Distribution, spent catalyst regeneration

In addition to the remarkable ingenuity observed in successive unit designs, substantial creativity was brought to the market in many areas such as feed distribution, riser termination, spent catalyst regeneration, etc. 

Both high CRC and afterburn in partial combustion regenerators can be overcome by proper design of the spent catalyst distributor and the air grid. Figure 6 shows one example of a modern spent catalyst distributor designed by Khouw et al. (1994), which distributes spent catalyst laterally through several horizontal arms. 

The CO promoter is added to most FCC units to assist in the combustion of CO to COj in the regenerator. The promoter is added to accelerate the CO combustion in the dense phase and to minimize the higher temperature excursions that occur as a result of afterburning in the dilute phase. The promoter allows uniform burning of coke, particularly if there is uneven distribution between spent catalyst and combustion air. 

There be a uniform distribution of air and spent catalyst. Air/ catalyst mixing in the regenerator can significantly affect the SO, pick-up efficiency. 

Air and spent catalyst distribution. Modifications to the air and spent catalyst distributors permit uniform dispersion of air and spent catalyst into the regenerator. Improvements are lower carbon on the catalyst and less catalyst sintering. The benefits are a cleaner and higher-activity catalyst, which results in more liquid products and less coke and gas. 

The main purpose of the regenerator is to produce a clean catalyst, minimize afterbum, and reduce localized sintering of the catalyst. For efficient catalyst regeneration it is very important that the air and the spent catalyst are evenly distributed. Although, in recent years, the design of air distributors has improved significantly, the same cannot... 

The regenerator review will include spent catalyst distribution, air distribution, and cyclones. If the test run with heavy feed indicates a temperature limitation, catalyst coolers, partial combustion, or riser quench should be considered. 

Spent catalyst being introduced into the regenerator should be distributed as evenly as possible across the catalyst bed. It is the nature of a fluidized bed that mixing... 

Regenerator doesn t remove ad carbon from the catalyst damaged air grid/insuffi-dent air/excessive regenerator velodty/poor spent catalyst initial distribution/ coarse particles. 

Excessive regenerator velocity Poor spent catalyst initial distribution... 

Poor initial distribution of the spent catalyst can account for an uneven temperature rise through the cyclones. For instance, in a relatively small regenerator (i.e., a regenerator where the flue gas superficial velocity exceeds 4 ft/sec or with an inventory of less than five minutes of catalyst circulation), catalyst flowing from the spent catalyst stripper may flow clear across the regenerator and accumulate on the side opposite the spent cataiyst inlet. The high concentration of spent catalyst, and hence coke in this portion... 

Figure 16. Spent Catalyst Distribution Designs for Various Regenerator Configurations Ross (1990)...

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