A new journal article examines the poor thermal efficiency and technical challenges associated with the pyrolysis of mixed waste and, by extension, other ‘advanced thermal treatment’ technologies such as gasification. The article written by Andrew Neil Rollinson (University of Loughborough) and Jumoke Mojisola Oladejo (University of Nottingham) is entitled “‘Patented blunderings’, efficiency awareness, and self-sustainability claims in the pyrolysis energy from waste sector”. It is schedule to be published by Elsevier in Volume 141 of the journal ‘Resources, Conservation and Recycling’ in February 2019 but is available for free from today until the 23rd of December 2018 from https://authors.elsevier.com/a/1X-E33HVLKaZLr.
According to the Abstract: “This paper examines the concept of pyrolysis, and the potential for a phenomenon which demands energy to be considered as something which can be engineered to provide energy. Using literature review and case study methods, along with civil permit applications and experimental results, it shows that a pyrolysis plant for self-sustaining Energy from Waste is thermodynamically unproven, practically implausible, and environmentally unsound. A linkage between widespread commercial failures and a lack of focus on thermodynamic fundamentals is also identified, along with an environment of indifference or ignorance towards energy balances and sustainability when these technologies are presented, assessed and financed…The situation presents a high risk to investors and has the potential to adversely impact on societal transitions to a more sustainable future.”
The authors describe the pyrolysis of mixed waste to heat water as requiring more energy “than by heating the water directly using, say, electricity”. As they explain: “This is because the second law of thermodynamics dictates that the extra process stages increase inefficiencies due to heat losses, meaning that the [pyrolysis] system is, in effect, an energy intensive water heater with numerous additional process challenges and pathways to environmental pollution. Moreover, to keep tar above its dew point, the process lines prior to the combustion chamber must be heated too thus incurring additional energy demands and additional (second law of thermodynamics) heat losses. The only way to overcome this is to have the Combustion Chamber ‘close-coupled’ to the Pyrolysis Reactor, which would then mean that the system was in effect an incinerator, with best practice determining that it should be grate fired for complete mixing, and then the whole design concept becomes redundant”.
The article highlights the need for energy balance diagrams to be provided, finding that: “Though until now not widely reported, it is common for the information on these system designs to be devoid of satisfactory energy balances and to promise capabilities which appear to ignore thermodynamic laws…This seeming indifference or ignorance to both antecedents and thermodynamic principles has been the rationale for this study. If society is to make a transition to a more sustainable future it is imperative that there is clarity on how these newly proposed EfW technologies manage energy and resource consumption. Equally, if the engineering profession is to maintain credibility it is fundamental that the laws of thermodynamics are obeyed in designs which are put forward for investment.” and “This study has found that the status of energy use and efficiency awareness in the pyrolysis of waste sector is at best poor, and that the failures of previous plants are not merely teething troubles of a new industry but due to fundamentals flaws with the concept in general and how it is presented, seemingly based on bias towards the theoretical plausibility of a technological innovation.”
Over and above the drawbacks of pyrolysis, the article notes the general unsustainability of destroying valuable resources to inefficiently generate energy, explaining: “In summary, in the search for alternative energy sources and solutions to the societal problem of municipal waste, it seems that many in the EfW sector have drifted away from the tenets of engineering design efficiency and the need for sustainability. With this, and without a complete information base, the scaling up of pyrolysis EfW systems to industrial implementation is easily identified as an improperly assessed technology, and one which can only result in a huge drain on future financial and material resources when put into practice…As an alternative energy source, and in answer to the immediate and escalating problems of global municipal refuse, it is recommended that the solution does not lie with pyrolysis systems at all; rather 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.”
In its conclusion, the study finds that: “This review has shown that when appropriate system boundaries are applied, a pyrolysis plant for self-sustaining EfW is thermodynamically unproven, practically implausible, and environmentally unsound…MSW pyrolysis cannot yet be considered as something which can sustainably provide energy for society…it is essential that proper energy balances are determined and in place at the outset, made possible by the first law of thermodynamics, and with a consideration of total plant energy and resource use. Furthermore, and in keeping with the historic pursuit of perpetual motion, it is imperative that the second law of thermodynamics is not simply ignored…”