How to turn plastic waste into diesel fuel cheaply

[Col]

Float level

I've wondered about a float in such harsh conditions too. The froth and frantic bubbles might affect buoyancy. A float would need to be made from a reasonably thick gauge metal. Could the float be filled with something other than air, perhaps a substance giving good buoyancy but less affected by retort activity?
One surprise happened that I'm attributing to a low oil level in the retort was that when feed was applied, it immediately flash-boiled. This resulted in dark red output with particles, presumably carbon.

I don't think I would want a float filled with air inside the retort come to think of it. If not air, then what? A large, disc-like float might be good, it would 'absorb' a lot of the violence inside the retort and give a more steady read, but the bigger the float is the more it impinges on the surface area of the oil which we need for evaporation.
If we had a pipe off to the side of the retort (to get away from the splashing etc) with a steel ball floating in it, and made the pipe of borosilicate or some other non-metallic material, we could use the floating steel ball to actuate a series of magnetic relays which would then tell us the oil level - like this...

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The level readings from all three could be assisted by putting baffles made from perforated sheet around the level sensor. You could also program the controls for the feed pump to wait for the sensor to stabilise over a period of a few seconds before actuating the pump, just to be sure.

Apart from the colour and sediment, what was the quality of the product produced by flash-boiling? Still ok?

[Excalibur]

Someone has suggested measuring the mass of the distilled/cracked products in order to match the feed to the output. That could be done I guess except for the off gases, and there would be a delay between the oil cracking and the vapours condensing resulting in fluctuations in oil level, which may not be a major problem in a retort filled deep with feedstock, but if we aim for a shallow retort how do we maintain a steady oil level? I expect the bubbling will be too violent for a float level to work, even if it could handle the harsh conditions. Perhaps the only way to reliably do it is to run a few feed rates through it and monitor conditions, when the feed rate gets too high you've found your maximum rate.
A thought - I expect the heat supply will be one of the more difficult things to control if using a liquid fuel. If you settle on a good heat supply and just keep it steady you could manipulate the feed rate up and down to control the temperature. If you have enough temperature readings in the right places you wouldn't need to know the oil level, you could tell what was going on inside the retort by what the temperatures are doing.
I would appreciate anyone's thoughts on this.
Thanks, Col

Col, good on you for giving this aspect some proper focused thought. Yes, matching feed to output is cumbersome. While I haven't measured, the off gases probably amount to a few percent. Yes, if feed matched output and the heat input could be stable, that would be magic. In practice it hasn't been so easy. Originally, I thought I'd be able to crank the heat up high, then apply the feed till a state of equilibrium was reached. One upgrade I'm planning is to use a needle valve instead of ball valve for improved flow control of feed. A ball valve is on or off with little adjustability in between.
I've wondered about a float in such harsh conditions too. The froth and frantic bubbles might affect buoyancy. A float would need to be made from a reasonably thick gauge metal. Could the float be filled with something other than air, perhaps a substance giving good buoyancy but less affected by retort activity?
One surprise happened that I'm attributing to a low oil level in the retort was that when feed was applied, it immediately flash-boiled. This resulted in dark red output with particles, presumably carbon.

[Col]

tube furnace for a continous system

Thank-you, mercedes 308, for posting this link. A tube furnace might be just what is needed for the person interested in a continuous process system.

References are made to rpm but it doesn't seem to say that the tube is rotated. I assume the rpm references are for the cylinder rotation as some people are doing for tyre pyrolysis. What is the benefit of this method for a continuous system? I guess it's one way to spread the feedstock over the heating walls and keep the feedstock mixed. Any other benefits?

[Excalibur]

On Ebay I picked up a copy of The Petroleum Handbook compiled by Royal Dutch Shell, 3rd edition 1948. I paid $1 and with shipping another $28. The book is a bit battered but perfectly legible.

I highly recommend the book for studying distillation and cracking of hydrocarbons. Some of the principles of refining are quite difficult to understand though this book delves into the subject, explaining the methods, procedures, etc in ways that a layman can grasp with relative ease. I'd read portions of this book on loan a couple of years ago.

The book is old but the basic fundamental principles have not changed. It might even be argued that the book is more relative to the DIY enthusiast because of the straight forward approach without use of super exotic materials, modern technologies and computer controlled programming.

658pages
Of interest is smell removal methods for fuels, naming it mercaptans, a hydrosulphide.

