AM-97-65 THE FUTURE OF FLUID CATALYTIC CRACKING

Description:

While fluid catalytic cracking was developed to be a gasoline machine, the last thirty years have seen the advent of significant new drivers that are expanding and reshaping the process. These external factors and demands include: A. Environmental Regulations B. Increasing Crude Oil Prices C. Reformulated Fuels D. Increased Petrochemical Feedstocks E. Residual Upgrading Such a diverse set of drivers has given the fluid catalytic cracking process new directions and has created new refining processes from the old. The Stone & Webster/IFP R2R residual cracking process and the Deep Catalytic Cracking technology are prime examples of these advances. The process drivers have prompted evolutionary changes but the actual advances in FCC technology listed in Table 1 have come from many sources and tend to act synergistically. These same factors will continue to propel the new variations on the cracking process in the future. Overall growth in catalytic cracking will be about 1% worldwide. Figure 1 shows the growth of the United States and the rest of the world for the last eight years with predictions until the end of the decade. These statistics are skewed by the recent inclusion of China (1995 & 1996) in the Oil & Gas Journal’s surveys. The actual number of new units being built may be somewhat larger due to the replacement of obsolete equipment. An average FCC unit is about 30,000 B/D, but the new units are usually larger, i.e., 40 - 50,000 B/D. Two important observations are that growth in the U.S. is flat and there is now more FCC capacity outside the U.S. and these trends will continue in the future. The United States will remain the FCC center of technology for the foreseeable future even though few new units will be built here. More variety in the types of FCC process will be seen. Figure 2 shows the number of FCCU’s designed specifically for resid processing in recent years while the actual number of units processing some resid is 2 to 3 times larger. This represents almost 25% of the worldwide FCC units. Most refiners prefer to install this flexibility in new units since it costs little and has a fast payback. Units designed for petrochemical feed production will make up a new category. Anywhere from 8 to 10 of these units will be operating by the year 2000. (Figure 3). Cracking catalysts have made a huge contribution to the development of catalytic cracking. They are in fact the heart of the process. After all, it is the catalyst that reacts with the feedstock, not the hardware. Even better catalysts will be produced in the future with the attributes shown in Table 2. Step changes are few but constant progress will push the boundaries of the current catalysts and equipment. One of the refiners’ biggest problems is the current obsession with lower costs. This is depriving many refiners of catalysts that could have a substantial positive impact on FCCU performance. Improvements in hydroprocessing of cracker feeds has a dramatic effect on the performance of the cracking unit and is well documented for vacuum gas oils. In Table 3 the capability of Vacuum Resid Desulfbrization is shown. The resulting product makes a good feed to a cat cracker and has been run quite satisfactorily without the addition of a catalyst cooler. In Figure 4 a graph of resid properties versus processability in a modem R2R resid cracking unit is plotted in the same manner as presented by Shell a few years ago. Without any pretreatment, the R2R process can handle about 20% of the world’s crudes without a catalyst cooler and about 30% when one is included in the design. The data from Table 3 suggests most of the world’s crude could be handled with an ARDS or VRDS in front of a resid cracker. Table 4 is a partial list of feedstocks that have been commercially processed. This technology will continue to improve with metals removal as the prime target for newer technologies. Refinery and petrochemical integration will take on increased importance in the future. The plants can use common equipment and produce more value added products. Deep Catalytic Cracking @CC), a process pioneered by the Chinese, is especially suited for this processing configuration. A comparison of the DCC yields in two different modes is made with both a conventional FCC operating to make light olefins and a steam cracker in Table 5. The olefin yields in the DCC process are enhanced and the gasoline produced is suitable for either RFG blending or BTX extraction. Better feedstock characterization for resid feeds will occur. The goal is to characterize each significant fragment of the feed molecules, sort them by class, and correlate them to yields and product quality. The gross properties such as gravity, sulfur, average boiling point, etc. give good results with gas oils but are not comprehensive enough for more complex, heavier feeds. Feed blends make the problem even more difficult. NMR techniques have been used with great success but this is being augmented with new methods that better describe the heavy feeds. All of the new FCC units will be environmentally compatible with future regulations. For the FCC this means low emissions of particulates, SOx and possibly NOx. Extensive feed desulfinization would limit the SOx in the flue gas to low levels (~300 ppm) that could be supplemented with a DeSOx additive to meet even more stringent requirements. Particulate emissions are typically met with third and fourth stage separators or electrostatic precipitators. These are sometimes arranged in series to further enhance catalyst separation. A wet gas scrubber is very attractive when both particulate and SOx removal are required. As the environmental rules become tougher to meet, the multistage contacting scrubber meets all the existing and proposed standards. Even NOx can be reduced in the future with this technology, though the FCC unit usually only has small concentrations of these compounds. The multistage scrubbers offer the following benefits over venturi scrubbers. l Lower Pressure Drops l Higher Efficiency (Multistage) l Less Tendency To Plug @ Lower Capital and Operating Costs l Modular for Treating PM, $0~ and/or NOx These scrubbers represent the best available pollution control technology. A picture of such a unit is shown in Figure 5.