(34d) Ensuring Reliability and Optimum Performance in Antisurge Applications

There are several compressors within an ethylene plant, cracked gas and refrigeration compressors are the major ones. These compressors are high capital cost items. Performance and reliability of these units are especially important. The antisurge control system is designed to protect this asset. A key component of this control system is the antisurge control valve; it is the main piece of equipment that protects the compressor from damage caused by a surge.

Antisurge control valves present many various challenges to ethylene producers and control valve manufacturers. There is an industry trend and desire to extend periods between maintenance cycles which increases the importance of ensuring a reliable control valve solution. These valves are required to stroke extremely quickly. For example, valves with travels up to 20 inches have been required to stroke in as little as 0.75 seconds. Improper selection of accessories needed to meet these stroke times will result in poor valve performance and tuning difficulties. During surge events, pressure drop and flow experienced can be high, causing excessive levels of noise that must be handled appropriately. Partial stroke tests can be required to ensure that the antisurge valve is functioning properly in the case of a surge event. While meeting all of the application demands, there is also a need to have an antisurge valve that can be easily implemented and serviced in the field. Complicated traditional configurations have historically been difficult, or impossible, to tune.

Fisher has designed an optimized antisurge control valve assembly to meet the needs of these demanding applications. There was a considerable engineering effort in order to understand from end users and process control companies how to integrate the valve, actuator, FIELDVUE® digital valve controller, and associated instruments into an effective design. Each component of the assembly has been examined and optimized with high reliability in mind. In addition, the Fisher Optimized Solution simplifies the tuning steps. Time spent during startup and commissioning is reduced and changes in the field can be done with the valve in service which results in less down time to make adjustments. By improving the performance of this control valve, it allows the plant to move the compressor's operating point closer to the surge limit line and therefore, operate more efficiently. This can result in significant savings to the plant.