*Article* **Assessment of Operational Effectiveness of Innovative Circuit for Production of Crushed Regular Aggregates in Particle Size Fraction 8–16 mm**

**Tomasz Gawenda , Agata Stempkowska \* , Daniel Saramak , Dariusz Foszcz , Aldona Krawczykowska and Agnieszka Surowiak**

> Department of Environmental Engineering, Faculty of Civil Engineering and Resource Management, AGH University of Science and Technology, Mickiewicza 30 Av., 30-059 Cracow, Poland; gawenda@agh.edu.pl (T.G.); dsaramak@agh.edu.pl (D.S.); foszcz@agh.edu.pl (D.F.); aldona.krawczykowska@agh.edu.pl (A.K.); asur@agh.edu.pl (A.S.)

**\*** Correspondence: stemp@agh.edu.pl

**Abstract:** The purpose of this paper is to analyze a modern and unique technological system producing common aggregates at the Imielin Dolomite Mine. The installation was built on the basis of inventions of AGH UST and consists of an impact crusher, innovative screens WSR and WSL, light fraction separator SEL and hard fraction separator SET, low-pressure hydrocyclone NHC and infrastructure. The study was carried out on the crusher and screen on the example of production of aggregates with grain size 8–16 mm from dolomite, granite, limestone, sandstone, and gravel. The results showed that cubic aggregates with a low content of irregular grains of less than 1% can be produced in this technological system.

**Keywords:** regular aggregate; innovative installation; separation

#### **1. Introduction**

Requirements for aggregate quality and minimization of energy consumption pose increasing challenges for raw material processing plants. A demanding market may in future require large quantities of products with narrow grain size distribution and specific grain shapes. The physical and chemical properties of the material, such as density, hardness, strength, and structure, depend on the place of exploitation (the origin of the raw material), and therefore, are generally invariable in the processing operations in mineral processing. On the other hand, specific particle size and shape or surface structure are achievable depending on the processing methods used during their manufacture (especially crushing) and can directly affect other properties [1–3]. The most important rock raw materials for civil engineering are fractured aggregates produced from magmatic, sedimentary, and metamorphic rocks [4–6]. The protection of the earth's natural resources and the increased use of industrial wastes have resulted in parallel research on the use of recycled and artificial aggregates [7]. Aggregates of the highest quality (e.g., basalt, melaphyre) are used in various branches of construction. The created precast elements that carry enormous dynamic loads, are subject to direct abrasion and adverse weather conditions. These structures should be made of aggregates with low abrasiveness, high strength, and resistance to water and frost. In addition, these aggregates should be characterized by particle shape close to spherical or cubic, sharp edges and rough fracture surfaces. All types of aggregates are commonly used for road pavement layers and structural elements of all types of concrete [8–12].

In the ongoing scientific research on the issues of mineral aggregate production [13,14], it has been noted that the hardness of the raw rock affects its shape. In general, the more compact the raw material, the more difficult it is to obtain cubic particles from it [15–18].

**Citation:** Gawenda, T.; Stempkowska, A.; Saramak, D.; Foszcz, D.; Krawczykowska, A.; Surowiak, A. Assessment of Operational Effectiveness of Innovative Circuit for Production of Crushed Regular Aggregates in Particle Size Fraction 8–16 mm. *Minerals* **2022**, *12*, 634. https://doi.org/10.3390/ min12050634

Academic Editors: Shuai Wang, Xingjie Wang and Jia Yang

Received: 7 April 2022 Accepted: 13 May 2022 Published: 17 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/).

Moreover, in the finer fractions of the crushing products, the largest number of elongated and flat grains is obtained. Therefore, it is advisable to use impact crushers (e.g., with a vertical shaft) at the final stages of crushing. As the crushing rate increases, the percentage of irregular (especially in fine fractions) aggregates also increases, thus crushers should be operated at a crushing rate that is not too high. However, all of these important factors influence the necessity to expand and use multi-stage systems, which usually lead to increasing both the investment and operating costs. There are many studies on the influence of grain geometry on the parameters (such as grinding ability) and properties of aggregates and materials made from them [19–22]. However, there is no data on how to produce cubic aggregates with a proportion of up to 100% apart from publications and patents by the author Gawenda et al. [14,23–26], and a few publications on how to increase the proportion of regular grains [13,27,28], especially in the industrial utilization of aggregate products in building industry [29–31]. important factors influence the necessity to expand and use multi-stage systems, which usually lead to increasing both the investment and operating costs. There are many studies on the influence of grain geometry on the parameters (such as grinding ability) and properties of aggregates and materials made from them [19–22]. However, there is no data on how to produce cubic aggregates with a proportion of up to 100% apart from publications and patents by the author Gawenda et al. [14,23–26], and a few publications on how to increase the proportion of regular grains [13,27,28], especially in the industrial utilization of aggregate products in building industry [29–31]. *Full-Scale Prototype of an Innovative Technological Circuit* 

