WITH the dismantlement of thousands of nuclear weapons and the demilitarization of millions of conventional munitions, the Departments of Energy and Defense face the problem of disposing of large quantities of energetic materials, including high explosives, propellants, and pyrotechnics. Some energetic materials can be recycled and reused, but others must be destroyed. Open burning, open detonation, and incineration have been the most commonly used destruction methods. Although in some cases the traditional methods are still the best, the trend today is toward alternative destruction processes.
A team at Lawrence Livermore National Laboratory, led by Ravi Upadhye, recently completed development of an environmentally friendly method for destroying these energetic materials from conventional and nuclear weapons. The process involves a crucible of molten salt in which the high explosives and propellants are reduced to carbon dioxide, nitrogen, and water. Depending upon the material being destroyed and the environmental regulations under which the user is operating, the gas by-product, or "off-gas," from the molten salt process may be sent through a cold trap or filter to remove small quantities of salt carried in the off-gas before it is released to the atmosphere. (See the photo and the diagram below.)
Livermore scientists have received two patents for their process and have two more patent applications pending. In 1995, the Northern California Section of the American Institute of Chemical Engineers named the team's molten salt destruction process their Project of the Year.

The Molten Salt Process
Energetic material waste is mixed with water to form a slurry that is introduced with air into a crucible. Inside the crucible are equal parts of sodium, potassium, and lithium carbonates. The temperature of these salts can be between 400Á and 900ÁC, but 750ÁC is the temperature of choice for destroying the wastes. The melting point of the salt is about 400ÁC.
The organic components of the waste react with oxygen in air to produce carbon dioxide, nitrogen, and steam. The inorganic components, in the form of ash, are captured in the molten salt bed as a result of wetting and dissolution. During the pyrolysis and oxidation processes, halogenated hydrocarbons in the waste generate acid gases, which are scrubbed by the alkaline carbonate component of the salt, producing carbon dioxide and the corresponding salt. (For example, hydrogen chloride produces sodium chloride, which is table salt.)
Bottles for sampling off-gas are attached to the crucible's exhaust line. After steady state has been achieved, infrared and mass spectrometers are used for real-time analysis of nitrogen oxides, carbon monoxide, nitrogen, carbon dioxide, argon, and hydrocarbons in the off-gases. As discussed above, the off-gas may be sent through a cold trap if necessary before being released to the atmosphere. Emissions from the process include no acid gases, such as hydrogen chloride or hydrogen fluoride. Furthermore, the quantities of nitrogen oxides are significantly lower than those produced during incineration.
At the end of the processing cycle, the salt can be separated into carbonates, noncarbonates, and ash. The carbonates can be recycled back to the process, and the neutral salts (such as sodium chloride) and ash are disposed of appropriately.
Livermore's latest molten salt unit has a capacity of 5 kilograms per hour (the equivalent of 60,000 pounds per year). It has a chimney-shaped, stainless steel crucible 2.2 meters tall, with a 40-centimeter nominal diameter at the top half and 20-centimeter diameter at the bottom. This design minimizes the amount of liquid salt droplets carried in the escaping off-gas. Waste is injected into the crucible through the top.
The whole assembly is placed inside an explosion-proof cell designed to contain a detonation of up to 10 kilograms of explosive. A remotely operated television monitor allows scientists to check on activity without entering the cell. All the mechanisms controlling the sample and feed sequences are operated remotely, and data are logged continuously by computer.
Upadhye noted, "Nitric oxide emissions from molten salt destruction of XM-46, a U.S. Army liquid gun propellant, were 100 times lower than those from incineration. The molten salt process also has the advantages over incineration of not having an open flame and of operating at lower temperatures. The team also compared it to a new method called supercritical water oxidation, which produced much more waste than the molten salt method. An added plus for the molten salt method is that it can be used to destroy chemical warfare agents."



From R&D to Field Use
The concept of using molten salt to destroy high explosives has been around for more than 20 years, but it took the end of the Cold War to prompt development of a usable system. In 1991, building on decades of experience with high explosives, Lawrence Livermore scientists began to do the chemical engineering necessary to take the molten salt method from theory to reality. They had at their disposal Livermore's state-of-the-art High-Explosives Applications Facility.
Livermore's initial laboratory-scale unit, with a capacity of 1 kilogram per hour (12,000 pounds per year), had a small side feeder and was used at first to destroy pure explosive powders. Then, a larger-diameter top injector was installed for feeding in real-world waste simulants such as machine shavings and sump sludge, including rust, metal parts, string, wood, sand, and floor sweepings. In every case, the waste simulants ran through the peristaltic pumps without clogging, and explosives were completely destroyed.
The 5-kilogram-per-hour unit was built in 1995 and has successfully completed a "shakedown run." In late 1996, it is scheduled to be dismantled and installed at Eglin Air Force Base in Florida for field demonstrations. Once the unit at Eglin is in full operation, it will be the first molten salt destruction system in the world that has proceeded past R&D and into field use.
Upadhye also noted, "Our process is safe, effective, and easy to use. We have built process controls and safety equipment into the system so that the unit can be operated after just minimal training." Ease of use is important because there is a huge job ahead--the Departments of Energy and Defense alone have hundreds of millions of pounds of energetic wastes to recycle or destroy.

Key Words: dismantlement, high explosives, incineration, molten salt destruction, open burning. open detonation.


For further information contact Ravi Upadhye (510) 423-1299 (upadhye1@llnl.gov).
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