Abstract
Prilling is a common process in the fertilizer industry, where the fertilizer melt is converted to droplets that fall, cool down and solidify in a countercurrent flow of air in a prilling tower. A vibratory granulator was used to investigate liquid jet breakup into droplets. The breakup of liquid jets subjected to a forced perturbation was investigated in the Rayleigh regime, where a mechanical vibration was applied in order to achieve the production of monodispersed particles. Images of the jet trajectory, breakup, and the formed drops were captured using a high-speed camera. A mathematical model for the liquid outflow conditions based on a transient two-dimensional Navier–Stokes equation was developed and solved analytically, and the correlations between the process parameters of the vibrator and the jet pressure that characterize their disintegration mode were identified. The theoretical predications obtained from the correlations showed a good agreement with the experimental results. Results of the experiments were used to specify the values of the process parameters of the vibration system, and to test them in the production environment in a mode of monodispersed jet disintegration. The vibration frequency was found to have a profound effect on the production of monodispersed particles. The results of experiments in a commercially-sized plant showed that the granulator design based on this study provided prills with a narrower size range compared to the conventional granulators, which resulted in a substantial reduction in dust emission.
Highlights
Population growth has led to an increasing demand for nitrogen fertilizers to enhance agricultural production yields worldwide
The prilling method is based on the forced disintegration of the melt jets of fertilizer into droplets outflowing from a rotating perforated bucket or a static system of fixed orifices, such as a shower head spray system, into a countercurrent flow of air stream inside the prilling tower [6,7,8,9,10]
Considering the melt jet hydrodynamic parameters, and its outflow from the holes of the vibration granulator perforated shell, the solution of Equation (3) for the case of non-stationary efflux is of particular interest, taking into account the changes occurring over time
Summary
Population growth has led to an increasing demand for nitrogen fertilizers to enhance agricultural production yields worldwide. The process of droplets cooling takes place during the free fall inside the tower, which may be associated with their crystallization These spray systems of melt jets operate under laminar conditions and have hundreds of low capacity openings that may become filled completely and generate strings of liquid that break up into the desired droplet size distribution [11]. Nonlinear dynamic aspects in the disintegration of the jet stream free surface and the appearance of the perturbations on it, which lead to different droplet structures, have been investigated [23]. The prilling towers are quite tall, and the heat transfer rate between air and crystals is very slow Such a phenomenon does not significantly contribute to dust emission, which is of main concern in this study. The study includes solutions of the equations for the perturbation along the liquid jet, the breakup of a liquid jet, and the reduction of dust emissions from the tower
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