The Wisconsin Public Service Commission on May 12 approved a March 25 application from Wisconsin Power and Light (WP&L) for a Certificate of Authority to undertake the installation of new plume abatement retrofits at the existing cooling tower at the Riverside Energy Center at an estimated cost of $13,750,000.
The 600-MW facility is a natural gas-fired, combined-cycle plant consisting of two combustion turbines, two heat recovery steam generators, one steam turbine, and a ten-cell cooling tower to provide thermally-regulated water for use in power generation. The facility is located in the town of Beloit, Rock County, Wisconsin.
The installation of new plume abatement retrofits, to improve safety and visibility for vehicle drivers and the public on the adjacent roads, is necessary and appropriate, the commission said.
When Riverside generates electricity, its cooling tower emits plume. A plume is a cloud of water vapor produced when the warm, moist air from the tower fan exhaust is cooled by the ambient air. A visible plume occurs around an ambient temperature of 35°F, and becomes more dense, or thicker, as the ambient temperature drops and the relative humidity increases. During most of the late fall through early spring, the Riverside cooling tower will produce a moderate to very dense plume resulting in dense fog and potentially icy conditions.
The more electricity the facility generates, the more frequent, denser, and larger the plume becomes. The amount of electricity produced at Riverside and associated frequency and density of the plume from the cooling tower have increased significantly over the last few years. The capacity factor at Riverside has increased from 16.3% in 2011 to 73.3% in December 2015.
In addition to installing flashing warning signs to alert the public and motorists of dense fog and icy conditions on Townline Road and the surrounding area, WP&L also considered: replacing the existing cooling tower with a new plume-abated cooling tower; and retrofitting or modifying the existing cooling tower to significantly impact the formation of fog.
The option of building a new cooling tower would cost between $30 million and $35 million. It would require an extensive outage of the power plant which would require additional costs for replacement power. This alternative was rejected by WP&L because of cost and because it would require extensive outages.
Parallel path wet/dry technologies have been the common plume abatement solution on the market for many years. Outside air is pulled into separated areas where a dry section heats the air to reduce humidity and a wet section creates warm humid air. The two airflows then mix and the air is discharged with reduced humidity to avoid creating a plume when meeting cooler ambient air. However, options for retrofitting the existing towers are limited, the plume abatement technology in this area is relatively new, and none has been implemented on a cooling tower the size of Riverside.
WP&L took bids, and EvapTech proposed to modify the existing tower by installing radiator (dry) sections inside the tower (between the fill and the mist eliminators) and additional support framing which essentially coverts it to a semi-plume abated tower during winter operation. The estimated cost of EvapTech’s proposal is $10 million to $15 million. WP&L elected to move forward with the proposal from EvapTech.
The existing tower would be converted one cell at a time while the existing electric generating units are operating. The height of the tower is not changed and, therefore, minimizes the amount of discharge head required by the circulating water pumps. This eliminates the need to replace the expensive circulating water pumps and, therefore, creates no negative impact to plant capacity or heat rate.
Being a relatively new retrofit technology installed on a few new towers of smaller size over the last two to three years, WP&L conducted a pilot test on one of the cooling tower cells last winter. The test cell performed as projected and WP&L decided to move forward with the modification of the remaining nine cells of the cooling tower structure.