The Tennessee Valley Authority (TVA) had its new John Sevier Combined Cycle plant trip off-line in August, possibly due to natural gas quality issues, the federal utility said in a Dec. 12 filing with the Federal Energy Regulatory Commission.
The TVA filing came in the form of initial comments in support of a stipulation and agreement related to Texas Eastern Transmission LP. TVA said it followed and participated in the discussion of the issues raised in this docket with great interest. TVA said that it, like most power generators, designs plant facilities based on gas quality readings provided by the serving pipeline. Sudden swings or wide swings outside the medium gas quality reading can trigger either automatic plant shutdowns (trip) or alarm warnings, depending on the type of equipment installed, it noted.
“TVA’s new John Sevier Combined Cycle (JSCC) generating plant experienced an automatic trip in August 2013,” TVA added. “An investigation of the cause for the trip is ongoing, but on that day, plant personnel noted and confirmed unusually high Wobbe readings at the plant. Natural gas had been purchased and nominated through the Transcontinental Gas Pipe Line/East Tennessee Natural Gas (ETNG) interconnect, although actual flow resulted in ETNG receiving Marcellus shale supply from Texas Eastern, which was delivered to JSCC on that day.”
TVA’s 880-MW John Sevier Combined Cycle plant in Tennessee began commercial operation in April 2012. The Wobbe index is a standard method used to indicate the interchangeability of fuel gases.
Previous gas quality tariff filings focused on the needs of end-users downstream of the Marcellus shale play, but advances in drilling technology coupled with market forces have shifted physical flows, TVA added. Some Marcellus areas produce gas with a high ethane level, causing a need to blend it with other gas to get the right quality for power production.
The current supply mix has created a back flow of shale supply on Texas Eastern into ETNG that was, presumably, never anticipated and not capable of being blended or controlled under Texas Eastern’s existing tariff. “For these reasons and concerns, TVA is supportive of Texas Eastern’s movement toward increased monitoring and vigilance over gas quality issues on its pipeline,” the federal utility said.
TVA is listed among the settling parties in this case. TVA was an active participant in the settlement discussions and told FERC that it recognizes that the settlement represents a comprehensive package of negotiated terms and concessions by all parties. “Any modification of this package would disrupt the delicate balance of interests and compromises,” it added. “Furthermore, TVA believes that the Settlement is fair and reasonable and in the public interest. Therefore, TVA supports the Settlement and urges that it be approved as filed.”
Settlement includes more vigilance on gas quality monitoring
These proceedings concern Texas Eastern’s June 28 filing to establish a second control point for the Control Zone exemption in its FERC Gas Tariff, Eighth Revised Volume No. 1.
“The Settlement provides for a complete resolution of the issues raised in the June 28 Filing,” said the settlement filed with FERC by Texas Eastern on Dec. 4. “The Settlement will lead to certainty for the parties at an earlier date. The Settlement also provides the parties with specifically tailored rights and protections that will maximize the ability to deliver gas into the Texas Eastern system while ensuring that the gas flow meets all applicable gas quality specifications. Moreover, the Settlement will benefit all parties by saving valuable time and resources through the avoidance of additional Commission proceedings and will remove the uncertainty involved in obtaining a Commission order on the merits.”
One section in this deal provides for Texas Eastern to issue an Action Alert at least three hours before the deadline for timely nominations if it anticipates that the commingled gas stream on any “Gas Day” will exceed the 12% limit on ethanes and heavier hydrocarbons (C2+) at the Berne Control Point in Ohio. The Action Alert will request voluntary assistance to increase supplies of low C2+ gas at receipt points designated by Texas Eastern.
There is a long list of parties to this settlement, including Piedmont Natural Gas, the New York State Public Service Commission, Chesapeake Energy Marketing, Exelon Corp., Consolidated Edison Co. of New York, Orange and Rockland Utilities, Duke Energy Carolinas LLC, Duke Energy Kentucky, Duke Energy Indiana, Duke Energy Progress and American Electric Power Service Corp.