(123b) Lifecycle Analysis of Brazed Aluminum Plate Fin Heat Exchangers (BAHX)

Plate fin heat exchangers, commonly referred to as brazed aluminum heat exchangers (BAHX), are widely used in cryogenic fractionation and processing because of their high thermal efficiency and reliability, compared to other heat exchanger types. Applications include air separation, natural gas liquefaction, nitrogen rejection, natural gas liquids recovery, ethylene production, hydrogen recovery and propane dehydrogenation.

Typical industry expectation for BAHX lifespan is approximately 20 years, although experience shows that units that have been operated diligently, with respect to the operating and maintenance guidelines, can double their expected service life. The same experience also reveals that lifespan depends entirely on the care afforded the BAHX, particularly with respect to thermal gradients and most are retired from service due to leaks caused by some form of thermal stress damage.

BAHXs don’t exhibit wear patterns during operation (like brake pads and tires) hence there has traditionally been no way of predicting change over time in BAHX performance due to operating conditions, that may eventually result in thermal fatigue. Chart has recently developed two tools to assess the impact of plant operations on the mechanical integrity of the brazed exchangers.

Distributed Control System (DCS) field data analysis provides quick proactive feedback on plant operations using Chart’s Installation, Operation & Maintenance (IOM) guidelines. Advanced dynamic thermal analysis performs advanced simulations to calculate BAHX fatigue life. These methods generally highlight process control improvements for greater reliability and prevention of harmful thermal gradients.