Regeneration Equipment

FIG. 16-49 Two-bed TSA system with regeneration equipment. Reprinted with permission of GPSA. Reference Engineering Data Book, 10th ed.. Gas Processors Suppliers Association, Tulsa, 1988, Sec. 20, p. 22. )... 

The advantages of the ease of catalyst replacement or regeneration are offset by the high cost of the reactor and catalyst regeneration equipment. 

Draw a process flow diagram for the plant. This should show all items of equipment approximately to scale and at the correct elevation. The catalyst regeneration, equipment should be shown. 

The purest caustic solution is obtained by extraction with ammonia. The initial 50 per cent caustic solution is led to the top of an extraction tower and flows countercurrently to a mixture of 75 per cent ammonia and 25 per cent water which rises from below. The two solutions are immiscible. The ammonia solution extracts almost completely the chloride and sodium chlorate from the caustic liquor so as to leave no more than 0.08 per cent NaCl (related to 100 per cent NaOH) and practically no chlorate. Ammonia regeneration equipment complements the extraction unit. If anhydrous liquid ammonia is used instead of an ammonia solution a certain degree of concentration of the caustic solution can be achieved at the same time as ammonia also extracts water from the caustic solution. 

If a wet method for collection is selected, such as a wet electrostatic precipitator, fiber-type self-draining mist eliminator, or wet scrubber, ammonia can be regenerated from the salt solution by reaction with a readily available metal oxide such as lime or zinc oxide with formation of a stable sulfur product for disposal. These metal oxides, however, as well as their reaction products, are insoluble and could cause deposition on heat transfer surfaces and/or clogging in the regenerating equipment. Therefore, as indicated in Figure 2, to ensure continuity and reliability of the process, a soluble metal oxide was utilized (in the form of sodium hydroxide solution) to regenerate the ammonia in the experimental work described. This procedure also allows more eflFective utilization of the metal oxide the soluble oxide (NaOH) can be regenerated in batch equipment outside the continuous portion of the process by reaction with either the aforestated insoluble reactants, lime, or zinc oxide. Better control is aflForded in a batch reactor with more eflBcient use of reactants. However, in full-scale equipment undersirable deposition of reactant and product may be controllable so that batch operation may not be necessary. 

In the few instances when EBZ-500 catalyst has been regenerated, it has been restored to essentially the same activity and selectivity as fresh catalyst. The regeneration is a mild carbon burn procedure that is relatively inexpensive. If required, in situ regeneration equipment can be incorporated into the design. This is not common and is usually considered only for locations were ex situ regeneration facilities are not readily accessible. 

The method used will vary according to characteristics of the plant site and properties of agiven system. Energy cost from carbon adsorption ranges from 5 to 25 % of the total operating cost. If carbon is thermally regenerated, equipment cost increases since a furnace, after burner, and a scrubber are needed. If carbon is not regenerated, a means of carbon disposal is needed. 

Minimizes the impact on plant reliability by using a simple scrubbing scheme somewhat decoupled from the regeneration equipment... 

Type of sand Regeneration technique Regeneration equipment Utilisation Borderline conditions Minimal quantity ftonnefh)... 

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