**1. Introduction**

Transportation of liquids or hydromixtures through conduits is an important element of technological solutions in many industries. The advantages of such transport include: low costs, maintaining high purity of the transported medium, the elimination of environmental pollution, as well as easy monitoring and automation of such a process.

The demand to pump hydromixtures consisting of increasingly finer solid particles with their increasing concentration in industrial installations has been growing. Pumping hydromixtures with high solids concentrations in pipelines requires the application of pumps with a high discharge pressure, which results in a significant energy consumption and leads to greater pump wear [1–3].

During the transportation process of hydromixture, a substantial reduction of frictional pressure drop in the pipeline may occur. It is therefore often necessary to consider the problems of calculating the power requirements for pumping through a given pipeline system, the selection of the optimum pipe diameter, the measurement and control of the flow rate, etc. The knowledge of these factors facilitates controlling the total plant cost installation operation [4]. Several studies for pressure drop prediction in slurry flow are available in the literature, for instance [5–7].

It is clear that the transportation of utilities through pipelines involves significant energy expenditure. In recent years, with the growing difficulties with obtaining energy and the need to optimize transport costs, it has become necessary to develop new energysaving technologies and methods of media transport that enable the reduction of energy

**Citation:** Jaworska-Jó ´zwiak, B.; Dziubi ´nski, M. Effect of Deflocculant Addition on Energy Savings in Hydrotransport in the Lime Production Process. *Energies* **2022**, *15*, 3869. https://doi.org/10.3390/ en15113869

Academic Editors: Phillip Ligrani and Roberto Alonso González Lezcano

Received: 30 March 2022 Accepted: 20 May 2022 Published: 24 May 2022

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**Copyright:** © 2022 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/).

consumption [8–10]. Such methods include: methods using the phenomena of the abnormal reduction of any pressure drop when macromolecular polymers are added to the transported medium (Toms effect), methods using surfactants (surface-active substances) or deflocculants (a chemical or compound that prevents flocculation) as additives to reduce pressure drop during media transport, two-phase liquid-gas transport methods using compressed air (mainly used while concentrated suspensions exhibit complex rheological properties, especially when non-Newtonian shear thinning liquids are transported), and methods of modifying the rheological properties of the transported media. Each of these methods has found a wide application in practice and has been the subject of many research works [11–15].

A great deal of works have been published in the literature devoted to explanation of the mechanism of pressure drop reduction [16–22]. Despite the fact that many hypotheses of this phenomenon have been put forward, it has not been possible to propose universal model equations for predicting the frictional pressure drop.

The objective of this study is to develop a method of reduction of the electrical power consumption in the transportation of hydromixture in the pipeline. Such studies are part of the issues of industrial process intensification and multiphase fluid mechanics due to their wide applicability.

## **2. Materials and Methods**

The hydromixture used in the study originated from an industrial installation of a Polish limestone mine. The solid fraction contained in the hydromixture consisted of dusty particles of quarried stone containing a high percentage of calcium carbonate. The grain composition of the solid fraction, determined using a laser grain size analyzer, is shown in Figure 1.

**Figure 1.** Grain size distribution curve of the tested hydromixture.

The grain size ranged from 0.5 μm to 163.5 μm, with an average grain size of 45.5 μm. The dust fraction with a mean grain diameter ranging from 2 μm to 50 μm had the largest share in the sample (about 65%). The sand fraction, characterizing particles with an average grain diameter larger than 50 μm, represented almost one third of all particles. The clay particles constituted only 3.38% of all the particles contained in the hydromixture. Chemically, the test hydromixture consisted mainly of calcium oxide CaO (73.6%) and silicon oxide (SiO2—13%). The other chemical compounds in the hydromixture were: magnesium oxide (MgO—0.6%), iron oxide (Fe2O3—0.3%), aluminum oxide (Al2O3—1.1%) and sulfur trioxide (SO3—0.3%). Substances that could not be identified accounted for approximately 11.1% of the total.

Rheological studies of hydromixture were performed using an Anton Paar (Lyon, France) MCR 302 rotational viscometer at T = 20 ◦C for hydromixtures with a mass concentration of Cm = (21.30−50.00)% and a solid volume concentration of Cv = (10−29)% in a range of hydromixtures density from about 1140 kg/m3 to 1410 kg/m3.

The effect of frictional pressure drop reduction in the pipeline was obtained by introducing to the hydromixture an addition of substances with highly dispersive properties, in the form of fine mineral particles and chemical compounds, called deflocculants (drag reduction agents—DRA). Such an effect is called chemical treatment and, due to its potential practical use, has become the subject of much interest in various branches of industry and scientific works [23–28]. This effect should result in frictional pressure drop reduction in the flow of the hydromixture with an increase in the concentration of the solid phase contained in it, and result in a reduction of the energy consumption necessary to overcome the friction occurring in the pipeline. The reduction in the frictional pressure drop entails a reduction in the total cost of the hydrotransport process.

The composition of the proposed deflocculant was developed based on years of experimental research, knowledge derived from the literature, and cooperation with an industrial enterprise.

Sodium water glass and calcareous groats were selected as the deflocculant components based on their easy access in the product market, low manufacturing/acquisition cost and environmental neutrality. In the case of sodium water glass, the unquestionable advantage is its common occurrence and low purchase cost. Sodium water glass is formed by the reaction between silica and sodium hydroxide or silica and sodium carbonate. The addition of sodium water glass was intended to lower the viscosity, leading to a reduction in the shear stress created in the transported hydromixture. Calcareous groats, a residue from the lime slaking process that produces hydrated lime, consist of mineral particles with a grain diameter of less than 1.8 mm and an average grain diameter of 240 μm. Figure 2b presents an image of the calcareous groats grains surface made by a Phenom Pro X (Thermo Fisher Scientific, Waltham, MA, USA) scanning electron microscope (SEM) after applying a 10 kV electron accelerating voltage.

(**a**) (**b**)

**Figure 2.** (**a**) Picture of dried lime slurry sample. (**b**) Surface image of calcareous groats grains made by scanning electron microscopy (SEM) with 1100× magnifications.

This substance is inexpensive and easy to obtain, and is stored in large amounts in the production plant area. Chemically, calcareous groats are mostly composed of calcium oxide and magnesium oxide (70.81%), silicon dioxide (1.52%) and aluminum (0.84%). The remaining substances are minor impurities formed in the process of hydration of a mixture of lime and water. Table 1 presents the results of the chemical composition analysis of calcareous groats performed with a scanning electron microscope integrated with an energy-dispersive X-ray spectrometer (EDS).

**Table 1.** Chemical composition of calcareous groats made using an energy-dispersive X-ray spectrometer (EDS).


These two substances (sodium water glass and calcareous groats) combined together in appropriate proportions, depending on the mass concentration of the hydromixture, were added to tested samples with a high solid phase concentration in order to reduce the viscosity of the hydromixture.
