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E Technologies for Converting Heavy Oil COMMERCIAL CARBON REJECTION PROCESSES Carbon rejection processes operate at moderate to high temperatures and low pressures and suffer from a lower liquid yield of transportation fuels than hydrogen addition processes, because a large fraction of the feedstock is rejected as solid coke high in sulfur and nitrogen (and gaseous product). The liquids are generally of poor quality and must be hydrotreated before they can be used as reformer or fluid catalytic-cracking (FCC) feeds to make transportation fuels. Delayed Coking Heavy oil or vacuum resid is heated to above 480C (900F) and fed to a vessel where thermal cracking and polymerization occur. A typical product slate would be 10 percent gas, 30 percent coke, and only 60 percent liquids, the coke percentage increasing at the expense of liquid products as feeds become heavier. Since sulfur is concentrated in the coke, the coke market is limited to buyers that can control, or are not restricted by, emissions of sulfur oxides (SOx). Fluid Coking Heavy oil is fed to a reactor containing a 480 to 540C (900 to 1000F) bed of fluidized coke particles, where it cracks to produce lighter liquids, gases, and more coke. The coke is circulated to a burner vessel where a portion of the coke is burned to supply the heat required for the endother- mic coking reactions. A portion of the remaining coke is returned to the 178

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APPENDIX E 179 reactor as fluidizing medium, and the balance is withdrawn as product. The net coke yield is only about 65 percent of that produced by delayed coking, but the liquids are of worse quality and the flue gas from the burner re- quires SOX control. Plexicoking Flexicoking is an extension of fluid coking. All but a small fraction of the coke is gasified to low-Btu gas (120 Btu/standard cubic foot) by addi- tion of steam and air in a separate fluidized reactor. The heat required for both the gasification and thermal cracking is generated in this gasifier. A small amount of net coke (about 1 percent of feed) is withdrawn to purge the system of metals and ash. The liquid yield and properties are similar to those from fluid coking. The need for a coke market is eliminated or mark- edly reduced. The low-Btu gas can be burned in refinery furnaces and boilers or probably could also be used in cogeneration units to generate power and steam; but it must be used near the refinery since its heating value is too low to justify transportation. Unlike with fluid coking, SOX is not an issue since sulfur is liberated in a reducing atmosphere (carbon mon- oxide and molecular hydrogen) inside the gasifier; however, hydrogen sul- fide removal is required. Resid FCC and Heavy Oil Cracking This is an extension of gas oil FCC technology. Resid (usually above 650F boiling point, not vacuum resid) is fed to a 480 to 540C (900 to 1000F) fluidized bed of cracking catalyst. It is converted to predominantly gasoline-range boiling materials, and the carbon residue in the feed is de- posited on the catalyst. The catalyst activity is then restored by burning the deposited coke in the regenerator. This also supplies the heat required to crack the feed in the next contacting cycle. The sulfur emissions are typi- cally controlled by additives that bind the sulfur to the catalyst for later reduction to hydrogen sulfide in the FCC reactor. The hydrogen sulfide is later processed to sulfur for sale as low-value by-product. In resid FCC the feed contains so much carbon residue that heat ex- changers (steam coils) must be installed to remove the extra heat when the added coke is burned. To be energy efficient, refineries must have an onsite use for high-pressure process steam or use it to generate electricity. Modern resid FCCs can process feeds containing up to about 10 percent carbon residue and 50 ppm of metals. This requires the use of additives to mitigate the poisoning of the catalysts by the nickel and vanadium in the feed. Since many virgin heavy oils and atmospheric reside have carbon residues of 10 to 20 percent and metals contents of 100 to 500 ppm, this

