The multiphase technology in power plant boiler during last ten years in Japan have been reviewed. The most important events on utility boiler are the appearance of coal fired supercritical sliding pressure operation boiler, the increase in steam pressure and temperature for higher plant efficiency, and the increase in number of gas turbine combined plants. Concerning these events, some key technology were developed in multiphase field. The detailed study on boiling heat transfer in rifled tube realized the vertical tube type boiler, which had more simple furnace wall structure than the spirally wound type ones. The ultra supercritical pressure boiler achieved 5% higher efficiency than the normal pressure ones. The natural circulation waste heat boiler with horizontal evaporating tubes, which enabled low cost construction, was designed under attentive thermal and hydraulic studies, and successfully started to operate. The condensing heat transfer of ammonia-water mixture was investigated and the high efficiency of the mixture cycle was demonstrated through test plant operation. Regarding fuel, coal oil mixture, coal water mixture, and orimulsion were introduced. For clean and efficient usage of coal, PFBC and IGCC are expected as the important future power generation system.
