Plugging mist eliminators

Centrifugal mist eliminators separate liquid dropi by centrifugal force. These can be more efficient than either wire mesh or mist eliminators, and are the least susceptible to plugging. However, they are not in common use in production operations because removal efficiencies are sensitive to small changes in flow. In addition, they require relatively large pressure drops to create the centrifugal force. 

Mist eliminator candle replacement (plugged during deactivation furnace system (DFS) rocket runs, probably due to fiberglass). Time minimized by having a spare eliminator on hand. 

The mist eliminator was clean during the entire run. The system was free of plugging and scaling and there was no increase in solids or scale deposits on the scrubber internals during Run 907-1A. 

The mist eliminator was completely clean at the end of the run, and there was no evidence of plugging or scaling within the spray tower. 

If mist eliminators are used, they must be carefully designed, specified, and supported. Plugging of mist eliminator pads is not an uncommon problem. Occasionally, a dislodged part of a mist eliminator pad is sucked into the compressor rotor or becomes lodged in downstream piping (232, 239). These potential problems should be discussed with the manufacturer. The beneficial effects and the various types of mist eliminators available are extensively described elsewhere (101, 165, 270, 431 33). 

There are other comments to be made about this type of application. The liquid spray nozzle should supply liquid to the face of the mixing elements without appreciably wetting the vessel wall. A 30° full cone nozzle is typically used. Ideally, the spray should consist of droplets in the range 1000 to 2000 p-m range. A quick review of spay nozzle literature indicates that the appropriate spray nozzle for 44 gal/min of alkaline water would operate at about 100 psi pressure drop. Multiple nozzles could be used if a lower liquid-side pressure drop is desired. Fine atomization spray nozzles should be avoided since fine spray drops are difficult to separate in downstream mist eliminator equipment. A Alter or strainer should be installed on the liquid feed to prevent plugging the feed nozzle, especially if the nozzle orifice size is small. 

Currently, site-specific tests are often conducted to estimate the consumption and effects of additives (Moser and Owens, 1991). Some significant major process variables to examine when considering use of an additive are additive concentration, pH of the absorber feed slurry, and dissolved calcium concentration (Moser et al., 1990). Other important factors to consider in additive use are pH meter maintenance and opmtion, thickener operation, absorber and mist eliminator plugging, foaming (caused by soap-like impurities) in the recirculation tanks, system water balance, and corrosion of the additive feed system (Babcock Wilcox, 1992B). 

The elimination of fine droplets of entrained slurry from the gas leaving the absorber has proven to be a difficult problem, primarily due to the tendency of the recovered liquid to deposit solid material on the mist eliminator surfaces causing plugging and inefficient operation. A number of points relevant to mist eliminator design and operation follow ... 

Plugging saturation Poor limestone udlization hifrequeat washing of the mist eliminators Low wash intensity... 

Molten salt from the reducer is next processed to convert sulfides back to carbonates for recycle to the absorber. This is accomplished in a regeneration column, which operates at about 800°F and uses a mixture of carbon dioxide and water vapor to displace hydrogen sulfide gas from the molten salt. The hydrogen sulfide-rich gas stream from this step is fed directly into a Claus type sulfur plant. Work on the process was terminated after a small demonstration unit developed mechanical problems, including plugging of a mist eliminator at the absorber outlet and corrosion in some lines carrying hot molten salt. 

Fiber-bed scrubbers are used to control aerosol emissions from chemical, plastics, asphalt, sulfuric acid, and surface coating industries. They are also used to control lubricant mist emission from rotating machinery and mists from storage tanks. Fiber-bed scrubbers are also applied downstream of other control devices to eliminate a visible plume. Despite their potential for high collection efficiency, fiber-bed scrubbers have had only limited commercial acceptance for dust collection because of their tendency to become plugged. 

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