Process Modeling

A leading Power Provider was evaluating the performance of their compressed air energy storage train, which had been plagued by acoustic resonance in the discharge piping of an intermediate stage of compression.

A field performance test was conducted to determine if there was an aerodynamic instability in the compressor, or whether one of the intermediate stages of compression was experiencing surge.

The purpose of the field testing was to isolate the characteristics of the acoustic signature in the piping, and isolate the root cause.

• High Pressure Gas Expander
• Low Pressure Gas Expander
• Generator/Motor
• SSS Clutch
• Gearbox
• Axial LP Compressor
• Centrifugal IP Compressor
• Centrifugal HP Compressor

The analysis was done using a combination of hand calculations and computer modeling, using industry standard software (IPSEpro) and generally accepted approximations where instrumented equipment data was not available. Using OEM compressor design data for Head and flow curves, the operating performance of the entire compressor train was measured, corrected to design conditions, and compared to OEM performance. The operating data revealed that the flow through the first section of the intermediate compressor was too low, and this was creating a rotating stall in one of the stages. The rotating stall was stimulating a resonant frequency of the structural piping that resulted in an acoustic signature that was detrimental to the piping and intercooler connected to the intermediate stage of compression.

A temporary solution was implemented to increase the flow through the intermediate compressor by opening a blowoff valve that permitted exhausting compressed air from the train to atmosphere. This allowed the volumetric flow through the compressor to increase and alleviated the acoustic instability. A long-term solution was developed to overhaul the preceding stage Low Pressure axial compressor to increase the inlet flow to the intermediate compressor and provide long-term stable operation.