Packing, fouling

Ignore the bleed - inadequate bleed means concentration of salts, change of pH and pack fouling. 

Plugging of several spray nozzles caused packing fouling. Plugging resulted iiom relying on filter aystems that were too distant from the column and using carbon steel piping downstream of filters. 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Replace the tower packing in the still column, if fouled or powdered. 

The actual number of trays needed for a particular separation duty depends on the efficiency of the plate, and the packings if they are used. Thus, any factors that cause a decrease in tray efficiency will also change the performance of the colunm. Tray efficiencies are affected by such factors as fouling, wear and tear and corrosion, and the rates at which these occur depends on the properties of the liquids being processed. Thus the proper materials of construction must be selected for tray construction. 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

Packing attrition, corrosion, fouling or plugging, distributor condition (for wet type), functioning instrumentation... 

Direct contact heal exchangers should be considered whenever the process stream and the coolant are compatible. The equipment used is basically simple and cheap and is suitable for use with heavily fouling fluids. For liquids containing solids, spray chambers, spray columns, and plate and packed columns are used. 

Figure 9-6QQ. Nutter Snap-Grid high-capacity grid packing with good structural integrity (interlocking) and reduced fouling. Used by permission of Nutter Engineering, Harsco Corp., Bull. CSG-2.

Figure 9-6RR. Intalox Grid-type packing useful for fouling, solids and heat transfer high-strength, low-pressure drop, high capacity, better efficiency than most structured and random packing. Used by permission of Norton Chemical Process Products Corp., Bull. IG-1.

Random and structured packings are susceptible to surface fouling due to process conditions and/or the presence of oxygen as may be related to bacterial growth. Some systems will precipitate solids or crystals from solution usually due to the temperature and concentration effects. Bravo [135] discusses air-water stripping and illus-... 

Packed towers are used in some distillation operations in preference to plate towers. Usually the selection requires an understanding of the fouling characteristics of fluids of the system. These towers have been used even in polymer forming operations. However, other contacting devices can be cleaned easier. For some processes the packed tower is much more effective as well as cheaper than a tray tower. 

The liquid distributor is the most important internal structure of a packed column. The distributor strongly influences packing efficiency. It must spread the liquid uniformly, resist plugging/fouling, provide free space for gas flow, and allow operating flexibility. 

Fouling (caused by precipitation, lodgment of loose material and debris damaged packing)... 

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