Development of Cycloid-Shaped Roll Charging Chute for Sintering Process for Energy Decarbonization and Productivity Improvement in Steel Plants

Abstract

The global steel industry is rapidly transitioning towards energy decarbonization to address the climate crisis. Sintering is one of the main sources of greenhouse gas emissions from steel mills. Traditional sintering processes use straight inclined chutes to feed raw materials into the sinter machine. However, this design suffers from insufficient horizontal momentum, resulting in poor segregation of the layered materials. This study proposes an improved charging chute design profile that uses a cycloid curve and rolls to enhance segregation, thus reducing coal consumption and increasing productivity. To achieve this, we first modeled a charging chute using the cycloid curve. Secondly, building upon the cycloid concept, we created a roll-type chute by strategically placing rollers along the cycloid trajectory. Finally, the cycloid roll-type charging chute, integrating the cycloid trajectory with the roll-shaped charging chute, was simulated. Pilot tests comparing the cycloid roll-type and straight chute models demonstrated a significant increase in dispersion for the cycloid roll-type design, with a 65% improvement in the Strand-ward segregation (Sw) index compared to the straight chute. Furthermore, actual filed implementation in a sintering process achieved a 2.9% increase in operational productivity and a 6% reduction in fuel consumption. This study is significant not only for proposing an optimal chute design, but also for successfully implementing it in a full-scale steel mill, contributing to a reduction in fuel consumption and carbon reduction in steel mills.

1. Introduction

1.1. Background of Study

Due to the climate crisis caused by global warming, the steel industry is actively engaged in technological developments to reduce fossil fuel consumption and mitigate greenhouse gas emissions. Technological development activities are underway in the sintering sector in steel plants, focusing on improving the internal permeability of blast furnaces to enhance CO gas utilization and increasing the vertical segregation of raw materials to improve the efficiency of coal usage.

The steel processes are divided into iron making, steel making, and rolling processes. The sintering process refers to a stage in the ironmaking process, positioned at the front end of the iron production process along with the fuel coke process. It involves uniformly improving the quality of iron ore and forming it into a consistent size before being introduced into the blast furnace [1]. Figure 1 illustrates the sintering process in the ironmaking operation using a blast furnace.

Sintering is the process of bonding fine iron ore particles together by heating them at high temperatures. Through this process, the iron ore becomes harder and denser, and impurities are removed, resulting in increased purity. The porous mass produced through the sintering process is called sinter. Sinter has a high iron content, making it easier to extract iron at steel mills, and the low level of impurities allows for the production of high-quality iron. Although sintering plays an important role in the ironmaking process, it is energy intensive. Therefore, there is a demand for the development of technologies to save energy and reduce carbon emissions.

The sintering process proceeds as follows. The raw materials, including fine iron ore, coal, and limestone, with a particle size of 8 mm or less, are discharged from their coke bins according to the mixing ratio, evenly mixed with water in the mixer, and then charged into the sintering machine through the charging chute. The coal on the surface layer of the raw materials is burned by the flame of the ignition furnace, the heat is transferred to the bottom of the raw material layer by the suction pressure of the main blower, and sintering proceeds.

While the raw materials pass through the sloping chute before being stacked in the sintering machine, raw materials with large particle sizes and high specific gravity fly further and accumulate at the bottom first. In contrast, small and light raw materials fall closer to the chute and accumulate on the upper part. In this way, better vertical segregation of the raw material layer leads to better air permeability, and the coal components are distributed in the upper part, which can improve productivity and quality and reduce the amount of coal used. To maintain the quality while increasing the sintering productivity, increasing the height of the raw material layer stacked in the sintering machine is advantageous.

The increase in the height of the raw material layer stacked in the sintering machine has the advantage of enhancing sinter productivity and reducing heat loss, thereby increasing fuel efficiency [2]. However, there is a debate surrounding the quality of the sinter produced in the top layer. As the height of the raw material layer increases, the materials in the top layer are exposed to more pressure and heat. These conditions in the top layer can lead to excessive sintering, and there is an argument that the quality of the sinter produced in the top layer may be degraded due to the uneven temperature distribution within the sintering machine. On the other hand, it is argued that the high temperature and rapid gas flow at the top layer promote efficient gas exchange, facilitating the sintering reaction.

As the raw material layer is stacked higher, the area of the surface layer with insufficient heat retention time is reduced, and the quality of the entire sinter can be increased [3]. Sufficient air permeability must be secured to stack the raw material layer high, and coal components must be allowed to accumulate on the upper part to transfer the heat from the top to the bottom effectively. Because a higher raw material layer imposed greater constraints on the operation, it would be best to balance the capabilities of the blast furnace and sintering machine. To prevent excessive sintering and maintain uniform heat distribution, the optimal layer height should be set.

Increasing the productivity of sintering is imperative due to the insufficient sintering capacity compared to blast furnace production capacity. The existing issue during raw material loading through straight chutes involves inadequate separation by particle size, with the formation of attachments on the upper part of the chute obstructing the flow of raw materials. Furthermore, insufficient segregation of sintered material accumulated at the top layer of the sintering machine further deteriorates permeability, causing excessive heat accumulation in the lower layer, which in turn reduces productivity and coal utilization efficiency. To reduce coal consumption and improve productivity, it is necessary to improve the existing charging chute to maximize the segregation effect of raw materials.

1.2. Problem Statement and Research Objectives

Insufficient permeability within the raw material layer can impede the smooth combustion of the sintered raw materials, leading to reduced productivity. Sinter mix is a raw material used in the sintering process, which is a mixture of iron ore, fuel such as anthracite coal, and flux such as limestone before being sintered into sinter. If there is an excess accumulation of heat in the lower part of the raw material layer, it can cause overheating of the pallet floor, leading to thermal deformation. In severe cases, the pallet floor may be damaged, resulting in a shortened lifespan of the equipment. The mentioned disadvantages are inherently related to the heat propagation phenomenon in the downward suction sintering process [4]. Immediately after ignition, the combustion of the coal component in the mixed raw materials takes place within the raw material layer, and due to downward suction, a narrow combustion layer progresses in the form of a heat wave. As the heat propagation process continues, the height of the combustion layer and molten layer increases towards the lower part of the raw material layer.

The charging of sintering raw materials in the sintering process refers to the process where the raw materials mixed in the mixing drum are loaded through the charging device into the sintering machine [5]. The charging process of sintering raw materials involves the filling of the surge hopper, and the sintering raw materials are then transported through the charging chute, stacking in the sintering machine. During this process, the charging chute plays a crucial role in inducing vertical segregation when the mixed raw materials are charged into the sintering machine. Figure 2 provides a schematic diagram of the charging chute targeted in this study.

The internal permeability of the raw material layer in the sintering equipment is a crucial factor for stable operation and extended lifespan of the facility. To ensure the internal permeability of the raw material layer in the sintering machine, several measures can be taken. Firstly, increasing the air intake of the sintering machine to supply sufficient air to the internal raw material layer. Secondly, improving the thermal conductivity of the sintering machine’s floor to efficiently transfer heat. Thirdly, the raw material layer is arranged on the sintering machine evenly to facilitate smooth airflow within the raw material layer [6].

The purpose of this study is to improve productivity by increasing the internal permeability of the sintering layer by maximizing the segregation effect of the sintering raw materials during charging. The ultimate goal of this study is to improve the segregation effect of the sintering machine by improving the existing charging chute. To achieve this, two main approaches were implemented. Firstly, the charging chute was modeled in a cycloid shape to ensure that the horizontal velocity of the materials passing through it is maximized. Secondly, to induce effective particle segregation by vertical vibration in the raw material layer on the chute, multiple rolls were strategically placed along the cycloid trajectory. Each method was designed, modeled, and simulated.

1.3. Literature Review

Prior research on strengthening sinter charging segregation, improving sinter productivity, and the application of cycloid curves was reviewed to conduct this study.

