How to turn plastic waste into diesel fuel cheaply

[Col]

Controlling the temperature of the reflux

Hi guys
Thanks for all the help so far.
My retort is 440mm diameter. My reflux is the same diameter, though much shorter. I am wondering if I will have sacrificed uniformity of temperature across the diameter of the reflux by going so wide. Oh well, will never know because I didn't put TC's in there, just one at the top of the exit pipe.
Is anyone actually heating / cooling their reflux to control the temperature or just insulating it and adding / removing insulation? Do you find there is a need to baby-sit the reflux temperature or once you get the physical dimensions and distances right (ie - the 'sweet spot') is looks after itself?

[Excalibur]

My understanding is that oil refineries use vacuum distillation when they want to avoid cracking. For us we need to reach cracking temperatures to achieve finished product viscosity. My last run had retort temperature mainly between 380°C & 420°C.
Shell Petroleum handbook says cracking commences at 350°C so a feedstock that boiled under vacuum below that marker would be below cracking threshold.
Col, my retort/reflux is tall and skinny so quite the opposite of yours. I think either design will have strengths and weaknesses, pros and cons.
I'm adding/removing reflux insulation to achieve an average target so I'll allow it to drift high or low but so long as it averages out then my fuel SG will be within spec.
Re cracking temperature, there will be a sweet spot where the feedstock cracks to diesel at a good rate but without causing unwanted problems from driving the process too fast (wax, gum, excess off-gas etc). It would be a mistake to think that more heat was always better.

[wheels]

My understanding is that oil refineries use vacuum distillation when they want to avoid cracking. For us we need to reach cracking temperatures to achieve finished product viscosity. My last run had retort temperature mainly between 380°C & 420°C.
Shell Petroleum handbook says cracking commences at 350°C so a feedstock that boiled under vacuum below that marker would be below cracking threshold.
Col, my retort/reflux is tall and skinny so quite the opposite of yours. I think either design will have strengths and weaknesses, pros and cons.
I'm adding/removing reflux insulation to achieve an average target so I'll allow it to drift high or low but so long as it averages out then my fuel SG will be within spec.
Re cracking temperature, there will be a sweet spot where the feedstock cracks to diesel at a good rate but without causing unwanted problems from driving the process too fast (wax, gum, excess off-gas etc). It would be a mistake to think that more heat was always better.

Commercial refineries vary around the world, but the one common similarity is that they all have very complex and controlled means of cracking that we don't have. It also depends on what range of oil is being refined. Not all refineries take a full crude product ad not all Crude Oils are the same.
One of the reasons (just one of the many) that they crack in a vacuum is no oxygen present to oxidize chains till they can be cracked into what they require as a final product.
The temperature of cracking a chain depends on two things of which both come back to temperature. A long chain requires a higher temperature to release it from the base stock. Lets just say that is 360deg. A short chain may release earlier with a much lower temperature, lets day 150deg, but being more stable, needs far more heat to vibrate it enough so it breaks by temperature alone. Lets say that breaking temp is once again 360deg.
Very high temperatures can cause many problems. So being able to crack at lower temperatures allows a more stable product to be produced. under a vacuum, the temperature can be greatly reduced as I described earlier.
In commercial refineries, as far as I know, every stage is employing a catalyst for controlled cracking. Plus many refineries use high pressure high temperature Steam. Steam is a great way to control the temperature of the environment.
Boiling points of heavy chains can be very high. As much as 400+degC. WMO is very unlikely to have Chains of that weight. But you still want to have an operating temperature high enough to get rid of the very last of the heavy weight stuff from the bottom of the retort. If you don't, the carbon left behind will be spongy and oily when cold, and not dry hard carbon.
A reflux needs to be hot enough to allow the lighter fractions to pass on through, but cool enough to allow the very long chains to condense and be recycled back to the Retort, so they can be reheated and bounce around some more and hopefully crack. A Catalyst needs a working temperature and so you would want that part after the Reflux and heated to it;s requited temp.

[rozier56]

rozier56

Excalibur, just wondering why you connected your retort/reflux vessel's with a 3 inch pipe between them? Why not connect the reflux vessel directly to retort top?
Also noticed that you have a long pipe leading from the reflux vessel to the condenser! What is the point of this,is it to assist cooling ?
Your retort vessel is made of what thickness material?

