WCW24

PUMP SELECTION AT THE WINNIPEG PERIMETER ROAD PUMP STATION
The Perimeter Road Pump Station (PRPS) acts as the headworks for the West End Water Pollution Control Centre (WEWPCC), conveying wastewater from western Winnipeg to the influent screen channel at the plant. The PRPS has four different pumps in parallel, each with a unique suction and discharge piping arrangement. The PRPS also uses a branching force main system, with two force mains of different sizes and different lengths which separate from each other at the PRPS and rejoin in the WEWPCC just upstream of the discharge into the screen channel. The force mains and pipe network have changed since construction, but the pumps are mostly original, meaning they no longer operate in their original design conditions, and they require a specialized control strategy to keep pumps maximally operating in their allowable ranges.
The pumping system is also subject to a large set of operational constraints. Neither the PRPS or the WEWPCC are supplied with potable water services. The process water at the WEWPCC is supplied by the incoming wastewater from the PRPS. Therefore at least one pump at the PRPS is required to be running at any given time. The wet well is also relatively small for the flows to the station so the pumping system is required to precisely match their discharge rate to the incoming flow. The incoming flows vary widely, therefore, the pumps are required to cover a very wide range of flows by varying their speed.
Therefore, pumps with large and specific allowable operating regions were required. The smaller of the two pumps was required to meet the minimum measured dry weather flow during nighttime operation. The larger of the two pumps was required to achieve a maximum of almost 8 times the minimum flow. Finally, the two pumps were required to have ranges significantly overlapping each other and the ranges of the other two dissimilar pumps in order to smoothly stage one pump to the next in many possibly scenarios.
Finally, valuable operator insight into historic performance demanded additional constraints on the pump speed and impeller free channel size. Meeting all of these constraints simultaneously required many hours of precise hydraulic modelling and coordination with many pump vendors in order to identify a set of two ideal pumps.
Precise modelling of a relatively complex system was required. Two complementary models – one in Bentley WaterCAD, and the other an internally-designed program based on the Darcy Weisbach formula – were created. These models were calibrated with the help of City operators, and were then used to complement each other in the precise prediction of pump performance in a wide array of possible combinations of running pumps, pump speeds, and open force mains, and thereby develop a control strategy complementing the four pumps in the station.