Public Utilities Reports

PUR Guide 2012 Fully Updated Version

Available NOW!
PUR Guide

This comprehensive self-study certification course is designed to teach the novice or pro everything they need to understand and succeed in every phase of the public utilities business.

Order Now

Leaning on Line Pack

Green energy mandates might overburden gas pipelines.

Fortnightly Magazine - January 2011

to meet the intra-day gas nomination and confirmation cycle associated with quick-start resource requirements.

Reasonably straightforward operational actions, implemented across the supply chain from the wellhead to the citygate, can avert or reduce the prospect of harm to core gas customers. Pipeline operators as well as the gas suppliers behind the network of interstate pipelines might need to alter the traditional packing and drafting of the system. For example, with timely notice, suppliers can increase production at the wellhead or at gas gathering and purification facilities to inject more natural gas into the pipeline. Since gas moves through the interstate system at transport speeds no greater than 25 miles per hour, increased scheduling at the wellhead or at interconnects deep in the production center won’t bolster the requisite line pack in the market center.

Additionally, pipeline companies can increase the amount of horsepower at key compressor stations along the supply path, particularly in segments where CC plants or quick-start generation are expected to pull gas from the system to furnish ancillaries. Based on preliminary transient pipeline modeling work, one pipeline reported that under normal operating conditions on a summer design day—and, of course, subject to appropriate tariff services being implemented—the pipeline could accommodate the ramp-up and subsequent two-hour operation of up to 10 LMS100s by increasing the horsepower at major compressor stations located deep in the market area.

Pipeline companies can quickly modify the scheduling of gas at key interconnects in the market center to bolster line pack across affected route segments. Pipelines can even reverse the flow of gas across bidirectional route segments when required to increase line pack or respond to gas-side contingencies. Likewise, storage operators in the market center can step up storage withdrawals on a firm or interruptible basis, subject to tariff provisions and other operational safeguards. Regasification of LNG can be increased as well, where there is good access to LNG import terminals such as at Cove Point, Md., Suez Distrigas near Boston, Repsol Cannaport in New Brunswick, or Costa Azul, Mexico. There may be other opportunities to use peaking gas as a source of ancillary services as well.

U.S. pipelines already have a dazzling array of new services that affect how line pack is managed. Park and loan; firm and interruptible storage service, premium hourly services; and cash outs for imbalance charges are just a few of the services that form part of the solution associated with accommodating increased wind penetration. But they haven’t been tailored for quick-start units and CC plants that run afoul of rigid NAESB scheduling protocols. Streamlined coordination and communication among gas- and electric-side participants, including natural gas suppliers and storage operators, is therefore an integral part of the challenge of unleashing the power of line pack to integrate wind into the resource mix.

In the final analysis, there’s only so much line pack to go around. During cold snaps line pack is and should always be reserved for system integrity to ensure that entitlement holders’ superior requirements are met. However, the rest of the year there is a veritable gold mine