Sandia LabNews

Solution to some of country's energy woes might be little more than hot air

The solution to some of the country’s energy woes might be little more than hot air.

That’s a route Sandia researchers are helping explore in an inactive limestone mine in northeastern Ohio.

A Sandia team led by Steve Bauer (6113) has been working with Houston-based Haddington Ventures and its subsidiary Norton Energy Storage LLC to determine the feasibility of using a 2,200-foot-deep inactive mine near Norton, Ohio, as the storage vessel for a compressed air energy storage (CAES) power plant.

"The intent is to cycle air pressure into the mine using compressors during off-peak electrical power times like evening and weekends to increase air pressure in the mine," Steve says. "During the daily peak needs for electricity, air pressure will be bled off through modified combustion turbines to generate electricity. The energy is stored as pressure, but the mine must hold air to store the pressure." Working pressures in the mine will range between about 1,600 and 800 psi.

Sound impossible? Not to Haddington and Norton Energy. The goal is to have the plant on line in two years. In October 1999 Norton Energy purchased the site and the limestone mine, and in July 2000 Norton Energy signed an agreement with the City of Norton to cooperate to build the plant. The appropriate permits are currently being sought through the state’s regulatory agencies. Norton Energy will build and operate the plant. On March 20, the Ohio Power Siting Board issued a staff report recommending approval of authorization to build the plant.

While the technological concept of compressed air energy storage is more than 30 years old, only two such plants exist in the world — a ten-year-old-facility in McIntosh, Ala., about 40 miles north of Mobile, and a 23-year-old plant in Germany, both in caverns created in salt deposits. The Norton mine will be the first in a limestone mine.

Sandia’s role has been to characterize the rock mechanics and air-flow properties of the limestone and overlying shale in response to pressure cycling. The characterization included

in situ and laboratory testing and analyses to assess the existing geologic, hydrologic, and rock physics data. Without clear understanding of the behavior of the rock in the pressurized state, and the behavior of fluids in the rock, regulatory and funding agencies would have been reluctant to support the project. Sandia teamed with Hydrodynamics, a consulting group, in completing the characterization.

Steve and other members of the Sandia team spent six months — November 1999 through April 2000 — in Norton studying the mine’s geology.

"Most of that time we were underground taking core samples, completing a number of

in situ measurements, and studying the physical nature of the exposed rock."

Dense rock, few fractures

The Sandia team working on the project found that the mine consisted of a very dense rock with low permeability. It was stiff and strong and had few, if any, natural fractures. The absence of open natural fractures is uncommon in rock. The flow analyses indicated that pressurized air will move less than 100 feet in 50 years away from the mine — which will have almost no effect on the air compression and decompression cycling and, more important, on the economics of the project.

"This all led to the conclusion that the mine would likely hold air at the required storage pressures and would work well as an air storage vessel for a compressed air energy storage power plant," Steve says.

The team documented its findings in a series of six technical reports, which are being used to support permitting, licensing, and operation of the facility.

The Pittsburgh Plate Glass Company operated the mine between 1943 and 1976 for the production of synthetic soda ash used in the manufacture of glass. It covers an area about 7,000 feet by 4,000 feet (643 acres) and is built in a room and pillar mine configuration — rooms separated by pillars, leaving 338 million cubic feet of space. Despite being well below the water table, the mine is virtually dry.

The power plant will be built in continuous construction units brought on line in increments of 300 megawatts as units are completed. Ultimately up to about 2,700 megawatts will be built, which will be enough generating capacity for about one million homes.

The power from the plant will not be sold directly to consumers. It will generate wholesale electric power for sale to utilities and marketing companies for use during peak energy usage times.

In addition to providing more power during peak times — and possibly helping Ohio and the surrounding region avert blackouts and brownouts — the compressed air energy storage power plant has the advantage of being environmentally friendly.

"During electric generation, some gas will be burned to super-expand the compressed air," Steve says. "When it is at its full production stage of 2,700 megawatts it will be producing the same amount of emissions as a 600-megawatt gas-powered combustion turbine power plant."

Steve says Sandia has worked with Larry Bickle, a former Sandian and now a principal of Haddington Ventures, on several efforts that helped create new markets in the energy sector, especially for gas and storage services. Success in those projects has drawn on Sandia’s unique ability to apply a wide breadth of technical capabilities to commercially viable ventures.