Speaker
Description
In a global context where the decarbonization of high-temperature industrial processes for material transformation or energy conversion is an important issue, heating technologies based on electric radiants are once again being studied. Academic work shows that the best possible electric radiant is one whose directional spectral emissivity is analogous to that of the Planck black body as shown by the thermal balances involving a radiant source and a receiver to be heated. Commercial radiants are far from having this propensity, due to the choice of refractory materials used: semi-transparent alumino-silicate ceramics, refractory metal alloys with moderate emissivity, carbon ribbons with higher emissivity but having to work in a protective atmosphere, silicon carbide ceramics with high emissivity that become brittle at 900°C due to chemical corrosion. An original, but little-known approach consists of creating a coating of mixed rare-earth oxide with very high emissivity on the surface of an electric plane radiant (200643 mm, 1000 and 1500 W) made of cordierite-mullite. As long as the microscopic mechanisms responsible for the oxide's intrinsic high emissivity are active, the overall radiative character is pseudo-blackbody-like. The thermal-radiative data available to date on this family of oxides shows that a operating temperature of 1000°C under air can be targeted today. Electrical data suggest that higher working temperatures can be achieved. In this work, we will show how the use of high-temperature X-ray µ-tomography combined with scanning electron microscopy can highlight the crucial role of the micro-porosity of high-temperature spray-pyrolysis Pr2NiO4+d deposits in their high-temperature radiative behavior. Multi-scale modeling combining a macro-scale ray-tracing method, a meso-scale Maxwell-Garnett model and a micro-scale Drude-Lorentz model confirms the key role of this internal micro-porosity. We will discuss the link between the elaboration process put in evidence, the dual-scale texture of the deposits and the thermal radiative properties obtained. The challenges posed by this study will also be discussed, ranging from characterizing the radiative properties of these coatings up to 1500°C, to characterizing micro-porosity using advanced methods (X-ray nano-tomography, USAXS, SANS, FIB-SEM, etc.) up to choosing effective media laws that take into account possible cooperative electromagnetic effects. Considerations for large-scale industrial deployment (900 MW steam cracking furnace, foundry furnace) will also be addressed.
| Country | FRance |
|---|---|
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