Projektiranje i uvećanje mjerila biokemijskih reaktora s višestrukim miješalima

Mechanically agitated gas-liquid contactors are frequently used in the chemical, food and biochemical industries as fermenters and as hydrogenation or chlorination reactors. However wide is the usage of such vessels, their design is not based on chemical engineering data, but is still rather empirical. Thus, it is highly desirable to have a tool for the rational design of agitated gas-liquid contactors that is based on fundamental chemical engineering parameters that are transferable to other systems and operating conditions. Focusing on liquid film-controlled processes and using the data from fermenters of different scales, we develop kLa correlations that are suitable for scale-up. First, we discuss how to determine the proper experimental kLa values, which are not distorted by other equipment parameters as is the gas residence time. We demonstrate the possible kLa distortion on the pilot-plant experimental data by comparing the results obtained by two different experimental techniques. Further, we present physically correct kLa data for fully non-coalescent (sodium sulphate solution) batch. The data are presented both for laboratory and pilot-plant fermenters. We identify the process parameters, the values of which are dependent on the vessel scale when operated under the same power input per volume, and, using these parameters, we develop common kLa correlations suitable to describe the data for various scales of the vessel. The correlations developed reduce the uncertainty in predicting the volume of industrial scale fermenters from almost 1/2 to 1/4 of their total volume, thereby enabling significant reductions in both the initial costs, and operating costs.Uređaji za mehaničko miješanje sustava kapljevina-plin često se upotrebljavaju u kemijskoj, prehrambenoj i biokemijskoj industriji kao fermentori i kao reaktori za hiodrogeniranje i kloriranje. No u širokoj primjeni takvih reaktora njihov se dizajn ne temelji na kemijsko-inženjerskim podatcima te je još uvijek prilično empirijski. Dakle, vrlo je poželjno imati alat za racionalno projektiranje/dizajn uređaja za mehaničko miješanje sustava kapljevina-plin koji se temelji na fundamentalnim kemijsko-inženjerskim parametrima koji su prenosivi i na druge sustave i druge radne uvjete. Usredotočivši se na procese kontrolirane tekućim filmom i primjenjujući podatke iz fermentera različitih mjerila, razvijene su korelacije kLa koje su pogodne za uvećanje mjerila. Najprije se govori o načinu kako utvrditi odgovarajuće eksperimentalne vrijednosti kLa koje nisu narušene drugim parametrima kao to je to vrijeme zadržavanja plina. Pokazuje se moguća distorzija eksperimentalnih podataka kLa poluindustrijskih postrojenja usporedbom rezultata koji su dobiveni dvjema različitim eksperimentalnim tehnikama. Nadalje, prikazuju se fizički ispravni podatci kLa za smjesu (otopinu natrijeva sulfata) u potpunosti bez koalescencije (spajanja). Podatci su prikazani i za laboratorij i za fermentore poluindustrijskih postrojenja. Utvrđuju se procesni parametri vrijednosti koje su ovisne o mjerilu reaktorske posude, kada djeluju pod istom ulaznom snagom po jedinici obujma i primjenom ovih parametara razvijaju se uobičajene korelacije kLa prikladne za opisivanje podataka za različita mjerila reaktorske posude. Razvijene korelacije smanjuju nesigurnost u predviđanju obujma fermentora industrijskih razmjera s gotovo 1/ 2 do 1 / 4 od svog ukupnog obujma i time omogućuju znatno smanjenje početnih operativnih trokova.</p

Liquid mixing time and gas distribution in aerated multiple-impeller stirred tanks

Gas-liquid fluid dynamics and mass transfer are crucial aspects of aerobic fermentation and robust methodologies for their determination in industrial bioreactors are expected to provide significant improvements in many production processes. In this work, a gas-liquid stirred tank of high aspect ratio, that replicates the geometry of typical industrial aerated fermenters, is investigated. In particular, the liquid phase homogenization dynamics and the gas phase spatial distribution are determined. The selected methodology is based on the analysis of the conductivity measurements obtained by Electrical Resistance Tomography. The gas-liquid flow regimes and the mixing time are identified at various gas flow rates and impeller speeds, thus covering different gas-liquid regimes. Data col lected with vertical and horizontal arrangements of the electrodes allow to obtain a tailed picture of the equipment working mode and to gain insight into the gas-liquid flow dynamics under optically inaccessible conditions. Quantitative evaluation of the bility of the collected data is attempted by comparing the results obtained with the tical and horizontal arrangements in the same locations

