hydrocarbon dew point control - gas processing · pdf filehydrocarbon dew point control a.03...
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AustraliaProcess Group Pty Ltd
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Hydrocarbon Dew Point ControlA.03
Introduction
Hydrocarbon Dew Point Control Units (DPCUs) are designed to inhibit the formation of solid hydrates in gas streams and by default they perform a level of dehydration. This is achieved through the injection of a liquid Hydrate Inhibitor directly into the gas stream. The Hydrate Inhibitor is selected based on low viscosity and low freezing temperature rather than dehydration ability.
There are 2 common types of liquid Hydrate Inhibitor used for Dew Point Depression:
• Mono-EthyleneGlycol(MEG)• Methanol(MeOH)
The type of Hydrate Inhibitor used and the package design dependsonseveralfactors,andtheend-usersspecificrequire-ments and objectives for the gas stream being processed. Eachpackageistypicallydesignedincloseconsultationwiththe client to ensure the best overall design is achieved.
Design Basis
The design of a DPCU follows a basic structure. However, there are a number of approaches to achieve the end means – Hydrocarbon Dew Point Depression.
Eachsystemistypicallydesignedandbuiltasacompleteturn-key package with particular emphasis given to the following issues:
• Dischargegashydrocarbondewpoint,• Dischargegaswaterdewpoint,• Minimuminhibitorlosses,• Minimumpowerconsumption,• Optimumplantefficiency&designintegrity,• CompliancewithHSErequirements,• Environmentallyconscientiousdesign.
The resulting design will be influenced by all of these factors, andtheemphasis&importancegiventoeachparticularissue.
Photograph:MEGDPCU(155TJ/day)package for Blacktip Project, N.T. Australia.
Rev11/2012
Represented by:
Hydrocarbon Dew Point Control
A.03
Process Description
InatypicalMEGInjectionDewPointControlUnit(DPCU),thegasisfirstpassedthroughanInletSeparator(1)whereanyfreeliquidsareremoved.
Justpriortoenteringthegas/gasexchangerpressurisedLeanMEGisinjectedintothegasstream(2).AdditionalMEGisinjectedandtheMEG-gasmixtureisthenfurthercooledthrougheitherExpansion(Joule-ThompsonValve/Orifice)orRefrigeration(3).
Thefurthercoolingcondensesanyresidualwaterand/orhydrocarbons.ALowTemperatureSeparator(LTS)(4) is located downstream to remove any free liquids – now including the condensed water, condensed hy-drocarbonsandinjectedMEG.Thecooledgaswithadepresseddewpointiscirculatedbackintothegas/gasexchangerforpre-coolingoftheinletgas(2).
TheLTSisgenerallya3-PhaseSeparatorwhichallowsthe effective separation of not only the gas from the liquids, but also the aqueous and hydrocarbon liquid phases from one another.
Theaqueousphase,containingthewaterandMEGisroutedtotheMEGRegenerationPackagewherethewa-terisdrivenofftoproduceLeanMEG.Theliquidhydro-carbonphaseisusuallymixedwiththeliquidsfromanyinlet separation and either routed to storage or further processinginaCondensateStabilisationPackage.
© Process Group Pty Ltd, 2008 – 2012.
(OPTIONAL)
CONDENSATE STABILISATION UNIT
Hydrocarbon Dew Point Control Unit
OUTLET GAS
INLET GAS1
MEG REGENERATION PACKAGE
EXPANSION2
6
REFRIGERATION
3
5
4