Energy engineer Dr Andrew Rollinson sets out the case as to why pyrolysis and ‘plastic to fuels’ is not a sustainable solution to the plastics problem.
Compounded by the breakdown of the global recycling market, it seems that most governments and local authorities throughout the world are grasping at straws to find a quick fix for the plastic waste problem. Plastic is piling up on land and threatening the biosphere through its contamination of the oceans. At the same time most governments exhibit a morbid fear of doing anything which could oppose continuous economic growth.
Wonder technology fixes such as pyrolysis for ‘plastic to fuels’ (1) and green energy from waste (EfW) are therefore offered up as the future solution. For, if such machines were capable of simply and sustainably converting plastic into fuel or energy, then citizens may feel encouraged to buy more and waste more, liberated from guilt with the knowledge that anything they saw and wanted could be purchased.
But this premise is inherently flawed. Pyrolysis of plastic can never be sustainable. In a recent academic journal, I detail why the concept is thermodynamically unproven, practically implausible, and environmentally unsound (2).
Pyrolysis occurs when solid organic matter is heated, resulting in the release of gases, oils, and char, hence the word’s etymological root of “loosening or change by fire”. It is an old technology, formerly applied by heating up wood to produce substances such as methanol, acetone, and creosote, prior to petrochemical refining routes. When wood is slowly pyrolysed the char is called ‘charcoal’; when coal is pyrolysed the char is called ‘coke’; and with plastics there is little or no char produced at all.
R. Fludd, Tractatus Secundi Pars VII De Motu. in libros quatuor divisa, pp. 433-468 (Oppenheim: de Bry, 1618).
The modern notion is to pyrolyse plastic (and other municipal refuse) into a gas or oil which is then useable as a commodity, invariably a “fuel”, in its own right. This conveniently ignores the fact that pyrolysis is an energy consuming process: more energy has to be put in to treat the waste than can actually be recovered. It can never be sustainable.
And what of the fuel from these ill-conceived schemes? All pyrolysis EfW or ‘plastic to fuels’ products must be combusted to liberate energy, thus releasing the same quantity of carbon dioxide than if the plastic had been incinerated directly. The product’s existence has merely been an intermediary stage in the combustion of fossil fuels.
But the idea is even more imprudent. There are substantial flaws with the pyrolysis of plastics concept. It has been tacit knowledge for almost one hundred years that this type of waste is practically incompatible with these technologies (3). Also, heavy metals and dioxins become concentrated in the resulting products making then unsuitable as fuels, because when combusted they are released to the environment.
Despite this many governments continue to waste millions deceiving the public in pursuit of an ‘innovation’ that holds the sustainable answer. They ignore the above-mentioned scientific antecedents, and a wake of commercial failures (4).
Academic research has also been drawn in, attracted by the competition for financial rewards. With a prevalence in many countries for grant funding which links industry, innovation, and academic research, ethical hazards have been created and these have yielded poisoned fruit (2).
Many modern academic research articles present pyrolysis with positive connotations, appraising it in terms of “energy recovery” or “conversion” efficiencies. This is despite huge overall energy demands. In one study the concept was described as “high efficiency”, but results showed that the system operated with gross negative efficiencies, using between 5 and 87 times more energy than could be obtainable from the pyrolysis products.
Graphical abstract from: Rollinson, A., Oladejo, J.M. 2019. ‘Patented blunderings’, efficiency awareness, and self-sustainability claims in the pyrolysis energy from waste sector. Resources, Conservation and Recycling, 141, pp. 233-242.
Perhaps worst of all, some research groups have recently claimed that pyrolysis plants can be self-sustaining. By doing so they commit a blunder which exposes them to instant discredit, for they ignore the second law of thermodynamics. Such a folly is akin to the antiquated pursuit of perpetual motion.
Perpetual motion is impossible because it violates the laws of thermodynamics. These laws underpin all engineering, and indeed all universal interactions. The first law states that energy must be conserved – what goes in must come out. The second law states that whenever there is energy transfer some quantity must always be lost to a system’s surroundings (measured as “entropy”).
The inviolable nature of the second law was perhaps best explained by Arthur Eddington in his famous Gifford Lectures (5):
“There are other laws which we have strong reason to believe in, and we feel that a hypothesis which violates them is highly improbable; but the improbability is vague and does not confront us as a paralysing array of figures, whereas the chance against a breach of the second law can be stated in figures which are overwhelming.”
