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Item type:Publication, Access status: without files , Simultaneous local determination of mass transfer and residence time distributions in organic multiphase systems(Elsevier, 2017-04-01); ; ; ; A new method for simultaneous local determination of mass transfer coefficients and residence time distributions in continuously operated bubble columns has been developed. Since for organic liquids not many experimental data sets are available in respect to mass transfer, measurements were carried out with the organic gas/liquid multiphase system consisting of cumene (1-methylethylbenzene) and carbon dioxide. The concentration of carbon dioxide in the gas phase was adjusted by mixing with nitrogen. To measure concentrations of compounds in the liquid phase, attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR) was applied: five ATR probes integrating silver-halide optical fibers with a length of 1.5 m were integrated in a bubble column of 128.5 cm height and a diameter of 10 cm. The probes were distributed over the height of the reactor and could be shifted within the reactor to measure radial profiles of the mass transfer coefficients in steady state operation mode at different positions. The superficial liquid velocity of the system was adjusted in the range of 0.7–1.4 cm s−1. The used superficial gas velocities were between 1.5 cm s−1 and 2.1 cm s−1 to ensure a homogeneous flow regime. Furthermore, tracer experiments with benzaldehyde for the investigation of the residence time distributions were performed. From the FTIR spectral data, CO2 and benzaldehyde tracer concentration data were determined simultaneously by conducting multivariate chemometric models. The corresponding mass transfer coefficients were calculated using a compartmental method for stationary flow. The residence time distributions were calculated from the benzoic aldehyde concentration data. Both parameters could be determined successfully. For the mass transfer coefficient of carbon dioxide into cumene, an interesting profile could be observed, which arose from several influences like areas of different bubble densities, caused by bubble breakage and coalescence, superficial velocities of gas and liquid as well as the applied type of sparger.Publicationtype: Journal Article96 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Bubble size and bubble velocity distribution in bubble columns under industrial conditions(Wiley, 2017-01-19); ; ; ; Bubble column reactors are widely used in many industrial applications due to their simplicity and safety of operation. Despite these advantages, the design and scale-up of bubble column reactors is still challenging especially for industrial conditions at elevated pressure and temperature. One reason is the uncertainties concerning the specific interfacial area which is directly dependent on the bubble size distribution, bubble velocity, and gas hold-up. All these parameters are difficult to measure under industrial conditions due to the opaqueness of the bubbly flow and the safety risks of using organic solvents at elevated pressures and temperatures. This article introduces endoscopic bubble image velocimetry, a new measuring method that enables the detection of bubble sizes and bubble velocities in organic solvents at elevated pressure and temperature (pmax= 1.85 MPa and Tmax = 70 °C) for maximal gas hold-ups of 16 %. For this system it becomes evident that the bubble size distribution for low superficial gas velocities is almost unaffected by pressure and temperature, whereas the bubble velocity decreases slightly.Publicationtype: Journal Article141 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Bubble columns operated under industrially relevant conditions - Current understanding of design parameters(2015-04-04); ; ; ; Despite the fact that bubble columns are widely established within the process industry as multiphase reactors and gas-liquid contactors, common research has been focused on the description of bubble column hydrodynamics under atmospheric conditions. Industrial production is usually conducted at pressures above atmospheric and temperatures above ambient in processes primarily involving the use of organic solvents. Because hydrodynamic parameters such as gas holdup and backmixing determine the necessary reactor design and impact reactor performance, detailed knowledge of these variables is crucial for optimal design and operation of bubble column reactors. The purpose of this article is to give an overview of research studies that deal with bubble column hydrodynamics at elevated pressures. A recommendation for further research concerning this topic is provided as well.Publicationtype: Journal Article40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modellierungsparameter für Blasenströmungen [Modeling parameters for bubbly flows]In the 1980s and 1990s intensive and successful research has been conducted to improve the integral description and design of bubble column reactors. At the turn of the century, in particular local measurement and modeling methods were refined. The results of these local models have often been poorly incorporated into the design of integral equations, as there is a significant gap between the observed temporal and spatial scales. Appropriate averaging and filtering processes are missing as much as transfer rules, to proceed from the most academic material systems and conditions towards industrial applications. The article describes the status quo in the field of modeling of bubbly flows and outlines novel methods that may lead to a more comprehensive modeling and better transferability in the future.Publicationtype: Journal Article136