Solar Parabolic Trough Charcoal Oven

[DougF]

Thanks Michaelangelica,

I found them very interesting,

most of the new stuff is based on this technology and they will tell you about the improvements assuming you already know how they got there.

 

This fills in some of the blanks for me, Thanks. :(

[Nitack]

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

OK, so this got me thinking really hard ;):(:)

 

Introducing the copper piping into the material might be a possibility. That would take some of the heat transfer issues out of play. Also, dropping your vessel into earth would help insulate it too. Here is my thought...

 

Method

Creating a reservoir as your base. In here you would fit either water (safe choice) or oil (no so safe choice but better heat transfer). This reservoir should be large enough for your vessel (dutch oven or eventually trash can) to sit on top. Copper piping could be pumped directly from the reservoir into the vessel. The piping would coil through the vessel and distribute heat at multiple points. The piping would exit the vessel at the top, and connect back to your reservoir at the base. This way if you keep the heat focussed on the reservoir heat will transfer up the piping.

 

Benefits

• Using a closed loop system will help you to retain heat.
  
• Having the coils in direct contact with the biomass will allow for more heat to hit the medium.
  

 

Possible issues

• If you use water (the safer option), it is possible that the steam produced will never get up to the superheated thresh hold you need.
  
• If your steam does get up to the thresh hold you need, the huge increase in pressure will very likely blow a hole in your closed loop at a weak point and you start losing heat and water.
  
• If you use oil, you are creating a very serious fire/safety concern. Superheated oil burns very quickly when exposed to oxygen and an ignition source... like a concentrated sun beam. This option might land you on the radar of local cops and fire departments...
  
• Copper tubing is extremely expensive.
  
• 
  

[Divegod]

Very good summary of my concerns about using using tubing and a liquid conductor. Its just primed for failure when doing that sort of thing on an amateur level. Compressed water vapor can seriously injure, and oil is even more dangerous. Solid state system would be the way to go for a backyard unit. Fewer moving parts is usually best for backyard type units. Murphys law and all that.....

You also touch on my concern about a vessel that holds the items to be carbonized vs. a 'dutch oven' type of arrangement. When concentrating solar, you get a very hot point source. Diffused heat would be much easier to work with and much less likely to rupture the carbonization chamber, which is my primary concern (release of hot gases and contamination with oxygen being the main drawbacks of such a failure). Thus, Im left with a system that relies on the conduction properties of a more robust primary recipient of concentrated solar radiation in close contact with a carbonization chamber. The primary material can withstand the concentrated beam, while diffusing this heat through its mass and conducting this heat to the carbonization chamber. Getting involved with tubing and a liquid conductor is a job for well funded professionals. Static conduction (!?) of the heat is preferrable from a safety, simplicity and probably materials cost standpoint.

DG

[Nitack]

DG, love your insights... Just as an FYI though, about a year ago some of us did some very involved testing trying to use similar systems to what you propose. The results were not promising. Too much heat was lost to simple air flows. partially burying the vessel might work, but I am not sure you will actually be able to get it hot enough. even a slight breeze will sap out heat. That was when we started postulating that copper piping might be the answer. I still think that it might be the best option, if not inside the vessel, surrounding the outside.

[Nitack]

My friends I think i may have our answer if we wanted to use Divegods methodology. Steel plates are not the answer... however what about the Miracle Thaw? Read this, Skeptic Friends Network - Miracle Thaw - The Bogus Miracle. It is not great for it's designed use, but for our purposes it is perfect. Made from metal that easily conducts ambient heat... so we raise the temperature on one part of the plate and the rest of the plate will swiftly get that hot... solar powered cook top!

[freeztar]

I'm not sure about that Nitack. Apparently it is just teflon coated aluminum.

 

There are pans with heat diffusers built into the bottom of them, but you'd still lose a lot of heat from the sides and you would almost have to use the buried pot/mirror idea that we discussed last year.

[Nitack]

I'm not sure about that Nitack. Apparently it is just teflon coated aluminum. :confused:

 

There are pans with heat diffusers built into the bottom of them, but you'd still lose a lot of heat from the sides and you would almost have to use the buried pot/mirror idea that we discussed last year.

 

Aluminum is a great heat transferring material, hence we use it for pots and pans. So although we don't need the thawing plate, for $10 at a cooking store, we won't worry about ruining it. Although you can just use an old pan... big thing as always is heat loss... so perhaps burying most of it and let the earth insulate?

