Paul Cyr, James Price and Andrew Feimster
November 14, 2012 | 2 Comments
Innovative engineering and design is turning a 30-year-old flood storage dam into a hydroelectric power producer at Jordan Dam.
The 4.4-MW Jordan Hydroelectric Project, installed on the discharge tower of a U.S. Army Corps of Engineers flood storage dam, is truly the first of its kind. The project involves the installation of two conventional vertical Kaplan turbine-generators located on the upstream side of the discharge tower.
Each turbine-generator is installed in an enclosure that seals (like a headgate) to the upstream side of the tower's intake. While the two turbines have a total discharge capacity of 1,100 cubic feet per second (cfs), the hydroelectric project controls flow releases of up to 3,100 cfs through project equipment. Above 3,100 cfs, the units are raised to allow flows to pass underneath while continuing to generate power. When flows exceed the hydraulic capacity of the hydro project, the equipment is raised to restore the full discharge capacity. The project required negligible modifications to the discharge tower and does not affect the Corps' operation of the tower or control of flow releases.
The first turbine became commercially operational in January 2012 and the second in July 2012. Many design features implemented in the Jordan Hydroelectric Project could be used at other dams that contain a similar discharge tower.
Jordan Dam in Moncure, N.C., was built in 1982 and is a rock-filled structure 113 feet high and 1,200 feet long. It is owned and operated by the Corps for flood control and water quality for the Haw River downstream. The dam is typical of many flood storage dams, with flows released from a multi-gated, rectangular concrete discharge tower and returned to the river via a non-pressurized outlet conduit. Under normal pond levels, the dam creates a 15,000-acre impoundment, with a gross head of 57.5 feet at normal pool. With the impoundment at flood control level, the tower's discharge capacity is 17,000 cfs.
Since its construction, Jordan Dam has released enough water to have generated more than 500,000 MWh of electricity. The Jordan Hydroelectric Project began to harness that energy on January 20, 2012, when the first of two turbine-generators became commercially operational.
The Jordan Hydroelectric Project consists of two vertical Kaplan turbine-generators (65-inch runner), each with a capacity of 2.2 MW under a gross head of 57.5 feet and a flow of 550 cfs, for an estimated combined annual generation of 16,900 MWh. Each turbine-generator is installed in a 180-ton steel enclosure - the power module - located on the upstream side of the discharge tower, sealing off the 12-foot-wide by 30-foot-high intake opening. The modules are 12 feet square, 77 feet tall from invert to generator floor, and 120 feet tall overall. Each module contains two 3-foot-wide by 4-foot-high spillgates to discharge flow above the turbine's capacity. The vertical synchronous generators are direct-connected, 327 rpm air-cooled units located inside an enclosure about 10 feet above normal pool level.
Licensing of the project with the Federal Energy Regulatory Commission began in 1993, with a license received in 1997 and amended in 2006 for the two-unit project. Design and construction documents were submitted to the Corps for review between October 2008 and December 2009, and the 408 Permit from the Corps was received in November 2010. On-site work began immediately with the construction of a 23-kVA transmission line to connect the facility to the local utility (Progress Energy Carolinas).
The project team included the Corps as dam owner; developer Jordan Hydroelectric Limited Partnership; structural designer Kleinschmidt Associates; designer, fabricator and lead contractor North Fork Electric Inc.; consultant Diehl Engineering Co. as marine engineer for shaft analyses and bearing requirements; turbine-generator manufacturer China Huadian Engineering Corp.; and fabricator and underwater diving contractor Grainger Underwater Services.
The modules are located upstream of the discharge tower's emergency and service gates, in the maintenance bulkhead slots. Under normal operating conditions, the head differential can vary from 57.5 to 64 feet. The modules are designed to the same criteria as the Corps' service and emergency gates and are capable of withstanding the hydrostatic loading associated with a flood pool at elevation 240 feet and the tower dewatered (a 90-foot differential).
With the impoundment at flood pool level, the generators would be 6 feet underwater. Designing the modules to withstand flood pool loadings continues to provide the tower with three levels of water shutoff. The modules are also suitable as maintenance bulkheads during repairs to the tower and its emergency and service gates.
Each turbine has a hydraulic capacity of 550 cfs, and each of the modules has two spillgates each with a hydraulic capacity of 500 cfs. The total 3,100 cfs capacity of the two modules will control the flows out of Jordan Dam 86% of the time. When discharge exceeds this capacity or the impoundment reaches the uppermost grease-lubricated bearing at elevation 223 feet, the modules are raised up to 46 feet, permitting the tower's service gates to control the flow.
Based on historical flow records, it is estimated the modules will be raised five times a year for flood releases. Initial commissioning tests have shown the turbines will operate with the modules raised up to 5 feet while passing water underneath. This will extend the generation of the units up to flows of 8,000 cfs, a flow that is exceed only 5% of the time.
The 180-ton modules are fabricated of 50 ksi structural steel, hot-dipped galvanized for corrosion protection. A module is assembled in four distinct sections (turbine, flume, intake and generator). The turbine section acts as a headgate with the turbine strapped to the upstream side, sealing against the tower's 12-foot-wide by 30-foot-high intake opening.
A structural tubing cage encloses the lower part of the turbine section to guard the draft tube from damage in the event the module is lowered onto debris sitting on the tower sill. This cage also protects the draft tube from debris when flow is discharged beneath the module in the raised position. The upstream portions of the module's turbine section are enclosed by removable steel plating to prevent the wicket gate operating mechanisms from being damaged or jammed by debris. The module bears on the tower's invert only along the downstream edge seal, 4.5 inches wide, resting on the existing steel gate sill. The module's intake section is enclosed within fixed trashracks that bear on a concrete slab and forms the roof of the existing concrete grizzly racks
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