Reactors fluid catalytic cracking

While these techniques have been applied to energy-related processes such as heat-integrated distillation columns and fluid catalytic cracking reactors, there is still extensive research required before the concept of plant design/control is reduced to practice. 

Buyan, Frank M., and Ross, Mark S. Fluid catalytic cracking reactor multi-feed nozzle system, USP 4650566 (1987) Campbell, H. W., and Hurn, E. J. Circulating Fluidized Bed Combustion on Stream at California Portland Cement Company, Coal Technology (Houston), 8th (3-4), p. 19 (1985). 

Combined Pressure and Temperature Loads During the Operation of a Reactor. The reactor considered here is a fluid catalytic cracking reactor [5-7] its fundamental design is shown in Figure 5.9. The materia) is 15 Mo 3. Reactors of this type are used in petrochemical plants for the fission of heavy hydrocarbons. 

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

The ethylene feedstock used in most plants is of high purity and contains 200—2000 ppm of ethane as the only significant impurity. Ethane is inert in the reactor and is rejected from the plant in the vent gas for use as fuel. Dilute gas streams, such as treated fluid-catalytic cracking (FCC) off-gas from refineries with ethylene concentrations as low as 10%, have also been used as the ethylene feedstock. The refinery FCC off-gas, which is otherwise used as fuel, can be an attractive source of ethylene even with the added costs of the treatments needed to remove undesirable impurities such as acetylene and higher olefins. Its use for ethylbenzene production, however, is limited by the quantity available. Only large refineries are capable of deUvering sufficient FCC off-gas to support an ethylbenzene—styrene plant of an economical scale. 

The most dominant catalytic process in the United States is the fluid catalytic cracking process. In this process, partially vaporized medium-cut petroleum fractions called gas oils are brought in contact with a hot, moving, freshly regenerated catalyst stream for a short period of time at process conditions noted above. Spent catalyst moves continuously into a regenerator where deposited coke on the catalyst is burnt off. The hot, freshly regenerated catalyst moves back to the reactor to contact the hot gas oil (see Catalysts, regeneration). 

Fluid catalytic cracking units present formidable emission control problems. Contaminants are present in both reactor product gas and regenerator flue gas. The reactor product contains hydrogen sulfide, ammonia, and cyanides, plus combined sulfur and nitrogen in the liquid products. Hydrogen sulfide, ammonia and cyanides are handled as part of the overall refinery waste water cleanup. The combined sulfur and nitrogen may be removed by hydrotreating. 

Fluid bed reactors became important to the petroleum industry with the development of fluid catalytic cracking (FCC) early in the Second World War. Today FCC is still widely used. The following section surveys the various fluid bed processes and examines the benefits of fluidization. The basic theories of fluidization phenomena are also reviewed. 

Many factors enter into the design of a fluid bed reactor which are unknown in more familiar reactor types. These can be illustrated with reference to fluid catalytic cracking. 

The Houdry fixed-bed cyclic units were soon displaced in the 1940s by the superior Fluid Catalytic Cracking process pioneered by Warren K. Lewis of MIT and Eger Murphree and his team of engineers at Standard Oil of Newjersey (now Exxon). Murphree and his team demonstrated that hundreds of tons of fine catalyst could be continuously moved like a fluid between the cracking reactor and a separate vessel for... 

Fluid catalytic cracking is one of the most important conversion processes in a petroleum 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 since 1942. 

The first cracking catalysts were acid-leached montmorillonite clays. The acid leach was to remove various metal impurities, principally iron, copper, and nickel, that could exert adverse effects on the cracking performance of a catalyst. The catalysts were first used in fixed- and moving-bed reactor systems in the form of shaped pellets. Later, with the development of the fluid catalytic cracking process, clay catalysts were made in the form of a ground, sized powder. Clay catalysts are relatively inexpensive and have been used extensively for many years. 

McPherson, L. J. Reactor Coking Problems in Fluid Catalytic Cracking Units. Akzo Catalysts Symposium, Scheveningen, The Netherlands, 1984. 

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.

Indicated in Fig. 2 is a representative fluid catalytic cracking unit, comprising ( )a reactor (2) a regenerator (3) the main fractionator (4) an air blower or compressor (3) a spent-catalyst stripper (6) catalyst recovery equipment, including cyclones internal in the reactor and regenerator and slurry settler, and possibly an electrostatic precipitator and (7) a gas-recovery unit. The catalyst used is essentially u specially prepared composite of silica and alumina. 

The feeds to these types of units are usually atmospheric and vacuum residua. The products include feeds for the production of transportation fuels, fuel oils, olefins, etc. However, the operating conditions of the reactor, whether it is a fluid catalytic cracking unit or a fixed-bed unit, is dependent upon the desired product slate and the properties of the feed. 

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. 

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