Coal, O&M

Salt caverns offering high-deliverability storage to natural gas industry

Derwent, Ohio, Dec. 30, 2002 — The days when natural gas companies injected gas all summer and withdrew all winter are history, one industry member asserts.

“The load profile has changed for our natural gas clients over the last few years, and now fuel is required more erratically, rather than merely meeting peak seasonal demands,” reports Doug Law, Project Manager for Basic Systems, a consulting engineering firm that specializes in facility design and automation for the natural gas industry. He adds, “This trend is causing salt caverns to become the storage option of choice for the industry.”

Of the three main types of natural gas storage– depleted gas wells, aquifers, and salt caverns– salt cavern use is gaining momentum because it can be injected into and withdrawn from at high rates, allowing gas to be turned around and cycled several times a year to meet demand. “Salt caverns are high-deliverability, since there is little to impede the flow of the gas in or out of a cavern,” Law explains.

Storage requirements have changed for a number of reasons, but it’s due in large part to merchant power plants that wholesale power to the highest bidder coming online when the electricity price is high and going offline when the price is low. Additionally, recent trends toward natural-gas-fired electric generation have created demand for natural gas during the summer to power air conditioners.

According to Law, anyone undertaking a project involving engineering, procurement, and construction of salt cavern surface facilities can avoid potential problems that may arise by:

– Checking pipe & fittings. The pressures in salt cavern storage can be considerably higher than transmission pipeline pressure, so it requires pipe and fittings of a very heavy wall or high-yield strength/grade. High compression ratios used in storage injection result in high gas discharge temperatures, requiring derating of the pipe, fittings, and flanges. Hot gas piping must be flexible for thermal growth without overloading equipment connections and restraints.

– Finding valves with proper specifications. The high pressure-temperature ratings required for salt cavern storage facilities typically require valves with special lead times or valves that are not common stock. This affects ball valves, control valves, check valves, and relief valves.

– Deterring ultrasonic noise interference. Ultrasonic meters are now being used in gathering lines, since they’re bi-directional and work well with injection and withdrawal. However, pressure-reducing valves generate noise in the ultrasonic frequency range, which can interfere with an ultrasonic meter. This problem can be mitigated through piping geometry and location of meters relative to the control valves.

Additionally, for successful natural gas storage projects, “Only the storage projects strategically located with connection to several pipelines and the ability to access multiple gas production sources and customers will be successful, ” advises Jack Gatewood, who has seen many projects firsthand as a principal at SGR Holdings, a Houston-based company involved in the development, ownership, and operation of underground, salt cavern, natural gas storage facilities.

Basic Systems, Inc. is a consulting engineering firm headquartered in Derwent, Ohio that specializes in facility design and automation for the natural gas industry. Basic Systems is an integral part of the BSI Group of companies, which offers clients a complete solution for their engineering, construction, installation, hardware, and automation needs.