Catalyst coolers

Bed-to-Surface Heat Transfer. Bed-to-surface heat-transfer coefficients in fluidized beds are high. In a fast-fluidized bed combustor containing mostly Group B limestone particles, the dense bed-to-boiling water heat-transfer coefficient is on the order of 250 W/(m -K). For an FCC catalyst cooler (Group A particles), this heat-transfer coefficient is around 600 W/(600 -K). 

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. 

Fig. 11. Catalyst cooler configurations where (a) is backmix cooler and (b) is flow-through catalyst cooler (69).

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. 

Adding a catalyst cooler may back a boiler down, or it may require more BFW and a home for the steam. New feed nozzles may require more steam. A cogeneration unit can be an attractive option. 

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

Favorski-Babayan conditions, 24 479 FCC catalyst coolers, 11 728-729 FCC catalysts. See also Fluid catalytic cracking (FCC)... 

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.

During the R D of the upflow type catalyst cooler, using catalyst CRC-1 (pp = 1,700 kg/m), the influence of vertical heat transfer tubes on bed density was investigated by LPEC in a dt 0.36 m cold test model, with 0.04 m o.d. tubes and 0.08-0.2 m shell side equivalent diameters. The gas velocities and solid mass velocities were 1.0—1.6 m/s and 70-180 t/(m2 h), respectively. Average bed density was correlated by the equation... 

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.

The bayonet tube element is fitted on the outside with a plurality of small diameter tubes or welded with longitudinal fins to enhance heat transmission from the fluidized bed (Zhang et al., 1990 Jiao et al, 1991). The heat flux is normally about 150 to 200 kW/m2, and the heat duty is about 11-22 MW for a typical upflow catalyst cooler with vessel diameter 1.6 to 2.2 m. 

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. 

Operating Data of Commercial External FFB Catalyst Coolers... 

Table IX presents heat transfer data for an external catalyst cooler of the FFB type. Heat flux of 70-150 kW/m2 and heat transfer coefficient of 350-490 W/(m2-k) were obtained, both somewhat less than those of a turbulent bed internal cooler (horizontal coil type), but approximately equal to those of the external cooler of the bubbling bed type.

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. 

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

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