Breadcrumbs

Home > Resources and Tools > Engineer Resources > PowerConnect Newsletter > March 2015 > Study for Department of Defense Suggests that the US Natural Gas Infrastructure Could be Considered
Study for Department of Defense Suggests that the US Natural Gas Infrastructure Could be Considered Onsite Storage

Study for Department of Defense Suggests that the US Natural Gas Infrastructure Could be Considered Onsite Storage

3/17/2015

Federal, state, and local regulations, and National Fire Protection Association (NFPA) codes require backup power systems to have onsite fuel storage for safety and security purposes. Many Authorities Having Jurisdiction (AHJ), assume the onsite fuel requirement excludes the use of natural gas as the sole source of fuel for an emergency backup generator, however a 2013 study* commissioned by the Department of Defense and prepared by the Massachusetts Institute of Technology Lincoln Laboratory, disputes this claim. In fact, the study supports the premise that the country’s natural gas infrastructure could be considered onsite storage, and that it has the capability to last significantly longer than a tank of diesel fuel during an electrical grid failure.

“Initially, the study appears to fly in the face of logic as electricity is needed for natural gas production,” said John Hoeft, Generac Power Systems’ Director of Power Solutions Management. “However, once the natural gas has been extracted from the ground, the system is much less dependent on the electrical grid. Furthermore, the large number of wells combined with historically reliable transmission and distribution systems, makes natural gas a resilient fuel option for backup power.”

Overview of the U.S. Natural Gas Delivery System
There are three main components in the natural gas delivery system:

  • Gathering of gas from multiple small wells
  • Transmission of gas by long-distance pipelines
  • Distribution of gas to local customers

Natural gas is collected from multiple small wells that are powered by two main methods - gas that comes from the well (self power) and electric motors dependent on a local supply. Electric motors tend to be more common in locations that have stringent emissions requirements, such as California and Colorado (Diesel motors are also used, but that is primarily for off-shore production.)

Once the gas is extracted, it is compressed and sent to the processing plant. At the processing plant, water, natural gas liquids, CO2 and other impurities are removed. There are many gas processing plants located throughout the country to serve various regions so no one area of the country is vulnerable (see map).

Source: US Energy Information Administration

Once clean, dry gas is produced, it is compressed and sent to the transmission pipelines. These large transmission lines crisscross the country and meet at 90 intersections called hubs. This interconnectivity significantly reduces the vulnerability of the transmission lines, as others can be used should lines become inoperable (see map).

Source: US Energy Information Administration

For long-distance transmission, the gas needs to be recompressed periodically due to friction losses. The compressor stations are often powered with gas-fired engines or turbines, using the natural gas in the pipeline to self-power the transmission portion of the system. Again, there are some locations with emission restrictions so those compressors are powered by the local electrical utility.

Once the gas reaches its destination, it goes through a gate where it is metered and distributed to customers, or goes into storage for use at a later date. In the distribution phase, compressor stations are typically no longer required. Instead, gas is distributed to the end user through pressure regulators that reduce the pressure of the gas to the expected level for the consumer.

These regulators are operated by many different companies, and are controlled and monitored on the way to the customers. The equipment that is used to monitor the properties and the flow of natural gas relies on microwave communication, satellite links and/or telephone lines, to respond to changes in users’ natural gas needs. Electric power is not needed for operation of the distribution/monitoring equipment. And, should communications fail or be interrupted, natural gas distribution continues at the last recorded setpoint.

This essentially means that the natural gas network has few single points of failure that could lead to a system-wide collapse. There are a large number of wells, storage is relatively widespread, the transmission system can continue to operate at high pressure even with the failure of half of the compressors, and the distribution network can run unattended and without power.

One concern with using natural gas has been the cost of fuel and lack of price stability. However, a review of gas costs from 1998 to 2014, at one of the key natural gas hubs in Louisiana—the Henry Hub, shows the cost of natural gas has stabilized since 2009, due to the large shale deposits currently being drilled within the U.S. In addition, large end-users have the ability to negotiate long-term pricing contracts to help mitigate variation in supply and pricing.

Source: US Energy Information Administration

Study Conclusions
Based on a review of the natural gas infrastructure and using several very conservative assumptions, [link to Study Assumptions below the article] the study found that the natural gas system is robust enough to handle moderate electricity outages occurring between two weeks and three months, with minimal risk of interrupted deliveries. Compare this to a diesel powered generator that will only last about three days during an outage.

It also shows that America’s natural gas infrastructure is strong and should be considered a significant asset when energy security and reliability are factors, Hoeft said. In addition, natural gas production is less carbon-intensive and can be part of the increased resiliency power.

*Information for this article was gathered from Technical Report 1173, “Interdependence of the Electricity Generation System and the Natural Gas System and Implications for Energy Security”, prepared for the Office of the Secretary of Defense by Lincoln Laboratory, Massachusetts Institute of Technology.


More Articles