How to turn plastic waste into diesel fuel cheaply

[imakebiodiesel]

A vacuum pump is the wrong approach. You want to have a small positive pressure inside your retort so that if a leak should occur then hydrocarbon gas will escape, This is a fire risk but will not cause an explosion.
If you have a vacuum in your retort and a leak occurs then air will enter the retort and Boom!
Remember that the auto ignition temperature of diesel vapour is as low as 250C. At this temp, if air is present, it will ignite WITHOUT a flame or spark.

The idea of using the waste heat to produce fuel rods is an interesting one and would certainly simplify a continuous feed system.

[Heartburn]

By stabilization I assume you mean hydrogenation, adding hydrogen atoms to saturate, unsaturated hydrocarbons. This will only happen at very high pressures and temperatures in specially designed reactors. It wont happen in the pipework leading away from our type of retort. The hydrogen will exit the system via the bubbler mixed with the uncondensable gases,
Im sure a method could be developed to pyrolyse plastic and tyres together by raising the temperatures in steps but it seems hardly worth the trouble. If you process them separately you will get better results with less contamination.

That is what i was thinking. I had assumed that since the fuel oxidized in air, it would easily take a free hydrogen atom in the pipes. The rest does come out with the uncondensables and since hydrogen burns hotter, it would reduce the cost of the process.

[Heartburn]

Dealing with HCL

I've been trying to get an electronic copy of the study I talked about for copper and HCL but I can't find in anymore. You can buy the book though.

Here is a quote from Wiki's page for Polyvinyl chloride in the Dioxins chapter that refers to this study;

PVC produces HCl upon combustion almost quantitatively related to its chlorine content. Extensive studies in Europe indicate that the chlorine found in emitted dioxins is not derived from HCl in the flue gases. Instead, most dioxins arise in the condensed solid phase by the reaction of inorganic chlorides with graphitic structures in char-containing ash particles. Copper acts as a catalyst for these reactions

The study is called "Formation Decomposition of Polychlorodibenzodioxins and Furans in Municipal Waste"

so basically you need "dirty" copper. An educated guess on how to best use this process would be to mix ashes with high coke content with copper at the base of the reflux with and aluminum wad on top. The release of the chlorine in contaminated feed stock would react with the ashes with the help of the copper and hydrogen released from the resulting HCL with the aluminum to make Aluminum chloride (AlCl3) Then the reaction goes to:

"Reactions with water

Aluminium chloride is hygroscopic, having a very pronounced affinity for water. It fumes in moist air and hisses when mixed with liquid water as the Cl- ions are displaced with H2O molecules in the lattice to form the hexahydrate AlCl3·6H2O (also white to yellowish in color). The anhydrous phase cannot be regained on heating as HCl is lost leaving aluminium hydroxide or alumina (aluminium oxide):

Al(H2O)6Cl3 → Al(OH)3 + 3 HCl + 3 H2O

On strong heating (~400°C), the aluminium oxide is formed from the aluminium hydroxide via:

2 Al(OH)3 → Al2O3 + 3 H2O

Aqueous solutions of AlCl3 are ionic and thus conduct electricity well. Such solutions are found to be acidic, indicative of partial hydrolysis of the Al3+ ion. The reactions can be described (simplified) as:

[Al(H2O)6]3+ ⇌ [Al(OH)(H2O)5]2+ + H+

Aqueous solutions behave similarly to other aluminium salts containing hydrated Al3+ ions, giving a gelatinous precipitate of aluminium hydroxide upon reaction with sodium hydroxide:

AlCl3 + 3 NaOH → Al(OH)3 + 3NaCl "

(from Wiki)

What do you think ?

[Heartburn]

Antifreeze

Beyond Biodiesel, here an interesting doc about antifreeze.

[jonathan]

retort explosion

ok thanks my friend l dont know what l am going to make ? if l put a presure valve is a good idea?

[PLASTICTRIX]

In small experimental reactors a small quantity of water added to the waste plastic will create steam at 100C and purge the system initially. However this will not help at the end of the process. As the remaining gases in the retort cool down they create a partial vacuum and will suck air in back through the bubbler. My solution to this was to collect the gas in a large mylar balloon and then allow it to be sucked back into the retort.
With larger reactors it is very dangerous to operate without a proper purging system. Sooner or later you will have a fire and most likely an explosion.

On my 125 gal. reactor upon finish, the back draw on it is huge and would suck my 20 gal. bubbler dry within a few mins of cooling..so on the 3'' pipe just before it enters the bubbler i installed a 3"X1/2 bypass tee with a 3" ball valve below and threaded the 1/2" outlet on the tee to accept the hose from my co2 tank.. so upon finish and shutdown just about when the bubbles stop and the positive pressure starts to drop out and starts into vacuum, i shut the ball valve keeping the water from being sucked up, then i open the co2 just enough to maintain a slight positive pressure in the system as it draws back and cools to a safe temp. It would be very bad if the water made it all the way back to the retort. it would make a big boom, or at very least intensely blow oil filled steam out of the safety blowoffs possibly causing great injury.

