How to turn plastic waste into diesel fuel cheaply

[imakebiodiesel]

Hello guys, the rumours of my demise have been greatly exaggerated. I ve just been very busy, lots of orders for biodiesel processors came in while I was away in the US so Ive got my nose to the grind stone for a while.
Water boost, my guess is the white/gray crystals are therphthalic acid. There is a lot of this stuff in PET and it sublimates ( turns directly from gas to solid) at 300C. While this is not very toxic the real danger of it is that it could block the pipework and cause an explosion.

When considering purging it is important to remember that effective purging is needed at both the beginning and the end of the process. A small amount of water in the retort will safely purge the system at the beginning but that method cant be used at the end. In my small processor I use a mylar bag to collect off gas during processing and then allow that to flow back into the system as the retort cools down. For a small system a party ballon or even a wine box inner will be sufficient. Ill do a diagram shortly and post it.

In my larger processor I purge with gas both before and after cracking.

[imakebiodiesel]

Here is a sketch of what I described in the last post. During cracking the bag is filled with off gas so that when the system is stopped and the retort cools, off gas instead of air is drawn back into the system. Obviously this method will only work for a small experimental setup. a proper gas purging system should be installed for a full size processor.



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[Beyond Biodiesel]

Thank-you imakebiodiesel, for posting your further thoughts on a system that controls gasses in a pyrolsyis unit. Some comments here are:
1) To avoid sucking back water from the bubbler with a simple loop, as you described, then the loop will have to be 30 feet (10meters) tall, otherwise a check valve might be easier.

2) I too thought of capturing all of the gasses liberated from a pyrolysis process; however, my guess is the volume of gas will be too large for a gas bag, unless it is quite large. Do you ( or anyone else know) just how much gas is liberated from the pyrolysis of plastics per unit volume of mass? I have thought of just buying a gas meter to measure the volume coming off my unit, but I have yet to see a gas meter at my usual scrap yards, and thrift stores.

[imakebiodiesel]

The mylar bag could be placed before the bubbler to avoid the need for a very high loop. In my small outfit the bubbler was made from a water filter and had quite a small capacity. The loop was about 3 feet high.
Gas output will vary with a number of factors. Keeping the retort temp below 400C, using an efficient catalyst and a cold condenser will minimize off gas. In my small outfit a 1kg batch of PE and PP will just about fill a 3 litre mylar bag of gas.

[ZoneFibras]

Type of Valves?

Hi everyone!

Thank you Jetijs for starting this forum.

Thank you Imakebiodiesel, Beyond Biodiesel, Asad, and everyone who have contribuid.

I would like to ask one question:

1) What type of pressure relief valves do you use?

I saw on Imakebiodiesel's retort, and the two pressure relief valves looked like the ones you buy st a plumber's store, but they can only handle temperatures until 100 ºC Can these handle the 400 ºC of the retort?
What type of pressure relief valve should I use?

Thanks alot everybody!

[Excalibur]

This is the way I see it...
A suck back high loop could be of a relatively large diameter and therefore be short. Effectively the respective part of the loop only need hold captive the amount of water that would be drawn back should a vacuum situation occur. That part of the loop could be of any shape so long as it had the required minimum volume to act as a water trap.
Untested theory so please correct me if I'm wrong.

[imakebiodiesel]

Yes Excalibur, in fact that is precisely how my own loop on my larger outfit works.
Ive amended the sketch to show this .
Alternatively the bag could be installed before the bubbler. Special gas sampling bags of up to 20litres can be bought on line. These are designed to hold hydrocarbon gases safely but they are quite expensive. The inner bag of a 3 litre box of wine would do the same job.


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[imakebiodiesel]

An added advantage of using a wine box is that you get the pleasure of emptying the box first.
I no longer use the pressure relief valves shown in earlier pictures for exactly the reason you mentioned. The plastic parts of the valve would not withstand hot gases passing through the valve. The valve I now use is all brass and stainless steel and ca be adjusted from .5 to 15bar. Here is a link.
WL Hamilton Bronze, 0-35 Bar Adjustable Pressure Relief Valve - Pressure Relief Valve, Adjustable 0-35 Bar, Bronze Bodied - Valves - Pressure Relief - Valves (All Types) - Oilybits.com - The U.K's Premier Bio Fuel Equipment Superstore

[Excalibur]

Yes. the bag is a good idea. . I've been looking out for something much larger like a waterbed bladder for example. I was wanting to be able to store enough to start up on gas for the retort heat, possibly supplementing with homemade methane.

