Residue FCC

T. Sinhora and S. Kasada, "A Real Time Dynamic Simulator for the Residue FCC Process," paper presented at Eastern Simulation Conference, Orlando, Fla., Apr. 18-21, 1988. 

F.H.H, Khouw, M.J.R.C. Nieskens, MJ.H. Borley and K.H.W. Roebschlaeger "The Shell Residue FCC Process Commercial Experiences and Future Developments, 1990 NPRA Annual Meeting, 25-27 March T90, paper AM-90-42. 

The Shell Residue FCC Process Commercial Experiences and Future Developments",... 

If cracking catalysts are used to support the cracking process, the sulfur and metal contaminants must be removed upstream since they poison the catalyst, such as in the residue FCC process [3]. 

The desulfurized bottoms from the HDS mode meet the usual quality targets for residue FCC feedstock. The acceptable quality of residue FCC feedstock depends on the design of the catcracker. 

In pretreatment of residual FCC feedstock, downstream catalysts with high coke resistance are essential to obtain sufficient catalyst life. 

Besides the aforementioned conventional applications, there are many other HDT technologies that have emerged in the changing environment of the oil industry. The majority of these are focused on the upgrading of the heaviest feedstocks. The atmospheric residue/vacuum residue desulfurization processes (RDS/VRDS), which have been developed to meet a variety of objectives such as preparing feed for FCC, residue FCC, coker, and residue HCR, are cases in point [14, 15]. 

RFCC = residue FCC unit or reduced crude FCC unit, which are specially designed to process feeds that contain high concentrations carbon-forming compounds. 

Bechtel, R.R., Wisdom, L.I. 1991. Sequential operation of H-oil and residue FCC. American Institute of Chemical Engineers. In Symposium on Resid Upgrading Processes, Houston, TX, April 7-11. 

Figure 3.12 shows the spectrum of carbon 13 obtained from a distillation residue and Table 3.10 gives average parameters for two FCC feedstocks as measured by NMR. 

Figure 10.7 presents the case of an FCC feedstock comprising a mixture of vacuum distillate and light atmospheric residue, and the case of an FCC feedstock composed of vacuum distillate and DAO, as well as the constraints of such configurations. 

Figure 10.8 presents a variant of the FCC process, the RCC (Residue Catalytic Cracking) capable of processing heavier feedstocks (atmospheric residue or a mixture of atmospheric residue and vacuum distillate) provided that certain restrictions be taken into account (Heinrich et al., 1993). 

Residue to lube oil plant, steam cracking plant, FCC... 

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. 

Another approach used to reduce the harmful effects of heavy metals in petroleum residues is metal passivation. In this process an oil-soluble treating agent containing antimony is used that deposits on the catalyst surface in competition with contaminant metals, thus reducing the catalytic activity of these metals in promoting coke and gas formation. Metal passivation is especially important in fluid catalytic cracking (FCC) processes. Additives that improve FCC processes were found to increase catalyst life and improve the yield and quality of products. ... 

Most refineries produce sufficient gas oil to meet the cat crackers demand. However, in those refineries in which the gas oil produced does not meet the cat cracker capacity, it may be economical to supplement feed by purchasing FCC feedstocks or blending some residue. The refinery-produced gas oil and any supplemental FCC feedstocks are generally combined and sent to a surge drum, which provides a steady flow of feed to the charge pumps. This drum can also separate any water or vapor that may be in the feedstocks. 

The circulating catalyst in the FCC unit is called equilibrium catalyst, or simply E-cat. Periodically, quantities of equilibrium catalyst are withdrawn and stored in the E-cat hopper for future disposal. A refinery that processes residue feedstocks can use good-quality F-cat from a refinery that processes light sweet feed. Residue feedstocks contain large quantities of impurities, such as metals and requires high rates of fresh catalyst. The use of a good-quality E-cat in conjunction with fresh catalyst can be cost-effective in maintaining low catahst costs. 

