Insights into local wall erosion characteristics and prevention measures for cyclone separators

The primary function of cyclone separators is to efficiently separate micrometer-sized particles from a fluid flow at an optimal velocity while minimizing pressure drops. These impressive pieces of engineering machinery are notable for their simple design (without moving components), simple and low-cost manufacture, straightforward installation, and low maintenance requirements.¹ Owing to these advantages, cyclone separators have found extensive industrial application.^1–7 They are used for gas–particle separation under a wide range of conditions, even in highly erosive environments, in processes such as the separation and transport of a variety of solid materials, such as wood chips, sand, and powdered metal, and the removal of mist from compressors and processing units. Figure 1 illustrates the methods used for removing various types and sizes of particles from gas streams. It can be clearly seen that the effective range of application of cyclone separators is for particles larger than 2 μm. Our previous studies have also found that for particles in the 0–2 μm range, the separation efficiency of cyclone separators decreases sharply to nearly zero as the particle size decreases.⁸ 

Although the fundamental principles governing the operation of centrifugal cyclone separators are now well established,⁶ for further development of this technology, it is essential to obtain a detailed understanding of the swirling flow behavior within rotationally symmetric cyclone systems,^9,10 as well as particle characterization and fluid–particle interactions. Dimensional analysis has long played a key role in understanding cyclones, providing important guidance for cyclone modeling and scaling, and since the 1980s, there has been increasing use of computational fluid dynamics (CFD) simulations to analyze fluid and particle behavior within cyclones. This latter approach offers clear advantages in obtaining a more comprehensive understanding of the relevant flow dynamics.^11,12 During the initial stages of CFD development, techniques for modeling separation performance suffered from limited accuracy. However, with the development and improvement of computer hardware and CFD techniques, accuracy levels are now comparatively high, with relative errors being maintained within ∼5% for performance evaluation and validation of velocity/pressure profiles.¹³ Many studies now involve deep integration of numerical simulation with experiments, providing mutual validation.^4,14–16 This complementary approach again allows a more comprehensive understanding of cyclone behavior and performance.

There have been numerous extensive experimental and numerical investigations of the influence of geometrical factors on the overall performance of cyclones, considering both individual factors and interactive effects.^17–23, Figure 2 illustrates the axial gas flow pattern in both the straight-through and centrifugal deduster types of cyclone. The straight-through type is significantly more widely used in industrial applications. A number of global parameter sensitivity analyses have been conducted using screening experiments, such as fractional factorial experiments, to identify significant cyclone design factors among numerous variables. This method is commonly employed to evaluate the contribution of individual factors to the overall response.^24,25 The main effect of each factor is determined by analyzing the absolute value of the slope of a line plot. The most influential factors have been identified as the inlet height a, inlet width b, vortex finder diameter D_e, and cone height H_c.²⁶ Numerical optimization of cyclone structures has been performed to understand the interactions between various factors and to identify the best geometric configuration from a set of available alternatives based on specific criteria.²⁷ In such optimization problems, the objective is to maximize or minimize certain functions, such as pressure drop and collection efficiency, by systematically adjusting the values of various statistically significant independent variables.²⁸ 

In addition to structural optimization, there has also been a focus on innovative modification of cyclone structures, resulting in significant improvements in performance and cost efficiency. Four main categories of key modifications concern the vortex finder, inlet, body, and dust collector.²⁶ Considering factors such as cyclone complexity, commercial feasibility, manufacturing costs, and enhancements in performance, novel designs such as the slotted vortex finder (SVF),^14,29,30 integrated compact-bend cyclone (ICBC),³¹ gas cyclone–liquid jet separator,³² and enhanced cyclone with a shunt device (ECSD)^33–35 have been extensively evaluated and recommended for practical application.

In various types of cyclones, the strong interaction between the gas–solid two-phase flow and the wall can lead to abrasion and erosion, posing significant challenges to the lifespan, reliability, and safety of the cyclone separator as well as the entire system.¹  Figure 3 presents statistics on publications and citations regarding wall erosion of cyclone separators from 2000 to 2024. It can be seen that there has been a rising trend in both publications on cyclone erosion and their citation over this period.

