Cover Story. Gas-Fired Top Plants: Tenaska Virginia Generating Station, Scottsville, Virginia

Power, Sep 2007

face= Bold; Owner: Tenaska Virginia Partners LPface=-Bold;

face= Bold; Operator: Tenaska Operations Inc.face=-Bold;

face= Italic; Not every facility that face= Bold; POWERface=-Bold; singles out as a Top Plant has a unique design. Some, like this one, may be recognized for an excellent operations record and being a good corporate citizen. At Tenaska Virginia Generating Station, a formal program to make O&M personnel aware of best industry practices--and apply them on the job--has shortened the plant's start-up time and elevated its availability, making it much more dispatchable and profitable.face=-Italic;

face= Italic; By Dr. Robert Peltier, PEface=-Italic;

Tenaska Virginia Generating Station (TVGS) is a three-year-old, dual-fueled combined-cycle plant in Scottsville, Va. Tenaska Inc. developed the facility and formed Tenaska Virginia Partners LP to build, own, and operate it.

Rated at 885 MW, TVGS (Figure 1) has a fairly common, 3 x 1 configuration: three 175-MW GE Frame 7 combustion turbines exhaust into three Deltak heat-recovery steam generators (HRSGs) whose outputs are combined to feed a single 395-MW GE D-11 steam turbine. The combustion turbines normally fire natural gas. But for added reliability, and as part of the plant's permit application, Tenaska can also burn lower-sulfur diesel fuel. TVGS has an on-site, 2.1-million-gallon fuel oil storage tank.

Tenaska likes to begin building a plant with a long-term power-purchase contract in place. For TVGS, that agreement is with Coral Energy, a unit of Royal Dutch/Shell Group. Under the contract, TVGS converts the energy in the fuel delivered by Coral into electricity that Coral then sells on the regional wholesale market.

Gilbert Southern Corp., a subsidiary of Kiewit Corp. (www.kiewit.com), was retained to engineer, procure, and construct (EPC) the plant. Bibb and Associates Inc. (www.bibb.com), another Kiewit subsidiary, provided design, procurement, and field support to Gilbert during construction and start-up, and then handled performance testing. The project broke ground in July 2002, and the plant entered commercial operation on May 1, 2004.

face= Bold; Training pays big dividendsface=-Bold;

The results of using best operating practices at TVGS are the biggest reason POWER considers it a Top Plant of 2007. Some of the practices were developed at other plants in Tenaska's 9,346-MW operating portfolio (Figure 2); the rest were brought in from outside sources.

The company's emphasis on best practices is primarily driven by the need for plants to operate more efficiently and respond more quickly to grid dispatchers' calls for capacity in deregulated wholesale markets. But it also reflects Tenaska's realization that well-trained employees, dedicated to excellence, remain the key to any plant's success.

TVGS has proved that extraordinary results can be produced by a formal and wide-ranging training program (see box) and state-of-the-art management systems working in concert. Operations inevitably improve when operators and technicians apply in the field the best practices they have learned in the classroom.

Following are two examples that highlight the big returns TVGS has gotten from its relatively small investment in best-practices training.

face= Bold; Faster steam turbine start-up.face=-Bold; The integration and application of best practices developed by units of Tenaska Inc., Gilbert Southern Construction Group, and General Electric Product Services has reduced average steam turbine start-up times at TVGS by 25%. In addition to reducing the cost of start-up fuel, the shortening of plant start-up times makes TVGS more likely to be dispatched, benefiting Coral's bottom line.

The positive results were achieved by a formal TVGS and Tenaska corporate task force charged with accelerating steam turbine start-up. Members of the task force began by identifying the most-efficient and safest procedures for starting up and shutting down a steam turbine used across Tenaska's fleet. These best practices then were distilled into a training curriculum.

The efficiencies gained have been considerable. For example, before the training program was put in place, during steam turbine shutdowns the top priority for operators in the TVGS control room (Figure 3) was minimizing fuel usage during the next start-up, which they did by maintaining maximum design steam system temperature and pressure. Now, thanks to procedures that the operations team helped develop, they can do that and much more. Trained in the theory and practices of steam turbine start-up, the operators are knowledgeable enough to tweak the start-up sequence to improve the time from shutdown to minimum load. The 25% reduction in average steam turbine start-up time has produced significant economic benefits. The cost of fuel needed per start-up is less. Because plants that start up faster are more likely to be dispatched, the savings on fuel multiply as the number of start-ups increases, setting up a virtuous circle.

face= Bold; Real-time response using AGC.face=-Bold; Implementing best practices at TVGS also has allowed the plant to respond to calls for changes in dispatch in five minutes or less. Plant management realized that the best way to achieve this responsiveness was to develop an automatic generation control (AGC) system covering all plant load ranges and options for configuring its combined-cycle gas turbines.