GAMMAMONITORING

Michael Ritchie, MIOwen Complex, Australia, and Michael Edwards, Scantech

International Ply Lld, Australia, describe the use of online monitoring of natural

gamma radiation in coal ash to maintain coal quality.

Mt Owen coal operations are located25 km northwest of Singleton in theupper Hunter Valley of New SouthWales, Australia. Mt Owen Mine

produces high-quality thermal andsemi-soft coking coal, low in both ashand sulphur. The mine is a truck andexcavator operation producing coalsmostly destined for export throughthe Port of Newcastle. Raw coal

quality is maintained by Coalscan1500 online ash analysers, and theproduct quality is controlled by aCoalscan 3500 analyser. This article

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discusses the operations at the MtOwen minesite and discusses the

mine's use of online analysers, inparticular the Coalscan 1500 NaturalGamma analysers, to aid the mine'sprocess control.

Coal quality is carefully monitoredand controlled during all phases ofproduction and preparation to ensurethat contract specifications are metand uniform quality is maintained.The quality of the in situ coal isdetermined by detailed boreholeanalysis. Raw coal quality is

monitored by two Coalscan 1500online ash analysers, which arelocated on the raw coal bin feed

conveyors. Product coal quality ismonitored by a Coalscan 3500 onlineash analyser on the product conveyor.

Stringent coal quality controlsensure that no extraneous matter

contaminates the customer's cargoesand that the coal delivered meets

specified quality requirements. Thecoal in each train is sampled andanalysed during discharge atNewcastle. During ship loading

September2009 I World Coal 29

Coalscan 3500.

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Coalscan 1500 north ROM ash (22 - 30 March 2009).

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Differences in product ash results (May 2009).

operations the coal is sampled and analysed by an independentand certified superintending company. Thus, the Coalscan resultsare regularly compared with two independent laboratory results,and any calibration maintenance folJows.

HistoryThe first development consent was obtained for the Mt OwenMine in November 1991. The mine was initiaIJy approved toproduce 1.4 million tpa of ROM coal, with mining operationscommencing in November 1993. A further DevelopmentApplication (DA) and Environmental Impact Statement (EIS) werelodged for the Mt Owen Mine extension in late 1993.Thisproposal was given consent in July 1994, aIJowing the mine toproduce 5.3 million tpa of ROM coal. Development consent wasgranted for the construction and operation of the rail loadingfacility in 1995. During 1998, the mine was fuIJy acquired byXstrata Coal, which, in 2001, increased saleable coal productionfrom 3.5 to 5 million tpa.

The adjacent Swamp Creek Mine, subsequently known as theRavensworth East Mine, was closed in 1991. In 2000, approvalwas obtained for reopening the operation as a new4 million tpa coal mine and integrating the operations with MtOwen operations.

In 2003 the nearby GlendelJ Mine was also fuIJy acquired byXstrata Coal and was integrated into the Mt Owen complex. Atthe end of 2004, Mt Owen mining operations were granted anew Development Approval for an expansion to increase ROMcoal production and processing to 15 million tpa. The result ofthese activities is that Mt Owen is a large and complexoperation, with the mine's coal handling and preparation plant(CH PP) processing coals from the three adjacent miningoperations.

GeologyCurrently one of the deepest and most sophisticated open-pitcoal mines in the world, Mt Owen is situated between two

regional thrust faults: the Hunter Thrust and the Hebden Thrust.These limit the lateral extent of the coal seams. Seam dips vary

throughout the deposit, with dips being steep (up to 45°) in theareas near the Hunter and Hebden Thrusts, where paraIJelthrusts dislocate the seam by up to 40 m.

Up to 22 mineable coal intervals have been identified, rangingin thickness from 0.4 m to 10 m, within a stratigraphic interval ofabout 350 m. The coal seams comprise a total thickness of about55 m.

Mining is undertaken at depths greater than 280 m, whichmakes Mt Owen one of the deepest open-pit coal mines in theworld.

Monitoring natural gamma radiation incoal ashMt Owen uses two types of online analysers to maintain coalquality. The Coalscan 3500, and subsequent model analysersbased on the same technology, is very weIJ known throughout theindustry. This section will thus focus on the Coalscan 1500Natural Gamma Ash Monitor, which has also been marketed for

some years but is less well known.The Coalscan 1500 Natural Gamma Ash Monitor determines the

ash content of coal on a moving conveyor belt by measuring thelevel of naturally occurring radioactive elements in the coal ash.

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30 WorldCoal September2009 www.worldcoal.com

There is no contact with, or interference

to, the coal or the conveyor's operation.Unlike other ash monitors, it containsno radioactive sources.