It is known that the failure of cyclone walls results from a complex erosion process, but there is still a significant gap in our understanding and of systematic investigations of this issue. In industrial settings where coal, sand, fly ash, coke powder, and alumina-based catalysts are separated, wall erosion caused by solid particles in cyclone separators is a leading cause of unplanned downtime. Understanding erosion characteristics is crucial, since they have a direct impact on the relationship between particle concentration and airflow velocity distribution within cyclones.^30,36

The internal flow dynamics of cyclone separators are characterized by strong three-dimensional rotation, vigorous phase interaction, and intensified turbulence,^9,37 all of which can readily lead to erosion of the cyclone walls. Understanding erosion in cyclone separators is crucial for maintaining process efficiency, prolonging equipment lifespan, addressing safety issues, mitigating environmental effects, and cutting down on costs. Hence, this paper centers on the significant erosion challenges faced by cyclone separators in real industrial scenarios. It presents a consolidated description of recent research efforts aimed at assessing the gas–solid two-phase flow field and analyzing wall erosion within cyclone separators. While the existing literature has explored the influence of fundamental geometric factors of cyclones, structural optimization, and innovative modifications, there has not yet been a critical and comprehensive review specifically focused on cyclone wall erosion and structural safety. There is a pressing need to fill this gap. The present overview of current research on cyclone wall erosion highlights its critical significance in ensuring overall system safety during production. Addressing this gap not only helps advance cyclone development, but also serves to provide a valuable reference for future design, operation, and maintenance of cyclone separators.

Gas–solid cyclone separators separate solid particles from gas streams by utilizing the centrifugal force produced by the swirling motion of the gas–solid mixture within conical or cylindrical vessels.¹ The swirling motion creates a complex flow region marked by turbulence, which is essential for efficient particle separation. This swirling motion is mainly initiated by tangential entry and results in the formation of a dominant vortex within the separator.⁴ Various factors, such as inlet velocity, cyclone geometry, and particle properties, influence this swirling motion.³⁰ 

Earlier flow pattern modeling approaches, ranging from the two-vortex theory to more systematic three-dimensional velocity distributions, were pioneered by ter Linden in 1949.^38, Figure 4(a) illustrates the velocity distributions within a cyclone separator at various axial cross-sections, revealing a relatively consistent distribution trend.³⁹ The tangential velocity distribution typically exhibits a Rankine vortex profile, characterized by a combination of quasi-forced and quasi-free vortex patterns. In this profile, the axial flow direction is downward in the outer region but upward in the inner region. By contrast, the radial flow direction is directed toward the center in the outer region but centrifugal in the inner region.³⁸ Across various cyclone designs, velocity distributions typically exhibit a similar trend. The well-known Rankine vortex model, a representative semi-empirical model, is widely employed to characterize the tangential velocity distribution within cyclone separators.²⁶ 

The swirling flow inside cyclone separators exhibits turbulent behavior marked by chaotic fluctuations in velocity, pressure, and particle concentration. Turbulence plays a crucial role by enhancing mixing and promoting the dispersion of solid particles within the gas stream, thereby facilitating particle–particle and particle–wall interactions. Turbulent eddies and vortices emerge within the cyclone, contributing to the complex flow patterns that are observed. In Figs. 4(b) and 4(c), the loci of the maximum tangential velocity and zero vertical velocity serve as indicators marking the boundary between the inner and outer vortices. These markers can be utilized to identify the boundary between the upward and downward flows. Figure 4(d) illustrates that the radial velocity values are distributed symmetrically, fluctuating between positive and negative values, and resembling a double helix structure. This distribution is closely related to the eccentricity of the vortex. Figure 4(e) depicts a typical isosurface of static pressure equal to 1000 Pa.

Undesirable secondary flow within cyclones generally denotes flow patterns that deviate from ideal conditions, potentially impacting efficiency or performance.^8,43–45 Figure 5(a) shows a diagram displaying the typical secondary vortex flow within a cyclone separator, which includes phenomena such as short-circuit flow,⁴⁰ formation of a top ash ring, and particle re-entrainment at the dust collector. Short-circuit flow, as illustrated in Fig. 5(b), describes scenarios where particles or gas within the cyclone bypass the intended separation process, resulting in incomplete separation or collection and thereby significantly reducing efficiency. As solid particles like ash undergo separation from the gas stream within a cyclone, they often gather near the top of the chamber, forming a ring-like deposit known as the top ash ring [Fig. 5(c)].⁴¹ This accumulation depends on factors such as centrifugal force, particle size, and the distribution of gas velocity within the cyclone. Particle re-entrainment at the dust collector is the process wherein particles that have been separated and collected are loosened from the collector surface and reintroduced into the gas stream. This phenomenon can occur within the dust collector section of a cyclone separator, as shown in Fig. 5(d).⁴²  Figure 6 provides a detailed depiction of the vortex within a cyclone separator, along with its geometric center. Identifying the center of the vortex is crucial for analyzing the swirling vortex behavior, a method that has been extensively utilized in research on cyclone separators. Owing to the intense turbulent nature of unsteady swirling flow within cyclones, even in cases of axisymmetric geometrical structure, the rotation center and the geometric center are not perfectly aligned [Fig. 6(a)]. Figure 6(b) illustrates the three-dimensional spatial distribution of the vortex core center obtained from CFD. It is noticeable that the vortex core center consistently spirals upward along the axial direction, as noted by Zhang et al.⁴⁶ 

