Computational flow modelling and design of bubble column reactors

Numerical simulation of the dynamics of two-phase gas—liquid flows in bubble columns

https://ris.utwente.nl/ws/files/6773317/computational_fluid.pdf

Computational fluid dynamics applied to gas-liquid contactors

Publisher Summary This chapter presents a new emerging tool that is a combination of fluid dynamics (CFD) and numerical mathematics backed up by the immense growth of computer power: computational fluid dynamics. CFD offers great potential for the chemical engineer and that this rapidly emerging new hybrid science of mathematics and mechanics at present already has a profound impact on chemical reaction engineering. It is expected that the role of CFD in the future design of chemical reactors will increase substantially and that CFD can reduce the experimental effort required to develop industrial reactors. A well-known traditional approach adopted in chemical engineering to circumvent the intrinsic difficulties in obtaining the “complete velocity distribution map” is the characterization of nonideal flow patterns by means of residence time distribution (RTD) experiments where typically the response of a piece of process equipment is measured due to a disturbance of the inlet concentration of a tracer. Applications of CFD may be divided into broad categories—those involving single-phase systems and those involving multiphase systems. Within single-phase systems, a further distinction can be made between systems involving laminar flows, turbulent flows, flows with complex rheology, and fast chemical reactions. In many processes encountered in industrial practice, multiphase flows are encountered and, it can be stated that, because of the inherent complexity of such flows, general applicable models and related CFD codes are nonexistent.

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Computational fluid dynamics applied to chemical reaction engineering

Eulerian¿Lagrangian simulations of liquid¿gas¿solid flows in three-phase slurry reactors

A heterogeneous fluid dynamic model has been developed to describe the complex flow structure of two-phase in bubble columns. The equation of continuity and momentum balances form the basis of the model. Coupling of the two phases occurs via an interaction force, deduced by a force balance around a single rising bubble. Multiphase flow mixing processes are taken into consideration by introducing turbulent viscosities of the two phases involved. The Simulation program was extended to reactive system, taking into account the mass balances of a second order gas-liquid chemical reaction as well as the different absorption/reaction regimes. The gas phase concentration profiles show pronounced axial and radial dependences, while the liquid phase can be regarded as a CSTR with respect to the liquid component. With reference to the gaseous component, which is being absorbed in the liquid phase, the degree of back mixing does not show CSTR behaviour as the influence of different absorption conditions in different axial and radial reactor positions is superposed on that of turbulent motion of the liquid carrier of the dissolved gaseous component.

Harald Kömpel

Papers

A fluid‐dynamically based model of bubble column reactors