Modern Refinery: Hydrocracking
Transcription
Modern Refinery: Hydrocracking
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We help clients deal with the challenges of today’s market through: Design and EPC Services for the Refining Industry Accelerating Business Performance The Turnaround Optimization Specialists Strategic Solutions Operating Solutions Organisational Solutions Capital Solutions Environmental Solutions www.mustangeng.com AMER +1 281 293 8200 EMEA +44 1932 242424 ASIA +65 6735 5488 www.burnsmcd.com www.kbcat.com www.tacook.com For more information contact Warren Kennedy • (816) 822-3384 • [email protected] Must_OGJpos_100308 1 2/5/10 1:25 PM KBC_OGJpos_100308 1 1/28/10 2:43 PM Berlin Birmingham London Raleigh Rio de Janeiro • Delivering Measurable Benefits in Duration and Costs • Implementing Turnaround Management Optimization • Providing Solutions to Turnaround Challenges BurMcd_OGJpos_100308 1 Abox4u_OGJpos_100308 1 2/1/10 2:42 PM 2/1/10 3:18 PM Noot_OGJpos_090316 1 2/23/09 9:55:49 AM 919-510-8142 TACoo_OGJpos_100308 1 (YDROGEN )SOMERIZATION UNIT ,IGHTNAPHTHA ® Modern Refinery: Hydrocracking Editorial direction and coordination from Warren R. True, Chief Technology Editor www.npra.org www.mustangeng.com Content by the Mustang technical team: Lambert Guzman, Sr. Process Consultant; Kuo Yu, Principal Process Consultant; Doug Purdy, Piping Design; and Tara Johnson, Marketing Communications Coordinator Distributed in partnership with National Petrochemical & Refiners Association (NPRA) Artwork & rendering: Beau Brown, Industrial3d.com Graphic coordination: Chris Jones, Xenon Group | xenongroupdesign.com however, is an attractive alternative to fluid catalytic cracking when production of jet and diesel fuel is important. Process A variety of hydrocracker flow schemes have been used. The following is typical. Hydrocracker feeds are typically gas oils from the crude vacuum unit and the refinery’s coker. These feedstocks can contain carbon residue, metals, and coke fines. Proper filtration of the feed will prevent plugging of the top catalyst bed in the reactor, a serious problem that leads to shutting down the unit for maintenance. Typical filtration includes a system to back flush the unit automatically. The filtered gas oil is pumped into the high-pressure reactor circuit where it mixes with hydrogen. The combined feed is heated by reactor effluent in the alloy feed/effluent heat exchangers 1 . The preheated gas oil and hydrogen mixture is further heated in a furnace 2 to a temperature at which the hydrotreating reaction can start. The hydrotreating reactor 3 contains several beds of nickel or cobalt and molybdenum catalyst. Sulfur and nitrogen removal and olefin saturation are the principal reactions that occur in the hydrotreating reactor. Other important reactions include metals removal and some aromatics saturation. Because these reactions are exothermic, releasing energy in the form of heat, one or more quench hydrogen streams may be needed to limit the temperature rise across each hydrotreating bed. The hydrotreated gas oil/hydrogen mixture proceeds to the hydrocracking reactor 4 . The hydrocracking catalyst formulation and process conditions (temperature, pressure, and quantity of catalyst) are chosen to achieve targeted products. Hydrocracking reactions are also exothermic. A hydrocracking reactor typically requires one or more quench streams to limit the temperature rise across each bed. The hydrocracking reactor effluent is cooled by the feed and routed to the hot high-pressure separator (HHPS) 5 . Formation of mercaptans in the hydrocracking reactor is undesirable. High mercaptan content in the naphtha portion of the reactor product precludes direct routing to a naphtha reformer. Mercaptan content is lowered by employing commercially available technology solutions. Vapor from the HHPS is further cooled by the feed and in the reactor effluent air cooler (REAC) 6 . As this stream is cooled, most of the hydrocarbons condense. Corrosive ammonium bisulfide can also be deposited inside the REAC. Strategies to minimize corrosion include: • Water wash system to remove ammonium bisulfide from the REAC. •B ifurcated (specially designed symmetrical piping arrangement) REAC inlet and outlet piping 7 to ensure proper distribution of the three phase (vapor, hydrocarbon liquid, and aqueous liquid) mixture to each REAC bay. • Proper selection of materials to withstand the corrosive environment. • Limitation of the mixture velocity in the piping and exchanger to less than 20 fps. (Higher velocities are acceptable with use of high-alloy metallurgy.) The cooled HHPS vapor results in three phases, which are separated in the cold high-pressure separator (CHPS) 8 . Vapor from the separator moves to the recycle-gas scrubber where it is contacted with an amine stream to remove H2S. The scrubbed hydrogen is then compressed by the recycle-gas compressor 9 . The compressed hydrogen is mixed with fresh hydrogen from the makeup hydrogen compressors 10 . The mixed hydrogen stream then flows to the beginning of the reaction circuit and to the various quench streams. Rich amine from the recycle gas scrubber is sent offsite for regeneration. Liquid from the HHPS is routed into the hot low-pressure flash drum (HLPFD) 11 where dissolved