Belt cleaner success at St Marys cement plant

Located along the Rogue River in Detroit, the St Marys Cement plant produces 200 to 250 short tph (181 to 226 tph) of portland cement. Front loaders transfer limestone and gypsum aggregate onto the #14 belt.

Inclined approximately 20° at the point of loading, the belt conveys cargo for 20 ft up to ground level, moves horizontally for 200 ft (61 m), then begins another long 30° incline to the top of a 50 ft tower. The conveyor discharge zone, with only enough room to fit one primary cleaning blade, offloads into a chute.

Roughly 30 000 short t (27 215 t) of raw material and clinker arrives weekly by truck and ship. The aggregate is offloaded to an outdoor storage area, where the material can become saturated when the weather is wet and cold. This causes large amounts of mud and sludge.

Operators found that polyurethane cleaner blades were unable to completely clean the belt: “the fines and mud take on the tacky consistency of toothpaste, causing it to cling to the belt along with smaller pieces of aggregate and shale,” said David Accomando, Plant Maintenance Supervisor for St Marys Detroit.

“This led to a lot of carryback spilled along the return path, where it fouled idlers and built up so high under the loading zone that it would encapsulate the tail pulley.”

Maintenance technicians periodically had to stop other essential duties and shut down the system to replace frozen return idlers and prevent further damage. After digging out the tail pulley, workers needed to clean the face, which often had abrasive buildup that could reduce the belt life. The cleaner required regular tensioning, and periodically needed to be removed, recut and shaped. In addition, 2 to 3 workers spent up to 8 hr twice a month cleaning the loading zone and the belt path using shovels and a vacuum truck.

Martin technicians concluded that the #14 conveyor would benefit from the Martin^® CleanScrape^® primary cleaner, which requires considerably less space than other primary cleaners, can be effective enough to eliminate the need for a secondary blade, and is proven to deliver as much as 4x the lifespan of urethane blades.

The flexible cleaner is installed diagonally across the discharge pulley, forming a 3D curve beneath the discharge area that conforms to the pulley’s shape. The design incorporates a matrix of tungsten carbide teeth and is tensioned lightly against the belt to prevent damage to the belt or splices. Despite extremely low contact pressure, it has been shown to remove as much as 95% of potential carryback material.

Designed for belt speeds up to 780 ft/min. (4 m/sec.) for mechanically spliced belts, pulley diameters up to 50 in. (1270 mm), and belt widths up to 96 in. (2438 mm), the CleanScrape is engineered to perform under the punishing conditions of cement applications and other bulk handling industries. The patented design requires very little maintenance. The tensioners are tightened during initial installation, and typically no further adjustment is required over the life of the blade.

As cargo with a moisture level of 10 – 15% was loaded onto the belt, dust and fines built up into a thick paste as usual – but were fully removed from the belt.

“For this application, we were very surprised by how well it worked,” Accomando said. “The return side of the belt might have a little bit of wet material still on it, but nothing even remotely close to what it used to be.”

After a full year of continuous operation, with little downtime through conditions that included cold slush and mud, as well as hot and dry dusty material, the original cleaner continues to perform consistently well. The cleaning schedule has been altered from a 2 to 3 person crew over a full shift twice per month, to just a single worker hosing down critical areas for an hour or so, once a month.

Note: this article was contributed by Martin Engineering. Edited by Jonathan Rowland.

Read the article online at: https://www.worldcement.com/the-americas/06092017/belt-cleaner-success-at-st-marys-cement-plant/