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johansen
Posted: February 28, 2012 06:53 am
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I went ahead and built a flange for my 25 gallon propane tank.

This is the tank I mentioned I was interested in using to test the theory that plastic insulated wire could be "environmentally-friendly" burnt if you were to stuff it in a tank, heat it up to ~200C without oxygen and condense the vapors that came out. (On that note, the lowest condensate i can think of is chlorine; at -40C boiling point, easily collected.)

I've already hydro tested this tank to 80 psi.
After torquing all of the 50, 1/4-20 bolts to the yield point, determined by twisting a few of them off. The bolts are surplus and probably grade 2, though they feel a bit soft if they are.
So i went ahead and ordered a box of grade 8 bolts, grade 5 nuts and washers.

Anyhow, should i re-drill all the holes and buy 3/8th inch bolts?
the standard tables for 1/4th inch bolts say:
grade 2 bolts snap at 2350 pounds
grade 5 bolts snap at 3800 pounds
grade 8 bolts snap at 4750 pounds

3/8th inch bolts are about double those numbers.

At 80psi, there is 320 pounds tensile stress per bolt.

FYI: propane tanks are designed for 240 psi, tested at twice that and supposedly burst at ~900PSI.
the side wall of this tank is 3/32" and its 14 inch diameter.
900 psi makes ~70,000 PSI hoop stress. nono.gif

I don't intend to use this tank above 40 psi in any circumstances. smile.gif

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Geek
Posted: February 28, 2012 07:46 am
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Has any DF member blowed themselves up yet? huh.gif


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AwesomeMatt
Posted: February 28, 2012 09:33 am
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So I ran this by a chemist friend of mine. Keep in mind I don't quite get what's supposed to happen, but as I described it, he didn't think it would work.

He said 200'C is probably not hot enough to pyrolyze most plastics, and if the insulation is a chlorinated plastic, he doesn't think oxygen-free is ideal. Said to look into studies on air presence during a burn versus dioxin levels. Recalled something about oxygen being useful for minimizing dioxins but levels had to be controlled decently.

Said if the plastics are chlorinated, the condensate could be one horribly noxious, extremely carcinogenic soup if done wrong.. and hell no you don't want to be *adding* chlorine to anything in there.

He's skeptical of it working, since plastic molecules are too large to really boil, they just crack into free radicals.

Some more quotes:
--
Polystyrene does this really smoothly. I took a torch to some polystyrene in a distilling setup and fractionated the product to give 67% yield of pure styrene monomer back. The residue was volatile compounds that were heavier than styrene....probably mostly 2-5 of them stuck together.

Things like polyethylene and polypropylene will give poorly defined mixes of unsaturated hydrocarbons.
PETE will probably give appreciable benzene content and other crud.

I think a lot of that typically ends up as "char". Black mostly carbon junk that won't break down any more, but easily removed from say, copper, by just melting it into an ingot. The carbon will float like styrofoam in water.

I'm suggesting that he's not going to get the wire clean that way. It'll still have burnt looking black crud on it. Either manually strip it, or burn it, then melt it into clean ingots.
--

He said you could blow air over the wire while roasting it. The char should burn off as CO2 but you might as well just melt it at that point.

So, there you go. Not that I wouldn't be happy watching you demonstrate it, or blow something up.
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johansen
Posted: February 28, 2012 09:54 am
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hmm..
200C may indeed be not hot enough, as your chemist friend said...that's only 390F.

I have had a strip of kapton tape wrapped around the outer shell of my hakko soldering iron for some time now and its still there. black and charred, but still holding on with some structure.
However I can easily get it just a bit warmer, say 300C.
I am not interested in allowing oxygen into the tank, its going to get corroded enough from the outside in.

Anyhow, i'll be using this tank to distill some beach wood this weekend or next, and then later distilling some dry firewood to find out how why dry beachwood has such a low thermal value.

Indeed, most plastic insulated wire has chlorine in it. It will be a mess of unsaturated hydrochlorinated compounds.


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Sch3mat1c
Posted: February 28, 2012 08:49 pm
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I'd suggest stainless and add steam. High pressure steam is supposed to effectively crack a variety of polymers. Now that you're making a steam boiler, you want to be very, very careful about what you're doing -- and guessing by the rusty, lumpy construction, no steam boiler inspector is going to approve your contraption...

