Pumps help flood prevention - Case Study

Published:  18 May, 2016

KSB and Ferrier Pumps Ltd recently continued their long standing partnership working on a flood prevention scheme for Renfrewshire Council. PWE reports.

The scheme involved planning and collaboration on the front end design, pump testing, supply, installation and commissioning of all the pumps and ancillary equipment. The project involved KSB supplying four variable speed submersible pumps from their axial flow Amacan pump range and one variable speed sump pump of type Amarex KRT, to the North Renfrew Flood Prevention Scheme near Glasgow. KSB also supplied the 800mm diameter pump discharge canisters which are currently installed in the Storm Pumping Station situated on the south bank of the River Clyde.

The flood prevention scheme will protect more than 300 homes and businesses in North Renfrew and comprises a 3m high embankment and a new underground pumping station at the Mill Burn at Fingal Road. The embankment, which runs westward for 1km from Ferry Road, provides a barrier against direct flooding from the Clyde. The pumping station containing KSB pumps will ensure that tidal surges on the Clyde do not cause the Mill Burn to overflow and flood local properties.

The new scheme will see an end to periodic flooding which has affected many homes and businesses in the area at least once a year. The combination of tidal surges and overflow from the burn has created flooding problems in the north end of Renfrew since the area was reclaimed from the river 300 years ago.

The pumping station provides a capacity of 5.5m3/s to provide standard protection against tidal flooding from the River Clyde and fluvial flooding from Mill Burn. The pumping station’s maximum flow rate has been specified to cover a 1 in 200 year flood event. KSB Amacan pumps were chosen for this station as their characteristics ideally suit the transfer of very high flows of water at low heads. KSB’s technically advanced pumping equipment is well-suited for flood control and the Amacan pumps ensure flood-prone areas are reliably drained.

KSB Amacan submersible pumps are typically used in land drainage applications and have a compact and slim design, but are extremely powerful. The Amacan’s slim design makes the submersible pump ideal for installation into narrow discharge canisters. Ferrier Pumps Ltd carried out the mechanical installation at the Renfrew project site and found the pumps were easy to install as the Amacan pump’s own weight ensures self-centering seating of the O-ring seals in the discharge canisters, a simple but effective design feature. The Amacan pumps come with bearing temperature monitoring, thermal motor protection and leakage sensor in the motor. They also have a low-vibration hydraulic system and a bellmouth optimised for vortex-free inflow making them an excellent choice for the Renfrew project.

Pump discharge rates have been defined as 1253l/s (at 7.8m pumping head), 1560l/s (at 3.3m pumping head) and 1375 l/s (at 6.1m pumping head) under normal conditions. The maximum design flow for the station has been defined as 5500l/s, which is based on four pumps working simultaneously and delivering 1375l/s each. The pumps selected offer the best efficiency over the required operating points. The number and speed of operational pumps is controlled by PLC system, based on the water level in the pump well. Well level is continuously monitored by an ultrasonic sensor and pump operation is determined by optimisation of efficiency. When the River Clyde levels begins to rise and the water level reaches the lower limit of the modulating band the first KSB Amacan pump will be initiated at minimum speed. If the inflow is less than the pumped outflow at minimum speed, the level in the pumping station will fall and the pump will be stopped at the defined “cut out” level.

If the inflow is greater than the minimum pump discharge rate, the level in the wet well will continue to rise after the Amacan pump starts. The sump water level will now be within the modulating band and the pump controller will modulate the speed of the pump in proportion to the level until the pump can stabilise the level at, or around the set-point level. If the duty Amacan pump operates at full speed and the level continues to rise, a second Amacan pump will be initiated ramping up from base speed until the inflow can be matched with a level within the modulating band. When there is a heavy rainfall, all four Amacan pumps can be called to run depending on the water levels in the main sump tank.

Ferrier Pumps also installed in the main sump chamber a KSB Amarex KRT submersible solids-handling centrifugal pump, specifically manufactured in abrasion resistant materials to remove storm water as well as handling a relatively high concentration of solids in the pump station. This variable speed pump is used for sump drain down following cessation of a storm event.

KSB also supplied the pump discharge canisters, which were designed at its UK Head Office in Leicestershire, and were digitally prototyped and tested using the latest 3D design software. The canisters were manufactured by Powerrun Project Management Ltd of Keighley and each 800mm diameter canister was supplied to site in 3 off individual double flanged sections with a combined weight in excess of 3000 Kgs and an overall assembled length of nearly 10 metres. The top section of each canister incorporates a DN800mm x 180-degree open ended discharge that feeds into the discharge chamber of the pump station from where the flow gravitates away from the Clyde. After fabrication the canisters were coated with a fusion bonded epoxy coating.

Before any manufacturing of products or site work began, a report covering the testing and development work was undertaken on a physical hydraulic model of the proposed North Renfrew Pumping Station and associated discharge chamber arrangement. The model was constructed to a scale of 1/7th full size and the purpose of the pumping station model study was to investigate and confirm the pumping station hydraulics, the proposed operating philosophy and the self-cleansing characteristics of the initially proposed design. The purpose of the discharge chamber was to confirm the discharge bend geometry, optimise energy dissipation and deaeration and to assess and improve outlet losses. Where required, suitable modifications were developed in each case to optimise each component of the overall arrangement to ensure acceptable operation could be maintained across the required flow and level range and with varying combinations and number of operative KSB pumps. This report proved invaluable in preventing expensive problems, at a later date, further into the project.

Ferrier Pumps Ltd, a KSB distributor in Scotland, carried out the mechanical and electrical installation for George Leslie Ltd who was the main contractor for the £3.6m project. The work was commissioned by Renfrewshire Council as part of the overall £10m flood prevention scheme for the town.

For further information please visit: www.ksb.com

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