Figure 7(a) depicts the relative distribution of the vortex core center in the axial direction. According to Zhang et al.,⁴⁶ the maximum deviation of the vortex core center is observed at the cone tip, reaching four times the minimum deviation observed at the straight section. This implies that the areas most significantly affected by the precession motion are the cone tip section, followed by the vortex finder section. The particle flow path follows a spiral line on the cyclone wall, and the spiral pitch exhibits a similar pattern to the relative vortex core center distribution.^47, Figure 7(b) illustrates the movement and distribution of particles within the gas cyclone. It is observed that the majority of particles gather on the wall upon entering the cyclone and subsequently descend along the wall. The behavior of solid particle flow in a cyclone separator is dictated by a combination of centrifugal force, gravity, and air drag forces.³⁹ Solid particles, carried within the incoming gas stream, enter the cyclone through the inlet nozzle.⁴⁷ The inlet geometry induces a downward spiral motion in the gas stream, generating a vortex. Because of their inertia, particles tend to maintain their motion, leading them to collide with the cyclone walls near the inlet. As the gas stream spirals downward, centrifugal force acts on the particles, compelling them to migrate toward the outer wall of the cyclone.^48,49 Heavier particles are subject to stronger centrifugal forces, causing them to be pushed closer to the wall, while lighter particles tend to remain closer to the center of the cyclone. Lighter particles and finer particulates, which are less influenced by centrifugal force, become entrained in the inner vortex near the cyclone center. This inner vortex ascends owing to the pressure gradient within the cyclone.⁵⁰  Figure 7(c) illustrates the effect of different inlet injection areas on particle flow behavior. A distinct variation can be observed, as shown by the black spiral lines on the cyclone sidewall.

Another crucial concept for understanding the unsteady flow characteristics of cyclone separators is the natural vortex length, as shown in Fig. 8(a). Up until now, identifying the exact nature of the vortex end has proven elusive. The commonly accepted explanation is that the vortex end adheres to the side wall, causing the vortex core to bend and rotate or swirl around the wall at a rapid rate.¹ The natural vortex length is recognized as a factor with a significant influence on the separation efficiency and the distribution of erosion in the cone section of a cyclone separator.⁵¹  Figure 8(b) depicts the trajectory of the vortex core as it revolves around the separator wall, rotating about its own axis.

When a particle impacts a surface, it causes scarring of that surface. The shapes of the scars depend on many parameters, including surface material, particle size, and impact angle. Studies have indicated that the mechanism of erosion depends on the ductility of the surface. Figure 9 illustrates the different particle erosion mechanisms in ductile material and brittle material.⁵⁵ 

Wall erosion in gas–solid cyclone separators poses a significant challenge in numerous industrial processes.⁵⁶ Upon entering a cyclone separator, the gas stream rapidly rotates, generating a vortex rope within the chamber. The centrifugal force produced by the rotation drives particles within the gas stream toward the outer walls of the separator, allowing the purified gas to exit through the center.^37,52 The high-speed impact of particles against the wall causes erosion over time, leading to wall degradation, decreased efficiency, increased maintenance requirements, and potential safety risks.⁵⁷ In severe cases, wall erosion may culminate in structural failure and the release of hazardous materials into the surrounding environment.⁵⁸  Table I presents the summary of relevant erosion models. Numerous factors have been confirmed to influence wall erosion in gas–solid cyclone separators, including the size, shape, and hardness of the solid particles and the velocity and pressure of the gas stream. Furthermore, the design and material composition of the cyclone separator itself are critical in determining its resistance to erosion. Further elaboration of these aspects is provided in Sec. IV B.

To address wall erosion in gas–solid cyclone separators, strategies may include employing erosion-resistant materials for construction, implementing regular inspection and maintenance procedures, and optimizing operating parameters. These approaches are described in Sec. IV C. Additionally, numerical and experimental methods are utilized to enhance comprehension of erosion mechanisms and formulate effective erosion control strategies. Indeed, mitigating wall erosion in gas-solid cyclone separators is crucial for maintaining their reliability and efficiency in industrial operations while also adhering to safety and environmental standards.

