Banishing buildup

A continuous material flow without any obstruction is a primary requirement for dry-process cement manufacturing, but the accumulation of coating and blockages can hamper a plant’s overall productivity – and ultimately its profitability. Coating formation and buildup reduce the effective operational cross-section area, causing bottlenecks in the process that impact the material flow and operational efficiency. If they become severe enough, flow problems can jam the process and bring production to a complete stop.

Consequently, cleaning measures – either manual cleaning or the use of flow aids such as high-speed air cannons – are required to limit downtime and improve productivity, adding costs and time to the maintenance plan along with potentially increasing complexity in the production process. Additionally, refractory walls can be worn or damaged by tools or cleaning techniques, necessitating more frequent repairs or relining.

Feed pipes pose a particular challenge

The feed pipes play a vital role in delivering a controlled and consistent flow of raw meal mix into the preheater tower and between its cyclones. But they also pose a special challenge by having a narrow cross-sectional area with a relatively low airspeed of the passing raw meal, catering to a higher risk of deposits sticking to the pipe walls, especially in lower cyclone stages with higher temperatures.

The coating formation and buildup in this area seems to depend heavily on the particular chemical composition of the raw meal mix in the clinker manufacturing process. Some plants have negligible coating issues, while others fight a tough battle to minimise and reduce the buildup. For instance, chlorides may be present in the mined chalk or an elevated percentage of MgO in the limestone, which subsequently can react with other components in the process, resulting in a stickier material mix. Furthermore, the burning of alternative fuels – and hence the introduction of additional corrosives like alkalis, sulfates, and chlorides into the preheating process – can in many cases worsen the coating formation on the refractory surfaces.

Counteracting the sticky material

Manually removing the buildup from the feed pipes requires frequent cleaning. In severe cases, cement plants may face the need to shut down operations to clean the coating and buildup, resulting in significant costs in terms of process time, maintenance hours, and wasted energy during the restart.

To avoid the need for manual cleaning and to minimise the associated downtime, several measures can be employed in the process to counteract the potentially sticky raw meal mix in the feed pipes. Flow aids, such as air cannons and blasters, can dislodge accumulated material and facilitate a smoother flow of materials through the pipes. While these flow aids can be beneficial, they may also add complexity to the overall system.

The quality of the refractory lining inside the feed pipes 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 material, it can promote buildup issues. By creating a smoother surface and utilising high-quality refractory materials, the passing material becomes less likely to stick to the feed pipe walls.

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Read the article online at: https://www.worldcement.com/special-reports/13102023/banishing-buildup/