Ismael Coello, “Performance of Alumina-Forming Austenitic Alloys in Decoking Environments”
Mentors: Benjamin Church & Lizeth Ortiz, Materials Science & Engineering
Ethylene is one of the most used petrochemicals because it acts as a building block for many everyday plastics. The environment in the tubes where ethylene is made develops solid carbon, or coke, that deposits onto the surface of the tubes, requiring a costly decoking procedure to eliminate the buildup. Decoking takes about 48 hours with a 30-90 day frequency and is typically done with a mixture of steam and air or only steam while the furnace is shut down. The reactor tubes are typically made from alloys that form a protective chromium oxide layer or, more recently, an aluminum oxide layer due to its resistance to coke accumulation. This study aims to compare the effects of three decoking environments on alumina-forming alloys in comparison to the baseline chromia-forming alloys to determine which environment is most beneficial to the tube. Further, a secondary conclusion regarding which alloy performs better in these conditions will be described. Samples will be analyzed after being placed in an atmosphere similar to what they would experience in a petrochemical plant. The decoking environments will differ only in their oxygen partial pressure from only air, only steam, and a mixture of both. Both materials will be characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, light microscopy, microhardness, and mass changes to understand how various procedures alter the alloys. The close inspection after every processing step will determine which alloy exhibits greater coke and carburizing resistance. Also, the decoking environments will show the effect of oxygen activity on the carbon layer and on both alloys. These results will potentially decrease the cost associated with manufacturing downtime.