Once one fully understands these laws, the folly of such schemes, and the sophistry of corporate attempts to claim “sustainability”, becomes instantly clear. It is therefore essential to grasp this concept if ever humanity is to make a transition to a sustainable future.
Pyrolysis can never be a sustainable answer to the inconvenient truth of Big Plastic. This lies in the widespread implementation of strategies for “reduction” and “re-use”, along with a preference for creating products with in-built recyclability and/or which are built to last. The elephant in the room is capitalism (6) and the throwaway culture that the present version of this economic system has created – ever demanding new markets, more sales, more consumption, and more waste.
The full text of the paper can be accessed for free here in Resources, Conservation and Recycling until 23rd December 2018.
1. Phan, A. How we can turn plastic waste into green energy. The Conversation, 1st October 2018.
2. Rollinson, A., Oladejo, J.M. 2019. ‘Patented blunderings’, efficiency awareness, and self-sustainability claims in the pyrolysis energy from waste sector. Resources, Conservation and Recycling, 141, pp. 233-242.
3. Mavropoulos, A. 2012. History of Gasification of Municipal Solid Waste through the eyes of Mr Hakan Rylander (online), 19th April 2012.
4. Tangri, N., Wilson, M. 2017. Waste gasification and pyrolysis: high risk, low yield processes for waste management. A technology risk analysis (online).
5. Eddington, A.S., The Nature of the Physical World, 1927. Cambridge University Press: London. pp.68-71.
6. Pigott, A. Capitalism is killing the world’s wildlife populations, not ‘humanity’. The Conversation, 1st November 2018.
Doctor Andrew Rollinson specialises in small-scale biomass gasification research and is the author of Gasification: succeeding with small-scale systems published by Lowimpact.org.
J Socci said on February 28, 2019
The paper referenced by A. Rollinson that discusses whether prolysis plants can be self-sustaining refers to MSW as a feedstock. Here the author is referring to plastic wastes as a feedstock, which will have much higher heating values (more energy), therefore the energy balance will be completely different.
Andrew Rollinson said on February 28, 2019
Dear J Socci,
I am the author of both articles.
My journal paper covered pyrolysis of MSW (and sewage sludge – literally a MSW, though not often categorised as such). Plastic is a high component of MSW for most countries, so the reference to plastics here is relevant. Indeed, my journal paper specifically referred to the extra problems of plastic pyrolysis, namely: the amorphous nature of the plastic hydrocarbons meaning that usually zero char can be produced (relevant because char usually has the highest energy density of the three pyrolysis product phases), and that dioxins concentrate in the pyrolysis oils.
Pure plastic will have a higher energy density than raw MSW, but the fact is inescapable that to pyrolyse this material requires energy. In my paper I show that the energy produced in the pyrolysis gas and oil is less than the energy needed to pyrolyse it (enthalpy for pyrolysis) along with the entropic losses and auxilliary electricity associated with the concept of this type of plant.
Of course there was another theme to my journal paper, and this blog, which is the absence of satisfactory energy balances when these technologies are presented. Some don’t even mention the need for energy inputs at all while simultaneously claiming that their process is “sustainable”. I absolutely include “plastics to fuels” in that category.
Andrew
J Socci said on February 28, 2019
Why are you bothered about the production of char from plastics when the hydrocarbon gases are readily combustible to provide energy for the process? There are understandable issues surrounding the toxic byproducts generated by the pyrolysis of certain plastics, this can be negated through proper feedstock selection.
I don’t think you provide any tangible figures referencing energy balance values. A paper on the energy balance of a 1kg/h test rig (https://dx.doi.org/10.5541/ijot.5000147483) calculates that for beech wood all the energy losses for the process equates to only 6.5 % on HHV basis. Plastic generally has a much higher HHV than biomass, therefore it would be expected the combustion of the produced non-condensable gases would provide more than enough energy to drive the process. I do agree that there are some reasonable environmental considerations for the pyrolysis of plastics, but the pyrolysis of pure plastic waste and MSW is very different.
Andrew Rollinson said on February 28, 2019
I mentioned char because it is the most energy dense of the three pyrolysis products. Many of the proposed waste pyrolysis concepts claim to make use of char to heat the retort. It is just not feasible.