gases vaporize from the liquid. The vapor from this drum is cooled and mixed with the liquid from the CHPS. The three-phase mixture flows to the cold low-pressure flash drum (CLPFD) 12 . Vapor and water from this drum flow offsite for treating. Liquid from the cold flash drum and hot flash drum move to the H2S stripper 13 . The stripper uses steam to remove H2S from the reactor products. Gas from the stripper is routed offsite for treating. The complicated system of HHPS, CHPS, HLPFD, and CLPFD improves heat conservation, hydrogen purity, safety, and gas recovery. The stripped reactor products are then preheated by various fractionator product and pumparound streams before final heating in the fractionator feed heater 14 . The hot reactor products flow to the fractionator 15 for separation into naphtha, kerosine, diesel, and hydrotreated FCC feed or unconverted oil. In a full conversion unit, most of the unconverted oil from the fractionator is recycled to the hydrocracking reactor. A small portion of the unconverted oil is purged to avoid buildup of heavy poly-nuclear aromatics (HPNAs) in the reactor loop, which would lead to excessive exchanger fouling. Full-range naphtha is produced from the overhead accumulator. Kerosine is drawn from the column and stripped of light material in a sidestripper. Feed to the fractionator is preheated by heat exchange with diesel and fractionator bottoms. All products are finally cooled by air and cooling water and routed to storage or downstream units. 3 4 (YDROGEN ,IGHTENDS 2/5/10 1:24 PM /FFGAS /FFGAS Hydrocracking Hydrocracking is a petroleum refining process that upgrades heavier than diesel petroleum fractions to more valuable finished and intermediate products. Typically a once-through operation, mild hydrocracking is often used in refineries that also have fluid catalytic cracking (FCC) units. The mild hydrocracker improves the quality of the FCC feed by removing sulfur and nitrogen and infusing it with hydrogen (“hydrogenating”), while simultaneously converting some of the gas-oil feed to LPG, naphtha, and distillates (diesel and jet fuel). A full-conversion hydrocracker converts essentially all of the gas-oil feed to LPG, naphtha, and distillates. Hydrocrackers can be designed to produce a large amount of high-quality diesel. For this reason, hydrocrackers predominate in Europe where diesel consumption exceeds motor gasoline. Naphtha from hydrocrackers requires further processing with catalytic reforming to make it suitable to blend with gasoline. Naphtha from hydrocrackers is an excellent feedstock for aromatic hydrocarbon operations, which produce benzene, toluene, and xylenes. A mild hydrocracker with an FCC can be a powerful combination for a refinery. The diesel from the mild hydrocracker can be sent directly to diesel blending. The light cycle oil (LCO) produced by the FCC that is running hydrocracker heavy gas oil is much better quality than LCO from an FCC with poor quality feed. FCC gasoline quality is also improved by running hydrogenated feed. High capital cost can deter new hydrocracker construction. The hydrocracker reaction circuit is designed for high pressure (up to 3,000 psig) and constructed with expensive, high alloys such as 347 stainless steel, Incoloy, and Duplex 2205. Hydrocrackers also have a high demand for hydrogen. Hydrocracking, ConFab_OGJpos_100308 1 2/2/10 5:11 PM Modern Refinery OIL & GAS JOURNAL 1455 West Loop South, Suite 400 Houston, TX 77027 www.ogjonline.com CONTRACT FABRICATORS INC. ENGINEERING • FABRICATION • QUALITY • WWW.CONTRACTFAB.COM (YDROGEN 2EFORMERFEED .APHTHA HYDROTREATER .APHTHA /FFGASES /FFGAS 2EFINERYFUELGAS !MINE TREATING #ATALYTIC REFORMER 2EFORMATES 3TRAIGHTRUNGASOLINE Inlet diffuser .APHTHA #RUDEOIL Top distributor !TMOSPHERIC DISTILLATION 'ASOLINE BLENDING 'ASOLINES +EROSINE $IESEL 'ASOIL /FFGAS ,0' (YDROGEN "OTTOMS .APHTHA (YDROGEN Catalyst bed $IESEL 6ACUUM 6ACUUMGASOIL DISTILLATION *ETFUELKEROSINE $ISTILLATE HYDROTREATER $IESEL (YDROCRACKER *ETFUELKEROSINE $IESEL Catalyst support 6ACUUM TOWER BOTTOMS Quench mixer Redistributor tray /FFGAS (EAVYCOKER GASOIL $ELAYED COKER #OKERNAPHTHA 3OURWATER STRIPPER ,IGHTCOKERGASOIL 3ULFUR RECOVERY UNIT ,0' #OKE Outlet collector 13 15 14 6 7 10 9 12 8 5 11 1 4 Shaping a Secure Energy Future A SMART Refinery: Your Pathway to the Top Quartile Learn more at www.SmartRefinery.com visit us at: www.npra.org EmePro_OGJpos_100308 1 2/1/10 2:13 PM NRA_OGJpos_090316 1 3 CAMERON’S PROCESS SYSTEMS DIVISION NPRA speaks for the petrochemical and rening industries on issues important to their business. We seek to inform policymakers and the public how these industries help improve their lives, strengthen the economy, protect the environment and promote national security. SMART Process Safety • SMART Rotating Equipment Reliability • SMART Energy Management 2 2/12/09 11:35:45 AM Total Solutions. Total Integration. One Leading Provider. www.CameronAcquiresNATCO.com Cameron’s Process Systems division offers the full continuum of processing solutions and best-in-class project delivery. From concept to completion, Cameron is the processing industry’s Total Solutions Provider. www.c-a-m.com www.recip.com /api618 Willb_OGJpos_100308 1 Came_OGJpos_100308 1 2/5/10 4:59 PM Burck_OGJpos_100308 1 2/2/10 11:30 AM 2/1/10 11:21 AM