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Steam Reformer

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Information about Steam Reformer
Science-Technology

Published on November 9, 2011

Author: baher

Source: authorstream.com

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Steam Reformer: Steam Reformer Construction and main damage mechanism By: Baher EL Shaikh baherfm@yahoo.com Introduction: The steam reformer is one of the main critical equipment in Methanol and Ammonia production plants The cost of the reformer is a substantial part of the investment of the complete plant The steam reformer is used in the production of synthesis gases from the natural gas steam is mixed with the natural gas and the combined stream is further heated and routed through tubes in a reforming furnace containing nickel oxide catalyst. Introduction Description: The steam reformer is a rectangular insulated structure containing vertically supported tubes filled with nickel oxide catalyst in which the steam rforming takes place at elevated temperatures. The endothermic heat of reaction is supplied from downward firing burners situated in the roof of the Reformer arranged in rows between the reforming tubes. Description Main components: Burners (main and auxiliary burners) Catalyst tubes Inlet and Outlet Pigtails Convection section coil (steam super – heaters and mixed gas heaters) Ducting (air and flue gas) Refractory lining Steel work Reformer gas main (cold collector) Flue gas stack Main components Reformer Tube Assembly: Reformer Tube Assembly Reformer Tube Assembly: Tubes are fabricated from centrifugal cast materials. This material provides high potential to withstand the operating conditions that it has superior stress-to rupture strength at high temperature. The most successful alloy is the micro-alloys, which is obviously the stronger alloy (e.g. CA 4852-Micro). These materials have high stability of carbide, increased creep strength, higher durability and oxidation resistance compared to the conventional materials. Reformer Tube Assembly Reformer Tube Assembly: Advantages of using cast micro-alloys: Possibility of operation of the reformer at higher temp. & pressure Reduced reformer tube wall thickness Increased quantity of catalyst packing in the same space These materials provide high resistant to metal dusting. Uniform oxidation of the alloys definitely inhibits carburization and metal dusting temporarily through formation of protective scales Reformer Tube Assembly Outlet Manifold Assembly: Outlet Manifold Assembly Outlet components such as manifold tube, Cone sections and T-pieces are made from centrifugal casting material Outlet Pigtail (Hairpin): Outlet Pigtail (Hairpin) Outlet pigtail is fabricated from pipes under the rules of ASME B31.3 . The Outlet pigtails are made from ASTM B 407 alloy 800H ( 30%Ni, 20%Cr). Alloys 800H and 800HT are the standard materials for Intermediate temp.(620:925°C ) Inlet Pigtail (Hairpin): Inlet Pigtail (Hairpin) Inlet pigtail is fabricated from pipes under the rules of ASME B31.3 . The inlet pigtails are made from Austenitic st . st . 304H Inlet Pigtails operates at temp. lower than outlet pigtail Damage Mechanisms Affecting Reformer Tubes: Damage Mechanisms Affecting Reformer Tubes The main damage mechanism for reformer tubes is the combination of thermal stresses across the tube wall and internal pressure stresses causing CREEP damage. The damage process results in diameter increase and creep damage( cavitation ) at the inner diameter. Final rupture occurs in a longitudinal direction. Another main damage mechanism can be overheating by catalyst degeneration or by operating upsets causing creep damage over a small part of the circumference and over a short (axial) part of the tube Damage Mechanisms Affecting Outlet Manifold Assembly: Damage Mechanisms Affecting Outlet Manifold Assembly The main damage mechanism for outlet component is hindered thermal expansion. The outlet system cannot expand or shrink freely during shutdown and start up The damage starts at the outer diameter and concentrates near the welds. The final rupture occurs in circumferential direction. Another damage mechanism is creep under internal pressure resulting in diameter increase and creep damage at theouter diameter. Final rupture occurs in longitudinal direction. Damage Mechanisms Affecting Outlet Pigtails: Damage Mechanisms Affecting Outlet Pigtails The commonly reported failure mechanism in the outlet pigtails is intergranular oxidation cracking, due to the combination of creep, oxidation. This mechanism involves interaction of mechanical fatigue, high temperature creep, diffusion of carbon and chromium, and high temperature oxidation. Refrences: Refrences ASM handbook Volume 13 "Corrosion". API 571 “ Damage mechanisms affecting fixed equipment in the refinery industry Kirchieiner . R. and Woelopert , P. Niobium in certified cast tubes for petrochemical applications. NACE paper no. 01374; correlation of oxidation, carburization and metal dusting; "controlling corrosion by corrosion". NACE paper no. 03657; Failure mechanism of alloy 800H in steam reformer furnace pigtails. Paper of the 6th Schmidt + Clemens Group Symposium; "Life assessment and inspection techniques in reformer furnace". Paper of Johnson Matthey Catalysts about Re-tubing your primary reformer the Katalcojm performance concept. Thanks: Thanks By: Baher EL Shaikh baherfm@yahoo.com

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