Do you have any evidence of a pyrolysis of waste plant where (as you say) “the hydrocarbon gases are readily combustible to provide energy for the process”. I’d like to see that evidence please of such an operational plant. It is no good saying “…would be expected…” and “…would provide…” Such claims constitute the crux of my paper.
Thanks for the link to the test rig fed with beech wood. I’ll read it over the weekend.
Andrew
Andrew Rollinson said on February 28, 2019
I’ve just had a quick look at that beech wood test rig paper on fast pyrolysis. Here is what Tony Bridgwater said about fast pyrolysis in 2012:
“The by-product gas only contains about 5% of the energy in the feed and this is not sufficient for pyrolysis” (Biomass and Bioenergy, 38, pp.68-94).
By the way, I’ve met Tony a couple of times. A nice man. And, I am friends with a couple of people in his group at Aston. We probably agree that pyrolysis has a niche and is an interesting technology. I just want there to be more transparency on its practical utility and energy demands, for many people are passing it off as being a sustainable solution to waste. It isn’t.
J Socci said on February 28, 2019
Yes, he is my supervisor! You now have another friend in his group at Aston! 🙂
I guess that paper is talking about fast pyrolysis of biomass, in which case the major product is organic liquid yield and the gas in mainly composed of CO and CO2. My point is when pyrolysing plastics, depending on process parameters, there will be a high yield of combustible hydrocarbon gases (alkanes and alkenes), as well as a liquid fraction. So I think to compare plastic pyrolysis to a perpetual motion machine is misleading.
Totally agree, and I think proponents of pyrolysis often overlook the high CO and CO2 yields, however, pyrolysis may be a better alternative to incineration which a large proportion of waste is subjected to currently.
Cheers
Joe
Mark F. Martino said on March 8, 2019
I’m only a mediocre engineer who hasn’t designed anything in years so I appreciate your indulgence with my musing and any suggestions.
While plastics cause a lot of trouble, they are not going away for a while and there is a lot out there. Even if the energy in is more than the energy out, there is a way to make plastic pyrolysis viable. If homes, apartments, and businesses had there own pyrolysis units, they could convert their waste into energy on site. The syngas could be used to generate electricity directly. This would save the energy used to transport and sort the waste. It also prevents the pollution from the vehicles transporting the waste. And maybe other waste could be processed.
Andrew Rollinson said on March 11, 2019
Dear Mark,
There are practical problems with domestic pyrolysis of waste/plastics machines. These relate to heat losses from the reactor during feeding, corrosion and erosion caused by the high ash and chlorine content, removing ash (and again having to maintain high internal temperature in the reactor while doing this), and the tarry nature of the pyrolysis gas which sticks to downstream components necessitating system shutdown for repeated cleaning. All these relate to pyrolysis on any scale.
The above are reasons why the concept of a domestic pyrolysis reactor is an impractical pipe dream. Yet, surprisingly, you will find people promoting that they have developed the concept…. and seeking naive investors for the gadget that is the answer to all domestic waste. Avoid these people.
Notwithstanding the practical aspects above, let me explain again about the energy balance: The practical aspects do impact on the energy balance because each time the reactor is opened to feed or to clean, the internal temperature cools down, this demands greater energy input and also dramatically changes the chemistry of the gas and oils that are produced. But, let us assume that you can discount them and that you have heated up your reactor containing plastic:
Assuming that you had heated your reactor up to 550C. This cost you 10 kWh of electricity. You then need to pyrolyse all the plastic, and this will cost you a further 3kWh of electricity, then the gas and oil is burned in an adjacent combustion chamber where it heats water and the water is used to turn a generator so that in total you can produce 5kWh of electricity. Overall you have disposed of your plastic at a cost to you of 8kWh. This could be electricity from the grid or your battery bank.
These are NOT renewable energy devices.
Yes, it seems ideal to be able to convert your domestic waste into energy in a kitchen appliance type gadget, but fundamental universal laws dictate that it is not possible. The idea is, as I have said, akin to the antiquated pursuit of perpetual motion.
Andrew
Andrew Rollinson said on March 11, 2019
Dear Mark,
I’ve just re-read your post, and I believe that I perhaps haven’t answered it:
Yes, IF the systems could be made to work, and IF one is willing to pay high energy costs for melting plastic at home, then it would obviate having to transport and sort the waste on a regional level, and would remove some vehicular pollution.
