Troubleshooting and Evaluating Air Condenser Limitations

When an operating air condenser fell short of meeting its design heat duty on hot summer days, a troubleshooting team set out to determine the cause.

Air condensers provide effective heat transfer for countless industrial processes. However, there are many cases in which they fall short of achieving their expected heat transfer, bottlenecking plant capacity. When this occurs, it is important to correctly diagnose the root cause and take adequate action to improve heat transfer. This is what happened at Elkem, a leading manufacturer of silicon and carbon-based materials, in 2020.

The tower and its condensers began operation in 2014. By September 2020, the performance of the air condenser (not a Fluor design) fell well short of the design, and it was unable to achieve the design heat duty at the design air temperature of 35°C. As Fluor and Elkem were engaged in a new plant design that had a similar tower, identifying the cause of the poor heat transfer was critical. The most cost-effective path to optimizing the condenser design for the new plant was to gain insight into the existing plant’s problem. To achieve this, a Fluor-Elkem task force was assembled, and it conducted a troubleshooting and evaluation study involving thermal camera scans, plant data analysis, and heat transfer calculations using the Heat Transfer Research, Inc.’s (HTRI’s) methods.

The investigation showed that most of the condenser’s performance loss was due to restriction of the air passages by fouling material. The rest of the performance loss — equivalent to losing about 17–23% of the surface area — was due to an undersized condensate line. The subsequent fouling of the bottom row of tubes made very little difference, as this row was performing little heat transfer in the first place.

This article presents lessons learned from the investigative study, which include the importance of making the air condenser design robust enough to prevent airflow restriction when fouling is a possible issue, eliminating sources of solids that can restrict the air passages, and having all condensate lines to the reflux drum designed for self-venting flow. A broader takeaway is the immense value of conducting proper plant tests, performing thorough thermal camera surveys, and understanding observations through heat transfer calculations for diagnosing air condenser problems...