Solar Parabolic Trough Charcoal Oven

[Nitack]

So I just had a thought, and feedback would be much appreciated. Right now we are trying to use the fresnel lens to transfer heat to a container (dutch oven) and from there to our organic matter. But why do we need the dutch oven? Why not just use a glass box/tube? With tempered glass the light can pass through right to our organic matter. If it is packed there is not much oxygen and what there is will quickly burn off, from there the chared matter will conduct heat very well and will pass it through contact with the rest of the material. Of course we would need an outlet for gas and such. But why do we need the dutch oven if with the fresnel we can heat the medium directly?

[freeztar]

@GPS

Thanks for the info and for posting your results. I look forward to seeing the videos.

 

@Nitack

Your idea makes sense, but I wonder if glass is up for the task. I cracked pryex in a matter of 15 secs. with only a 8"x10" lens. I think it cracked because of the rapid heat change. Perhaps the tube could be pre-heated with an unfocused beam to prevent the cracking from a sudden temperature spike. :confused:

[Nitack]

Okey dokey, here is what I have found.

 

Our ideal working material would be VYCOR. 96% pure silica and can withstand temperatures into the 2k range. At almost a thousand dollars for a 50 ml crucible with lid it is not going to happen!

 

Pyrex could handle it, but not your standard pyrex, we are talking the Pyrex VISTA stuff. top operating temperature in the 800s. It would be pushing the envelope and we would have to get the lighting just right or risk cracking the damn thing.

[freeztar]

Pyrex could handle it, but not your standard pyrex, we are talking the Pyrex VISTA stuff. top operating temperature in the 800s. It would be pushing the envelope and we would have to get the lighting just right or risk cracking the damn thing.

 

Yeah, that's pretty close to the 700 degrees we are looking to obtain. Not only that, but there is pressure to deal with as well which seems like it would compromise the system with such a small margin of error, even with a vent. :shrug:

 

What about a solar oven for the recepticle? In other words, a box within a box with the outer box having a small window of glass where the concentrated beam can penetrate and heat the black box inside. The outside box acts as insulation for the inner box and should not get as hot as the inner box.

:shrug:

[GREENPOWERSCIENCE]

Consider a cement casted box with a glass covering. To test it and save time just use a standard cement block or corner block. Pour cement in the bottom to make it air tight and lay clear sheet of glass on top. Cement is a good insulator. If you need more depth to save the glass, cement 2 blocks together. A cement block will hold water for several hours. That should be air tight enough. If this works, cement ovens are easy to make.

[freeztar]

Consider a cement casted box with a glass covering. To test it and save time just use a standard cement block or corner block. Pour cement in the bottom to make it air tight and lay clear sheet of glass on top. Cement is a good insulator. If you need more depth to save the glass, cement 2 blocks together. A cement block will hold water for several hours. That should be air tight enough. If this works, cement ovens are easy to make.

 

That sounds like it might work. I'm assuming you have experience making these? Were you able to get a temperature reading inside the box using this method?

[GREENPOWERSCIENCE]

Leave or drill a small hole, place a probe thermometer (High Temp Model) in and close up with cement paste. I have a simple design for the oven. I built one for just cooking/using yard debris for boiling water, it worked great. I have since recycled it and it is now filler for a poured cement wall. That one was big 3' x 3' x 2.5' x 2" thick and it took heat fine.

[GREENPOWERSCIENCE]

It works.

[Nitack]

It works.

 

WOO HOO! Happy days are here again... now please elaborate on what exactly it is that works :D

 

Have you tested a cement oven and gotten it up to the required temperature? Have you produced coal? Have you found a way to focus the light of a hundred Fresnel lenses into one small SOLAR DEATH RAY? :)

[freeztar]

I got my 44x33 lens yesterday and plan on building a stand this weekend (hopefully). :)

 

I might try the concrete oven idea, but before I do, I think I might try some cinder blocks and pyrex. A large concrete box is nice, but not very portable, which is important for my situation. Also, we do not need an airtight seal as the pyrolysis gases need to escape, so some cinder blocks should work fine. I'm not sure of the R value of cinder blocks, but I would guess it is lower than concrete due to the porosity.

