energies Article Effect of Adding Surfactants to a Solution of Fertilizer on the Granulation Process Bernard Michalek 1, * , Marek Ochowiak 2 , Katarzyna Bizon 3 , Sylwia Wlodarczak 2 , And ˙ zelika Krupi ´ nska 2 , Magdalena Matuszak 2 , Dominika Boro ´ n 3 , Bla ˙ zej Gierczyk 1 and Radoslaw Olszewski 4   Citation: Michalek, B.; Ochowiak, M.; Bizon, K.; Wlodarczak, S.; Krupi ´ nska, A.; Matuszak, M.; Boro ´ n, D.; Gierczyk, B.; Olszewski, R. Effect of Adding Surfactants to a Solution of Fertilizer on the Granulation Process. Energies 2021, 14, 7557. https:// doi.org/10.3390/en14227557 Academic Editor: Attilio Converti Received: 15 October 2021 Accepted: 11 November 2021 Published: 12 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Chemistry, Adam Mickiewicz University, ul. Uniwerystetu Pozna´ nskiego 8, 61-614 Poznan, Poland; hanuman@amu.edu.pl 2 Department of Chemical Engineering and Equipment, Poznan University of Technology, Plac Marii Sklodowskiej-Curie 5, 60-965 Poznan, Poland; marek.ochowiak@put.poznan.pl (M.O.); sylwia.wlodarczak@put.poznan.pl (S.W.); andzelika.krupinska@put.poznan.pl (A.K.); magdalena.matuszak@put.poznan.pl (M.M.) 3 Faculty of Chemical Engineeringand Technology, Cracow University of Technology, ul. Warszawska24, 31-155 Krakow, Poland; katarzyna.bizon@pk.edu.pl (K.B.); dominika.boron@pk.edu.pl (D.B.) 4 PPC ADOB, ul. Kolodzieja 11, 61-070 Poznan, Poland; radoslaw.olszewski@adob.com.pl * Correspondence: bm9309@st.amu.edu.pl Abstract: Granulated chelates are innovative fertilizers that are highly effective and versatile, and they ensure the best start-up effect for plants. The final properties of granules are influenced by the method of their preparation and the used substances. The diameters of the obtained granules, their size range, and the final costs of the produced fertilizer are of great importance. The paper describes granules that were produced using an agglomeration of ZnIDHA in a fluidized bed with the aid of an aqueous solution of this substance with a high dry matter content. The aim of the study was to evaluate the effect of surfactant addition to the solution on the evolution of granule size distribution during the process carried out in a batch mode and to access the possibility of describing the process dynamics using population balance approach. A sieve analysis was performed in order to determine the size of the granulate, and numerical calculations were performed to determine the value of the constant aggregation rate. Based on experimental studies, it can be seen that the increase in the diameters of granules is mainly caused by the agglomeration process, and to a lesser extent by the coating process. The addition of surfactant increased the median size of the granules in the initial granulation stage, and also lowered the surface tension. This in turn enables a lower spraying pressure to be used. A comparison of different aggregation kernels constituting an integral part of the population balance model proved that the physically motivated equipartition kinetic energy kernel performs best in this case. Moreover, the computational results show an increase in the aggregation rate when the surfactant additive is used and confirm that population balance allows the extraction of physical information about the granulation. Keywords: granulation process; fertilizer; surfactants; agglomeration; granule properties 1. Introduction Granulation is the process of producing grains (granules), or enlarging existing solid particles [1]. Its main goal is to obtain a convenient and acceptable final form of a product for users [2]. Granulation, understood as the controlled agglomeration of powders with a high degree of dispersion, is a technique that is implemented in various ways. It can be divided into wet and dry granulation [3]. The most important difference between them is that in the case of wet granulation, it is necessary to apply an additional substance- granulating liquid [4,5]. The phenomenon of agglomeration occurs in the widely used wet granulation. The increase in grain size can be regulated by coating the grains with a layer of solution. The process involves the spraying of a liquid binder onto small particles that are Energies 2021, 14, 7557. https://doi.org/10.3390/en14227557 https://www.mdpi.com/journal/energies