High Climate Model Dependency of Pliocene Antarctic Ice-Sheet Predictions

The mid-Pliocene warm period provides a natural laboratory to investigate the long-term response of the Earth’s ice-sheets and sea level in a warmer-than-present-day world. Proxy data suggest that during the warm Pliocene, portions of the Antarctic ice-sheets, including West Antarctica could have been lost. Ice-sheet modelling forced by Pliocene climate model outputs is an essential way to improve our understanding of ice-sheets during the Pliocene. However, uncertainty exists regarding the degree to which results are model-dependent. Using climatological forcing from an international climate modelling intercomparison project, we demonstrate the high dependency of Antarctic ice-sheet volume predictions on the climate model-based forcing used. In addition, the collapse of the vulnerable marine basins of Antarctica is dependent on the ice-sheet model used. These results demonstrate that great caution is required in order to avoid making unsound statements about the nature of the Pliocene Antarctic ice-sheet based on model results that do not account for structural uncertainty in both the climate and ice sheet models

Transportní charakteristiky konfigurací s více míchadly Lightnin A315 v disperzích kapalina-plyn

This article deals with transport characteristics of multiple-lightnin A315 impellers in gas-liquid dispersions

Transportní charakteristiky různých vícemíchadlových konfigurací v míchané disperzi kapalina-plyn s vyšší viskositou

Mixing intensity, gas hold-up and volumetric mass transfer coefficient of various multiple-impeller configurations are measured in a vessel of inner diameter 0.29 m equipped with three impellers on a common shaft. Five types of impellers are used. Distilled water with 3 vol.% Sokrat 44 is used as a liquid phase with Newtonian behaviour and viscosity 12.9 mPa.s. Air is used as gas phase. Mixing intensity was measured using tracer experiment and Dynamic Pressure Method was used for the measurement of volumetric mass transfer coefficient. Transport characteristics are presented for individual impeller configurations as functions of power consumption and superficial gas velocity. The impellers are compared each other and with transport characteristics for non-viscous solutions measured previously

The Design and Scale-Up of Multiple-Impeller Fermenters for Liquid Film Controlled Processes

Mechanically agitated gas-liquid contactors are frequently used in the chemical, food and biochemical industries as fermenters and as hydrogenation or chlorination reactors. However wide is the usage of such vessels, their design is not based on chemical engineering data, but is still rather empirical. Thus, it is highly desirable to have a tool for the rational design of agitated gas-liquid contactors that is based on fundamental chemical engineering parameters that are transferable to other systems and operating conditions. Focusing on liquid film-controlled processes and using the data from fermenters of different scales, we develop kLa correlations that are suitable for scale-up. First, we discuss how to determine the proper experimental kLa values, which are not distorted by other equipment parameters as is the gas residence time. We demonstrate the possible kLa distortion on the pilot-plant experimental data by comparing the results obtained by two different experimental techniques. Further, we present physically correct kLa data for fully non-coalescent (sodium sulphate solution) batch. The data are presented both for laboratory and pilot-plant fermenters. We identify the process parameters, the values of which are dependent on the vessel scale when operated under the same power input per volume, and, using these parameters, we develop common kLa correlations suitable to describe the data for various scales of the vessel. The correlations developed reduce the uncertainty in predicting the volume of industrial scale fermenters from almost 1/2 to 1/4 of their total volume, thereby enabling significant reductions in both the initial costs, and operating costs.<br

Non-Stationary Noise Analysis of Magnetic Sensors using Allan Variance

The presented paper describes methodology for the non-stationary noise analysis of the magnetic sensors' data using the dynamic Allan variance. The methodology was developed for the characterization of clock behavior. In the article the theory is applied for the magnetic sensors noise analysis and verified by the simulations and experiments. Results of the data analysis are graphically presented and statistically evaluated and prove the correctness of the initial hypothesis and confirm suitability of the dynamic Allan variance approach for magnetic sensors with the non-stationary noise behavior

Impact of Curved-Blade Impellers on Gas Holdup and Liquid Homogenization Dynamics in Stirred Tanks

Design and optimization of aerobic fermentation processes in stirred tanks must factor in specific features, such as the formation of gas cavities on the rear of impeller blades and the need for high power input. Here, the ability of a curved-blade impeller to reduce these drawbacks, which are typical of flat-blade impellers, is investigated. The analysis is based on gas holdup distributions and liquid homogenization dynamics collected by electrical resistance tomography in a pilot-scale stirred tank of geometry similar to typical industrial aerated fermenters. A wide range of gas flow rates and impeller speeds in single-impeller and multiple-impeller configurations are considered and the differences arising when a Rushton turbine is replaced with a Bakker turbine are discussed