Solar Parabolic Trough Charcoal Oven

[Nitack]

So this may be the most lowtech idea of making my frasnel lens actually make charcoal, but I actually think it might work. This came to me as I was testing out a traditional burner and retort (which did not work because I used unseasoned, large pieces of wood). I never got the retort to fire, but I came up with an idea. I am going to take apple sauce jars, the big mothers, punch a few holes in the top, pack them with mulch, and then sit them in the fire to char and eventually give off wood gas to help fuel the burn for my 55 gallon drum.

 

But I was thinking, why wouldn't that also work with a Fresnel directly on the mulch in the jar? As long as I pack the much there should be relatively low oxygen. Additionally, as long as I don't completely focus the beam, it should get hot enough to char everything. The stuff towards the inside may not get hot enough for long enough, but the stuff around the outside should all char right? :)

 

I think the biggest mistake I was making with the Fresnel was to just try to make one point supper hot and then have conduction/convection heat the material. Too damn much heat was being lost to the air around me. Thoughts?

 

Edit: finding the most long and skinny jar I can should probably help as well.

[Turtle]

So this may be the most lowtech idea of making my frasnel lens actually make charcoal, but I actually think it might work. This came to me as I was testing out a traditional burner and retort (which did not work because I used unseasoned, large pieces of wood). I never got the retort to fire, but I came up with an idea. I am going to take apple sauce jars, the big mothers, punch a few holes in the top, pack them with mulch, and then sit them in the fire to char and eventually give off wood gas to help fuel the burn for my 55 gallon drum.

 

But I was thinking, why wouldn't that also work with a Fresnel directly on the mulch in the jar? As long as I pack the much there should be relatively low oxygen. Additionally, as long as I don't completely focus the beam, it should get hot enough to char everything. The stuff towards the inside may not get hot enough for long enough, but the stuff around the outside should all char right? :)

 

I think the biggest mistake I was making with the Fresnel was to just try to make one point supper hot and then have conduction/convection heat the material. Too damn much heat was being lost to the air around me. Thoughts?

 

Edit: finding the most long and skinny jar I can should probably help as well.

 

By Jove; that just might work! :) Make sure those holes in the lid are big enough so the jar doesn't over-pressurize and burst, and maybe -while having/leaving the cap above-ground- to insulate the jar, bury it so that only enough clear glass is exposed to admit your Fresnel beam. Any uneven heating may just break the jars though? :shrug: As always, wear eye protection! :shrug: Let us knows how it goes.

 

PS I think putting the jars in the fire will break them and I see no advantage of it over metal containers. :)

[Nitack]

By Jove; that just might work! :) Make sure those holes in the lid are big enough so the jar doesn't over-pressurize and burst, and maybe -while having/leaving the cap above-ground- to insulate the jar, bury it so that only enough clear glass is exposed to admit your Fresnel beam. Any uneven heating may just break the jars though? :shrug: As always, wear eye protection! :) Let us knows how it goes.

 

PS I think putting the jars in the fire will break them and I see no advantage of it over metal containers. :)

 

They are readily available ;)

 

I'll inform you all on the results with the Fresnel since it should be a very quick and easy thing to test. Hopefully we have sun this weekend. :shrug:

 

I'll take pictures for you ;)

[freeztar]

Cool, I look forward to the results, and pics!

 

I finally moved into my own house with a huge garage (read laboratory) with a workbench built in and a whole wall lined with tool chests. :) I've got a nice big yard too! Only problem...the trees are conspiring against me. It looks like I will not be able to get any good sun, but we'll see once summer's on its way.

[Nitack]

Cool, I look forward to the results, and pics!

 

I finally moved into my own house with a huge garage (read laboratory) with a workbench built in and a whole wall lined with tool chests. :) I've got a nice big yard too! Only problem...the trees are conspiring against me. It looks like I will not be able to get any good sun, but we'll see once summer's on its way.

 

I think you need to selectively remove a couple trees in order to gain a clear path for sunlight and feedstock for the production of biochar. It is for the greater good!

[Nitack]

:)

 

Last weekend, cloudy. This weekend, expected to rain. How the hell am i supposed to save the planet if it won't cooperate with me??? :shrug:

[Michaelangelica]

Hows it going?

I haven't checked out this thread in a while

Did you see this?

BBC NEWS | Science & Environment | Prize for 'Sun in the box' cooker

Prize for 'Sun in the box' cooker

By Richard Black

Environment correspondent, BBC News website

Painting box

At the heart of the idea is a simple black painted box...

 

A cheap solar cooker has won first prize in a contest for green ideas.

 

The Kyoto Box is made from cardboard and can be used for sterilising water or boiling or baking food.

 

The Kenyan-based inventor hopes it can make solar cooking widespread in the developing world, supplanting the use of wood which is driving deforestation.

