Challenge

The Millstone Point Facility, operated by Northeast Utilities, identified multiple issues in their plant operation revolving around macrofouling problems due to large flow requirements and the intake structure orientation.

1. Inadequate travel speed for storm-induced algae loads.
2. Insufficient head capacity for storm-induced algae loads.
3. An excess corrosion rate of TWS materials.

Solution

Design changes were based on testing done in Wisconsin with several hundred pounds of Long Island Sound algae that had been shipped in. This testing led the team to make the following changes and upgrades to the plant:

• Replace the two-speed TWS capability with four-speed.
• Increase the maximum speed from 20 feet per minute to 32 feet per minute.
• Increase the motor horsepower from 7.5 to 20.
• Replace carbon steel baskets with nonmetallic baskets.
• Replace the carbon steel frame with a 3161 stainless steel frame.
• Increase head capacity from 5 feet to 10 feet of water.
• Add cathodic protection, a rear-side debris spray header for emergency and back flushing use, and screen wash blowback valves.

Results

• The new high-capacity installations have enabled the facility to stay on-line during severe storms.
• Outage time caused by traveling water screens has been reduced by over 10 days per year. This will save $7.6 million over a ten year period.
• Further savings will be realized from reduced corrosion-related failures of carbon steel components and the ability to clean the screenwash piping on-line.