Solar Parabolic Trough Charcoal Oven

[Turtle]

Originally Posted by Turtle

with the Fresnel or parabolic dish any increase in size of the 'roundish' shaped receiver just puts it outside the focus and so requires multiple load/process/extract cycles.

I'm not sure I understand you here.

 

OK; I'll try to kill as many birds with one throw as possible.

First the one at the top of the pecking order, which is a affirmative secular "the devil is in the details."

The detail I meant to convey above. Suppose you have a dish and a trough which have a focus point on a plane that is the same in one dimension (call it height). The dimension of the focus plane width for the dish is also the same as its height (circular) wheras the width of the focal plane for the trough is as long as the trough.(rectangular) All else being equal, the trough can accomodate a larger receiver and so expose a larger area to focussed Sun. Let me know if that's still not clear or if you think it's mistaken.

The rest of the flock is one detail after another, because all things are not equal in much of this at all. All of the plans put forward here appear feasible to me given the proper 'this material' and the correct 'that measure' in the such-n-such a 'given circumstance'...well, you get the idea.

The upshot is, if you have an idea then give it a try and let us know how it works out. :shrug:

PS The water storage idea will work, but even small power generation at night I think would require a very large reservoir. I think a water tower tank in every yard is a good idea for many reasons outside the scope of this thread.

[freeztar]

OK; I'll try to kill as many birds with one throw as possible.

First the one at the top of the pecking order, which is a affirmative secular "the devil is in the details."

The detail I meant to convey above. Suppose you have a dish and a trough which have a focus point on a plane that is the same in one dimension (call it height). The dimension of the focus plane width for the dish is also the same as its height (circular) wheras the width of the focal plane for the trough is as long as the trough.(rectangular) All else being equal, the trough can accomodate a larger receiver and so expose a larger area to focussed Sun. Let me know if that's still not clear or if you think it's mistaken.

 

Roger that. But getting back to what Nitack stated, the surface area of the dish/trough should determine output, not the surface area of the receiver. If a 42" fresnel lens can melt glass, then there is something to be said for a 'circular' approach. A 42" fresnel pointed at a steel drum (slightly off focal) should produce very high temperatures even at the 'antipode' of the surface being heated.

 

The rest of the flock is one detail after another, because all things are not equal in much of this at all.

Agreed.

 

All of the plans put forward here appear feasible to me given the proper 'this material' and the correct 'that measure' in the such-n-such a 'given circumstance'...well, you get the idea.

The upshot is, if you have an idea then give it a try and let us know how it works out.

 

I hope to build a dish at some point. If I can bring the DIY cost below the cost of buying a prefabricated parabola, then I will be more motivated. I still might do it anyway, for kicks, but at present it is a 'top-of-the-shelf' pursuit.

 

PS The water storage idea will work, but even small power generation at night I think would require a very large reservoir. I think a water tower tank in every yard is a good idea for many reasons outside the scope of this thread.

 

Indeed. Perhaps we should start a new thread, or multiple threads that can be spawned from this one.

I agree that you would need a very large elevated reservoir and a substantial turbine to reclaim the energy on demand. Batteries would still be efficient in this setup, but not as necessary as in a Stirling-dish. It would be a good setup for a landowner with lots of unused land, which met the topology requirements. I don't see potential for large scale applications of this principle, outside of dams of course.

 

What do you think about the PVC idea for making a parabolic trough/dish?

[Turtle]

Roger that. But getting back to what Nitack stated, the surface area of the dish/trough should determine output, not the surface area of the receiver. If a 42" fresnel lens can melt glass, then there is something to be said for a 'circular' approach. A 42" fresnel pointed at a steel drum (slightly off focal) should produce very high temperatures even at the 'antipode' of the surface being heated.

 

roger roger the experimental approach seems the right one.

 

 

 

Perhaps we should start a new thread, or multiple threads that can be spawned from this one.

 

build it & they will come.

 

What do you think about the PVC idea for making a parabolic trough/dish?

 

I think the resulting curve will be a catenary and not a parabola. Here's another thread we have on the DIY dish/mirror scheme. >> http://hypography.com/forums/science-projects-homework/7501-building-parabolic-mirrors.html?highlight=parabolic+mirrors

[Nitack]

Roger that. But getting back to what Nitack stated, the surface area of the dish/trough should determine output, not the surface area of the receiver. If a 42" fresnel lens can melt glass, then there is something to be said for a 'circular' approach. A 42" fresnel pointed at a steel drum (slightly off focal) should produce very high temperatures even at the 'antipode' of the surface being heated.

 

Whether you are reflecting the energy using a parabola or concentrating using a lens the amount of energy you start with is absolutely the same per area squared. What we are trying to do is refine how much energy is lost in the transfers and possibly increasing the surface area (extra lenses and mirrors) in order to increase the starting energy.

 

By spreading out the foci of the energy (parabola) we lose more heat energy because there is more area to lose is from. By focusing the heat energy into specific spots there is less surface area for which to lose the energy to the air and more will be transfered to the inner kiln where our carbonization will take place.