Structurally, I'd be most concerned about processing chlorinated plastics because hydrochloric acid is a likely byproduct, especially in the presence of water, which will in turn make quick work of the steel (even stainless) at elevated temperatures. A safe alloy for that kind of mix would be monel or inconel ($$$).

Cracking with some limestone tossed in might not be a bad idea.

Kapton is ridiculously awesome stuff and can withstand transients to 400C without too much embrittlement. That's almost red hot plastic.

Tim


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tekwiz
Posted: February 28, 2012 09:32 pm
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Increasing the bolt size will offer limited benefit, as it's likely the holes would stretch first, unless you also use hardened clamping washers. The same goes for using anything more than Gr 5 fasteners, as they are holding mild steel together, which is roughly Gr 3.


BTW: Why are you so bent of pyrolyzing insulation? Wouldn't it be better to simply heat it up past the melting point, then just allowing the plastic to drip off & drain it out of the bottom. If this turns out to be not effective enough, a simple box die & hydraulic press could be used to compress the resulting half cleaned wire at heat, which would squeeze most of the remaining plastic out & leave the remains is compact form. Wire doesn't have to be perfectly clean to fetch good prices as scrap. Get the plastic percentage down to similar levels to enamaled wire, & you'll get better prices than for burnt wire. About the only extra prep required on the wire itself is to seperate it by type of plastic.
I've been toying around with the idea of a hot centrifuge for insulation removal. wink.gif


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tekwiz
Posted: February 28, 2012 09:50 pm
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As to the caloric value of wood, the main reasons beachwood has lower heating value are because it's usually at least partially waterlogged, & because much of the solidity rots away from weathering quite quickly. The moisture content has the greatest effect. Completely dry hardwood contains far more heat value than the same wood green or with high moisture content. I learned this when I heated with wood for my last 2 years in Ontario. My firewood came from two sources...the place where the city dumped their trees, & from hardwood steel pallets from the stamping plants, which are completely dry 4x4's for the most part. Beachwood from salt water should never be burned, as the chlorine from the salt produces large quantities of dioxins & other highly toxic chlorinated organic compounds in the smoke.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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MikeGyver
Posted: February 29, 2012 04:25 am
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Holy hell that is scary... blink.gif
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johansen
Posted: February 29, 2012 06:27 am
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Good idea, throwing limestone in the tank.
or NaOH, i'm sure that will make quick work of the plastic, could also throw in a whole concoction of V2O5, FexOx, whatever else is cheap..

@tekwiz, I'm not bent on pyrolysis of insulation, its just an idea. i have no intention of using this to strip more than about 50 pounds of wire once. If it works great i've got more but i'm not about to offer the locals a higher price per pound than where ever they are currently going.

About the firewood. i've already accounted for the water, but what i think missing is the water pulls the organics out somehow. i would not be surprised to find less than half of the VOC's from beachwood compared to dry wood.


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tekwiz
Posted: March 01, 2012 01:21 am
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QUOTE (johansen @ February 28, 2012 09:27 pm)

About the firewood. i've already accounted for the water, but what i think missing is the water pulls the organics out somehow. i would not be surprised to find less than half of the VOC's from beachwood compared to dry wood.

That's exactly what happens, except it's microbes that do the 'leaching', by breaking down insoluble organics into soluble waste products. The softer parts of the wood's structure will go first, of course. Over time, the wood comes to resemble a porous fiber sponge with little mass left.

What has the biggest effect on VOCs is the temperature & completeness of the combustion. VOCs are primarily the products of incomplete combustion.
The powerhouse of the local paper mill is wood fired. They burn some 800 tons of hog fuel a day.
All of this combustion produces no visible smoke at all.



BTW:What about catalytic cracking? Could that be of value to you? Catalysts are readily available in the form of salvaged car cat converter contents. Nickle is another catalyst metal, available cheap in the form of pure nickle TIG or stick electrodes. These are common & reasonably cheap.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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johansen
Posted: March 02, 2012 01:06 am
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derailing this thread into chillers.

I've got (3) 6cc/rev dehumidifier compressors that are fairly indestructible. i don't doubt that they will push against 600 psi.