The corporate-sector waste contractors who have locked-in local authorities to supplying them with municipal waste for a term of 25 years would probably have something to say about it.
Mark F. Martino said on March 11, 2019
Dear Andrew,
Thank you for filling in details of my understanding of the pyrolysis of plastic, especially the numbers you included in your explanation. I thought I had found a pretty good approximation of a solution when I discovered the Dung Beetle project in Africa, which involves a portable pyrolysis unit. I can see how it has the problems you pointed out. So, even at a small, controlled scale, pyrolysis is not the way to dispose of plastic or other kinds of trash.
I appreciate the research and work you are doing and hope there is another solution beyond recycling and composting. Here in Kirkland, Washington, we’ve been recycling for decades, but there always seems to be massive amounts of plastic and other trash that cannot be recycled. Instead, it goes to a collection site about a half mile from my home. From there, trucks haul it to a railroad station where it is loaded onto railroad cars and taken to a landfill in Oregon. I watched this happen for many years. It really seemed to me that the local pyrolysis of the trash in small, discrete batches had to use less energy and cause less pollution than that. Thank you for showing me why we need to pursue other solutions.
Wally said on March 22, 2019
I wouldn’t even go as far as to say I know something about this topic. But I do have a question. Using tires and plastics to create a diesel fuel, although it requires a lot of energy to do. Wouldn’t it still help to solve a problem that has to be dealt with? Doing something with waste. Or is it only moving the problem to another area?
Andrew Rollinson said on March 26, 2019
Dear Wally,
True, it would “do something” with the waste. Some people attempt to pass this of as being sustainable, but it isn’t.
Zhao Zhang said on April 1, 2019
An impressive paper by Dr. A.
I resolutely oppose small pyrolysis systems in your home, your backyard or in the community as it maybe encouraged.
Small pyrolysis systems are often open systems without any tail gas treatment. They may bring problems of serve air pollution as the pyrolysis gases often contains PAHs, N-PAHs, HCN, CO, etc. In a open system, these gases can be easily leak to the air and cannot fully converted in the combustion systems.
When I saw the small pyrolysis systems making biochar in household, I was very sad.
These systems discharge a lot of dark smoke, but the farmers thought they are saving the world. When we talk about the carbon negative of Biochar, has anyone thought the emmission of Black carbon and brown carbon?
Many thanks to Dr. A for the critical review, which reveal the truth of this field.
John Whitby said on June 5, 2019
Not about pyrolysis, but regarding the plastic waste problem.
Is there any reason why the heavier grade plastics (milk containers, bottles, food containers up to hard plastics), couldn’t be shredded and then compressed into blocks or panels using either a resin or cement type binder. The thermal insulation properties of these blocks should at least equal that of cinder blocks, making a strong thermally efficient building system at a reasonable cost, whilst recycling huge amounts of plastic waste. In fact you could pre-bond the insulation and timber frames to the panels, meaning the only extra work needed would be fitting the plasterboard and skimming.
Depending on the construction, as pre-compressed panels, they would certainly be suitable for fast-build, lightweight single story dwellings (even the roof tiles could be made from the same type of material, just of thinner construction), and probably two storey dwellings also.
Mike said on July 6, 2019
I understand this is an old article but I recently read about a plant in Japan which claims to be producing net energy from plastic waste while meeting high emission standards. I wonder if the author of this article would mind commenting on this plant.
I found a video with the details here – https://www.youtube.com/watch?time_continue=620&v=KKTAdZFc-ss
No doubt the creators of the video are highly biased, but they are claiming 4MWe of electricity is being exported to the grid and almost 9 million litres of oil being reclaimed from plastic waste, along with solid fuel and hydrochloric acid.
Andrew Rollinson said on July 9, 2019
Dear Mike,
I watched the Youtube film all the way through. I didn’t see or hear any mention of the plant claiming to operate using only the energy available in its plastic waste products. There was one statement about something called a “normal pressure separator” using oil from the plant.
I strongly maintain that it is impossible for plants such as this to function wholly from the energy contained in the products that come out of their processing line.
Andrew
Grace said on July 9, 2019
Hi Andrew
Just chanced upon this, its a great read and thank you so much for your insights in pyrolysis space.
I was just wondering if you could share with the full text of the paper here with me, unfortunately, i only chanced upon this article after the deadline.