[freeztar]

I think the resulting curve will be a catenary and not a parabola. :) Here's another thread we have on the DIY dish/mirror scheme. >> http://hypography.com/forums/science-projects-homework/7501-building-parabolic-mirrors.html?highlight=parabolic+mirrors

 

I think you are right. While reading up on catenaries, I came across this tidbit:

Free-hanging chains follow the curve of the hyperbolic function above, but suspension bridge chains or cables, which are tied to the bridge deck at uniform intervals, follow a parabolic curve, much as Galileo originally claimed (derivation).

 

When suspension bridges are constructed, the suspension cables initially sag as the catenaric function, before being tied to the deck below, and then gradually assume a parabolic curve as additional connecting cables are tied to connect the main suspension cables with the bridge deck below.

Catenary - Wikipedia, the free encyclopedia

 

So it seems possible still, but requires more connection points to be winched down. Now where can I find some cheap wenches...:)

[freeztar]

What we are trying to do is refine how much energy is lost in the transfers and possibly increasing the surface area (extra lenses and mirrors) in order to increase the starting energy.

 

I like your idea of using additional mirrors and lenses, but is it really necessary? How much focused heat will be needed to char a steel barrel full? Remember, we don't want it TOO hot. Of course, that would be a good problem to have at this point eh? :)

[Nitack]

I like your idea of using additional mirrors and lenses, but is it really necessary? How much focused heat will be needed to char a steel barrel full? Remember, we don't want it TOO hot. Of course, that would be a good problem to have at this point eh? :)

 

I thought about that, about possibly having too much heat. My thinking was that we want more than one point of heat.

 

First, even with an insane temperature like 900 °F , it will still take quite a while for that heat to build up inside if it is only coming from one spot. By having multiple spots it would raise the inner temperature faster.

 

We also saw that even though Turtle was able to focus the energy of his parabolic trough, it did not capture enough heat to carbonize his materials. We don't know if it was an issue of energy loss or not enough reflecting area. This will ensure that we can capture enough energy to heat it up to 500+.

 

Finally, if we captured too much heat what would be our product? My understanding in charcoal making is that the hotter the kiln the more impurities are burned off, leaving you with purer charcoal. I checked and the melting point of carbon is 8000 °F. No way we will get up to that temp, meaning that most likely we will just have incredibly pure charcoal.

 

Added bonus, I have been thinking about this solar capture method and it could also be converted to form a very simple electric generator using some piping and a cars water pump and an alternator. In this case more heat = better. If we were able to generate electricity from this method we could power a solar tracker which would then allow this kind of generator to run all day long. If it were closed loop and we used something non-corrosive (not water) it could run continuously. In essence a solar generator without the costly silicon panels.

 

My mind is really flying on these ideas

[freeztar]

I thought about that, about possibly having too much heat. My thinking was that we want more than one point of heat.

 

That would certainly be ideal.

First, even with an insane temperature like 900 °F , it will still take quite a while for that heat to build up inside if it is only coming from one spot. By having multiple spots it would raise the inner temperature faster.

 

I agree. Though perhaps we could use something like copper coils around the barrel to conduct the heat more evenly?

We also saw that even though Turtle was able to focus the energy of his parabolic trough, it did not capture enough heat to carbonize his materials. We don't know if it was an issue of energy loss or not enough reflecting area. This will ensure that we can capture enough energy to heat it up to 500+.

 

I get the impression that Turtle thinks the area needed to be increased, but I'll let him speak to this.

Finally, if we captured too much heat what would be our product? My understanding in charcoal making is that the hotter the kiln the more impurities are burned off, leaving you with purer charcoal. I checked and the melting point of carbon is 8000 °F. No way we will get up to that temp, meaning that most likely we will just have incredibly pure charcoal.

 

While (nearly) pure charcoal (activated charcoal) is ideal for consumption purposes, it is not ideal for a soil ammendment. From what I've read, leaving a little bit of impurities in the final product increases the amount of wee beasties that take advantage of it. So there is an advantage to keeping a controlled temperature if you plan to use the char as a soil ammendment. Otherwise, I suppose it doesn't matter much.

 

Added bonus, I have been thinking about this solar capture method and it could also be converted to form a very simple electric generator using some piping and a cars water pump and an alternator. In this case more heat = better. If we were able to generate electricity from this method we could power a solar tracker which would then allow this kind of generator to run all day long. If it were closed loop and we used something non-corrosive (not water) it could run continuously. In essence a solar generator without the costly silicon panels.

 

This is something my friend and I have pondered in depth. We like the simplicity of the aeolipile. I can't seem to find efficiency numbers on it now, but it is quite efficient with super heated steam IIRC.

 

My mind is really flying on these ideas

 

I'll try to keep up. :) :)

[Nitack]

This is something my friend and I have pondered in depth. We like the simplicity of the aeolipile. I can't seem to find efficiency numbers on it now, but it is quite efficient with super heated steam IIRC.

 

I also like the super heated steam option, but the corrosion issue was something I was thinking about. Are you familiar with any non-corrosive liquides with a boiling point in the 150-200 range? Trying to increase the efficiency by reducing the amount of energy required to vaporize while negating corrosion. I thought of Methanol and Ethanol. They are both easy enough to come by. Methanol is actually produced in charcoal making. The question is will they corrode the system? I liked a system I read out using just a automobile water pump and an alternator because the parts are already mass produced and produce AC current so it does not have to be converted from DC.