[Excalibur]

Excalibur, just wondering why you connected your retort/reflux vessel's with a 3 inch pipe between them? Why not connect the reflux vessel directly to retort top?
Also noticed that you have a long pipe leading from the reflux vessel to the condenser! What is the point of this,is it to assist cooling ?
Your retort vessel is made of what thickness material?

I reasoned that the 3inch connecting pipe would give the best chance of creating and maintaining the two distinct vessels at their respective target temperatures. These vessels work in harmony and sympathy with each other and are finely balanced. Finding the balance that gives correct results is the trick and may require some trial and error. Directly connecting the vessels or indeed using the very same vessel with the lower part in the hot zone and the upper in a cooler zone has been the subject of earlier discussion on this forum. I see no reason why it would not work though I've not tested the theory. What's critical is the temperatures, not so much the shape, size or distance apart.
The long pipe leading from the reflux just serves as a bit of extra initial cooling before vapor/condensate gets to the heat exchanger. The pipe was used at the exact length it was picked up from the steel rack, not so much by design.
From memory my retort wall thickness is 8mm, retort floor is 10mm and flanges about 22mm each.

[rozier56]

rozier56

Thks Excalibur.

[Babataku]

metal fatigue

Another question:

I am currently using a Diesel Burner for heating my retort. And the rate of metal fatigue is unbelievable! The Flame is not in direct contact with the retort...I have installed some 4mm mild steel plates in between the burners flame and the retort which can be easliy changed out but I'm just amazed at the rate at which the metal just degrades...

My question is: can I expect my retort (6mm Mild steel) to suffer same fatigue from the heat? Since its not in direct contact with the burner flame? If I was using electric heater bands would this even be a concern?

I am thinking safety here!

Any comments and suggestions are welcome please.

[wheels]

Another question:

I am currently using a Diesel Burner for heating my retort. And the rate of metal fatigue is unbelievable! The Flame is not in direct contact with the retort...I have installed some 4mm mild steel plates in between the burners flame and the retort which can be easliy changed out but I'm just amazed at the rate at which the metal just degrades...

My question is: can I expect my retort (6mm Mild steel) to suffer same fatigue from the heat? Since its not in direct contact with the burner flame? If I was using electric heater bands would this even be a concern?

I am thinking safety here!

Any comments and suggestions are welcome please.

If you do not have direct flame on the Retort, it should be OK. But you need to keep an eye on the Retort, both inside and out. Outside damage if any, will be from the Burner. Internal damage can be caused by Acids, which some plastics create. So if by accident you get the main feedstock contaminated by a piece of PVC for instance, then Chlorine and Hydrogen Chloride will be created and with the retort at such a high temp, any Acid will work double time on steel.
So basically, the Flame is the rapid oxidation, via a chemical reaction, of the Diesel fuel and Oxygen. Rust/Corrosion or steels is exactly the same thing, except it happens very slowly. So now if you take the flame and blast it onto Steel, you dramatically speed up the Oxidation process. So steel does not last long.
Not all, bit most Stainless steels will handle heat without oxidation.
Most austenitic steels, with chromium contents of at least 18%, can be used at temperatures up to 870°C and Grades 309, 310 and 2111HTR (UNS S30815) even higher. Most martensitic and ferritic steels have lower resistance to oxidation and hence lower useful operating temperatures. An exception to this is the ferritic grade 446 - this has approximately 24% chromium, and can be used to resist scaling at temperatures up to 1100°C.

[Excalibur]

Agreed, overheating steel is going to decay it. The retort contents will try to reduce the temperature of the steel but extreme applied heat will mean the liquid won't be behaving in any kind of calm fashion. It's likely to be dancing on the hot spot/s.
Babataku, your 4mm steel plate shields will have nowhere to lose their heat so they will sit there and glow super hot, oxidize and eventually crumble.

