fluorosilicic acid fluoride dosing skid
Fluoride

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Dioxide Pacific have many years experience in the design, manufacture, installation and commissioning of fluoride dosing systems for potable water. Fluoridation is typically accomplished with safe and accurate dosing of fluorosilicic acid, sodium fluoride or sodium silicofluoride. Fluorosilicic acid is a liquid and both sodium fluoride and sodium silicofluoride are powders.

Downflow Design for 5kg Tamper Proof Jars
Dioxide Pacific fluoride saturators are a down-flow design saturation tank suitable for 5kg jars of granular sodium fluoride, with tamper-proof seal and screw lid. The SF 5kg jar saturator tanks are available up to 1,000L which would be suitable for flow up to 3 ML/day. Sodium fluoride reaches saturation at a concentration of 4% w/w inside the tank. It is then dosed into the water supply using metering pumps. Most municipal regulations require the use of two independent flow devices in series to initiate dosing. Normally, this would be either a flow meter and flow switch or two flow meters. Overdosing protection is critical – dosing pump output is limited using the metering pump speed (stroke rate) with password protection at 100% stroke length, so that maximum fluoride dose of 1 ppm can be dosed proportional to flow.

Options Available

  • Softener for removal of hardness from the saturator makeup water.
  • High level switch interlock to close makeup water solenoid on high level in saturator tank.
  • Low level switch in saturator tank to stop the dosing pump.
  • Conductivity monitor – since sodium fluoride is saturated at 4%, the conductivity of a saturated solution will be fairly constant. When fluoride powder is depleted, conductivity will drop and this is an alarm point to prompt operators to add more powder to the tank.
  • Portable building mount – many customers prefer to have the saturator system installed in a building. The system is tested at our workshop and then delivered to site where simple power, water and dosing line connections are made. This method of delivery minimizes time required on site. Portable buildings can be steel, concrete and be cyclone rated with lightning protection.
  • Withdrawble injection lance – for dosing fluoride solution into the main.
  • Mains flow switch – for installation into the main.
  • Control panel. FRP IP65 (NEMA4X) enclosure with PLC, HMI (touchscreen) and 4G router for remote internet access.
  • Fluoride analyzer. After the dosing point, a water sample should be directed to a fluoride analyzer. This analyzer is an ISE (Ion Selective Electrode) and measures free fluoride (F-). No buffers like TISAB are required. Sample water can be collected and automatically pumped back into the main or directed to waste. Some fluoride dosing installations have two fluoride analyzers: one immediately after the dosing point to ensure the dosing system is accurate and the other after the clear water storage (CWS) to ensure water is safe for consumers.
  • Booster pump for saturator make-up. Sometimes water is only available at low pressure at the water treatment plant. We need 2 Bar for operation of the softener so a booster pump can be provided where necessary.

Brochure
Please download the Sodium Fluoride Saturator brochure to view the options available with this system. Once you have selected your preferred configuration via the ident code, you can email it to us and we will provide a quotation.

Fluorosilicic acid (H3O)2SiF6 is also called Hexafluorosilicic acid and can be referred to as FSA. It is delivered at concentration (20 +/- 0.5% w/w) via tanker. Tanker drops vary from 5,000L to 25,000L depending upon the vendor and the site requirements. The main components of an FSA dosing system are as follows:

  • Unloading driveway for tanker. This is a concrete bund driveway where the tanker can park and safely unload. The volume of the driveway is usually around 9,000L and will drain to a secure location. An unloading station includes 3 phase power for the tanker transfer pump, start/stop buttons and run/fault lights for the transfer pump, display of the bulk tank level and fault reset button. The tanker transfer hose connects to a 2 inch male camlock.
  • Bulk chemical storage tank. Usually HDPE or FRP (fiberglass). Rotomolded MDPE tanks can be used but weld and seam integrity are sometimes below par. Bulk tanks are fitted with a level transmitter (ultrasonic or radar), high and low level switches, overflow with fume trap, drain, fill point, vent with fume trap. All connections are flanged with EPDM gaskets and Fiberstrut non-metallic fasteners.
  • Day tank. Many municipal water authorities require transfer from the bulk tank to a day tank. The day tank is sized so that transfer from the bulk tank to the day tank occurs only once per day. In the worst case scenario, should overdosing of FSA occur, only the contents of the day tank can enter the water supply. The day tank is placed on load cells to monitor weight and an ultrasonic or radar transmitter to monitor volume. Weight and volume are continuously compared to ensure the correct consumption of fluoride is continuously occurring.
  • Dosing pumps. Very accurate dosing pumps in a duty/standby arrangement are mounted in an HDPE skid with load valve, pressure relief valve, mag flow meter and flushing. Dosing usually occurs into a dilution line where 25:1 dilution of the concentrated FSA occurs. The dilution line is pumped to the injection point at the main. Dosing is accurately flow paced to a flow meter in the main and a second flow signal is used in series as a flow permissive. Dosing pumps are sized so that a maximum dose of 1ppm cannot be exceeded at 100% stroke length.
  • Fluoride analyzer. FSA dosing systems usually include one or two fluoride analyzers.
  • Central control system. A control system with PLC, HMI and ethernet connection will operate the plant.
  • Chemical resistant parts. FSA is very corrosive to metal. Fiberstrut is 100% resistant to FSA and should be used for bolts, nuts, washers, channel and pipe clips. We have returned to many FSA installations after 5 and 10 years and the Fiberstrut looks new.

