Dry Ice Cleaners
Dry Ice Cleaners or blasting is a form of abrasive blasting, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it.
The method is similar to other forms of abrasive blasting such as sand blasting, plastic bead blasting, or sodablasting but substitutes dry ice as the blasting medium. Dry-ice cleaning leaves no chemical residue as dry ice sublimates at room temperature.
Method
Dry-ice cleaning involves propelling pellets at extremely high speeds. The actual dry-ice pellets are quite soft, and much less dense than other media used in blasting-cleaning (i.e. sand or plastic pellets). Upon impact, the pellet sublimates almost immediately, transferring minimal kinetic energy to the surface on impact and producing minimal abrasion. The sublimation process absorbs a large volume of heat from the surface, producing shear stresses due to thermal shock.
This is assumed to improve cleaning as the top layer of dirt or contaminant is expected to transfer more heat than the underlying substrate and flake off more easily. The efficiency and effectiveness of this process depends on the thermal conductivity of the substrate and contaminant. The rapid change in state from solid to gas also causes microscopic shock waves, which are also thought to assist in removing the contaminant.
Equipment
The ice used can be in solid pellet or shaved ice block forms. The shaved ice block produces a less dense ice medium and is more delicate than the solid pellet system. Dry ice blasting generally uses one of two delivery systems to combine compressed air with ice and accelerate particles out of the delivery nozzle:
Single-hose technology
This was developed by Cold Jet, LLC in 1986, and uses a single hose to deliver air blasts and dry ice. The single hose system can use a longer hose than the double-hose counterpart without a significant drop in pressure when the ice leaves the hose. The additional power comes at the cost of increased complexity. Single-hose systems are used when the surface to be cleaned has a heavier build-up or when the surface to be cleaned is vertical or at a greater height than the hopper and gas compressor.
Two-hose dry-ice blasting
This was developed before the single-hose system. Compressed air is delivered in one hose, and ice pellets were sucked out of a second hose by the venturi effect. Compared with a single-hose system, the two-hose system delivers ice pellets with less force (approximately 5% for a given air supply) than a single-hose system. Theoretically two-hose systems have a limit to the vertical distance between the machine and applicator. This limit however is well in excess of 25 feet. Two-hose systems are generally less costly to produce due to a much simpler delivery system and they allow finer particles of ice to be delivered with lower velocity as the late combination of warm air with cold ice results in less sublimation in the hose. The latter properties allow for more delicate surfaces to be cleaned.
Uses
Dry-ice cleaning can be used to clean food processing equipment to effectively decontaminate surfaces of Salmonella enteritidis, E. coli, and Listeria monocytogenes such that these microorganisms are not detectable using conventional microbiological methods.[4] It may also be used to clean some equipment without disassembly and without producing fire or electrical hazards. The EPA recommends dry ice blasting as an alternative to many types of solvent-based cleaning. Dry ice blasting can clean numerous objects with differing, complex geometries at once. Dry-ice blasting can be used to clean many different applications including:
- Turbines and generators used in the power generation industry
- Printing presses and other paper industry related machinery
- Fire, soot and smoke damage
- Mold, spore and mildew remediation
- Plastic and rubber molding equipment including injection and extrusion molds
- Paint preparation including paint stripping
Safety
Carbon dioxide is increasingly toxic starting at concentrations above 1%, and can also displace oxygen resulting in asphyxia if equipment is not used in a ventilated area. In addition, because carbon dioxide is heavier than air, exhaust vents are required to be at or near ground level to efficiently remove the gas. At normal pressure dry ice is −78 °C (−108 °F) and must be handled with insulated gloves. Eye and ear protection are required to safely use dry ice cleaning equipment. Compared to other blasting-cleaning methods, dry ice blasting produces fewer waste products and does not require clean-up of a blasting medium.
History
The first patent regarding dry-ice technology was U.S. Patent 2,421,753, issued in 1947. The first patents regarding development and design of modern-day single-hose dry-ice blasting technology were awarded to David Moore of Cold Jet, LLC in 1986, 1988 (U.S. Patent 4,617,064 and U.S. Patent 4,744,181).