How to turn plastic waste into diesel fuel cheaply

[wheels]

Wouldn't the thickness be just as important as grade? A thin walled vessel of 304 would Crack where a 3 inch thick vessel would have a much harder time cracking. By the way that pressure vessel is not a dairy industry product it's a 125L industrial pressure vessel with a 4 inch sanitary fitting on top. Figured 4"-3" reducer to a 3" x 31" reflux, all stainless. Water cooled dephlegmator and several liebig condensers with needle valves for water flow to control temps.

I work with SST, so know a bit about it. SST cracks not so much because of the heat, but because it work hardens and then fatigue's due to becoming brittle. The fatigue points tend to be around welds. If by some chance the vessel has a weld around the middle, then that weld edge is something you need to keep an eye on, but it may be totally OK. It depends on how the SST moves. Thickness does not really matter, but a thicker wall section may reduce the ability of movement and thus last a little longer.
Simply, there is no one perfect material. Currently, I use mild steel, because it is cheap and easy to make, because for my processing, it does not last as long. I am processing Plastics that produce Acid. In saying that, I have been working on a whole new design for that part of the process to make my system automated and continuous. I will be going back to SST, but there will not be a retort vessel in this design. Sorry I can't tell you anything more about that part at the moment. But it is a form of FVT (fast vaporisation technique) although there are variances in what FVT can stand for. As well as many different methods.
Anyway, back to discussion. Wall thickness determines how quickly the heat transfers through the wall. SST is not the best at heat transfer so a very thick wall section takes time to transfer heat. A thin wall will transfer it much faster.
The bigger issue to remember is that plastic is terrible at heat transfer. It is a good heat insulator. So don't have too big a vessel, or it takes ages for the heat to get right through the plastic. This is the main reason why there are so many different designs in the commercial realm. All the ideas revolve around trying to get the plastic to the heat as fast and efficiently as possible. As the plastic breaks down and more and more carbon is created, the remaining plastic is more and more insulated from the heat.

[mindxploration]

I'm not gonna risk ruining a $500 aluminum pressure cooker or risk my safety. That setup has just become my main canner. Rather do things right the first time. Thanks for the help guys.

[Excalibur]

Yes, thickness would be as important as grade. Yes I think thick wall would win for more crack resistance.

Run your existing retort for the experience, so that you'll have a better idea of how to proceed with mk2..

[mindxploration]

Wouldn't the thickness be just as important as grade? A thin walled vessel of 304 would Crack where a 3 inch thick vessel would have a much harder time cracking. By the way that pressure vessel is not a dairy industry product it's a 125L industrial pressure vessel with a 4 inch sanitary fitting on top. Figured 4"-3" reducer to a 3" x 31" reflux, all stainless. Water cooled dephlegmator and several liebig condensers with needle valves for water flow to control temps.

[Excalibur]

Give some thought to the grade of stainless. In the dairy industry 316 and 304 are common but are known for cracking at temperatures much less than 400°C+. A crack in a retort at operating temperature would create a runaway fire that would make the 6 o'clock news! A crack would allow hot hydrocarbon liquid or vapor into the flame zone!!

Have a look at this website as a start for making a study. Once you decide on a grade that gives a high safety margin, consider cost, wall thickness, etc.

It might be that the cost outweighs the benefits but in considering the prospect you should allow for cleaning out of the retort so hatches/flanges will be needed. The ability to work/cut/weld stainless is another factor.

Earlier on the forum there was a report of a used stainless vessel as a retort. That vessel cracked and a replacement was made from new stainless of a "heat resistant type".

[wheels]

What would be a better choice for retort? Basic cheaper steel vessel cheap to replace when needed or a certified stainless pressure vessel good to 85psi at 100c as pictured? Its looking like one with sanitary fittings is gonna work best for connecting up to my reflux and connecting temp and pressure guages. Should i work on graphite seals or exhaust cement for the sanitary tri clamp connections? You got me rethinking my retort plans bigtime.

