OSMOSIS POWER
By Jeffrey Winters

Many desalination plants around the world rely on reverse osmosis membranes, which enable water molecules to separate from brine with the application of power. Forward osmosis, where water molecules transverse a semi-permeable membrane to dilute a salt solution, is easier to achieve, but it hasn’t been seen as terribly useful. What’s the point of wasting perfectly good, fresh water?

In November, however, a facility was opened in southern Norway that could put the phenomenon to good use. The Norwegian utility Statkraft cut the ribbon on a plant that uses the pressure of fresh water trying to dilute salt water to power a turbine.


This plant taps the force of fresh water.

The potential for osmotic power is substantial. Salinity gradients exist almost anywhere rivers flow into the sea. According to research conducted in the 1970s, the osmotic pressure difference between fresh water and seawater is equivalent to 240 meters of hydraulic head—greater than that of Hoover Dam. By one estimate, harnessing that phenomenon could generate as much as 2.6 terawatts of power worldwide. And unlike solar or wind power, osmotic pressure is more or less constant, meaning a power plant utilizing this force could run around the clock.

Statkraft has been studying osmotic power for more than a decade, but the plant that was dedicated at Tofte in November was the first to produce electricity. And even the power produced, about 4 kilowatts, is minuscule. The plant employs about 2,000 square meters of membrane.

One of the goals of the pilot plant is to increase the amount of pressure across the membrane that can be harnessed. By the middle of the decade, Statkraft hopes to have a full-scale osmotic power plant covering a few acres that uses 5 million square meters of membrane to generate 25 megawatts.   

SOLUTION SEARCH
By Jean Thilmany

In November, the American Institute of Mathematics developed what it calls the AIM problem lists, designed to help researchers track and add their expertise to unsolved math problems.

The nonprofit institute’s goal is to expand mathematical frontiers via research projects. It’s located in Palo Alto, Calif.

Mathematical problems can take decades, years, or even centuries to answer. And partial solutions spawn new problems along the way, according to AIM’s executive director, Brian Conrey.

“Keeping track of all the problems is difficult, even for experts,” he said. “Sometimes the solution needs an idea from another field, and it can take a long time for someone to notice the connection.

“Old problems need new ideas, and the AIM problem lists open up the world of mathematics to a broader audience,” he added.

The list of unsolved mathematical problems—accessible via the institute’s Web site, www.aimath.org—provides the problems in the context of related research. It also offers expert commentary on possible approaches to a solution and talks about how the problem applies to a specialized area of research, Conrey said. The list is also accessible at http://aimpl.org/pl/.

Problems are assigned permanent numbers and are also assigned permanent Web addresses. Though the list can be edited by anyone, an approval system is in place that includes oversight by expert editors, who provide a guarantee of scholarly integrity, Conrey said.

In this way, the problem list can grow and change, but still maintain continuity, Conrey added.

All versions of the problem lists will be permanently archived through the Harvard University IQSS Dataverse Network, said Micah Altman, senior research scientist at Harvard’s Institute for Quantitative Social Science. These records will allow historians to track developments in a way that previously has not been possible, he said.

“The record of changes to a problem list will provide a moving picture of progress in mathematics research,” Altman said.   

N.C. UTILITY TO PHASE OUT UNSCRUBBED COAL-FIRED PLANTS
By Harry Hutchinson

An energy provider has told the North Carolina Public Utilities Commission that it will stop operating coal-fired plants without SO2 controls in the state. The closures are to be complete by the end of 2017.

Progress Energy Carolinas said it will close 11 coal-fired units, many of them built in the 1950s and totaling nearly 1,500 megawatts, at four sites: the 600 MW L.V. Sutton Plant near Wilmington, the 316 MW Cape Fear Plant near Moncure, the 172 MW W.H. Weatherspoon Plant near Lumberton, and the 397 MW H.F. Lee Plant near Goldsboro.

The L.V. Sutton Plant, shown here under construction in 1950s, is due to close.

Plans to close the Lee Plant were announced in August, when Progress Energy Carolinas proposed to replace it with a 950 MW combined-cycle power plant fueled by natural gas. The company is considering other gas-fired plants, including a replacement for the Sutton Plant. The company may also convert some of the sites to burn biomass to comply with state regulations setting quotas for energy derived from renewables.

Progress Energy said the plans assume there will be an increase in environmental requirements, and it is cheaper to replace the coal-fired plants than to refit them with emission controls. The utility said it might change its plans if the regulatory outlook changes.

Lloyd Yates, president and CEO of Progress Energy Carolinas, said coal will remain in the company’s portfolio. He added, “But as environmental regulations continue to change, and as even more significant rule changes appear likely in the near future, the costs of retrofitting and operating these plants will increase dramatically. We believe this is the right decision for our customers, our state, and our company.”

The company will continue to operate three North Carolina coal-fired plants in which it has invested more than $2 billion to install emission controls. They are the 2,424 MW Roxboro Plant and the 742 MW Mayo Plant, both in Person County, and the 376 MW Asheville Plant in Buncombe County. Emissions of nitrogen oxides, sulfur dioxide, mercury, and other pollutants have been reduced significantly at those sites, the company said.

The utilities commission approved the construction of the combined-cycle plant in late October and at the same time ordered the company to provide retirement plans for the other unscrubbed coal-fired units within 60 days.

About 260 people work at the plants to be closed. Progress Energy Carolinas said it will try to place as many as possible into other jobs in the company.