The implementation of novel technologies in refractory materials, such as gel-bonded cement-free gunite, are transforming cement plant operations and cutting downtime. With new variations and the ongoing energy transition, that evolution looks set to continue.
by Stephen Karns and Robert Piestrzynski, United Refractories Co, USA
Refractories are indispensable in the cement industry, primarily in the higher temperature areas of the process, critical for clinker production. These heat-resistant materials line key components such as rotary kilns, preheaters and clinker coolers, withstanding extreme temperatures, thermal shock, exposure to chemical attack and abrasion. Given the demanding nature of the clinker manufacturing process, the performance and longevity of these refractories are crucial to protect equipment and operational efficiency.
In recent years technological advancements in refractory materials have led to more versatile, efficient and extended service-cycle solutions, resulting in cost savings and improved performance. Among these, a groundbreaking refractory system has gained significant attention for its versatility and performance in cement plants: gel-bonded cement-free refractory gunite. This article delves into the innovative gel-bonded cement-free gunite refractory system, its contributing property characteristics and how it is used with success in the cement industry.
Product evolution
Since the initial development of a 60 per cent alumina version of the gel-bonded cement-free gunite system in 2021, approximately 1100t of this version of the product have been put into service. Prior to this, a gel-bonded cement-free shotcrete had been supplied with very good success.
However, while gel-bonded shotcrete was a good solution, there was a clear need in the industry for reduced installation complexity. Using a similar technology to the shotcrete gel-bonded cement-free system, the gunite system was developed starting with an all-purpose 60 per cent alumina, cement-free product. Designed with ease-of-use in mind this product maintained excellent physical properties and incorporated accelerated dry-out capabilities.
The result was a product that had high alkali resistance, superior abrasion resistance, and excellent thermal stability with a service temperature limit of 1700˚C (3100˚F). This made it ideal for use in virtually any area of the clinkerisation process that can reach temperatures of 1450˚C (2645˚F) in a highly alkaline environment.
Features and benefits
Installation and operational efficiency
The system allows for easy application using standard equipment and nozzle configurations. There is no need for the addition of complex additives (such as colloidal silica), reducing operational costs and set-up complexity. It is also easier to handle and apply in tight or difficult-to-reach areas, reducing installation time.
Low dusting and rebound
The system exhibits low rebound (10 per cent or less), adhering effectively to surfaces without much material loss and resulting in a cleaner work environment and reduced material waste. This gel-bonded gunite does not require pre-dampening and has been designed to have installation characteristics comparable with low-rebound shotcrete. Despite being a gunite that does not require pre-dampening, it has a very low dust generation.
Veneering
The gel-bonded refractory system is a one-part formulation notable for its extreme stickiness and outstanding bond adhesion strength. These properties ensure that the material adheres effectively to both clean and pre-existing refractory substrates. This makes it an excellent choice for both veneering and applications which require full-depth design thickness. These excellent flashing and bond strength properties ensure that it can handle extreme temperature variations and thermal cycling without degrading or failing prematurely.
Abrasion resistance
The base system performs well in the abrasion resistance test (ASTM C704) with a typical result of 7-8cc loss or better. This ensures longevity in high-wear areas such as kiln hoods, coolers and ductwork.
Accelerated heat-up and reduced downtime
The absence of calcium aluminate hydrate phases enables, with high-temperature dehydration points, the use of a shorter dry-out schedule for gel-bonded gunite. The system’s fast installation and drying times lead to less downtime, ensuring that plants can resume operations quickly without compromising performance.
Alkali resistance
One of the stand-out benefits of this gel-bonded cement-free system is its superior alkali resistance, outperforming low-cement gun mixes in environments exposed to alkali and other chemicals typically found in the cement manufacturing process. This reduces the risk of cracking and degradation due to chemical penetration.
Extended shelf life and storage
One of the most significant advantages of the gel-bonded system is that it is cement free and does not require a colloidal silica liquid binder. Products based on the gel-bonded cement-free system react simply and conveniently with water at the discharge nozzle. Since it is not dependent on cement or a separate liquid binder, the gel-bonded system provides an extended shelf life compared with industry-standard alternatives.
Proven experience
In the first cement outage season following the launch of this gel-bonded cement-free gunite product, it was selected for projects by multiple end users. Feedback highlighted low dust, high stickiness, and excellent adhesion. Installations included clinker coolers, cyclones, and repairs over worn brick linings, showcasing versatility and performance that outperformed traditional materials.
New versions with added zirconia, silicon carbide, and 70 per cent alumina were developed for enhanced resistance and cycling tolerance. A magnesia-based variant was also introduced for magnesia brick repairs.
Conclusion
Refractories are a crucial component of cement plant operations, ensuring efficiency, safety, and equipment longevity. The gel-bonded cement-free gunite system offers improved performance, easy installation, and minimal downtime. Its success in cement plants and other high-heat industries like lime production and biomass units highlights its versatility and robustness. As the cement industry shifts toward alternative fuels and carbon-neutral production, such systems will play a key role in supporting these transitions.
Download the Advancing refractories with cement-free gel-bonded gunite here.