The benefits of ANG give severaladvantages over alternativeapproaches, such as linepack,ow-pressure (LP) gasholders1 andpressurised storage2 includingcompressed natural gas (CNG) at200 barg.

The technology has been underdevelopment by Advantica for severalyears and now it is being brought closeto the point of implementation on a realdistribution network.

Applications The applications of ANG range fromsmall-scale on-board fuel storage fornatural gas vehicles includingmotorbikes, cars, buses, trains andships, through to strategic local networkstorage. Despite the same operatingprinciples, the process requirements aredifferent and need to be understood andoptimised for each application.

ANG local network storage could beimplemented as a new installation as analternative to linepack, or retrofitted atthe sites of existing LP gasholders andpressurised storage vessels by fillingthe vessels with activated carbon togain from the enhanced storagecapacity.

How does it work?Using low-cost activated carbonmaterial, natural gas is stored inadsorbed form, ideally at 7-40 barg. Thisallows substantially higher volumetriccapacities than pressurised storage atan equivalent pressure.

The adsorption capacity of a solidadsorbent is determined by itsmicrostructure, storage pressure andtemperature. Depending on systemconditions and carbon characteristics,

an enhancement factor of three to fivetimes over pressurised storage can beexpected at 25 barg. Retrofitting at a LPgasholder site for 7 barg ANG storagecould achieve a 30-fold volumetricenhancement. This is equivalent to asix-fold increase using an ANG vessel offive times smaller internal volume, if thesame low-pressure discharge ismaintained.

As the adsorption uptake is non-linearwith pressure, a relatively large amountof gas can remain on the carbon at

pressure above 1 barg. Discharge to aslow a pressure as possible is importantto maximise the use of the availablestorage capacity.

The ANG Operation ANG technology relies on sequentialadsorption and discharge (desorption) ofgas in a vessel filled with activatedcarbon according to demand. Keycomponents of an ANG system are:(i) Guard bed. Pre-adsorption vessel

removing higher hydrocarbons (C5+)

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Gas network storage

Adsorbed NG moves closerLay Yen Lau and Robert Judd of Advantica explain how AdsorbedNatural Gas (ANG) technology has the potential to revolutionise theapproach to local network storage. It benefits from medium-pressureoperation, high volumetric storage capacity, process simplicity andinherent safety.

Storage capacity chart.

Simplified process flow diagram of ANG.

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and odorants which will causedegradation of the main adsorptionbed.

(ii) ANG storage vessel. Packed withactivated carbon and storing gas at7-40 barg.

(iii) Carbons. Different carbons areselected for the guard bed and mainbed for their preferential adsorptionof various components.

(iv) Gas heater. To allow the desorptionof higher hydrocarbon and odorantson guard bed back to the gas duringdischarge phase for gas qualityassurance.

Advantages Compared to other network storagetechnologies, the ANG local networkstorage offers advantages such as:

Implementation at the point of needand reduced dependence on thetransmission system.

Flexibility of siting and close to point-of-use location.

Phased investment. Linepack isnormally constructed at the start ofa long-term network uprating plan,with CAPEX spent at the start of theinvestment period. ANG storage,however, allows CAPEX phasingwith a just-in-time approach toconstruction. The modular natureof the design can allow theconstruction of a single vessel orbanks of units.

Lower CAPEX. CAPEX is likely to behighly competitive with linepack forcommercial-scale installations.

Lower OPEX. Nearly 10 times lowerOPEX than the LP gasholders.

Safer system compared to CNG (7-40barg vs 200 barg). Even at anequivalent pressure, ANG isinherently safer than pressurisedstorage due to the nature of adsorbedstorage, despite the higher gasinventory.

Lower footprint and visual impact thanLP gasholders. 30-fold volumetricenhancement can be achieved over LPgasholders at 7 barg storagepressure. Below ground installation isultimately possible.

Gas trading opportunity. Whenmultiple sources or pricings areavailable, local storage gives theflexibility to take more gas at off-peakprice or from the cheaper source whenit is available. This can be stored forpeak-time use, gaining from the pricedifferential.

Gas Quality Guard bed operation and systemintegration was developed anddemonstrated in the 3-millionANGUARD (ANG System with Guard BedDevice) project led by Advantica withfour other European partners3, andsupported by the European Commission.

The heavier hydrocarbons andodorants adsorbed on the guard bedneed to be regenerated each cycle intothe gas during discharge to ensureconsistent pipeline gas quality. A simpleoptimised heating profile for the guardbed was established to achieveconsistent desorption of thecomponents from the guard bed carbonand a multi-component adsorption modelwas developed for complete simulationof the ANG system. Guard bed carbonswere also developed which optimise theprocess and minimise opex.

Recent case studyA techno-economic feasibility study hasbeen carried out for an overseas assetof BG, to compare the processes andfeasibility of various local networkstorage technologies versus ANG. ANGhas shown to be highly competitive withfavourable characteristics in meeting

the objectives of storage provision.These are:

To meet the diurnal demandrequirements and peak shaving. Todelay the city-gate capacity upgradingprocess by capping and optimising thepeak flow under its design capacity.

To maintain the distribution networkabove the minimum pressure neededfor effective operation of its CNGrefuelling stations. The local storage

provides supplementary flow duringpeak-time to reduce the pressure dropalong the distribution network,The subsequent network analysis

showed that the provision of ANGstorage gives a smoother diurnal profile.By locating the storage correctly, forexample, at the extremities of thenetwork where a pressure deficitproblem is likely, it also has significantimpact on maintaining the networkpressure. Despite its discharge to thelow-pressure (1 barg or less) distributionnetwork, the ANG storage acts as asecond supply source and decreasesthe amount of gas off-take from thehigh-pressure network, resulting inreduced pressure drop along thenetwork.

ConclusionsProcess simulation and economicanalysis have shown that ANG can be anattractive alternative to linepack, LPgasholders or pressurised storage dueto its simple, modular and relatively low-cost operation.

ANG technology is mature and wellunderstood. It has been proven inprinciple and is ready for demonstrationin actual operation. Advantica is working

with BG toprove it on areal networkthrough atechnicaldemonstrationproject. A pilotfull-scale ANGstorage vesselis expected tobe implementedfollowing thesuccessfuldemonstrationof thetechnology.

For more information contact eitherlayyen.lau@advanticagroup.com orrob.judd@advanticagroup.com

References1 LP gasholder: Storage at about

1 barg.2 Pressurised storage: Any higher storage pressure

than the LP gasholders. CNG is specifically usedfor storage at 200 barg.

3 Sucliffe Speakman Carbons, University of Lisbon,ISQ (Portugal) and IPGsrl (Italy).

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ANG network storageresults fromSynerGEE Gas onsimplified MGL net-work.

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