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ORNL Software for Salt Solutions Saves Time and Money

OAK RIDGE, Tenn., Sep. 5, 1995 — Highway maintenance crews battle icy roads by salting them. But how much salt should be sprinkled on the ice to melt it as quickly as possible? Moonis Ally of ORNL can provide the answer in a few minutes using a personal computer program he helped to write.

"If you add just the right amount of salt," Ally says, "the freezing point of the ice will be lowered as much as possible, and the ice will melt faster. But if you add too much salt, compounds called hydrates will form, raising the freezing point. The salt then becomes a burden instead of a benefit. In fact, too much salt not only wastes taxpayers' money but also can be toxic to roadside vegetation."

To develop the software, Ally, a researcher in ORNL's Chemical Technology Division, and retired consultant Jerry Braunstein developed the theory and algorithm, a step-by-step method for arriving at answers using available information; Andrea Sjoreen, a programmer in ORNL's Computing Applications Division, converted the algorithm into a computer program. The result is a labor-saving software package that rapidly and inexpensively predicts the properties of various water-based salt solutions. Called Aqueous Electrolytes (AE), the software eliminates the need for researchers to measure such properties in the laboratory-a time-consuming, laborious, and expensive process.

"In only one day," Ally says, "AE can predict the thermodynamic properties of mixtures of different salts in water that would take chemists several months or even a year to obtain in the laboratory. These properties include boiling and freezing points, density, and vapor pressure as a function of solution temperature, salt concentration, and salt composition.

"In addition, our software can predict the properties of aqueous electrolytes that have higher salt concentrations than those treated by competitive programs. Also, it can be used on difficult problems such as predicting when a salt solution will form solid crystals."

The patented software already has had several important applications at ORNL in waste treatment and energy conservation research.

For example, results obtained by the new software have confirmed that ORNL has selected the correct design for an evaporator. This device must supply enough heat to remove water from low-level liquid radioactive wastes in ORNL's eight Melton Valley storage tanks. The evaporator, which was ordered in October and will be installed in May, will further concentrate these wastes to make space for recently generated waste.

"The wastes are salt solutions, and their boiling points depend on the salt concentration," Ally says. "If a solution is 30% salt, its boiling point is higher than that of a solution that is 10% salt. Salt concentration also affects freezing points."

"Using the software, Ally also helped us determine whether the liquid wastes might freeze in the aboveground transfer lines if the evaporator is run in the winter," says Vic Fowler, a contractor with ORNL's Chemical Technology Division. "He found that the wastes will not freeze in winter, so costly heating equipment is not needed."

In another example at ORNL, a proposal was made to use a wiped film evaporator to evaporate water from some hazardous wastes containing zinc bromide that are stored in several ORNL buildings. But before making a final decision on treating the wastes, a decision was made to determine the thermodynamic properties of the waste solution.

"It would have taken too much time to get the answers in the laboratory," Ally says, "so we were asked to determine the properties of the waste solution using AE. We did it in 15 minutes. We found that boiling the wastes would require a higher temperature than the proposed evaporator could achieve. So that method was abandoned, and an alternative method was later used."

Ally also has used AE to help ORNL's Energy Division screen salt solutions in the search for the best refrigerants for absorption heaters and chillers-refrigerators under development that do not require energy-hungry compressors. Such refrigerants remove heat from the refrigerator cabinet at lower temperatures and reject it to the outside at higher temperatures. To make such machines more energy efficient, developers are trying to identify aqueous salt mixtures that have even better heat-transfer properties than the more fully understood mixtures of lithium bromide and water and of ammonia and water. Several potential salt combinations have been identified by AE for advanced absorption machines.

The development of the theory, algorithm, and the software was supported by DOE's Office of Industrial Technologies and the Technology Maturation Fund of the Office of Technology Transfer, Lockheed Martin Energy Systems.