PROCESS & CONTROL | OCTOBER 2019 9

CALIBRATION FEATURE

/ PROCESS&CONTROL

The monthly value of Asia’s LNGimports is regularly more than US$10

billion. With such vast sums of moneychanging hands daily, the importance ofaccurate measurement of the LNG qualityfor invoicing is clear. The analysers usedin this application are process gaschromatographs (GC’s) which measurethe heating value of the LNG as it istransferred from the ocean-going tankersto the land-based terminals. Theseinstruments are located on-board ships.So, they must tolerate vibration and beable to operate in a wide range ofambient temperatures.Steve Lakey, global product manager for

GC Products at ABB in the US puts theproblem into context: “This is not thehighly controlled laboratory environmentof bench-mounted GC’s, it’s the highseas. Our NGC 8200 series of process gaschromatographs can withstand ambienttemperatures from -18ºC to +55ºC.That’s certainly compatible with theintensity of the Australian climate, whereLNG is produced for export to Asianmarkets. Furthermore, with Class 1,Division 1 explosion-proof rating, they aresuitable for LNG tanker and FLNGapplications.When it comes to accuracy, modern

process GC’s can match many of theirlaboratory-based cousins. Lakeycontinued: “The requirement for a Class Adevice is an accuracy of plus or minus0.5%. The accuracy of the NGC 8200 is0.1% and therefore surpasses these

Stephen B. Harrison, principal at Nexant, Germany,explains the importance of process gas chromatographaccuracy and how to maintain it in all conditions

To achieve this accreditation, thereference material producer mustdemonstrate that their products andmanufacturing processes comply to themost stringent requirements. Coregas, atits specialty gases production facility inYennora, near Sydney, overcame thishurdle in 2018. Executive generalmanager, Alan Watkins, explains what thismeans for his team: “Our lab has been ISOGuide 34 accredited for many years by theNational Association of TestingAuthorities, Australia (NATA) and we havebeen one of Australia’s leading producersof accredited specialty gas mixtures inrecent decades.“The successful transition from the

Guide 34 to ISO17034:2016 means thatwe can continue to occupy our position atthe top of the metrological pyramid in theAsia-Pacific region and ensure that thecompanies trading LNG can do so knowingthat their billing will be fair andinternationally harmonised.”In addition to calibration gas mixtures,

gas chromatographs need a carrier gasand, if the instrument is fitted with an FIDdetector, they also need hydrogen and air.For land-based GC’s, cylinder gas suppliesare practical. However, on the ocean,generation of these instrumentation gasesin-situ is desirable to minimise cylinderlogistics costs.Heinz P. Schmidlin, sales & marketing

manager at the Gas Generator Division ofVICI AG International confirms the point:“The simple choice that analyticalinstrumentation users have is either tomake or buy their high purityinstrumentation gases. Whether it’s abench-top generator for the laboratory ora rack-mounted unit for process controlapplications, we offer instrumentationengineers and scientists the ability to bemore independent, whether they are onthe high seas or in a city-centre contractlaboratory, on dry land.”

new.abb.comwww.coregas.com.au

Coregas gas cylinders.The company has madethe successful transitionfrom the Guide 34 toISO17034:2016

An ABB NGC 8206 gaschromatograph on a gaspipeline in Louisiana

requirements by a factor of 5.Measurement accuracy is a big deal –every penny counts when trading theseprecious natural resources.”A major boost to the trade of LNG

between Australia and Asia took place inDecember 2018 with the start-up of thePrelude floating liquified natural gas(FLNG) facility. With LNG demand growth

in China projected to continue at 20% forthe next ?? years, this additional capacitywill quickly be absorbed. Preludeprocesses gas from the Browse Basin.When natural gas rises from the oceanbed, the desirable methane is laden withheavier hydrocarbons, carbon dioxide,moisture and hydrogen sulphide.A primary function of the FLNG facility is

to separate and liquefy the hydrocarbonsinto LNG, natural gas liquids (NGL) andcondensate. However, before this can takeplace the ‘sour’ gas stream must be made‘sweet’ by the removal of acid gases. Thegas must also be dried, since moisturewould freeze in the gas liquefactionequipment and cause blockages. ProcessGC’s are also used on the FLNG vessel forprocess control applications related to gasdrying and sweetening.To maintain their accuracy, these

offshore process GC’s must be calibratedin the same way that land based devicesare. However, the transportation ofcalibration gas cylinders to these offshoreapplications is an expensive logisticalchallenge. So, the longer the shelf-lifethat is associated with the calibration gasmixture, the greater its utility and value.One of the advantages of the recentlyintroduced ISO17034:2016 accreditationfor reference materials is that itguarantees the stability and homogeneityof certified calibration gas mixtures overtheir defined shelf-life.

ACHIEVE HIGH ACCURACY ON THE HIGH SEAS

LNG tanks at ShanghaiYangshan port

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