High vibrations were observed in one of the largest incinerator (6m diameter and 44m long) of recently commissioned all four SRU in GASCO plant (Fig. 1) which could lead to integrity concern and increase inspection and maintenance of the unit. Some damage of refractory, insulation and nozzle weld were also observed. This paper presents state of the art analysis and approach followed to not only identify the root cause but also provide solutions to mitigate the vibration.

The high vibration posed a challenge, as unlike rotating equipment/piping, no industry standard defines acceptable vibration for static-equipment. Actual vibration measurement across complete length of the incinerator were performed for various operating condition. Operating data were analysed for these condition. In order to study the acoustic response, natural frequencies of the system and identify source of vibration, 3D models of not only burner, but incinerator, superheater, stack and air and process gas ducting was also build. Further, instead of conventional CFD, specialized thermo-acoustic CFD analysis for numerous operating cases and FE/Fatigue analysis were performed to address this complex combustion issue.

Vibration measurement concluded that even though frequency of vibration is same throughout the incinerator, high amplitude upto 38rms with 11Hz frequency is in superheater and frequency drops by a decrease in temperature. As conventional CFD analysis could not identify the source of the vibration, a specialized complex thermo-acoustic analysis was carried out. Analysis concluded that vortices are formed in burner region due to improper mixing of combustion gases which created pressure fluctuations causing vibrations at frequencies correlating with field measurements. Hence improper burner design was identified as the root cause of vibration. FEA and fatigue analysis indicated potential premature nozzle failure in superheater region. Although conventional approach of replacing complete burner with new burner and ducting would have resolved the vibration and ensured integrity, however it would have costed 4MUSD. Instead, several options to eliminate the root cause were explored and provision of choke ring inside the incinerator was identified as optimum solution ($1.2M). To "Deliver More for Less" alternate solution of installation of a stiffener-ring ($80K) in super-heater region was recommended to change the natural frequency and reduce vibration to acceptable limits.

Vibration issues in the incinerator package may not only be due to flow but can also be related to combustion. Such issues are more complex especially for such a large incinerator and difficult to resolve with a conventional approach. This specialized study not only helped to identify root cause or source of vibration but also address the same in most economical way and success of analysis is supported by proper technical analysis and justification.

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