Date: Thursday, Feb 25th
Presenter: Jefferey Hawk, National Energy Technology Laboratory, Department of Energy, Albany, OR
Steam turbines have been providing electricity for well over 100 years, however, large-scale generation has only dominated energy production since 1950. Given the size of the boiler and accompanying steam turbine, materials of construction have typically been low cost, i.e., low alloy steels primarily. The workhorse steel for most steam turbines has been, and continues to be, Cr-Mo-V. Since the 1990?s there has been increased emphasis on improving the efficiency of large steam turbines, partly to increase the rate of return on initial investment, but more recently to decrease the amount of greenhouse gases emitted to the environment per unit mass of coal consumed in the boiler. The typical way to increase efficiency is to raise the temperature of operation of the steam turbine and/or increase the pressure. Doing either means that most current materials of construction are no longer adequate in meeting the stresses generated by the moving and stationary parts. This lecture will provide some background information on steam turbine technology as temperatures and pressures have increased over the past century, and address the way materials have been identified and selected for use in them. The materials currently used in steam turbines will be examined from mechanical and metallurgical points of view, with discussion on current strategies of alloy design for high temperature use. The last portion of the lecture will touch on the next generation of steam turbines designed to operate at temperatures in excess of 700°C.