Pump Systems Ltd was called on to participate in the upgrade of a large wastewater treatment plant in New Zealand, where existing gas mixing equipment operating on the seven 30 metre diameter digesters was to be replaced with a better, more efficient means of mixing. The answer was in a new nozzle mixing concept, developed in response to problems documented in efficiently mixing large circular tanks.
The revolutionary mixing system uses powerful jet nozzles to maintain or resuspend solids, and is engineered to take advantage of the hydraulic characteristics of circular tanks. The basics of the nozzle mixing system are a set of six fixed nozzles placed on the floor of each of the 30 metre diameter digesters, connected to a large externally mounted Vaughan Chopper Pump.
The nozzles are arranged to create a velocity that causes the contents of the tank to both revolve and rotate in rolling mixing configuration. This pattern rotates around the axis of the tank which causes a secondary mixing pattern to form in the centre of the tank. A total of eight large Vaughan H10P12 Chopper Pumps fitted with 75 kW, 4-pole speed electric motors and vee belt drives were used for this project, which consisted of seven duty pumps and one spare pump set.
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