The entrance impact section refers to the inner wall of the cyclone as observed from the entry direction. In all cases, wall erosion in cyclone separators reflects that observed in elbows within pneumatic conveying pipeline systems.^60,61 There have been several experimental studies of the erosion performance of elbows in gas-solid two-phase flow. They have investigated the influence of factors such as gas velocity, particle size, and powder concentration on the wear and penetration depth of pipeline elbows.⁶² Certain significant discoveries hold significance for both cyclone separator designers and operators. This is because the flow dynamics within elbows bear similarities to those within cyclone inlets. Moreover, in cyclone separators, smaller particles tend to advance with the airflow, whereas larger solid particles diverge from the gas streamlines and impact the cylinder wall.³⁰ Studies have indicated that the area most susceptible to erosion lies at the intersection between the direction of particle impact and the cylinder wall, typically at an angle of ∼20°. For commonly employed plastic structural materials like low-carbon steel or aluminum alloy plates, the highest wear occurs within a range of inclination angles from 15° to 35°.⁵⁷  Figure 10(a) presents an illustration of significant wall erosion at the entrance impact section and the streamline distribution at the top horizontal cross-section. The impulse of the gas–solid flow pattern on the entrance sidewall can be clearly observed by following the flow direction of the streamlines.

In industries such as power generation, cement production, and chemical processing, wall erosion caused by the top ash ring in cyclone separators is a significant concern.⁴¹ The top ash ring denotes the area near the cyclone outlet, specifically the top roof wall, where accumulated particulate matter is located before being discharged. Particles that have been separated and collected in the top roof corner can be re-entrained into the gas stream as a result of turbulence or alterations in operating conditions.⁴ Within the top annular region, the axial and radial velocities are notably lower compared with the tangential velocity. However, the axial and radial velocity components result in secondary vertical flow and subsequent effects. The ash ring continuously rotates near the top roof wall, exacerbating wall erosion, as depicted in the lower part of Fig. 10(b). The findings presented in Fig. 10 are derived from numerical simulations. The top ash ring, characterized by high particle concentration, is especially likely to cause this type of erosion. The detailed features of typical roof corner erosion are shown in the upper part of Fig. 10(b).

Erosion of the outer surface of the gas discharge section or vortex finder can result from a variety of causes. The most significant of these is direct impact between particles and the wall. If any portion of the vortex finder intersects with the projected paths of particles entering a cyclone, the incoming gas is likely to experience constriction. This can occur owing to either geometrical effects or the effect of the rotating gas flow.^1,63 To mitigate these effects, potential solutions include reducing the diameter of the vortex tube, increasing the barrel diameter, or installing two smaller inlets spaced 180° apart.⁶⁴ Indeed, the use of a helical roof design can effectively overcome the problem of incoming solids striking the vortex finder, since the width of the inlet duct then aligns with the annular space surrounding the vortex finder. Song et al.⁶³ investigated carbonaceous deposition on the outer surface of a vortex finder in a commercial RFCC cyclone and examined the role of gas flow in the buildup of these deposits. The unique distribution of coke deposits along the circumferential direction is attributed to the asymmetric tangential velocity and static pressure distribution. The pressure gradient toward the wall increases the likelihood of particle deposition, while the secondary vortex aids in transporting fine particles downward along the vortex finder wall, facilitating their deposit there. The high tangential velocity at the bottom of the vortex finder, just beneath the roof, exerts a considerable scouring action on the vortex finder wall. The erosion and deposition of solid particles on the outer surface of the vortex finder, along with an illustration of the mechanism, are depicted in Fig. 10(c).

Within a cyclone separator, the tangential velocity of the gas decreases near the wall owing to frictional resistance from the wall.^5,6,65 This occurs because the gas adjacent to the wall encounters elevated static pressure and reduced velocity, and occupies a region with a substantial radius of curvature. Consequently, the centrifugal force exerted on the gas flow is significantly reduced compared with the high-velocity gas located at smaller radii.^36,38,44 This difference in centrifugal force induces instability in the flow pattern. Hence, the gas–solid two-phase flow layer adjacent to the wall separates from the wall and is replaced by high-velocity gas from the inner region. As the dusty gas near the wall exits these areas, the particles attached to the wall experience lateral displacement. This sideward movement prompts particle aggregation, leading to the creation of a spiral-type erosion strip. This dynamic process highlights the complex interaction between pressure, velocity, and centrifugal force within the cyclone separator, ultimately influencing the characteristics of wall erosion. The downward rotating flow can be clearly observed in Fig. 10(d), indicating a definite relationship between the spatial position of particle rotation, flow behavior, and the location of wall erosion. The region where wall erosion occurs aligns with the area where the particle flow rotates inside the cyclone separator.

