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Materials & Components

in Fossil Energy Applications

A newsletter of the U. S. Department of Energy, Advanced Research and Technology Development Materials Program, and EPRI

Number 143 December 1, 1999

Development of technically and economically viable processes for the conversion and utilization of fossil fuels is a major objective of both the DOE Fossil Energy program and EPRI. Many new and different processes are being investigated in areas of coal gasification and liquefaction, improved power generation and advanced combustion. As these processes evolve to the pilot plant stage and beyond, materials selection and component design become increasingly important for reliable and economical operation. The newsletter is intended to serve as a medium for exchange of information and experiences pertinent to the use of materials and components among the communities interested in the development of fossil energy systems.

Microturbines Are Generating Interest

Deregulation of the gas and electricity industries has led to interest in new and different approaches to supplying energy services. Distributed generation (DG) systems are being promoted to serve a variety of roles: for instance, they could be used by a utility to locate generating capacity close to the user to relieve congestion of the distribution network. DG systems installed in large buildings such as hospitals and shopping malls could augment grid-supplied power, while location in remote sites without grid access is a further obvious application. An area of considerable current interest is the use of microturbines in DG systems.

Microturbine generators are small power plants that usually combine a compressor, turbine, generator, or power elec- tronics to produce electricity, heat, or mechanical power to, for example, compressors in refrigeration systems. Most microturbines are single-shaft designs that produce 20-100 kW(e), typically in the kHz range, which must be converted to high voltage DC and then inverted to 60 Hz. They operate at relatively low pressure-ratios (typically 3:1 to 5: 1). However, the natural gas distribution system does not generally provide gas at these pressures and most manu- facturers are offering a compressor as an option. Most microturbines use a single-stage compressor and one or two turbine stages; the compressor/turbine rotates at 50,000- 90,000 rpm. Where a two-stage turbine is used, the first stage drives the compressor, and the second stage drives the load.

Figure 1 is a schematic representation of a recuperated microturbine power generation system configured to pro- duce electricity as well as steam or hot water from a heat recovery system applied to the turbine exhaust. The effi- ciency of a non-recuperated microturbine can be low, rang-

ing from the upper teens to the low 20’s (percent, LHV). Currently, however, most microturbines employ an exhaust gas recuperator which preheats the combustion air, and this results in overall efficiencies in the high 20’s (percent, LHV). Where the waste heat (that is, the sensible heat in the microturbine exhaust that would otherwise be exhausted to the atmosphere) can be effectively used, overall system efficiency of a recuperated microturbine can be as high as 80 percent. Uses for waste heat (as hot water, or steam) will be determined on a case-by-case basis, but will probably be easy to find because of the relatively small amount of thermal energy produced by an individual microturbine.

Approaches that are used to raise the efficiency of large gas turbines, such as combined cycle operation, probably are too costly for adaptation to microturbine systems. Improve- ments from better fluid dynamic design would provide only small overall efficiency increases in microturbines because of the small size of the airfoils. Increase in the turbine rotor inlet temperature (RIT) and/or pressure ratio would lead to

In This Issue

Microturbines are generating interest...............................................p. 1 AEP tests a commercial microturbine generator..............................p. 4 Continued development of PFBCs...................................................p. 4 Testing at the Wilsonville Power Systems Development Facility...p. 7 Iron aluminide filters for hot-gas cleanup........................................p. 10 FETC becomes a National Laboratory.............................................p. 12 Development of ceramic oxygen separation membranes.................p. 12 Solicitation for concepts for next-generation gas turbine systems...p. 13

Development of low-cost options to upgrade natural gas................p. 14 Books and articles.............................................................................p. 14

Calls for papers.................................................................................p. 15 Meetings calendar....................................................................p. 15

A word from our sponsors.......................................................p. 16

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