A Naphtha Pre-treater was retubed to improve metallurgy in order to reduce scale build-up and other end of life factors. Besides the change in metallurgy, no other changes were made. The cabin style heater is designed with horizontal passes in a segmented serpentine pattern containing internal manifolds.
Follow up IR scans were taken of the newly installed tubes to ensure safe operation.
Operation over 200°F/93°C over the ROLH limit
Shielding the tubes that are not getting enough flow to uniformly increase the temperatures throughout the rest of the furnace
Furnace is now operating with all available burners online at outlet temperatures of >945°F/507°C
The IR scan revealed that the bottom pass in each set of manifolds was much hotter than surrounding tubes. Due to overheating, rates were cut to reduce the temperature to safe operating ranges. The furnace was modeled by a third party to determine the source of the issues. The simulation showed that the bottom passes had much lower flow rates leading to hotter fluid and hotter tubes.
Faced with the possibility of tube replacements, which would seriously increase the length of the forthcoming short turnaround, the refinery was aware of Cetek’s fired heater optimization experience and contacted Cetek for a solution.
Cetek quickly developed a shielding solution to prevent the overheating. It was proposed that the problem tubes should be shielded with a high temperature ceramic wrap and coated with Cetek’s proprietary ceramic coating to prevent deterioration of the ceramic substrate in service.
Cetek’s fired heater experts calculated the effects on the process tubes and estimated the reduction in temperature of the shielded tubes and the effect on the temperature of the unshielded tubes. The refinery also decided to install thermocouples on the problem tubes to monitor the temperature under the shielding.
Cetek’s Process Tube Protection was installed at the next short turnaround during a catalyst regeneration. TI readings after startup were very similar to the temperatures predicted by Cetek in the pre-project evaluation.
After 3 years in service, the shielding continues to perform as expected.
Inspection after 3 years in service