1.3.1. Reinforcing Sinter Charging Segregation

Mosby et al. examined the mechanism behind the phenomenon of particles separating into various forms based on their physical characteristics and indicated that the particle separation phenomenon is a variable affecting both process and quality [7]. Nevraev et al. confirmed that changing the charging suit from two layers to one layer resulted in improved productivity [8]. Nakano et al. utilized the Discrete Element Method (DEM) to visualize the charging phenomena of the supplied materials in the sintering apparatus [9]. Honorato and Seshadri introduced an intensified sifting feeder (ISF) into the sintering process and demonstrated that it reduces the fractionation of coarse and fine particles, thereby enhancing permeability and increasing productivity [10]. Selvam et al. introduced the Magnetic Charging Chute, incorporating magnetic force technology, to enhance the permeability of the feed material [11]. Kim et al. developed three forms of charging chutes that can enhance the compaction of charging materials in the sintering process and analyzed them using DEM [6]. Li et al. developed a 3-D sinter strand model utilizing DEM to analyze the influence of conveying velocity on the vertical size segregation of raw materials within the sinter bed [12]. Kim et al. analyzed a charging chute with an applied deflector plate using DEM [13]. However, there is a lack of analysis regarding the characteristics of the deflector plate for practical application. Xu et al. analyzed the impact of particle size distribution on the permeability of the burden packed bed in the sintering process using DEM [14]. Furthermore, they proposed indicators such as segregation degree (SD) and segregation tendency (ST) to quantitatively evaluate the phenomenon of particle size segregation. Terui et al. developed a numerical simulator capable of measuring coke blending in the upper layer of a blast furnace [15]. Ishihara et al. utilized DEM to simulate the behavior of charged materials in order to investigate the impact of ventilation bars on the porosity of the sinter bed [16].

1.3.2. Sintering Productivity Improvement

Higuchi et al. developed stand-support sintering to increase the porosity of the sinter bed [17]. Oyama et al. developed a coating granulation process wherein coke and limestone are injected into the final stage of raw material mixing to enhance the productivity and reducibility of sinter [18]. Ellis et al. investigated the impact of iron ore characteristics and moisture content on the permeability and strength of the sinter bed during the sintering process [19]. Ahn et al. proposed a sintering bed modeling method using a flowsheet process simulator, considering flue gas recirculation (FGR) and variations in inlet and outlet gas conditions [20]. El-Hussiny et al. investigated the impact of replacing 5% of iron ore concentrate with mill scale and adjusting the quantity of coke breeze on the sintering process [21]. Cores et al. classified 28 ores based on their granulation index (G index) and analyzed the impact of blending on the sintering properties [22]. Yamaguchi et al. proposed the Return Fine—Mosaic Embedding Iron Ore Sintering (RF-MEBIOS) process to enhance sinter productivity [23]. This process involves adding return fines, known as dried particles, to granulated raw materials before charging them into the sintering apparatus. Research results verified that the addition of dried particles increased friction, leading to improved permeability of the sinter bed. Fan et al. conducted simulations using artificial gas to analyze the influence of oxygen (O₂) content in circulating flue gas on the sinter bed [24]. Zhou and Zhou investigated the impact of granulation using hydrated lime on the sintering process and strength [25].

1.3.3. Application of Cycloid Curve

Malhotra and Parameswaran comprehended the operational principles and performance of a cycloidal speed reducer, performing calculations and analysis on forces and contact stresses for each component [26]. Blanche and Yang analyzed the occurrence of backlash and torque ripple in cycloidal drives due to machining tolerances [27]. Hoffman clarified misconceptions about cycloids and established accurate concepts [28]. Vecchiato et al. conducted a study and analysis on the profile geometric structure of a cycloid pump designed for liquid transport [29]. Jørgensen et al. introduced a ‘new permanent-magnet gear’ based on cycloid gearing with extreme torque density and a very high gearing ratio [30]. They achieved higher torque compared to conventional magnetic gears. Yong et al. proposed a non-raster scan method, a cycloid-like scanning pattern, for high-speed scanning in atomic force microscopy (AFM) [31]. Chen et al. created a novel cycloid drive by applying double-conjugate gear theory [32]. Liu et al. proposed high-pressure rotary positive displacement meters (rotary PD meters) incorporating a pair of cycloid rotors [33]. Wang et al. designed and fabricated a cycloid milling cutter to address severe wear, low efficiency, and quality issues encountered in titanium alloy machining, and revealed that milling cutter exhibited superior performance [34]. Maharjan et al. designed and fabricated a high-performance cycloid-inspired wearable electromagnetic energy harvester (CEEH) to harvest human motion energy for application in wearable electronic devices [35].

As mentioned above, the majority of previous studies applying the cycloid curve have been conducted to enhance the efficiency of drive mechanisms, conserve energy, and extend mechanical lifespan.

1.3.4. Differences from Previous Studies

Prior research on strengthening vertical segregation according to the particle size or weight of raw materials in the sintered layer has been actively conducted. In one study, the authors applied a numerical analysis method and reported that the vertical segregation was further increased when a curved chute was applied close to the direction of this study. However, with respect to the shape of the sinter charging chute, it was difficult to find studies that model the optimal curved surface according to the angle of entry or exit of the raw material, or the horizontal and vertical length of the chute. In order to replace the charging chute in the existing sintering plant, it is necessary to consider the spatial constraints, but there have been no studies of a design approach that models the optimal shape to suit the field conditions. In addition, there have been no reported studies that present a solution to the generation of stuck ore, which has been a long-lasting problem with existing linear charging chutes.

Through this study, the profile of chute was optimized using a simulator, a simulation device was manufactured, and the effect was verified through pilot test. In addition, it was possible to increase productivity and reduce fuel consumption ratio by applying it at a full scale to a sintering plant. It is different from previous studies in that it can contribute to improving competitiveness by expanding the research results to other sintering plants in Company P, which are mostly applying the existing straight slope chute.

To maximize the segregation effect, this study proposes two methods to improve the sintering raw material charging device. First, the straight-shaped charging chute was converted to a cycloid-shaped chute. Second, multiple rolls were placed on the charging chute along the cycloid trajectory. Finally, each method was modeled and simulated.

1.4. Research Framework and Development Process

The paper is organized as follows. Section 1 provides an overview of the study’s background, describes the issues with the sinter charging chute in the steel plant, and outlines the research objectives. In addition, the prior studies for improving the charging chute was investigated. Section 2 and Section 3 detail the research methodology for addressing the problems with the existing charging chute. It focuses on the study of the cycloid roll-type charging chute, which combines the particle behavior with the Convection in granular media. Section 4 integrates the cycloid trajectory with the roll-type chute to model the cycloid roll-type charging chute. Section 5 performs a pilot test by a model of the cycloid roll-type charging chute. Section 6 presents the application of the cycloid roll-type chute to an actual sintering process and compares operational productivity and fuel consumption. Section 7 calculates the financial effects of the operational improvement after on-site application. Finally, Section 8 summarizes the paper and describes the contribution of the study. It also presents the limitations of this study and the directions for future research. The overall structure of this paper is as shown in Figure 3.

2. Cycloid-Shaped Charging Chute and Modelling

2.1. Particle Behavior on a Straight Inclined Plane and Its Simulation

2.1.1. Particle Behavior on a Straight Slope

During sintering, the raw materials pass through the charging chute and are stacked on the bottom of the sintering machine, and the sintering machine moves in the opposite direction to the charging direction of the raw materials. Because of this mechanism, a longer falling distance for the raw material escaping the chute causes it to be stacked first on the bottom of the sintering machine, whereas material with a shorter falling distance accumulates in the upper part. When the raw materials escape the chute, a greater horizontal-direction velocity leads to a greater difference in the falling distance according to the particle size and specific gravity, and the dispersion range of the falling raw materials expands, which is advantageous for segregation. In the existing straight inclined surface chute, the falling energy of the raw material was reduced by the inclined surface and the horizontal kinetic energy was insufficient. Accordingly, the vertical segregation of the stacked raw material layer was low due to the short drop distance of the raw material. In addition, stuck ore are formed on the chute surface as a result of the moisture contained in the raw materials, which is a common problem in many other chutes that handle raw materials for iron making. In other chutes, it is usually not a significant problem as long as there is no clogging, and it can be solved through periodic cleaning, but the nature of the problem is different in the sinter charging chute. Stuck ore formed on the charging chute continuously interfere with the flow of the raw materials by themselves, and this may cause a charging density deviation in the width direction of the sintering machine. In this case, when sintering is performed using air suction in the downward direction of the sintering machine, the inflow of air is concentrated in a portion having a low charging density, rather than being dispersed to the entire sintering layer. Accordingly, a deviation in the intake air volume may cause a large deviation in the quality of the sinter. Figure 4 illustrates the operating principle of the raw material charging device on a straight slope. Figure 4a is a simplified schematic diagram of the straight slope charging chute, and Figure 4b is a graph depicting the operation principle of the falling raw material on the straight slope charging chute.

To calculate the falling time and escape velocity of the raw material on a straight slope, the following procedure was employed. First, we calculated the falling time (t) on the straight slope in Figure 4b using Equations (1)–(3) that induce uniformly accelerated motion [36].

