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Toward a Circular Economy for Plastics: Advanced Imaging and Numerical Modelling of Segregation and Transport of Plastics in Fluidised Beds

Project Description

Plastic waste is one of the great environmental challenges of our time. Recently, a promising new technique has been developed, which converts waste plastics into petrochemical feedstock by injecting them into a gas-fluidised bed of heated particles. Heat transferred to the plastic cracks long-chain molecules into shorter hydrocarbons which are extracted from the system and refined into valuable petrochemical products.
Despite its considerable potential, there remain significant impediments to the widespread adoption of this technology: while the cracking and distillation processes are well-understood, the systems’ internal dynamics remain unknown. Further, unlike for classical fluids, there exist no known laws governing the behaviours of particulate media, and the large, dense, opaque nature of the systems means that their dynamics cannot be directly observed using conventional techniques. Consequently, the specific influences of key parameters such as gas flow rate, system size and geometry remain unknown. As such, development and optimisation is a slow, costly and high-risk task, as any change to the system must be physically implemented in a full-sized pilot plant, with no guarantee of success.

To bring fluidised-bed-based waste-plastic recycling from a promising and potentially transformative nascent technology to a scalable, adaptable and commercially-viable reality, thus expediting its adoption and proliferation, and hence both expediting and augmenting the financial, societal and environmental impacts of this technology.

The project will directly address the three key issues of efficiency, scalability and adaptability highlighted above. The main project goals will be:

1) To develop and apply cutting-edge 3D experimental imaging techniques and numerical methods to image, model and hence better understand the internal dynamics of the systems of interest. This will allow us to determine the conditions under which the optimal distribution of particles for pyrolysis is achieved, i.e. for which efficiency is maximised [EFFICIENCY].
2) To assess the influence of system modifications (e.g. varying system geometry, placement of material inlets and outlets, design of gas distributor) on the observed dynamics [ADAPTABILITY].
3) To use data acquired in goals 1 & 2 to develop scaling laws allowing the prediction of optimal operating conditions for a system of arbitrary size [SCALABILITY].

Key measurable objectives:

- To use a unique combination of positron emission particle tracking (PEPT) and ultrafast x-ray radiography to gain valuable new insight into the internal dynamics of the optically opaque systems studied, in particular the dynamics, residence times and spatial distributions of plastic particles.
- To use data acquired using the above techniques to develop, calibrate, and validate a coupled discrete element method (DEM) and continuum fluid dynamics (CFD) model of the systems of interest.
- To work alongside industrial partners, Recycling Technologies, to validate the models developed against both small-scale test systems and operational pilot plants.

Benefits to the student:

The student will have regular access to the University’s Positron Imaging Centre, and the various world-leading particle and fluid imaging techniques possessed thereby, including the UK’s only PEPT facility.
The student will learn a variety of powerful techniques and transferable skills, including:
- The application of PEPT.
- X-ray imaging.
- Particle tracking velocimetry (PTV).
- The use of discrete element modelling (DEM) and continuum fluid dynamics (CFD), including the ability to create driver codes for various scientific and industrial systems of interest, develop and implement realistic DEM force models, and calibrate & validate models.
- The creation of radioactive tracers for use in non-invasive particle tracking.
The student will gain valuable industrial experience interacting and working with our partners Recycling Technologies.

The ideal candidate should hold a degree (Bachelor’s or higher) in a scientific or engineering field, having achieved - or being predicted to achieve - a 2:1 or higher (if Bachelor’s) and/or a Merit or higher (if Master’s). Due to the interdisciplinary nature of the project, candidates possessing degrees in chemical or mechanical engineering, computer science, mathematics and physics would all be highly suitable for the post, while outstanding candidates from other disciplines may also be considered.
The candidate should possess an aptitude for programming and knowledge of at least one language, ideally C++. A prior knowledge of numerical modelling methods such as CFD and/or DEM would be highly desirable, though certainly not necessary, as would some background knowledge regarding granular/particulate systems.
Most importantly, the candidate should demonstrate a provable enthusiasm for research, desire to learn new skills and explore new fields, and thirst for knowledge.

Funding Notes

This project is part of the Global Challenges Scholarship.
The award comprises:

Full payment of tuition fees at UK Research Councils UK/EU fee level (£4,327 in 2019/20), to be paid by the University;
An annual tax-free doctoral stipend at UK Research Councils UK/EU rates (£15,009 for 2019/20), to be paid in monthly instalments to the Global Challenges scholar by the University;
The tenure of the award can be for up to 3.5 years (42 months).

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