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ORNL pellet blaster makes paint stripping quicker, safer
OAK RIDGE, Tenn.,
March 31, 1997
Technology that may fuel tomorrow's fusion reactors can today safely and efficiently blast old paint from bridges and perform other tasks previously done with sandblasters.
The cryogenic pellet accelerator, developed at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL), shoots about 25,000 frozen carbon dioxide pellets per second at speeds up to 330 meters per second. The pellets strip paint or other contaminants from the surface, leaving nothing else to clean up, making it vastly superior to traditional methods of paint stripping.
"Conventional methods for removing paint and surface contaminants often require solvents or high-speed abrasive materials that affect the environment and can increase the amount of material to be cleaned up," said John Haines of ORNL's Fusion Energy Division. "Our pellet accelerator uses frozen pellets that strip the contaminant and then evaporate, separating the contaminant - such as paint or grease - from the cleaning media."
The high-speed centrifugal pellet accelerator was pioneered at ORNL to fuel experiments with fusion, which is the reaction that powers the sun. Refueling a fusion device is done by shooting fuel pellets (frozen hydrogen, deuterium or tritium) into the plasma at speeds of a kilometer per second or greater. ORNL has developed several types of high-speed accelerators for this purpose and quickly realized other potential uses for the centrifuge acceleration technique.
"We see the pellet accelerator having an immediate impact in the areas of defense, aerospace, environmental remediation and manufacturing," Haines said.
Centrifuge acceleration involves loading pellets onto a spinning wheel that slings them off its outer edge at high speeds. The wheel is spun using a brushless direct current motor, which provides precise control of the speed of the wheel and the speed of the pellets. This makes it possible to obtain a specific desired result, such as stripping a contaminant while leaving the base material unaffected.
While other commercially available systems use sandblasting-type equipment to accelerate dry ice pellets using compressed air, they have inherent disadvantages.
"Pneumatically accelerated pellet systems are limited in speed by viscous drag from the air stream, and they are inefficient for converting compressor power into cleaning power delivered to the surface," Haines said. "The sandblaster-type accelerator also requires a large compressor and exhaust gas-handling system for the large volume of compressed air needed to accelerate the pellets."
In contrast, the pellet blaster requires just 15 horsepower compared to 150 horsepower needed for the sandblaster-type accelerator. The frozen carbon dioxide floats on a self-generated gas bearing when placed on a smooth surface, so the pellets are accelerated with virtually no contact forces between the pellet and the accelerator. Moreover, it delivers pellets with forceful, even velocity, whereas the velocity of sandblasted pellets is limited and the pellets are unevenly dispersed.
Three companies have licensed the carbon dioxide cryoblaster: Cryogenic Applications F of Clinton; TOMCO Equipment Company of Loganville, Ga.; and Alpheus Cleaning Technologies Corp. of Rancho Cucamonga, Calif.
In addition to its uses for stripping paint and grease, the pellet blaster can be used for cleaning of ships, barges and process equipment, removal of lead paint from storage tanks and solvent-free removal of gummy, tar substances from surfaces. Haines also sees applications in the aerospace and electronics industries, where non-destructive super cleaning is essential.
Cryogenic Applications F has manufactured and sold units to the Army and National Defense Center for Environmental Excellence. Both customers are evaluating the technology's capability for reducing hazardous wastes generated during conventional cleaning.
Research that led to the pellet blaster was funded by DOE's Office of Fusion Energy Science and Warner Robins Air Logistics Center in Georgia. It was invented by Paul Fisher of the Chemical Technology Division and Cryogenic Application F's Chris Foster, a former member of the lab's Fusion Energy Division.
ORNL, one of DOE's multiprogram research facilities, is managed by Lockheed Martin Energy Research Corporation.