Implementing membrane gas separation systems have led to remarkable profits in both processes and products. This study presents the modeling and simulation of membrane gas separation systems using Aspen Plus ^® V8.6. A FORTRAN user model and a numerical solution procedure have been developed to characterize asymmetric hollow fiber membrane modules. The main benefit of this model is that it can be easily incorporated into a commercial simulator and used as a unit operation model in complex systems. A comparison between the model and the experimental cases at different operation conditions shows that calculated values are in good agreement with measured values. This model is suitable for future developments as well as design and performance analysis of multicomponent gas permeation systems prior to experimental realization.

Computational fluid dynamics (CFD) provides a flexible tool for investigation of separation processes within membrane hollow fiber modules. By enabling a three-dimensional and time dependent description of the corresponding transport phenomena, very detailed information about mass transfer or geometrical influences can be provided. The high level of detail comes with high computational costs, especially since species transport simulations must discretize and resolve steep gradients in the concentration polarization layer at the membrane. In contrast, flow simulations are not required to resolve these gradients. Hence, there is a large gap in the scale and complexity of computationally feasible geometries when comparing flow and species transport simulations. A method, which tries to cover the mentioned gap, is presented in the present article. It allows upscaling of the findings of species transport simulations, conducted for reduced geometries, on the geometrical scales of flow simulations. Consequently, total transmembrane transport of complete modules can be numerically predicted. The upscaling method does not require any empirical correlation to incorporate geometrical characteristics but solely depends on results acquired by CFD flow simulations. In the scope of this research, the proposed method is explained, conducted, and validated. This is done by the example of CO₂ removal in a prototype hollow fiber membrane oxygenator.

Extracorporeal membrane oxygenators are essential medical devices for the treatment of patients with respiratory failure. A promising approach to improve oxygenator performance is the use of microstructured hollow fiber membranes that increase the available gas exchange surface area. However, by altering the traditional circular fiber shape, the risk of low flow, stagnating zones that obstruct mass transfer and encourage thrombus formation, may increase. Finding an optimal fiber shape is therefore a significant task. In this study, experimentally validated computational fluid dynamics simulations were used to investigate transverse flow within fiber packings of circular and microstructured fiber geometries. A numerical model was applied to calculate the local Sherwood number on the membrane surface, allowing for qualitative comparison of gas exchange capacities in low-velocity areas caused by the microstructured geometries. These adverse flow structures lead to a tradeoff between increased surface area and mass transfer. Based on our simulations, we suggest an optimal fiber shape for further investigations that increases potential mass transfer by up to 48% in comparison to the traditional, circular hollow fiber shape.

Biorefinery systems play a critical role in the transition towards a sustainable bioeconomy, and bioreactors are a key component in these systems. While mechanically stirred reactors have been extensively studied, there is a lack of research on pneumatically driven systems like air-lift reactors (ALRs). This study aims to address this gap by examining the hydrodynamic behavior of a double draft tube airlift bioreactor using Computational fluid dynamics simulations. Ten different geometric configurations were investigated, with variations in draft tube placement, liquid height, distance between draft tubes and draft tube diameters. Results showed that the placement of the draft tubes heavily influenced hydrodynamic behavior, with smaller distances between draft tubes and a funnel configuration leading to higher velocities. Stable downcomer velocities were achieved by maintaining a consistent distance between the bottom clearance and the sum of the distance between draft tubes and the bottom clearance on the top clearance. The model was validated against literature experimental data. This study provides insight into the optimal design of ALRs, which can contribute to the development of more efficient and effective bioreactor systems. The findings can be used to forecast the most optimal configurations of airlift bioreactors and have significant value for the development of more efficient biorefining concepts in light of the increasing importance of studying biorefineries and their components in the shift towards a biomass-based economy.

The motion of non-spherical particles with sharp edges, as they are commonly involved in practice, was characterized by residence time distribution (RTD) measurement in a continuous drum. Particles with two sizes, 6 and 10 mm, and two densities, 750 and 2085 kg/m³, were used in the experiments. The effects of rotation speed (3–11 rpm), incline angle (2–4°), feed rate, and mixture composition were investigated and compared to the results of other researchers on particles without sharp edges. We also fitted the RTD with an axial dispersion model to obtain a better insight into the flow behavior. MRT of non-spherical particles with sharp edges depends on ω^−α similar to other shapes, while the value of alpha is higher for particles with sharp edges (0.9 < α < 1.24), especially at high incline angles. The MRT depends on incline angle, β^−b, where b varies between 0.81 (at low ω) and 1.34 (at high ω), while it is close to 1 for other shapes. Feed rate has a slight effect on the MRT of particles with sharp edges and the effect of particle size diminishes when rotation speed increases. The MRT linearly increases with volume fraction of light particles in a mixture of light and heavy particles (from pure heavy to pure light particles).

In the last decades, a large number of studies have been carried out on the utilization of membranes in separation processes. However, most of these studies deal with material properties, experimental investigations and process modeling. Only quite a few authors utilized computational fluid dynamics (CFD) to analyze the flow and mass transfer in membrane modules. Using CFD it is possible to obtain spatially resolved information on the behavior of membrane modules, allowing for the investigation of geometric effects on the performance of the module. This includes e. g. the positioning of the permeate outlets, the flow alignment (co- and/or counter-current), the use of spacers and other mixing promoters and also the subject of concentration polarization close to the membrane surface. In our present study we made use of OpenFOAM®, which is a free open sourced CFD toolbox. The toolbox enables for introducing new solver code, membraneFoam, based on the standard multicomponent solver reactingFoam. In membraneFoam suitable source and sink terms have been added to account for trans-membrane flux – in this case based on the solution-diffusion model for glassy polymer gas permeation membranes. The solver has been preliminary validated using literature data obtained from a process simulation code. In a first stage of the research work the positioning of the permeate outlet and the flow alignment have been investigated for a hollow fiber gas permeation module. By adjusting the position of the permeate outlet the shell side flow can be co-current, counter-current or mixed type relative to the retentate flow inside the fibers. Since this influences the driving force for the trans-membrane flux, effects on the module performance are expected which have been analyzed using the described membraneFoam CFD approach.