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Trying to recycle a daily ton of wet mixed plastic

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This topic contains 20 replies, has 9 voices, and was last updated by  Stan 4 weeks ago.

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Morris Housen mhpaperboy

Trying to recycle a daily ton of wet mixed plastic

31/03/2019 at 18:37

I operate a recycling paper mill in Massachusetts, USA.  We use Sorted Office Waste as our incoming raw material.  As part of our paper recycling pulping process, we separate out the contaminants.  One of the biggest contaminants is mixed plastics – anything that might be part of office waste (plastic folders, tape, buttons, etc.) and the pile of mixed plastics is wet and ground up from the pulping process.  We generate about a ton each day.  We want to turn this waste mixed plastic into something very crude, maybe pallets or lumber or similar at the very least, avoid sending it to the landfill.  Can wet plastic be extruded?  If we press it, will that get it dry enough for processing.  Any ideas?
Picture #1:  The raw material – waste from my office waste paper recycling operation
Picture #2: Plastic brick made from compressing waste plastic mixed with Liquid nails
Picture #3: Plastic brick made from compression alone

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new
05/05/2019 at 10:29
1

Wet plastic is very hard to process with a high moisture content.
You could dry it using some of your waste heat of your pulping process & then press or extrude it into moulds.
Here is one company making plastic timber.
https://www.youtube.com/watch?v=JauFhbvrEo4

How do you separate out the plastic from the paper ?

Keep up the good work.

starter
07/05/2019 at 09:29
1

Hey,

After solving the moisture content issue, I think the problem you’ll have to deal with a mixture of polymers. It seems you already work at a pretty big scale, so getting inspired by what these guys do (combining mixed polymers of soft and hard plastic in a recycling process) might be of interest to you:

I am wondering if we could bring this process to a smaller scale. Any thought?

starter
13/05/2019 at 19:17
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Marc Vruggink,

Thanks for replying and for sending the video.  I know so little about the chemistry of plastics.  In the video it looks like they are using only plastic bags.  I appreciate that they are using different types of bags (does that mean different polymers?), but I don’t know if that translates into so many different plastics like I have.  I’m going to contact the folks in the video to see if they can help.

Morris

starter
13/05/2019 at 19:24
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Mark,

Thank you for your reply and for sending the video.  We are very efficient in the paper mill and have little to no waste heat to use in drying the plastic.  If we set up an industrial-sized operation, we’d need to use expensive New England electricity – something that I am trying to avoid at this point.  We have a screw press that we are going to set up and that will get us to a certain level of dryness, but we’ll see if it gets dry enough.

The plastic dumps out of our pulper through a screening unit that allows small paper fiber to pass through, but anything larger (plastic, etc.) gets segregated.

My latest attempts involve drying the plastic through a tabletop press, mixing the relatively dry plastic with a variety of glue products and then pressing it again in a brick press.  I’m getting plastic “bricks”, but they don’t cure hard / firm enough to be used as lumber – too bendy.

starter
13/05/2019 at 20:55
1

Have you considered a centrifuge similar to the spin cycle of a washing machine.

starter
13/05/2019 at 22:00
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Makedo,

Thank you for your idea.  We do have a screw press that is designed for squeezing the plastic to a certain level of dryness.  We haven’t installed it yet, but will soon.  We’ve been trying to develop a solution at the “bench” level before we invest too much money in heavy equipment.

I’ve been pressing plastic material in a brick press to dry it, then mixing in some adhesive (Liquid Nails, Loctite, etc.) and then pressing it again.  We are getting solid blocks, but they are taking up to two weeks to cure / dry.  I think getting to bone dry will help this, but bone dry will require electricity which is expensive in New England.

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starter
15/05/2019 at 15:26
1

Morris,

They mix PP and PE in the process, which represents most of the soft plastics (as you seem to have on your pictures).

I can’t really help on the electricity issue. For sure, to recycle plastic, you’ll need heat and energy.

Maybe you could contact cementries or other industries that could be interested in using your mixed plastic in their process?

starter
22/05/2019 at 22:48
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I understand that this tech is for food but perhaps could be used for drying materials pre pressing into blocks or for the curing of pressed blocks.
https://www.motherearthnews.com/diy/tools/solar-food-dehydrator-plans-zm0z14jjzmar

Also could potentially used solar heated air and a blower shaft similar to what is used for feathers.

https://featherind.com/down-information/the-process/

Alternatively a solar oven with a conveyor system? I could make a technical drawing if needed to explain the concepts further.

All of these can be built with sheet metal and wood.

warrior
22/05/2019 at 23:37
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@mhpaperboy

I agree with @makedo ‘s original suggestion of a centrifuge, but would like to expand it to ‘vortex’ technology. So not a centrifuge per-sé, but more like a cyclone like used in he end of this video (sorry I don’t have a better example at hand):

 

A cyclone could dry, but even more interestingly, could also separate plastics (when grounded down) because of their different densities.

Plus cyclones are relatively cheap to achieve.

 

Please let me know if you’re interested in more information and I’ll dig deeper into my archives…

 

warrior
27/05/2019 at 13:12
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@mhpaperboy I think everyone here feels your pain, and the replies to this thread are all good.  But as you have probably come to realise, there are not going to be any easy solutions to your problem.