Many thanks
Grace
Andrew Rollinson said on July 9, 2019
Dear Grace,
I have just sent you a pre-print version by e-mail.
Best wishes,
Andrew
Anton said on July 12, 2019
What utter nonsense! Pyrolysis can be self sustaining I wonder if the author ever built a pyrolysis plant?? This article is testimony of his lack of knowledge on the science. I suggest he come and visit us so he can be educated before he shoots off his mouth on subjects he knows nothing about.www.recor.co.za
Dave Darby said on July 13, 2019
fight, fight, fight, fight
Lack of content there though Anton. Could you focus on something he said that you think is wrong, and why, then he can answer your point. At the moment, you haven’t made any.
Dan Esterhuyse said on July 13, 2019
Correct Anton. Just bullshitting the uninformed.
Dave Darby said on July 13, 2019
Dan – you sound like one of those kids who hide behind the bully, shout insults and run off. Make a point, and back it up with something.
Henry Raymond said on July 13, 2019
I have to say I disagree to some extent with these conclusions. First, pyrolysis cannot only be done with plastic but many other feedstocks so the idea that it is unsustainable is questionable in my opinion. Secondly, plastic is and has been is use for decades and so there is plenty of it available. It is unlikely to go way anytime soon. Plastic bottles, food containers, milk jugs, oil, detergent, and many, many other products are sold this way and some areas do have recycling programs for pickup already. The main observation seems to be that the process uses more energy on analysis than is generated by it. This assumes that you are using electricity to heat the mass. Some energy can be obtained from the process itself by burning the gasses that are generated from the breakdown either of plastic or biomass. No mention is made however of solar power which is readily available in many parts of the country particularly in summer or the use of wind power. Both of these, once the original capital costs have been absorbed basically generate free power. Even hydroelectric power could be used AND most importantly it is difficult to store energy except where it is being converted to liquid fuel. Pyrolysis in my opinion does provide an answer to alleviating our massive pollution problem with plastic and bio waste etc., and it is converted to liquid fuel which can be transported. Remember, fossil fuels aren’t free either.
Andrew Rollinson said on July 15, 2019
Dear Henry,
Pyrolysis is wood can be sustainable if the wood is from sustainably managed forest, but it will still be a process that uses energy. Additional wood is burned to drive the process. One would need to plant trees to replace those used for pyrolysis and more trees for those burned to drive it.
Pyrolysis of plastics cannot be sustainable because the plastics are made from oil. Ultimately the products that are created are burned to release energy and ultimately the same amount of CO2 as if the oil had been burned directly. On top of this more fuel (oil, wood), needs to be burned to drive the process. Therefore, the process is not, and can never be, sustainable. It is more of the same for increasing energy consumption and greenhouse gas emissions
Wind turbines and solar panels could not drive the pyrolysis process as they do not generate sufficient energy for long enough. Anything that heats up (irons, cookers, tumble dryers, kettles) needs tremendous amounts of energy in comparison to, say, light bulbs, computers, radios. Pyrolysis is a process of heating up and therefore in the former category, but it also needs sustained and high temperatures for long periods. It is very energy intensive.
I am a gasification engineer, who has also worked with pyrolysis (but the two are similar processes). Anyone who has worked with these systems will know the truth of what I have described above. It is fundamental. I wrote the journal article, and this blog, because “entrepreneurs” and quack scientists/engineers (who by the way were attracted by government funding), along with unscrupulous consultants, were trying to pass off these systems as being sustainable. They were baffling planning and permitting officers, higher-level decision makers, and targetting ethical investors who in turn were losing their savings. See for example reference number 4 in the blog and also this: http://www.ukwin.org.uk/files/pdf/UKWIN_Gasification_Failures_Briefing.pdf
There are also inherent problems with practically implementing pyrolysis of waste/plastics. I have written enough already, but the details are in my journal article with explanations and case studies. This also is fundamental to anyone who has operated these systems.
Andrew
Andrew Rollinson said on July 15, 2019
Sorry. This should start: “Pyrolysis OF wood…”
WillRau said on July 18, 2019
Andrew – I also have come to this discussion late. Could I also please have a copy of the full text paper? Thank you in advance.
-Will
Andrew Rollinson said on July 19, 2019
Certainly Will.I have just sent you a copy.
