Challenge

The City of Lafayette is nestled in the rolling hills of Colorado’s Front Range in southeast Boulder County, just 18 miles north of Denver and 10 miles east of Boulder. Drinking water for the community of 24,000 is provided by the city’s 13 million gallons per day (MGD) surface water treatment plant.

In late 2000, the Lafayette plant staff decided to switch from using gaseous chlorine to sodium hypochlorite (NaOCl) as the primary disinfectant for the water treatment system. “The decision to switch to NaOCl was made after much research and careful consideration,” says Water Superintendent Mark Hartman. “Our key issues when considering a new chemical feed system were safety, maintenance and reliability.” Lafayette plant staff wanted to find an alternative to distributing NaOCl under pressure to avoid the potential for problems associated with leaks and chemical offgassing in a pressurized system. As a result, the plant staff selected a chemical feed system that utilizes vacuum induction to provide precise dosing of sodium hypochlorite.

Solution

The gaseous chlorine feed system was replaced with a LVN-2000 Liquid Chemical Feed System from Siemens Wallace & Tiernan Products, equipped with additional rotameters for seasonal plant flow rate fluctuations. The old gas system was removed with the exception of the water injector piping, which was retained and modified for the new W&T injector.

The LVN-2000 has a maximum flowrate of up to 7.7 GPM.

The V-Notch variable orifice of the LVN-2000, field-proven in thousands of installations worldwide, along with the system’s compound loop control via mag meters on both the chemical and process water lines and a residual analyzer feedback system, provide accurate, reliable chemical metering.

The result: precise, smooth feed rate adjustment over a range of 20-to-1.

Results

The design of the LVN-2000 system makes its installation much simpler than other chemical delivery systems and yielded several cost saving advantages for the Lafayette plant.

• By replacing the gas feed equipment with the LVN-2000, the plant’s existing water piping could still be used. And since plant staff elected not to use motor-driven metering pumps, no additional conduit, wiring or SCR control panels were needed.
• The plant has a small backup pump on-hand, however, due to the reliability and low maintenance requirements associated with the new system, plant staff decided not to install a backup feeder, providing further savings for the project.
• The wall-mounted LVN-2000 provides multifunctional touchpad controls, facilitating flow monitoring and adjustment, resulting in precise chemical dosage and residual control.
• The LVN-2000 system also provides a high level of safety. Because the new feed system is vacuum-induced, if there are ever any leaks in the plant’s piping, the system will pull in air rather than spill sodium hypochlorite. “We have been impressed with the performance and reliability of the LVN-2000 system,” says Hartman. “It has performed beyond our expectations.”