SST is perfect. Pressure tested even better, even though the process is carried out with no pressure. It simply proves the vessel has very good and tested welds.
Mild steel is still a good choice though. It works, it is cheap, easy to weld, drill, cut, thread etc etc. And should you decide the process is not what you want to continue with, then it has not been an expensive outlay.
Seals are easier to do with Tri-clamps. I think they are a great choice. And this is a very big plus using SST, the fact that there are many fittings off the shelf available, along with Valves and threaded bits and pieces etc, that make adding and changing things easy. And surprisingly, it's not all that much more expensive, apart from the Tank usually, which can make your eyes water re the price.
I make a very simple seal using a soft copper wire ring, that fits in the groove of the Tri-clamp. But you have to weld the wire into a ring. Not so easy for most. So you could cut a thin slice of copper tube/pipe that fits in the groove, or failing that, some copper sheet and cut into a flat seal that is deformed into the groove. The copper exposed is simply not enough to cause any worries.
I have tried all sorts of materials in these tri-clamps and the copper ring has worked the best. In the less hot areas, a flat graphite material or a sealant as a gasket works well and in the very warm down to cold areas, the rubber seal that comes with those fittings works fine. Gasket Silicons will work in temperatures up to 200degC. But NEVER use Gasket Silicons on the retort itself.

[mindxploration]

What would be a better choice for retort? Basic cheaper steel vessel cheap to replace when needed or a certified stainless pressure vessel good to 85psi at 100c as pictured? Its looking like one with sanitary fittings is gonna work best for connecting up to my reflux and connecting temp and pressure guages. Should i work on graphite seals or exhaust cement for the sanitary tri clamp connections? You got me rethinking my retort plans bigtime.

[wheels]

Thanks for that better clarification on ignition temp issues. I plan on extensively testing b4 an actual pyrolysis run. I have looked at papr units for better safety around possible fumes. I don't plan on taking any shortcuts etc and I would hope from the looks of my setup that is apparent. I could upgrade to stainless retort but do not see why aluminum should have any problems if kept below 450c and no direct flame contact. Which is why I have steel plates between burner and base of retort. Money is not my concern it's having a proper setup for my needs. I started looking at multifuel diesel generator and electrical heating after bbd's comment but realise that route makes me not want to further explore plastic pyrolysis as I would be in like 6 grand with centrifuge, genny etc...
will move forward with ordering stainless reflux and setting up my thermal siphoning condenser system. Thanks everyone again for the advice. Scares and all.

Aluminium is a unique metal in regards to how strength is given to it in the first place. It is work hardened. But by raising temperature above 177degC, it begins to change and the tensile strength begins to change. At temperatures above 200degC, the tensile strength becomes a factor of both time and temperature. In other words, the longer the time it is at a set temp, the less strength it has, or raise the temperature and the faster it loses strength till basically all that tensile strength that was gained in the processing is gone. Once that happens, Aluminium is actually very soft. The other thing to think about is corrosion. As temp rises, the less corrosive resistance the metal has.
What I suggest is that you use the vessel one time only, then do a good clean and inspection of it and make sure all mating surfaces between lid and vessel perfect. By the way, you need a good mechanical seal. There is no other material that can be used as an effective seal.

[mindxploration]

Thanks for that better clarification on ignition temp issues. I plan on extensively testing b4 an actual pyrolysis run. I have looked at papr units for better safety around possible fumes. I don't plan on taking any shortcuts etc and I would hope from the looks of my setup that is apparent. I could upgrade to stainless retort but do not see why aluminum should have any problems if kept below 450c and no direct flame contact. Which is why I have steel plates between burner and base of retort. Money is not my concern it's having a proper setup for my needs. I started looking at multifuel diesel generator and electrical heating after bbd's comment but realise that route makes me not want to further explore plastic pyrolysis as I would be in like 6 grand with centrifuge, genny etc...
will move forward with ordering stainless reflux and setting up my thermal siphoning condenser system. Thanks everyone again for the advice. Scares and all.

[wheels]

Hello everyone , new here and hoping for some feedback on my current setup.

Hi and welcome.
I add in my 2 cents starting with the easy part first. Electric or flame! I understand exactly where BBD is coming from, but actually, there is no difference in a Flame or an electrical element when it comes to danger of ignition. The heating element is way beyond the temperature of ignition and in fact, can be an even greater ignition source simply because there is good oxygen content around the element. Where as a flame is using up the oxygen. However, what really must be taken from BBD's comment is that this entire process is dangerous and needs careful thought to all aspects of safety.

Forget a pressure gauge. The bubbler tells you all. By the time you see a pressure rise, the pressure is already there and the fact that a blockage has already occurred and the biggest issue is stopping that pressure rise. If you turn the heat off, there is still pressure rising. It is better to have decent pipe size for good flow as Excalibur suggests.

Don't use copper. Copper acts as a catalyst, but not the right type of catalyst.

Don't use Aluminium. Ally has a melting point of 630degC. You will be getting close to that temperature and that means the vessel material will be losing strength. Should some issue develop, you don't want vessel failure. You want it all to hold together till the temperature drops enough for pressure to drop.

