Emission Reduction Methods Recognized for Excellence
Duke Energy Gas Transmission (DEGT) received a 2005 Natural Gas STAR Continuing Excellence Award from the United States Environmental Protection Agency (EPA). The award was presented in recognition of DEGT’s ongoing efforts to reduce methane released into the atmosphere during the course of standard natural gas transportation operations.
DEGT’s U.S. transmission and storage business first entered the Natural Gas STAR program in 2000. The voluntary partnership encourages companies across the natural gas and oil industries to adopt cost-effective technologies and practices that improve operational efficiency and reduce emissions of methane. In 2002, DEGT received a “Transmission Partner of the Year” award from EPA after only one year of eligibility.
Methane can escape to the atmosphere during pipeline venting and repair or, to a lesser extent, from valves and seals at compressor stations. DEGT uses four methods to reduce methane emissions:
Hot taps
The method resulting in the highest emission reduction for DEGT—hot taps—is used to connect a pipeline lateral to a mainline without shutting down the mainline. A connector tap is welded to the pipeline and then a hole is bored into the mainline so that gas will flow through the connector into the lateral—while it continues to flow along the mainline.
Sleeve repairs
A “sleeve” is a steel or composite wrap that is welded, bolted or otherwise attached to the pipeline. A sleeve is an acceptable alternative repair method to pipe replacement for some anomalies.
Emergency shutdowns
Annual emergency shutdown tests are conducted per Department of Transportation regulations at DEGT facilities without venting natural gas to the atmosphere. The technicians accomplish this feat by capping the blowdown vents.
Pipeline pulldowns
In some areas along DEGT’s system, more than one of the company’s pipelines can lie near one another in the same easement. In this case, DEGT temporarily connects two parallel pipelines, redirecting the natural gas from the pipeline scheduled for maintenance into an adjacent DEGT pipeline rather than venting it to atmosphere.
Using these methods, DEGT has quantified methane emission reductions of almost 7 billion cubic feet from 1993 through 2004. In 2004 alone, the avoided methane emissions resulted in estimated cost savings of $8.9 million.