Fluid cracking design

An improved design undertaken by Sacony used high-velocity gases to replace the mechanical elevator systems as catalyst carriers. These so-called air-lift units improved upon the Thermofor process both in terms of economies and octane numbers. It was, however, only with the fluid cracking process that catalytic technology realized fully continuous production. 

Steam pre-treatment of fluid cracking catalysts has been conventionally employed to represent the deactivation occurring in a commercial FCC unit. Appropriate steam pre-treatment methods have been developed so that the activity and selectivity of the steam pre-treated catalyst is equivalent to a commercially deactivated catalyst (12). However, a unique steaming method may not be suitable for catalysts of varying compositions (12). Two steaming methods designed to simulate deactivation in a commercial unit of the two types of catalysts used in this work were employed. Super-D was treated for 8 hours at 732 C with a steam pressure of 2 atmospheres. The catalysts containing ZSM-5 were treated for 12 hours at 827°C with a steam partial pressure of 0.2 atmosphere. 

For industrial fluid cracking units most of the modeling work in the literature is based upon a highly empirical approach that helps in building units and in operating them, but does not elucidate the main features and characteristics of the units in order to help improve the design and control of such units, or to optimize their output. 

Sadeghbeigi, R. 1995. Fluid Catalytic Cracking Design, Operation, and Troubleshooting of FCC Facilities. Gulf Publishing Company, Houston, TX. 

The test requires the use of a standard batch of gas oil as a feedstock and a set of equilibrium fluid cracking catalysts with consensus mean conversion values assigned in a reactor of specified design. The gas oil and the set of equilibrium cracking catalysts are useful reference materials. Conversion for any equilibrium or laboratory-deactivated fluid cracking catalyst can be measured and compared to a conversion calibration curve. Conversion is measured by the difference between the amount of feed used and the amount of unconverted material. The unconverted material is defined as all liquid product with a boiling point above 216°C. 

Fm. 30. Flow diagram of fluid cracking unit—upflow design, [Murphree et al., Ind. Eng. Chem. 36, 768 (1943). Reprinted by permission.]... 

Fig. 32. Fluid cracking unit—downflow design. [Courtesy of Standard Oil Company (Indiana).]...

Compressor drives. Compressors and blowers in fluid cracking units may be either steam or electrically driven (209). Steam turbines were preferred over electric-motor drives in the design of early units, partly because of fear of a power failure. However, under some circumstances, the economics favor the use of electric motors. Several units have been built with electrically driven main air blowers, and at least one refiner has selected electric motors for the air blower, gas compressor,... 

Fig. 44. M. W. Kellogg Company, Orthoflow design of fluid cracking unit. [Petroleum Refiner 30, No. 9, 178 (1951). Reprinted by permission.]...

Vanadium, while not the only contributor to fluid cracking catalyst (FCC) deactivation, frequently dictates the amount of fresh catalyst added to the FCC unit to mmntain activity. Improvements have been made to both zeolites and matrices to minimize the effect of vanadium [1]. Another method of protecting the catalyst from vanadium deactivation is to use traps that prevent the vanadium from contacting the catalyst in the first place. Vanadium traps have frequently shown more promise in laboratory testing than has been realized commercially[2,3]. Sulfur, present in commercial operations, has been known to interfere with previous traps ability to capture vanadium. Recently it has been shown vanadium traps can be designed to perform successfully under commercial conditions. 

H.L. Occelli Ed., Fluid Cracking Concepts in Catalyst Design, ACS Washington DC 1991, Vol. 452... 

Figure 17. Flow diagram of fluid cracking unit-upflow design. (Reproduced from reference 48. Copyright 1943 American Chemical Society.)...

In the 1930 s, Standard Oil of New Jersey (now Exxon) attempted to license the Houdry technology but were discouraged by the high license fee set by Houdry of 50,000,000 (13, 14). This fee, adjusted via the Consumer Price Index, is over 750,000,000 in today s currency This led the Standard Oil Co. of New Jersey (Jersey) to develop new catalytic cracking technology. Their initial work was based upon the fixed bed concept but was quickly refocused upon the more efficient fluid bed design to avoid the inefficiencies and complexities of the cyclic fixed beds (15). 

In fluid catalytic cracking, a partially vaporized gas oil is contacted with zeoflte catalyst (see Fluidization). Contact time varies from 5 s—2 min pressure usually is in the range of 250—400 kPa (2.5—4 atm), depending on the design of the unit reaction temperatures are 720—850 K (see BuTYLENEs). 

Since the first fluid-bed catalytic cracking unit was commissioned in 1942, more than 300 additional units have been built. During this time, the process has evolved and has seen considerable improvement in mechanical constmction, reflabiUty, and process flow. A modern FCCU typically operates continuously for three to four years between turnarounds, during which time 10 kg of feedstock are processed and 7 x 10 ° kg of catalyst circulated. Early FCCU designs, (53) were complex compared with the compact configuration of more recent design (Fig. 1). 

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