Challenge

When a makeup demineralizer is 30 years old and requires more funds and effort to maintain each year, it’s a losing battle. That was the case at a major power plant in California. In addition to a new demineralizer, the plant needed to meet new pH discharge requirements and treat two different types of feed water.

For four months of the year, the plant draws from the Colorado River, and the rest of the time receives a blend of northern California river water and town well water. Colorado River water has high conductivity, high hardness, high organics and moderate silica. The remaining water has high hardness and higher silica, but lower conductivity and lower organics.

The power company performed an economic evaluation of the technologies that could be used to treat the water, either individually, or in combination, using distillation, ion exchange, reverse osmosis, electrodialysis reversal and electrodeionization (EDI). The results indicated reverse osmosis combined with CDI® systems from Siemens Water Technologies would have the lowest operating cost.

Solution

Siemens Water Technologies built a pilot system to demonstrate the long-term reliability of CDI® technology under conditions of high organics and silica, and its ability to consistently deliver water with silica levels below 10 ppb. The system consisted of H-Series CDI® modules. After 30 months of full-scale operation, the system produced more than 80 million gallons of demineralized water with virtually no maintenance. Water usage was typically 945 gallons per 1,000 gallons of demineralized water processed, up from less than 700 gallons per 1,000 gallons with a four-bed demineralizer. The improvements also resulted in the elimination of hazardous chemicals and an untreated wastewater pH well within environmental regulations.

Results

The water treatment system continuously produced the specified treated water quality without any interruption in service. In 1999, when the plant was sold to another power company, the new company determined that a water treatment system upgrade was needed. They considered the following options:

• Replacing four of the original H-Series 40-gpm CDI® modules
• Eliminating the CDI® system altogether and replacing it with service ion exchange polishers
• Replacing the four CDI® modules with two complete 75-gpm CDI® systems that incorporated the new CDI-LX™ modules

After careful evaluation, the power company concluded the costs for all three options were comparable. They chose the CDI-LX™ systems for several reasons:

• The LX modules use a thick cell design that totally eliminates the leakage inherent with the H-Series’ thin cell design
• Unlike the H-Series and other manufacturers’ thick cell designs, the LX does not require a recirculation pump, thus reducing power consumption
• Unlike the H-Series and other thick cell designs, the LX does not require brine addition to enhance ion transport
• The LX is modular, allowing easy expansion, and also has a smaller footprint, which would allow the new system to be installed in place of the old one

The new 75-gpm CDI-LX™ systems were installed and placed into operation in November 2001, and began producing the specified water quality within minutes.