Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 94 of 707

not be advised due to the chemical reaction that occurs when live steam is used to desorb the carbon vessels to recover the captured solvent. Note: The injection of live steam is the most common and preferred method for chlorinated and other solvents recovery in the industry when using a traditional carbon adsorption system. When one uses live steam with nPB solvent, a chemical reaction occurs that removes the stabilizers from the solvent. This destabilization could create problems with the solvent and/or equipment. With the latest carbon adsorption technology available today, it is possible to capture nPB solvent emissions without incurring problems to the carbon adsorption system, recover the solvent for re-use in the degreasing system without damage to the recovered solvent, and/or any work being processed in this solvent. This new technology is made possible by a patent-pending design that deals with a chemical and mechanical system installed on the carbon adsorption system to ensure neither the solvent nor equipment is affect- ed during the adsorb/desorb process. This process ensures the solvent that has been reclaimed through normal steam injection will be able to be reused in the original degreas- er process without chemical reaction to the solvent in the degreaser, to any other solvent it comes in contact with, any other equipment con- taining solvent (such as another degreaser or distillation unit), or actu- al products being degreased with this reclaimed solvent. HOW IT WORKS The following description explains the nature of a carbon adsorption sys- tem designed for use with nPB. ADSORPTION Solvent-laden air is directed from the exhaust source to the activated carbon bed by a blower/fan assembly. The carbon adsorbs the solvent vapor, and resid- ual purified air is exhausted through the ventilation duct. This process continues until the entire carbon bed is near saturation. (See Fig. 1.) DESORPTION At the end of the time allowed for adsorption, the unit will automatically switch the incoming air flow from the first carbon bed to a second carbon bed. This will allow incoming solvent-laden air to flow through a fresh activated carbon bed while the first bed is desorbed or stripped. The first bed is now injected with steam, which passes through the carbon bed vaporizing the adsorbed solvent. Additionally, the physical 93

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