

Originally Posted by Turtle

You could spread your heat from your Fresnels using oil in coils, but you would have to add a powered pump to circulate the fluid. So much for "the Sun did it!"

Not necessarily. If you had the Fresnel heat a reservoir of fluid below your coil and made it a circular system, the difference in density of the cooler liquid and hotter liquid would cause a natural current or flow to develop and the heat would circulate that way.

[Turtle]

Originally Posted by Nitack

Not necessarily. If you had the Fresnel heat a reservoir of fluid below your coil and made it a circular system, the difference in density of the cooler liquid and hotter liquid would cause a natural current or flow to develop and the heat would circulate that way.

Agreed. I do think however that the difference-circulation is so slow that getting useable work from it, as in making charcoal, presents some engineering challenges that pumping isn't susceptible to.

That's all I got; my sunny Dutch disposition may return when the Sun does.

[Nitack]

It might also be prudent to point out that super heating oil might create a very dangerous situation. Once super heated it will be much more easily burned.

Good news, I will be able to resume my experiments soon as in a few months I will be moving to a place that has room for my experimentation.

[freeztar]

Originally Posted by Nitack

Good news, I will be able to resume my experiments soon as in a few months I will be moving to a place that has room for my experimentation.

Same here.

The sun is already getting high enough to be useful. Unfortunately my stand took a hit from a falling limb and lost a leg. My roomate then dragged it across the yard, which broke two more legs.

So I just need to rebuild the legs and I'm ready to go.

[Divegod]

Sorry if this is the wrong area, as Ive read a number of 'making charcoal with solar energy' threads today.
It seems to me that one of the huge difficulties is transferrence of concentrated heat to the biomass. Barring any very complex solutions, it seems that one could take advantage of heat conductance in metal to accomplish this without focusing the rays directly on the pyrolisis chamber. Heres what I mean:
Dig a small trough deep enough to set both the pyrolysis chamber (a small metal trash can would seem sufficient. A 55 or 30 gal 'oil drum' if you want/need something more sturdy) and an additional 1-2ft of clearance to one side. Set thick section of metal plating (something like they use to cover roadwork ditches. An inch thick should suffice) on some bricks in the bottom of the pit. Set metal pyrolysis chamber on this. Fill around the chamber with dirt, leaving 1ft of the metal liner exposed. Concentrate solar energy on the metal plate, which would conduct the heat to the pyrolysis chamber, beginning the char process. If you dig the trough on an east west axis, and leave a sloping end on the side away from the pyrolysis chamber, you should be able to take advantage of several hours of sunlight from morning to mid day with a fresnel lens mounted to track sunlight. If that is insufficient to create temps needed, an identical arrangement could be used on the west side to create an almost full day of heat concentration and transfer to metal plate, thence to pyrolysis chamber.
The pyrolysis chamber would have at least half its surface on the submerged portion insulated via earth (other surface/sides exposed by the trough), and the heat accumulation and retention in the metal plate (insulated from below by air and earth and protected from winds) should be sufficient to maintain a fairly high temp. Let me try to illustrate a cross section


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\____|_|____/



Sorry, this is crude, but on the uppermost level I show two Fresnel lenses flanking the pyrolysis chamber. Lowest point is the metal plate. Side of the trough shown sloping to allow entrance of sufficient sunlight/angling of Fresnel lenses to accomodate rising and then setting sun.
Okay, sorry, my first post, maybe I just got excited.

Divegod

[Turtle]

Originally Posted by Divegod

Sorry if this is the wrong area, as Ive read a number of 'making charcoal with solar energy' threads today.
...
__ __
____|_|____/


Sorry, this is crude, but on the uppermost level I show two Fresnel lenses flanking the pyrolysis chamber. Lowest point is the metal plate. Side of the trough shown sloping to allow entrance of sufficient sunlight/angling of Fresnel lenses to accomodate rising and then setting sun.
Okay, sorry, my first post, maybe I just got excited.

Divegod

Welcome aboard. We love excitement. Let's not confuse crude with simple.

I think you have the right idea about using some massive steel in a Fresnel setup to keep it from burning through. The rest that you describe sounds practical, and only adaptation to a specific circumstance will tell the tale.

That's a wrap.

[freeztar]

Originally Posted by Divegod

Sorry if this is the wrong area, as Ive read a number of 'making charcoal with solar energy' threads today.
It seems to me that one of the huge difficulties is transferrence of concentrated heat to the biomass....
Okay, sorry, my first post, maybe I just got excited.

Divegod

Great post! Enthusiasm is very much welcome here.

The main problems I see with your idea is that a) expensive materials and b) how do you shape 1" thick steel plates to form close contact with the chamber?

Another thought about your idea...Why not start on a smaller scale? A trashcan sized operation would require a lot of resources and work. I suggest starting small to test the efficiency first.

I've been considering trying out the oil filled copper tubing technique suggested earlier in this thread. Properly designed, it might just work.

[Divegod]

Yes, the metal plate would likely be a bit expensive. The copper coil idea makes sense, but I wonder if it can sustain the temps being discussed/used. If it can, why not just route hot copper tubing into the chamber itself. That way you can heat the mass, but not have to worry about the containment/pyrolysis vessel being able to withstand the heat? Frankly, those are some of my top concerns when working with a concentrated beam of heat like is produced by a Fresnel. You can diffuse the beam a BIT, but you rapidly lose sufficient heat in that manner, and you have to have pretty precise adjustments. I think using some sort of impervious material to conduct the heat to the vessel is going to be part of the solution....Im going to price out some plate steel. Maybe its not as expensive as Im afraid it is.
Another thought: using a concrete block lined pit and heating, thru an opening, to a thermal mass (Again, plate steel?) that lies within the pit. Alternatively, heating a tubing and running that thru the pit. Hmmm, now Im going to have to try some variations.....Gotta get a Fresnel.....Ack! Another experiment!
DG