Improving Tube Design of a Problematic Heat Exchanger for Enhanced Safety at Minimal Costs

As part of a preliminary hazard analysis for a new phenol plant, the results of a hazard and operability study (HAZOP) conducted in the initial stages of the project design were re-evaluated due mechanical failure detected during the test operation. Out of the possible mechanical defects for the crude phenol column (CPC), the fact that the lowest risk grade was given to the column without consideration for any safety devices, was recognized as the cause of failure. After examining the design specifications of the safety valves of CPC, it was confirmed that the tube rupture case of the overhead condenser was also not taken into consideration. With this case included in HAZOP, the size of the safety valve had to be increased from 6Q8 to 8T10. In summary, when taking into consideration the economic impact on modification and re-purchase of the safety valve and the redesign of the piping system might have, it was determined that completely removing any possibility for the tube rupture case by mechanically reinforcing the overhead condenser would be the most economic decision. Therefore, the overhead condenser was mechanically reinforced in areas determined to require strengthening according to the results of the vibration analysis, and by adding these results to the safety device factors of the mechanical defects of CPC, the lowest safety risk grade could have been maintained.