• Differential equation for uniform acceleration motion on a straight slope (Equation (1)):

  $$dt=\sqrt{\frac{1+m^2}{2gmt}}dx$$

  (1)

  where t represents the falling time, m is the slope of the charging chute, and g denotes the acceleration due to gravity, which is equal to 9.81 m/s².
• Slope m of the straight slope (Equation (2)):

  $$m=\frac{h}{d}$$

  (2)

  where h is the vertical length (height) of the slope (charging chute), and d denotes the horizontal length of the slope (charging chute). The angle θ formed between the base and the slope on a straight slope is determined by the horizontal length (d) and vertical length (h) of the slope, and the length (s) of the slope is also determined.
• Falling time (t) on a straight slope (Equation (3)):

  $${\int }_0^{t}dt={\int }_0^x\sqrt{\frac{1+m^2}{2gmx}}dx$$

  (3)

Next, In order to calculate the escape velocity (V_E) of particles on a straight inclined charging chute, Equations (4)–(7) were applied [36].

• The escape velocity (V_E) of particles on a straight slope (Equation (4)):

  $$V_E=a\times t$$

  (4)

  where a is the acceleration; V_E is the particle’s escape velocity (drop speed at point E).
• Equation (5) represents the formula for calculating acceleration on a straight slope.

  $$a=g\times \mathrm{s}\mathrm{i}\mathrm{n} \theta$$

  (5)

  where g is the acceleration of gravity, 9.81 m/s²; θ is the angle between the floor and the slope.
• The escape velocity can be decomposed into horizontal escape velocity (V_Eh) and vertical escape velocity (V_Ev), as shown in Equations (6) and (7):

  $$V_{Eh}=V_E \times \mathrm{c}\mathrm{o}\mathrm{s} \theta$$

  (6)

  $$V_{Ev}=V_E\times \mathrm{s}\mathrm{i}\mathrm{n} \theta$$

  (7)

Through this process, the fall time (t) and the escape velocity of Figure 4b can be calculated. The integral equation (Equation (3)) was applied to the simulation of particle movement on the straight slope.

2.1.2. Simulation for the Particle Behavior Analysis on a Straight Incline

To analyze the behavior of particles on a straight incline and compare it with that on a cycloid curve, simulations were conducted. Initially, the simulation was conducted using the integral equation (Equation (3)) to analyze the motion of particles on a straight inclined. Excel’s Visual Basic Application (VBA) program was employed for simulation [37]. The following code illustrates the programming of Equation (3) using VBA to calculate the falling time (t) on the straight incline. The code utilizes n squares to approximate the sum of areas when performing the integration. Here, n represents the number of squares used to calculate the sum of areas for the integration of the equation. To obtain results closely approximating the actual solution, the value of n was set to 10,000.

Sub Integral( )

Lx0 = Range(“c26”). Value

Lx1 = Range(“c27”). Value

n = Range(“c29”).Value

m = Range(“c28”).Value

dx = (Lx1 − Lx0)/n

For x = Lx0 + dx To Lx1 Step dx

MySum = MySum + dx*(((1 + m^2)/(m*x*2*9.81))^(1/2))

Next x

Range(“c32”).Value = MySum

End Sub

In the simulation of a straight incline, Lx1 represents the horizontal length of the slope, and LY1 represents the vertical length. When Lx1 and LY1 are input as variables, the length of the slope is calculated using the Pythagorean theorem. The falling time is computed by Equation (3), and ultimately, velocity values are calculated through simulation. Consequently, the simulation allows for the automatic verification of vertical velocity values closely related to the vertical segregation effect based on input variables. The UI of the simulation results screen is as shown in Figure 5.

2.2. Particle Behavior on a Cycloid Shaped Charging Chute and Its Simulation

2.2.1. Particle Behavior on a Cycloid Curve

In the process of researching the sinter charging chute, it was necessary to consider inducing vertical segregation according to the particle size and specific gravity when the raw material was charged into the sintering machine as a top priority. Until recently, several chute designs have been proposed to enhance particle size segregation. These are the intensified sifting feeder (ISF), and magnetic braking feeder (MBF), which were reviewed in prior studies, and most chutes are based on the shape of a straight slope [10,11]. The existing straight slope can change the chute angle by adjusting the angle, but it is difficult to increase the trajectory segregation efficiency because the angles of the upper part where the mixed raw materials enter the chute and the lower part where they leave the chute are dependent on each other.

Of the curve-based continuous trajectories, the one with the highest efficiency with respect to converting potential energy into kinetic energy is the cycloid curve, which is commonly known as the brachistochrone curve [38]. On this curved trajectory, the object increases its velocity within a short time by using the falling energy, and it moves to the target within the shortest time by changing only the direction horizontally while keeping the acceleration due to inertia. It is a curve that can convert vertical movement into horizontal movement by minimizing energy consumption and the basis of the roundabout accumulation theory, as it is an optimal trajectory that accumulates energy during descent, after which it releases during horizontal movement [38]. Figure 6 illustrates the operating principle of the raw material charging device in the cycloid slope charging chute. Figure 6a presents a simple schematic of the cycloidal incline charging chute, and Figure 6b is a graph showing the operating principle of the raw material falling in the cycloid slope charging chute.

To calculate the departure velocity and time of the sinter mix raw materials from the charging chute with a cycloidal curve, we adapted Equations (8)–(11) [38].

• The x and y coordinates of the cycloid curve (Equations (8) and (9)):

  $$x=r\left(\theta -\sin \theta \right)$$

  (8)

  $$y=r\left(\cos \theta -1\right)$$

  (9)

  where x represents the x-coordinate of the cycloid curve, y is the y-coordinate of the cycloid curve, θ is the parameter of the cycloidal curve, and r denotes the radius of the cycloid curve.
• The entry angle (φ_S) of the charging chute (Equation (10)):

  $${\theta }_S=2{\phi }_S$$

  (10)
• The exit angle (φ_E) of the charging chute (Equation (11)):

  $${\theta }_E=2\left(\frac{\pi }{2}-{\phi }_E\right)$$

  (11)

  where S represents the position where the sinter mix raw materials the charging chute from the drum feeder, E is the position where the raw material leaves the charging chute, φ_S is the entry angle at S, and φ_E represents the escape angle of the charging chute.
• Exit velocity (V_E) at the point where the raw material leaves the charging chute (E) (Equation (12)).

  $$V_E=\{2\times g\times r({\cos \theta }_S -{\cos \theta }_E ){\}}^{\frac{1}{2}}$$

  (12)
• The horizontal exit velocity (V_Eh) is given by Equation (13):

  $$V_{Eh}=V_E{ \times \cos \theta }_E$$

  (13)
• The vertical exit velocity (V_Ev) is given by Equation (14):

  $$V_{Ev}=V_E \times {\mathrm{s}\mathrm{i}\mathrm{n} \theta }_E$$

  (14)
• And the travel time within the chute (t) are shown in Equation (15):

  $$t=\sqrt{\frac{r}{g}}\left({\theta }_E-{\theta }_S\right)$$

  (15)

The d influences the exit velocity of the mixed material. A longer chute length results in a faster exit velocity. φ_S affects the exit velocity and travel distance of the mixed material. A smaller entry angle leads to a slower exit velocity and shorter travel distance. φ_E influences the exit velocity of the mixed material. A larger exit angle results in a faster exit velocity. Additional formulas related to the cycloid curve can be found in Appendix A.

2.2.2. Simulation for the Particle Behavior Analysis on a Cycloid Curve

If the charging chute is modeled with a cycloid curve trajectory, the material falling from the chute will have a maximum horizontal velocity depending on the d, h, φ_S, and φ_E of the chute. Based on this theory, a simulator that can analyze particle behavior on the cycloid surface has been programmed.

The angles (${\theta }_S,{\theta }_E$) through which the circle passes were formulated to be calculated from φ_S at which particles reach the charging surface and φ_E at which particles escape the charging surface. When the values of φ_S, φ_E are input into the tangential angle of the simulator, ${\theta }_S \mathrm{a}\mathrm{n}\mathrm{d} {\theta }_E$ are, respectively, converted to radian values to be displayed as values of start theta0 and end theta1. Moreover, when d of the cycloid chute is input, logic was made to calculate h, t, and escape velocity using the cycloid equation. The simulator was completed by formulating the horizontal and vertical escape velocities to be decomposed from the calculated escape velocities. The completed particle behavior simulator on the cycloid curved surface is shown in Figure 7.

2.3. Comparison of Particle Behavior in Simulation between a Straight Incline and Cycloid Curve

The horizontal escape velocities of the two models were compared using the completed particle behavior simulator on the straight slope and the cycloid curved surface. The horizontal length was set to 1 m considering the installation space of the charging chute of the actual sintering plant. In the case of the cycloid charging chute, the horizontal escape velocity was calculated while changing the angle of incidence within the range of 5–50° and the angle of escape within the range of 10–60°. This was to set the angle of incidence and angle of escape within the range of the height that does not exceed, considering that the height can be up to approximately 2.7 m in the installation space of the site. In this way, the horizontal escape velocities were calculated by changing the heights on the straight slope to be the same as the heights of the cycloid chute, which were set according to the change of the angle of incidence and angle of escape. The authors initially conducted simulations on the cycloid surface, setting the incident and exit angles as parameters. Subsequently, the height, fall time, exit velocity, and horizontal exit velocity were calculated.