 

Other finalists in the $75,000 (£51,000) competition included a device for streamlining lorries, and a ceiling tile that cools hot rooms

BBC NEWS | Science & Environment | Prize for 'Sun in the box' cooker

Some audio at site too.

More here

NIGERIA BLOG, FREE INTERNET, MARKETING, WEB HOSTING, DESIGN, SOFTWARES, A CARDBOARD BOX COOKER WINS TOP PRIZE IN AN ENVIRONMENTAL COMPETITION

and

The finalists | Forum For The Future

[Michaelangelica]

The interesting thing about this article is the temperatures produced by the solar array.

The process does not stack up against charcoal production and sequestration IMHO

 

Can technology clear the air? - environment - 12 January 2009 - New Scientist

 

*

400C just nice for your everyday charcoal

*

800+ pretty close to producing activated charcoal

 

Solar scrubber

Can technology clear the air? - environment - 12 January 2009 - New Scientist

 

The ETH concept is a modified version of an energy-generating technology called concentrated solar power that has been blossoming lately in deserts around the world (New Scientist, 10 April 2004, p 26). Such power plants consist of fields of sun-tracking mirrors that focus sunlight to generate steam that drives a generator. "We remove the boiler," explains Steinfeld. "We put our solar reactor there. In this we remove CO2 from the air."

 

Steinfeld's reactor is a transparent tube filled with pellets of calcium oxide. In the table-top version the tube is a few centimetres high and an arc lamp replaces the sun. As the light heats the tube and its contents to 400 °C, air mixed with a small amount of steam is pumped in at the bottom and up through the pellets. At this temperature, the calcium oxide reacts with CO2 to form calcium carbonate. "By the time the air leaves, there is no CO2," says Steinfeld. "We go from 385 parts per million to practically zero."

 

In less than 15 minutes, the pellets are mostly converted to calcium carbonate. At that point, Steinfeld closes the intake valve and intensifies the light, raising the temperature in the reactor to 800 °C.

This drives off the CO2 as a stream of pure gas, which can be sent for sequestering, and converts the calcium carbonate back into calcium oxide. The researchers have run their reactor through five cycles of absorption and release with no decline in performance. Steinfeld believes his device could be scaled up to take significant amounts of CO2 out of the atmosphere, though as yet he doesn't know how much it would cost per tonne.

Using sunlight to strip CO2 out of the air clearly has advantages over a kiln. But Lackner suggests that if you're going to fill a desert with solar concentrators, it might make more environmental sense just to convert that sunlight into electricity.

 

Lackner's own strategy is to drastically reduce the amount of energy required to strip CO2 out of the air. He and his colleagues have experimented with various designs, but the heart of each is an ion exchange resin, a polymer impregnated with sodium hydroxide.

The sodium ions are firmly attached to the polymer but the hydroxide is loose and easily displaced by CO2, which binds to the sodium to form sodium bicarbonate. The chemistry is essentially the same as in the Calgary device, says Lackner, but because of the enormous surface area of the resin sheets, the reaction goes much faster.

 

Scientists Develop Air "Scrubber" Capable of Sucking Up One Ton of CO2 a Day : TreeHugger

[rebelcat1]

I'd like to build an automated char maker, as outlined in this article: (that I can't site because of my too low post count) try: bidstrup (dot)com /carbon (dot)htm

 

 

So on consideration, the design worked out to something like this - a piece of pipe, blackened on the outside to facilitate the absorption of the heat, about three or four inches inside diameter, and about ten to fifteen feet long, is suspended over a trough reflector, shaped into a parabola in cross-section, with the pipe suspended at the focal point, parallel to the length of the trough. The trough would be about eight to ten feet wide, and is lined on the inside with the solar reflectorizing material, which is nothing more than shiny metal - in a pinch, aluminum foil, shiny side up, could be simply glued to ordinary sheet metal to provide the shiny surface (the shiny aluminum surface could be sprayed with clear acrylic to preserve the shine). The resulting device is mounted with the length on an exact east-west line. If this is done, the only adjustments that need to be made to keep the furnace operating at peak efficiency is to keep the reflector tilted to the current seasonal sun angle. No hourly or daily adjustments need be made. Simply push the feedstock in one end, and if it gets heated to more than 470 degrees during its transit through the pipe, out the other end comes low temperature charcoal, ideal for soil carbonization. Easy as that.

 

There are endless variations on this theme that are possible. For industrial furnaces, the farmer's feedstock tool could be replaced by an auger screw. A gearmotor, switched by a thermal switch, would come on when the sensor detected that the temperature of the furnace pipe exceeded the setpoint, turning the screw and loading the feedstock from the bin and carrying it to the far end of the pipe. It would run until the sun went down or behind a cloud, and the temperature dropped below the setpoint. Loading of the intake bin could be done automatically, too, with another auger screw or a conveyor belt, which could load several furnaces at a time. Output could drop into a hopper emptied by yet another auger screw.

