One of many best practices that will be shared among participants at the upcoming Western Turbine Users annual meeting is the natural-gas blowdown system recently installed at Lincoln Electric System’s Terry Bundy Generating Station to assure a safer working environment. TBGS is a 170-MW, LM6000-powered facility that connects to a main interstate gas pipeline via a 6.5-mile, 20-in.-diam feeder.
NFPA-56, “Standard for Fire and Explosion Prevention during Cleaning and Purging of Flammable Gas Piping Systems,” required improvements in what had been generally accepted design and O&M practices for natural-gas supply systems. Action was motivated by several deadly gas-line explosions—one as the Kleen Energy Power Plant, a 2 x 1 F-class combined cycle in Connecticut, was made ready for commissioning activities. Dig deeper: NFPA-56, A game-changer?
The Bundy safety enhancement was submitted by the utility for recognition in the CCJ’s annual Best Practices Awards program. Results of the judging have not yet been made public.
At TBGS, a remotely operated isolation valve is installed on the gas line in the plant’s metering station. In the unlikely event of a natural-gas leak in the plant’s distribution piping, the isolation valve would be closed to stop gas from flowing into the plant. However, there is a significant amount of distribution pipe charged with 690-psig gas downstream of the valve. The main concern is that a gas leak within a GT enclosure would continue to charge the enclosure with gas even if the isolation valve were closed.
To reduce this potential hazard, a remotely operated blowdown system was installed just downstream of the main isolation valve. If a leak were to occur, this system would allow the control-room operator to initiate the safe release to atmosphere of gas stored in the plant’s distribution system. A 4-in.-diam vent line equipped with a plug valve was installed. A Shafer™ operator uses 120-Vac to allow stored hydraulic pressure to open the plug valve. Alternatively, plant personnel can use a hand pump to increase the hydraulic pressure for opening the valve.