Challenge
Engineers in charge of designing the water treatment system for the Rijnmond Energy Center in the Netherlands faced some challenges: raw water with high and variable amounts of total dissolved solids and total suspended solids, and periodic oil contamination; and the need for the plant to export steam to a nearby refinery.

The raw water supply for the plant comes from a canal on the tidal Maas River.  The total dissolved solids (TDS) level in the canal can fluctuate widely, depending on the season, the tides from the Rhine, and the amount of water from the North Sea that ends up in the Maas River.  The conductivity of the water ranges between 2,000 and 10,000 microsiemens per centimeter and changes between these extremes in a matter of days. 

The raw water intake is 20 meters (22 yards) from a petroleum unloading pier in the Shell Oil refinery.  Ships and barges pull in and out of the dock to support the unloading, stirring up the bottom of the river.

Solution
The Bechtel-Enka Joint Venture and Siemens Water Technologies (formerly USFilter) teamed on the project, meeting the challenges head on.  They reviewed data, performed on-site tests and listened to Rijnmond Energy Center's needs, ultimately designing a 1,288 m3/hr (5,667 gpm) water treatment system to supply clarified cooling tower water and high-purity boiler feed water at the new gas-fired plant, located 15 kilometers (9 miles) from Rotterdam.

The water treatment system includes the following technologies, supplied by Siemens:

• Bar racks, grab-style trash rake and traveling water screens
• Packaged steel clarifier systems designed to handle extremely variable waters and produce consistent, high-quality effluent.  Four of these sand-ballasted, high-rate clarifiers were coupled together to handle the substantial flow rate required (1,000 m3/hr, or 4,400 gpm) to feed the cooling tower for the 790-megawatt combined cycle power plant
• Particulate and oil-absorbing cartridge filters
• Double-pass reverse osmosis systems
• CDI-LX continuous electrodeionization systems
• Pre-coat condensate polishing system
• Chemical feed systems
• Solids dewatering systems

Results
Started up in various stages beginning in November 2003 and completed in April 2004, the water treatment system is producing exceptional quality water.  The conductivity of the RO/CDI system product water averages less than 0.07 microsiemens per centimeter; the sodium concentration is about 1 ppb, and the silica concentration is below 3 ppb.

The system's performance significantly exceeds the water quality specifications, which require conductivity of less than 0.10 microsiemens per centimeter and sodium and silica concentrations of less than 10 ppb.

The effluent from the plant, which is discharged back into the canal, is considerably cleaner than the water coming in.

The power plant exports steam to a nearby refinery.  The treatment system is able to meet normal plant water needs for the majority of the year, then ramps up production for steam host mode.  The system is designed to operate as two independent high-purity trains, with one train in standby until needed.