Public Service of New Hampshire

PSNH is installing "scrubber" technology at Merrimack Station, which will significantly reduce sulfur dioxide and mercury emissions.

Using wet flue gas desulfurization technology—a “scrubber” system—the Clean Air Project is expected to capture at least 80 percent of the mercury in the coal and reduce sulfur dioxide emissions by more than 90 percent. By law, the project must be operating no later than July 2013. The Clean Air Project will supplement more than $50 million in previous investments at Merrimack Station to reduce particulate emissions and nitrogen oxides.

Key Benefits for New Hampshire:

• Drastic reduction in mercury and sulfur emissions—upon completion, Merrimack will be among the cleanest coal plants in the nation
• Continues to support New England’s fuel diversity, enhancing the stability of the power supply in the region.
• Coal generation powers 45% of the nation and 6% of New England
• Will serve as a “bridge” over the next 10 to 20 years as we develop and build alternative energy sources on a much larger scale.

Key Benefits for PSNH Customers:

• PSNH believes that coal will continue to be a competitively priced fuel. Operated as regulated generation, this provides value to customers.
• Continued operation of Merrimack Station, with the new mercury and sulfur reduction technology installed, will help maintain the diversity of PSNH’s generation portfolio. That diversity helps ensure a reliable supply of energy at a reasonable price.

What is “scrubber technology”?

During a wet scrubber process, limestone is mixed with water to create a slurry, which is “rained down” on the flue gas before it enters the stack. The wet slurry absorbs the SO₂ and reacts to form gypsum. After a dewatering process, the solid gypsum can be sold to wallboard manufacturers. The mercury is removed in a new state-of-the-art waste water treatment facility.

 Please click here for a larger version of the diagram. 

Merrimack Station Facts:

• 440 MW Total Output; Unit 1 (110), Unit 2 (330), two combustion turbines (40)
• Produces 3 million MWh of low-cost power annually—enough energy for approximately 190,000 New Hampshire homes—35% PSNH's total
• More than $50 million has been invested in environmental initiatives since 1989, significantly reducing particulate emissions and nitrogen oxides (NOx)
• Merrimack Station currently meets all state and federal clean air requirements. When the scrubber is operational, the facility will meet the strict requirements of New Hampshire’s mercury reduction law and will be among the cleanest coal burning plants nationally.