Regenerator catalyst cooler

Regenerated-catalyst cooler. Cracking capacity is usually limited by coke-burning capacity, which is directly related to the rate at which... 

It is worth noting here that the absence of a regenerator catalyst cooler does not automatically entail a delta-coke-constrained operation, while on the other hand if heat removal facilities are present, the unit operation can still be constrained by delta coke, for instance if the objective is to increase the resid content of the feed. 

Thus the amount of heat that must be produced by burning coke ia the regenerator is set by the heat balance requirements and not directly set by the coke-making tendencies of the catalyst used ia the catalytic cracker or by the coking tendencies of the feed. Indirectly, these tendencies may cause the cracker operator to change some of the heat-balance elements, such as the amount of heat removed by a catalyst cooler or the amount put iato the system with the feed, which would then change the amount of heat needed from coke burning. 

Catalyst cooler(s). Installing a catalyst cooler(s) is a way to control and vary regenerator heat removal and thus allow processing of a poor quality feedstock to achieve increased product selectivity. 

The regenerator is already a cold-wall vessel re-rating is not often practical. High regenerator temperature typically requires installing either catalyst coolers, operating with partial combustion, or injecting a quench stream into the riser. 

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. 

Catalyst Cooler is a heat exchanger that removes heat from the regenerator through steam generation. 

A two-stage stripper is utilized to remove hydrocarbons from the catalyst. Hot catalyst flows at low velocity in dense phase through the catalyst cooler and returns to the regenerator. Regenerated catalyst flows to the bottom of the riser to meet the feed. 

Fig. 1. A 1 MMTA fluid catalytic cracking unit with fast fluidized bed regenerator (courtesy Gaoqiao Petrochemical Company). 1, regenerator 2, first-stage FFB regenerator 3, second-stage FFB regenerator, 4, main fractionator, 5. FFB catalyst cooler 6, catalyst hoppers 7, cyclone...

Fig. 2. Flowsheet of a typical FCCU. 1, riser 2, disengager 3, FFB regenerator 4, catalyst cooler 5, main fractionator 6, LCO stripper 7, HCO drum 8, accumulator I, fresh feed II, recycle feed III, slurry oil IV, LCO V, catalytic naphtha VI, rich gas VII, air VIII, flue gas IX, steam X, water/steam mixture XI, water.

Fig. 8. Installation of external catalyst cooler. 1, riser 2, first-stage regenerator 3, second-stage regenerator 4, catalyst cooler S, distributor I, combustion air II, fluidization air, III, water IV, steam and water.

Hot catalyst from the regenerator is introduced to the bottom of the catalyst cooler through a standpipe, while fluidization air flows upward with the catalyst, passing along the surfaces of the heat transfer elements and leaving the cooler at the top. The cooled catalyst and air are sent back to the dense bed of an ordinary regenerator or the middle zone of an FFB regenerator for continued utilization of 02. A typical assembly of an upflow catalyst cooler is shown in Fig. 8. 

Excessive heat generation in the regenerator is a particular problem when using residual feed when coke formation is higher. Residual fuel FCC operations generally have additional heat removal mechanisms in the regenerator. This can be steam raising coils or external catalyst coolers. 

The main feature of such an RFCC revamp is increasing the coke-burning capacity of the regenerator while maintaining the FCC unit in heat balance (often by incorporating catalyst coolers in the regenerator). Also, the employment of improved catalysts that reduce coke formation and enhance tolerance for metals (notably V, Fe, and Na) has enabled this development in RFCC. 

Model I Side-by-side configuration Fast fluidized upflow riser regenerator Low pressure High elevation external cyclones Catalyst coolers Full feed pre-vaporization... 

UOP in collaboration with Ashland Petroleum developed the Residue Catalytic Cracking (RCC) process (27). The first RCC imit was brought on line in Catlettsburg, Kentucky, in 1983. The landmark design feature of this unit was the first external, dense phase FCC catalyst cooler enabling regenerator... 

As the regenerator temperatures drop, the regenerated catalyst flowing back to the reactor through the regen slide valve cools. This in turn drops the riser outlet temperature, unless the catalyst circulation rate is increased. The cooler riser results in less conversion and hence less coke make. This effect further reduces the coke on the spent catalyst and lowers the regenerator temperature. 

Many modem FCC units are designed to process significant amounts of vacuum residue. These units use catalyst coolers (e.g., steam coils) in the regenerator or a second regeneration zone to remove excess heat from the unit. This is because vacuum residue generates substantially more coke than conventional FCC feeds, and excess heat is generated when the extra coke is burned away from catalyst. 

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