How to turn plastic waste into diesel fuel cheaply

[alejandroramallo]

Hello everyone. Although long ago that I have been following the Forum, and conducting experiments on the subject, my results are not as advanced as many of you. However I wanted to provide a picture and a video of what I have achieved so far. If my English is not good, I ask forgiveness. I am using a translator to write. My language is Spanish.
[VIDEO]https://www.youtube.com/watch?v=0c_zMXGcYyw[/VIDEO]

[Excalibur]

Rozier
Without pics or diagrams it becomes difficult to understand your exact situation so I hope my comments are helpful...
I think a better plan would be to make the diesel condenser much longer. In this way the vapor can be subjected to longer resident times because of the sheer length of travel. In addition use coolant in counter-current style if not already doing so.
My plant runs at up to 1 psi at a guess but only because of the attached gas-jar. Even then the backpressure is relative to the amount of gas in storage. I consider the 1 psi max back pressure a compromise and I'd rather have 0 psi.

BTW, if you run with some means of vapor stream restriction and thereby create back pressure, I think a pressure alarm warning system would be prudent. Should the alarm sound off, at least you'd have an opportunity to remedy and stabilize the situation.

[wheels]

Thanks folks,
When i asked about back pressure measurement, i was wondering if some of you have tested your own system and what sort of levels are out there?
My new system has one way valves and flow meter , no water system anymore due to irregular pressure flows and difficult to control production flows.
My current back pressure related after the condenser is 0.4bar.I intend to vary this with steam pressure valves that are adjustable on the run to determine the best back pressure to achieve max diesel condensation in condenser.Thereby maximizing output in this area.
All my production is done with mixed ldpe/hdpe and polypropylene.

0.4 bar????? !!!!! You sure? That is nearly 6 PSI and that is far too high. Should that figure be millibar?? The pressure should be virtually unmeasurable if you are using "bar" scale. Perhaps your pipe size is far too small or you have a restriction in a valve or a connection that is causing back pressure. As I have stated in my last post, the water allows a backpressure of just a fraction of a PSI.
Pressure needs to be as close to zero as is possible. By increasing pressure, you increase the temperature needed to cause the plastic to vaporize. This slows down the process because you need a higher temp for the plastic to start to release vapor, which means more energy and it takes more time to get to the higher vaporization temp. The cracking also changes. Although just how will be hard to know as it's different due to many variables. But chances are, you will get more Gas and more lighter fractions.
The water also acts as the very last means of trapping condensable liquids, leaving you with a "Clean" Gas discharge.

[rozier56]

rozier

Thanks folks,
When i asked about back pressure measurement, i was wondering if some of you have tested your own system and what sort of levels are out there?
My new system has one way valves and flow meter , no water system anymore due to irregular pressure flows and difficult to control production flows.
My current back pressure related after the condenser is 0.4bar.I intend to vary this with steam pressure valves that are adjustable on the run to determine the best back pressure to achieve max diesel condensation in condenser.Thereby maximizing output in this area.
All my production is done with mixed ldpe/hdpe and polypropylene.

[wheels]

Has anybody measured the back pressure in their system?Trying to establish residence time required!
Also would like to know the exhaust gas outlet proportion in case we are not liquefying all the diesel we should be and driving some to atmosphere.

Back pressure, are you meaning the pressure required to overcome the water bubbler? It depends on the depth the pipe is down in the water. Lets say for instance, the end of the pipe is down at a depth of 4 or 100mm. So the gas has to push that water back out of the pipe and that is the same as if it was 4" / 100mm head of water pressure. That's a mere 0.000145037738 PSI or 1 Pa.

The Residence time... are you heating Plastic or WMO?