 

 

I've scoured the web with little success. The elements that make me reluctant to just jump into the project are:

1. If the feed stock is not completely dry, I think you would need to vent the tube in the middle to allow water vapor to escape. Otherwise you'd have steam shooting out the end, hindering the carbonization process as I understand it. Can it happen in the presence of moisture? If you do need to vent it than you may have to have two separate tubes with a hopper between them and their own auger control. Given a set furnace length, the ratio of time required to drive off moisture vs time to carbonize will shift when moisture content of the feed stock shifts. If you knew exactly what the moisture content would be then you should be able to calculate at what point there would be enough energy to drive of all the water and put a vent at that point. But if the water content was lower the vent would need to be closer to the intake and visa-versa. Otherwise, since there would only be one auger you'd have poor control over final temp.

 

2. How would you limit oxygen's access? The article says that charcoal would simply block the entrance, but would that work? One thought I had was that you'd have to cool the charcoal before it contacted o2 or else it would ignite. So you could have your tube extend a length beyond the parabola to allow cooling, and given enough length and densely packed material you could exclude oxygen. You could use the same approach on the intake side, giving a distance of pipe before the parabola. I don't know if that would be necessary or not....

 

3. And complicating number 2, how do you capture the gasses? If energy weren't a problem you could have a vacuum pump on the hopper that the material is dumped into, then separate out the gasses you want from the atmosphere that would inevitably leak into even a well sealed hopper. This whole thing adds a lot of expense and energy input, but I don't know if its enough to make it unfeasible. It probably puts it out of my range as a tinkerer.

 

So, has anyone else answered these questions? Any ideas? To me, this is where the answer is at. Make it easy. Put it on a truck and drive it around to different farms or villages that have been stock piling their material. I think the lower tech various also have their place without a doubt, capable of going where the larger ones can't, but with draw backs like no capture of the gasses.

 

Thank you,

rc1

[rebelcat1]

As an afterthought, looking over my post there may be a simpler answer to number 2: you could have independent control over the parabolas angle to the sun in the "drying" section and the "furnace" section and a set vent. With a computer control you should be able to bring the material to the desired set points by varying energy input. For example: if, when then dryer is at 100% it is still not reaching set temp at the vent, then the furnace power is reduced (thus slowing the auger, still controlled by a thermoswitch set to 470*F) until the dryer is able to meet set point at the vent.

 

I think that would be simpler... (should I apply for a patent? I hope not... someone else should have come up with this by now and the only reason to patent is to keep BP or Shell from burying the tech.)

 

Eagerly awaiting ideas...

rc1

[Turtle]

As an afterthought, looking over my post there may be a simpler answer to number 2: you could have independent control over the parabolas angle to the sun in the "drying" section and the "furnace" section and a set vent. With a computer control you should be able to bring the material to the desired set points by varying energy input. For example: if, when then dryer is at 100% it is still not reaching set temp at the vent, then the furnace power is reduced (thus slowing the auger, still controlled by a thermoswitch set to 470*F) until the dryer is able to meet set point at the vent.

 

I think that would be simpler... (should I apply for a patent? I hope not... someone else should have come up with this by now and the only reason to patent is to keep BP or Shell from burying the tech.)

 

Eagerly awaiting ideas...

rc1

 

Build it first, patent it later. I think I suggested augering earlier here, but now in retrospect I don't see any advantage. For any given load of wood and Sun conditions, the time needed to charcoalize it is the same regardless of if it's moving in the receiver or not. Adding the augering and other equipment then is a virtual waste, especially if you are talking about a portable unit.

 

So I'm thinking set the unit up, load it, run it to completion, and then use a plunger on a long pole to push out the goods. If the receiver is easily removed from the reflector, when a load is done the receiver can be set out to cool, and a new load and receiver put in the reflector. Add more reflectors to increase capacity and have sufficient receivers to keep the system working while Sun is available.

 

On the steam venting, whether augering material in the receiver pipe or not, simply give a smidgeon of tilt to the setup so that one end of the receiver is slightly higher than the other. Small drain hole at low end for water to drain, adjustable vent hole at high end for steam & gases to vent and restrict fresh air entry. :naughty:

 

PS Here's rebelcat's link 'til he's up to code. :eek_big: http://www.bidstrup.com/carbon.htm

[rebelcat1]

Thank you for the prompt reply. From my perspective the advantage of angering is that the whole process becomes automated. I'm thinking of a system where you're loading material into the feed hopper with a loader, 1+ cubic yards at a time, with a throughput on the order of 10 to 500 cubic yards per day. Of course any prototype I build will be much smaller, but that's why I want to aim for an auger.

