Session: 40-02: Axial Compressor Instabilities and Stall

Paper Number: 151663

Validation of Compressor Surge Rundown Trajectories: Comparative Analysis of Transient Model Predictions and Test Rig Measurements 

General-purpose modelling tools based on dynamic simulation are used in the process industry to analyse transient operating scenarios as part of design and operability studies. Increased utilisation of digital capabilities and industrial automation has reaffirmed the significance of these simulation tools. Accurate transient models are essential to the development of first-principles digital twins and process-based condition monitoring systems. Such applications are of great interest to improve the operation of complex systems utilising turbomachinery, such as pipeline, flash-gas, and export compressors.

The application of generalised simulation tools in the analysis of compression systems has historically been limited to well-defined areas of operation, that is, within the bounds of the normal performance map. Specialised models, based on the approach developed by Greitzer and further refined by others, have been necessary to study compressor system instabilities. Recent development in system modelling, involving the integration of surge models with general-purpose modelling tools, allows for an expansion of the operating area available to dynamic flowsheet models to include severe off-design operation. This in turn enables detailed transient analysis of events in which surge is a primary concern, namely process failures and emergency shutdowns. This type of analysis has previously been incomplete due to the simplified representation of the surge behaviour.

In this study, the actual and simulated performance of an industrial-sized compressor test rig subjected to critical operating scenarios are documented. Several test cases are presented to highlight the system sensitivity and show model-system agreement over a wide range of operating conditions and system layouts. The case studies involve emulated power outages and driver trips (typical of modern variable-speed electric motor drives), realistic compressor protection system responses, and variations in the compressor characteristics to assess impact on stability and surge response. In particular, the system stability and transient behaviour are examined through a sensitivity study considering two plenum volumes; open- and closed-loop operation; and a steep and a flat compressor characteristic (i.e., different head rise to surge). The pre-trip operating point is established using inlet guide vanes, speed control, and discharge throttling and is chosen such that it remains constant across the different setups. This enables comparisons of transient responses of different systems that adhere to the same pressure rise and flow requirements imposed by the process.

The test rig features comprehensive instrumentation following ASME PTC 10 and ISO 5389 guidelines, with expanded instrumentation to document the fast surge transient behaviour. A modular setup allows for a wide range of system geometries to be tested, and this capability is utilised to demonstrate the influence of system layout. The dynamic modelling tool is Hysys Dynamics by AspenTech, a software which is widely used within the process industry. However, the proposed method is generalisable to other similar simulation environments. The dynamic model is tuned using dynamic and static performance test data. It incorporates a surge model inspired by Greitzer’s approach but revised to use the polytropic performance method, which is necessary to obtain generalisable results across varying operating conditions. The results are contrasted against simulations made using the default no-surge model to reveal the significance of accounting for surge behaviour in such studies.

The results highlight the accuracy and reproducibility attainable when using properly developed dynamic models, suggesting that these tools can serve as an excellent foundation for modern system analysis techniques. Moreover, they pinpoint limitations in previous studies describing in-surge rundown behaviour by clearly showing the deviations incurred when foregoing the effects of surge.

Presenting Author: Ola Ilseth Pronk Norwegian University of Science and Technology (NTNU)

Presenting Author Biography: Ola Ilseth Pronk is a PhD student enrolled at the Norwegian University of Science and Technology (NTNU). He graduated in 2023 with a master's degree in mechanical engineering from the same institution. Ola's research interests are related to thermal turbomachinery and the application of digital solutions within process and energy industries.

His current work centers on the development of a digital twin for a full-sized centrifugal compressor test rig. His PhD project is part of an ongoing collaboration between NTNU and industrial partners that is aimed at developing robust and energy-efficient compression systems for the Norwegian oil and gas industry.

Authors:

Ola Ilseth Pronk Norwegian University of Science and Technology (NTNU)
Alberto Serena Norwegian University of Science and Technology
Lars Eirik Bakken Norwegian University of Science and Technology (NTNU)