25. Octubre 2019
Day-to-day operations of two identical belt presses operated in parallel revealed that throughput, service life, and cost-effectiveness were impeded by the screen belts from the OEM that were being used for mechanical sludge dewatering. The extremely hard, high-chloride water in Bad Salzuflen caused heavy calcification on the belt presses. The belts displayed creases, resulting in damage to the area around the seam. The Bad Salzuflen sewage plant, located 20 kilometers from Bielefeld, has a capacity of 96,000 population equivalents (PE). With a cleaning performance of four million cubic meters of wastewater, 3,800 tons of sewage sludge are produced each year. Since 2007, the sewage plant has been using the belt type supplied by the manufacturer for the two belt presses in mechanical sludge dewatering. However, their bulging rubberized seams regularly displayed increasingly large folds caused by creasing in the belts after just a few months. Holes then began to appear due to abrasion by the scrapers, meaning that the belts failed after just a short period of use. Plus, the plastic scraper blades had to be cleaned several times a day and needed to be replaced two to three times per year. The woven GKD 5090 screen belt with an extremely flat PAD-15 seam offered initial relief from this high susceptibility to errors, exhibiting significantly less creasing with comparable throughput. The sewage plant’s good experiences with this belt type prompted it to conduct extensive comparisons with two different innovative spiral fabric belt types from GKD.
Stable thanks to stretching
In the first comparative test, the woven GKD 5090 screen belts were compared with the S20-6508-370 spiral fabric belts filled with flat wire in parallel operation. In three months of operation, both belt types achieved a dry-matter content of 21-27 percent, which matched the dry-matter content of the OEM belts. However, the GKD screen belt displayed slight seam distortion. Although the spiral fabric belts filled with flat wire also exhibited slight screen distortion, this was compensated by the lack of a rigid seam. These belts further impressed with a sensational 30 percent higher throughput. In the second comparative test, this spiral fabric belt type filled with flat wire was compared with an S14-6508-460 spiral fabric belt filled with four round wires. Both belt types displayed equally good results in a direct comparison. The better dewatering performance compared with the woven belts was apparent right from the feed area. The water sank down quicker, so that the sludge was already considerably drier at the end of the feed area than with the mesh belts used previously. The belts combine transverse stability with the advantages of a seamless, movable dewatering belt. Since their installation in the Bad Salzuflen sewage plant, they have been running without any issues and deliver consistently high throughput of eleven cubic meters of sludge per hour. No more creasing has occurred and there is now no need to clean the scrapers every day or replace them several times per year, as was previously the case.