Pressure vessels for coal conversion systems

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Abstract
Pressure vessels for coal conversion systems are long-lead-time, difficult-to-replace items; as suggested in some commercial conceptual designs, they will be the largest units ever fabricated anywhere in the world. They will probably be designed to Section VIII of the ASME Boiler and Pressure Vessel Code. Further, because of their size and complexity they will probably be built to the rules of Section VIII, Division 2. Economics and operating conditions will dictate that these large vessels be fabricated from carbon and low-alloy steel plates and forgings that range from 0.2 to 0.3 m (8 to 12 in.) in thickness. Current ASME Code toughness requirements need to be reassessed for their adequacy to assure safe and reliable service over the 20 to 30 year design life of these vessels. An example is the minimum requirement of 20 J (15 ft-lb) for steels with ultimate tensile strength of 517 MPa (75 ksi). Moreover, there are no rules in the Code that require that the owner consider the influence of process environment on the toughness of a pressure vessel during its operational lifetime. These codes were developed for units that do not operate under combinations of variable process stream conditions as harsh as thosemore » that will be encountered in commercial coal conversion systems. Further, the extremely thick-walled vessels that are proposed in a number of conceptual designs may not provide the margins of safety and reliability that thinner walled materials can assure; in particular, the conservativeness of a leak before fracture criterion.« less

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