Predictive Model for Particle Residence Time Distributions in Riser Reactors. Part 1: Model Development and Validation

In this computational study, we model the mixing of biomass pyrolysis vapor with a solid catalyst in circulating riser reactors with a focus on the determination of solid catalyst residence time distributions (RTDs). A comprehensive set of 2D and 3D simulations were conducted for a pilot-scale riser using the Eulerian-Eulerian two-fluid modeling framework with and without subgrid-scale models for the gas-solid interaction. A validation test case was also simulated and compared to experiments, showing agreement in the pressure gradient and RTD mean and spread. For simulation cases, it was found that for accurate RTD prediction, the Johnson and Jackson partial slip solid boundary condition was required for all models, and a subgrid model is useful so that ultra high resolutions grids, which are very computationally intensive, are not required. We discovered a 2/3 scaling relation for the RTD mean and spread when comparing resolved 2D simulations to validated unresolved 3D subgrid-scale model simulations.