It has been demonstrated that the erosion rate and extent of wall damage in cyclone separators differ along the axial position, influenced by the type and velocity of particles present.^66,67 Significantly, the erosion rate increases along the axial direction on the conical section, reaching its maximum at the bottom or base of the cone and resulting in distinct erosion peaks known as erosion rings. These peaks are primarily caused by the trailing end of the internal vortex instability shifting toward the lower section of the cone, ultimately making direct contact with the lower wall surface. The presence of solid particles exacerbates this phenomenon, intensifying the formation of more pronounced erosion peaks.⁶⁸ Although there may be some fluctuations caused by drifting of the vortex core tail, the general location of erosion peaks tends to remain relatively consistent across different structural designs of cyclone separators.^37,69 This highlights the importance of taking into account the ever-changing interaction of various factors that affect erosion patterns, which is crucial for maximizing the effectiveness and durability of cyclone separator systems. As noted by Hoffmann and Stein¹ there is a substantial increase in erosion with increasing axial distance down the cone section, peaking in the lowermost section or near it. This observation aligns with the findings illustrated in Fig. 10(e). On the basis of earlier studies, these peaks were attributed to a particular form of vortex instability where the “end” of the inner vortex adheres to and rotates around the lower cone walls.^1,51,70 This phenomenon, commonly termed the “natural end of the vortex,” is depicted in the lower part of Fig. 10(e).

Erosion failure of cyclone separators is a complex process influenced by a combination of physical and chemical factors.⁵⁷ Although physical forces are prominent, chemical processes, including corrosion, also play a role. In regions experiencing severe erosion, the mechanism of erosion is predominantly due to mechanical forces, and the factors influencing these forces are highly complex.⁶⁶ The degree of wall erosion is directly linked to the state of the gas–solid two-phase fluid dynamics, the characteristics of the solid particles, operational parameters, environmental conditions, structural configuration, materials, and manufacturing standards of the separator. Slight fluctuations in any of these factors can trigger changes in the erosion mechanism.^58,68,71 The surface roughness of the internal wall of a cyclone separator can profoundly affect the flow dynamics within the device. In recent years, there have been numerous in-depth studies of this topic, which have provided valuable insights.^{51,70,72–75} As the gas moves through the cyclone separator, it comes into contact with the interior surfaces. Rough surfaces can disrupt the flow, leading to the formation of boundary layers,⁷⁶ i.e., thin regions of fluid adjacent to a surface where the flow velocity decreases to zero because of friction. The presence of rough surfaces can promote the formation of turbulent boundary layers, affecting the overall flow dynamics within the cyclone.^{46,47,54,69,77} Such rough surfaces may induce flow separation and the creation of recirculation zones within the cyclone separator. When gas encounters rough surfaces, this can trigger the formation of eddies and vortices, resulting in localized areas of reversed flow or recirculation. This phenomenon can adversely affect the efficiency of particle separation and elevate the pressure drop within the cyclone.⁵¹ 

As can be seen from Fig. 11, the erosion rate is notably greater in the cone section compared with the cylindrical part. It is also important to note that the erosion rate decreases significantly, as indicated by assessments across various solid mass flow rates. Zhou et al.⁵¹ discovered that as the surface roughness increases in a cyclone, the tangential velocity decreases. This is attributed to increased flow resistance and a reduction in swirling strength. Moreover, excessive surface roughness leads to a decrease in radial velocity and an increase in upward axial velocity within the central region of the cyclone. Consequently, this enhances particle retention in the vortex core area. As the surface roughness increases, the natural vortex length gradually decreases.¹ From Figs. 11(a)–11(c), it is evident that the global erosion rate exhibits an almost linear increase with increasing inlet velocity, particle diameter, and solid loading. Additionally, surface roughness is shown to have a significant impact on the global erosion rate under similar operating conditions.

