A clarifier scraper design to minimise nuisance lifting

A new Short Retention Time (SRT) juice clarifier was installed and commissioned in the 2023 season. The mud scrapers on this type of clarifier have been reported to lift in previous installations while under normal mud loading and conditions. Mud scraper lifting under normal conditions can result in several performance issues, including mud holding up and ‘rat-holing’ of juice through the mud outlet. Previous reports noted instances of scraper lift failing the scraper support hanger due to the change in forces exerted on the hangers when the scraper is in a more horizontal position. As part of the design of this new clarifier, an approach to design the scrapers to prevent lifting was developed. The approach involves understanding previous installations, developing heuristics based on these, and developing a method of calculating the resulting force exerted on the scraper face by the mud. This approach complements existing scraper design methods, which are typically based on mud volume movement caused by the scrapers moving mud towards the outlet of the clarifier. This work provides heuristics that can be used to better design mud scrapers for SRT juice clarifiers.