Gently does it for the best of relief
15 Jan 2000
On BP Exploration's Miller platform in the North Sea pressure relief valves from Anderson Greenwood have been installed to gently let down excess pressure from the platform's gas separation system, so avoiding sudden pressure changes that could upset the process.
The pilot-operated modulating pressure relief valves, POPRV, are set to relieve pressure at 14.21barg.
However, their modulating action opens the valves proportionally to the severity of the process upset, minimising product release to only that required to keep the system at or below the set point. To increase system throughput, the non-flowing pilot and main valve can be tight as high as 98 per cent of set pressure, reducing product emissions even further.
The Miller platform gas separator comprises three stages: high, medium and low pressure. The Series 400 POPRVs are on the medium pressure separator which has a pressure of 10barg, service temperature of 74 C and a viscosity of 0.0134cP.
The platform recovers around 150 000 barrels a day of crude oil, which is piped via the Forties pipeline to Grangemouth, with a separate gas line taking sour gas as fuel to Peterhead power station.
The compact design of the POPRVs manufactured in Duplex stainless steel to cope with the rigours of the sour gas makes them well suited to offshore duty. It also allows the set pressure to be fixed and verified without having to adjust the main valve; thus minimising the costs and inconvenience of process downtime, while providing continuous overpressure protection.