The velocity of the gas entering the separator emerges as the primary factor influencing wall erosion.^78–82 Numerous experimental studies have revealed a direct correlation between erosion wear and the square or cube of the velocity.¹ The magnitude of the velocity directly determines the kinetic energy of solid particles in motion and the frequency of their impact on the inner wall of the separator per unit time.^83,84 With increased velocity, the intensified impact energy consequently worsens the severity of wear.

Increased solid particle loading results in more frequent collisions between particles and the walls of cyclone separators, thereby accelerating the erosion rate.^66,74 Furthermore, owing to centrifugal forces, particles tend to accumulate near the walls, creating a denser concentration of particles in this region at higher particle loadings. Consequently, there is an increased probability of particle buildup and agglomeration on the cyclone wall. This accumulation can lead to the formation of an abrasive layer, intensifying erosion by offering additional material for particles to collide with.⁸⁵ Increased particle loading can also affect the gas flow dynamics within the cyclone separator, leading to changes in particle trajectory, velocity, impact angle against the wall, and, potentially, the erosion rate.^12,86 Solid particles, particularly if they are hard and abrasive, can induce significant wear on the wall material. With increasing particle loading, the cumulative impact of abrasion becomes more pronounced, leading to accelerated erosion. Additionally, the distribution of particle sizes within the solid particle loading can also influence erosion rates. Mixtures containing a wide range of particle sizes can lead to diverse erosion patterns: larger particles typically cause more localized damage, whereas smaller particles contribute to more generalized erosion.⁸⁷ Furthermore, it is important to acknowledge that there might be a threshold beyond which increasing the solid particle loading does not result in a proportional increase in erosion. This could be attributed to factors such as particle interference, alterations in gas flow patterns, or limitations on the erosive capability of the particles themselves.⁸⁸ 

The geometrical structure and manufacturing quality are also crucial factors influencing wall erosion in cyclone separators. The cone angle plays a significant role in shaping both the velocity distribution of the gas stream and the centrifugal forces acting on solid particles.^17,89 A steeper cone angle can result in higher particle velocities near the walls, leading to increased erosion rates, and vice versa. The design of the inlet significantly influences the flow pattern within the cyclone. An inappropriate design may induce turbulence or an uneven particle distribution, ultimately causing localized erosion.^90–92 The diameter of the cyclone body plays a key role in determining the residence time of particles. A larger diameter may reduce particle velocity and erosion rates by allowing more time for particles to settle before reaching the walls.²⁶ Selecting appropriate materials for the construction of a cyclone is crucial. Abrasion-resistant materials such as hardened steel or ceramics have superior resistance to erosive wear compared with standard materials.⁹³ Additionally, wall thickness influences erosion resistance: thicker walls offer more material to withstand abrasive forces and may be less susceptible to erosion.⁹⁴ A smooth surface finish can help minimize particle adherence and buildup on cyclone walls. Conversely, rough surfaces or manufacturing imperfections can encourage particle accumulation, resulting in increased erosion.⁵¹ Therefore, employing high-quality manufacturing processes such as precision machining or surface treatment can effectively reduce erosion. Inadequately sealed seams or joints in the cyclone structure can permit gas and particle leakage, resulting in localized erosion at these vulnerable points. To address this concern, it is essential to ensure tight seals and proper alignment during manufacturing. Implementing effective quality control measures, such as inspecting dimensions, surface finish, and material integrity, is crucial for producing cyclone separators with minimal defects and consistent properties.⁷⁵ Any deviations from design specifications or manufacturing defects can result in localized erosion and premature failure of the cyclone separator.

Wall erosion has the potential to modify the geometry and surface smoothness of cyclones, consequently affecting airflow patterns and separation efficiency.^72,95 Preventing such erosion is therefore crucial for cyclones to sustain their designed performance and ensure efficient particle separation.⁶ Furthermore, erosion can result in structural weakening and eventual failure of cyclone separator components, leading to expensive repairs or replacements. Preventing erosion or weakening its effects extends the lifespan of equipment and ensures stable process conditions and product quality, thereby reducing downtime and maintenance expenses.

