Fired Heater Convection Section Steam Generation Tube Failure (Understanding the impact of flow regime and high peak heat flux profiles)

Two catalytic reformer unit heaters were facing convection section steam generation tube failures recurring every year. This problem was determined by low-pressure drop across steam generation banks and subsequent IR scanning of tubes. It demanded frequent removal of failed tubes. Initially, caustic gouging, poor tube side flow regime, high localized heat fluxes and improper flue gas flow distribution were thought as a possible reason for tube failure. However, water chemistry was being looked at and was not a contributing factor for the tube failures as other heater receiving the same boiler feed water was not facing tube failure issues.

Further, CFD modeling was adopted to study the flue gas flow distribution between the heaters. A damper was installed in the flue gas duct of the heater to control the flue gas flow distribution. Thus, high peak heat flux and poor tube side flow regimes were identified as the major factors causing tube failures.

• The heaters were operating with circulation ratio in the range 7 to 9 and the peak heat flux in the tube failure region was also very high (25,000 – 50,000 Btu/hr-ft²).
• An unstable slug flow regime was predominating in the tube failure region of both the heaters.

This paper describes the scheme to overcome these issues and eradicate tube failures.