This dissertation begins with a description of the history of the events leading to ethylene pyrolysis tube failure. During service, hydrocarbons pass through the radiant heater coils at temperatures up to ∼ 1100 C. The catalytic activity between the feedstock and the tube wall leads to heterogeneous coke formation. The accumulation of coke, a homogeneous event, leads to localized temperature excursions, pressure variations, and potential tube plugging which all play a significant role in premature tube failure by creep and stress rupture.
During normal operation, the tube metal temperature is frequently reduced to pass high pressure steam or steam air mixtures through the tubing to eliminate coke, a process know as decoking. At ∼ 1100 C, depending on the materials of construction, a variety of topologically close packed phases (η, M 23C6, σ, M7C3, etc.) form which can lead to premature tube failure by embrittlement during the decoke cycles.
In this dissertation, two techniques are discussed which have the potential for overcoming premature tube failure: (1) upgrading the metallurgy to a material that forms a protective oxide coating at the service temperature and also shows resistance to the formation of topologically closed pack phases and (2) a novel technique which can deposit coke resisting coating on the inner diameter of pyrolysis tubing.
|School:||State University of New York at Stony Brook|
|School Location:||United States -- New York|
|Source:||DAI-B 69/10, Dissertation Abstracts International|
|Subjects:||Chemical engineering, Mechanical engineering, Materials science|
|Keywords:||Coating, Coke, Dictra, Ethylene pyrolysis, Pulsed laser deposition, Thermo-Calc|
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