Lime dosing gets upgrade solution

At North West Water's Cumwhinton wastewater treatment works near Carlisle, operators were experiencing problems with a lime dosing system. They had all the common faults associated with handling hydrated lime - inconsistent flow rates and blockages in the storage silo and transfer chutes to the milk of lime mix tanks.

Contractors IIES (Northern) Project Engineering called in Portasilo Technical Services to find a solution and upgrade the existing silo. At the heart of Portasilo's answer is a Rotoflo discharge valve to ensure consistent and controlled flow from the silo. Two flexible screw conveyors - one on duty, one on standby - will transfer the lime from the silo into two mix tanks. Special valves on the conveyor outlets will also eliminate any problems associated with the critical wet-dry interface.