Exhaust Gas. In basic, the Hotter you heat the Vessel, the more Gas that tends to be produced. But it does also vary between WMO or Plastic and the WMO depends on what is in the WMO mix. So unless it is just plain Sump oil, then it does become very difficult to know exactly what is going to come out. If the WMO has come from a Vehicle Service facility, then there is a chance that the mix could have Cleaners/ Solvents, Petrol, Transmission fluid and Brake fluid along with the Sump Oil. You do need to very careful with this stuff. It can be highly Toxic depending on what has been dumped. Getting back to the Gas, well as you can imagine, it can become difficult to low and vary between batches, depending on what is in it. With Plastic, it is mostly temperature related. The higher the Temperature, the more non condensable Gases are created. It has been established temperature of around 460 DegC is a Balance point between best quantity of Liquid to Gas and coupled to time of process. Temperatures below 450, the more liquid, the longer the process time and thus more heating energy used. Temperatures above 450, more Gas, less processing time, maybe more energy used to gain the heat, less liquid, so the process is inefficient. Unless of course the aim is to produce Gas.
Did that help?

[Excalibur]

Thanks,
So the stainless will be filled in the reflux/distillation column up to 80%?

It might just happen to turn out to be 80% because inside the reflux chamber, I want a small gap at the bottom and top.

The 80% figure I was earlier referring to is the retort maximum fill capacity, for safety reasons.

[rozier56]

rozier56

Has anybody measured the back pressure in their system?Trying to establish residence time required!
Also would like to know the exhaust gas outlet proportion in case we are not liquefying all the diesel we should be and driving some to atmosphere.

[rozier56]

rozier56

Thanks,
So the stainless will be filled in the reflux/distillation column up to 80%?

[Excalibur]

Excalibur, your reflux vessel! Have you completely filled that chamber with your packaging?
Is that the same one you will use on your new retort chamber as well?
What was the volume of your old retort?
What volume will the new one be at?

The retort and reflux vessels are the same except retort is shortened about 150mm. It has only lost 2 or 3 liters. I think volume was 47L (but only filled to about 80% max capacity). The packing is a job still to be done, probably I'll use light gauge stainless.

[rozier56]

rozier56

Excalibur, your reflux vessel! Have you completely filled that chamber with your packaging?
Is that the same one you will use on your new retort chamber as well?
What was the volume of your old retort?
What volume will the new one be at?

[wheels]

In this case it might be an advantage not keep the diesel at temperature for the duration of the run (8-12hr) because prolonged exposure to heat may encourage more oxidation. Better could be to extract light fractions quickly then quench/chill the diesel..

Yes. Although it is even more complex than just this. It is also the key reason why everyone's plant designs produce things differently. As in why one can have a nice clear Diesel produced and another ends up with Wax. Every single aspect affects the type of output. For the Amateur backyarder, the output is not so critical, as long as it is a usable Fuel. But if someone is after a specific product or quality of product, the design becomes more and more important and complex in both it's build and understanding in how to design and Build it. As a couple here on this Forum have discovered. It is also why I am very skeptical of the many companies that Build processing plants for sale. Not all of them have designs that actually work or work well.
What you produce as an output is reliant on many factors which I will list below.
Heat energy to melt the plastic. There is actually a required energy input required to pyrolyze plastics correctly. Even though plastics vaporize OK by just applying any decent heat source, there is actually a specific heating time to take Plastic through the various stages to vaporization. This allows for the most efficient energy input, the best Fuel quality output and the least non-condensable Gases produced. This is probably the most important of all aspects, because not enough heat, or too much heat can both be problems and be one of the main causes of Wax production. Wax can be produced in three ways. The temperature at time of Pyrolyzing being too high or too low can both create Waxes. As well as any further cracking on through the Plant, where residence times, which determines the cracking into what weight of Hydrocarbons, can also produce Waxes. Mostly though, too much heat can produce more non condensable gasses and we don't want to waste our Fuel turning into Gas.
Speed of pyrolysis is going to be determined by Spped of throughput and energy input.
Feedstock. This has a major affect on the output type, because what type of Plastic determines what Chain length is mostly produced at the very start of the cracking process. If you start with long chains, then reflux and Catalyst if used, is important to breaking those chains. But if you are starting with shorter chains, then Reflux time or temp could make the chains too short for the type of fuel you want and also produce more Gas.

[wheels]

It's good to try things and test theories because without that you struggle to learn better ways of production. For that matter talking and bouncing ideas around is a wonderful way of finding solutions.
.

