This paper is established on the basis of experience accumulated in the F C C (fluidized-bed catalytic crackers in petroleum refinery) flue gas expanders. It first discusses design features and design criteria based on erosion and aerodynamics; then erosion, deposition and corrosion characteristics; design alternatives and machine train arrangement; and finally prospects for design, research and development of the pressurized fluidized bed combustion (PFBC) gas expander.