[Nitack]

So I have been giving this more thought lately. I do think that aluminum will be the way to go. The way that it conducts ambient heat will achieve the same heat disbursing effect that we were looking for with the coil and oil setups. Our main concern will still be heat loss though. Even a slight breeze is going to kill us, so I have a few thoughts.

 

Goal:

To get the heat inside a sealed or semi-sealed container to reach 400+ degrees F. The idea of this, at least when we start, is to bring a rather small container to the heat we want

 

Method:

Our active methods have all centered around heat concentrating setups. My preference is the use of a Fresnel lens because I find the "Solar Death Ray" angle appealing. My design (to be tested in a month or so when I am out of my apartment and back in a house) is to use my fresnel lens focused on an aluminum plate/sheet that our vessel will sit on top of. For a vessel I had been using a cast iron dutch oven. I am going to switch from that to this:

Gibraltar Industries Standard Size Black Premium Aluminum Rural Mailbox - ALM110B0 at The Home Depot. It is an aluminum mail box. direct contact with the aluminum plate should allow it to heat quite nicely. Finally, the issue of wind has come up to us many times. I think what might be a cheap and easy fix (previously suggested by Freeztar, is to build surrounding walls using cinder blocks. And, to complete the insulation and even create a greenhouse effect... a sheet of glass to go over the top. That way the heat should all be trapped inside there, getting us high enough to create charcoal.

[freeztar]

I like the "greenhouse" idea. It's like a solar oven. I wonder how hot those can get?

[Nitack]

I like the "greenhouse" idea. It's like a solar oven. I wonder how hot those can get?

 

I actually thought of a passive design with the same setup. Put your vessel in the center, put angled mirrors on all four sides to redirect light, and a sheet of glass up top to trap heat but let light through.

 

Interesting thought going back to the parabolic mirror and pipe design...

 

Why not run the pipe through a cinder block structure like this? One of the main reasons that the pipe did not work was probably it's being exposed to wind, however it was still able to get up over 200 degrees... so why not shield it from the wind?

[MarkB]

I actually thought of a passive design with the same setup. Put your vessel in the center, put angled mirrors on all four sides to redirect light, and a sheet of glass up top to trap heat but let light through.

 

Interesting thought going back to the parabolic mirror and pipe design...

 

Why not run the pipe through a cinder block structure like this? One of the main reasons that the pipe did not work was probably it's being exposed to wind, however it was still able to get up over 200 degrees... so why not shield it from the wind?

 

This seems the right idea to me. The sunlight is providing an energy (heat) input, to get a high temperature you just need to insulate the system well enough that it loses heat slower than it comes in.

 

I would be trying to design something with roughly 2 boxes, one above the other :

- the bottom one would be enclosed on 3 sides (maybe partly dug into the ground?) with a glass cover on the 4th side. Light would enter through here and roughly focus on a metal receiver which would form a pillar of some kind inside the box.

- the box on top would be your chamber to put stuff in and would sit on top of the heated pillar. This would be heavily insulated on all sides and the top to retain the heat rising from the heating element. You would need a air escape somewhere and I imagine that would be best as some kind of hole/pipe at the bottom of the oven chamber leading down to minimize hot air loss.

 

The idea is that light doesn't have to be accurately focused on the heating pillar - my understanding is that it doesn't make any difference how tight you focus it, a given size of lens is going to supply the same total energy whether it's going into a half-inch spot or into a 4 inch spot ... the point is that you want to keep that heat in there. So you enclose the heating element behind glass/similar and cover the oven itself up completely. (I'm not good on insulation at these temps, so suggestions gratefully received.)

 

A question from me - how many hours would this need to be getting the sun? I'm wondering if you could half-dig this into a South or SW facing slope to help with the insulation? I'm thinking maybe a foot wide window, with an 8 inch heating element a couple of inches behind it, would allow a fair range of angles, assuming your lens arrangement could be moved around it ...

 

MB

[freeztar]

Mark, I would need to see a diagram to fully envision what you are proposing. I think I have the idea, but I'm not quite sure.

 

A question from me - how many hours would this need to be getting the sun?

 

It depends on lots of factors such as efficiency of the system, wind, cloudiness, etc.