[freeztar]

I also like the super heated steam option, but the corrosion issue was something I was thinking about. Are you familiar with any non-corrosive liquides with a boiling point in the 150-200 range? Trying to increase the efficiency by reducing the amount of energy required to vaporize while negating corrosion. I thought of Methanol and Ethanol. They are both easy enough to come by. Methanol is actually produced in charcoal making. The question is will they corrode the system? I liked a system I read out using just a automobile water pump and an alternator because the parts are already mass produced and produce AC current so it does not have to be converted from DC.

 

 

I'm not familiar with the corrossion issues. Perhaps the surface of the container could be coated with something to give it longevity, or maybe sacrificial annodes could be employed. :)

Perhaps a chemist will happen along and suggest some other methods...

 

Do you have a link for the water pump/alternator setup? It sounds promising.

[Nitack]

Here is an article on some MIT kids already working on this idea. I like the approach of the girl who wants to use a tesla turbine as opposed to the water pump but having a hard time finding a tesla turbine. If I could construct it the cost would go down considerably.

 

Technology Review: How To Build a Solar Generator

[Turtle]

We also saw that even though Turtle was able to focus the energy of his parabolic trough, it did not capture enough heat to carbonize his materials. We don't know if it was an issue of energy loss or not enough reflecting area. This will ensure that we can capture enough energy to heat it up to 500+.

 

We certainly do know. The trough was too small and the receiver needed insulating. Making the trough larger and insulating the receiver would have given me the temps I wanted. While we discussed ways to insulate the receiver tube, the preferred method is a Dewar tube. (using smaller diameter pipe for the receiver would reduce heat loss too and so raise the temp.)

 

I get the impression that Turtle thinks the area needed to be increased, but I'll let him speak to this.

 

OK I'll try this again. I was suggesting that a larger volume receiver in the trough is possible because the area of focus is larger. With a larger volume the process may take longer per

Whether you are reflecting the energy using a parabola or concentrating using a lens the amount of energy you start with is absolutely the same per area squared

but you don't have to change out the receiver contents as often.

 

...Trying to increase the efficiency by reducing the amount of energy required to vaporize while negating corrosion. I thought of Methanol and Ethanol....

:ebomb: :eek: Sounds like an invitation to disaster. Commercial solar trough reflectors use a synthetic oil as I recall. >> http://www.nrel.gov/docs/legosti/fy98/22589.pdf

 

So it seems possible still[bending tube into parabola], but requires more connection points to be winched down. Now where can I find some cheap wenches...

 

I would suggest drawing out a full scale parabola on papaer and using it as a pattern to make a wooden form, and then clamp your tubes to the wooden form while you secure it to that shape.

 

:cup: :shrug:

[Turtle]

... I liked a system I read out using just a automobile water pump and an alternator because the parts are already mass produced and produce AC current so it does not have to be converted from DC.

 

This is a bit misconstrued. Auto alternators are AC generators, but they contain a diode array that delivers DC at around 12 volts. The reason we don't have DC generators in autos anymore is because they increase/decrease their voltage as the engine speeds or slows. In the old days before alternators, driving a night road was a nighmare because as you slowed down, the headlights dimmed making visibility even worse. :shrug:

 

But I digress. Here's a link >>Automotive alternator : AC CIRCUITS

[Nitack]

But I digress. Here's a link >>Automotive alternator : AC CIRCUITS

 

So if I understood that page correctly, and I think I did, the alternator would not work because it requires a power supply in order to create the electromagnet first in order to work. It can not create electricity just by spinning, it must first be hooked up to an electrical source. So instead a permanent magnet generator would be needed and then would have to go through an inverter to be converted to AC power...

 

Very interesting, although this is all very ahead of where I am at considering I am still waiting on my damn lenses... the waiting explains all my time to be posting.:shrug:

[freeztar]

So if I understood that page correctly, and I think I did, the alternator would not work because it requires a power supply in order to create the electromagnet first in order to work. It can not create electricity just by spinning, it must first be hooked up to an electrical source. So instead a permanent magnet generator would be needed and then would have to go through an inverter to be converted to AC power...

 

I could be wrong, but if it is hooked up to a car battery, then everything should be ok. In a car, the battery fires the spark plug which turns the engine. Once the engine is going, it supplies the alternator with power, which charges the battery. I think I have that right...Turtle, can you confirm or deny please?

I'm certainly on shaky ground when talking about cars and especially electricity. Time to do some wiki reading I suppose.

[Nitack]

in that case, it may work in a grid tie in system, but that is a far way down the line from where we are at this moment. Considering I am still waiting for my damn lenses. I still don't know if this will even work for charcoal, which is my main purpose at the moment.

[freeztar]

I still don't know if this will even work for charcoal, which is my main purpose at the moment.

 

It will work, it's just a matter of tweaking the system until we get the right temperature and heat spread. What size lenses did you order and where did you order them from?