Using precast modular lining to counter kiln inlet area build-up

As cement producers strive to reach net-zero emissions, the growing reliance on alternative fuels (AFs) introduces complex operational challenges. Key areas of concern include increased wear on refractory linings and severe build-up in the preheater system, particularly in the smoke chamber and feed pipes, forcing costly shutdowns. Innovative refractory solutions, like HASLE’s Precast Modular Lining, offer a way to mitigate these issues. With smoother surfaces and greater resistance to chemical attacks, these linings can improve plant efficiency while supporting the transition to greener energy sources.

On the journey towards net zero, the increased utilisation of alternative fuels (AFs) in cement production poses several operational challenges. Chemical attacks put pressure on the longevity of refractory linings, increasing the risk of coating formation and build-up in different parts of the preheater, as well as causing improper heat distribution due to incomplete or localised combustion of different grade AFs.

The smoke chamber (inlet box) and feed pipes in the lowest part of the preheater are areas of significant concern. The linings in these areas are typically prone to high wear due to the abrasion from the passing raw mix at elevated temperatures, usually ranging between 850-1050?C.

Additionally, the presence of corrosive chemical agents in the gas phase from burning AFs can exacerbate conditions, as different corrosives such as alkalis, sulphates and chlorides can react with the refractory lining or the raw meal, forming heavy coating deposits on the surface of the lining.

This build-up reduces the effective operational, cross-sectional space, leading to bottleneck issues with the risk of jamming, impacting both throughput and operational efficiency. In severe cases, cement plants may face the need to shut down operations to clean the coating and build-up, resulting in high costs in terms of process time, maintenance hours and wasted energy during process restart.

Mitigating material build-up

Cleaning measures are often required to remove the build-up, limiting downtime and improving productivity. To avoid the need for manual cleaning and to minimise the resulting downtime, several measures can be employed in the process to counteract the potentially sticky raw meal mix. Flow aids, such as air cannons and blasters, as well as pressurised water jets, can dislodge accumulated material and facilitate a smoother flow during operation. While these flow aids can be beneficial, they may also add complexity to the overall system, as well as exposing the refractory lining to a higher level of wear, potentially reducing its lifetime.

The quality of the refractory lining is another crucial factor influencing the deposition of raw meal mix. If the surface of the refractory lining is rough and susceptible to chemical reactions with the passing raw meal it can promote build-up issues.

By creating a smoother surface and utilising high-quality refractory materials, the passing raw meal becomes less likely to stick to the refractory lining. Therefore, optimising the refractory lining and its surface can be a cost-effective tool to minimise build-up as no extra complexity is added to the production process.

Introducing AFs to the preheater

A cement plant in central India was commissioned in 2014 with a designed capacity of 10,000tpd. It was facing issues with severe coating formation in the preheater. Initially, the cement plant was using coal as its main fuel, but in recent years, coal has been partly replaced by petcoke in the main burner, while various AFs are fed into the calciner. The current fuel composition is 60 per cent petcoke, 35 per cent coal and five per cent AFs.

However, when the plant started using AFs, heavy coating formation appeared in different parts of the preheater such as the smoke chamber, feed pipes and parts of the cyclones. This heavy coating formation disrupted the regular operation of the plant, necessitating frequent cleaning of these areas, especially the smoke chamber, to ensure the smooth operation of the plant. Moreover, due to heavy chemical attack, along with wear From the frequent cleaning, the existing refractory lining was eroding fast and needed frequent repairs during every shutdown, adding both time and costs to the maintenance plan.

Precast solution with a smooth surface

The plant turned to HASLE Refractories for assistance in addressing the coating issues. After discussions with the company’s engineers, the plant decided to install one of Hasle’s precast modular lining solutions in the kiln inlet slope area of the smoke chamber, where coating was most critical. The goal was to extend the lining’s lifetime and significantly improve the plant’s run factor by minimising coating formation in this area.

As an alternative to traditional in-situ castings, the company’s precast modular lining system provides a durable lining with a smooth surface. The lining system is based on standardised precast shapes measuring 25 x 25cm, designed for easy handling and installation.

To achieve a high quality, all precast elements are made exclusively from virgin materials and manufactured under strict controls at Hasle’s facility in Denmark. Specialised casting equipment, such as vibration tables and tailor-made moulds, is used.

