(102c) Compressor System Performance at Abnormal/Non-Design Conditions

When attempting to optimize facility performance or determine process safety system requirements, accurate evaluation of compressor systems at conditions deviating from design is critical.  This paper presents a joint study between the Atlantic LNG Company of Trinidad and Tobago and ioMosaic Corporation.  At the Atlantic LNG facility, a large feed gas compressor was tested at non-design conditions and the operating data was analyzed to determine the impact of varying inlet conditions on compressor performance.  This analysis was used to develop a rigorous calculational method for predicting compressor behavior based on empirical data and current design methodologies.  Particular emphasis was placed on facility performance optimization and development of design limitations for process safety systems.

Compression ratio, discharge pressure, heat of compression, and flow rate are major components of facility performance optimization, yet all of these parameters can fluctuate a great deal with varying inlet conditions.  Techniques were derived for assessing the impact of varying suction pressures, suction temperatures, feed gas compositions, and relative recycle flow rates along with available operating power, on system capacity, required operating power, and heat of compression.

Small elevations in suction pressure and blocked vapor outlet lines often lead to deviations in discharge pressure above safe operating conditions.  Lifting of large pressure relief valves on the compressor discharge often leads to large fluctuations in flow that can result in unnecessary damage or wear to some of the most expensive and vital equipment at the heart of many facilities.   Analytical methods for determining the appropriate process safety measure such as upstream pressure limitations, high-integrity protection systems, and pressure relief valves were developed in this study as well.