(50f) Successful Resolution of Site Issues for Cryogenic Expanders at LNG Liquefaction Plants | AIChE

(50f) Successful Resolution of Site Issues for Cryogenic Expanders at LNG Liquefaction Plants

Authors 

Davidor, B. - Presenter, Ebara International Corporation


SCOPE This paper discusses two issues related to cryogenic expanders that occurred in 2006 at two different sites. This abstract outlines the methodology used to analyze these problems which eventually resulted in a successful resolution. This methodology is the same for both issues and includes activities such as 1. Problem description, 2. Site visits by EIC personnel to collect information and data, 3. Developing a list of root causes, 4. Analysis by EIC's Engineering Department, 5. Factory testing to confirm accurate problem diagnosis and 6. Testing of field hardware to confirm successful resolution.

CASE A: NOZZLE VANE VORTEX SHEDDING During commissioning of an expander a high frequency noise was detected with sound levels well above acceptable limits. Field data identified that the frequency of the noise was related to vortex shedding from the stationary nozzle vanes. Analysis indicated that parameters defining the Strouhal Number, i.e. the characteristic frequency of the noise, the flow velocity in the nozzle and a characteristic linear dimension resulted in a Strouhal Number between 0.20 and 0.25. A review of the open literature concluded that the source of the noise was from a less than optimum trailing edge configuration of the nozzle vanes. Factory testing of unmodified and modified trailing edge configurations confirmed the root cause was vortex shedding. Modified components were installed on the equipment in the field. The field test confirmed that with the new, modified components the noise levels were significantly reduced. In addition sufficient data was taken to demonstrate that the noise did not migrate to another regime within the operating range of the expander.

CASE B: STRUCTURAL FAILURE In 2006 EIC was advised that an expander was taken out of service as a result of elevated vibration levels. Inspection revealed that the expander inlet housing had experienced a structural failure. Since this component also houses the upper generator radial bearing the failure of the inlet resulted in lateral bearing misalignment which caused the increased vibration levels. Since this component is used at other sites that have not experienced this problem the investigation focused on the method of cooling down and the procedures for maintaining the expander in a cooled down state when idle. Analytical work consisting of Finite Element Analysis, along with destructive testing at the factory and a metallurgical analysis of the failed component confirmed the original hypothesis that the failure resulted from activities associated with cooling down and/or maintaining the expander in cooled down state.