[Col]

Auto levelling of oil for a continuous system

As for maintaining a certain level in the retort maybe this would work - set a horizontal pipe at the desired oil level, passing from inside the retort out to another tank. This tank has a removable lid for checking on the level, and a quality floating valve similar to those used in a toilet cistern, but all metal. This tank can be made as small as is practical to fit the float valve in, 40L? The float valve is fed from a bulk oil drum which can be topped up as required. As the vapours pass from retort to condensers, oil flows from intermediary drum to retort and oil feeds from bulk drum to intermediary drum via float valve. The oil finds it's own level between intermediary drum and retort, this level is set by the float valve.

This idea I suggested some time back has whiskers on it - if the oil feed malfunctioned/stopped for any reason (bulk supply ran out, feed pump to header tank faulted, float level jammed) and the retort kept going the oil level would drop until there was no longer an oil/liquid seal and air would enter the retort - KABOOM!
Someone has suggested measuring the mass of the distilled/cracked products in order to match the feed to the output. That could be done I guess except for the off gases, and there would be a delay between the oil cracking and the vapours condensing resulting in fluctuations in oil level, which may not be a major problem in a retort filled deep with feedstock, but if we aim for a shallow retort how do we maintain a steady oil level? I expect the bubbling will be too violent for a float level to work, even if it could handle the harsh conditions. Perhaps the only way to reliably do it is to run a few feed rates through it and monitor conditions, when the feed rate gets too high you've found your maximum rate.
A thought - I expect the heat supply will be one of the more difficult things to control if using a liquid fuel. If you settle on a good heat supply and just keep it steady you could manipulate the feed rate up and down to control the temperature. If you have enough temperature readings in the right places you wouldn't need to know the oil level, you could tell what was going on inside the retort by what the temperatures are doing.
I would appreciate anyone's thoughts on this.
Thanks, Col

[Beyond Biodiesel]

Came upon this though could be useful here.
Pyrolysis of grasses and leaves to produce bio oil.

Thank-you, mercedes 308, for posting this link. A tube furnace might be just what is needed for the person interested in a continuous process system.

In response to further questions and comments here, I have been exploring vacuum distillation for the last 2 years. I do it in a 5-gallon (20L) system. I reason that I can easily adapt that system to a continuous process flash evaporator when I wish to move forward; however, distilling 5-gallons (20L) of WMO every day is as much fuel as I need at this time.

[Excalibur]

I was wondering after reading Excalibur`s account of his efforts, if you want to create a continues feed system, should you reduce the amount of feedstock in your retort to get a faster reaction from processing the feedstock?

Will it not be better to have less feedstock with temperatures that can almost instantly convert your continues feed into gas than to heat the feedstock up to the correct temperature because the feedstock level is to high, thereby when introducing new colder feedstock dropping the temperatures in the retort and slowing down the process?

If one would want to create a system that can deliver 50 liter diesel per hour, how big should the reactor unit be to allow for such a system?

If the feedstock level can be kept lower but the pyrolysis takes place on a faster scale, will that allow to have a smaller reactor unit or will that defeat the purpose to try and create a chamber where the reaction can take place faster in a shorter time period? A smaller reactor means a faster time to achieve the heat requirements, less feedstock in the chamber, can also reduce boil over of feedstock, but that also means that maybe you can`t reduce the size of the reactor?

How should you determine the scale for your reactor based on the amount of fuel you want to produce per day or per hour?

This is a very interesting question that I agonized over when I built my current "Orion" retort. One thing has become clear, is that one present limitation is the amount of heat that can be poured in. If incoming feedstock isn't matched by heat applied, then the it doesn't matter so much whether the retort level is high or low. The temperature can only drop. I'd need to slow down the feed to match heat or increase heat to match feed. Another possible is to increase the heat of the feedstock itself. I have a huge amount of heat I can generate, it's just that I'm not applying it in the most efficient manner.

To size the retort you could take Excalibur's figures of fuel used : oil distilled, over the lapsed time and work from there.

I would just caution, those figures will be distorted because of the unknown quantity of retort gases used to make heat.

Hi Excalibur.
What do you mean by a 'reducing bush'?

Think of this terms of a simple method of reducing the throat size between the two chambers.

[Col]

reducing bush

A plate welded at the desired dividing point between the two chambers would have a center port hole bored. Reflux temperature might be controlled by the insertion of a "reducing bush", so in this way the heat can be manipulated.

