Large LNG compressors require large Anti-Surge Valves which in turn present complex engineering challenges. Valves with shorter travel (the distance the plug moves) and suboptimal control compromise the efficiency and reliability of the compressor. But traditionally, it’s difficult to control valves with a long stroke involving more than 12” of travel.

With extensive experience developing Anti-Surge Valves, Severn resolves these challenges. Our expert valve selection, integration, setup and calibration enable large valves with up to 24” of travel to meet stringent performance and safety specifications.

Anti-Surge control valves must act extremely fast – within a two-second window – when process upset is detected on an LNG liquefaction train.

To facilitate a rapid inflow of surge gas, these valves typically have an oversized capacity of 1.8-2.2 times the maximum volume they are likely to handle. However, this important safety feature has implications for valve size, weight, and travel.

It is harder for large Anti-Surge valves to achieve the balance of speed and precise control required for compressor protection and optimal flow management. To compensate for this, LNG surge management systems involving large valves are often configured so that valves are activated at a lower threshold. This approach ensures plant safety, but it can compromise plant efficiency.

The whole valve package: focusing on the trim, actuator, and positioner improves operability

Severn’s proven Anti-Surge Control Valve technology takes a complete, highly engineered approach to overcome performance challenges for optimally selected valves where travel exceeds 12”.

Our bespoke valve trims for precise pressure let down, are integrated with sophisticated, carefully selected actuators and positioners. The impressive power and controllability of the actuation package is an integral feature of our valves. Precision control is enabled using high-power piston actuators which ensure a rigid and robust instrumentation setup. This enables us to implement a longer stroke – giving better control of the surge management process – while meeting the application’s exacting requirements for speed and accuracy.

The entire valve assembly is expertly integrated and calibrated as a complete system to deliver optimum performance. Valves are tested using a Profiler tool which measures and validates performance according to the specific Anti-Surge specifications. The tool is independently calibrated, ensuring valve performance is verified against end user standards without concession.

Our experienced valve engineers leverage test outcomes to fine-tune the actuator, positioner and boosters. Treating the Anti-Surge solution as a system of carefully selected, finely orchestrated components facilitates optimised, compliant valve performance.

Control optimisation boosts LNG productivity and efficiency

As the below graph indicates, when compressor Anti-Surge Valves are primed for speed, accuracy, and reliability, liquefaction trains can operate within the compressor’s maximum efficiency zone. The entire LNG plant benefits from this. Controlling surge quickly and safely without it escalating into a major event allows operators to maintain higher liquefaction flow/pressure rates which boost overall productivity.

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Severn’s Anti-Surge Control Valve technology enables this balance of speed and accuracy to be achieved consistently, even with large valves. With our ongoing commitment to R&D, Severn carried out stringent Anti-Surge specification testing on a valve with a nominal bore of 30” and a linear stroke of 24”. It performed the full 24” stroke in less than two seconds and achieved incredibly precise positional control ensuring specifications can be met without concessions on all valve sizes.

Contact us to find out more.