Modelling and Flexibility Analysis of Hydro Cracker Unit
Milan Motta1, Shadab Imam2

1Prof. Milan Motta, Department of Mechanical Engineering, Columbia Institute of Engineering & Technology, Raipur (Chhattisgarh), India.
2Prof. Shadab Imam, Department of Mechanical Engineering, Christian College of Engineering & Technology, Bhilai (Chhattisgarh), India.
Manuscript received on 10 November 2013 | Revised Manuscript received on 18 November 2013 | Manuscript Published on 30 November 2013 | PP: 1-4 | Volume-3 Issue-6, November 2013 | Retrieval Number: F1340113613/13©BEIESP
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Abstract: Hydro cracking is an extremely versatile catalytic process in which feed stock ranging from Naphtha to Vacuum Residue can be processed in presence of Hydrogen and catalyst to produce almost any desired products lighter than the feed. Primary function of Hydrocracker unit (HCU) is to maximize middle distillate production. First stage feed heater is a twin cell cabin heater with horizontal radiant tubes supported through 3 nos ladder type coil supports. Radiant Coil vibration was observed in tubes some remedial measures pertaining to mechanical aspects were studied and implemented. However, a need of comprehensive study to identify and minimize the coil vibration problem was felt to ensure reliable operation of the heater. In this work, Flexibility analysis of Heater Radiant Coil by modeling applied end conditions and various temperature cases was performed to verify the mechanical design and to understand the probable reasons of coil lifting. Fatigue analysis of the vibrating coil with maximum stress amplitude obtained by Flexibility analysis was performed. The maximum possible slug forces was calculated and dynamic analysis of reactor inlet piping along with heater coils was carried out to check whether slug, if any, has any impact. Maximum tube metal temperature for a definite span of operation was estimated. Purpose of this work is carried to identify the probable reasons of heater radiation tube lifting and vibration and to suggest remedial measures to continue safe operation of the heater. Heater tubes have a life of definite span which is directly related to the operating tube metal temperature. Due to furnace running on high tube metal temperature, rupture design study was also carried out for remaining life assessment of the tube. Based on the flexibility analysis of radiant tubes and maximum tube metal temperature calculation, heater operation could be sustained safely without unit interruption due to heater.
Keywords: Fired Heater, Hydro Cracking, Tube Lifting, CAESAR Analysis.

Scope of the Article: Heat Transfer