 

I'm wondering if you could half-dig this into a South or SW facing slope to help with the insulation? I'm thinking maybe a foot wide window, with an 8 inch heating element a couple of inches behind it, would allow a fair range of angles, assuming your lens arrangement could be moved around it ...

Ah yes, the moving problem...

When I was doing my initial trials, I had to move the stand and or lens every couple of minutes to maintain a strong beam. We've proposed solutions to this earlier in the thread, but all propositions are quite complex/expensive. If you have any ideas on this, I'd sure like to hear them.

 

Welcome to Hypography btw.

[Turtle]

...Ah yes, the moving problem...

When I was doing my initial trials, I had to move the stand and or lens every couple of minutes to maintain a strong beam. We've proposed solutions to this earlier in the thread, but all propositions are quite complex/expensive. If you have any ideas on this, I'd sure like to hear them.

 

Welcome to Hypography btw. B)

 

 

I heard this guy on the radio the other night; he is using an array of fresnels on a single mount, and drives it by computer to track the Sun. :) He said his steam system operates at ~400 lb/in^2, and that he & his crew have custom made a turbine to drive a generator. You might get some ideas here: B) >> Xenotech Research Forum :: View topic - Solar energy

[Nitack]

I read Physics for Future Presidents by Richard Muller when it came out. Fascinating book. Among the many things I learned from the book, one was about the feasibility of a solar powered car. A car that ran directly off of sunlight is in fact not possible. The reason that it is not possible is that a square yard of surface receiving sunlight contains roughly the energy equivalent of one kilo-watt of power. This was disheartening for those dreaming of a direct solar car when you take a couple more steps down the line. A car has about 2 sq. meters of surface space. 1 KW is equal to 1 horse power. The most power you could get directly from the sun to power a car at 100% efficiency is 2 horse power, which any car enthusiast knows is no where near the power of even the smallest/weakest automobiles. So died my dream of an directly solar powered car. Doesn't exclude something with a lot of batteries and that has time to recharge between usages though.

 

This realization about the power contained in a square yard of sunlight has a great deal of relevance for those of us who are trying to produce solar powered charcoal makers. We are trying to focus a large area of sunlight into a small area in order to use the energy of a larger area to heat a smaller area to the temp we need.

 

So the question now may better be defined for us to figure out how to make a solar charcoal maker. How many KW/volume does it take to reach a high enough temperature to create charcoal. I think this also highlights the necessity of insulation in order to create a compounding effect. Additionally, is it still a solar powered charcoal maker if you use a retort and burn the wood gas once it starts being released?

[Turtle]

I... This realization about the power contained in a square yard of sunlight has a great deal of relevance for those of us who are trying to produce solar powered charcoal makers. We are trying to focus a large area of sunlight into a small area in order to use the energy of a larger area to heat a smaller area to the temp we need.

 

So the question now may better be defined for us to figure out how to make a solar charcoal maker. How many KW/volume does it take to reach a high enough temperature to create charcoal. I think this also highlights the necessity of insulation in order to create a compounding effect. Additionally, is it still a solar powered charcoal maker if you use a retort and burn the wood gas once it starts being released?

 

I agree that we know all the theoretical constants at play to derive a theoretical design for a charcoal cooker. Really that's the basis for our experiments. For my design starting this thread off, I further agree that insulation is very important. Here again, the theoretical/proper solution is a Dewar tube around the receiver holding the material for charcoalfication, but the practical problem is getting that made.

 

If it is the Sun making the wood gas, then yes the system is still 'solar powered'. :hihi:

[freeztar]

I heard this guy on the radio the other night; he is using an array of fresnels on a single mount, and drives it by computer to track the Sun. :) He said his steam system operates at ~400 lb/in^2, and that he & his crew have custom made a turbine to drive a generator. You might get some ideas here: :) >> Xenotech Research Forum :: View topic - Solar energy

 

I found this somewhat randomly and found it especially relevant for this thread. :)

 

Solar PV tracker

[Michaelangelica]

Is this article any help?

(I haven't been following the discussion. I can't make anything that says together for more than 5 mins)

 

Solar Cooking Demonstration in San Diego

Solar Cooking Demonstration in San Diego : Eat. Drink. Better.

They say it gets up to 330 degrees but it dosen't say if that is F or C.

If it is Centergrade it is not far to go for charcoal production (+50-150?)