Merrimack Power Station, owned and operated by the Public Service of New Hampshire (PSNH), sits on the west bank of the Merrimack River in Bow, N.H., USA. The facility burns 4,000 tons of coal a day as it generates enough power to satisfy the needs of a third of New Hampshire’s population.
During the process of generating electricity, the fly ash, or ash produced during the combustion of coal, contains a trace amount of mercury that is emitted into the atmosphere. To meet environmental standards, PSNH executives chose to install a wet, limestone-based flue gas desulphurization system (FGD system) to limit both mercury and sulfur dioxide emissions.
Chicago Bridge & Iron Company (CBI), a leading engineering, procurement, and construction company, built the primary processing system for the FGD system that included six carbon steel tanks located side by side and ranging between 24 and 56 feet in diameter.
Once constructed, the interior of the tanks required a special coating to ensure protection against constant exposure to abrasive and corrosive conditions.
CBI hired G.C. Zarnas, a national industrial and commercial painting contractor based in Bethlehem, P.A., to blast all six tanks and apply a Ceilcote fiberglass inlay coating to the metal. Bob Mudri, northeast superintendent with G.C. Zarnas, oversaw the project.
“The major threat to the integrity of the coating was the possibility of formation of rust bloom – corrosion that occurs immediately on steel surfaces between the blasting phase and application of the paint, during moist conditions,” said Mudri. To prevent rust formation and to properly apply and cure the coating, Mudri required the temperature of the metal to be a minimum of 50 degrees Fahrenheit (°F) and humidity levels inside the tank below 50%.
Adding to the challenge – the project was scheduled to begin in the middle of winter in northern New Hampshire, where temperatures can reach as low as negative 15°F.
Mudri contacted Polygon to design a system to control moisture and temperature during the blasting and coating process. “We’ve been using Polygon for more than 15 years for various blast and coat projects requiring heat and desiccant dehumidification,” said Mudri.
Polygon technicians delivered a 4500 CFM desiccant dehumidifier and two inline electric heaters and installed the equipment near the tanks. Polygon personnel used ductwork to connect the climate control equipment to the tanks via manways at the base of each structure. Once operational, the equipment provided a dew point differential of 17°F and steel surface temperatures of 50°F. This allowed G.C. Zarnas to blast an entire tank before coating it.
“Without the proper climate, we would have had to put a coat of paint or primer on each day to prevent rust,” said Mudri. “It would have taken much longer – possibly twice as long – because we would have to sandblast, clean, and then paint. The project was completed as planned thanks to Polygon’s assistance and a skilled and dedicated crew. Truly a team effort.”
PSNH faced weather constraints and environmental compliance issues. Our team helped develop a plan tailored to their unique and complex coating issues.
Reduced Power Consumption
With dehumidifiers that can burn natural gas or propane, the Merrimack Power Station was able to solve their problems and efficiently use power. We are leaders in the design and supply of the most energy-efficient equipment in the coatings market, allowing our clients to save up to 40% on electrical requirements.