Gas Oil HDS: How Correct Two Phase Flow Design Can Reduce Risk of Overheating and Debottleneck Unit Capacity

Betzalel Blum, Bazan Group, Haifa, Israel

ORL has a Diesel HDS unit that was built at the beginning of the millennium. The unit limitations were found to be insufficient feed preheat and poor cooldown of the diesel product due to imbalance in the temperatures among parallel heating trains. The most severe issue identified was that less then 50% of the surface area of the air coolers was effective for heat transfer. This led to the hazard of overheating the air coolers tubes and tube damage (bending). The bending generated a high risk of tube leaks.

Investigating the stream flow regime identified the cause of the uneven two-phase flow and the consequent low surface area effectiveness. After piping rearanging  to bring to within good design practices for two phase flow, as well as making some changes in the equipment configuration during the turnaround, the unit was returned to service. The result was effective utilization of all the heat exchangers  and cooler surfaces, eliminating the tube overheating risk, excellent heat recovery, and 20% feed rate  capacity increase.

This paper stresses that Poor correct hydraulic design of two-phase pipes can lead to overheating hazards and bottleneck an entire unit. It also demonstrates the importance of correctly identifying and solving the issues to achieve good operation