To compare the particle behavior on both the straight slope and the cycloid curve, the simulation on the straight slope was re-run with only the height derived from the cycloid curve simulation results. This paper reorganized the results based on height to compare the simulation results between the cycloid curve and the straight slope. Afterwards, the horizontal escape velocities of the two charging surfaces were compared. Figure 8 shows the comparison results of the horizontal escape velocity between the cycloid curve and the straight incline.

The comparison results of horizontal escape velocity between the cycloid curve and the straight incline show that, for the same charging chute length (fixed at 1 m) and height (2.7 m or less), the horizontal escape velocity in the cycloid chute was higher by an average of 30% and a maximum of 67%. This means that the horizontal escape velocity is always higher on the cycloid surface than on the straight slope for all ranges of considerable height and chute length. Further, when designing the chute in a cycloid shape, the effect of vertical segregation according to the particle size and specific gravity of raw materials can be increased. As shown in the graph, the difference in horizontal escape speed between the two models varies greatly depending on the setting of the chute length or height, but the two lines representing the horizontal velocity on the cycloid curve and the straight slope do not intersect. Therefore, it was confirmed that the segregation effect is significant in the cycloid shape regardless of the height and length of the chute.

Also, the results of the comparison of the horizontal velocities of the two models for the same horizontal length and height show that the horizontal escape velocities of the particles in the two models vary as the chute height changes from 0.787 to 2.689. As you can see from

Table 1. Difference in horizontal velocity on a cycloid curve and a straight slope (horizontal speed by vertical height).

Height (m)	Horizontal Velocity (m/s)		Difference on Cycloid Curves and Straight Slopes (%)
	Cycloid Curve	Straight Slope
0.787	3.866	3.081	25%
0.825	3.483	3.096	13%
0.878	3.900	2.996	30%
0.951	4.059	3.012	35%
0.955	3.749	2.884	30%
0.973	4.105	3.109	32%
0.995	3.385	3.081	10%
1.079	3.985	3.105	28%
1.163	3.659	3.088	18%
1.179	4.165	3.047	37%
1.210	4.219	2.922	44%
1.316	4.190	2.513	67%
1.333	3.917	3.052	28%
1.417	3.389	3.108	9%
1.478	4.125	2.791	48%
1.664	3.672	2.996	23%
1.894	3.919	2.825	39%
1.976	4.002	2.573	56%
2.114	3.220	3.092	4%
2.525	3.519	3.018	17%
2.689	3.613	2.734	32%

, the horizontal velocity of the particles in the cycloid chute is always higher than that of the particles in the straight chute. The difference in horizontal velocity increases as the chute height decreases. For example, for a chute with a height of 1.316 m, the horizontal velocity of the particles in the cycloid chute is about 67% higher than that of the particles in the straight chute. This difference in horizontal velocity is due to the fact that the trajectory of the cycloid curve provides particles with more energy than the trajectory of the straight slope. The cycloid curve’s trajectory provides particles with more rotational force, which in turn provides them with more kinetic energy and, therefore, a higher horizontal escape velocity. Table 1 shows the horizontal velocities and difference for the two models that have the same horizontal length and height.

The results of this comparison suggest that cycloid curved chutes can be a more efficient and effective way to charge sintering mixture than straight chutes. Cycloid chutes generate higher horizontal escape velocities, which helps to ensure that particles are charged more evenly and efficiently. Based on the simulation results, it was proven that the horizontal escape velocity of the raw materials is always higher in the cycloid curved chute when manufacturing two types of chute with the same width and height within the charging chute installation space allowed in the sintering process. In other words, if the chute is manufactured in a cycloid shape, the degree of vertical segregation increases when raw materials are stacked in the sintering machine. Furthermore, due to these advantages, the use of a charging chute based on the cycloid curve is expected to enhance the discharging characteristics of mixed materials and improve the efficiency of the charging chute.

3. Optimization of Roll-Type Charging Chute

This section describes the theory of roll arrangement according to the cycloid trajectory in the sintering charging chute and its simulation.

3.1. Trajectory Segregation

In the sintering process, if the coal component is not ideally distributed in the upper part of the sintering layer, the upper part may lack sufficient heat, leading to inadequate sintering and a decrease in sinter strength. On the other hand, the lower part may receive excessive heat, causing the surface of the sinter to melt, making it challenging to secure the necessary porosity during the reduction of the sinter in the blast furnace. Segregation can lead to increased porosity and decreased density, which can lead to increased permeability and reduced blast furnace productivity. Thus, the effects of segregation on sinter quality can be significant.

Segregation refers to the difference in the proportion of the particle distribution of raw materials depending on the location where they are charged into the sintering machine pallet [39]. Segregation in the horizontal direction is called horizontal segregation, and vertical direction is called vertical segregation. Horizontal segregation can lead to irregular sintering speed and uneven sintering condition at the discharge end, resulting in decreased yield or production speed, which can lead to decreased productivity. Therefore, it is important to pay attention to width segregation. The two main causes of generating horizontal segregation: segregation in the charging hopper and adhesion of ore on the discharge plate [39]. It is desirable to form vertical segregation in order to improve the aeration and heat efficiency of the sinter layer and improve sinterability. In particular, it is essential to induce vertical segregation in which fine ore and light coke are mainly stacked at the top and coarse ore is concentrated at the bottom in terms of production, quality, and energy efficiency. Figure 9 shows a simple principle of trajectory segregation that separates agglomerates and fine ore in the charging chute.

To improve productivity and reduce fuel costs while maintaining high sinter quality, it is necessary to improve the charging chute. When the raw materials that pass through the charging chute are stacked in the sintering machine, vertical segregation should be better than before, and there should be no attachments on the charging chute. The mixed raw materials stored in the hopper located at the upper part of the charging chute fall to the upper part of the chute, and the potential energy is converted into horizontal kinetic energy by the inclined charging chute. The falling distance of the mixed raw material particles is determined by the horizontal escape velocity and the density and size of the particles. The particles are stacked at the bottom of the sintering machine pallet the longer the falling distance, and they move towards the surface of the raw material layer the shorter the falling distance.

Thus, the segregation charge of the mixed raw materials is determined according to the trajectory segregation principle, and the horizontal displacement of the particles escaping the chute is shown in Equation (16) [22].

$$\mathrm{L}=\frac{U{\rho }_p{d}^2}{18\mu }$$

(16)

where U is the initial horizontal velocity of the particle, ${\rho }_p$ is the density of the particle, d is the diameter of the particle, and μ is the viscosity of the fluid.

Each particle escaping the chute causes a difference in the falling distance in proportion to the square of the size, and segregation occurs in the vertical direction as it is stacked on the sintering bogie moving in the opposite direction to the particle [22]. The higher the density and diameter of the particles and the higher the initial horizontal velocity, the greater the falling distance. Even for particles that have the same density and diameter, as the initial horizontal velocity increases, they are stacked at the bottom of the raw material layer. As the deviation of the horizontal falling distance between particles increases, the degree of segregation increases, and permeability can be improved because more space is secured between particles. It can be seen that increasing the horizontal velocity of particles escaping the bottom of the chute is effective for segregation charging.

3.2. Rise of Coarse Particles by Vibration (Convection in Granular Media)

Particles passing through the charging chute fall along the chute surface while forming a layer of constant thickness. Inside the flow layer, particles of various particle sizes and densities are mixed. The falling distance of particles is determined at the moment of escape from the chute by trajectory segregation, but even if trajectory segregation occurs from the flow layer in a mixed state, there is a possibility that the deviation in the horizontal falling distance may be reduced owing to inter-particle interference. In order to further increase trajectory segregation efficiency, it is ideal to place particles with large diameters in the upper part of the flow layer and lighter particles with smaller diameters in the lower part. Accordingly, it is advantageous for large-diameter particles to be induced to the upper part by segregation occurring in the direction perpendicular to the direction of travel inside the raw material layer passing through the chute.

Particle size-dependent segregation mechanisms can be classified as follows:

• Trajectory segregation: The horizontal movement distance of particles increases in proportion to horizontal velocity, size, and density [40].
• Percolation of fine particles: Small particles move down when a particulate material of different-sized particles moves [41].
• Rise of coarse particles on vibration: When the charged particles are vibrated, large particles rise, and small particles penetrate the generated void space [42].

