Sophisticated Anti-Surge valve technology from Severn leverages advanced actuation capabilities to deliver precision control, maximising LNG plant efficiency, safety, and productivity.

Controlling centrifugal compressor surge is a fundamental aspect of efficient LNG production, and Anti-Surge Control Valves play a vital role.

Surge events can damage critical rotating equipment, harm plant performance, and result in costly unplanned downtime. Yet a conservative approach to surge risk management compromises plant efficiency and productivity by constraining the compressor’s operating envelope. Identifying an acceptable trade-off between these two extremes is increasingly difficult as trends in LNG production evolve.

The escalating challenge of LNG surge control

Challenges surrounding compressor surge control have become significantly more difficult in the quest for optimised efficiency. With global demand for LNG growing, the capacity of existing and future ‘mega trains’ is increasing. This requires larger valves sizes, which makes it harder to achieve fast, accurate control in anti-surge applications.

Surge events can occur within milliseconds and without warning, meaning Anti-Surge Control Valves must operate with exceptional speed and precision. However, fundamental principles of physics and engineering make it harder to achieve critical performance parameters as valve size increases. The mass of larger valves introduces greater mechanical inertia, so more force is required to control the travel of the plug (the main moving part). Handling larger volumes of gas also introduces significant dynamic inertia and pressure delays, further impeding valve response times.

On LNG plants where Anti-Surge Control Valve travel exceeds 18”, operators traditionally had to tolerate conservative surge control measures, compromising overall plant efficiency. Until now…

Raise the surge control line, boost efficiency

Severn’s latest innovation addresses issues associated with larger Anti-Surge Control Valves head on. Our engineers have applied their technical expertise to the development of a robust, highly engineered solution.

Benefits include fast operability, high controllability, excellent reliability, and extremely accurate valve control. This means the valves respond very quickly (in less than two seconds, including any deadband), without compromising controllability when surge is imminent. As the below diagram shows, these superior performance characteristics enable centrifugal compressors to operate closer to the surge control line, optimising performance and efficiency.

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Sever recently completed testing on a proof-of-concept Anti-Surge Control Valve with a nominal bore of 30” and a linear stroke (the distance the actuator travels) of 24”. The valve specimen’s pressure rating was ANSI 150, and it was designed with a flow coefficient (Cv) exceeding 7700, in line with the process conditions of a typical Anti-Surge application.

Testing showed that the valve meets all required parameters of the world’s most stringent Anti-Surge specifications. A significant highlight was its ability to perform the full 24” stroke in less than two seconds while simultaneously achieving incredibly precise positional control. The exceptional performance enables accurate and reliable control close to the compressor surge control line, striking an effective balance between safety and efficiency without concession or compromise.

There is a great variation in centrifugal compressor process conditions, in terms of feed gas properties and operating parameters such as flow rate, pressure, and temperature. It follows that Anti-Surge Control Valves must be individually specified and designed to optimise compressor performance and, in turn, maximise LNG plant performance and efficiency. Future articles in this series will explain how technical aspects of our Anti-Surge Control Valve technology, such as control optimisation and trim design, are customised to meet specific application needs and requirements.

Meanwhile, if you’re looking for expert technical input on centrifugal compressor surge control or other severe or critical service LNG valve applications, contact us at sales@severnvalve.com

Severn has a strong track record in the design and manufacture of valves that overcome the most challenging technical issues. LNG projects we’ve supplied in the past include Ichthys and Gorgon.