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180 APPENDIX E process usually cannot be used as a stand-alone method for converting resid to transportation fuels. Upstream processing such as solvent deasphalting or RDS (resid desulfurization) is required. DEVELOPMENTAL CARBON REJECTION PROCESSES WITH LIMITED COMMERCIAL DEMONSTRATION Asphalt Residue Treatment (ART) Process ART is a coking and vaporization process developed by the Engelhard Company, in which resid is reduced in metals and carbon residue in a prereactor similar in design to an FCC. The feed is contacted briefly with an inert solid at about 480C (900F) to volatilize all components of the feed except metals and carbon residue. After stripping the volatiles from the inert particles, the coke is burned off the solid in a regenerator to produce the required process heat. This is an elaborate method of distilling the feed without significant cracking. Feeds containing up to 15 percent carbon residue and 300 ppm metals can be processed, but the cost of the inert solid can become prohibitive for extremely high metals feeds. Also, flue gas desulfurization is required to handle the SOX emissions from the regenerator. The liquid product yield is high, but quality is low and re- quires further upgrading. The product is suitable feed for a conventional gas oil FCC. COMMERCIAL HYDROGEN ADDITION PROCESSES Hydrogen addition processes include catalytic or thermal hydrocracking or donor solvent type processes. All operate at high pressure (1000 to 3000 psi) and moderate temperatures (371 to 427C t700 to 800F]~. Fixed Bed Residuum or Vacuum Residuum Desulfurization (RDS/VRDS) This was originally developed over 20 years ago to remove sulfur from residual fuel oils. As available crude oils become heavier and the market for fuel oil decreases, the process is increasingly being viewed as feed pretreatment for downstream conversion units. In this process, atmospheric or vacuum residual oil contacts catalyst and hydrogen at 354 to 427C (670 to 800F) and about 2000 to 2500 psi", consuming about 700 to 1300 scf of hydrogen per barrel of feed. The process typically removes most of the metals and sulfur and over half of the coke precursors ("carbon resi-

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APPENDIX E 181 due") and hydrocracks 20 to 50 percent of the vacuum resid in the feed to primarily gas oil products. The higher conversions achievable at higher operating temperatures are not feasible with fixed bed RDS because of reactor coking and plugging. The process is not practical for extremely high metals feeds (over 250 ppm) because catalysts deactivate so fast that catalyst replacement costs are high and run lengths become prohibitively short. RDS/VRDS does not convert much heavy oil to transportation fuels directly, but it can convert many of the heaviest oils into acceptable feed for resid FCCs. Alternatively, the unconverted vacuum resid can be fed to a coker or used as a fuel oil blend stock. Bunker Flow or Hycon Process This process for hydrotreating resid is very similar to that for a fixed bed unit, but with the following important feature: Catalyst can be added to the top of the bed and catalyst can be withdrawn from the bottom while the unit remains onstream. This feature permits somewhat higher cracking conver- sions, a more uniform product slate, and longer times onstream between shutdowns. Ebullating Bed Processes Such catalytic hydrocracking processes known as LC-fining (developed by the Lummus Company) and H-oil (developed by Hydrocarbon Research, Inc.) can be used to demetallize, desulfurize, and hydrocrack any heavy oil. The process involves high-pressure catalytic hydrogenation but runs at higher temperatures than fixed bed RDS (about 426 to 441C t800 to 825F]~. The feed passes upflow, expanding the catalyst bed with the ebullation and producing a back-mixed isothermal system. Reactors are very large relative to fixed bed and are frequently staged to overcome the kinetic penalties associated with back mixing. A big advantage is the ability to add and withdraw catalyst while the unit is onstream, which allows the processing of oils with high metal concentra- tions than is practical with conventional fixed beds. However, catalyst replacement-costs will still be high with high metals feeds. Also, the ebul- lating bed eliminates coke plugging problems and allows high-temperature operation and high (70 to 90 percent) vacuum resid conversions. The disad- vantages include hydrogen consumption that is 20 to 100 percent higher than that for fixed bed RDS, and loss of liquid and hydrogen to high gas yields. The distillate products are low quality and require further hydro- treating and conversion to produce transportation fuels. Like fixed bed units, an economic "home" for the unreacted vacuum resid is still required.

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182 APPENDIX E DEVELOPMENTAL HYDROGEN ADDITION PROCESSES WITH LIMITED COMMERCIAL DEMONSTRATION Many slurry hydrocracking processes have been developed, including CanMet, Aurabon, Veba Combicracking, and Microcat. These processes are all variations of thermal (426 to 468C [800 to 875F]), high-pressure (1500 to 3000 psi) hydrocracking. In a cracking reactor a dilute slurry of fine particle size, high surface area additive is present to suppress coke formation and attract feed metals, removing them from liquid products. These additives include vanadium sulfides, molybdenum sulfides, iron, and cobalt-molybdenum deposited on coke or coal. Conversions of vacuum resid are high (60 to greater than 90 percent). The uncracked bottoms are of poor quality, and at high conversions they are probably suitable only as coker feed, hydrogen plant feed, or to burn for process heat. The additives are not very active hydrogenation catalysts, so the products from the crack- ing reactor are fairly high in sulfur and nitrogen unless they are further hydrogenated in a second stage. Several processes have an integrated fixed bed catalyst second stage to further hydrogenate, desulfurize, and identify the cracked products with boiling points below 538C (1000F).