Andrew
purist thundewrath said on July 23, 2019
Hi,Andrew,what about tires,I see they get shredded and used elsewhere.would it be financially feasible to microwave pyrolysis them into fuel.for me it seems more productive to use all stored energy in them to power actual vehicles or plants instead burning straight up after shredding.
Ps. I’m uneducated pleb ,enlighten my dark mind with some powerful knowledge 😌
Andrew Rollinson said on July 24, 2019
Dear purist,
You pose your question in a way that is interesting and revealing about both the current societal mindset and prevailing misunderstandings with respect of efficiency and sustainability. You ask, is it “financially feasible to microwave pyrolysis [tyres]”. My answer is “yes, it may be”. Governments financially support these ventures to make them financially feasible. But, financial feasibility has absolutely no correlation between engineering efficiency nor resource or ecological sustainability.
Tyres are made from petroleum and to convert them to fuels ultimately means to burn them since burning a fuel is the only way to release its energy into a useful form. Therefore it is more of the same in terms of greenhouse gas emissions. The petroleum has merely spent a part of its existence as a tyre rather than being burnt directly.
Notwithstanding the above, the perceived benefit of recycling tyres into fuel is that it offsets using virgin petroleum. But this notion is completely undermined when one considers that enormous amounts of extra fossil fuels (coal, petroleum oil) have to be consumed to process the tyres in this way. Solar panels and wind turbines will not provide the amount of energy required for this. The proposal to use microwaves is particularly energy intensive and dangerous. There is the energy needed to finely shred the tyres, then mix them with metal catalyst (which has been known to cause a fire hazard during the pyrolysis process), but more importantly it is the energy needed for pyrolysis. It was with microwave pyrolysis that I referred to in my blog as consuming 5 to 87 times more energy than could be obtainable from the pyrolysis product (a study which – despite the gross negative efficiencies – was described as “high efficiency” by the way). Another study, not mentioned in the blog, operated with 18 to 21 times negative efficiency for the same reasons.
Andrew
Christine Mayles said on July 28, 2019
Hi Andrew. Thank you for your article. Whilst the process is not a sustainable solution to the plastics problem, do you not think that perhaps it has a place? My belief is that to tackle the worlds waste problems involves a many pronged attack. In our money orientated society I believe hitting business and the general public in the pocket is the way to change the capitalist and throw away culture (needless to say I wouldn’t be voted in as a politician any time soon!) That said the UKs packaging waste regulations became a toothless tax that many financially affluent businesses just paid off and changed nothing, so any legislative changes would need to be robust and policed. Plus if people had to pay more for their plastic waste to be removed I believe the general public would be less inclined to purchase items containing it (fly tipping aside of course!).
The pyrolysis solution would have a place to recycle that which still remains whilst not giving people the false representation that plastic is now guilt free. Whilst it is not a perfect solution at present, it would be nice to see government investment in improving the technology for renewable energies and the technologies for the efficient processing of waste for the future.
And yes I am a waste reduction obsessed optimist!
JD said on July 28, 2019
Greetings.
My local municipality is looking to implementing pyrolysis as a means to combat the plastic waste problem. They’re mostly clueless in regards to environmental concerns, and think that implementing this is a solution to our plastic waste problem. Is there any way I can see your paper, or receive it in email, so that I can use it to highlight the potential drawbacks during municipal sessions? I don’t want them to think that this is a magical solution.
Andrew Rollinson said on July 29, 2019
Dear JD,
For you and any others who may be interested, here should be a link to the pre-print version of my full journal paper – http://blushfulearth.co.uk/wp-content/uploads/2019/07/Manuscript.pdf
Please let me know if it doesn’t work.
The circumstances you describe about your local authority are sadly commonplace. It will end in failure, abandonment lost investments, and likely a risk of toxic waste by-products if it ever gets to the stage where it is built. People may seem indifferent to local authorities losing investments but such folly obviously has a direct impact on service provision.
Dear Christine,
No, I do not think that pyrolysis of plastic has a place in a transition to a sustainable future. Pyrolysis and gasification technology, fed with horticultural waste and arborial off-cuts from sustainably managed land does have a place. Plastics pyrolysis does not, for the reasons that I have described.
All energy from waste is down at second from bottom of the waste hierarchy for good reason. We need to reduce and re-use materials and/or create them with inbuilt recyclability. Single-use plastics need to be banned.