The consistent operation of cyclone separators is vital for numerous industrial processes, including gas–solid or liquid–solid separation in chemical processing, mining, and power generation.¹⁰ Additionally, erosion can lead to the formation of sharp edges or weakened areas on cyclone walls, thereby elevating the risk of accidents such as leaks or ruptures. Erosion can lead to the release of particles or contaminants into the environment, posing risks to air or water quality.⁹⁶ Preventing erosion helps minimize the potential for environmental pollution, thus promoting sustainable and responsible industrial practices. Hence, implementing appropriate suppression measures to address wall erosion in cyclone separators is essential for ensuring operational efficiency, equipment reliability, safety, and environmental protection across diverse industrial applications.¹ 

Proper control of operating conditions is crucial for preventing wall erosion in cyclone separators. The design of the inlet section greatly influences the velocity and direction of the incoming flow. Adjusting the inlet geometry can help distribute the flow more evenly across cyclone walls, thereby reducing localized erosion. Furthermore, by fine-tuning both the diameter and configuration of the inlet, it becomes possible to regulate the speed at which particles enter the separator, thereby reducing any potential damage to the walls. Modifying the flow rate and pressure of the fluid or gas introduced into a cyclone separator can also effectively reduce erosion. Operating within the recommended flow rate range designated for a given separator helps prevent excessive particle impact on the walls. Consistent monitoring and fine-tuning of the pressure also guarantees that the flow velocity stays within safe parameters, thus minimizing erosion. Recognizing the particle size distribution within the incoming stream is crucial in preventing erosion. It may be necessary to make adjustments to control the size and concentration of abrasive particles entering the cyclone separator. The use of pre-filters or particle removal systems upstream can effectively eliminate larger or more abrasive particles, thereby decreasing the erosive effect on the walls. Implementing monitoring systems and feedback control mechanisms ensures the maintenance of optimal operating conditions for erosion prevention. Access to real-time data regarding flow rates, pressure, temperature, and particle concentrations enables operators to make the necessary adjustments, averting erosion-related problems promptly.

Substituting components of equipment that are particularly vulnerable to erosion with erosion-resistant materials is a widely adopted strategy in industrial settings.⁸⁶ The widespread occurrence of erosion, characterized by the gradual deterioration of materials owing to external elements such as water, wind, or chemical reactions, emphasizes the necessity for such measures.^97,98 While erosion is a natural phenomenon, human activities or infrastructure can expedite its occurrence. In numerous applications, especially in the case of infrastructure subjected to severe environmental conditions, such as coastal barriers and pipelines, accelerated erosion can result in structural instability, diminished lifespan, and higher maintenance expenses. Therefore, the utilization of erosion-resistant materials becomes important to alleviate these concerns.¹ For structures exposed to saltwater or acidic environments, commonly employed materials include stainless steel, titanium, and other corrosion-resistant alloys. High-density polyethylene, fiberglass, and carbon fiber composites exhibit outstanding erosion resistance and serve as lightweight alternatives to metals.^93,94 When substituting segments that are vulnerable to erosion with erosion-resistant materials, engineers must take into account various factors. These include material properties such as mechanical strength, durability, chemical resistance, and cost-effectiveness, as well as environmental conditions such as exposure to water, temperature fluctuations, chemicals, and abrasive forces. Additionally, structural requirements such as compatibility with existing structures, load-bearing capacity, and integration feasibility need to be considered. Anticipating and guaranteeing the performance of materials throughout their intended lifespan via modeling, testing, and monitoring is imperative. Moreover, it is crucial to acknowledge that the use of erosion-resistant materials typically incurs higher costs compared with traditional materials, and this may potentially influence project budgets. The installation of erosion-resistant materials may require specialized equipment or techniques, and ongoing maintenance may be essential to maintain performance standards. Ensuring compatibility with existing structures and interfaces is crucial to prevent issues such as galvanic corrosion or structural mismatch.

Enhancing the geometrical arrangement or integrating additional components into cyclone separators can notably reduce wall erosion.⁴ The use of CFD enables engineers to improve cyclone structure by forecasting flow patterns, particle paths, and impact forces.^{8,24,25,99–101} This capability aids in pinpointing zones that are prone to erosion and assessing design adjustments to alleviate the consequences of erosion.