A representative method of causing the segregation of particles by generating a disturbance inside the flow layer is used to add some vibration. Particle size segregation by vibration is known as the Convection in granular media [43]. It is a segregation method in which large particles rise toward the surface layer when a mixture of particles with different sizes is vibrated vertically. In other words, when vertical vibration with a constant frequency and amplitude is applied to the mixture, large-diameter particles rise, and the phenomenon in which small particles fill the resulting empty space created is repeated, and the large particles move to the surface layer [43]. When the material moves on the charging chute surface, if the chute surface is designed to cause the Convection in granular media phenomenon, it can further enhance the trajectory segregation effect. Therefore, it is crucial to be must be considered in the modeling of the chute.

3.3. Roll-Type Chute Optimization

3.3.1. Selecting the Roll Diameter

In the process of charging raw materials into the charging chute, operational challenges arise due to the formation of adhering materials on the chute surface, caused by moisture contained in the raw materials. When attachments are formed in the chute, the flow of raw materials is hindered, causing a charging deviation in the width direction of the sintering machine and deteriorating quality.

To solve this problem, the chute surface was designed as a discontinuous roll-type rather than a continuous plate shape. When the rolls are arranged and driven at appropriate intervals, even if attachments are formed on the surface of the rolls, they do not exceed the gap between the rolls, and the chute surface layer can always be maintained consistently. It is analyzed that when the roll rotates during the feeding of the raw material, the roller acts as a scraper, preventing the attachment of foreign substances.

Finally, the concept design was made with a structure in which several driving rolls are arranged in a cycloid shape. If the charging surface is made using this roll method, it could be an ideal shape because attachments can be removed while driving even if one is formed on the surface of the roll in a thin form. Besides, when modeling using the roll-type, the Convection in granular media can occur because of vertical direction vibration as the raw materials move along the chute surface. As particle size segregation occurs on the chute surface, trajectory segregation can occur more effectively when the raw materials escape from the lower part of the chute. To maximize this effect, the optimal roll diameter was reviewed by the mathematical analysis of the Convection in granular media generation mechanism. If the Convection in granular media can be generated when the raw materials move through the charging chute, when the raw materials escape the bottom chute surface, the coarse particles in the upper part can fly away with a larger trajectory, which may be advantageous for particle size segregation in the final sintered layer. Equation (17) describes the Convection in granular media using the dimensionless acceleration a [44].

$$a=\frac{(2\pi f{)}^{2}A}{g}$$

(17)

where, $f$: vibration frequency, A: amplitude, $g$: gravitational constant.

In relation to the Convection in granular media, when the dimensionless acceleration a is greater than 8, the Convection in granular media occurs regardless of the particle density ratio and size ratio. Moreover, when it is less than 8, the Reverse Convection in granular media occurs [44]. Figure 10 shows the results of varying the roll diameter for chute design considering the Convection in granular media and the particle’s exit angle. Figure 10a illustrates the vibration mechanism and the phenomenon that segregation occurs when particles move on the roll-type chute surface. The roller diameter was varied from 0.1 to 0.25 m, in 0.05 m increments, and the chute escape angle was varied between 40°, 45°, and 50°. Calculating the value of ‘a’ on the surface of the chute showed as Figure 10b that Reverse Convection in granular media occurs when the roller diameter exceeds 0.15 m, regardless of the chute escape angle.

In addition to the experiments in Figure 10, the material and diameter of the roll were selected through various methods, including structural analysis of the steel pipe. Because, in practice, the raw material throughput exceeds 1000 tons/min during the sintering process, the final hollow roller was designed from stainless steel (STS) with a diameter of 0.148 m to ensure the rigidity of the roll with a width of 4.5 m.

3.3.2. Selecting the Gap between the Rolls

The gap between the rollers is another important design factor. Roller gap specification was influenced by several considerations. The rollers must rotate smoothly, without interference; simultaneously, the coarse particles of the raw material must not fall through the roller gap. Furthermore, a sufficient gap is needed to prevent the overgrowth of adhesive on the roller surfaces. Among these, preventing the loss of coarse particles is of the highest priority. The coarse particles lost through the gap will not travel along the chute surface to their intended deposition point; they will fall and accumulate on the top-most layer of the sintered layer. As the surface of the sintered layer is the most vulnerable layer in terms of thermoelectric mechanism, the accumulated particles are not sintered and are reflected back, thereby adversely affecting the productivity and quality of sinter.

The particle size of raw material which has the potential to fall through the gaps is S × cos $\theta$_x, where each roller on the curved surface of the cycloid is arranged at a different angle $\theta$_x, and S is the gap between the rollers in the vertical direction. Considering the material mixture for sintering included particles with sizes below 8 mm and the particle sizes of the coarse materials were in the range of 5–8 mm, the roll-to-roll spacing was set so that the vertical gap was less than 5 mm to prevent material loss through the gap. Figure 11 illustrates a graph depicting the values for the gap between rolls in the roll-type chute model, taking into account the Convection in granular media.

Considering the production and installation tolerance, gaps between rollers were set to one of two values: 5 mm for rollers #1~8 and 10 mm for rollers #9~11. From the top roller, #11, to the bottom-most roller, #1, the angle of the cycloid curve to the ground decreases, resulting in the actual gap gradually increasing. For example, moving from roller #11 to #9, the actual gap between the rollers (10 mm × cos $\theta$_x) increases. If the roller gap were 10 mm for the whole set, then the actual gap would exceed 5 mm from roller #8, resulting in the loss of large raw material particles through the roller gap. Accordingly, the roller gap for rollers #8 ~1 is set as 5 mm, so that the actual gap is 5 mm or less.

Table 2. Gap setting value between rolls.

Roll Number	Gap between Rolls (mm, Setting)	Angle (Deg)	Actual Gap (Projection, mm)
1	-	-	-
2	5	36.6	4.0
3	5	39.8	3.8
4	5	43.1	3.6
5	5	46.7	3.4
6	5	50.5	3.2
7	5	54.7	2.9
8	5	59.4	2.5
9	10	64.8	4.3
10	10	71.6	3.2
11	10	80.7	1.6

shows the numerical values of the gap settings and resulting actual vertical gap (S × cos $\theta$_x) values for all 11 rolls. As a result of varying the roller gap between 5 mm and 10 mm, the actual maximum vertical roller gap does not exceed 4.3 mm.

Table 2 demonstrates the effect of roll gap on the escape angle of particles in a roll-type chute model that considers the Convection in granular media. The roll gap is the distance between the rolls. A smaller roll gap means that the particles have less space to move between the rolls. This makes it more likely for the particles to collide with the rolls, which increases the frictional force. Table 2 also shows that the escape angle increases as the roll gap decreases. This increase in the escape angle is significant and can have a positive impact on the quality of the sinter. This is because a smaller roll gap increases the frictional force between the particles and the rolls, making it more likely for the larger particles to roll over the smaller particles.

The roll gap should be set to a value that is small enough to increase the frictional force between the particles and the rolls, but large enough to allow the particles to flow smoothly through the chute. The optimal roll gap will depend on the specific properties of the particles and the chute design. The experimental results showed that the maximum actual roll gap was finally set to not exceed 4.3 mm. This is within the desired range and is expected to improve the trajectory segregation effect. It is important to note that the results presented in Table 2 are based on a specific set of assumptions and parameters. The actual effect of roll gap on the escape angle may vary depending on the specific properties of the particles and the chute design.

4. Integrated Modeling of Cycloid Trajectory and Roll-Type Charging Chute

In this section, the charging surface of the roll with a cycloid trajectory is modeled based on the selection results of the roller diameter and gaps. The optimal cycloid trajectory under the given layout was modeled using the cycloid particle behavior simulator from Section 2.2. Then, using the roller diameters and gap values from Section 3.3, the cycloid roll-type charging chute was modeled.

The roll positioning on the cycloid trajectory was derived as follows. First, using the cycloid simulator and the cycloid x- and y-coordinate equations, the cycloid trajectory was represented in the two-dimensional coordinate system. The cycloid trajectory was drawn automatically, based on the incidence angle, escape angle, and the input chute horizontal length. Then, each roller was modeled and positioned on the trajectory based on the diameters and gaps set in

Table 3. Profile index of rolls on a cycloid shaped chute.

Roll Number	Gap between Rolls (mm)	Angle (Deg)	Actual Gap (Projection, mm)	Roll Center (X Coordinate)	Roll Center (Y Coordinate)
1	-	-	-	0.000	0.000
2	5	36.6	4.0	0.145	0.107
3	5	39.8	3.8	0.283	0.222
4	5	43.1	3.6	0.414	0.345
5	5	46.7	3.4	0.538	0.477
6	5	50.5	3.2	0.652	0.615
7	5	54.7	2.9	0.756	0.762
8	5	59.4	2.5	0.848	0.917
9	10	64.8	4.3	0.925	1.080
10	10	71.6	3.2	0.981	1.251
11	10	80.7	1.6	1.001	1.370

. For each roller, eighteen coordinates were calculated, centered at (x_o, y_o), and keeping the roller radius constant, while moving the coordinates by (sin $\theta$, cos $\theta$) at 20° intervals in the circumferential direction. These 18 coordinates were connected to draw a single roller. Table 3 shows the angles and center coordinates of each roll located on the cycloid shape chute.

