Emission from enclosed vapor degreasers

Table 4.14 Cost Analysis for Operation of Adsorbers with Emissions from Enclosed Vapor Degreasers...

The cost of providing utilities (steam, electric power, and CTW (cooling tower water]) is considerably reduced for treatment of emissions from enclosed vapor degreasers relative to the same from lip vents of open-top vapor degreasers. 

The focus of this fourth chapter is treatment of emissions bdng ddiberately orimintentionally emitted from enclosed vapor degreasers and open-top vapor degreaseis. 

The key aim is still the same — to have no voliunes (or areas) in the workplace contain solvent at concentrations above the posted exposure limit. This is done as with emissions containing higher concentrations of solvent from enclosed vapor degreasers — cost-effective collection of contaminated air and treatment of it by an adsorption bed containing aaivated carbon. Because of the low concentration of solvent, another and different tteattnent step is wauanted. 

This simple, basic idea is tme — whatever cleaning process can be conducted in an open-top machine can be condurted in an enclosed vapor degreaser with the benefit of reduced solvent emissions. That s the usual reason enclosed machines are built — to house some cleaning process and limit the emissions of solvent from it. 

But the volume of solvent in the air vented from the apparatus of Figure 2.30 can represent a substantial volumetric emission of a solvent which may well be a FIAP (methylene chloride, trichloroethylene, perchloroethylene, and possibly in the future, n-propyl bromide). The volume of solvent-contaminated air is at least one and probably more volumes of the work chamber - probably one or more dozen cubic feet. This is because the entire volume of the airless enclosed vapor degreaser, nitrogen saturated with solvent at atmospheric pressure, is released for condensation and emission every cleaning cycle. 

All emission from the actions described in Table 2.4 must be directed to a solvent treatment system (Chapter 4). And the enclosed vapor degreaser in which this solvent is contained could be classified as an airless (if inert is used) or an airtight (if air is used) vapor degreaser. 

Emissions purged from airless enclosed vapor degreasers are relatively rich in solvent, and... 

The difference in adsorption capacity is significant. An adsorption bed which is perfectly useful to treat the vapor emissions from the lip vents of an open-top vapor degreaser may provide only short-term restricted service when used to treat vapor emissions from an enclosed vapor degreaser. This loss of bed capacity is demonstrated in the non-logarithmic Figure at below. 

That is to manage the level of solvent emissions which will be exhausted from the enclosed vapor degreaser. 

Emissions from Work Chamber of an Enclosed Vapor Degreaser ... 

For most situations with a small enclosed vapor degreaser, a dmm holding 200 to 500 pounds of pelletized activated carbon should suffice well. Treatment of air emissions from lip vents on an open-top vapor degreaser... 

In fact, the operation pays for itself on an "out-of-pocket" basis (Figure 4.60 for trichloroethylene) — treatment of the trichloroethylene emissions from an enclosed vapor degreaser does not on the net cause cash to leave the coffers of the enterprise ... 

Such comprehensive data for present consumption are not any longer collected by EPA, which does not mean that there is no improvements. It is known from literature that open systems are analyzed and modelled to reduce emissions and closed systems are popular in industrial applications. Vapor degreasing is an example of enclosed systems which permits control of solvent emissions. n-Propyl bromide is a popular new solvent used in metal cleaning. 

This emission of solvent can t be avoided unless the freeboard zone is flushed with nitrogen (as is done with enclosed machines). However, solvent emissions can be minimized by reducing the temperature of the air at the top of the freeboard zone so that more of the solvent is condensed, and retained within the degreaser. Liquid solvent can be removed from the entrained air because it is heavier than air, but vaporized solvent cannot be removed and escapes with air from the degreaser into the work area. 

---