When my steel refractory burnt out last year I moved away from direct flame on the retort vessel. Instead I heat the refractory bricks and give the flame somewhat of a 'torturous path'. I call this "softening the heat" and the firebox is now more of an oven than a blast furnace.
In addition I moved the burner head further away.
For some time I've had a TC on the flame inlet duct so the burner can be adjusted to give the required flame temperature to match retort conditions.

Suggestions:
Fit a TC on the flame so you know exactly how much heat you are dealing with.
Use refractory bricks as a type of heat storage and direct the flame front onto them.
Work out a way of controlling burner temperature, perhaps multiple or adjustable diesel jet/s.

[Babataku]

cast iron

Thanks for the replies.

I was thinking of using Cast iron for the Firebox. I'm not sure though how this will affect time to heat up the retort and if this will solve steel oxidation problem. Has anyone tried this out? I don't have any local suppliers for stainless steel.

And also Excalibur, using refactories and creating a flame path like you did...how does this affect heating up time? Do you use more fuel to get to temperature and maintain that temp? And by the way on your runs how long does it take you to get to 400deg?

[wheels]

Thanks for the replies.

I was thinking of using Cast iron for the Firebox. I'm not sure though how this will affect time to heat up the retort and if this will solve steel oxidation problem. Has anyone tried this out? I don't have any local suppliers for stainless steel.

And also Excalibur, using refactories and creating a flame path like you did...how does this affect heating up time? Do you use more fuel to get to temperature and maintain that temp? And by the way on your runs how long does it take you to get to 400deg?

Cast iron is good. It is much slower to rust away. For SST, also consider scrap items like heat shields in old appliances. Toasters, Heaters etc. It does not have to be thick metal.
I have the Diesel heater blowing the hot air around the retort. I have spirals around the retort so as the hot air is swirled around and up to the exhaust outlet, so ot creates a more even heat distribution. The other jacket is insulated to retain as much heat as possible inbetween the two steel vessels.

[Excalibur]

Cast iron would be more resistant to heat. For stainless, try a scrap metal yard. Best would be refractory brick so look out for old log-fire boxes. These have thin refractory tiles lining their mild steel fireboxes. Ones I've seen are about 1" thick and are a proper firebrick.

I've only fired the rebuilt firebox set up once so far and I was constricting the flame temperature to below 800°C during warm up. This took longer than before, somewhere over 2 hours but also there was some breakdown repairs to attend to. However I was heating a full retort perhaps 40L feedstock. The insulation needs improving as well. Fuel usage was not recorded. Logically the refractory will take longer to heat up but then it will hold and release heat a lot longer as well.
Where firebrick refractory could work nicely is at the conclusion of a run. With flame shut down, residual heat from bricks would ensure the retort dried out completely.

Anyone considering alumina refractory bricks should note there are 2 types. Light weight brick which has good insulating quality and heavy dense type which is better at heat storing. Ordinarily one would choose the brick to suit the work and have the character intended. At first I couldn't decide which would be better but dense bricks turned up for free so that's what I'm using.

[Babataku]

cast iron

Thanks for the replies.

Will search for some scrap SST and some firbricks too.

[kenssurplus]

Convert Mother's gasahol unit for pyrolysis

Hi All,

Top notch information and people in this thread. I have read through this monster of a thread over the past few years, and recently searched for any post about using Mother Earth News' gasahol distillation unit. Not finding anything posted about this, my question is: Do you think these plans can be easily modified for a plastic pyrolysis unit?
What parts of the plans can be used as is without modification?

I see in the plans, sections filled with marbles, and coiled copper tubing cooling sections. I suppose that all these sections necessary for gasahol production, would be in the way and just clogging up the works so to speak.

Any insights would be appreciated.
ken

[wheels]

Hi All,

Top notch information and people in this thread. I have read through this monster of a thread over the past few years, and recently searched for any post about using Mother Earth News' gasahol distillation unit. Not finding anything posted about this, my question is: Do you think these plans can be easily modified for a plastic pyrolysis unit?
What parts of the plans can be used as is without modification?

I see in the plans, sections filled with marbles, and coiled copper tubing cooling sections. I suppose that all these sections necessary for gasahol production, would be in the way and just clogging up the works so to speak.

Any insights would be appreciated.
ken

It's a similar method, but a very different product and thus very different parameters and processes.