BUT PLEASE!!!!! don't do this inside your Motorhome, just in case you are considering that. It is far far too dangerous, right from fire to explosion to dangerous gasses.

[Excalibur]

They have finned siphon snubbers that reduce heat by 75% it states, as well as protects from extreme pressure spikes etc. Then a diaphragm seal which is basically a bag of fluid that let's pressure changes occur while blocking the oil from contact with the guage itself. I'd feel safer knowing exactly when a block in the reflux happened if at all... fingers crossed knocking on plastic...
I was trying to go all stainless, or mostly stainless and zero electric. Would love to get a system dialed enough for fire heating using biomass. I live in the country, plastic and burn ables all over.
What were the effects on the copper or fuel production excalibur?

Placing a pressure gauge for safety purposes was something I gave quite some thought. Running a tube directly off the reflux to a gauge might work if the gauge was overhead and had free draining back to the reflux vessel. The unknown factor was how much uncracked plastic could be around. The reflux function is to separate uncracked heavy fraction from lighter weight so uncracked hydrocarbon could potentially solidify even in the gauge/apparatus itself. If you mount a gauge, periodically remove and test it, else test just prior to a batch run.

I say make all your pipework/fittings of a generous size and be mindfull of aspects of the plant that could even accidentally plug the vapor stream.

Talk about copper and brass was earlier on in the forum. I've just forgotten how it went. I think it was a chemical problem between hot hydrocarbon and copper.

[mindxploration]

Detailed refinery system

[Beyond Biodiesel]

I'm trying to not go electric heating for my retort as I live off grid with far fewer panels then was it you beyond biodiesel? I remember someone here having 30 some panels. I live in my 34' motorhome and have 2kw solar but it's not optimally placed and it's fall now here in the PNW.

Correct I was attempting to operate a pyrolysis unit that was powered by 30 133w solar panels. Yes, I was able to do it, but it was not without a great deal of effort. If I am to do it again, then I will have to have it plugged into the grid, or have a 6-10KW diesel generator delivering the power to run it.

I'm using a bayou classic stainless high pressure cooker.

As much as I understand your limitations, and value the cost reduction in burning gas or liquid fuel to fuel a pyrolysis unit; nonetheless, doing so is so dangerous, that you, and everyone else near you, would be better off if you went out and bought a gun and shot yourself; because pyrolysis of hydrocarbons is extremely dangerous and explosive. It should only be done by people who have been trained at graduate level chemistry to do so; but heating it with electricity is the only safe way that I can think of to do so. Heating a pyrolysis with a flame is shear suicide/murder.

Already bought my thermowell and thermometer for the retort, 15 inch drops right down into the mix for reading true temp. Also trying not to use power for guages or water flow through condensers. I'm thinking of setting it up for the thermal siphoning to move water through a heat exchange of some sort. Also looking at an actual reflux column with Dephlegmator and Liebig Condenser. Thinking it could allow for 2nd distills of cleaner lighter fuels as well as emergency/overheat cool down. I tend to overthink and over build things ☺ what do you guys think of this column? Made with DHP copper Rod that melts at around 1,700° F not soldier which melts at 400f.

Such a condenser will be just fine for the low temperature end of your system. I made one myself, and it worked just fine. However, it would corrode into a useless piece of oxidized copper at 400c.

My system fractionates on the fly producing the fractions that are common in a petroleum refinery. It is the most efficient way to do it.

[mindxploration]

They have finned siphon snubbers that reduce heat by 75% it states, as well as protects from extreme pressure spikes etc. Then a diaphragm seal which is basically a bag of fluid that let's pressure changes occur while blocking the oil from contact with the guage itself. I'd feel safer knowing exactly when a block in the reflux happened if at all... fingers crossed knocking on plastic...
I was trying to go all stainless, or mostly stainless and zero electric. Would love to get a system dialed enough for fire heating using biomass. I live in the country, plastic and burn ables all over.
What were the effects on the copper or fuel production excalibur?

[Excalibur]

You could run an old PC fan, blowing air into your bowl. They're 12v. Might work well enough.

The aim is to have no retort pressure though there'll be a very small amount created by any bubbler (and gas-jar if so fitted). I run a pressure gauge in the petrol/gasoline condenser where it's less than 20°C but it has never read anything above zero. It would only read if downstream was plugged. If upstream became plugged of course it would not read anyway. A gauge will only handle so much heat. I overheated one once to the point of being useless. Perhaps a remote gauge with a tube might be the go, however there has been reports of gauges/lines plugging from uncracked, solidified plastic.

I believe stainless or terracotta packing would be better than copper. I went to some effort to remove all copper and brass from vapor/condensate stream.