The teed to the cat cracker in a typical refinery is a blend of gas oils from such operating units as the crude, vacuum, solvent deasphalting, and coker. Some refiners purchase outside FCC feedstocks to keep the FCC feed rate maximized. Other refiners process atmospheric or vacuum residue in their cat crackers. In recent years, the trend has been toward heavier gas oils and residue. Residue is most commonly defined as the fraction of feed that boils above 1,050°F (565 C). Each FCC feed stream has different distillation characteristics. 

One area of cat cracking not fully understood is the proper determination of carbon residue of the feed and how it affects the unit s coke make. Carbon residue is defined as the carbonaceous residue formed after thermal destruction of a sample. Cat crackers are generally limited in coke burn capacity, therefore, the inclusion of residue in the feed produces more coke and forces a reduction in FCC throughput. Conventional gas oil feeds generally have a carbon residue less than 0,5 wt for feeds containing resid, the number can be as high as 15 wt lf. 

Four popular tests are presently used to measure carbon residue or concarbon of FCC feedstocks ... 

The Conradson test (ASTM D-189) measures carbon residue by evaporative and destructive distillation. The sample is placed in a preweighed sample dish. The sample is heated, using a gas burner, until vapor ceases to burn and no blue smoke is observed. After cooling, the sample dish is reweighed to calculate the percent carbon residue. The test, though popular, is not a good measure of the cokeforming tendency of FCC feed because it indicates thermal, rather than catalytic, coke. In addition, the test is labor intensive and is usually not reproducible, and the procedure tends to be subjective. 

FCC feedstocks contain sulfur in the form of organic-sulfur compounds such as mercaptan, sulfide, and thiophenes. Frequently, as the residue content of crude oil increases, so does the sulfur content (Table 2-5). Total sulfur in FCC feed is determined by the wavelength dispersive x-ray fluorescence spectrometry method (ASTM D-2622), The results are expressed as elemental sulfur. 

Sulfur Content of Coke vs. Quantity of Residue in FCC Feed ... 

Caustic that is added downstream of the crude oil desalter. Caustic is injected downstream of the desalter to control overhead corrosion. Natural chloride salts in crude decompose to HCl at typical unit temperatures. Caustic reacts with these salts to form sodium chloride. Sodium chloride is thermally stable at the temperature found in the crude and vacuum unit heaters. This results in sodium chloride being present in either atmospheric or vacuum resids. Most refiners discontinue caustic injection when they process residue to the FCC unit. It can still be present in purchased feedstocks, however. 

For FCC feeds, particularly the ones containing residue, the TOTAL... 

Hydroprocessing reduces the Conradson carbon residue of heavy oils. Conradson carbon residue becomes coke in the FCC reactor. This excess coke must be burned in the regenerator, increasing regenerator air requirements. 

DO is the heaviest product from a cat cracker. DO is also called slurry oil, clarified oil, bottoms, and FCC residue. Depending on the refinery location and market availability, DO is typically blended into No. 6 fuel, sold as a carbon black feedstock (CBFS), or even recycled to extinction. 

An RFCC is distinguished from a conventional vacuum gas oil FCC in the quality of the feedstock. The residue feed has a high coking tendency and an elevated concentration of contaminants. 

Hood. R and Bonilla, J., Residue Upgrading by Solvent Deasphalting and FCC, presented at the Stone Webster 5th Annual Meeting, Dallas, Texas. October 12, 1993. 

Dean, R. R., Hibble, P. W., and Brown, G. W., Crude Oil Upgrading Utilizing Residual Oil Fluid Catalyst Cracking, presented at Katalistiks 8th Annual FCC Symposium, Budapest, Hungary, June 1-, 1987. 

Letzsch, W., Mauleon, J. L. Jones, G., and Dean, R., Advanced Residual Fluid Catalytic Cracking, presented at Katalistiks 4th Annual FCC Symposium, Amsterdam, The Netherlands, May 18-19, 1983. 

---