[PLASTICTRIX]

My reason for letting it only draw in the co2 that it needs from the bubbler end is that it seems to save me allot of co2. for some reason i use almost twice as much if i send it in from the retort end while it cools. I haven't figured out why yet..

[Heartburn]

Filling in the void

On my 125 gal. reactor upon finish, the back draw on it is huge and would suck my 20 gal. bubbler dry within a few mins of cooling..so on the 3'' pipe just before it enters the bubbler i installed a 3"X1/2 bypass tee with a 3" ball valve below and threaded the 1/2" outlet on the tee to accept the hose from my co2 tank.. so upon finish and shutdown just about when the bubbles stop and the positive pressure starts to drop out and starts into vacuum, i shut the ball valve keeping the water from being sucked up, then i open the co2 just enough to maintain a slight positive pressure in the system as it draws back and cools to a safe temp. It would be very bad if the water made it all the way back to the retort. it would make a big boom, or at very least intensely blow oil filled steam out of the safety blowoffs possibly causing great injury.

I've been researching this aspect of the process and found we are not alone. Found this thread that suggest that using argon or nitrogen is the cheapest and easiest way to go.

But, I was thinking since these gases might not be readily available to all, since letting water in freely can/will create a steam explosion, what about injecting controlled amounts of water in slowly as the system cools down ?

Another simple solution would be to pipe in the exhaust of a lawnmower engine in the system.

[PLASTICTRIX]

I've been researching this aspect of the process and found we are not alone. Found this thread that suggest that using argon or nitrogen is the cheapest and easiest way to go.

But, I was thinking since these gases might not be readily available to all, since letting water in freely can/will create a steam explosion, what about injecting controlled amounts of water in slowly as the system cools down ?

Another simple solution would be to pipe in the exhaust of a lawnmower engine in the system.

Around here co2 seems to be the cheapest way as far as bottled gas goes.
and dry ice is fairly in expensive and right down the street and from solid to gas expands approx 700X volume. dry ice pellets fit nicely into a 3/4 inch pipe and could be introduced via a double valved air locked pipe.. i have often wondered the benefits of dry ice being so cold and because of its incredibly compact nature.. for pre purge on a 125gal retort it would only take like 6 oz. of pellets to completely evacuate all of the oxygen.

I like the lawnmower/engine exhaust idea. it seems like a cheap no brainer answer to the issue. It should work, but if the engine happened to stall,or was running rich for one reason or another, partially burned gasoline/air mixture blown into a hot retort could possibly pose an issue.

As far as introducing small amounts of water into the retort would in general make sense..it would help out as far as descaling the retort from coke/and sticky carbon residue,(kind of like hitting a greasy hot frypan under the faucet cleans it quick) but i would want to further research and test the pros/cons and possible dangers of it on a smaller unit. I would be very scared to try it on a 125gal retort. I wonder if the h20 could end up vaporizing and mixing with other left over hydrocarbon residue possibly making some sort of at least semi explosive/ semi flammable mixture? after all h2o isn't far off from just plain H... kind of like the hydrogen and water injection systems burn in car engines, but that is under compression.. I dunno.

[mjohnson1]

On my 125 gal. reactor upon finish, the back draw on it is huge and would suck my 20 gal. bubbler dry within a few mins of cooling..so on the 3'' pipe just before it enters the bubbler i installed a 3"X1/2 bypass tee with a 3" ball valve below and threaded the 1/2" outlet on the tee to accept the hose from my co2 tank.. so upon finish and shutdown just about when the bubbles stop and the positive pressure starts to drop out and starts into vacuum, i shut the ball valve keeping the water from being sucked up, then i open the co2 just enough to maintain a slight positive pressure in the system as it draws back and cools to a safe temp. It would be very bad if the water made it all the way back to the retort. it would make a big boom, or at very least intensely blow oil filled steam out of the safety blowoffs possibly causing great injury.

Have you tried placing a sealed container before your bubbler? If suckback occurs, any water from the bubbler will fill that sealed container and not go into your retort. Since the sealed container isn't hot you don't have to worry about a steam explosion. Adding a ball valve to the bottom will allow you to drain it.

[PLASTICTRIX]

Have you tried placing a sealed container before your bubbler? If suckback occurs, any water from the bubbler will fill that sealed container and not go into your retort. Since the sealed container isn't hot you don't have to worry about a steam explosion. Adding a ball valve to the bottom will allow you to drain it.