 

BTW, GPS, I saw your video with the mirrors and was pretty impressed. That seems like a lot of work to setup. Earlier in this thread we had discussed using mirrors, but on the other side of the lens. Do you have any experience with this?

[GREENPOWERSCIENCE]

Yes, a mirror can redirect sunlight so 2 lenses pointing the same direction can be directed in exactly the same spot but you have an angle issue. It would never make it inside a box. Works for surface stuff, metal etc. Almost impossible to track the sun unless you have free floating hinge armed stands. If you need any help with your regular stand, let me know or copy the photo from my website. The center support gives tons of stability but creates a fire hazard and if you use metal it is tempting to grab it to readjust your lens. No big deal unless it is hot. I turned around for one minute a few years ago and the wind shifted the lens horizontal. I refocused the lens to my target and grabbed the metal bar to readjust the stand. My rubber based glove melted right to it and burned. No harm done but I took that bar off asap.

 

Good luck Freeztar

[freeztar]

Yes, a mirror can redirect sunlight so 2 lenses pointing the same direction can be directed in exactly the same spot but you have an angle issue.

 

I'm not sure I understand. I was talking about using one lens to focus onto a mirror, which would then reflect onto a surface (a dutch oven in this case).

 

Almost impossible to track the sun unless you have free floating hinge armed stands.

 

What is a free floating hinge armed stand?

 

If you need any help with your regular stand, let me know or copy the photo from my website.

 

I might take you up on that. I like your stands, but I'm still trying to brainstorm a more adjustable setup. Nonetheless, I'll probably make a regular one to start with. I'm going shopping for the materials on Saturday. We'll see..

 

The center support gives tons of stability but creates a fire hazard and if you use metal it is tempting to grab it to readjust your lens. No big deal unless it is hot. I turned around for one minute a few years ago and the wind shifted the lens horizontal. I refocused the lens to my target and grabbed the metal bar to readjust the stand. My rubber based glove melted right to it and burned. No harm done but I took that bar off asap.

 

Yeah, I'm not too fond of the center support for the reasons you mentioned. I imagine it will be stable enough without it for my purposes.

Good luck Freeztar

 

Thanks

[GREENPOWERSCIENCE]

Sorry about the confusion. Yes a single mirror works in the winter or evening or further north of the equator. Here in Florida during the summer you are working almost vertical and the pot gets in the way. Lift the pot 10 " above the mirror and adjust lens accordingly. Any closer and the spot will damage the mirror.

[GREENPOWERSCIENCE]

What is the plan of use for the coal?

[freeztar]

What is the plan of use for the coal?

 

This is explained in the first post , but it's always nice to renew the purpose.

 

The char will be used as an agricultural soil amendment in an attempt to mimic Terra Preta soils of the Amazonian basin.

Here's the thread that started it all.

 

The bonus of using char in the soil is carbon sequestration.

 

So, rather than burning material to make the char, we are attempting to find a solar method to produce the char.

[Michaelangelica]

Is this of interest?

Quite a detailed article with lots of info and links 9/10

Hot off the grid / Solar ovens utilize nature's rays for energy-efficient, everyday cooking -- even in foggy San Francisco

 

Hot off the grid

Solar ovens utilize nature's rays for energy-efficient, everyday cooking -- even in foggy San Francisco

Solar cookers like the Sun Oven can maintain temperatures of 350 degrees or higher and start around $230. Less-insulated and simpler versions such as one called the CooKit cost about $32 and cook food in the low to mid 200 degrees -- hot enough to boil water, which is all you need for most cooking.

 

Is that 350C? If so, thats all you need to make good char.

[freeztar]

Is this of interest?

Quite a detailed article with lots of info and links 9/10

Hot off the grid / Solar ovens utilize nature's rays for energy-efficient, everyday cooking -- even in foggy San Francisco

 

 

 

Is that 350C? If so, thats all you need to make good char.

 

That would be 350 degrees F as it is a US paper in your link.

 

Nonetheless, a solar oven is what I have in mind in conjunction with the fresnel lens. I still need to build my stand though. It rained all weekend here, which is good though.