Structure Analysis of the Fractionator Overhead Vapor Line of a Delayed Coker Unit

Abstract

In view of the great impact of the pipeline system in a delayed coker unit (DCU) on production and operation safety, we applied computational fluid dynamics (CFD) to investigate the flow in a fractionator overhead vapor line connected to an air cooler in a previous study. The causes of the pipeline damage and the strategies to alleviate the occurrence of the damage were discussed. It is found that if two 24″ pipes are connected and five 18″ pipes are also connected, the force uniformity can be improved, and the forces on the caps, reducers, and T-junctions can be reduced. In this paper, we further applied the finite element method to perform structure analysis to confirm the strength of the original and the improved pipeline system. It is found that the static stress is larger when the pipelines are connected. The first four modes of the pipeline vibration are primarily affected by the vibration of the 30″ main pipe, while the fifth and the sixth modes are primarily affected by the vibration of the smaller pipes. In the case of a magnitude 1 earthquake (parallel mode) and a magnitude 2 wind, the maximum harmonic response stresses (stresses obtained from harmonic response analysis) occur at the same locations. After the pipelines are connected, some positions of the maximum harmonic response stresses are shifted from the 30″ main pipe to the 24″ pipe. In terms of the wind effect, the pipelines connected or unconnected can both withstand moderate typhoons of magnitude 13 without fatigue damage. In terms of the seismic effect, the pipelines connected can withstand a strong earthquake of magnitude 5(+) without fatigue damage, while the pipelines unconnected can withstand a very strong earthquake of magnitude 6(−) without fatigue damage, which is better than the pipelines connected. Under the action of a magnitude 17 severe typhoon, the stresses for the pipelines connected or unconnected are both lower than the yield strength and the ultimate tensile strength (UTS). There is no danger of immediate damage in terms of the wind effect. The pipelines connected or unconnected can withstand magnitude 7 earthquakes up to accelerations of 1718 gal (17.18 m/s2) and 2236 gal (22.36 m/s2), respectively, without exceeding the UTS. The pipelines unconnected are slightly better than the pipelines connected in terms of earthquake resistance. The purpose of this series study is to explore the flow development and the structural strength of the DCU pipeline system to improve its operational safety.

Keywords

• delayed coker unit
• fractionator overhead vapor line
• vibration
• stress analysis
• earthquake
• wind