Catalytic Cracking Fluid

Like coking units, catalytic cracking units usually include some form of fractionation or steam stripping as part of the process configuration. These units all 

The main task of fluid catalytic cracking is the conversion of a wide range of both virgin and cracked hydrocarbon residues into lower molecular weight and more valuable products. 

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The preheated raw oil feed meets a stream of hot catalyst from the regenerator at the base or lower part of the reactor riser. Heat from the catalyst vaporizes the oil, and the catalyst and oil travel up to the reactor. The cracked hydrocarbons, separated from the catalyst in cyclones, leave the reactor overhead and go to the fractionation column. 

The spent catalyst falls down into the stripping section within the reactor. Steam removes most of the hydrocarbon vapor and the catalyst then flows down a standpipe to the regenerator. 

The spent catalyst mixes with air and clean catalyst at the base of the regenerator. Here the coke deposited during cracking is burned off to reactivate the catalyst and provide heat for the endothermic cracking reactions. The recirculating loop of clean catalyst provides added heat for initiation of the carbon bum. The catalyst and air flow up the regenerator riser and separate at a T-shaped head. The flue gas is further cleaned of catalyst in cyclones at the top of the regenerator. 

Cerium(IV)-oxide, Ce02, (see Fig. 5.4) is, like La(lII)-oxide, used in fluid catalytic cracking. 

In this section we will present some examples of using the EMMS-based multi-scale CFD to solve industrial problems, including fluid catalytic cracking (FCC) and CFB combustion. 

The collaboration is still going on. The full-loop, 3D simulations of MIP reactors are being performed to help further scale-up. To some extent, the multi-scale CFD is beginning to take the place of virtual experiment for solving industrial problems, and it is emerging as a paradigm beneficial to both industry and academia. 

The rate of circulation of the solids is dictated by the heat balance and activity level of the catalyst the beat produced by the regenoation is carried to the reactor by the catalyst and there it evaporates, heats, and cracks the oil. The transfer lines have to be designed in such way that they are not eroded by the catalyst The catalyst also has to withstand attrition. 

Some typical operating figures for fluid catalytic crackers [from J0  

Medium size capacity 15,000 barrels/day = 2390 gasoil/day Catalyst silica-alumina zeolite catalyst or molecular sieves 20-80 p Total catalyst inventory 250 tons Amount in regenerator 100 tons Catalyst bulk densities 

Superficial velocity in reactor and regenerator 0.5-1.3 m/s Velocities in standpipes 1.7 m/s 

After the reaction, a number of products are formed that require further processing to separate and clean the desired chemical streams. A separator and an alkaline substance are used to remove [strip] the acid. The stripped acid is sent back to the reactor, while the remaining reactor products are sent to a distillation tower. Alkylate, isobutane, and propane gas are fractionally separated in the tower. Isobutane is returned to the alkylation reactor for further processing. Alkylate is sent on to the gasoline blending unit. 

During operation, gas oil enters the reactor and Is mixed with a superheated powdered catalyst (the cat in catcracking). The term cracking is appropriate for this process because, during vaporization, the molecules literally split they are then sent to a fractionation tower for further processing. The chemical reaction between the catalyst and light gas oil produces a solid carbon (coke) deposit. This deposit forms on the powdered catalyst and deactivates it. The spent catalyst 

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Ecole Nationale Superieure du Petrole et des Moteurs Formation Industrie end point (or FBP - final boiling point) electrostatic precipitation ethyl tertiary butyl ether European Union extra-urban driving cycle volume fraction distilled at 70-100-180-210°C Fachausschuss Mineralol-und-Brennstoff-Normung fluid catalytic cracking Food and Drug Administration front end octane number fluorescent indicator adsorption flame ionization detector... 

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. 

Refinery Production. Refinery propylene is formed as a by-product of fluid catalytic cracking of gas oils and, to a far lesser extent, of thermal processes, eg, coking. The total amount of propylene produced depends on the mix of these processes and the specific refinery product slate. For example, in the United States, refiners have maximized gasoline production. This results in a higher level of propylene production than in Europe, where proportionally more heating oil is produced. 

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). 

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). 

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). 

Deep C t lytic Crocking. This process is a variation of fluid catalytic cracking. It uses heavy petroleum fractions, such as heavy vacuum gas oil, to produce propylene- and butylene-rich gaseous products and an aromatic-rich Hquid product. The Hquid product contains predorninantiy ben2ene, toluene, and xylene (see BTX processing). This process is being developed by SINOPEC in China (42,73). SINOPEC is currentiy converting one of its fluid catalytic units into a demonstration unit with a capacity of 60,000 t/yr of vacuum gas oil feedstock. 

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). 

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

FCC = fluid catalytic cracking Of inised-lanthaiiide composition. In oxide-type compound. 

A dephlegmator process can be used to recover ethylene—ethane and heavier hydrocarbons from fluid catalytic cracking (FCC) unit off-gas (Fig. 7). Pretreated feed gas is cooled to about 230 K and then further cooled and rectified in a dephlegmator to recover 90 to 98% of the ethylene, 99 % of the... 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Ethylene as a By-Product. The contribution to world ethylene production is small, but not zero. In petroleum refining fluid catalytic cracking (FCC) units, small amounts of ethylene are produced but generally not recovered, except in a few locations where large FCC units are adjacent to petrochemical faciUties. 

FCC process description adapted by permission from Fluid Catalytic Cracking Handbook, R. Sadeghbeigi, Gulf Publishing Company, Houston, Texas, 2000, pp. 3—17. 

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

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