Numerical simulation of plastic pyrolysis in fluidized bed reactors under continuous and batch-wise feeding

Numerical simulations were conducted to study the pyrolysis of polypropylene (PP) in a fluidized bed reactor (FBR). For that purpose, a Eulerian–Lagrangian solver was developed, incorporating the gas–solid hydrodynamics in FBR, particle-level heat transfer, and a five-lump pyrolysis reaction kinetic model. This framework captures the mutual interplay among these physicochemical processes and enables predicting the yields of permanent gas (G), light fraction (LF), and heavy fraction (HF). Analysis of the characteristic timescales confirms that the pyrolysis reaction is significantly slower than convective heat transfer. At 505 °C, LF was the dominant product (67.4 wt%), followed by G (29.6 wt%) and HF (3 wt%), and the product distribution significantly shifted toward G formation with increasing reactor temperature. In contrast, variations in particle size (1.5–2.5 mm) and operation mode (batch-wise vs. continuous) affected the transient thermal behavior but had minor effects on product yields, as heat transfer is not rate-determining under the investigated conditions.