Solar Parabolic Trough Charcoal Oven

[Nitack]

Greetings my fellow nerds. I have not lost my interest in this, but have lost my testing facility. Moved out of the house I own and have been renting it out. My apartment is obviously not a suitable testing ground, so I did try continuing my research at the house. Sadly it REALLY freaked out the tenants. A bunch of sorority girls who just saw spontaneous smoke and me wearing welding goggles...

Unfortunately my efforts to save the planet are on hold for the moment.

[freeztar]

Originally Posted by Nitack

A bunch of sorority girls who just saw spontaneous smoke and me wearing welding goggles...

I could totally envision that.

I know the pain of testing grounds as I'm renting the basement of my friend's house. As I was finishing up on my stand yesterday, my friend told me that he does not want the lens and stand to be left outside. I didn't plan on leaving the lens outside, but the stand is much to big for my small space in the basement. So I have to figure out something there...
He's apprehensive about me using it there, but he'll be out of town this weekend, so....

[freeztar]

Originally Posted by davidgmills

I don't get it. Apparently posters on this thread do not appreaciate the problem because people apparently have never made charcaol.

I repeat, making charcaol does not take any kind of sustained external heat.

I think you're missing the point David. There's a million ways to skin the cat. This thread is about using the sun's energy to create charcoal. It started with a solar parabolic trough idea and has migrated to the same concept using fresnel lenses. It's easy enough to start a fire with the lens and make charcoal using your method. It's much more challenging to use the sun for pyrolysis at VERY high temperatures.

It's really just for the fun of science and experimentation.

[davidgmills]

freeztar:

What do you consider a high temeperature? Terra Preta charcoal was presumably made in temps in the 400 degree F range or less.

From my playing around, the real problem seems to be with variations in heat. Hot spots create areas where the biomass turns to ash. To me the danger of high heat would be in creating ash. So a system that avoided hot spots would have some real value.

I do know however that there are some charcoals that are made in temps of 800 degress or more. I presume that to make these there would have to be some mechanism to limit air to keep the biomass from turning to ash.

No one seems to know whether these charcoals make good terra preta though.

Is your idea to make charcoal from a near zero oxygen system and to drive out the water, gas and oil in a near zero oxygen environment? If so, what would be the advantages of this? Just curious.

[freeztar]

Originally Posted by davidgmills

freeztar:

What do you consider a high temeperature?

Well, the fresnel lens I have is capable of generating temps around 2000 degrees F. That's high temps!

Terra Preta charcoal was presumably made in temps in the 400 degree F range or less.

Yes, I've read that as well, and it makes sense if you consider their technology.

From my playing around, the real problem seems to be with variations in heat. Hot spots create areas where the biomass turns to ash. To me the danger of high heat would be in creating ash. So a system that avoided hot spots would have some real value.

With pyrolysis, you don't get ash presumably. Anytime you introduce O2, you are going to have some burning occuring.

I do know however that there are some charcoals that are made in temps of 800 degress or more. I presume that to make these there would have to be some mechanism to limit air to keep the biomass from turning to ash.

With pyrolysis, you not only limit air, you eliminate it completely. No O2 allowed.

No one seems to know whether these charcoals make good terra preta though.

There's a good way to find out.

Is your idea to make charcoal from a near zero oxygen system and to drive out the water, gas and oil in a near zero oxygen environment? If so, what would be the advantages of this? Just curious.

One possible advantage is a more pure form of char. This would be beneficial for using on the grill, where you don't want impurities being burnt. I also suspect that creating charcoal under high temps will dramatically speed up the process. But you see, until I experiment, I will never really know.

These are the types of questions we seek to answer.

[freeztar]

I was able to do my first trial on Saturday. Unfortunately, I only had about 20 minutes of direct sunlight. The sun's inclination at this time of year is not ideal for testing. Other parts of the yard became lit, but it would require moving the assembly multiple times and I lost my help (roomate) after the first 20 minutes.

Anyhow, I was able to concentrate the lens on a peice of black pipe that contained yard waste (leaves, twigs, etc.) shoved into the open end (other end sealed off). The concentrated beam almost immediately started vaporizing my layer of black paint. I was able to make the pipe glow red in a spot about the size of a dime. Yet, no charcoal produced.

I think the biggest challenge is going to be finding a way to spread the heat. Also, I need to find another area to test at as my yard is too full of trees.

[Turtle]

Originally Posted by davidgmills

...
I do know however that there are some charcoals that are made in temps of 800 degress or more. I presume that to make these there would have to be some mechanism to limit air to keep the biomass from turning to ash.

