Long-Lasting Lining

Preecha Chowjarearnsuk HASLE Refractories, discusses the role of refractory lining in preheater cyclones and explains how short lining lifetimes in vertical bull nose areas can be addressed with a tailored, curved precast solution.

The design and shape of the vertical bull nose in preheater cyclones is critical for directing the gas flow and optimizing material separation efficiency within the cyclone. However, this area can present significant challenges for refractory linings due to its inherent vulnerability. The bull nose area is subjected to intense abrasion from turbulent, high-velocity air currents and passing raw meal particles, particularly in lower-stage cyclones where peak temperatures often exceed 900 – 1000?C. The sharp angles of the bull nose structure, combined with mechanical loads from the airflow, further increase the risk of cracking and spalling of the lining, necessitating frequent repairs or relining. These harsh conditions are exacerbated by alkali and other chemical attacks, which are intensified by the increased use of alternative fuels (AFs).

Relining the bull nose area poses additional complications due to its elevated position within the cyclone, requiring extensive scaffolding for access. Castable solutions demand precise, labor-intensive formwork to accommodate the sharp angles, while gunning materials, though faster to apply, may have limited durability due to higher open porosity. Although precast solutions involve a higher initial cost, they can be a viable alternative to achieve longer lifetimes in these demanding and potentially fragile vertical bull nose areas of the lower-stage cyclones.

Only 12 months of service life

A 4000 tpd cement plant in Australia, operating on a fuel mix of 70% coal and 30% AFs, faced persistent challenges with the refractory lining in the vertical bull nose zones of its lower-stage cyclones. The used gunning material failed to withstand the harsh conditions, necessitating frequent repairs.

The vertical bull nose lining, subjected to severe abrasion and temperatures up to 950?C, cracked at the leading edge of the bull nose, resulting in a short service life of 12 months and relining needed every year. This not only consumed significant man-hours and material costs but also required complex scaffolding, further adding both time and costs to the maintenance plan. Seeking a more durable refractory solution, the plant aimed to extend the lining's lifespan, thereby minimizing downtime and overall maintenance costs.

Tailored Curved Precast Solution

As an alternative to in-situ cast and gunning solutions, HASLE Refractories proposed a precast solution based on its Modular Lining concept.

Originally developed in the 1990s, HASLE’s precast Modular Lining is designed as a hot-face refractory lining system for critical areas in high-temperature industries, based on 25 x 25 cm standardized precast elements. These elements are highly durable, with a smooth impact surface that minimizes abrasion and coating formation while offering excellent resistance to chemical attacks. Additionally, the system features a flexible anchoring design that can be customized to fit specific dimensions, lining thickness, and insulation needs to maximize energy retention.

Manufactured under strictly controlled conditions at HASLE’s facility in Denmark, the Modular Lining precast elements are exclusively made from virgin raw materials to ensure high quality. The production process employs vibration tables, precision molds, and dry-out ovens. The green precast bodies are pre-fired over several days, reaching a peak temperature of 500?C to effectively remove all free and chemically bound water. This meticulous process achieves a very low open porosity of 8 – 10%, resulting in a smooth, impact-resistant surface of the elements. Leveraging the refractory material's high resistance to chemical attacks from alkalis, sulfates, and chlorides, the precast solution effectively minimizes corrosion issues. Further-more, an optimized grain size distribution boosts the material's density and robustness, where the strong matrix provides high resistance to both abrasion and chemical degradation.

While the Modular Lining was initially developed for flat surfaces like roofs, slopes, and walls, the vertical bull nose area in cyclones features a sharply curved geometry.

Hence the standard, 'flat' precast elements were unsuitable for this application, prompting HASLE’s engineers to design a custom solution, while still retaining a high degree of modularity.

To address this, precast elements with varying angles were developed to match the curvature of the bull nose, including applications with a 60? inner angle, as found on the vertical bull nose areas at the Australian plant. The system also incorporates a flexible steel anchoring system, and an interlocking tongue-and-groove design embedded within the precast elements. This combination ensures both durability and ease of installation, making it an ideal solution for the specific requirements of the vertical bull nose in cyclones.