Almost all coal ash contains trace

amounts of potassium, thorium anduranium. These elements naturallyemit low levels of gamma radiation.They are common in shale and claybands and partings, but are not

generally present in the coal. For anyindividual coal deposit, the absoluteamount of these elements varies in

proportion to the amount of ashpresent. The use of a sensitivedetector, combined with careful

screening of the detector to removeother natural radiation, such as solar

and terrestrial radiation, gives suitableaccuracy for many applications, suchas monitoring raw coal feed to apreparation plant as at Mt Owen,identifying dilution from clay bandsand partings in raw coal ormonitoring ROM coal beforestockpiling.

The system consists of a largescintillation detector that is mounted

in a lead lined enclosure, which is

bolted longitudinally between thestringers underneath the conveyorbelt. Additional shielding is placed ina frame over the conveyor to furtherlimit the background radiation,thereby maximising the signal:noiseratio.

The natural gamma rays aredetected, amplified and transmitted toa digital multi-channel analyser(DMCA), which processes the countsand passes the data to the onboardcomputer. The computer thencalculates the ash value. Theelectronics control cabinet is also

connected to a belt weigher to enablecalculation of instantaneous ash

content and mass-weighted ashcontent as the tonnage rate on the beltvaries. Either output can be user­selected to display in real-time on adigital LED readout on the cabinetdoor. The signals can also be fed to aplant control system or to an optional,proprietary display system.

The Coalscan 1500 is particularlyuseful for monitoring the following:

• Coal types with highly variableiron or calcium content, as largevariations in these elements

impact on the accuracy of low

Shed in which Coalscan 3500 is installed.

energy gamma transmissiontechnology ash monitors.

• Thick bed depths on conveyors:this application is ideal for theanalyser, as the larger masspassing the detector improvesthe accuracy. In fact, unlike other

coal analysers, the bed depth isunlimited.

• Coal in plants that do not wishto hold radiation sources and

appropriate licences, as thereare no radioactive sources in theCoalscan 1500.

The analyser is an alternative forapplications requiring indicative ashcontent with minimal installation

expense.

Recent activitiesThe December 2004 developmentapproval saw the followingexpansions of the Mt Owenoperations:

• Ravensworth East integrated intomining operations.

• Construction and operation of aROM coal receival facility andhaul road to enable Mt Owen

CHPP to receive and processROM coal from RavensworthEast and Glendell mines.

• Modifications to the Mt Owen

CHPP allowing for the increasedthroughput and establishmentof an additional product coalstockpile.

South ROM infrastructure was

completed in August 2005.

Top view of typical Coalscan 1500 installation,

showing lead shielding surrounding analysed coal.

Side view of typical Coalscan 1500 installation,

showing the detector below the conveyor belt

and the electronics cabinet on the ground before

being installed on side mounting.

OperationsThe sequence of mining involvesclearing the vegetation and topsoil,drilling and blasting of overburden andthe excavation and haulage ofoverburden from a series of sequentialmining blocks to the emplacementareas. The coal that is uncovered is then

hauled to the CHPP for processing. Themajority of the clean coal is conveyed tothe product stockpile before being

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The raw coal is sent to dual RaMS. After a three-stage crusher, the coal is fedto a 2000 t surge bin. Three identical feeders feed, from the bottom of thesurge bin, the coal to be processed in the CHPP. In 2007, the CHPP upgrade .to three modules was completed.

The niw coal sized at 1.4 mm is processed on a multi-sloped 3.6 x 6.1 mdesliming screen and the> 1.4 mm coal is treated in a dense mediumcyclone at a typical specific gravity of 1.65.The dense medium cycloneproduct is dewatered by 1400 mm horizontal basket centrifuges.

There is a desliming screen underflow « 1.4 mm w / w) fed to classifyingcyclone cluster (8 x 500 mm) with the underflow (1.4 mm x 0.105 mm)passing to spiral classifiers. The 1.4 mm x 0.105 mm product is dewateredusing horizontal fine coal centrifuges.

South ROM Mt Owen Coalscan 1500.

transported by rail for about 120km toNewcastle for export. A small amountof coal from Ravensworth East Mine is

supplied to local power plants forelectricity generation via an overlandconveyor system.

The raw coal quality is monitored

by the Coalscan 1500 ash analyserslocated on both north and south raw

coal conveyors. The analysers providethe operators with trends of the rawcoal ash content and the likely yieldfrom the plant. This enables theoperators to maximise the plantoperation with respect to the qualityof the feed. The north conveyoranalyser was installed several yearsago, whilst the south conveyoranalyser was installed in 2008,following the completion of thissecond line.

Initial justification for raw coalanalysers was based on the complexity

The CHPP

North ROM Mt Owen Coalscan 1500.

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of the mining operation and therequirement to control the feedquality to maintain plant yield. Whenthe south ROM was designed, theintention was to maintain this ability.

SummaryROM coal is received and processedat Mt Owen CHPP from Mt Owen,Ravensworth East and Glendell

mines. Strict process controls, whichinclude the use of on line ash

analysers, guarantee that qualitytargets are met, and consequently thatthe high-quality export thermal andsemi-soft coking coals produced arekeenly sought after in Southeast Asiafor domestic power generation andfor use in steel production. GC

/1I

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