After roller #1 was drawn, the coordinates of the intersection between the trajectory of roller #1 and the cycloid curve were translated by the corresponding roller gap, such that the trajectory of roller #2 could be drawn using the same method. The model therefore allows all the rollers, from roller #1 to the top-most roller, to be drawn on the cycloid curve using the x- and y-coordinate. In this way, the profile of the cycloid roll-type chute is completed, and the final modeling result of the cycloid roll-type chute is shown in Figure 12.

In the case where the rolls overlap, as shown in Figure 12a, a program was utilized to adjust the number of rolls, roll gaps, and cycloid angle. The program used for this test is part of another study and is not explicitly discussed in this research. The completed cycloid roll-type chute simulator is a basic modeling tool for further design of the charging device. Based on this, a suitable motor was selected for driving each roller, the roll chute frame was fabricated, and the Motor Control Center (MCC) panel for motor drive control, the inverter panel for rotational speed control, and Local Operational Panel (LOP) for field control were all designed in detail. Before applying it to the actual sintering plant, a prototype of the cycloid roll-type chute was manufactured in our in-house research laboratory, and the effectiveness was verified through a pilot test.

The modeling of this study has several distinctive features. First, the chute was modeled to maximize the horizontal velocity of the raw materials passing through the chute. To do this, we used a simulator that can model the shape of the chute to optimize the profile of the chute. Second, the model was designed to induce the stratification of particles on the chute’s surface, guiding larger particles to be positioned in the upper layer. This facilitates effective classification without interference between particles when they exit the chute. The induction was achieved by promoting vertical vibration in the material layer on the chute. Third, the model was designed to prevent structural attachments from forming in the chute or to keep them at a constant thickness. This is to prevent the formation of attachments by the chute itself, not by external devices for removing attachments.

5. Pilot Test and Result

This section describes the results of a pilot test after manufacturing and testing models of straight and cycloid roll-type charging chutes before installing them in an actual sintering plant.

Following the optimization of chute profiles using a simulator, pilot tests were performed under the same conditions for both types of chutes using a mockup. To evaluate the performance of the cycloid roll-type charging chute, particle dispersion calculated through the trajectory of raw material free fall and vertical segregation calculated through the size distribution of layered sinter were used as measurement indicators, and the test results were compared and analyzed. Models of straight slope and cycloid roll-type charging chutes were produced based on modeling results. In the experimental procedure, the sintered raw materials were fed into the hopper and then passed through the chute to be deposited into the model bin by opening the gate. Data collected in this manner were used to measure and compare particle dispersion and vertical segregation.

5.1. Dispersion Test and Result

Dispersion is one of the indicators that shows how the loaded material is distributed in the processing process [45]. It is a measurement method used to prevent uneven processing by understanding the effective distribution of the raw material by considering the particle size and shape of the raw material in manufacturing or processing. In this study, the dispersion was measured by observing the discharge shape of the raw material when raw material was added to the straight-type charging chute and the cycloid roll-type charging chute, respectively. This method has the advantage of being relatively simple and inexpensive to measure dispersion. However, experience and skill are required to accurately analyze the characteristics of the discharge shape. This study focused on range among several methods of measuring dispersion, and Equations (18)–(20) are the calculation formulas for measuring dispersion in this study [45].

$$h^{*}=\frac{h}{H}$$

(18)

$$L^{*}=\frac{L}{H}$$

(19)

$$S^{*}=\frac{S}{H}$$

(20)

where raw material dispersion was measured at the chute exit: the height of the raw material layer (h), the width of the raw material (L), and the minimum exit distance (S) were recorded. These were divided by the height from the floor to the exit point (H), resulting in the dimensionless values h*, L*, and S* to evaluate the dispersion.

As h* increases, the segregation of particles based on average diameter increases at the top of the chute, resulting in increased segregation at the floor. Similarly, as L* increases, the dispersion range of the raw material increases, and as S* increases, the minimum horizontal travel distance of the raw material increases, meaning the segregation increases when the material stacks on the floor. A value close to 0 for dispersion of range indicates a low dispersion, meaning that the material introduced is uniformly distributed throughout the processing operation.

The degree of dispersion was analyzed by photographing the trajectory of the raw material falling from the straight chute and the cycloid chute. The gate of the upper hopper was set so that the raw materials were discharged at a constant speed for both chute types. The dispersion of the raw materials was compared after measuring both drop trajectories from the drop point to the floor at the same scale. Figure 13 shows the measured results of the falling trajectories in two types of chutes. Figure 13a displays the measured values of h, L, S, and H during the dispersion of material in the linear chute, while Figure 13b provides photos showing the measured values of h, L, S, and H in the cycloid roll-type chute.

Table 4. Comparison of distribution value from the dispersion test (straight vs. cycloid chute).

	L*	S*	h*
Straight shaped chute	0.93	0.19	0.21
Cycloid shaped chute	1.08	0.56	0.27
Difference	+0.15	+0.37	+0.06
Growth rate	16.13%	194.74%	28.57%

shows the results of the dispersion measurement of the straight-type chute and the cycloid chute.

In the straight chute, h was 5.7 cm, L was 25 cm, S was 5 cm, H was 26.8 cm, and in the cycloid roll type, h was 5.24 cm, L was 21.2 cm, S was 11 cm, and H was 19.6 cm. The results showed that the values of h*, L*, and S* were all higher for the cycloid roll-type chute, by 29%, 16%, and 195%, respectively, compared to the straight chute.

The higher the value of dispersion, the more dispersed it is. Theoretically, the cycloid shape can induce effective distribution of the material. As seen in the theoretical numerical values before, it was confirmed that the horizontal displacement significantly increased compared to the straight chute. Additionally, the increase in h* due to the cycloidal surface shape and the vibration of the roll suggests the formation of conditions that can lead to increased horizontal displacement of larger particles.

5.2. Vertical Segregation Test and Result

The vertical segregation test is a widely used method for measuring the vertical segregation of mixed materials. It is used to identify the directional properties of the mixed materials. In particular, if segregation affects the quality of the product in the process, the vertical segregation can be adjusted to set the appropriate process conditions. The vertical segregation test has the advantage of being relatively simple and cost-effective for measuring segregation. In this study, the strand-ward segregation (Sw) index suggested by Nakano et al. was used to measure vertical segregation [9]. In this study, Sw index was calculated by measuring the height of the accumulated materials passing through the straight charging chute and the cycloid roll-type charging chute. Equations (21)–(23) represent the formulas used to evaluate the Sw in the assessment of vertical segregation.

$${dm}^{*}=\frac{dm}{h\_avg}$$

(21)

$$x^{*}=\frac{x}{h\_max}$$

(22)

$$Sw=\frac{{dm}^{*}}{x^{*}}$$

(23)

where vertical axis (dm*) is the average diameter of particles (dm) measured at location x, divided by the overall average diameter (MS), and the horizontal axis (x*) is the total height of the raw material layer divided by the layer height. The vertical segregation increasing as the slope of the graph (Sw) increases.

The Sw index can be influenced by the materials, particle size, particle shape, and charging method. A high Sw indicates a high vertical segregation, implying that the materials are highly aligned in the vertical direction. When the vertical axis dm* is 1, it means that the particle size is equal to the average size, and a smaller value indicates finer particles. On the horizontal axis, x* being 0 signifies the bottom layer, while 1 signifies the surface layer. In the case of stacked mixture materials on the sinter pallet, higher vertical segregation results in heavier materials like iron ore moving downward, while lighter materials like coal move upward. This leads to an enhanced heat exchange effect.

The vertical segregation test was conducted five times under identical conditions, and the average values were determined. The results of the test found that the Sw value of the cycloid roller-type chute was 0.3407, 65% higher than that of the straight chute, which was 0.206. The degree of vertical segregation was also higher in the cycloid roller-type chute, with reverse segregation evident in the upper layer of the straight chute samples. As a result, it was confirmed from the result of the dispersion test that the dispersion range and horizontal speed increased in the cycloid roll-type chute. In addition, from the results of the vertical segregation test, it was confirmed that the degree of segregation in the vertical direction of the raw material layer stacked on the bottom of the sintering machine was improved. Figure 14 shows the results of the vertical segregation test comparing cycloid and straight-shaped chutes.

