Troubleshooting frequent issues faced in fired heater operation How best to address some of the most common issues with fired heaters, which can severely affect refinery operations
Shilpa Singh and Rupam Mukherjee Engineers India Limited
F ired heaters account for more than 60% of the total energy consumed in refining crude oil. While most fired heaters are designed for certain sets of operating conditions, it is commonly seen that the actual operation of fired heaters in refineries differs a lot from their design. Further, due to operation under severe conditions, component degradation and deterioration become inevitable over time. As a result, fired heaters often end as an ‘Achilles heel’ for many refineries. Troublesome fired heater operation can lead to severe production losses as well as efficiency losses, which can translate into millions of dollars lost each day. In many cases, refineries are forced to take shutdowns to accommodate fired heater trips. Restarting units can be both troublesome and a hindrance to safe refinery operation. This article attempts to highlight some of the common issues affecting fired heaters, which can severely affect refinery operations. While remedial measures for these problems can be multi-variate and case-specific, appropriate real-life case studies have been included in the article to illustrate the structured and methodical approach adopted in troubleshooting fired heater problems. It is expected that many refiners will relate to these common cases of fired heater limitation, and the article will give a good insight into how to approach these issues. Increased rate of coking and high tube metal temperature (TMT) in vacuum heaters Vacuum heaters process the reduced crude oil (RCO) from the bottom of the crude column. RCO is considered to be a heavier component of the crude oil, given that the lighter ends are distilled
or separated in various sections of the crude column. Thus, arguably, the heavier component of RCO, which is further processed in the vacuum distillation unit, requires a higher degree of care, sensitive operation, and control. This is due to the fluid’s inherent nature to crack and form coke compared to crude oil. In one of the refineries with a relatively older vacuum unit operating for more than 20 years, it was observed that the heater run length over the last three cycles had reduced sharply. The refiner had to undertake a shutdown every six to eight months since the pressure drop and tube metal temperature across the vacuum heater coils were were reaching cut-off limits. The tube metal temperature skin thermocouples were also verified through infrared scans of the tube, which indeed indicated elevated tube metal temperatures. A detailed study was undertaken to identify the root cause. Interestingly, the heater was apparently operating within its design process parameters, and nothing starkly abnormal, such as flame impingement, was observed. During interactions with the operating team, it emerged that the steam injection nozzle at the heater crossover location had experienced a past recurrence of heavy chocking due to coke deposition or debris accumulation. Steam was directed to the coils at two locations primarily: one at the crossover and the other downstream in the radiant section just before the coil expands to a larger size to accommodate high vapour volume and Mach number. However, coking in the crossover nozzle left this steam injection location redundant. Due to the fact that the furnace was in operation and no shutdown or modification was anticipated,
Refining India
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