Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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64 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS SELECTION & DESIGN U India has large deposits of coal seams in deep layers. Exploitation of such coal has been envisaged through un- derground coal gasifcation. This is a means of green fuel generation in which controlled combustion of coal yields syngas that is drawn out and used as fuel. The process involves high-temperature corrosion, and suit- able corrosion-resistant alloys have been identifed as materials for well conduits. Underground coal gasification (UCG) is a process of converting deeper layers of unworked coal into a combustible gas for h e a t i n g , p o w e r g e n e r a t i o n , a n d t h e manufacture of hydrogen, synthetic natural gas, and diesel fuel. UCG technology allows countries endowed with coal to fully utilize this resource from otherwise unrecover- able coal deposits. The process is economi- cally viable and environmentally safe. Use of syngas prevents the discharge of fly ash and acid gases into the atmosphere. India has large deposits of deep coal seams in various parts of the country and exploita- tion of such coal has been envisaged by Oil and Natural Gas Corp., Ltd . (ONGC), a government of India undertaking. The UCG process involves drilling two wells into the coal, one for injection of the oxidant (air/steam) and another well some distance away to bring the product gas to the surface. The coal at the base of the first well is heated to ignition temperatures. Combustion follows by pyrolysis and gasifi- cation , w hich produces syngas that i s drawn out of the second well. The conduits of UCG process wells are exposed to com- plex gas mixtures from the combustion of coal at high temperatures. This article presents detailed analyses for assessing the severity of corrosion from high-temperature oxidation, sulfidation, and carburization, and identifies suitable corrosion-resistant alloys (CRAs) as mate- rials of construction. Underground Coal Gasification Well Completion The UCG process involves two types of wells: injector and producer wells. 1 Com- pressed dr y air is injected into injector wells to ignite the coal seam and generate the heat required to facilitate the reaction between steam and coal to form syngas. An additional injector well on the coal seam path is also drilled for injection of air/ steam to improve efficiency of the combus- tion process, and the fire front advance along the coal seam path is facilitated by additional injection of air or steam into the path. The resulting syngas is withdrawn through producer wells and sent to a com- mon gas pipeline. Injector Well Completion The typical completion for the injector well has only a casing with an ignitor Material of Construction for Underground Coal Gasifcation Wells S. Bhat, Bipin Kumar, and m.V. KatarKi, Oil and Natural Gas Corp., Ltd. (ONGC), Panvel, Navi Mumbai, India

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