Distributor corrosion

AH columns, distributors, and ancHlary hardware such as piping, valves, and pumps must be constmcted of corrosion-resistant materials, or coated with an appropriate substance. AH streams that contact the hardware during each step of the cycHc operation need to be considered in this selection. 

Standard stainless steels have significantly greater corrosion resistance to oleum than carbon steel, but higher price may make these materials less economical, except for special services such as valves, Hquid distributors, oleum boilers, etc. 

Some units have been built and successbilly operated with simple slot-type distributors made of heat-resistant steel. This requires a heat-resistant plenum chamber but eliminates the frequently encountered problem of corrosion caused by condensation of acids and water vapor on the cold metal of the distributor. 

Proper liquid level, seal fluid contaminants, foam, vessel corrosion, distributor pluggage, functioning instrumentation... 

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

Adsorbers, distillation colunuis, and packed lowers are more complicated vessels and as a result, the potential exists for more serious hazards. These vessels are subject to tlie same potential haz. uds discussed previously in relation to leaks, corrosion, and stress. However, llicse separation columns contain a wide variety of internals or separation devices. Adsorbers or strippers usually contain packing, packing supports, liquid distributors, hold-down plates, and weirs. Depending on tlie physical and chemical properties of the fluids being passed tlirough tlie tower, potential liazards may result if incompatible materials are used for llie internals. Reactivity with llie metals used may cause undesirable reactions, which may lead to elevated temperatures and pressures and, ullinialely, to vessel rupture. Distillation columns may contain internals such as sieve trays, bubble caps, and valve plates, wliicli are also in conlacl with tlie... 

Methoxy,w-propylamine (MOPA, or 3-MPA), CHgCXCH NHj, MW = 89.1. Sp. gr. = 0.874. Flash point = 73 °F/22 °C. Flammable and corrosive liquid. Commonly available through chemical distributors. Good thermal stability. 

Ladder and spray distributors rely on pressure for their action. They provide a large gas flow area but a somewhat limited liquid flow area they are light and cheap but are sensitive to corrosion, erosion, and to a certain extent plugging. They are most suitable for high gas/liquid ratio applications. 

An important issue is the proper design of the distributors for the solvent and an adequate liquid holdup in the pump sump to balance fluctuation in the liquid flow sometimes caused by foaming. Foaming may require addition of suitable antifoaming agents. To reduce the mechanical energy demand the laden solution is depressurized over a hydraulic turbine mounted on the pump shaft. In processes which need addition of inhibitors to prevent corrosion, careful control of inhibitor concentration is required. 

The distributor perforations are a high-velocity area and are likely to deteriorate in service, particularly if the service is corrosive or erosive. Correct material selection is therefore important. 

Impingement of high-velocity jets issuing from distributor perforations on column walls and other internals should be minimized. Cases have been reported (215, 410) in which such impingement caused severe corrosion in other situations, it may also cause mechanical damage and erosion. 

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