Absolutely and as they say, the only stupid question is the one not asked. I have the view that everyone, no matter what experience level, has something to give. Possibly because I am a Kiwi. Living in a very distant and remote Country, especially in earlier years before we had the world shrinking Internet and these kind of Forums, us Kiwis had a very practical view of making things work. We had no one to say it couldn't be done. We just figured out how to do it instead. I was brought up in that Era of how to make something work with the least of resources. Sadly our country has caught up to the rest of the World in being smothered by Red tape and Laws stopping us from doing things.

[Excalibur]

It's good to try things and test theories because without that you struggle to learn better ways of production. For that matter talking and bouncing ideas around is a wonderful way of finding solutions.

In this case it might be an advantage not keep the diesel at temperature for the duration of the run (8-12hr) because prolonged exposure to heat may encourage more oxidation. Better could be to extract light fractions quickly then quench/chill the diesel. From this point of view a row of diesel condenser vessels could be something to consider.
Consider this example of 3 vessels filled in 'rotation':
Vessel #1 is full and has a light vacuum applied to pull the last of the volatile fractions off.
Vessel#2 is in the process of being filled from retort production.
Vessel#3 is empty, awaiting its' turn.
Once vessel#2 is full, it has vacuum applied, feed gets diverted to vessel#3 and vessel#1 is pumped out, product quench/chilled to storage.
So at any one time, one vessel is empty, one is getting filled and one is under vacuum. More complicated would be valving and pipework. To help evaporation each vessel could optionally have an electric heater & thermostat.

Just a thought...

[wheels]

In my opinion evap'ing light fractions from diesel is more about the balance between temperature and residency time. Using a higher temperature will shorten residency time while a lower temperature will lengthen it. In a continuous production plant a diesel holding vessel that is small will inevitably mean the product will be pumped out prematurely meaning any residual light fractions will need to be extracted later.
Consider this example: Diesel vessel is held at say 80°C. When it becomes full the contents is pumped out to side tank where it's dropped to say 50°C. It will still continue to release light fraction but at a slower rate and continue to fall with the temperature decline. One workaround to continue pulling off the light fractions at a good pace would be applying a vacuum which reduces vapor pressure and boiling point.
My preference would be to have the diesel tank with sufficient volume to accommodate the entire run of diesel production.

As one or two have found, the Cracking and Distillation is very complex. Temp and R Time both have a factor in Cracking. Even though the Fractions have passed the stages of Retort and then Reflux and are now in a much lower temperature environment of the first Still Pot, some Fractions will continue to Crack into the more unwanted unsaturated type Fractions and much lighter fractions are often broken into non condensable Gasses. My Pots have just been re fitted so they can continuously drain off the condensed liquids as they are produced, so as to get the Fractions out of the heat as quickly as possible. This should allow the production of a more accurate range of fractions in each Pot an hopefully allow for a far more stable end product. I will let you know the result end if this week, as the Plant should be running again early in the Week.

[Excalibur]

Do you think is it the throughput to holding tank volume ratio that is key here in getting the lighter fraction to evaporate out of the diesel before the diesel is drawn off, or do you think it is the throughput to available surface area for evaporation ratio that is more important? I am thinking of using a 250mm diameter horizontal round pipe (could be 1m long, could be 6m long, just so long as it is kept at the right temperature) - the condenser feeds into one end, the pipe level is kept half full, the condensate flows from one end to the other and out a drain pipe which turns up to a tap at the half full point. The drain pipe could be run back along the length of the 250mm pipe without insulation for cooling before exit. This way achieves a high surface area to volume ratio which I believe is important to efficient vaporisation and identified as the ideal fill point in lab set ups.
Col

In my opinion evap'ing light fractions from diesel is more about the balance between temperature and residency time. Using a higher temperature will shorten residency time while a lower temperature will lengthen it. In a continuous production plant a diesel holding vessel that is small will inevitably mean the product will be pumped out prematurely meaning any residual light fractions will need to be extracted later.
Consider this example: Diesel vessel is held at say 80°C. When it becomes full the contents is pumped out to side tank where it's dropped to say 50°C. It will still continue to release light fraction but at a slower rate and continue to fall with the temperature decline. One workaround to continue pulling off the light fractions at a good pace would be applying a vacuum which reduces vapor pressure and boiling point.
My preference would be to have the diesel tank with sufficient volume to accommodate the entire run of diesel production.