The Wisconsin Power and Light subsidiary of Alliant Energy (NYSE: LNT) in a Sept. 30 letter to the Wisconsin Public Service Commission outlined its current plans to deal with a plume problem out of the cooling tower at its gas-fired Riverside Energy Center.
The Riverside Energy Center is a natural gas-fired combined cycle facility located in the Town of Beloit, Rock County, Wisconsin. WPL purchased it from Calpine Corp. (NYSE: CPN), and took ownership on Jan. 1, 2013. The role that Riverside Energy Center has played in WPL’s generation fleet has increased, operating as a baseload facility with a capacity factor of 70% for the first three months of 2015, with an overall capacity factor of 55% through August. The frequent dispatch of the facility is expected to continue into the future.
“As the Riverside Energy Center’s operational profile has evolved, safety concerns regarding the cloud of water vapor, or plume, which is produced by facility’s cooling tower, have increased,” said the company. “Over the winter months, late fall, and early spring (anytime ambient temperatures are near 35 °F or below, regardless of ambient humidity levels), severe fogging conditions develop due to the relatively warm condensing moisture coming from the cooling towers.
“During most of this time period, when the wind is out of the South, Southwest, or West, and winds are above 10 to 15 miles per hour, the cooling tower plume at least partially impacts visibility in the nearby section of West Townline Road, the neighborhood to the North of Townline Road (Edgewater Estates), as well as WPL’s adjacent Southern Area operations building. In addition, there are times when the fog forms ice.
“In the last five years, significant fogging conditions have occurred many times. However, with the more frequent dispatching of the Riverside units since January 1, 2015, fogging conditions occurred roughly 74 times during the first three months of this year with the wind coming from the south or west greater than 80% of that time. The fogging still exists the remaining 20% of the time, but there is no wind, or the wind blows the plume to the south or west and therefore does not impact Townline Road, the neighbors, or Southern Area.”
WPL has been investigating various options to mitigate the plume from the existing cooling tower. Initially, this focused on building a combined cooling tower to serve both the existing Riverside Energy Center and WPL’s proposed, 650-MW Riverside Expansion, which is currently before the commission. However, due to costs and the logistics necessary to engineer, construct, and operate such a facility, this option proved to be prohibitive. Due to land constraints, a combined cooling tower would need to be located much further away from the existing cooling tower location. This would require significant piping, pump replacement/upgrades, as well as upgrades to the facility’s electrical system.
WPL issued a request for proposals to investigate what other plume mitigation options exist. WPL found three cooling tower suppliers that have potential retrofit solutions or modifications for the existing cooling towers that would reduce the current amount of fog and ice. The proposals considered included:
- The addition of heating cooling coils above the mist eliminators of the tower structure;
- Modifying the existing tower to utilize ambient and plenum air for plume abatement through the use of plastic plate and frame heat exchangers in the plenum area;
- Modifying the existing tower by installing radiator (dry) sections inside the tower (between the fill and the mist eliminators)
WPL is moving forward with a proposal from EvapTech. This proposal focuses on modifying the existing tower by installing radiator (dry) sections inside the tower (between the fill and the mist eliminators) and additional support framing, which essentially converts it to a semi-plume abated tower for winter-time operation only. The tower could be converted one cell at a time (there are ten cells) while the units are on-line. The height of the tower is not changed and, therefore, minimizes the amount of discharge head required by the circulating water pumps. This creates other benefits, most notably likely eliminating the need to replace the circulating water pumps (saving approximately $2 million) and, therefore, creating no negative impact to plant capacity or heat rate.
This is a relatively new retrofit technology, but has been installed on a few new towers of smaller size over the last two to three years. Given the relative infancy of the technology and the first retrofit application of the technology, WPL is proposing to conduct a pilot test on one of the cooling tower cells this winter. If the test cell performs as projected, WPL will submit a Certificate of Authority in 2016, seeking permission to move forward with the modification of the remaining nine cells of the cooling tower structure.
Costs for this proposal range from about $10 million to $15 million depending upon the number and size of coils required to get the desired effect, including the cost of increased structural support for the coils.