Fluid catalytic cracking unit

The process of fluid catalytic cracking (FCC) is the central process in a modem, gasoline-oriented refinery. In U.S. refineries, the amount of feed processed by fluid catalytic cracking units (FCCU) is equivalent to 35% of the total cmde oil processed in the United States (1). As of January 1991, installed FCCU capacity in the United States was 8.6 x ICf m /d (5.4 x 10 barrels/d). 

Thus the ECCU always operates in complete heat balance at any desired hydrocarbon feed rate and reactor temperature this heat balance is achieved in units such as the one shown in Eigure 1 by varying the catalyst circulation rate. Catalyst flow is controlled by a sHde valve located in the catalyst transfer line from the regenerator to the reactor and in the catalyst return line from the reactor to the regenerator. In some older style units of the Exxon Model IV-type, where catalyst flow is controlled by pressure balance between the reactor and regenerator, the heat-balance control is more often achieved by changing the temperature of the hydrocarbon feed entering the riser. 

Because of the thermal coupling of reactor and regenerator, any change on the reactor side creates a rapid change on the regenerator side, which, in turn, influences the reactor side, and vice versa. This dynamic interaction rapidly comes to equiUbrium, and the catalytic cracker adjusts to a new steady-state. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Thus the amount of heat that must be produced by burning coke ia the regenerator is set by the heat balance requirements and not directly set by the coke-making tendencies of the catalyst used ia the catalytic cracker or by the coking tendencies of the feed. Indirectly, these tendencies may cause the cracker operator to change some of the heat-balance elements, such as the amount of heat removed by a catalyst cooler or the amount put iato the system with the feed, which would then change the amount of heat needed from coke burning. 

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Reduced Emissions and Waste Minimization. Reducing harmful emissions and minimizing wastes within a process by inclusion of additional reaction and separation steps and catalyst modification may be substantially better than end-of-pipe cleanup or even simply improving maintenance, housekeeping, and process control practices. SO2 and NO reduction to their elemental products in fluid catalytic cracking units exemplifies the use of such a strategy (11). 

A. P. Kreuding, "Power Recovery Techniques as AppHed to Fluid Catalytic Cracking Unit Regenerator Flue Gas," presented at 79thFEChE... 

A satisfactory smdy of the application of the flue gas expander to a particular fluid catalytic cracking unit must include the following steps ... 

In support of the power recovery expander market for fluid catalytic cracking units in refineries, some turboexpander manufacturers have an ongoing program to improve the solid particle erosion characteristics of the machine. Improved erosion characteristics will result in longer blade life, less downtime, and consequently greater profits for the users. 

Various companies worked on the development of Fluid catalytic cracking units. During World War II, the government requested some of the leaders in this field to pool their knowledge so as to speed the production of aviation gasoline. The fact that so many Fluid units were constructed and put into operation in such a short time shows that this joint effort was successful. However, because of this effort, many of the basic Fluid patents were held for many years in combination with other companies, some of which also developed their own Fluid designs. 

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 catalytic cracking units (FCC or FCCU) are the major processing units to reduce boiling ranges of those crude oil components that have boiling points higher than the final boiling points of the transportation fuels—typically above 650°F (343°C). These... 

A fluid catalytic cracking unit in Joliet, Illinois, converts bea components of crude oils into high octane gasoline and distillates. (Corbis Corporation)... 

Norco, Louisiana (Ref. 15) 7 (6 in buildings) A corrosion-induced propane leak in a fluid catalytic cracking unit resulted in an explosion that destroyed the control room. Six fatalities occurred in or near the control room the seventh was caused by a falling brick wall. 

The desire to have catalysts that were uniform in composition and catalytic performance led to the development of synthetic catalysts. The first synthetic cracking catalyst, consisting of 87% silica (Si02) and 13% alumina (AI2O3), was used in pellet form and used in fixed-bed units in 1940. Catalysts of this composition were ground and sized for use in fluid catalytic cracking units. In 1944, catalysts in the form of beads about 2.5 to 5.0 mm in diameter were introduced and comprised about 90% silica and 10% alumina and were extremely durable. One version of these catalysts contained a minor amount of chromia (Cr203) to act as an oxidation promoter. 

Figure 4.8. Schematic of a fluid catalytic cracking unit.

Spent caustic. At the end of 1990, 100% of the spent caustic was recycled onsite or offsite. The alkylation/dimersol and fluid catalytic cracking unit (FCCU) spent caustic... 

Strategies for Catalytic Octane Enhancement in a Fluid Catalytic Cracking Unit... 

Catalytic Control of SO Emissions from Fluid Catalytic Cracking Units... 

Hydrocarbon feedstocks for fluid catalytic cracking units (FCCU s) contain organo-sulfur compounds. The sulfur content of these feedstocks is about 0.3% to 3.0%, expressed as elemental sulfur. 

Venugopal, R., Selvavathy, V., Lavanya, M., and Balu, K. Additional Feedstock for Fluid Catalytic Cracking Unit. Petroleum Science and Technology 26 (2008) 436-45. 

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

Selective Catalytic Reduction (SCR) has been commercially used since the mid 1980s on fired equipment with the hrst application on a boiler in 1976. The first SCR unit installed on a fluid catalytic cracking unit was at Saibu Oil Company in Yamaguchi, Japan in April 1986. Since then, nearly two dozen ECC units have installed SCR units to remove NO from the flue gas and more are slated to be built in the future. Vendors and catalyst suppliers of this technology include Haldor-Topsoe, Mitsubishi Power Systems, Hitachi, Technip, BASE, and Cormetech. 

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