Composite stacks save money at wastewater facility

Filament-wound, all-composite stacks, made using AOC epoxy vinyl ester, measure 96 inches in diameter and 72 ft tall and provide durability and corrosion resistance.

Camden County (N.J., USA) Municipal Authority has installed two new composite exhaust stacks designed to reduce initial and maintenance costs for the project and provide durability and corrosion resistance.

The stacks, 96 inches diameter by 72 ft tall (2.4m by 22m), were designed, built and installed by odor control specialist Bay Products (Stateline, Nev., USA). Bay Products made the stacks and odor control system components with corrosion-resistant and fire-retardant Vipel K022 bisphenol A epoxy vinyl ester from AOC (Collierville, Tenn., USA).

To meet the specification for freestanding stacks without guy lines, the Authority initially selected stacks made of steel. A thin inner liner of fiber-reinforced polymer (FRP) composite was to be added to protect the metal for corrosive exhausts. Director of design and manufacturing Jeff Jones pointed out how all-composite stacks could do the job better for less.

“We explained how composite can be engineered to be freestanding and to withstand the same forces that the steel stacks were designed for. In addition, the solid composite ensures superior corrosion resistance and a Class 1 fire rating throughout the entire structure — inside and out.”

The stacks were manufactured via filament winding. One design parameter that helped each composite stack meet the freestanding requirement was to manufacture the cylinder wall to be more than 1 inch/25.4 mm thick. Building a composite that thick can compromise laminate integrity because of excess exotherm, the heat generated when a composite resin cures into a structural solid.

“Controlled exotherm was another benefit of using the AOC material. AOC’s Eric Stuck worked with us to develop a resin formulation that keeps exotherm down until the resin was fully cured.”

The stacks were a natural extension of an odor control system designed to move 120,000 ft3 (3,400 m3) per minute of air. The system’s 100-inch/2,540-mm) diameter, filament wound composite ducting and open-molded composite covers and dampers were also made with Vipel K022 vinyl ester.

Vipel K022 resin resists the highly acidic internal operating environment of the anti-odor system where pH levels can get as low as 2. Furthermore, with minimal synergist addition, the resin meets ASTM E84 Class 1 flame spread and smoke requirements.