Structured packing use in fluid catalytic cracker (FCC) main fractionators significantly impacts unit pressure profile. Unit pressure balance links the FCC main fractionator, reactor, regenerator, air compressor and wet gas compressor (Fig. 1). Many FCC units have capacity and/or conversion limits set by the wet gas compressor capacity or the air blower. A typical main fractionator has approximately 5 psi (0.35 kg/cm2) pressure drop, while a packed fractionator has a 1.0 psi (0.07 kg/cm2) pressure drop. This 4 psi (0.28 kg/cm2) can be recovered and used to debottleneck the wet gas compressor or air blower. Unit pressure balance should be viewed as a design variable when evaluating FCC unit revamps. Depending upon limitations of the particular FCC unit, capacity increases of 12.5% to 22.5% have been achieved without modifications to major rotating equipment, by revamping FCC main fractionators with structured packing. An examination of three FCC main fractionator revamps show improvements to pressure profiles and unit capacity.
FCC units form an integral part of modern refineries' processing sequences for upgrading crude. Expanding these units often presents great difficulties and is expensive due to limitations on the main fractionator, wet gas compressor and air blower capacities. The packed main fractionator reduces pressure drops from the reactor outlet to the wet gas compressor. Reduced pressure drop benefits include:
Additionally, structured packing allows for enhanced heat recovery options within the main fractionator. This can lead to additional benefits that include simplified overhead systems (additional pressure drop reduction). Actual benefits in any particular case depend upon balances derived from operating characteristics of the equipment in question.
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