Case Study: Rotary Gate Valve0 pages
Revolutionary New Valve
nnnnRotary Gate Valve
nnnnFMC/StatoilHydro - Ormen Lange project
nnnnCase Study
nnnnExcellent
nnnnPower & Industrial
nnnnSolutions T
nnnnPOWER & INDUSTRIAL
nnnnThere are very few genuine new
nnnndevelopments in the valve world, new
nnnnideas are mostly developed along a
nnnntheme, however, one completely new
nnnnconcept in valve design is the Rotary
nnnnGate Valve developed by Weir Valves &
nnnnControls UK Ltd part of the Weir Power
nnnn& Industrial Division in the UK.
nnnnThe valve has been successfully supplied
nnnnto FMC/StatoilHydro for the Ormen
nnnnLange project in Norway where there
nnnnwas a particular problem in controlling
nnnnregenerated Mono Ethylene Glycol (MEG)
nnnninjection to prevent hydrate formation.
nnnnSubsea equipment has been supplied
nnnnfor over 25 years, with more and more
nnnndiscoveries are being declared viable in
nnnndeep and ultra deep waters. The Ormen
nnnnLange project situated off the north western
nnnncoast of Norway was developed in water
nnnndepths of 1,100 metres on the edge of
nnnnthe Arctic Circle and has an ambient sea
nnnntemperature which can reach -2°C. Gas
nnnnproduced from the field contains entrained
nnnnwater which if left untreated would form
nnnnhydrate and potentially block up the
nnnnprocess lines. Gas from the Ormen Lange
nnnnproject is piped to an onshore terminal
nnnnwhich is 120 kilometres from the subsea
nnnntemplate.
nnnnHydrate Formation
nnnnHydrates are an ice-like lattice structure
nnnnof hydrocarbons, which form when the
nnnnentrained liquids are taken below the
nnnnhydrate formation curve. When these
nnnnoccur, equipment is usually required to
nnnnbe brought to the surface for removal or
nnnn'melting' of the hydrates. Downtime is very
nnnncostly to the producer, so it is important to
nnnnprevent the formation of hydrates. MEG is
nnnnused as a type of anti-freeze to inhibit the
nnnnexpected water content in the hydrocarbon
nnnnat the given well head pressure, in order
nnnnto eradicate hydrate formation in the gas
nnnnproduction line. Even 5-10% loss of MEG
nnnninjection can lead to hydrate formation and
nnnnit is critical to maintain injection, therefore
nnnnthe valve used has to be totally reliable.
nnnnHydrates in the process line
nnnnValve Development
nnnnThe valve was originally developed to
nnnnisolate flow, with the ultimate advantage
nnnnof not having a cavity (zero displaced
nnnnvolume during stroke). This is significant,
nnnnbecause the valve will not drift on failure of
nnnnthe operator, and will not be detrimentally
nnnnaffected by a cavity, which could
nnnnotherwise become pressure locked and/
nnnnor blocked by hydrates of line debris. The
nnnnturndown ratios far exceed those of more
nnnntraditional controlling devices, and whereas
nnnnconventional control and choke valves have
nnnnan inherent leakage, the rotary gate valve
nnnngives zero leakage since the gate is based
nnnnon conventional through-conduit gate valve
nnnntechnology.
nnnnSo Why Was a New Style of Valve
nnnnRequired?
nnnnMEG dosage is probably the most critical
nnnnprocess on applications where hydrates
nnnnare present, so if the dosage valve was
nnnnto fail then the operation would have to
nnnnbe shut down and the hydrates cleared.
nnnnThe Ormen Lange project was the first
nnnnto use regenerated MEG and therefore
nnnnno other valve design had been tried in
nnnnthe application. Other valve types were
nnnnconsidered (described below), but the
nnnnRotary Gate Valve was selected due to its
nnnnsuperior design.
nnnnScrew and Piston Design
nnnnOn screw and piston design applications
nnnnpressure loss is achieved by the flow as it
nnnnpasses along a course screw thread. This
nnnndesign has a low tolerance to impurities and
nnnncan very quickly become damaged or stuck
nnnnalong the threaded area.
nnnnNeedle and Piston Design
nnnnThe needle and piston design valve relies
nnnnon a two stage needle and seat to achieve
nnnna pressure drop. This design is not normally
nnnnused on applications with high levels of
nnnnimpurities, as the impurities bridge across
nnnnthe flow orifice and erode the needle.
nnnnSpline Choke Valves
nnnnThe spline choke valve has to distribute the
nnnnpressure drop across a segmented plug. The
nnnnplug clearances of this design means that
nnnnthe valve is often subject to blockages, and
nnnnimpurities in the flow mean that erosion can
nnnntake place across the valve plug.
nnnnThe Rotary Gate Valve
nnnnWeir Power and Industrial Case Study 1
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