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Report RSE 18002403

The metallic and ceramic materials that can be used for the manufacturing of a highefficiency micro-turbine



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A. Cavaliere (RSE SpA), C. Guardamagna (RSE SpA) , F. Cernuschi (RSE SpA) , A. Cammi (RSE SpA) , S. Capelli (RSE SpA), S. Concari (RSE SpA) , L. Lorenzoni (RSE SpA)

CONVENERGIA 2017 - Small scale energy conversion plants

The experimental activities for the characterization of metallic materials, the development of EBC coatings and the design and construction of a steam jet rig to evaluate their effectiveness in protecting bulk material are described.

Co-generation plants with micro-turbines are an interesting alternative to reciprocating engines, sincethey add more fuel flexibility to the advantage of low emissions. In fact, even liquid or solid fuels can beused as an alternative to different gaseous fuels, ranging from natural gas to biogas and landfill gas.Prototype applications of either direct combustion of pyrolyzed solid biomass or external combustion ofwood chips are reported in the literature.

For the microturbine-based technology, in order to become competitive, it is necessary to increaseelectrical efficiency, so as to make it convenient to use even in the case of pure electricity generation, inthe absence of heat demand.

As a matter of fact, the increase in electrical efficiency would widen the type of potential applications, inparticular in the residential and/or tertiary sector, where typical users have seasonal thermal needsprofiles strongly variable over time, that does not justify the use of a cogeneration technology with arelatively low electrical efficiency.

As highlighted by the literature analysis and by studies carried out by RSE in previous years, anelectrical efficiency higher than 40% can be achieved only by increasing the turbine input temperature.This means, in fact, that the hot parts of the turbine must be made with materials capable of operating attemperatures that go beyond the current state of the art, which can be estimated at around 950°C.
Considering that any technological solution hypothetically capable of leading to a significant increase inefficiency has a certain degree of uncertainty, an activity plan has been launched on several alternativeand partly complementary fronts which includes the identification and characterization of advanced highperformance metallic materials, as well as the completion of the characterization of monolithic ceramicmaterials already identified in recent years. Furthermore, new technologies such as additivemanufacturing (or 3D printing) that is already successfully applied in several industrial sectors, havebeen considered as well.

In this perspective, in this report the results of the characterization of the mechanical properties of asingle crystal nickel base superalloy are summarised. These data will be the input for designing themicro-turbine hot paths able to operate at a turbine input temperature equal to 1050C.

As concerns ceramic materials, the activities have been mainly focused on the production of samples ofprotective coatings made with different techniques including thermal spray techniques.

Finally, a Steam Jet Rig was designed, built and tested to evaluate the functional performance anddegradation phenomena of ceramic materials and protective coatings when exposed to high speed, hightemperature steam rich air at 1200 ° C, in conditions representative of the real case of a high efficiencymicro-turbine.

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