Heat and Mass Transfer in Adsorption Columns
Creators: Baliga, Chinmay R
Publisher: name: University of Alberta Library
Year: 2023

<p>Fixed beds are widely used in the chemical and process industry due to their simple yet effective performance. They find applications in heterogeneous catalysis (e.g., dry reforming of methane, methanol synthesis, etc.) and in adsorption (hydrogen from steam methane reforming, post-combustion CO2 capture, oxygen concentration, helium purification).<br>
Determining heat transfer at the wall in a fixed bed is crucial to predict the performance of the column or reactor. Literature review concludes that most adsorption modeling studies followed a simplified one-dimensional (1D) approach. Multidimensional simulations could potentially unlock additional insights into temperature and flow profiles. Chapter 1 introduces the fundamentals of adsorption principles and provides a framework of the transport equations involved in the adsorption process. Developments in computational modeling and a 1D process modeling study of an adsorption cycle for CO2 capture are briefly discussed.<br>
The fluid-wall heat transfer coefficient is currently obtained experimentally and is fitted via optimization to match the thermal breakthrough profiles of the system. This limits the range of applicability. Chapter 2 investigates the fluid-wall heat transfer in fixed beds, primarily from the aspect of wall Nusselt number determination via particle-resolved computational fluid dynamics (PRCFD) simulations and comparing vis-à-vis various correlations in literature. A fixed bed comprising 374 particles is generated using gravity sedimentation- assisted discrete element modeling (DEM). Steady-state, three-dimensional coupled flow and heat CFD simulations are conducted to investigate fluid-wall heat transfer. Additionally, the effect of buoyancy-driven flows on the wall heat transfer number is studied.<br>
The main objective of Chapter 3 is to validate boundary conditions for a hot object cooled down in a cold environment due to natural convection. The cooling of hot water in a cup is modeled via 2D and 3D CFD and conduct lab-scale experiments for validation purposes. User-Defined Functions, or UDFs, are developed and compiled within Fluent to expand the solver’s capabilities. Thus, a UDF module capable of simulating the combined effects of natural convection, radiation, and evaporative cooling has been developed. To date, CFD solvers do not yet possess natively the option to apply the natural convection or evaporative boundary conditions. This validated UDF may be ported for fixed beds and adsorption columns for improved prediction of thermal profiles in both lab-scale and industrial units.<br>
Chapter 4 deals with 2D transient CFD-based adsorption Dynamic Column Breakthrough simulations. The convective and radiative heat transfer coefficients are determined via physics-based modeling, eliminating the need to fit these coefficients to a particular system. The development of temperature profiles along the bed is analyzed. Our CFD model is validated against published experimental results for a small-scale pilot unit). The success of these simulations would form the framework for column-ambient heat transfer modeling in cyclic pressure vacuum swing adsorption (PVSA) CFD simulations.<br>
Chapter 5 summarizes the CFD angle to adsorption in fixed beds, laying down conclusions and future work. Through the undertaken “serial by simplification” multi-scale modeling approach, correlations developed on multidimensional (2D &amp; 3D) representative geometries may be employed in 1D adsorber models. The novelty of our work is implementing adsorption equilibria data for various adsorbents rigorously obtained by experiments in conjunction with CFD modeling in an attempt to identify and optimize the most critical design and operating factors, such as column geometry/flow distribution asymmetries/ scale-up, etc.</p>