Additionally, the system’s adaptability extends to the thermal performance. By using different insulation materials – such as ceramic fibre blankets and backup insulating castables – behind the precast elements, the heat transfer characteristics of the lining can be tailored to meet plant-specific requirements.

Precast Installation in Two Cyclones

As similar cracking issues were observed in the existing lining in both lower-stage cyclones, the HASLE precast solution was installed in both the lowest and second-lowest stage cyclones at the Australian cement plant. The installation process was initially carried out in stages, starting with the vertical bull nose area in the second-lowest cyclone (height: 3 m) during the annual shutdown in November 2012. A year later, in November 2013, the precast lining was installed in the larger lowest-stage cyclone with a height of 4.5 m.

Installing HASLE’s Precast Modular Lining proved to be both fast and straightforward. Steel anchors were welded to the cyclone wall and then connected to the precast elements using a bolt-and-washer system, allowing easy adjustment during mounting. Each precast element weighs only 15 – 16 kg, eliminating the need for special lifting equipment. The precast elements feature tongue-and-groove joints, which interlocked securely and were filled with 2 – 3 mm of mortar during installation. This design minimizes the penetration of gases into the insulation layer and anchoring system behind the elements. Additionally, fibre blankets were placed at specific intervals to accommodate thermal expansion. Once the precast elements were in place, HASLE BS1200, an insulating castable, was poured behind them to minimize heat loss and protect the casing structure. The entire installation was completed under the technical supervision of a HASLE engineer, ensuring precise implementation and quality control.

Successful Design Optimization Achieves 7-Year Lifetime

Both vertical bull nose installations remained in operation until the spring of 2017, more than tripling the lifetime of the previous lining solution with a gunning material. Satisfied with the performance, the plant sought additional improvements to further optimize the precast bull nose design for even greater durability.

Given the high sulfur content in the system, the stainless steel used in the original precast installation was upgraded to grade 253MA to ensure enhanced resistance to the potential sulfur-induced corrosion. Additional retainer plates were incorporated into the structure to improve its robustness, while the anchoring system was further optimized with the addition of C-rails to allow easier adjustments during installation.

In January 2018, during the annual shutdown, the updated HASLE Precast Modular Lining design was installed in the bull nose areas of both the lowest and second-lowest stage cyclones. Since installation, the solution has operated continuously without requiring any repairs. An inspection in January 2024 confirmed that both installations remain in good operating condition. They are now approaching an impressive 7 years of uninterrupted service life, and are still both in operation. By choosing HASLE’s precast solution, the Australian cement plant significantly reduced maintenance man-hours and material costs, as no repairs or relining were needed to maintain the bull nose zones during this period. This has led to improved production stability and reduced maintenance costs.

Further Successes Showcasing Precast Modularity

The HASLE precast Modular Lining system has proven effective in addressing similar challenges at other cement plants, where its modularity offers significant benefits in terms of easy adaptivity.

A cement plant in Thailand, with a capacity of 7500 tpd and a dual-string preheater design, operating on a fuel mix of 85% coal and 15% AFs, faced similar challenges with short lifespan of the refractory lining in the vertical bull nose zones of its lower-stage cyclones due to a high level of abrasion.

Seeking to extend the lining lifetime and reduce long-term maintenance costs, the plant installed HASLE’s precast Modular Lining solution in October 2015 in the vertical bull nose areas of both the lowest and second-lowest stage cyclones in one of the two strings. The design accommodated a tighter inner angle of less than 45?, further demonstrating the adaptability of the HASLE solution.

In the lowest stage cyclone, the precast bull nose installation achieved a service life of 5.5 years without need for repairs. Higher up in the second-lowest stage cyclone, the lining remained operational until September 2022, delivering a remarkable lifespan of 7 years.

In October 2023, the lowest-stage cyclone was relined with a new HASLE precast Modular Lining solution, which continues to operate reliably to this day.

About the author

Preecha Chowjarearnsuk is the Head of Sales and Technical Support for Southeast Asia and Australia at HASLE Refractories, Thailand. Preecha holds a bachelor’s degree in industrial engineering from Mahidol University and has 16 years of experience working with refractories in high-temperature industries.

______

Originally published in the January 2025 issue of World Cement Magazine; published on Linkedin with permission from the magazine.