[Beyond Biodiesel]

The mylar bag could be placed before the bubbler to avoid the need for a very high loop. In my small outfit the bubbler was made from a water filter and had quite a small capacity. The loop was about 3 feet high.
Gas output will vary with a number of factors. Keeping the retort temp below 400C, using an efficient catalyst and a cold condenser will minimize off gas. In my small outfit a 1kg batch of PE and PP will just about fill a 3 litre mylar bag of gas.

Thanks for the very useful information on the volume of gas released from your pyrolysis unit.

This is the way I see it...
A suck back high loop could be of a relatively large diameter and therefore be short. Effectively the respective part of the loop only need hold captive the amount of water that would be drawn back should a vacuum situation occur. That part of the loop could be of any shape so long as it had the required minimum volume to act as a water trap.
Untested theory so please correct me if I'm wrong.

I was thinking of the water still forming a barrier to oxygen, which would require the 30 foot high loop. On the other hand, if one employed a 30 foot high loop, then the entire apparatus would have to be able to handle a delta P of 15 PSI (1bar).

Since I am doing vacuum distillation, then my equipment can of course handle the pressure, and the vacuum pump provides the barrier to the atmosphere. But, I would like to bag all of the gasses released to contain any unexpected releases of poisonous or explosive gasses until I consume or neutralize them.

I have noticed that there is a guy on eBay who sells military surplus weather balloons for cheap, so I have thought of buying one of them for the purpose.

[ZoneFibras]

An added advantage of using a wine box is that you get the pleasure of emptying the box first.
I no longer use the pressure relief valves shown in earlier pictures for exactly the reason you mentioned. The plastic parts of the valve would not withstand hot gases passing through the valve. The valve I now use is all brass and stainless steel and ca be adjusted from .5 to 15bar. Here is a link.
WL Hamilton Bronze, 0-35 Bar Adjustable Pressure Relief Valve - Pressure Relief Valve, Adjustable 0-35 Bar, Bronze Bodied - Valves - Pressure Relief - Valves (All Types) - Oilybits.com - The U.K's Premier Bio Fuel Equipment Superstore

Thanks!

[imakebiodiesel]

Here is the solution to gas storage and usage. Wouldnt do a lot for the streamlining, but what the hell, free fuel. Unfortunately maximum range is about 10 miles.


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[fibuslitero]

"...but what the hell, free fuel..."


This is one of my favourites (wood gas truck) :https://www.youtube.com/watch?v=aRbYiP0cJmg

Here is the solution to gas storage and usage. Wouldnt do a lot for the streamlining, but what the hell, free fuel. Unfortunately maximum range is about 10 miles.


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[imakebiodiesel]

Just a note of caution about over boiling.

I was doing a batch yesterday in my new larger processor. I had collected 7 litres of nice clear fuel and I got a bit over enthusiastic and allowed the temp to rise to 425C while the retort was still nearly full. Hot waxy liquid began to spew out of the fuel outlet pipe. I turned off the heat and got the process under control but by that time about a litre of waxy stuff had contaminated the 7 litres. I changed the container and finished processing the batch.

Over a period of about 2 hours the whole 8 litres turned into solid wax! There would seem to be a chain reaction or radical reaction at work here. Even a small amount of semicracked wax can ruin a larger amount of good liquid fuel.

[Beyond Biodiesel]

Just a note of caution about over boiling.

I was doing a batch yesterday in my new larger processor. I had collected 7 litres of nice clear fuel and I got a bit over enthusiastic and allowed the temp to rise to 425C while the retort was still nearly full. Hot waxy liquid began to spew out of the fuel outlet pipe. I turned off the heat and got the process under control but by that time about a litre of waxy stuff had contaminated the 7 litres. I changed the container and finished processing the batch.

Over a period of about 2 hours the whole 8 litres turned into solid wax! There would seem to be a chain reaction or radical reaction at work here. Even a small amount of semicracked wax can ruin a larger amount of good liquid fuel.

Thanks for reporting your findings. Over boiling is certainly an issue, but I did not know that it could cause cracked fuel to re-polymerize. Very interesting.