CFD–DEM–PBM coupled model development and validation of a 3D top-spray fluidized bed wet granulation process

• Published in: Computers & chemical engineering 2019-06, Vol.125, p.249-270
• Main Authors: Tamrakar, Ashutosh, Ramachandran, Rohit
• Format: Article
• Language: English
• Subjects: Computational fluid dynamics; Discrete element model; Fluidized bed granulation; Granulation; Hybrid particulate modeling; Population balance model
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/j.compchemeng.2019.01.023

•Mechanistic rate expressions developed in the PBM to links CFD–DEM results•The effect of CPPs (gas flowrate, inlet air temperature, spray rate) identified.•Excess air flow rates lead to collisions with high energy and smaller granule size.•High inlet temperature leads to increased breakage of granules.•High binder spray rate increases the size and speed of granule growth.•Granule GMD predicted over time and compared to dynamic experimental data. In pharmaceutical manufacturing, fluidized bed granulation is one of the common processing options available to achieve better flowability of powders through size enlargement of primary particles. In fact over the last 50 years, various fluidized bed operations including freezing, drying, impregnation, coating, etc. have become a common place in the chemical processing industry due to the high level of contacts between fluids and solids attainable in a fluid bed system. These complex interactions between the fluid and particles also mean that simulating fluidized beds are still a challenging endeavor. Generally, Computational Fluid Dynamics (CFD) packages are employed to model the pressure drops in fluids; however, the presence of high concentration of solids and the complexity of granulation behavior require more advanced particle models than are available with CFD software. As a result, coupled frameworks that utilize the strength of particulate simulations such as Discrete Element Method (DEM) and bulk granulation modeling such as Population Balance Model (PBM) in conjunction with CFD information are the next steps to developing practical fluid bed granulation models. This paper aims to provide a comprehensive description of the development and validation of a coupled CFD–DEM–PBM framework for a fluidized bed wet granulation operation. A two-way coupled CFD–DEM model is developed for a 3-dimensional, lab-scale, top spray fluid bed granulator to study the effects of process parameters such as inlet air flow rate and inlet air temperature on the particle flow dynamics and the residence time in the spray zone. A one-way transfer of data from CFD–DEM to PBM is then applied to relate the effects of particle-fluid interactions to granulation behavior occurring within the fluidized bed system. Mechanistic rate expressions were developed in the PBM to create links between CFD–DEM results and PBM rate kernels which can express the effect of critical process parameters (CPPs) such as air flow rate, inlet air temperature,