Closure Development for Multi-Scale Fluidized Bed Reactor Models: A CLR Case Study

Chemical looping reforming (CLR) processes offer textbook examples for challenges in chemical engineering with respect to transport limitations. Phenomena that potentially need to be considered in a rigorous reactor model include (i) diffusion in solids as well as nanometer-scale pores, (ii) heat and mass transfer between suspended particles and the ambient gas, (iii) meso-scale phenomena such as clustering [1], and last but not least (iv) large-scale phenomena such as particle and gas-phase dispersion in the reactor’s axial direction. Considering all these phenomena typically requires a “zoo” of software tools, which should to be tightly integrated to facilitate rapid knowledge transfer.

Here we summarize our efforts within the “NanoSim” project (www.sintef.no/projectweb/nanosim) that aim on quantifying the relative importance of these phenomena in CLR applications. This project established a simulation platform for online and off-line coupling, spanning (i) intra-particle simulators [3], (ii) Computational Fluid Dynamics (CFD) models in various flavors [4,5], (iii) particle flow simulators [6], as well as (iv) phenomenological models [2]. We present a new generation of closure models for both particle- and cluster scale phenomena that enable significantly more reliable simulations of reactive fluidized beds. Another key result of our project is the open-source co-simulation simulation platform “COSI”: this platform is not only useful for multiphysics co-simulation of industrial-scale reactive fluid-particle systems, but also for distilling generally-applicable closure laws to be used in traditional offline coupling. Closure law development is greatly accelerated with our tool “CPPPO” [7], which is highly scalable and flexible. A key conclusion of NanoSim is that already at the particle scale significant uncertainties are introduced. This is due to the nature of gas-particle flow, i.e., the spontaneous formation of heterogeneities that strongly impact flow and species transport.

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