Hoosier Energy Rural Electric Cooperative, Inc. (Hoosier Energy) is a generation and transmission utility supplying electric power and related services to 18 member distribution cooperatives that serve more than 290,000 customers in 48 central and southern Indiana counties and 11 southeastern Illinois counties. The Merom Station is a Hoosier Energy coal-fired power plant consisting of two boilers, Units 1 and 2. AECOM Process Technologies (legacy URS) conducted an upgrade to the flue gas desulfurization (FGD) systems on Units 1 and 2 to achieve a greater than 99% SO₂ removal and reduce the gas side pressure drop across the FGD systems by about 0.6 inches.

As part of the FGD system upgrade, AECOM Process Technologies installed key elements of its innovative Co-Flo™ Scrubber (patent pending) technology. These new features not only allowed for the improvement in SO₂ removal and pressure drop, but also helped control FGD chemistry. Chemistry improvements were centered on conversion from inhibited oxidation to forced oxidation, resulting in the production of gypsum and improving the overall FGD system reliability. Another of the key new features drawn from the Co-Flo technology was co-current gas and liquid flow inside the scrubbing zone of the FGD absorbers. It is this feature that allowed the new system to operate with a reduction in gas side pressure drop compared to the current arrangement.

AECOM Process Technologies developed the innovative FGD upgrade with guidance using a state-of-the-art CFD engineering study. AECOM’s in-house CFD engineering group performed flow studies to optimize flue gas distribution, gas/liquid contact and mist eliminator performance in the absorber towers, and forced oxidation performance in the reaction tanks. One of the flow challenges involved the conversion to forced oxidation chemistry. The addition of oxidation air into the reaction tank created the potential for air entrainment into the slurry pumps. With insight gained from the CFD model, AECOM Process Technologies developed a baffle configuration in the reaction tank that reduced slurry pump air entrainment to manageable levels.

The scrubber upgrade design at Merom included more than 2,000 ft of 30‑inch fiberglass reinforced plastic (FRP) recycled piping and more than 600 ft of large bore (greater than 16-inch) alloy forced oxidation air piping. The piping design required the piping to be installed inside an already congested scrubber building. To facilitate the design in this fast-track project, AECOM Process Technologies used laser scan technology to ensure all piping was installed in a timely manner with minimum interferences using the laser scan clash detection feature. All of the piping was installed on one of two units with only one minor FRP piping interference (approximately 1/4 inch) reported with diagonal bracing. The interference was corrected with a minor modification to the diagonal brace. The laser scan was also an effective tool for conducting model and design reviews to see the impacts of the new design with existing plant equipment and structures.

???An example of the new piping design (recycled piping on either side and oxidation piping in the middle) integrated into the laser scan model can be seen in the pictures on the previous page on the right.???

As part of the Merom upgrade, Hoosier Energy elected to have AECOM Process Technologies design and replace approximately 250 ft of the inlet ductwork to the scrubber. Hoosier Energy also furnished new scrubber inlet guillotine dampers and expansion joints which the AECOM Process Technologies design had to interface with.

Under this project, AECOM Process Technologies also installed limestone grinding capacity upgrades. These improvements eliminated current production limitations and reduced the daily runtime from 24 to 16 hours, thus helping reduce system operating costs. New ball mill systems were installed to replace older technology that was used for preparing the limestone for use in the FGD system.