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Application: Fluorosilicic Acid (FSA) Storage & Dosing for Fluoridation of Potable Water
Dioxide Pacific was engaged by a Water Authority in Victoria to design, supply and install a fluorosilicic acid storage and dosing facility. This facility is designed to dose 0.8 - 1.0 ppm into a maximum flow of 110 ML/day. The plant installation is an upgrade of an old sodium silicofluoride dosing system which was past its useful life. It was determined that storage and handling of fluorosilicic acid represented a lower OH&S risk than sodium silicofluoride.
The existing sodium silicofluoride plant was installed in two dedicated plant rooms. The first room was for bulk storage of the powder and transfer via conveyor to the dosing room. The dosing room contained a screw feeder, hopper and solution tank where sodium silicofluoride is mixed with dilution water and transported to the dosing point. The powder plant was removed and the bulk storage room converted by installing a concrete storage bund in the floor of the room to house a bulk storage tank for fluorosilicic acid. The dosing room was gutted and upgraded for installation of the chemical dosing equipment for fluorosilicic acid (FSA).
Fluorosilicic acid storage consists of a 10,000L HDPE bulk storage tank with ultrasonic level sensor, point level sensors, 250L day tank with ultrasonic level sensor, point level sensors, weigh platform with load cells and transfer pump. The concrete bund area contains both the bulk and day tanks.
Chemical is supplied by bulk tanker. The tanker is parked in a purpose built concrete tanker unloading driveway. This driveway is designed to comply with EPA Vic Bunding Guidelines and to house a significant spill of chemical should this occur during transfer.
Chemical is transferred from the bulk storage tank to the day tank using a mag drive pump. Chemical dosing is with duty and standby ProMinent Delta dosing pumps. Dosing pumps, dosing pipework and valves are installed in an HDPE dosing cabinet in the dosing room. Concrete surfaces in the bund and unloading area are coated with a chemical resistant paint.
The fluorosilicic acid dosing system is operated from a central control panel which includes an Allen Bradley Control Logix PLC and PanelView Plus touchscreen. Modifications to the site Citect SCADA were made to include the fluoride FSA dosing plant. There are many safety features built into this plant to prevent under and overdosing of FSA including the monitoring of flow from the dosing pumps using a mag flow meter and comparison of actual flow with calculated flow. The system has been built virtually metal free. All fixings, pipe clamps and strut are Fiberstrut Vinylester which are fully chemical resistant.
Fluoridated water entering and leaving the clearwater storage is monitored continuously with on-line fluoride analysers. These fluoride analysers are used for alarm purposes to shut down fluoride dosing if overdosing occurs. Fluoride residual is controlled through flow pacing within tight concentration limits specified by DHS.
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