Challenge

The Exelon Nuclear, Limerick Generating Station in Limerick, PA injects sodium hypochlorite into the lower basins of two cooling towers to treat the circulating water and protect the condenser from biological fouling. For many years, the oxidizing biocide had been delivered to the cooling water systems via positive displacement chemical metering pumps, with each cooling tower served by two 4 GPM pumps.

The previous sodium hypochlorite feed system had been plagued from the onset by leaks, metering pump maintenance concerns, and poor chemical performance. “The pump and system PVC piping suffered severe fatigue and failed at mechanical joints, due primarily to the pressure/velocity pulses generated by the pumps,” says Eric George, chlorination system manager for the station. “We installed post dampeners and tried other remedies, but the problems persisted.”  Mechanical joints were replaced over time with solvent weld fittings to reduce leakage. While this resulted in less seepage at the joints, a significant rise in catastrophic piping failure occurred, resulting in sodium hypochlorite leaks requiring environmental cleanups.

Compounding the problem was the fact that the chemical feed system was undersized to adequately meet the summer demands of the power station’s cooling water system. “Occasionally, during the summer months, the pumps operated at maximum capacity simultaneously, and at times came close to falling short of the desired chlorination injection,” says George. “If one of the pumps had experienced mechanical failure during these times this would have greatly increased the likelihood of condenser fouling and loss of condenser performance when it was most critical.

In addition, sodium hypochlorite feed rates had to be manually adjusted directly at each pump, and no means of monitoring flow had been designed into the system. “But probably our biggest concern,” says George, “was the safety impact of personnel handling sodium hypochlorite under a pressurized system, cleaning up spills, disposing of the spilled chemical and repair of piping.”

Solution

The existing sodium hypochlorite feed system was replaced with four LVN-2000 Liquid Chemical Feed Systems, from USFilter’s Wallace & Tiernan Products, equipped with eductors to draw sodium hypochlorite from supply tanks to the points of application at a maximum flowrate of up to 7.7 GPM each.

• Two units have been installed to serve each tower.
• The V-Notch variable orifice of the LVN-2000 System, field-proven in thousands of installations worldwide, provides accurate, reliable chemical feed control and excellent repeatability needed for this application.

Results

“Our new system works great, and we’ve had no problems with the LVN-2000 liquid feed system. The system has allowed us to eliminate leaks, overcoming safety and environmental concerns,” says George. “We also now have better, more consistent chlorination and have been able to meet our cooling system demands under varying conditions.” The LVN-2000 system provides multifunctional touchpad controls, facilitating flow monitoring and adjustment. Unlike the positive displacement pumps, which had been a long-standing maintenance concern, George says the LVN-2000 has required virtually no maintenance. “The increased system reliability and availability has, in turn, increased condenser cleanliness, thereby increasing generation efficiency. The increased cleanliness of the main condenser provides cooler condensate, to our deep bed demineralizers and reduces the long-term sulfate exposure to our Reactor Pressure Vessel.”