Natural gas recovered during offshore production is generally compressed on the platform for transmission via pipeline to a processing facility. Compressors used for this purpose should be capable of handling expected volumes safely and without disrupting other platform activities. They must be sized accordingly and capable of absorbing pressure spikes, or slugs, as well as dips in the supply pressure. Such variations can cause surges or starvation. Some compressors may, in severe cases, attempt to reverse the flow of gas, which can damage the machine and possibly create a safety hazard.
Fisher surge control valves, which remain closed on the output side of the compressor during normal operation, are designed to open quickly when necessary and allow gas exiting the compressor to recycle back to the intake side to counteract the effects of starvation. When there is an overabundance of gas with excessively high pressure at the compressor’s intake port, a Rosemount pressure sensor can activate a Fisher relief valve, causing the gas to be diverted to flare. In addition, Global Exergy has extensive experience in designing and implementing control systems and instrumentation for compressing natural gas into liquid (LNG) for shipment aboard specially constructed tankers. Floating LNG plants are being designed for use in world areas where there is an abundance of natural gas coupled with minimal demand.