Abstract
The effect of high emissivity coatings on the radiative heat transfer in steam cracking furnaces is far from understood. To start, there is a lack of experimental data describing the emissive properties of the materials encountered in steam cracking furnaces. Therefore, spectral normal emissivity measurements are carried out, evaluating the emissive properties of refractory firebricks before and after applying a high emissivity coating at elevated temperatures. The emissive properties are enhanced significantly after applying a high emissivity coating. Pilot unit steam cracking experiments show a 5% reduction in fuel gas firing rate after applying a high emissivity coating on the refractory of the cracking cells. A parametric study, showing the effect of reactor coil and furnace wall emissive properties on the radiative heat transfer inside a tube-in-box geometry, confirms that a non-gray gas model is required to accurately model the behavior of high emissivity coatings. Even though a gray gas model suffices to capture the heat sink behavior of a reactor coil, a non-gray gas model that is able to account for the absorption and re-emission in specific bands is necessary to accurately model the benefits of applying a high emissivity coating on the furnace wall.
Highlights
Accepted: 28 January 2021Coatings modifying the emissive properties of surfaces are gaining more and more recognition in various applications including high-temperature nuclear reactors, photovoltaic solar cells, aerospace technology, military applications, the iron and steel industry, and thechemical industry [1,2,3,4,5]
For materials encountered in steam cracking furnaces, namely high temperature alloys and refractory firebricks, experimental data in scientific literature related to emissive properties are scarce
Below 5 μm, the spectral normal emissivity of the high emissivity coating is significantly higher compared to the uncoated refractory results
Summary
Accepted: 28 January 2021Coatings modifying the emissive properties of surfaces are gaining more and more recognition in various applications including high-temperature nuclear reactors, photovoltaic solar cells, aerospace technology, military applications, the iron and steel industry, and the (petro-)chemical industry [1,2,3,4,5]. The classical electromagnetic wave theory can be used to predict all radiative properties, including emissivity, absorptivity, and reflectivity, of any material. There is a need for an extended set of experimental data providing values for the emissive properties of a wide range of materials. No such database is available, with information on material emissive properties being spread over different publications and textbooks [7]. For materials encountered in steam cracking furnaces, namely high temperature alloys and refractory firebricks, experimental data in scientific literature related to emissive properties are scarce
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