Abstract
The hydrodynamics within counter-current flow packed beds is of vital importance to provide insight into the design and operational parameters that may impact reactor and reaction efficiencies in processes used for post combustion CO2 capture. However, the multiphase counter-current flows in random packing used in these processes are complicated to visualize. Hence, this work aimed at developing a computational fluid dynamics (CFD) model to study more precisely the complex details of flow inside a packed bed. The simulation results clearly demonstrated the development of, and changes in, liquid distributions, wetted areas, and film thickness under various gas and liquid flow rates. An increase in values of the We number led to a more uniform liquid distribution, and the flow patterns changed from droplet flow to film flow and trickle flow as the We number was increased. In contrast, an increase in gas flow rate had no significant effect on the wetted areas and liquid holdup. It was also determined that the number of liquid inlets affected flow behavior, and the liquid surface tension had an insignificant influence on pressure drop or liquid holdup; however, lower surface tension provided a larger wetted area and a thinner film. An experimental study, performed to enable comparisons between experimentally measured pressure drops and simulation-determined pressure drops, showed close correspondence and similar trends between the experimental data and the simulation data; hence, it was concluded that the simulation model was validated and could reasonably predict flow dynamics within a counter-current flow packed bed.
Highlights
Global warming and climate change attract much attention worldwide, and a large amount of the anthropogenic CO2 emission is reported to be responsible for it [1]
The results of computational fluid dynamics (CFD) assessments of gas–liquid flows are generally validated by comparing pressure drops obtained from modeling and experimentation
Pressure drops, measured at each experimental condition, are displayed in Table 2; they increased with the increment of either liquid or gas flow rates, but were more sensitive to gas flow rate variations than to liquid flow variations
Summary
Global warming and climate change attract much attention worldwide, and a large amount of the anthropogenic CO2 emission is reported to be responsible for it [1]. Increase in atmospheric CO2 concentrations since preindustrial times, and this increase is primarily due to fossil fuel combustion [2]. If the deleterious effects of rising CO2 concentrations are to be averted, an imperative need exists to reduce the extent to which it is emitted into the atmosphere [3]. Technologies are under development for capturing and sequestering CO2 , with a primary focus on power generation; these include pre-combustion, post combustion, oxy-fuel combustion, and Energies 2018, 11, 1441; doi:10.3390/en11061441 www.mdpi.com/journal/energies. Energies 2018, 11, 1441 chemical looping combustion scenarios. Post combustion capture removes CO2 from the flue gas, a stage when fuel has already been combusted.
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