The green precast bodies subsequently undergo a five-day pre-firing process, reaching a peak temperature of 500?C. This carefully controlled procedure effectively eliminates all free and chemically bound water, resulting in an impressively low open porosity of just 8-10 per cent, compared to the 15-20 per cent typically found in in-situ cast linings. The outcome is a very smooth surface of the precast elements, boasting heightened resistance to coating. Furthermore, leveraging the refractory material’s exceptional resistance to chemical attacks from alkali, sulphates and chlorides, the precast solution effectively minimises build-up and corrosion issues.

The HASLE Modular Lining is highly customisable in terms of dimensions and lining design, available for both straight and circular walls, slopes, roofs and bull noses as well as cylindrical applications such as feed pipes. The thickness of the modular lining can easily be adjusted to meet individual requirements through its flexible anchoring system.

This adaptability also extends to the heat transfer pattern of the lining, which can be tailored by using different insulation and low thermal conductivity materials behind the precast elements, such as ceramic fibre blankets and backup insulating castable.

Flexible installation

HASLE supplied its Modular Lining solution of about 20m2 to be installed at the Indian cement plant during a scheduled shutdown in December 2020. To ensure a smooth transition to the neighbouring walls, the original lining thickness of 375mm was maintained. The lining comprised HASLE precast elements: hot face lining, hasle insulating castable BSI1200 and insulating blocks.

The company also supplied all the accessories, including both metallic and non-metallic components. Each precast element was securely fastened using a bolt and washer, sliding into a steel rail mounted to the wall. The precast elements feature tongue-and-groove joints on all four sides, which interlock and were filled with 2-3mm mortar during installation. This minimises the penetration of gases into the insulation layer and anchoring system behind the elements. The installation was completed under the technical supervision of a HASLE engineer.

Since its installation, the HASLE precast lining solution has been performing well. During its 3.5 years of operation, the Modular Lining has stayed intact. Its only repair was required after two years of operation when a 1m2 area needed to be repaired. More importantly, the formation of coating in the area has been greatly reduced and therefore, also the need for extra cleaning measures. This has allowed the plant to maintain a high run factor by avoiding otherwise resource-intensive cleaning and build-up removal.

During a scheduled shutdown in July 2024, the kiln inlet slope area was inspected and a thin layer of coating was observed along with erosion of some of the precast elements, leading to the decision to reline the area fully with a new hasle precast Modular Lining solution.

Other case studies

Several other Indian plants have also successfully implanted the company’s precast solutions in their kiln inlet area. In southern India, a 4800tpd cement plant sought to reduce its coal consumption by incorporating petcoke and agricultural waste. As the plant increased the use of these AFs, this shift led to a surge in coating within the smoke chamber and riser duct, hindering plant efficiency and demanding extensive cleaning efforts during operation and shutdowns.

In search of a cost-effective solution to manage the coating issue, the plant opted to implement a HASLE Modular Lining on the kiln inlet slope within the smoke chamber. The lining was tailored to the plant’s specific requirements, resulting in a 254mm-thick lining that created an effective insulation layer behind the precast elements. Here, calcium-silicate boards and a back-up insulation castable were incorporated to optimise thermal performance, ensuring high heat retention within the process.

The first HASLE Precast Modular Lining in this plant was installed in the summer of 2017 and demonstrated impressive durability, lasting four years. In early 2022, the kiln inlet slope was re-lined with the same hasle solution. A recent inspection, conducted after 18 months of operation, confirmed that the precast lining was in excellent condition with virtually no coating present.

Conclusion

Across a wide range of operating conditions, including high levels of AFs, HASLE’s tailored Precast Modular Lining solutions have consistently demonstrated long lifetimes, typically around 4-5 years.

These solutions also offer excellent anti-coating properties and high abrasion resistance in other critical areas of the preheater, such as smoke chamber walls, feed pipes and vertical bull noses. By implementing HASLE precast solutions, cement plants can effectively navigate the challenges associated with sustainable fuel conversion, thereby increasing their thermal substitution rate and improving operational efficiency.

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Originally published in the November 2024 issue of International Cement Review; published on Linkedin with permission from the magazine.