FLUIDIZED BED PAINT STRIPPER
fluidized bed paint removal process is an alternative method to chemical
paint stripping and degreasing of non-aluminum and non-heat-sensitive metal
parts. The most notable pollution prevention benefit of this process is
that it produces no solvent wastes. The fluidized bed paint stripper (FBPS)
can be used for forged steel, but not aluminum or aluminum alloys.
The FBPS process removes paint or other organic coatings by heating the part too greater than 650 degrees F to cause pyrolysis and decomposition of the organic portion of the paint. The FBPS typically consists of the following four components: 1) fluidized-bed furnace or retort, 2) fluidized-bed cooling system, 3) off-gas treatment system consisting of a cyclone, afterburner and scrubber, and 4) low energy shot-blast unit. The fluidized-bed furnace or hot bed is where pyrolysis of the coatings takes place. A granular material, aluminum oxide (alumina) in most cases, is used as a heat transfer medium. Air passing through the bed keeps the media fluidized. Parts to be cleaned are lowered into the fluidized bed, which quickly heats the part and its surface coatings (paint, grease, oil, etc.) to a temperature at which organic components of the surface material
pyrolyze into carbon oxides, other gaseous combustion products, and char. The fluidized-bed cooling system or cold bed is used to cool the parts after the organics have been pyrolyzed. Carbon monoxide and volatile organic compounds (VOCs) generated during pyrolysis are burned in the afterburner. The thermal decomposition of paint leaves some carbon and inorganic char on the part. Most of the char may be removed in the fluidized bed; however, most parts require further cleaning before they can be repainted. The shot-blast unit is used to remove the inorganic coatings and char to prepare the parts for repainting.
This process removes and destroys paint and grease from non-aluminum or non-heat sensitive materials. Waste streams from this process include spent heat transfer medium, spent blast media, exhaust air from the afterburner and scrubber, water discharge from the scrubber, and dust from the cyclone separator. The heat transfer medium, blast media, and cyclone dust will contain metals from the stripped paint.
Field demonstrations of the FBPS have been performed at two Army Depots: Letterkenny, PA and Red River, TX. The findings and conclusions of these demonstration projects noted specific limitations of the FBPS process.
The Air Force does not have many rework facilities where the components are primarily steel and can be heated to the temperatures required by this process. Consequently, it will be difficult to find sufficient workload suited to this process and to justify the capital investment. It is an excellent process and it would be recommended where appropriate and after engineering approval.
Use of a fluidized
bed paint stripper will help a facility decrease the amounts of solvents
used and stored on site and therefore, decreases the possibility that
a facility will meet reporting thresholds for solvents under 40 CFR
355, 370 and EO 12856.
The FBPS process is not suitable for use with aluminum and aluminum alloy parts because these materials lose essentially all of their hardness or temper when exposed to the 700 to 800 degree F process temperatures.
|Safety and Health:||
Inhalation of lead
and zinc chromate paints can lead to irritation of the respiratory tract.
Some lead compounds are carcinogenic. Solvent-based paints can irritate
the lungs and mucous membranes. Prolonged exposure can affect respiration
and the central nervous system. Proper personal protective equipment should
cost elements of the FBPS are compared to stripping using Water Blast Plus.
The following economic analysis shows the FBPS to have a lower annual cost
than Water Blast Plus. Water Blast Plus was chosen as the comparison technique
instead of chemical stripping since it has a lower annual cost than chemical
stripping. Fluidized bed paint strippers can range from $7,000 for a small
parts stripper to $800,000 for an industrial scale stripper.
Annual Operating Cost Comparison for Paint Stripping by FBPS and Water Blast Plus
Economic Analysis Summary
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Due to the low potential application of this process within the Air Force, technical guidance for this process will not be provided by the Air Force Corrosion Program Office. Any implementation of this process will require approval of the engineering authority for specific Weapon System Managers and Equipment Item managers.
|Points of Contact:||
Segers Better Technology
No.TR-FBS-86-01 dated January 16, 1986 by Procedyne Corporation.