I've got a crude chiller set up using propane as a heat fluid and i've found that at -40C i can get in theory, only about 6 watts of cooling power at that temp. I would like to go as low as -50 or -60C with 100 watts of heat load. But to do that typically requires two stages.
however, i'm lazy and i'd rather not build a cascade.

i'm about to try filling what i have with Co2 instead of propane and hope nothing explodes, but is there any other cheap alternative to Co2 for those temps?

if i try to get to -50C with Peltier coolers then i have to build a system to handle 200-300 watts of heat flux at -20C, and that's almost as difficult i suppose with propane as a heat fluid, unless i parallel all three compressors...


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tekwiz
Posted: March 02, 2012 10:02 pm
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You may have to ditch the hydrocarbons & go with freon. Hydrocarbons don't have enough specific heat & therefore require too much flow to get any reasonable heat transfer. The new freon made for home air conditioning should do what you want.
Another thing that might work is that Red Tek stuff. It's hydrocarbon based, but also rather expensive. It's made for direct replacement of freon, but i've found the characteristics vary quite a bit from the real thing.

Too bad you live south of the border...I've got about 10lbs of genuine Freon 22 hanging around, left over from when I was repairing refrigeration systems before I got into the metal cutting trades. That would be ideal for your app. Can't think of any way to get it to you, though.
What about salvaging some R-22 from an old room AC unit? The pressures are such that you can use a fridge compressor to pump it into a propane tank.


BTW: Why so much cooling power to support a TEM? I know they are inefficient as hell, but modern ones offer up to 80C temperature differential.
I've seen them up to 500W capacity. Using one of thos may get you your 100W without requiring lower than 0 on the hot side. This is easily obtained from a modified 5000-8000BTW room AC or large dehumidifier. It should be possible to mod it for this without opening the sealed cooling system. Only a line tap valve would be required in order to lower the system pressure enough to get 0 from it.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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johansen
Posted: March 02, 2012 10:30 pm
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@tekwiz, i highly recommend you take a look at this chart.
http://johansense.com/bulk/Refr.ptchart2.pdf

you might be right about R-22 with a higher specific heat of evaporation but at -40C its only pushing .6 psi gauge.

R-13b1 is looking really good.

i've run the numbers again and it might be possible to get 200 watts of cooling with a single compressor at -20C with propane. i've got some new capillary tubing in the mail so in a few days i'll be able to get some actual numbers.
200 watts of heat transfer at -20C would be sufficient to get 30 watts of cooling at -55C using two 90 watt TEC coolers in parallel, or one 150 watt module.
The electrical load would be 130 watts plus 30 =160 watts dumped into the -20C side.

The application requires continuous duty, ie 24/7
To get the 60 watts of cooling i need i would just build two parallel systems, which would also provide redundancy in case one fails.

link to TEC calculator
http://www.tetech.com/Peltier-Thermoelectr...d=0&emailsent=0
note on the calculator: the suggestions system is broken, it always gives you links to coolers that are oversized. in this case the link will give you the numbers i put in, and if you click graph on the first cooler suggested for smallest size, it happens to be the right size for lowest power.


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tekwiz
Posted: March 02, 2012 10:48 pm
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Nice document, thanks. thumbsup.gif

Rember that low pressure isn't necessarily a problem as long as the flow is there. After all R-22 was used in commercial & consumer deep freezers that run at -40.
I've seen room ACs that were almost out of gas running colder than that.
It shouldn't be too difficult to score larger compressors...those in home central air systems can go over 5hp. After than, you start getting into the 3 phase stuff.
As long as you don't need continuous operation for more than an hour, you may be able to use a larger system running at low pressure. Any longer than that & internal cooling of the compressor becomes an issue



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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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johansen
Posted: March 23, 2012 02:53 pm
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I have a quart mason jar with 5mm of liquid propane in the bottom, boiling away at -26C according to my thermocouple. which reads somewhere between 5 and 8C high.

so it looks like i'll need to build a fractionating column to separate out the isobutane and or butane from the propane.
looking at the data here: http://zenstoves.net/Canister.htm i can extrapolate from the charts that only 20-30% butane or isobutane would be needed to shift the boiling point up 10C.


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