As the mechanism of the sintering process causes the upper layer to be most vulnerable to sintering quality degradation as a result of poor ore quality, reverse segregation in the upper layer must be prevented. Based on these results, it is expected that the operation index can be substantially improved by utilizing cycloid roller-type chutes over straight chutes in actual sintering plants.

6. Full-Scale Implementation

This section evaluates the practical impact of installing the cycloid roll-type chute in an actual operation after installing the cycloid roll-type chute newly manufactured for on-site application in a real sintering plant. To do so, data on operational performance and fuel consumption were collected for the year preceding the replacement of the charging chute and the three months immediately following the replacement. The sintering machine newly installed in the sintering plant has a width of 4 m and a length of 105 m, equipped with the cycloid roll-type chute. Minitab was used as a tool for statistical analysis [46]. The statistical analysis of this study has two limitations. First, the statistical data table in this study does not provide the sample size or the results of the statistical significance test. Second, no control variable analysis was performed to exclude factors that could potentially affect the analysis results other than the cycloid roll-type chute.

6.1. Comparison of Operational Productivity

Figure 15 compares the productivity before and after the replacement with the cycloid roll-type chute, with Figure 15a representing the period before the replacement and Figure 15b representing the statistical analysis results of operational productivity after the replacement.

The metrics used in Figure 15, such as Mean, StDev, Lower Specification Limit (LSL) denotes, Upper Specification Limit (USL), and Target are valuable for assessing data distribution and quality, each carrying the following significance [47]. Mean signifies the arithmetic average value, reflecting the central tendency of the data. In the context of Figure 15, here it corresponds to the operational productivity. StDev refers to the standard deviation, indicating the level of data dispersion in a histogram. A higher StDev indicates a wider spread of data, while a lower StDev suggests a more consistent process. LSL denotes the minimum acceptable value; values lower than LSL in the histogram are considered defective. Conversely, USL represents the maximum allowable value, and data exceeding this threshold are deemed defective. Target denotes the desired value in a product or process, typically reflecting optimal performance, and in a histogram, the target value should fall within the specification limits.

The operational productivity increased from 31.2 t/d/m² before replacing with the cycloid roll-type chute to 32.1 t/d/m² after replacement, confirming a productivity increase of 0.91 t/d/m². This is attributed to the improvement in the quality of the surface layer of the raw material, leading to enhanced recovery of sinter, and the increased effective airflow of the blower due to improved permeability, among other factors contributing to the increase in sinter productivity.

6.2. Comparison of Fuel Consumption

The fuel consumption was measured for coal. Figure 16 analyzes the data on fuel consumption using a histogram. Figure 16a shows the histogram of fuel consumption before the introduction of the cycloid roll-type chute, indicating a coal consumption rate of 58.3 kg/t-sinter. Figure 16b represents the histogram of fuel consumption after the introduction of the cycloid roll-type chute, displaying a coal consumption rate of 54.7 kg/t-sinter. Comparing the two histograms, there is a reduction in coal consumption of 3.57 kg/t-sinter, approximately a 6% decrease, after replacing the chute with the cycloid roll-type chute.

6.3. Discussion

The changes occurring in the operation of the sintering machine after replacing it with a cycloid roll-type chute are summarized in the table below. Comparing the operational productivity before and after replacing the charging chute, the sinter productivity increased by approximately 3% from 31.2 t/d/m² to 32.1 t/d/m² with the cycloid roll-type chute. Additionally, the StDev decreased by 0.792, and the Sigma level increased by 0.32. The StDev is an indicator of the spread of data points, and a decrease in the StDev implies a reduction in the dispersion of data. The Sigma level, calculated by dividing the standard deviation by the mean value, increasing indicates that the data are distributed more closely around the mean. The narrowing of data distribution and proximity to the mean suggests an improvement in the consistency of the process. Along with the increase in productivity, the decrease in standard deviation and the increase in Sigma level indicate a reduction in operational variability, leading to improved stability.

In addition, the fuel consumption before and after replacing the charging chute decreased by approximately 6% to 3.57 kg/t-sinter. This is analyzed as an increase in raw material processing efficiency. The decrease in the standard deviation by 2.084 indicates an improvement in process stability, and the rise in Sigma level by 0.18 suggests an enhancement in process consistency, reducing uneven situations. Therefore, after replacing it with a cycloid roll-type chute, the coal consumption decreased, and the reduction in the spread of data points indicates an improvement in operational stability. This implies that the use of the cycloid roll-type chute allows for more stable control of coal flow compared to the conventional chute, leading to a reduction in coal loss. This is attributed to the increased fuel efficiency due to the upper segregation of coal raw materials such as fines and anthracite.

Through such statistical information, the changes after the introduction of the cycloid chute could be confirmed. Productivity increased, and the fuel consumption ratio decreased. The decrease in standard deviation and the increase in Sigma level indicate an improvement in operational stability. The reduced variability in productivity signifies enhanced process consistency and efficiency. These results suggest that the introduction of the cycloid roll-type chute had a positive impact on both operational productivity and stability.

Table 5. Comparison of productivity and fuel usage statistics before and after cycloid chute application.

	Productivity (t/d/m2)			Fuel Consumption (kg/t-sinter)
	Mean	StDev	Sigma	Mean	StDev	Sigma
Before cycloid	31.23	1.782	1.58	58.27	3.712	2.03
After cycloid	32.14	0.990	1.90	54.70	1.628	2.21
Difference	0.91	−0.792	0.32	−3.57	−2.084	0.18
Growth rate	2.91%	−44.44%	20.25%	−6.13%	−56.14%	8.87%

presents the statistical comparison of productivity and fuel consumption before and after applying the cycloid chute, as shown in the histograms.

This study has several distinctive features. Firstly, the design of the slope surface of the charging chute in the sintering process is in the form of a cycloid curve. This design creates a trajectory with a cycloid shape when the raw materials exit the charging chute, allowing larger particles with higher density to be loaded first. Additionally, the application of multiple rollers on the slope surface of the chute enhances the segregation of the raw materials, improving permeability. Another noteworthy aspect is the modeling and simulation of the charging chute with a roll shape that follows a cycloid trajectory. Furthermore, the study stands out by replacing the existing straight chute with the cycloid chute in the actual operation of the integrated steel plant sintering process and verifying the effects by comparing operational productivity and fuel consumption. These unique aspects contribute to the distinctive novelty of this research.

7. Economic Assessment of Improvement

7.1. Financial Effect

IRR and NPV were calculated to evaluate the financial benefits to Company P, in terms of productivity increase and fuel cost reduction, as a result of improving the charging chutes at its sintering plants [48,49]. First, the contribution of the cycloid charging chute to the improvement of the operation index was determined; the contribution was evaluated as 10%, after consultation with 10 persons, including the facility and operations managers of the sintering plant, chief manager, facility and operation engineer, and researcher and investment manager of this study. Only 50% of the effect was applied, considering that the result data was short at 3 months, and the overall replacement of old facilities at the sintering plant was carried out simultaneously during the same period, taking into account the effect of facility innovation as 30%. In addition, as a new technology applied during the replacement construction of old facilities, not only the charging device, which is the result of this study, but also the automatic control system called the firing detection system was applied, reflecting the effect of 10%. This is a system that automatically controls charging speed and charging density in the width direction by analyzing the temperature distribution of exhaust gas generated in the sintering process and the uniformity of the sintered layer at the sintering completion point with a camera.

The total investment cost for device development was USD 14.9 K, the IRR of this study was calculated as 23.3% (15 years of depreciation period, 24.2% corporate tax applied), and the NPV was calculated as USD 14.7 K. The financial effect was calculated as a result of increasing productivity, reducing fuel consumption ratio, and reducing CO₂ generation. Firstly, in terms of productivity, the resulting cost reduction was USD 1.2 M per year, which is the product of the increase in plant production (146 K tons/year) and the fixed processing cost of USD 7.9/ton. Secondly, the total fuel cost reduction was USD 2.7 M per year, which is the product of the annual fuel reduction amount (20 K tons/year) and the fuel unit price of USD 138/ton. Finally, the reduction of CO₂ generation generated a cost reduction of USD 588.3 K per year, which is the product of the CO₂ generation source unit (3.4 ton-CO₂/ton-coal) and the CO₂ unit price (USD 8.7/ton-CO₂). The resulting total savings were USD 4.5 M per year, and the annual savings from the application of the cycloid chute were calculated to be USD 446.7 K (reflecting its proportional contribution of 10%).

Table 6. Prerequisites for calculating financial effects.