Crafting seamless transitions between the inlet,^90,91 body,¹⁰² and outlet^103,104 sections can reduce turbulence and particle impact on the wall and thus erosion. Refining the curvature and shape of the wall can effectively guide particle-laden flow toward the center of the cyclone, away from its walls, thereby reducing erosion.¹⁰⁵ Ensuring an adequate wall thicknesses maintains structural integrity and provides a shield against erosion. Reinforcing vulnerable regions susceptible to erosion can prolong the cyclone’s lifespan. Incorporating replaceable wear liners made from abrasion-resistant materials, such as ceramic tiles and polyurethane liners, along cyclone walls provides an additional layer of defense against erosion. Well-designed auxiliary devices play a crucial role in regulating the flow pattern within a cyclone, reducing turbulence and preventing particles from hitting the walls.^106–109 Strategically positioned baffles, extra inlets, or vanes in a cyclone can redirect particle-laden flow away from the walls, thus reducing erosion and enhancing separation efficiency. For example, to reduce wall erosion in cyclone separators caused by the top ash ring phenomenon, Liu et al.¹¹⁰ proposed a cyclone design with extra inlets in the top roof wall. Secondary flow (clean air) is injected through these extra inlets, which are installed at an angle to the cyclone. Thus, the tangential velocity components of the extra inlets and the primary inlet are in the same direction. The results obtained with this design indicate a 14.5% reduction in pressure drop and a 10% increase in total separation efficiency. The erosion of the optimized cyclone is also significantly reduced around the cone bottom. The use of specialized coatings or surface treatments on internal parts of a cyclone can increase erosion resistance and mitigate material degradation.^111,112 Ongoing research and development efforts focusing on advanced materials, coatings, and innovative design concepts have the potential to enhance erosion resistance further and extend cyclone lifespans.

In many cyclone installations, abrasive wear or erosion is a major concern for plant operating and maintenance departments. The erosion of cyclone walls presents a significant challenge, often resulting in unplanned unit shutdowns, especially in facilities that process highly abrasive particles such as coal, sand, fly ash, coke, and alumina-based catalysts. The erosive forces within cyclone separators are particularly pronounced owing to the high-speed rotation of gas–solid mixtures, leading to accelerated material degradation. Erosion not only disrupts production schedules, but also increases maintenance costs and compromises the overall efficiency of the separation process. Furthermore, the consequences of erosion extend beyond immediate operational setbacks. They can potentially pose safety hazards to personnel and environmental risks due to leaks or releases of particulate matter.

Therefore, addressing erosion in cyclone separators is crucial for ensuring continuous operation, minimizing maintenance expenses, and maintaining safety and environmental compliance standards. Efforts to mitigate erosion should be prioritized through the implementation of appropriate preventive measures, such as the use of erosion-resistant materials, optimization of cyclone design, and regular maintenance and inspection protocols. Additionally, ongoing research and development initiatives focusing on advanced materials, coatings, and innovative design concepts hold promise for further enhancing erosion resistance and extending the lifespan of cyclone separators.

The primary locations of erosion in gas–solid cyclone separators, including the entrance impact section, cyclone roof corner erosion, vortex finder outer surface, spiral-type erosion strip, and lower cone section, have been elucidated in detail in this paper. Furthermore, the main factors influencing wall erosion have been thoroughly discussed, encompassing inlet flow velocity, solid particle properties and loading, geometrical structure, and manufacturing quality. Finally, several practical preventive measures for wall erosion have been presented, including the adjustment of operating conditions, utilization of erosion-resistant materials, and optimization of geometrical structures by the addition of auxiliary devices. These measures are crucial for ensuring operational efficiency, equipment reliability, safety, and environmental protection in various industrial applications. These advances in preventive measures encompass materials science and surface coating technologies, with the aim of effectively reducing erosion rates and thereby extending the lifespan of cyclone separators.

The primary objective of this paper has been to provide valuable insights and inspire research teams and engineers in industry and thereby accelerate advances in related research and engineering practices, ultimately leading to the development of more reliable and efficient solutions for industrial production. For research teams, this paper should serve as a foundational reference to previous research findings, on the basis of which they can explore novel and effective approaches to dealing with erosion in cyclone separators. This facilitates the exploration of innovative solutions that can further enhance equipment reliability and efficiency. For engineers working in industry, the knowledge gained from this paper should provide a practical guide for applications, equipping them with the necessary information to effectively manage erosion problems within cyclone separators, to optimize equipment performance, and to achieve operational excellence in industrial settings.

This work was made possible by support from various funding sources, including the National Research Foundation of Korea (Grant No. 2021K2A9A2A06039055) and the National Research Foundation of Korea’s Brain Korea 21 FOUR Program at the BK21 FOUR ERICA-ACE Center of Hanyang University. Additional support was provided by the Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (Grant No. P0012769, HRD Program for Industrial Innovation).

The authors have no conflicts to disclose.

Ming Guo (郭明): Conceptualization (equal); Investigation (equal); Validation (equal); Writing – original draft (equal). Gaoju Xia (夏高举): Formal analysis (equal). Penghui Guo (郭鹏辉): Data curation (equal). Sivakumar Manickam: Writing – review & editing (equal). Joon Yong Yoon: Writing – review & editing (equal). Xun Sun (孙逊): Supervision (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.