Abstract
Mixing is one of the most crucial processes in the chemical industry. Homogeneity is a requirement for all feedstocks and industrial products. The degree of mixing depends on the hydrodynamic properties of the fluid in the units. The Residence Time Distribution (RTD) was investigated in a tank of a special geometry. Mixing was investigated using various geometries of the tank by applying the Heaviside function in step-response experiments. After obtaining experimental results, the RTD function was calculated. The flow structure in the tank was approximated by fitting black-box transfer function models onto the RTD function of the system. Two general model structures were defined and their fitness compared. By evaluating the fitted models, a relationship was established between the flow structure in the tank and its geometry.
Highlights
In industrial processes, the thorough homogeneity of materials is a necessity to ensure the quality of the finished products and the safety of the production process
The geometry consisting of 5 cylinders was originally modeled using a second order transfer function that yielded the best fit for the experimental Residence Time Distribution (RTD) curve (92 %)
In order to determine the relationship between the flow profile and geometry of the tank, step-response experiments were conducted
Summary
The thorough homogeneity of materials is a necessity to ensure the quality of the finished products and the safety of the production process. The optimal type and geometry of these stirred tanks can be approximated by specific models which take the properties of the materials to be mixed and the desired degree of homogeneity into consideration [1]. In the case of the homogenisation of large volumes of liquids (petrochemical and radiochemical industries), external recirculation can be more advantageous since it is considerably more inexpensive in terms of both installation and operation. The operation of stirred tanks has been thoroughly investigated by using mathematical and experimental methods, research on mixing achieved by external recirculation is lacking [2]. Optimization of the mixing process to achieve the most homogenous product possible in an external recirculation tank can only be achieved after the flow structure of the unit is known. The aim of this research was to analyze the flow structure in a tank of special geometry, to determine the connection between the flow structure and geometry of the tank
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