Umpinaisen paperimassan lajittimen roottoreiden numeerinen simulointi

Pulp and paper manufacturing is an energy-intensive industry. One high-energy process is pressure screening to remove contaminants from the pulp. The screen is equipped with a rotor with hydrodynamic elements, which accelerates and keeps the pulp at a high tangential velocity. The pulp is forced through narrow apertures in the screen, which serves as a barrier to contaminants and oversized fibers. Pressure screens are critical in ensuring high quality pulp, which in return affects the quality, appearance and strength of the resulting paper products. The goal of this study was to reduce rotor energy consumption by optimizing the hydrodynamic element shape. The optimization was conducted using computational fluid dynamics (CFD) simulations done with FLUENT. Element performance was evaluated with the max. and min. pressure coefficient value, Cp, and vorticity around the element which creates drag. The element shape was controlled by four variables; chord length, position of maximum height, leading and trailing edge angles. The effect of rotor variables, element height, gap, rotor diameter and tip speed, were studied as well. The results show a -11% increase in the negative Cp peak and a -5% decrease in the positive Cp peak. Increase in the negative Cp peak results as a -15% decrease in rotor power consumption. The vorticity around the element was significantly reduced. In addition to these results, this study has shown that CFD is a powerful tool to research and develop specific rotor designs for industrial pressure screens