(135b) Novel Positron Imaging and Numerical Modelling of Bubbling Fluidised Beds: Toward an Improved Understanding of Pyrolysis-Based Waste Plastic Recycling

Positron emission particle tracking (PEPT) is a technique which allows the three-dimensional dynamics of particulate and multiphase systems to be imaged with high temporal and spatial resolution. This high-resolution imaging, combined with its ability to penetrate optically-opaque materials, make PEPT highly valuable for the study of industry-relevant systems, where both the particulate media and the walls of the system are opaque. It is particularly well suited to applications such as gas-fluidised beds, whose rapid dynamics can be difficult to capture with more conventional methods such as x-ray CT.

In this talk, we focus on the application of PEPT to plastic recycling systems, in which fluidised-bed pyrolysis reactors are used to convert plastic waste into valuable products such as clean, low-sulphur fuels and virgin-quality plastic feedstocks. While this technology carries the potential to revolutionise our approach to the waste plastic crisis, the hydrodynamics of the systems used are highly complex and thus difficult to model, and thus optimise. As such, the transition from a promising proof-of-concept to an efficient, reliable, and thus commercially-viable system represents a significant challenge.

In this talk, we present key findings from a long-term project with industrial partners Recycling Technologies Ltd, providing an overview of the manner in which PEPT imaging has been combined with CFD-DEM and MP-PIC modelling to provide valuable, novel insight into the dynamics of their fluidised-bed-based plastic recycling systems. We will cover:

• How PEPT can be used to acquire valuable information regarding key hydrodynamic behaviours such as flow patterns and flow rates, bubble rise velocities, turnover rates, and both the rate and extent of mixing within a fluidised bed.
• The use of modular PEPT systems to perform on site imaging of active industrial pyrolysis reactors, extracting not only the above data, but also data pertaining to the rate of melting and volatilisation of plastics within the reactor.
• How these data can be used to calibrate and validate detailed CFD-DEM and MP-PIC simulations of the systems of interest.
• An overview of key results to date, including:
  • The influence of particle shape on the distribution of plastics through a binary sand-plastic bed.
  • The influence of plastic loading on flow dynamics and mixing rate.
  • The influence of distributor design on flow dynamics, mixing, and fluidisation quality.