#### *Full-Scale Prototype of an Innovative Technological Circuit* In order to increase the quality of aggregates and reduce the number of crushing stages, research was undertaken as part of the implementation of the NCBiR application

more compact the raw material, the more difficult it is to obtain cubic particles from it [15– 18]. Moreover, in the finer fractions of the crushing products, the largest number of elongated and flat grains is obtained. Therefore, it is advisable to use impact crushers (e.g., with a vertical shaft) at the final stages of crushing. As the crushing rate increases, the

crushers should be operated at a crushing rate that is not too high. However, all of these

*Minerals* **2022**, *12*, x FOR PEER REVIEW 2 of 15

In order to increase the quality of aggregates and reduce the number of crushing stages, research was undertaken as part of the implementation of the NCBiR application project: Action 4.1 of the Operational Programme Intelligent Development 2014–2020. HTS Gliwice in cooperation with scientific and research units (AGH in Krakow, ICIMB Łukasiewicz Research Network) built a full-scale prototype of an innovative technological system for refining mineral aggregates. The tests were carried out in real conditions. The installation of the technological system was placed in the Imielin Dolomite Mine and consisted of crushing, enriching, and classifying machines, as shown in Figure 1. project: Action 4.1 of the Operational Programme Intelligent Development 2014–2020. HTS Gliwice in cooperation with scientific and research units (AGH in Krakow, ICIMB Łukasiewicz Research Network) built a full-scale prototype of an innovative technological system for refining mineral aggregates. The tests were carried out in real conditions. The installation of the technological system was placed in the Imielin Dolomite Mine and consisted of crushing, enriching, and classifying machines, as shown in Figure 1.

**Figure 1.** Technological line in the Imielin Dolomite Mine, image from a drone. **Figure 1.** Technological line in the Imielin Dolomite Mine, image from a drone.

consisting of: Impact crusher, three-deck rotary specialized vibrating screen (WSR),

buffer cages, control and power supply, belt conveyors, chutes, pumps);

I. *Formator*, which is an installation for the production of regular and irregular fractions

The process line includes:

II. Light contaminant separator (SEL);

The process line includes: in Figure 2. This is the unique plant in the world that includes the production of innovative

IV. Low pressure hydrocyclone (NHC).

I. *Formator*, which is an installation for the production of regular and irregular fractions consisting of: Impact crusher, three-deck rotary specialized vibrating screen (WSR), three-deck linear specialized vibrating screen (WSL), infrastructure (feeding and buffer cages, control and power supply, belt conveyors, chutes, pumps); refined aggregates with regular grains in the range of 2–8 mm and 8–16 mm and a sand fraction of 0.1–2 mm. The aim of this paper is to present the operation of the *Formator* technological system that produces 8–16 mm class of shaped aggregates (regular particles = RP) from various

A schematic of the pilot plant used for process testing on an industrial scale is shown


III. Separator of difficult-to-separate fractions (SET);

*Minerals* **2022**, *12*, x FOR PEER REVIEW 3 of 15

IV. Low pressure hydrocyclone (NHC). marked on the technological diagram with a dashed line (Figure 2). It was built in

A schematic of the pilot plant used for process testing on an industrial scale is shown in Figure 2. This is the unique plant in the world that includes the production of innovative refined aggregates with regular grains in the range of 2–8 mm and 8–16 mm and a sand fraction of 0.1–2 mm. accordance with the concept of the patent PL-231748B1. The assumption for the construction of this system was the possibility of producing aggregates with a content of non-formed grains (irregular particles = IP) below 3%, which is not possible in conventional technological systems.

**Figure 2.** A simplified flow diagram of the installation for the mineral aggregates refinement in the Imielin Dolomite Mine. **Figure 2.** A simplified flow diagram of the installation for the mineral aggregates refinement in the Imielin Dolomite Mine.

Table 1 provides a brief comparison of an innovative device with a typical device. The aim of this paper is to present the operation of the *Formator* technological system that produces 8–16 mm class of shaped aggregates (regular particles = RP) from various rock materials. The analyzed system consisting of an impact crusher and a WSR screen is marked on the technological diagram with a dashed line (Figure 2). It was built in accordance with the concept of the patent PL-231748B1. The assumption for the construction of this system was the possibility of producing aggregates with a content of non-formed grains (irregular particles = IP) below 3%, which is not possible in conventional technological systems.

Table 1 provides a brief comparison of an innovative device with a typical device.


**Table 1.** Advantages and disadvantages of the innovative and ordinary screens in the technological system for the production of regular aggregates.
