QUESTIONS AND ANSWERS--I.FCC/A.PROCESS/SUMMARY

                                       I. FLUID CATALYTIC CRACKING/A.PROCESS

                                                                 SUMMARY 

Fluid Catalytic Cracking is one of the most important conversion processes in a Petoleum Refinery.The process incorporates most phases of chemical engineering fundamentals,such as fluidization,heat/mass transfer,and distillation.The heart of the process is the Reactor-Regenerator,where most of the innovations have occurred.



.The objective of the FCC unit is to convert low-value,high-boiling-point feedstocks into more valuable products such as gasoline and diesel.FCC is an extremely efficient process.The cracking reactions result in deposition of coke on the catalyst.The catalyst activity is restored by burning off the coke with air.The catalyst -burning step supplies the heat for the reactions through circulation of catalyst between reactor and regenerator



The hot pooduct vapors from the reactor are recovered in the main fractionator and the gas plant.The primary function of the main fractionator is to separate the heaviest products,such as light-cycle and decanted oil,from the gasoline and the lighter products.The gas plant seperates the main fractionator overhead vapors into gasoline,C3's,C4's and fuel gas.These products contain sulfur compounds and need to be treated prior to being used. A combination of amine and caustic solutions are employed to sweeten these products


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FCC catalyst can only be made to flow like a liquid if the pressure force is transmitted through the catalyst particles and not the vessel wall.This means that the catalyst must always remain in a fluidized state as it makes a loop around the reactor/regenerator.The only proper way to evaluate the performance of a cat cracker is by conducting material and heat balance tests.Predictions and evaluation of changes in feed stocks,catalyst,operating parameters,and any mechanical hardware can be made by carrying out these tests.

The material balance test run provides a standard and consistent approach for daily monitoring of a cat cracker.It allows for accurate analysis of yields and proper comparison of unit performance.The heat balance provides a tool for in -depth insight into the operation of a cat cracker.Heat balance surveys are used to determine catalyst circulation rate,delta coke,and heat of reaction.The pressure balance provides an insight into the hydraulics of the catalyst circulation.Performing pressure balance surveys will help the unit engineer to recognize circulation " pinch points" and also to get the most out of the common constraints:the air blower and the wet gas compressor.Finally,the process control features control schemes to operate the unit smoothly and safely.