Making the World a Safer Place
|
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
 |
THIS WET OXIDATON PILOT testing facility was used to test seven alloys to see how they would perform in
the break down of effluent waste from the U.S. Army's program to destroy chemicals used in the production of
nerve agents. |
 |
A THREE DIMENSIONAL graphic of a modular wet air oxidation system. |
 |
A WET AIR OXIDATION module being assembled at U.S. Filter Zimpro Products in Wisconsin. |
 |
WET AIR OXIDATON flow chart. N02200 will be used in all areas where pressurized, heated water comes into
contact with the process equipment. |
Nickel is enabling the United States to dispose of chemicals used to make nerve
gas
By Dean Jobb
Nickel Magazine, July 2005 -- A U.S. company has developed a process to dispose of the effluent waste from the U.S. Army's destruction of chemicals used in the production of nerve agents. The process relies on a commercially pure grade of nickel sheet and tubing.
Pennsylvania-based U.S. Filter tested seven alloys to see how they would perform in its wet air oxidation process, a proven wastewater treatment system that is being adapted to break down and destroy the compounds as an alternative to incineration.
Only N02200 and N02201 were able to withstand the highly corrosive process when exposed to the neutralized chemicals. Both grades are 99% nickel, with traces of copper, manganese, silicon, carbon and iron.
"We tested a spectrum of materials; pretty much everything failed in one case or another except for the pure nickel," says Clay Maugans, a hydrothermal research specialist with a U.S. Filter subsidiary, Zimpro Products, in Rothschild, Wisconsin, U.S.A.
As a first step, DF and QL (precursors used to make chemical weapons) are neutralized in water, rendering them useless for weapons production and, as a result, safe to transport. The neutralization will be completed as part of a U.S. Army program to fulfil commitments under an international treaty, the Chemical Weapons Convention, to dispose of chemical warfare material. The Zimpro process uses dissolved oxygen to break down the remaining organic contaminants, leaving water pure enough to be discharged.
Oxidation occurs at temperatures ranging from 150 to 320°C and at pressures from 10 to 220 bar. For Zimpro, the challenge was to find a metal that would hold up under these conditions for at least a year – the time needed to dispose of the wastes.
"Hydrothermal processing is incredibly corrosive," says Maugans. "The hotter you get it, the more corrosive it becomes. The same processes that makes the water tear apart the [chemicals’] molecules also makes the water want to tear apart the metal."
For the pilot project, samples of seven metals were inserted in a test reactor and immersed in the neutralized materials for 300 hours, at a maximum temperature of 300°C and at a pressure of 160 bar. Zimpro’s test results indicate that three grades of nickel alloy cracked, and a sample of titanium showed evidence of hydrogen embrittlement. While some mild pitting was discovered on the nickel samples, the problem turned out to be the pH of the start-up water used in the tests. "Once it was adjusted, they came through with flying colours," says Maugans.
The company chose N02200, which contains slightly more carbon than N02201 (a maximum of 0.15%, compared to the 0.02% maximum found in N02201).
A full-scale processing plant is being designed and engineered for installation at Texas Molecular LLC, a commercial treatment, storage and disposal facility in Deer Park, Texas. The nickel is being used in all areas that will be exposed to the pressurized, heated water. Tubing and heat exchangers are fashioned of solid nickel and the twin cylindrical reactors – each one roughly 1.2 metres in diameter and 15 metres tall – are lined with sheet 3.2 millimetres thick that has been explosively bonded to carbon steel. In all, Maugans estimates the plant will use 18 tonnes of N02200.
The plant is expected to be in operation by the end of 2007. Maugans says the project has demonstrated
that pure nickel can be the material of choice for high pH industrial wastewater applications. "We haven’t
traditionally used pure nickel a lot, but we’re starting to use it more."
Dean Jobb is a Halifax, Nova Scotia-based freelance writer.
PHOTOS: U.S. Filter / Zimpro Systems
Jessica Mattmiller |
