Fluidized-bed catalytic cracking units

Fluidized-bed catalytic cracking units (FCCUs) are the most common catalytic cracking units. In the fluidized-bed process, oil and oil vapor preheated to 500 to SOOT is contacted with hot catalyst at about 1,300°F either in the reactor itself or in the feed line (called the riser) to the reactor. The catalyst is in a fine, granular form which, when mixed with the vapor, has many of the properties of a fluid. The fluidized catalyst and the reacted hydrocarbon vapor separate mechanically in the reactor and any oil remaining on the catalyst is removed by steam stripping. 

An important advantage of the fluidized-bed reactor over the fixed-bed type is that the catalyst can be regenerated without disturbing the operation of the reactor. In fluidized-bed catalytic cracking units a portion of the solid particles is continuously removed from the reactor and regenerated in a separate unit. The regeneration is accomplished by burning off the carbon with air, and the reactivated catalyst is continuously returned to the reactor proper. In the fixed-bed reactor the closest approach to... 

It is noteworthy that the JG operator has also been successfully incorporated into a Multi-objective Simulated Annealing technique (Sankararao and Gupta, 2007 see Chapter 4 in this book). The performance assessment of this algorithm was done on three well-known test (benchmark) problems commonly used in the evolutionary MOO field. This algorithm was then employed for the MOO of an industrial fluidized-bed catalytic cracking unit. 

Kasat, R. B. and Gupta, S. K. (2003). Multiobjective optimization of an industrial fluidized-bed catalytic cracking unit (FCCU) using genetic algorithm with the jumping gene operator, Comput. Chem. Eng., 27, pp. 1785-1800. 

Orthoflow A fluidized-bed catalytic cracking process in which the reactor and regenerator are combined in a single vessel. Designed by the MW Kellogg Company and widely used in the 1950s. First operated in 1951 by the British American Oil Company at Edmonton, Alberta. By 1994, more than 120 units had been built. 

Figure 1731. Fluidized bed reactor processes for the conversion of petroleum fractions, (a) Exxon Model IV fluid catalytic cracking (FCC) unit sketch and operating parameters. (Hetsroni, Handbook of Multiphase Systems, McGraw-Hill, New York, 1982). (b) A modem FCC unit utilizing active zeolite catalysts the reaction occurs primarily in the riser which can be as high as 45 m. (c) Fluidized bed hydroformer in which straight chain molecules are converted into branched ones in the presence of hydrogen at a pressure of 1500 atm. The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc. cit.). (d) A fluidized bed coking process units have been built with capacities of 400-12,000 tons/day.

Catalytic cracking using a fluidized bed is the most popular form of cracking and is the emphasis of this section. To reaffirm this statement, there are more than 370 fluid catalytic cracking units in use worldwide with the capacity to produce more than 460,000,000 gallons of gasoline from heavier feedstocks (Slade, 1998). 

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...

In the fluidized-bed (fluid catalytic cracking) units, the cracking reactions take place in the riser to form products, including coke. In the riser, the catalyst and the feedstock and products rise up the reactor pipe, and because the reactions are predominantly endothermic, the reaction temperature declines from bottom to top. At the top of the riser, the mixture... 

There are processes in which the total amount of catalyst is entrained by the gas. The reactors then belong to the category of transport reactors. Examples are some of the present Fischer-Tropsch reactors for the production of hydrocarbons from synthesis gas and the modern catalytic cracking units. Fig 10.11 shows the Synthol circulating solids reactor. In the dilute side of the circuit, reactant gases carry suspended catalyst upward, and the fluidized bed and stand-pipe on the other side of the circuit provide the driving force for the smooth circulation of the solid catalyst. For the removal of heat, heat exchangers are positioned in the reactor. 

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