Andrew
JD said on July 29, 2019
The Philippines actually, which is the 3rd worst plastic polluting country into our oceans, sadly. We need to do something but I think they’re just grasping for answers blindly without thinking things through.
Andrew Rollinson said on July 29, 2019
Dear JD,
Yes, I am aware of the situation. Governments and local authorities don’t know what to do, and they are under enormous pressure from entrepreneurs who come to them saying that they have a technology which can be a silver bullet to plastic waste.
Andrew
Mike McKeen said on July 30, 2019
Has there been any investigation into the use of solar thermal as a source for process heat? I live near the Ivanpah Valley solar power station, but I know that they use a considerable amount of natural gas in order to keep the plant running 24/7 and to avoid wasting the early morning and evening sun to preheat. But what if it were used to pyrolize plastics instead of heating water for electricity? Of course, the economics require a rather expensive solar thermal array be constructed as the temperatures are not trivial, but I was more thinking about the thermodynamics of the system. Rather than a more energy intensive source like gas or electricity, would a concentrating array give the needed temps at a rate quick enough to make production worthwhile?
Andrew Rollinson said on July 31, 2019
Dear Mike,
Thanks for your comment.
Large-scale solar thermal concentrators like the one at Ivanpah Valley would definitely generate a sufficient level of temperature for pyrolysis.Of course, this is purely theoretical.
Interesting about natural gas being used to supplement the facility. This is done with large-scale wind turbines linked to the grid in the UK. Here we now burn mostly natural gas for this reason due to the short-start up times of these large-scale fossil fuel power plants. I often tell people who advocate for grid-tied wind power that they are actually supporting the burning of fossil fuels and in particular (fracking) shale gas, but they generally don’t comprehend this. Why? Because it is another area where education is needed and where the government needs to “tell the truth” (as Extinction Rebellion demand).
Back onto topic – I was just hearing about how shale gas in the US is driving forward an exponential increase in plastics production in your country, due to how cheap it is. Natural gas/shale gas is the reagent for plastics production.
Andrew
Sunil Chunduru said on August 9, 2019
Hi,Andrew
I am an undergraduate student working on converting plastic to electricity in that I need use pyrolysis of plastic to generate gases.By reading your article on pyrolysis is not sustainable to plastic.I need to know is there any efficient methods for converting plastic into gases other than pyrolysis. Please let me know
Andrew Rollinson said on August 11, 2019
Dear Sunil,
No, I don’t know of any.
Andrew
Bui Hoang Linh said on August 16, 2019
Article claims: Pyrolysis is net negative energy production
Fact: You burn a plastic bag, it continues to burn without having to supply power
How can I get extra energy from a proclaimed to be net negative energy production?
Andrew Rollinson said on August 19, 2019
Dear Bui,
It is difficult for me to understand your comment. Are you perhaps asking why when try to burn a plastic bag it melts and gives off heat, and isn’t this therefore proof that the process can be energy positive? If so, “no”, you are confused:
Pyrolysis is not the same as burning. With pyrolysis you are excluding oxygen. It is an endothermic (heat must be continuously added) process.
With combustion the process is exothermic (heat released). Though there needs to be an ignition source to get the reaction to proceed (so some input of energy), it can (if the material is dry enough, and if the reactor is configured such that oxygen is completely mixed through the feedstock, and if ashes are satisfactorily and continuously removed) proceed spontaneously because of the freely available oxygen. And, it may then yield surplus heat, so be net energy positive. This combustion process description is the principle of incineration. For multiple reasons relating to the feedstock composition and practicalities of processing the waste, net plant efficiency is very low at ca. 10 to 30%, with the very high end only for very large plants.
What I am saying therefore is that the notion to batch process plastic and other mixed wastes by pyrolysis, i.e. the need to detach the pyrolysis stage from the combustion stage and drive this by externally supplied energy, added to which are the numerous challenges of feeding, transferring the gases post processing, cleaning the gases, maintaining the necessary high temperatures (all of which also use energy), push the energy balance into the negative. Case studies have shown this, and my new research has shown this. It cannot be sustainable. At a simplistic level, and discounting for now some of the other process challenges, what you are suggesting is the error made by many others in that you fail to consider the second law of thermodynamics which must incur greater inefficiencies when you add all the extra and necessary process stages.
Andrew