Submerged Scraper Conveyor
SKF South Africa engineered/ remanufactured Stub Shaft and sealing solutions installed on ash plant Submerged Scraper Conveyor (SSC) systems at two of the country’s power stations. They have delivered five years of uninterrupted performance, operating without leaks or failures.
Coal‑fired power stations rely on SSC systems to handle hot, abrasive, dust‑producing bottom ash (a by‑product of coal combustion) from boilers. By submerging the conveyor in a water trough, the system quenches and cools the ash while maintaining a critical airtight seal between the boiler and ash‑handling system. This prevents air ingress, ensures continuous ash transportation, reduces dust and supports improved environmental compliance.
Critical roles
“The Stub Shaft plays several critical roles,” explain SKF Key Account Manager, Duncan Mngomezulu and SKF Application Engineer, Cody Petersen, who teamed up on the project. “It enables rotation of the idler wheel that guides and supports the submerged conveyor chain, while housing the bearing and sealing system: the critical interface where seals and bearings are installed to ensure smooth, reliable operation.
“It also provides the structural mounting point that transfers loads from the rotating idler into the fixed housing and maintains water sealing integrity, preventing water leakage or seizure through the idler assembly.”
Recurring failures
Historically, the national power utility has struggled with the durability and efficiency of SSC components at some of its power generation plants due to recurring failures that typically manifest in leakages, seal breakdowns, operational stoppages and high maintenance costs. Leakage disrupts water overflow management and carries environmental consequences. Seal or bearing failures can seize the SSC, forcing unit shutdowns for repair, with expensive operational delays.
Partnering with suppliers who deliver innovative solutions is key to advancing efficiency and reliability at power plants. In line with this approach, the utility engaged SKF to provide long‑term, dependable systems that enhance operational performance while supporting environmental commitments.
Team expertise
“Within this market, demand for specialised components such as Stub Shafts for SSC systems is niche yet critical,” note Duncan and Cody, “with suppliers evaluated on their innovation, proven track record and ability to provide comprehensive support.
Following site visits and engagement with the power utility, the SKF team combined their expertise to produce an improved engineered Stub Shaft design featuring an integrated redesigned, advanced bearing and sealing arrangement that resolved historical leakage failures by ensuring zero leakage during submerged operation. The sealing system also eliminates SSC idler seizures, delivering multi‑year reliability.
Substantial gains
SKF rolled out the solution at the first power station, where the refurbished Stub Shafts have since outperformed expectations, exceeding the 18‑month service life set by the SSC Maintenance Execution Reliability‑Based Optimisation (RBO) goals. The gains for the power plants are substantial.
Proven Stub Shaft reliability minimises unscheduled downtime and disruptions, ensures smooth outage‑to‑outage operation, extends lifecycles, curtails maintenance costs, improves compliance and enhances overall efficiency and performance, ultimately lowering total cost of ownership.
Second facility
This success paved the way for adoption at a second facility, where SKF’s engineered Stub Shaft and advanced sealing solution have proven equally robust, with units at both plants operating since 2021 without a single leak or failure.
SKF’s sustainability impact is clear. By refurbishing and remanufacturing SSC Stub Shafts, the power utility replaces fewer full assemblies, reducing material consumption and extending component lifecycles. The advanced zero‑leakage sealing system prevents water contamination and stabilises SSC performance, cutting emissions linked to ash‑handling inefficiencies
