Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Anand Prakash

2nd Supervisor

Chao Zhang

Joint Supervisor

Abstract

Bubble column reactors are multiphase contactors that have found several industrial applications owing to various attractive features including excellent thermal management, low maintenance cost due to simple construction and absence of moving parts. In order to attain desired performance for a given application, these reactors are usually equipped with internals such as vertical tube bundles to facilitate heat transfer. The column hydrodynamics and turbulence parameters are altered when the column is occluded with internals which adds to the complexity of the problem. The use of Computational Fluid Dynamics (CFD) tools for the study of multiphase flows has gained a lot of traction over the recent years. In the current study, CFD is applied to a 2-Dimensional Eulerian-Eulerian model coupled with Population Balance Model (PBM) to simulate bubble column reactors in the presence and absence of internals. The significance of various interfacial forces on the numerical solution has been reviewed. Based on this, a suitable model is chosen which appropriately simulates the gas-liquid flow and has been selected to perform flow transition studies which covers the bubbly, transition and churn-turbulent regime. An increase in hydrodynamic parameters like centerline liquid axial velocity and gas holdup was noticed when the bubble column was occluded with circular tube internals. Furthermore, when dense vertical internals were introduced, the hydrodynamic values varied and consequently increased. When internals were added, a significant variation was noticed in the flow pattern which contributed to superior qualities of mixing.

Summary for Lay Audience

Bubble column reactors are cylindrical vessels that can facilitate substantial interactions between a liquid phase and the dispersed gas phase. Bubble columns, in recent years, have found their applications in numerous industries owing to their diverse advantages like low energy input, absence of moving parts, low pressure drops, construction simplicity and superior rates of heat and mass transfer. In general, bubble columns have been used in the process, chemical, metallurgical and biological industries. Lately, these reactors have also been employed in novel areas like production of clean fuels, methanol synthesis, Fischer-Tropsch synthesis, algae cultivation, biofuel production, biomedical sector as a blood oxygenator etc. Regardless of its wide applications, the scale up of these reactors is still an open challenge. The prime hurdle in the scale up process is the presence of complex fluid dynamics. When the bubble column is obstructed with innards or internals in the form of cylindrical rods, the flow pattern and hydrodynamics vary which adds to the complexity of the problem. In the current work, a numerical tool called Computational Fluid Dynamics (CFD) has been employed to model the bubble column reactor. Information that is vital to the reactor’s scale up is obtained using the tool. The use of such computational tools decreases the laborious time required to build pilot setups, thereby increasing the productivity and improving the economics.

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