Hydraulics & Pneumatics January/February 2022

CASE STUDY 32 HYDRAULICS & PNEUMATICS January/February 2022 www.hpmag.co.uk The modernisation project for Osberstown STF managed by Veolia involved the upgrade from a very energy intensive thermal drying plant to advanced anaerobic digestion using their Exelys thermal hydrolysis process. The scope of supply also included a new dewatering plant with three belt presses and three sludge cake pumps to transfer the dewatered sludge into the THP feed silos. Compact, energy-efficient and flexible system for complex process The upgrade project presented an immediate challenge: how to fit the new THP and dewatering plant into the restricted space of the existing building. The compact design of Veolia’s Exelys process significantly reduced the installation space required for the THP. However, due to these space restraints, using a conventional multi-stage pumping system required to transfer 18-27% DS sludge cake through a total of 50m including vertical pipework with long-radius 90-degree bends would not be possible. The dewatered sludge handling system needed to have the operational flexibility to accommodate a fully automated 24/7 operation with one, two or all three presses in operation at the same time, discharging into either of the two existing sludge cake silos through common discharge pipework. Low energy and low discharge pressure solution for sludge cake transfer Having worked together on many projects over the years, Veolia engaged with Seepex to explore how to install a sludge cake handling system within the reduced footprint. Upon consultation, Seepex’s Smart Air Injection (SAI) was selected: a highly efficient system involving a progressive cavity pump and pneumatic dense phase conveying technology, able to transport 16-40% DS dewatered sludge with a significantly lower operating pressure requirement. Seepex supplied and commissioned three sludge cake pumps with 2.5m custom-made hoppers to suit the dimensions of the dewatered belt presses, the associated BLI pumps as well as the SAI controls. The compact SAI system offered considerable savings by allowing the new plant to be installed within the existing sludge dryer building. By using dense phase conveying, Veolia was able to lower the discharge pressure from 16-18 bar to 3-4 bar, enabling smaller cake pumps compared to the 4-stage pumps otherwise required for a conventional system. The robust SAI system requires nearly 50% lower power compared to conventional pumping with subsequent energy cost savings. SAI has proven to have Seepex SAI Technology enables Veolia’s sludge cake handling system upgrade at Osberstown STF the operational flexibility required by the process and enables the pipework to be emptied when idle, eliminating the risk of cake line blockages; it is easy to operate and extremely reliable. Seepex’s engineered solution using SAI technology and their proven cake pumping expertise have enabled Veolia to upgrade their sludge cake handling system which feeds their THP process at Osberstown STF. Alan Whitty, principal mechanical engineer at Veolia, comments: “I have worked with sludge cake pumping systems for 17 years, but I have never seen anything like the SAI installation at Osberstown – I am extremely impressed with it…I would have to say that the SAI installation has fundamentally changed how I would approach sludge cake transfer design/plant layout in future.” www.seepex.com Discharge pipework from three sludge cake pumps joining a single common pipe. ABOVE: SAI technology is an energy efficient solution for long distance pumping, proven to significantly reduce operational and total investment costs. Seepex open hopper pumps sit under the belt presses.