Particle-scale modelling of the pyrolysis of end-of-life solar panel particles in fluidized bed reactors

Abstract

The end-of-life solar panels can be disassembled through pyrolysis by removing the binder - ethylene vinyl acetate (EVA) for panel recycling, yet its research is still in its early stages. In this study, a reactive discrete element method - computational fluid dynamics (rDEM-CFD) model is developed to study the physical-thermal characteristics of dense gas-solid reacting flow related to the solar panel particles’ pyrolysis in two typical chemical reactors - fixed bed (FB) and bubbling fluidized bed (BFB) reactors. The simulation results show that the overall EVA removal degree in the BFB is higher than that in the FB. Then the two key parameters are studied including wall temperature and superficial gas velocity in the BFB. The results show that the EVA removal degrees are improved considerably, from 91.03%, 94.89%, to 99.99%, as the wall temperature increases from 723 K, 773 K, to 823 K. In contrast, the EVA removal degrees at the superficial gas velocity of 1.25 m/s, 1.5 m/s, and 1.75 m/s are similar, i.e., 94.67%, 94.89%, and 95.45%, respectively. The underlying mechanism is explored: the BFB shows better heat and mass transfer performance than the FB, such as more uniform temperature distribution, higher Re and Nu numbers, and larger heat transfer fluxes; on the other hand, increasing wall temperature decreases the Re and Nu numbers while elevating superficial gas velocity enlarges the Re and Nu numbers in the BFB. The study is useful for pyrolyzer design and optimization for efficient solar panel recycling.