Ideally, you’d want the “office waste” to be separated at source – so that you only get the paper and card.  They tried doing that, where I work, some years ago – by having different shaped baskets for paper/card and “general waste” – but staff kept forgetting, and putting plastic coffee cups in the paper bins. And eventually we discovered the office cleaners were empying all the waste baskets into the same bags!  So sorting efforts have been abandoned – and all our garbage now goes to an “Energy from Waste” (EfW) facility.

As other people here have pointed out, there are two rather major problems you face (1) de-watering and thoroughly drying all the material filtered from your slurry, and (2) the intimately mixed material you have left has such a wide range of different polymers (and other crap) that the options for processing it into anything mouldable are quite low.  General office plastics will probably include PET, Polyethylene, Polystyrene, Polypropylene, PVC, and even natural rubber (there is an elastic band sticking out of one of the blocks in your photos!).  This is very bad news from a recycling perspective, as they all behave differently, and melt at different temperatures.

However, as the calorific value of this waste is probably quite good – there is a possibility that you could recover the energy to help with other processes in your plant.  This still isn’t simple – as the waste has to be fired at a rather high temperature to prevent toxic emissions (mainly from the PVC) – and the high moisture content will be fighting against that, unless you can dry the material first. And you might find that local environmental regulations make it difficult to get approval for most (if any) EfW facilities.

And, of course, energy from plastic waste is not “renewable” – it is still mainly derived from fossil sources – so still contributes to atmospheric CO2.  Utimately, secure (relatively local) landfill might still be the best way for this stuff to be confined, so it doesn’t spread into the wider environment.  What it shouldn’t be is exported to some poor underdeveloped country, where it just gets dumped in the open.

warrior
27/05/2019 at 13:39
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@mhpaperboy

I don’t often disagree with @frogfall , but I think you are here to look for some hope outside the ‘burn, baby, burn’ easy solution.

 

Wet mixed plastic only means the ‘wet’ solutions are the ones you’re looking for, and those are vortex based.

Wash, dry, sort, all in one.

You can still burn the leftovers, if you really really want to, but at least take advantage of the available tech to at least remove the easy parts while you’re drying anyway!

And yes, I am aware this ‘burning’ energy could be used to power the vortex…

warrior
27/05/2019 at 15:07
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I don’t often disagree with @frogfall , but I think you are here to look for some hope outside the ‘burn, baby, burn’ easy solution.

Hehe 😉  I didn’t even get as far as mentioning plastic to liquid fuel, via pyrolysis. 😉

Yes, it would be nice to reclaim some usable polymers from the stream.  BTW, vortices aren’t the only established way to separate particles of different density. There is always mechanical winnowing.

warrior
27/05/2019 at 17:02
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@frogfall

See, hard to disagree with this guy 🙂

 

Pyrolysis: check. Could even fuel itself.

Far from simple though as it’s almost rocket science (at least when done wrong).

 

Winnowing: will check further. I kinda already do this to sort out (bad) seeds and beans (simply remove the floaters), but did not know what it was called if you did it mechanically, so thanks. Hard to find something online, if you don’t know what it’s called…

new
06/06/2019 at 12:44
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Not a direct answer to the current solution, but if you separated the plastics prior to the pulping, you would avoid processing the plastics at all. Less waste / more yield etc.
Have you thought about a sensor based optical sorter somewhere upstream? Do you have a pic of the raw plant input?
Cheers, sandy

new
19/06/2019 at 11:20
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Hi, the only option that I think that could go is pyrolysis. For such a mixed material without having to pay for separation and drying. The pyrolysis consists in heating the waste to a temperature of about 400 oC. in a closed container without access of oxygen during operation. A petroleum derivative is created (depending on the amount of PP, PS, ABS, PE type of paper.) When it comes to paper, most of the coal is produced during the operation.The above method will probably be the best for utilizing waste at cost. . Greetings

starter
19/06/2019 at 19:50
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Donald,

I’ve found a used plastic extrusion equipment supplier who believes he can turn this material into 2 X 4s.  To dry material, he is placed it in a pillow case and tossed it into an industrial clothes dryer.  This may not scale up, but I’m most interested in the success of the extrusion process at this point.  I’ll post results when we have something.

starter
19/06/2019 at 19:52
2

Donald,
I like your idea of vortexes.  We use them in the pulping process as well.  I will likely give that a try when we scale up.  As I mentioned in another recent post, we are currently drying the material using a pillow case and a clothes dryer.

starter
19/06/2019 at 20:00
1

Frogfall,

Thank you for your empathy.  It is indeed a challenging problem for us.  Our raw material arrives “post-sorting” from the wastepaper dealer.  Our expertise is separating the paper fiber from the other, so that separation is ongoing.  We don’t generate enough of the plastic waste to invest in its separation.  As shown above, we have created “bricks” by drying the plastic, adding glue and pressing it into a brick shape.  This has worked in our bench model, but scaling up might be a challenge.  I’m hoping a newly found plastic extrusion equipment seller will be able to help turn this material into something of value.  The material is in his hands, so we should know soon.  Thank you!

starter
19/06/2019 at 20:04
2

Slepbee,

I’ve been to a pyrolysis plant up in Canada (the Liquid Smoke factory).  I’ll give that a try.  Are there small pyrolysis machines available?

warrior
20/06/2019 at 04:47
2

Did you see the Dung Beetle project @timslab posted in this thread https://davehakkens.nl/community/forums/topic/mobile-pyrolysis-plant-turning-waste-into-fuel/ ?

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