View a 3D presentation of a typical FSA dosing plant.

Sodium Silicofluoride is a powder, can be supplied in bulk bags (1,000 kg or 500 kg) and is generally the cheapest method of fluoridation for large flow systems. Sodium silicofluoride (SSF) is dissolved at up to 0.4% w/w into water using a by-pass as a fluoride carrier (variable concentration) or fixed concentration and flow paced.

SSF systems include the following components:

  • Bulk bag unloader. A bulk bag is placed by forklift onto a hoist and lifted up until the base of the bag is above a hopper. The bottom of the bag is clamped and joined to an intermediate hopper. At the base of the hopper is a flexible screw feeder which transfers the powder up into a larger hopper. The main hopper is designed to hold the complete contents of one or multiple bulk bags. When the bag is empty, it is sucked down and safely removed.
  • Screw Feeder. Dosing of fluoride is controlled by the accurate dosing of SSF by a screw feeder. This feeder is stainless steel and accurate +/- 0.5% over the speed range of the feeder motor.

a. Variable concentration dosing. If dilution water used as a carrier for fluoride, the feeder is flow paced to the main flow signal and the feeder output accurately calibrated so that it cannot exceed 1ppm dose. Powder is fed into a fixed dilution water flow and dissolved in a 10 minute reaction tank. This tank has a float valve for level control (always full) and a transfer pump (hose pump or PC pump) to pump the fluoride solution into the main. This method works well when flow variations in the main are slow.

b. Constant concentration dosing. Dilution water is fed at a fixed rate into a 10 minute reaction tank using level control. The feeder is flow paced to the dilution water flow and the feeder is accurately calibrated so that it cannot exceed 1ppm dose. The aim is to make constant concentration of 0.4% fluoride. A metering pump (hose pump or dosing pump) doses the fluoride solution into the main. This method works well when flow variations in the main are fast.

  • Fluoride analyzer. SSF dosing systems usually include one or two fluoride analyzers.
  • Central control system. A control system with PLC, HMI and ethernet connection will operate the plant.
  • Chemical resistant parts. Fluoride solution is very corrosive to metal. Fiberstrut is 100% resistant and should be used for bolts, nuts, washers, channel and pipe clips.

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 analyzers. These fluoride analyzers 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.

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 509.2 L/s. This is a new installation and included construction of a colourbond plant room shed.

The new fluoride dosing plant room contains separate concrete bund areas for the 10,000L bulk storage tank and 250L day tank. Fluorosilicic acid storage consists of a 10,000L HDPE bulk storage tank with ultrasonic level sensor, point level sensor, 250L day tank with ultrasonic level sensor, point level sensors, weigh platform with load cells and transfer pump.

Bulk tanker deliveries are arranged to transport chemical to regional sites in Victoria. When the tanker arrives on site, it reverses into a purpose built concrete tanker unloading driveway which is below ground level at the lowest point. 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 via 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 mounted on the plant room wall and draining into the day tank bund. Concrete surfaces in the bund and unloading driveway are coated with a chemical resistant epoxy paint.

The fluorosilicic acid dosing system is operated from a central control panel which includes an Allen Bradley SLC 5/05 PLC. The fluoride dosing system includes many safety features and interlocks 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. As always, this 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 ProMinent Dulcometer fluoride analyzers. These fluoride analysers are ion selective electrodes with high accuracy and reliability and do not require buffering with TISAB. The fluoride analyzers 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.

For more information on fluoride dosing systems or to obtain a quotation, please complete the feedback form on our Contact page.