Catalyst hopper

The activity of catalyst degrades with time. The loss of activity is primarily due to impurities in the FCC feed, such as nickel, vanadium, and sodium, and to thermal and hydrothermal deactivation mechanisms. To maintain the desired activity, fresh catalyst is continually added to the unit. Fresh catalyst is stored in a fresh catalyst hopper and, in most units, is added automatically to the regenerator via a catalyst loader. 

A catalyst hopper (see Figure 7-4) provides sufficient time for the initial deaeration of the catalyst. Proper catalyst deaeration should... 

Verify any recent design changes in the standpipes and/or catalyst hopper... 

The catalyst hopper had, at times, been operated at gas velocities above the minimum bubbling velocity. This caused bubbles as well as catalyst to be carried to the feed/catalyst... 

This change in catalyst hopper operation virtually eliminated the formation of coke deposits in the feed mixing zone. Catalyst-to-oil ratios as low as 2.5 have been achieved even with very heavy feedstocks. 

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...

Figure 5 Phillips Particle-forming process a) catalyst hopper b) double loop reactor c) flash tank d) purge drier e) powder-fed extruder f) impeller g) sedimentation leg.

Figure 6 Union-Carbide process, a) catalyst hopper b) fluidized-bed reactor c) cyclone ...

The mixture of catalyst and cracked-oil vapors passes overhead to cyclone separators for recovery of catalyst. Catalyst thrown to the walls of the cyclones by centrifugal force slides down into the spent-catalyst hopper, while the oil vapors leave through a central outlet pipe and pass to the fractionating tower. The small amount of catalyst powder still present in the oil vapors is recovered in the bottoms from the fractionating tower and can be returned to the reactor, if desired. 

Catalyst from the spent-catalyst hopper falls through a standpipe and slide valve into a carrier line in which it is transferred, in dilute suspension with air, to the regenerator. The diameter of the regenerator was so chosen... 

Flue gas leaving the cyclones contains a small r esidual concentration of catalyst and is passed through a Cottrell electrostatic precipitator recovered catalyst is returned to the regenerated-catalyst hopper. Catalyst losses for this type of unit have been reported to be within the range of 0.12 to 0.4 lb. per barrel of feed (232,233). The losses are compensated for by the intermittent addition of fresh catalyst. 

About 99.9% of the catalyst was separated fi om the cracked gas oil vapors by use of three cyclone separators in series which dropped the catalyst through aerated dip legs into the spent catalyst hopper. Flow of spent catalyst to the transfer line was regulated by a slide valve. The spent catalyst was picked up by a stream of air and carried into the regenerator. 

Regenerated catalyst and gas flowed out the top of the regenerator to three cyclone separators connected in series, where, approximately 99.9% of the catalyst was separated from the flue gases and deposited in the regenerated catalyst hopper. The stack gas was then passed through a waste gas fresh feed heat exchanger to a Cottrell electrostatic precipitator where 96-98% of the fine catalyst not separated by the cyclones was recovered and returned by air injection to the inlet of the tertiary regenerated catalyst cyclone. 

Regenerated catalyst to the reactor was drawn from the regenerated catalyst hopper through a standpipe in which slide a valve controlled the flow rates. The 113 foot regenerated catalyst standpipe operated with a pressure head of 31 PSI. 

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