Laramie River Station uses new coating technology

Preventing catastrophic failure is the No. 1 priority for power industry mechanical engineers and supervisors. Though a variety of factors can contribute to such failures and ensuing production downtime, engineers unanimously agree that corrosion is the single biggest contributor to these events. The Laramie River Station,located east of Wheatland, Wyoming,implements an aggressive facility maintenance schedule each year and now utilizes new coatings technologies to help protect new and existing assets from the devastating effects of corrosion. Laramie River Station is one of the largest consumer-operated, regional, joint power supply ventures in the U.S. and is owned by the Missouri Basin Power Project (MBPP).

Basin Electric Power Cooperative (BEPC) is one of six electric utilities that own MBPP, and it serves as Laramie River Station’s operating agent. The Laramie River facility is unique in that it delivers power to two separate electric grids: the Eastern and the Western Interconnections. The plant has three coal-based units, each rated at 550 MW, which began operating in 1980, 1981, and 1982. Electricity produced at Laramie River is sent to substations in Wyoming, Nebraska, and Colorado, where it is then delivered to MBPP participants.

Dan Hagel, Basin Electric’s on-site mechanical engineer at Laramie River, is overseeing several coating and lining projects, inspections, and major repair projects being conducted throughout the facility. Hagel’s first exposure to advanced coating technologies came in 2004 during a project to reline the plant’s 10 absorber feed tanks in the wet scrubbers on Units 1 and 2. Ceilcote, the manufacturer that had installed the original system in the tanks nearly 25 years earlier, introduced Hagel to a new generation of epoxy-based lining systems that are formulated with superior environmental and anticorrosion benefits. The 2005 to 2006 relining of these tanks went very smoothly with a coating that has a maintenance life of 20 to 25 years.
Peeling water tanks
In the spring of 2006, Laramie River’s water treatment operations team inspected several of the plant’s contact basins for damage and saw large areas of flaking in the original coal tar epoxy lining. Some flakes were the size of a hand; others were the size of a sheet of notebook paper. Hagel called the coating manufacturer to ask for a recommendation. Ceilcote’s western regional manager, Dave Brysacz, had previously worked on the absorber feed tank installation with the plant’s painting contractor of 15 years, Riley Industrial Services, so together they created a comprehensive maintenance plan to recoat and line the contact basin interiors.

“Using new coating technologies to prevent corrosion-related power failures makes sense,” said Hagel. “If we can extend the maintenance life-cycle of our assets and achieve greater safety and money-saving benefits in the process, then these technologies will have a longterm impact on the power industry at large.” The installation project will include a total of nine contact basins: six primary and three secondary basins. The primary contact basins used in the plant’s water treatment process combine lime and other chemicals with the lake water and groundwater to help reduce excess calcium and silica in the water (Figure 3). This treated water is then discharged into the secondary basins, where CO2 is added for pH control before it is transferred into storage tanks.

Stored water is then pumped through a reverse osmosis system and into the demineralizer system before being fed to the plant’s three boilers and to the six cooling towers serving all three units. In order to avoid unnecessary production downtime during the peak summer operating season, only two contact basins would be recoated and lined per year: one during the months of Januarythrough March and the other in October through December. The primary basins measure 85 feet in diameter; secondary basins are 100 feet in diameter. The sidewalls and floor of each basin are constructed from reinforced concrete, while the internal structure is made of carbon steel. Each contact basin is covered with a dome fabricated from aluminum (Figure).
Blast the old coatings
The first installation began on one of the primary contact basins in January 2007. Ceilcote’s technical representative, Tom Moran, met with Riley’s painting crew on-site for refresher training on the proper application of the new tank lining technology. The first step was removal of the old lining system inside the basin’s concrete interior and carbon steel interior structure. The basin’s steel interior was grit-blasted to a white metal finish, 2- to 3-mil profile. In some instances, a second grit blast treatment was needed to remove stubborn patches of the coal tar lining. Next, the reinforced concrete interior received one coat of Ceilcote

Winter snow coats the outside of the secondary contact basins. This is a view of the top portion of the concrete sidewalls and aluminum dome

This is the interior of the contact basin after grit blasting. The aluminum dome top attaches to concrete sidewalls

680 primer, which was spray-applied and back-rolled to penetrate, strengthen, and seal the concrete. Painters then troweled on one layer of Ceilpatch 610 to fill in pinholes and smooth out any remaining rough spots. Damaged areas of the concrete, in excess of a quarter-inch deep in some areas, were repaired with Corocrete 400 MP. The internal steel structure was sprayed with a coat of Ceilcote 680 primer, one layer of Ceilgard 664 as a base coat, and a second coat of Ceilgard 664 as a top coat. This solvent-free, moisture-tolerantepoxy coating with flake reinforcement offers superior permeation resistance and corrosion protection to steel and create

This is a view of the reaction well structure’s recoated interior and a portion of beam framework that supports the turbine and rake drive after the recoating process was completed. Dust on the framework is from grit blasting the concrete floor after the scaffolding was removed.

In this interior view of a contact basin after relining and recoating was completed and the basin was back in service, the foreground shows milky water in a reaction well where the lime slurry, sodium aluminate, and other chemicals are mixed.

crete structures in highly corrosive environments (Figure). Finally, one layer of Ceilcote 68 fiberglass-reinforced epoxy lining was handtroweled as a base coat for the concrete. This was immediately followed by application of a 1.5 oz. fiberglass mat, which was saturated in via an application of Lining 68BC Resin. The fiberglass mat,in combination with the permanently tough resin, gives this unique moisturetolerant lining system the excellent crack-bridging capability and tensile strength required for optimal concrete protection. This step was followed by rolling one layer of Ceilcote 664 as a top coat and the application of EJ3 or EJ4 in the expansion joints in the concrete floor (Figure).
Labor-intensive process
In all, Riley’s crew of 8 to 10 painters worked 10-hour days, six days per week for nearly three months to complete the surface preparation work and installation of the coating and lining system on one contact basin. Crews will use approximately 2,000 gallons of coatings per basin to achieve an overall film thickness of 120 mils. It is anticipated that completion of the nine contact basins will occur in December 2011.