CONTRIBUTING RE.ENGINEER
KnightHawk Engineering (KHE)
www.knighthawk.com
CHALLENGE
A petrochemical plant has experienced several failures in the past few years in the tubes of a recycle gas cracking furnace. A root cause failure analysis shows the failures are likely caused by vaporization in the coils causing thermal fatigue cracking. KHE was asked to determine possible solutions to prevent future failures.
SOLUTION
KHE created a heat and mass transfer model of the furnace. This model was used to predict outlet temperatures from the lower boiler feed water coil (LBFW) and showed that there was vaporization in the coils. KHE proposed the replacement of the bottom two rows of the LBFW with bare tubes instead of the preexisting finned tubes. Simulations showed the bare tubes increasing the overall efficiency of the furnace and preventing vaporization even under the worst case operating conditions.
RESULT
The client replaced the two bottom rows with bare tubes as recommended. As a result the unit has not experienced tube failures in almost 3 years of operation.