In the winter months, subzero temperatures, snowfall, and ice are common at the site of the 44-MW Station 5 hydroelectric plant on the Genesee River in Rochester, N.Y. These conditions could cause operational problems for the project’s four new spillway crest gates. To manage ice, project owner Rochester Gas & Electric (RG&E) uses a glycol heating system for the gate side seal plates and the concrete apron downstream from the gates. This type of system, often used for sidewalk and roadway heating, is more energy efficient than electric heating elements.
Choosing a heating system
The original gate configuration at the Station 5 dam consisted of two 100-foot-wide sector gates and four 50-foot-wide tainter gates, each 16 feet high. In 2002, when the Station 5 facility was 85 years old, RG&E hired Hatch Energy (formerly Acres International) of Amherst, N.Y., to perform a study of gate replacement alternatives.
During this study, Hatch Energy determined that the dam had excess spill capacity because a federal flood control dam had been installed 50 miles upstream in 1952. Operation of the upstream dam has kept river flows to a maximum of about 26,900 cubic feet per second (cfs), compared with the 72,000 cfs rated flow capacity of the original six-gated spillway. As a result, Hatch Energy recommended installing only four hydraulically operated crest gates at Station 5 and eliminating two of the old tainter gates.
Because reliable winter operation was a significant issue for Station 5, Hatch Energy recommended a heating system for the new gates. The team considered electric heating elements but instead decided to install a glycol heating system. This decision was based on the theory that a glycol system should be more reliable and economical over the life of the project than embedded electric heating elements.
The glycol heating system consists of stainless steel tubes welded to the back of the side seal plates, along with piping embedded in the concrete apron. The heating system is pre-set to commence operation when ambient air temperature drops to about 38 degrees Fahrenheit. A pump then circulates a heated 50-50 propylene glycol-water mixture through the piping at a rate of about 90 gallons per minute.
In addition to being more reliable than electric heating elements, the glycol system provides more accurate control of the amount of energy used for heating, thereby conserving energy. Each glycol pumping unit is supplied with a microprocessor-based control system and multiple heating elements. The number of elements that are activated depends on the return temperature of the glycol mixture. The microprocessor cycles the heating elements on and off as necessary to maintain the glycol mixture at the pre-set temperature. To ensure continued reliable operation should one heating unit malfunction or require servicing, Hatch Energy designed two systems that normally are operated independently to heat separate gates but have built-in redundancy by way of cross-over piping.
Another advantage of the glycol system is that maintenance typically is focused on the self-contained glycol heating units, which are located in the control house. The only external equipment is the embedded stainless steel and copper piping, which in theory will last as long as the concrete surrounding it. The entire system was pressure tested after installation and all embedded connections are welded, so no leaks should occur in the piping section.
If electric heating elements had been used instead, the tasks of troubleshooting, repair, and replacement would be costly undertakings that would require locating the failed element, breaking up concrete, replacing the failed element, and performing outdoor work to repair the spillway.
Installing the new gates
During Phase 1 of the gate replacement work, performed in 2003 and 2004, RG&E replaced the Bay 4 sector gate at Station 5 with two hydraulically operated crest gates and a new pier between the two gates.
During Phase 2, performed in 2004 and 2005, RG&E replaced the Bay 2 tainter gate with a crest gate and closed Bay 1 by removing the tainter gate and constructing a concrete plug within the spillway.
During Phase 3, performed in 2005 and 2006, RG&E replaced the Bay 5 tainter gate with a crest gate and closed Bay 6 by removing the tainter gate and constructing a concrete plug across the spillway.
The Bay 3 sector gate, the largest spill capacity gate at the facility, was upgraded in 2002 through the addition of two external stops and associated structural members. This gate was left in place because the dam safety criteria were based on the possibility that the largest gate could be out of service at the time of a flood event. With this configuration, the spillway can pass the inflow design flood even if the Bay 3 sector gate or any two of the smaller gates are out of service.
Bosch Rexroth Corp. supplied hydraulic equipment for the project, such as the operating cylinders and hydraulic power unit. Bosch Rexroth subcontracted the gate control system to MSE-Tetragenics of Butte, Mont. STS Steel of Schenectady, N.Y., provided the four crest gates. And Gerace Construction Corp. of Midland, Mich., performed the general construction work, including demolition and equipment removal, concrete and structural modifications, supply and installation of a new service bridge, installation of all electrical and mechanical systems, lighting and control upgrades, and installation of the glycol heating system. RG&E personnel performed project and construction management.
The dam and powerhouse at Station 5 are controlled and monitored remotely via a supervisory control and data acquisition (SCADA) system from MSE-Tetragenics. In addition to providing automatic control of the spill gates and generators, this system monitors operation of auxiliary systems such as the glycol heating units and site security system.
Since the first heating system was commissioned in December 2004, all have functioned as designed.
RG&E is now modifying the Bay 3 sector gate to provide glycol heating to the side seal plates, using the same heating units as the crest gates.
– By Gerold D. (Jerry) Westermann, project manager within Acres Water and Wind Power Division of Hatch Energy, 4342 Queen Street, P.O. Box 1001, Niagara Falls, Ontario L2E 6W1 Canada; (1) 905-374-0701, extension 5604; E-mail: [email protected]
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