Operating problems with startup valves in US and Japanese supercritical steam generators: Topical report

The evolution of the boiler start-up systems for once-through units (OTUs) in the United States is outlined. The service requirements for the control valves of a generic flash tank-based start-up system are described. ''Control-Valve Problem Questionnaires'' were prepared and distributed to operators of OTUs in the United States of America and Japan. The results from the questionnaires are presented for the superheater bypass, furnace outlet throttling, and turbine bypass control valves. The minutes of interviews with two US boiler manufacturers and four utility operators of OTUs are presented. The topic of discussion was OTU control valve problems and solutions. A summary of control valve problems at OTUs in Japan is presented. A distinction is made between base-loaded OTUs and the new cycling OTUs. Factors influencing the decision to replace original control valves with modern valves are summarized. 8 refs., 19 figs., 12 tabs.