No one seems to know whether these charcoals make good terra preta though. ...

The high temperature-no-oxygen charcoal is termed "activated charcoal", and is virtually pure carbon. From what I've read here, and at sources linked to from here, it is not desirable for terra preta. The low temp charcoals, termed "horticultural charcoal", still contain plant reisns etcetera that support the microbial colonies that foster many of the desirable qualities of terra preta.

Originally Posted by Freeztir

...
Anyhow, I was able to concentrate the lens on a peice of black pipe that contained yard waste (leaves, twigs, etc.) shoved into the open end (other end sealed off). The concentrated beam almost immediately started vaporizing my layer of black paint. I was able to make the pipe glow red in a spot about the size of a dime. Yet, no charcoal produced.

I think the biggest challenge is going to be finding a way to spread the heat. Also, I need to find another area to test at as my yard is too full of trees. ...

You can spread the heat by refocusing the beam so that it covers a wider area. Having the end open isn't going to work as the heat escapes. With the pipe (is it galvanized stove pipe like I used for the trough?) I think sealing it nearly completely will work, leaving just enough opening to allow steam and volatiles to escape. Here again I think the cast iron Dutch oven will perform better than the pipe at spreading the heat and maintaining adequate air-tightness. Keep up the good work!

[freeztar]

Originally Posted by Turtle

You can spread the heat by refocusing the beam so that it covers a wider area.

That was the plan, but the temperature dropped A LOT when I did that. Placing a stick exactly in the focal point caused it to burst into flames immediately, whereas the flames went out and it just smoked if I moved it even an inch either way. But I plan on experimenting with this more. I need to get a high temp thermometer, but all that I've found are VERY expensive.

Having the end open isn't going to work as the heat escapes.

The open end is plugged so tightly with leaves, that it should act as an insulator.

With the pipe (is it galvanized stove pipe like I used for the trough?)

No, I wanted to go with a real small peice of pipe just to get results, and then move up from there. But I think I will need to rethink it as the pipe walls (plumbing pipe) are fairly thick, which will probably limit heat transfer. The closed end is a fitted, screw-on cap. You can see now why I don't want to cap both ends.

I think sealing it nearly completely will work, leaving just enough opening to allow steam and volatiles to escape.

I need to find that sweet spot where I can build up a little pressure, while remaining safe.

Here again I think the cast iron Dutch oven will perform better than the pipe at spreading the heat and maintaining adequate air-tightness.

Yes, I completely forgot about the dutch oven. I've been wanting one for camping anyways, so I might as well get one. The only problem I see with the dutch oven is that it probably has fairly thick walls as well (all the cast-iron I've ever seen was pretty thick). So then it becomes a trade-off of having a better insulated container and more even heat transfer vs. not efficiently transferring the heat. I'll try to work out the optimal balance if I am able (off to look up equations now). [/quote]

[palmtreepathos]

Freez I wish you were up here in the north metro area, we could have such fun with our fire power... lol I have a nice sunny yard AND a dutch oven!

My son was in town over the weekend and was fascinated with my mirrored dish, and learned first hand about that "sweet spot" He asked what it is and I told him right now just an expensive cigarette lighter NO I don't smoke I just make smoke... Now that it has rained really well maybe they will let me make charcoal again, I will have to call the fire house to see what the burn rules are this year.

This isn't me but you can see what my toy is like here....

YouTube - 18" Solar Concentrator - Burning...

I need to make a stand for it like this one but I would like it so I don't have to bend over it as it is quite dangerous for the eyes, even a momentary glimpse at it leaves a print on the retina for hours, even from 5 feet away! It's eggzackly like looking at 200 sunspots...

[freeztar]

Originally Posted by palmtreepathos

Freez I wish you were up here in the north metro area, we could have such fun with our fire power... lol I have a nice sunny yard AND a dutch oven!

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?

My son was in town over the weekend and was fascinated with my mirrored dish, and learned first hand about that "sweet spot" He asked what it is and I told him right now just an expensive cigarette lighter

This isn't me but you can see what my toy is like here....

Fun! It looks fairly simple to track the sun with one of those.

I need to make a stand for it like this one but I would like it so I don't have to bend over it as it is quite dangerous for the eyes, even a momentary glimpse at it leaves a print on the retina for hours, even from 5 feet away! It's eggzackly like looking at 200 sunspots...

I recommend, actually VERY STRONGLY URGE, welding goggles/mask. I got a welding mask off ebay for about $12 that allows you to flip the dark lens up so you can see normally. Even with the welding mask, I try not to stare directly at the focal zone.