 

Also, once we get above even a fairly small scale the mechanics of hand loading a tube get very arduous. Other advantages include charcoal will be mostly powdered, especially if starting with material like straw and the larger scale make capture and use of the 'woodgas' or 'syngas' more feasible.

 

Another idea I had, if you were going to encase the thing in a vacuum tube you could have the top 25* of the pipe covered with some high temp insulation in such a way that it supported the vac. tube, adding to mechanical resiliency.

 

I still need to read the entire thread (I'm half way through) and more info on reflector design. I saw some really cool looking stuff about Fresnel reflectors, could be lighter and more resource efficient.

 

rc1

[rebelcat1]

I see another misunderstanding between us- I am talking about pushing the material all the way through and out of the solar collector. The purpose is not to agitate within a closed tube. Does that make sense? If it took say 6 hours to cook the stuff given X amount of radiation striking it than the transit time through the pipe would need to be six hours. For a faster throughput increase pipe length or radiation. I'm thinking about something with a length of around 40 feet and a reflector cross section of around 15 feet.

[Turtle]

Thank you for the prompt reply. From my perspective the advantage of angering is that the whole process becomes automated. I'm thinking of a system where you're loading material into the feed hopper with a loader, 1+ cubic yards at a time, with a throughput on the order of 10 to 500 cubic yards per day. Of course any prototype I build will be much smaller, but that's why I want to aim for an auger.

 

Roger. :) I was thinking continuous with the auger too, but as I say, I now think there is no gain. Isn't it a work problem as far as physics goes? x amount of wood and y amount of Sun? Then there is the matter of an auger stout enough to move the material, which is going to decrease the volume of wood in the receiver by its displacement. Then there is having to deal with clogs when a knot lodges between the auger and pipe halfway down. :eek:

 

Also, once we get above even a fairly small scale the mechanics of hand loading a tube get very arduous.

I think a hopper could speed up loading and some sawbucks to hold the cooling/cooled receivers while the charcoal is pushed out. Prolly could come up with a simple machine to drive a plunger to push the stuff out. :hihi:

 

Other advantages include charcoal will be mostly powdered, especially if starting with material like straw and the larger scale make capture and use of the 'woodgas' or 'syngas' more feasible.

Well, maybe. But it seems like you will have to use a lot of power from some source to drive the auger. Maybe the wood-gas itself?

 

Another idea I had, if you were going to encase the thing in a vacuum tube you could have the top 25* of the pipe covered with some high temp insulation in such a way that it supported the vac. tube, adding to mechanical resiliency.

 

The vacuum tube is the insulation. I was thinking about the vacuum/Dewer tube last night though in regard to the gas & steam venting you mentioned, and some special consideration will have to be made so pressure doesn't build. Maybe just havig one end open like the familiar Thermos® bottles would do? Also, for a down-n-dirty vacuum enclosure I was thinking maybe nested fish aquariums or something made of sheet glass so you avoid the expense of having a Dewar tube made by a glassblower.

 

I still need to read the entire thread (I'm half way through) and more info on reflector design. I saw some really cool looking stuff about Fresnel reflectors, could be lighter and more resource efficient.

 

rc1

 

Roger. One thing on the Fresnels (they are lenses, not reflectors) is that you have to add a drive unit of some kind to keep them focussed. Same with round parabolic reflectors. This is the great advantage of a parabolic trough reflector, it only needs to be set oriented on an East/West line and it works all day. True a trough could be made to track, but unlike the others it will work without tracking. I'll let you finish reading. :hihi: ;)

[freeztar]

Fresnel Reflectors exist as well as the lenses. It's probably a poor name for them, confusing at least, but there you have it.

 

Fresnel reflectors - Solar Cooking

[Turtle]

Fresnel Reflectors exist as well as the lenses. It's probably a poor name for them, confusing at least, but there you have it.

 

Fresnel reflectors - Solar Cooking

 

:) You're a sharp one Mr. Freeza. I agree the term Fresnel is misapplied here.

Fres·nel (fr-nl), Augustin Jean 1788-1827.

French physicist who supported the wave theory of light, investigated polarized light, and developed a compound lens for use in lighthouses.

Fresnel - definition of Fresnel by the Free Online Dictionary, Thesaurus and Encyclopedia.

 

Dare I suggest "compound parabolic reflector" for these devices? :) :eek:

[Lorenzotto]

This is something I designed several years ago. Perhaps it's of interest to this discussion.

 

Same idea: parabolic troughs, biomass particles are blown through and pyrolysis gas is recycled for drying and heating.

 

http://i3.photobucket.com/albums/y90/hybriddiesel/solar_torrefaction_concept.jpg

 

Nevermind the "torrefaction" reference; the concept can be used to produce char as well.

 

 

I don't think any of these general ideas are "patentable", because using solar for torrefaction / pyrolisis / gasification is at least several decades old. (See the solar furnaces in France).