Hi Excalibur.
What do you mean by a 'reducing bush'? I have made my splash plates out of 2 circle plates. The retort is 800mm diameter. The lower splash plate is a 700mm diameter, 5mm thick circle plate, centred in the retort, 50mm in from the retort walls. The second, higher plate is a large 'washer' which meets the retort walls at the circumference but has a 100mm hole in the centre. This way the vapours must pass from the liquid surface to the outer edge of the first plate, between the two plates which are about 50mm apart, then to the inner hole of the second plate, then up to the mesh pack in the reflux. I figure the vapours will pass easily but any splashing liquid won't reach the mesh packing. Is my second plate what you mean by a 'reducing bush'?
Col

[Col]

Small retort, fast distillation

Pfaulder has been doing this for a long time, Short path, high vacuum distillation in wiped film evaporators. At pressures of 0.1mmHg they evaporate up to 85% of the used oil between 260C to 301C. The water and light ends are separated before the WFE process. The remaining slurry can be used as a road base extender. The benefit of conducting the process under high vacuum is the lower temperatures don't cause degradation of the hydrocarbons. The short residence time also plays a part here, the heated evaporation plate is very near the condensers so the molecules are only 'hot' for a short time, also reducing the chance of degradation. They maximise volatile extraction by agitating/progressively wiping the feedstock down the heated wall of the retort.
While their website makes for interesting reading we are looking for principles we can apply in a DIY application. The principles here, as you have identified, are high heat, short residence time (if we could apply a strong vacuum we would go for a lower heat and short residence time). We can achieve this, as Asad said some time back, by using a wide, shallow depth of feedstock, over a series of smaller flames/heat source (with a mixer/wiper for further improvement). To size the retort you could take Excalibur's figures of fuel used : oil distilled, over the lapsed time and work from there.
Col

[Col]

Sizing of retort

How should you determine the scale for your reactor based on the amount of fuel you want to produce per day or per hour?

Hi Vast.

Here are some notes I made some time back while reading the comments from fellow contributors, and some YouTube videos, might help you in sizing the retort. Probably only relevant to smaller systems though.

Guys with 2kW heaters are getting their 19-20L retorts up to 400C in 1-2 hours, or 45mins to 350C.
BBD—2kW heater at base of retort, then extra heater bands and line wrap, 19-20L, 2hrs to heat, gets 1L/hr from start to finish, but nothing in the first hour while the temperature rises, so probably 2L/hr during the peak cracking/distillation period. 11hr batch time. 1L consumes 100W.
YouTube - an oil burner under a gas bottle was getting up to 1 gallon per hour but found it was too fast and hard to control so dropped it back to 1 gallon per 3 hours. He gets a gunky oil off the bottom and a good oil/diesel condensed off the top. Another guy seems to run at a similar speed with a similar sized system. Don’t know about residue left behind.

I have some information on instant evap v boiling pot methods. I'll dig 'em up and post shortly.
Col

[VAST]

Continues Feed System

I was wondering after reading Excalibur`s account of his efforts, if you want to create a continues feed system, should you reduce the amount of feedstock in your retort to get a faster reaction from processing the feedstock?

Will it not be better to have less feedstock with temperatures that can almost instantly convert your continues feed into gas than to heat the feedstock up to the correct temperature because the feedstock level is to high, thereby when introducing new colder feedstock dropping the temperatures in the retort and slowing down the process?

If one would want to create a system that can deliver 50 liter diesel per hour, how big should the reactor unit be to allow for such a system?

If the feedstock level can be kept lower but the pyrolysis takes place on a faster scale, will that allow to have a smaller reactor unit or will that defeat the purpose to try and create a chamber where the reaction can take place faster in a shorter time period? A smaller reactor means a faster time to achieve the heat requirements, less feedstock in the chamber, can also reduce boil over of feedstock, but that also means that maybe you can`t reduce the size of the reactor?

How should you determine the scale for your reactor based on the amount of fuel you want to produce per day or per hour?

[mercedes 308]

Catalytic Pyrolysis by Heat Transfer of Tube Furnace for Produce Bio-Oil

Came upon this though could be useful here.
Pyrolysis of grasses and leaves to produce bio oil.

[Beyond Biodiesel]

Hi folks,How is this idea?
My retort is 850mmlengthx333mmwidth radius.=296metres.

Sorry rozier56, this does not make any sense to me. Are you using the term 'width' to refer to 'diameter' or 'thickness,' or neither? You also switch from MM to meters??

Proposed retort to be placed directly on top of retort is 1meter x 12mm width radius =45 meters.

Same here, it does not add up.