Category	Value	Unit
Fixed cost	7.9	USD 1/ton-sinter
Unit cost of Fuel consumption	138	USD/ton
Unit cost of CO2	8.7	USD/ton-CO2
Total production per year	5,538,658	ton-sinter/year
Operating rate	98	%
Generating unit of CO2	3.402	ton-CO2/ton-Coal
Investment cost	14.9 K	USD
Corporate tax	24.2	%
Discount rate	8.8	%
Rate of cycloid chute contribution	10	% of total savings

¹ The exchange rate (USD/KRW): 1306 KRW as of 2023 average (Source: Exchange Rates UK).

shows the assumptions used for calculating financial effects.

7.2. Operational and Environmental Effects

In addition to the above financial effects, specific qualitative effects resulting from the chute replacement were observed. From an operational perspective, it was possible to enhance the segregation of the raw material without making significant modifications to the equipment. By strengthening the segregation of the raw material mix for sintering, the internal permeability of the sinter layer improved, leading to a more uniform internal structure of the sinter with higher durability, resulting in an improvement in quality. As a result, there was an effect of stabilizing the furnace condition by improving the internal porosity of the blast furnace, which is a subsequent process.

In addition, the Reducibility Index (RI), a high-temperature reduction index of sinter, improved by 1.4%, from 63.8 to 64.7. RI is an index that indicates the degree of reduction when the sinter is reduced inside the blast furnace, and ISO 4695 is the international standard for measuring RI [50,51]. The RI represents the degree of sinter reduction in a furnace. A higher RI value indicates a lower heat required for ore reduction in the furnace, thereby reducing the coal cost. It cannot be conclusively stated that the observed improvement in RI in this study is solely due to the chute modification. However, it is evident that the changes in the charging chute design contributed to the stabilization of the blast furnace operation.

Given that corporate environment society governance (ESG) management impacts both the value and sustainability of businesses, environmental effects are crucial. From an environmental standpoint, this study examines the effect of equipment optimization on reducing fossil fuel usage, thereby contributing to carbon emission reduction. The blast-furnace-based process using coal has been optimized and improved over the years, and has become the main process in the steel industry, established as the most energy-efficient process. While coal has traditionally been the most accessible and cost-effective option, there is an increasing demand to reduce coal consumption due to the CO₂ emissions generated during the process [52].

There are three main methods to reduce carbon emissions in steelmaking: preventing CO₂ emissions themselves, such as hydrogen-based direct reduction ironmaking (H-DRI), using electric arc furnaces (EAF) as a stepping stone, and reducing the use of fossil fuels through optimization of steelmaking facilities.

• Unlike the traditional blast furnace steelmaking process, which uses coal to extract iron, H-DRI utilizes hydrogen for reduction reactions, known for its environmentally friendly and energy-efficient iron production without CO₂ emissions [53]. This method is emerging as a key technology in the future steel industry. However, it is still in its early stages of technological development and faces challenges such as high production costs. Thus, significant improvements are needed for economic feasibility, production demonstration, and commercialization.
• Currently, as a realistic alternative to H-DRI technology, which has limitations at the current technological level, the introduction of the EAF methods are being introduced for low-carbon steel production. The EAF involves refining molten iron from the blast furnace by inputting scrap steel into the furnace rather than iron ore, garnering attention as an environmentally friendly steel production method to achieve carbon neutrality [54]. However, the EAF method also has several drawbacks, including fluctuations in production costs due to changes in scrap iron prices, instability in scrap iron supply, and limited production scale.
• Finally, another technological development for carbon reduction involves optimizing equipment to decrease coal usage rates. This study demonstrates that after replacing the charging chute in the sintering machine, coal consumption decreased by 6% compared to before the replacement. This is attributed to both productivity improvements and a reduction in CO₂ emissions. While the carbon reduction effect of such studies on individual equipment may be marginal, efforts to optimize operations and reduce fossil fuel usage through equipment optimization across numerous facilities within a steel plant can ultimately contribute to CO₂ emission reduction and carbon neutrality.

Company P is exploring decarbonization by employing all methods, including H-DRI to achieve zero CO₂ emissions, expanding the use of EAF, and reducing CO₂ emissions through equipment optimization. This study provides insights into the reduction of fossil fuel usage and the achievement of carbon neutrality through equipment optimization in steelmaking facilities. Particularly, as the use of EAF increases for low-carbon steel production, it is expected that this study can provide guidelines for improving existing EAF equipment.

In addition, the decrease in the creation of powder during the transportation of sinter led to a reduction in dust scattering. Another observed effect was the reduction of adhesive ore compared to that generated in the straight chute, reducing the workload of workers who had to remove the adhesive ore frequently and, in turn, reducing the risk of safety accidents. Also, a reduction was noted in the amount of fuel, such as coke powder and anthracite, being distributed at the bottom layer of the truck and being fused. This aided in preventing equipment from heating up and reduced the workload required to remove the fused ore.

8. Summary

8.1. Conclusions

To cope with the climate crisis caused by global warming, this study was conducted following the strategy to reduce fossil fuel use in the steel industry and maintain the competitiveness of sintering plants. This study aimed to improve the sinter quality by inducing vertical segregation during the charging of mixed raw materials into the sintering machine. The cycloid roll-type charging chute was developed by applying cycloid curves and rolls, and it was simulated and evaluated for performance. The cycloid curve was used to improve the particle size segregation problem of the straight chute. In addition, to suppress the adhesion layer formation on the chute surface and induce the Convection in granular media, a roll-type charging chute with rolls attached to the cycloid chute surface was modeled. The optimal roll diameter and spacing between rolls were determined. Ultimately, a cycloid roll-type charging chute that integrates a roll-shaped charging chute with a cycloid trajectory was modeled and simulated using a simulator.

The pilot test results revealed that the cycloid roll-type chute led to an increase in the dispersion of the stacked raw material layer in terms of h*, L*, and S* compared to the straight chute. The Sw index, which is a measure of vertical segregation, was also improved by 65%. The results of the on-site test showed that the cycloid roll-type charging chute increased operating productivity by 2.9% and reduced fuel consumption by 6%. The financial effect of improving productivity and reducing fuel costs was USD 446.7 K per year, and the IRR was calculated to be 23.3%. Additional positive effects included post-process stabilization, workload reduction, and environmental improvements.

The technical contributions and practical implications of this study can be examined. The technical contributions of this study are as follows. Although previous studies have attempted to improve the shape of the chute to increase the charging efficiency, most have used a variety of auxiliary methods while maintaining the straight chute shape. In this study, a new approach is implemented, applying the cycloid curve in the chute modeling stage and using the horizontal exit speed of the raw material as a key factor for increasing charging segregation. In addition, the segregation and permeability of the raw materials were improved by applying multiple rollers on the chute slope plate. Theoretical modeling and simulation were conducted for the charging theory with a roll shape featuring a cycloidal trajectory.

Practical implications from this study include the following. Firstly, the study was not limited to research, but the device was manufactured to identify the distribution and vertical segregation, and the effectiveness of the technology was verified by comparing the operating productivity and fuel consumption in the actual operation of the sintering process in the steel plant. Furthermore, the economic impact of applying the developed model to actual operational sites has been calculated through this study. This contribution is significant in achieving improved sintering productivity, reduced fuel consumption, and ultimately carbon reduction, even under conditions where raw material quality is gradually deteriorating.

The research also contributed to applying the proposed chute to its other sintering plants is likely to secure Company P a competitive edge over its competitors. The results of this study indicate that the proposed concept can be expanded and applied not only to sintering, but also to many similar processes that require inducing segregation or for other steel processing facilities to prevent the generation of adhesive ore.

8.2. Limitations and Further Study

The limitations of this study and the requirements for further research are as follows. First, although a basic design simulator for the cycloid roller-type charging chute was developed, there are parts of the calculation logic that do not sufficiently reflect some variables in the field. Further research is needed to introduce a modeling factor expressing the coefficient of friction, which is affected by moisture fluctuations in the blending material, and use it to adjust the incident angle, reflection angle, and chute when necessary. Second, there is insufficient research regarding optimal roller driving speed, a factor that can greatly affect the horizontal speed of the raw material and which is related to operating conditions such as the raw material charging amount. It is suggested that gradual upgrades be applied to the model through further research. Finally, the steel industry should strive for sustainable development through the long-term perspective of developing and implementing environmentally friendly steelmaking technologies. H-DRI holds promising future potential as an environmentally friendly steelmaking technology, but requires solutions for technological development, infrastructure establishment, policy support, environmental and social challenges, and commercialization. Moreover, enhancing the competitiveness of EAF steelmaking necessitates research into cost reduction and energy efficiency improvements through design and operational enhancements. Short-term efforts, such as facility optimization and operational efficiency improvement, should also be pursued in parallel. Continuous research is needed to reduce coal usage and save energy through the optimization, automation, and implementation of smart manufacturing systems in steelmaking processes, leveraging advanced technologies such as artificial intelligence (AI), the Internet of Things (IoT), and big data.