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Materials are often the limiting factor of cost-effective performance improvements in distributed energy technologies. Power-producing equipment is pushed to operate at higher pressures, higher temperatures, and higher speeds—all of which put increasing demands on materials. As these demands increase, materials with improved properties must be used or developed.
An example is the development of compact, turbine-driven electric generators, or microturbines. To operate more efficiently and with less pollution, these turbines may operate at temperatures approaching 2,500°F and at speeds of more than 50,000 rpm. But to operate at these conditions for long periods of time, stronger materials that do not degrade at high temperatures are needed.
Similar challenges exist for power generation technologies such as fuels cells, gas-fired reciprocating engines, and industrial turbines. Improved metal alloys and new ceramic materials are being considered for these applications. In addition, as materials are developed or improved, new manufacturing methods are often required. The Distributed Energy Program identifies materials and manufacturing technologies to enable power-generating equipment to meet goals of efficiency, life, emissions, and cost.
One high-priority area is ceramics and ceramic composites. Advanced ceramic materials are being incorporated into hot sections (combustion and hot-gas flow paths) of land-based industrial gas turbines and microturbines so these engines can meet strict emission standards by operating at higher temperatures. Silicon-based continuous fiber ceramic composites and monolithic silicon nitride are the primary materials under consideration for hot-section components. Over the past several years, advancements in the development of more environmentally stable continuous fiber ceramic composites and protective coatings (environmental barrier coatings) have resulted in the use of these materials as combustor liners in several microturbine engines. However, to have lifetimes greater than 25,000 hours, considerable materials development work must still be conducted. Research is under way at Oak Ridge National Laboratory to characterize the behavior of these materials and develop improved environmental barrier coatings.
Advanced microturbines will require improved high-temperature performance and reliability from their recuperators to achieve higher efficiency. This means materials with more oxidation/corrosion resistance and tensile/creep strength at higher temperatures must be developed or a more expensive alloy with better performance must be selected. Oak Ridge National Laboratory is working with microturbine manufacturers and materials suppliers to develop advanced alloys for high-temperature recuperators.
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