FCC unit

Figure 10.7 FCC unit using feedstock either as a VD-DAO. light mixture of VD-AR or a mixture of...

The treated water containing sodium chloride, cyanides, phenols and traces of H2S and NH3 is recycled to the crude desalting unit and used as wash water for the hydrotreaters and FCC units. 

Fig. 8. (a) Schematic for an FCC unit showing where the various fluidization regimes are found and (b) a corresponding phase diagram for Group A powder (FCC catalyst) where the numbers on the curves represent the superficial soHd velocity in m/s. A represents the bubbling regime B, the turbulent ... 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

C. A. Cabrera and D. Knepper, "Advanced Reactor Design for FCC Units," paper AM 90-39, presented at 1990 NPRA Annual Meeting San Antonio, Tex., Mar. 1990. 

Citric acid specifications are defined in a number of compendia including Vood Chemicals Codex (FCC), United States Pharmacopeia (USP), British Pharmacopeia (BP), European Pharmacopeia (EP), and Japanese Pharmacopeia (fP). 

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... 

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. 

FIG. 17-24 Modem FCC unit configured for high-efficiency regeneration and extra catalyst cooling. (Reptinted with peimission of UOF. RCC is a service ma7k of Ashland Oil Inc.)... 

The gas oil to a eonventional eraeker is primarily from the atmospherie eolumn, the vaeuum tower, and the delayed eoker unit. Additionally, many refiners blend some atmospherie or vaeuum residue with die eraeker feedstoeks to be proeessed in die FCC unit. 

Nearly every FCC unit employs some type of inertial separation device connected on the end of the riser to separate the bulk of the catalyst from the vapors. Most units use a deflector device to turn the catalyst direction downward. On some units, tlie riser is dhectly attached to a set of cyclones. The term rough cut cyclones (Figure 4-47)... 

Most FCC unit regenerators employ 6-16 sets of primary and secondary cyclones in series, depending on unit size. These cyclones are designed to recover catalyst particles that are larger than 20 p. The recovered catalyst particles are returned to the regenerator via the diplegs. The flue gas exits the cyclones through a plenum chamber. 

The motor-generator ean either produee or absorb power. In some FCC units, the expander horsepower exeeeds the power needed to drive the air blower. In this ease, the exeess power is transmitted to the refinery power grid. If the expander generates less power than required by the blower, the motor-generator provides the power to hold the entire train at the desired speed. 

In the mid-to-late 1960s, some were reluctant to use turboexpanders in FCC units. The reasons for the non-implemention often included ... 

The second problem in the foregoing list exists because the design of expanders for FCC service is a rather specialized field, especially in larger sizes of axial design. Only a handful of manufacturers are fully able to supply such expanders. The designs are generally similar (Figure 4-54) and all appear to offer machines that can reasonably be expected to remain on-stream for periods equal to the extended runs now common on major refiner s FCC units. 

Figure 4-56. Typical size chart for hot gas expanders in FCC units. (Source Elliott Company.)...

A seeond type of design allows the regenerator to operate at a pressure high enough so that the expander has a horsepower reeovery potential exeeeding the requirements of the air blower. Most new FCC units are likely designed for higher pressure. 

It is most likely that in designing a new FCC unit the expander will drive the air blower and produee enough horsepower in the end-of-bladelife eondition to supply the horsepower required by the air blower at the expander s end-of-run effieieney. There would also be an allowanee for deviations from expeeted expander performanee and air blower performanee. Thus, the expander ean be expeeted to have available, at start of run, a eonsiderable amount of exeess horsepower. This exeess horsepower must be used in some eeonomie manner without jeopardizing the eontinued safe operation of the FCC unit over its normal on-stream run time. 

Step 1. Selection of normal operating conditions for the regenerator system. This sets normal air blower flow and head, and expander flow and head. If the proposed installation is being designed for an existing FCC unit, only a... 

Interest in the application of turboexpanders turbine to FCC unit is very high, and deservedly so. The power recovery turboexpander offers practical improvement in FCC unit operating economics. Modern designs that encompass the entire system have fully overcome problems and concerns that may have existed decades ago. Expander metallurgy is available to vastly reduce erosion rates experienced when... 

Figure 4-74. Typical startup schematic for turboexpanders in FCC units.

A diorough evaluation of die turbomaehinery paekage proeess is required for eaeh partieular applieation. For most FCC units power reeovery expanders are a sound investment. In eases where diird-stage separation is required to meet emission standards, power reeovery paybaek periods are redueed to even more attraetive levels. New units and expansion of existing units provide energy eonservation opportunities far too important to overlook. 

Dziewulski, T. A. and Bews, J. H., Recover Power from FCC Units, Hydrocarbon Processing, December 1978. 

POWER RECOVERY EXPANDERS FOR FCC UNITS IN MAIN AIR BLOWER OR GENERATOR DRIVE SERVICE ... 

Load sharing or selective load shedding is of interest to many users of hot gas expanders. A particularly successful European FCC application is illustrated in Figure 6-43. The addition of an expander-generator set to the FCC unit at a major refinery presented a challenge because a trip of the expander could upset the process. The company that is the subject of this application case study, GHH Borsig, solved this problem with the installation of a computerized control system and through computer simulation of trips. 

Controlled catalyst circulation is one of the most important prerequisites for trouble-free operation of the FCC unit. Uniform circulation is ensured by controlling the differential pressure between the reactor and regenerator. The differential pressure in the existing plant is controlled by a differential pressure governor adjusting the position of the double slide valve upstream of the orifice chamber. 

If, however, the FCC unit should be operated at a different duty point, whether this is due to a different flue gas flowrate or a different regenerator pressure, the bypass valves would either open too wide or not wide enough. The result is fluetuation in the regenerator outlet pressure. 

There are many reasons for significant investment in FCC power trains and, thus, power train maintenance. These power recovery machines handle catalyst-laden gas at high temperature. Because the recovery system is connected to the processing plant, the steam pipe network and the electrical power grid, a power train upset is likely to rapidly extend from the FCC unit to the entire plant. 

As previously mentioned, FCC units produee hot flue gas as a byproduet. Hot gas is expanded in the expander turbine and then supplies meehanieal energy for proeessing. The exeess power is eonverted into eleetrieal energy by the motor-generator. Therefore, the power reeovery system is likely to raise the energy effieieney and profitability of the plant by substantial margins. 

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