Riser Catalytic Cracking

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. 

The thermal and catalytic cracking of PP, PS, and SBR waste, dissolved in light cycle oil, was studied in a riser simulator. 19 refs. 

Figure 7.7b shows the essential features of a refinery catalytic cracker. Large molar mass hydrocarbon molecules are made to crack into smaller hydrocarbon molecules in the presence of a solid catalyst. The liquid hydrocarbon feed is atomized as it enters the catalytic cracking reactor and is mixed with the catalyst particles being carried by a flow of steam or light hydrocarbon gas. The mixture is carried up the riser and the reaction is essentially complete at the top of the riser. However, the reaction is accompanied by the deposition of carbon (coke) on the surface of the catalyst. The catalyst is separated from the gaseous products at the top of the reactor. The gaseous products leave the reactor... 

Fluid-catalytic-cracking off-gas, 23 330 Fluid-catalytic-cracking riser technology, 16 835... 

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 The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc.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.

Riser Cracking—Applied to fluid catalytic cracking units where the mixture of feed oil and hot catalyst is continuously fed into one end of a pipe (riser) and discharges at the other end where catalyst separation is accomplished after the discharge from the pipe. There is no dense phase bed through which the oil must pass because all the cracking occurs in the inlet pipe (riser). 

In the process, a residuum is desulfurized and the nonvolatile fraction from the hydrodesulfurizer is charged to the residuum fluid catalytic cracking unit. The reaction system is an external vertical riser terminating in a closed cyclone system. Dispersion steam in amounts higher than that used for gas oils is used to assist in the vaporization of any volatile constituents of heavy feedstocks. 

In the S W fluid catalytic cracking process (Figure 8-15), the heavy feedstock is injected into a stabilized, upward flowing catalyst stream whereupon the feedstock-steam-catalyst mixture travels up the riser and is separated by a high efficiency inertial separator. The product vapor goes overhead to the main fractionator (Long, 1987). 

Riser the part of the bubble-plate assembly which channels the vapor and causes it to flow downward to escape through the liquid also the vertical pipe where fluid catalytic cracking reactions occur. 

Riser pipe the pipe in a fluid catalytic cracking process (q.v.) where catalyst and feedstock arc lifted into the reactor the pipe in which most of the reaction takes place or is initiated. 

Figure 13 The apparent flow regime diagram calculated with EMMS-based multiscale CFD and the intrinsic flow regime diagram for the air-FCC system (fluid catalytic cracking particle, dp = 54 m, pp = 930 kg/m3) calculated by using the EMMS model without CFD. The intrinsic flow regime diagram is independent of the riser height (Wang et al., 2008).

Increasing Motor Octanes by Using ZSM—5 in Catalytic Cracking Riser Pilot Plant Gasoline Composition Analyses... 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Fluid catalytic cracking (FCC) of heavy oil fractions is a well-known process in oil refineries. Numerous books (e.g., 1—3) and publications about the different aspects of this subject are available. This chapter is concerned with the modeling of the transfer line or riser reactor of an FCC unit (FCCU) or of a pilot plant. The riser reactor in FCCUs is a vertical pipe about 1 m in diameter and 10-30 m in height. The hot catalyst coming from the regenerator at about 710 ° C first comes in contact with steam and is fluidized. Then, at a height of some meters above, the catalyst is mixed with the preheated feedstock at about 300 ° C. 

This paper describes experience with residue processing in catalytic cracking units in the industry, both on a commercial and pilot plant scale. Specific changes which have been made to the design and operating procedures of the Shell Canada Oakville Research Centre (ORC) riser pilot plant are also discussed. 

M. Schlossman et al, "Riser Pilot Plant for Catalytic Cracking Studies", Katalistiks 7th Annual FCC Symposium, Venice, Italy, May 12-13, 1986. 

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