The effect of gas-phase density on bubble formation at a single orifice in a two-dimensional gas-fluidised bed.

In this study the effect of the gas-phase density on the process of bubble formation at a single orifice in a two-dimensional gas-fluidized bed has been studied experimentally and theoretically. Specifically, a detailed comparison between experimentally observed and theoretically calculated bubble growth curves has been made in the case where the density of the gas injected through the orifice (He and SF6) differs significantly from the density of the primary fluidizing agent (air). The calculations have been carried out using an earlier developed, first principles hydrodynamic model of gas-fluidized beds which has been extended with a species conservation equation to calculate the composition of the fluidizing gas in the vicinity of the evolving bubbles. Besides, the present experimental and theoretical results were compared with predictions obtained from adapted versions of approximate bubble formation models previously reported in the literature. The advanced hydrodynamic model appears to predict the experimentally observed diameters satisfactorily. In addition, the model correctly predicts the effect of the gas-phase density on the experimentally observed bubble growth. This effect can be explained satisfactorily in terms of the dependence of the interphase momentum transfer coefficient on gas-phase density. Finally, calculations with a three-dimensional version of our hydrodynamic model have been carried out to account for the effect of the front and back wall of the pseudo two-dimensional gas-fluidized bed used in our experiments. Our preliminary computational results indicate that the magnitude of the wall effect strongly depends on the boundary condition enforced for the gas-solid dispersion at these walls. In the case that the no-slip boundary condition was enforced in the calculations for the solid phase, the wall effect was significant and a considerable deviation between computed and experimentally observed bubble growth curves was found. However, when a more realistic partial slip boundary condition for the solid phase was implemented the agreement between theory and experiment could be improved by altering the slip parameter in the partial slip boundary condition expression

The solubility of hydrogen sulfide in aqueous N-methyldiethanolamine solutions

In this work the electrolyte equation of state as developed previously for the system MDEA-H2O-CO2-CH4 was further developed for the system MDEA-H2O-H2S-CH4. With this thermodynamic equilibrium model the total solubility of hydrogen sulfide and the speciation in aqueous solutions of N-methyldiethanolamine can be described quantitatively. The model results were compared to experimental H2S solubility data in aqueous MDEA in absence and presence of methane respectively. The application of equation of state models for this kind of acid gas – amine systems is a rather new development in the literature. An accurate description is difficult for this kind of complex systems with significant amount of both molecular and ionic species present in the liquid phase. The Schwarzentruber’s modification of the Redlich-Kwong-Soave EOS with a Huron-Vidal mixing rule is used as molecular part of the equation of state and ionic interactions terms are added to account for non-idealities caused by these interactions. With the new developed model a comparison with experimental data as presented was made