That would solve the water issue as long as the container has at least the volume of the water bubbler, so it could trap all the water if necessary.

However, it still does not solve the unwanted negative pressure on the system without adding inert gas to balance pressure in some form. The larger the retort, the more negative pressure volume occurs. So what i mean is that if your bubbler head volume is the same or larger than the volume of your retort, it should in theory have enough volume to satisfy the negative draw without pulling water in. On smaller systems this is easily obtainable. Lets say you have a 15 gal. retort, it is easy to have 15 gal. of head volume from the bubbler. With this being said, my retort is a 125gal. vertical propane tank. It would be near impossible for me to have 125 gal. of head volume from my bubbler. I guess in a properly sealed system the negative pressure could be negligible. But however it is still a dangerous factor to have negative pressure in general.

There is many factors to consider, the dia. of the bubbler pipe would make a huge difference. the smaller the pipe, the faster and easier the head draw would be to suck water in, (Bad). If you had a huge pipe going into the bubbler the draw would be slower and harder, causing more vacuum, but moving less water.

I will test this using some soup cans, silicone tubing, and a propane torch utilizing different sized hoses in the bubbler..

[mjohnson1]

That would solve the water issue as long as the container has at least the volume of the water bubbler, so it could trap all the water if necessary.

However, it still does not solve the unwanted negative pressure on the system without adding inert gas to balance pressure in some form. The larger the retort, the more negative pressure volume occurs. So what i mean is that if your bubbler head volume is the same or larger than the volume of your retort, it should in theory have enough volume to satisfy the negative draw without pulling water in. On smaller systems this is easily obtainable. Lets say you have a 15 gal. retort, it is easy to have 15 gal. of head volume from the bubbler. With this being said, my retort is a 125gal. vertical propane tank. It would be near impossible for me to have 125 gal. of head volume from my bubbler. I guess in a properly sealed system the negative pressure could be negligible. But however it is still a dangerous factor to have negative pressure in general.

There is many factors to consider, the dia. of the bubbler pipe would make a huge difference. the smaller the pipe, the faster and easier the head draw would be to suck water in, (Bad). If you had a huge pipe going into the bubbler the draw would be slower and harder, causing more vacuum, but moving less water.

I will test this using some soup cans, silicone tubing, and a propane torch utilizing different sized hoses in the bubbler..

What risks do you see besides the steam explosion possibility if the bubbler water reaches the very hot reactor?

With proper insulation the reactor shouldn't cool at that fast of rate. If the reactor is just filled with coke you don't have much risk of explosion. The hydrocarbon gasses should have condensed or exited the system when you are finished with that batch.

If you have a water bubbler with a level gauge hooked up to an external water supply you can ensure the bubbler never gets below a certain level.

From my understanding, the two ways to solve this are to continue the purge gas flow to maintain a positive flow of gas out the exit or have a deep enough bubbler so that air never enters the system but instead transports that water from the bubbler to a sealed container positioned before the bubbler. This way you effectively have a water seal. The only problem is this water pool would have to get bigger and bigger as your reactor size increases.

I don't think the bubbler and sealed container have to be that big as long as they have a way to add water to the bubbler and drain the sealed container.

[Beyond Biodiesel]

Beyond Biodiesel, here an interesting doc about antifreeze.

Thanks, Heartburn. Downloaded it.

I've been researching this aspect of the process and found we are not alone. Found this thread that suggest that using argon or nitrogen is the cheapest and easiest way to go.

But, I was thinking since these gases might not be readily available to all, since letting water in freely can/will create a steam explosion, what about injecting controlled amounts of water in slowly as the system cools down ?

Another simple solution would be to pipe in the exhaust of a lawnmower engine in the system.

Thanks for the link to sciencemadness.

Due to the soft drink industry compressed CO2 should be the cheapest inert gas available anywhere.

[TheQuietDan]

If you are going to inject water to try to make up for the volume of the cooling of the system, remember steam is about 1800X the volume of water used. I would think one drop at a time as water from the bubbler is starting to syphon up the tube keeping it from syphoning all the way up the tube.

I dont think that you would be able to reliably control steam pressure and contraction well enough to be safe. The expansion ratio of the water could really cause some trouble.

[imakebiodiesel]

When designing a safety system apply Murphys law.

" If a system can fail then it will fail".

Any purging system that requires careful adjustment by the operator at a critical moment will fail sooner or later with devastating consequences. Pressure relief valves protect against slow buildup of pressure, but are useless instantaneous increases associated with water being sucked into a retort at 300C.

One solution would be to store your uncondensable gases in a simple gasometer. Then when the vacuum occurs in the retort the gas could be drawn back through the bubbler. Ill do a sketch and post it it.