[rozier56]

Hi folks,How is this idea?
My retort is 850mmlengthx333mmwidth radius.=296metres.
Proposed retort to be placed directly on top of retort is 1meter x 12mm width radius =45 meters.
How does that sound keeping in mind that 1/4 of 296 =74meters.
Another point is that the retort temp in my case is always higher than my reflux temp.Temp is measured in retort open area and reflux at the top of the reflux.
THKS.

[Beyond Biodiesel]

Thks BB. It was good to talk to you on skype.

Yes, it was.

Hey folks,

Been quite sometime since I've been on the form I see a lot has happened the past while.

My question is regarding cracking the hydrocarbon does anybody know if you can crack it in the gas state or do you have to crack it in the liquid state. The point being, can the gases coming off at a lower temperature be cracked and a high temperature state or do you have to bring the whole liquid up to a higher temperature to crack it to lighter hydrocarbons before it boils off under pressure?

I am just sitting here reading the thread from the beginning as I am thinking of the little machine to do this? The cost of fuel is over a $1.50 per liter now and is getting ridiculous to commute to work.

Looking forward to your comments

Karl

Just keep in mind cracking temperature is 425C. Hydrocarbons are in vapor phase at that point.

Wide is better than tall - really?

Not really. You just do not want either your retort or reflux to be tall and skinny. A ratio or 1:4 or 1:3 between the diameter and the height is best.

My retort was 1200mm tall x 800mm diameter including a dish end floor. I cut it from a pressure vessel twice the height which had been a liquid / gas phase separator,

Sounds just right.

so it had a 300mm thick pad of stainless steel mesh packing part way up it. I cut out a 300mm segment of the tank and put the packing in there with flanges so it was a removable reflux zone. I put a couple of splash plates below the packing to keep it from being doused with violent splashes of black boiling oil.

Sounds just right.

I had intended to operate the two together until BBD pointed out to another forum member that it could be hard to control the reflux temp if the two were part of a 'single tank' so to speak.

Huh? I see no problem with your proposed design. If anything if the reflux is just the upper 1/4-1/3 of the report then it is likely to have the same temperature as the retort, which is good. If the reflux is at a lower temperature than the retort, then your fluid for cracking will just reflux for ever.

I recognised the reflux temperature is critical so binned the idea and was about to use an air compressor tank as a separate vessel a little way above the retort. But the air compressor tank is tall and not so wide (1275mm x 420mm) and the mesh filled segment of the first tank is short and wide (300mm x 800mm), same diameter as the retort. Coincidence has it that both are approximately 35% of the volume of the retort (but not 35% of the WMO fill level, which will be about half way down and constant as it will be a continuous feed system, so the reflux will be about 70% of the volume of the WMO in the retort).

I do not see any of this as a problem.

I expected that a tall reflux would be better than a short one, more opportunity for separation of molecules of different SG's. Is it that the narrower the column is the faster the flow rate will be and that disturbs the distillation process?

The point of a reflux zone is to reduce boil over, so you want the velocity of the vapor stream to slow down, to allow droplets of condensate to precipitate out of the stream.

Won't a short, wide reflux make it difficult to control the temperatures? less height to allow reduction of temperature from 425C in the retort to the desired reflux exit temperature? More width will also make it more difficult to keep the temperature uniform from core to shell. Perhaps the rising vapours will keep the core the right temperature and the waste heat circling the reflux can keep the shell at the right temperature.

The vapor stream heats the reflux, but it should be insulated and heated to the desired temperature. There should not just be 1 reflux zone, but several, one for each condenser trap, and the reflux is of course after the desired trap zone, not before it.

I have a good condenser I picked up from a neighbouring business shutting down selling off it's factory gear. It is a horizontal tube condenser with 100mm inlet and outlet pipes. I have put a 100mm vapour outlet on the retort / reflux exit. I expect with this set up I should be able to crank up the throughput later after proving the system first.

Sunds good

I've often pondered over the idea of retort-reflux being the same diameter.
It has a number of good things going for it. It could be fabricated using a continuous length of pipe saving time, effort and resources. A plate welded at the desired dividing point between the two chambers would have a center port hole bored. Reflux temperature might be controlled by the insertion of a "reducing bush", so in this way the heat can be manipulated.
For diesel fired plants, the reflux could be heated with the same flue gas and with minimal effort. A set of dampers could be employed to divert the hot flue gas directly to the stack or via the reflux.
These ramblings are untested theory...

Sounds good