Environmental Science & Engineering - www.esemag.com - September 2005
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Technological innovation for sodium hypochlorite dosing

By Nicholas Valente,Marc Larivière,Valérie Lefebvre and Julie Héroux

The Pulsar HypoPump features a patent-pending design that allows pressurized process fluid to cyclically flush vapours and liquids through the pump’s discharge check system while maintaining high performance and chemical dosing accuracy.

Water disinfection is the most critical process in the treatment of water and wastewater.

The world’s most universal and time tested means of water and wastewater disinfection is chlorination. Two fundamental methods include gas chlorination (Cl₂) and liquid chlorination (NaOCl) otherwise known as sodium hypochlorite. Chlorination was introduced as a commercial water purifier in 1908. Chlorination has since been acknowledged as the optimum method for water disinfection due to its unique ability to provide residual protection throughout the water distribution system.

As a result of safety concerns with handling gas chlorine, the application of Cl₂ continues to decline while liquid chlorination and other alternative yet more recent technologies such as UV (ultraviolet light) and Ozone (O₃) continue to be more promising and a safer means of disinfecting water and wastewater. Yet of great significance, sodium hypochlorite or liquid chlorination water disinfection has been proven to be a reliable application for treating water globally for over 50 years.

Sodium hypochlorite is widely used in various processes for disinfection and bleaching. Also referred to as NaCOI, bleach, hypo, or chlorine, it is subject to degradation within the piping and pump system as it releases oxygen gas and results in crystallization of the residual.

If the oxygen gas or vapour is allowed to build up within the piping and reagent head in sufficient volume, a typical reciprocating piston metering pump, used for accurately feeding chlorine to the process, will not function properly as gas in the pump head is compressed, minimizing the discharge check valve to open upon discharge stroke of the pump. Consequently, this effect could require that the pump be reprimed for operation. Conditions that tend to increase gassing in sodium hypochlorite solutions are:

Elevated temperatures.
High concentrating solution.
Exposure to sunlight or UV rays.
Reduction in pressure.
Cavitation.
Poor piping conditions.
Contact with metallic impurities.
Contact with organic impurities.
Age of solution.
Quality of solution.

Reciprocating piston metering pumps or diaphragm metering pumps have been historically preferred in the dispensing of sodium hypochlorite because of their superior ability to accurately dose chemicals into a process stream with great precision and repeatability at a constant pressure. Additionally, the diaphragm metering pump is sealless and leak proof by design with negligible maintenance and simple commissioning.

Traditionally, the diaphragm metering pump industry has promoted the use of degas valves on the discharge port of the pump which diverts gas back to the suction supply source of the bleach. This method has been widely accepted and successful in many applications. However, the small diameter ports in the valve system tend to plug and require continuous flushing or cleaning through human intervention since the system is open to atmosphere on the discharge side of the orifice. Additionally, an external bypass piping system and degas valve assembly require additional costs and maintenance while presenting more opportunities for undesired chlorine leak paths.

New technology developed Pulsafeeder has developed a new technology that provides a simple and intuitive pressurized flushing system integral to the pump head specifically designed for metering sodium hypochlorite solutions with great accuracy and repeatability.

The automatic valve assembly consists of a pressure balanced valve which opens periodically to allow fluid from the discharge line to bypass the discharge check valve and flow back into the pump head. The valve is actuated by a solenoid controlled by a solidstate timer. The system also has a Manual Override Button to enable faster pump priming at pump startup or other situations.

The Pulsar HypoPump was explicitly designed to meter the full range of concentrations of sodium hypochlorite and its vapours associated with heat and degradation of composition. The Pulsar HypoPump features a patentpending design that allows pressurized process fluid to cyclically flush vapours and liquids through the pump’s discharge check system while maintaining high performance and chemical dosing accuracy. The design is integral to the pump head and eliminates the need for expensive, unreliable, and undesirable bypass systems, including piping, valves, fittings, and instrumentation. Most notably, this system is closed-looped and not open to atmosphere crystallization of the sodium hypochlorite.

The exclusive and distinctive design also enhances self-priming capabilities since the pump system automatically evacuates entrained air in the piping system and pump head.

The Pulsar HypoPump is designed to enhance dosing applications by maximizing run time and minimizing downtime and human intervention.

The unit is available in PVC and PVDF construction with dosing rates from 0.5 gph through 110 gph (1.9 - 416.4 lph) and pressures as high as 150 psig (10 bar) through temperatures of 150°F (65°C). Also available with manual stroke adjustment, digital microprocessor based speed and stroke control, 4-20 mA stroke control, standard and custom DC and AC variable speed control, and SCADA communication protocol technology.

The Pulsar HypoPump has been installed in a wide variety of significantly troublesome installations throughout the United States in an effort to substantiate and demonstrate its performance in actual municipal and industrial water and wastewater applications.

Nicholas Valente is with Pulsafeeder, a unit of IDEX Corporation.
Contact: www.pulsafeeder.com
Marc Larivière, Valérie Lefebvre and Julie Héroux are with John Meunier Inc.
Contact: amc@johnmeunier.com

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