Improving TMT Accuracy Using IR Camera on Ethylene Cracking Furnace

Tube Metal Temperatures (TMT) of radiant section coils form an important parameter in the operation of the ethylene cracker furnace as the maximum reachable value is one of the criteria to start a decoking cycle. TMT increases over the furnace run length due to a coke layer build-up. Initiating decoking too early would reduce both furnace (and thus plant) availability and coil lifetime (due to material stress during decoking). Overheating coils on the other hand would lead to material degradation and in worst-case to a direct coil rupture. Hence knowing about TMT development over time is essential to ethylene plant operations. State-of-the-art is still the manual measurement using a pyrometer and logging by some manually maintained lists. Accuracy and reproducibility of the measurement depends very much on the individual and current operating conditions during the slot of measurement.

An alternative approach is the use of thermal cameras which is presented in this paper. The technology allows the 24/7 monitoring of the TMT for the significant parts of all coils. Temperature profiles are taken every five minutes, allowing the reliable monitoring even in the light of varying process conditions. Based on the amount of data an improved prediction of the remaining furnace run time is achieved, and the generation of an expected decoking schedule is possible. In addition, different performance parameters can be retrieved, indication different heat loads on different coils or fast changing temperatures. Last but not least the captured data allow the automatic detection of hot spots and other abnormalities in the temperature distribution.

The paper explains on the implemented features and summarizes the experience. Also some guidelines are given for the implementation of this promising technology.