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Indonesian Jvlining-Cenetel1gg-Sl4 ilbfujp!,l,lqlyyher 7-8. 2001, Jukarta.

INDONESIAN COKING COAL. A NEW BEGINNING

ian Wolff

PT. Marunda Graha

ABSTRACT

Most Indonesian export coal is for the steaming market, while other countries dominate the coking coal rnarkets ofAsia. P'l'. Marunda Grahamineral is prepaling to enter the coking coal marlcet. Simple techniques developed andapplied during the exploration stage may alert other coal companies to potential opportunities in this market. Thechallenge is to look for this type ofcoal.

I . INTRODUCT'ION

Indonesran has a long history of supplying steamingcoal to the donrestic and international nrarkets.More recently there have been rnoves towardssupplying sonle aspects of the steel industry,particularly through thc adverrt of Pulveriz"ed Coallnjection (PCI) technology. Almost all lndonesiancoal has little to no coking characteristics, cxch,rdingit from the coke manufacture markets. PT. Marunda(-irahaminerals has recently undertakerr a coalexploration program, where in a significant aspcctof the sampling and testing progranl enabled it tosuccessfully determine the coking characteristics ofthe coal.

2 . SAMPLING

In nrost Indonesian exploration prograntsj cfrannelsampling of the outcrops locuses on searnre1:resentation. Flowever when exploring foi cokingcoal, the aspect of oxidation is a significanl factor.Essential l l ' al l outcrop coal is l ikely to be sl ightlyoxidized, ancl as such, wi l i have signif icantlyledur;cd coking ciraracteristics. Thus submittingchannel samples of outcrop coal wiil tend tcrsfroirgly untler value the coking properties. Toidentily if the coal has coking properfies, it is rnorermportant that the sample should be fresh and of thebcs{ . : t ,al , r 'at l}er than be represcrrtat ive.

Florir the M(iM expelience it is recommended toexplore outcrops for coking properties by selecting aglab sample from the freshest and lcast ash porliono1'thc orrtcrop. Usually this may be found in a par.tof the outcrop that would be under water during thedry season, and to dig into the coal until thc cleathas least staining and the coal is "strong". Such agrab sample is left in large lumps and immecliatelydouble bagged with exccss liesh water in the bag,and minimal air.

In the case of drill core, the emphases is once againto retain tlie freshness of the core. From the MGMexperience it is recommended that on exposing thecore iiom rhe drill split, wash with clean water andinunediately vyrap iu plastic with some added water.{-Jpc,rn sampling the coal place in double plastic bagswith excess clean water, and minimal air. Alwaysstr;r's it, a shady place. If the core is fronr shalk_'wlioles, (less thau 6 rneters), then slightly oxidizedsectious of ccre rnay Lre sampled as separate plys.

Recording the date of dri l l ing and sampling wil lal low latter closs checks of suitabi l i ty of samplingmethod against ttre possible affects of oxidation.Note that in some coking coals, th:rt sonreparameters can be dramatically reduced in.just a fcwdays exposure to the air.

It is irn*portant to notify the labor atorv of the cokingpurposci of the testing plogrl1ln, as al'rangcrnents (rr)t'eceiving and treating the samples may be modiflcd.Tliis may include the need to draiu thc excess water,wet clush the samples, to prfioritizc the cohing tests,and to store residues in the fi'eezer.

In the r:ase of exploriLrg for coking coal, the keyanalysis include Crucible Swell Number (CSN) rrrFree Sv;el l Index (FSI), plus sonre Cieslel Fluidityand a few petrology tcsts, along 'with the starrdrrdanalysis of Proriurate, Sulpirur anrl Calol i f ic ValLre.f'o date only one laboratory in lndonesia has :rcal ibrated insh'urnent fo test Giesler Fluidity.Alt lrough the r-SN is a relat ively sirrrple test,calibration is irnportant, as a slightly cooltrr flanrccan lead to lorver CSN values. The laboratolysh<luld record the datc of santple prepiration ancldate of each coking property. Courparrng cokirrgproperties to the proximatc analysis rnay lte neeclerito fully interpret the resirlts.

3.1 Moisture

hi thermal coal the geologist ln:ry go to sorne e{'fortto prcserrr'e the Total Moisrure. tlou'ever for-cokingcoal the 'fotal Moisture is generalil, less than 9 7o,and laboratory analysis focus on Inherent Nloisture.Latter determination of Free moisture will tend torelate largely to crusliccl coal size and stockpilcconditions. Thus the aspect of adding water to thecoal sample is not too detrinrental to the testing.

3.2 CSN

If CSN is below 2 yz - 3, then the coal may beoxidized, or is l ikely not to be suitable for cokingcoai. If the CSN is 3 - 4 or more, then fulther'analysis of the coals coking potential rnay bejustifie,.l.

CSN is a relatively cheap ancl easy test, anci can treundertaken frequentll' to identify variatitrns inseams or locations.

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Indonesian lv[inins Conference and Exhibition. Novenber 7-8. 2001 . Jaknrta.

3.3 Giesler Fluidity

If maximum fluidity values are more than 0 ddm,(dial divisions per minute) then the coal isconsidered as having some fluidity. However valuesof more than 200 ddm are required for somemarketing considerations, while values of more than1000 ddm may have a premium in marketing.

Ciesler Fluidity tends to be a more expensive andsensitive test, and can be undertaken to look forpotential additional premium marketing value.

3.4 Petrology

Mean maximum reflectance of more than 0.7 arepreferred for the coking blend market, while valuesof more than 1.0 are desirable. Some analysisreview the statistics of 100 point measurements.Maceral counts are more useful when the detailedcomponents are provided.

Petrology is a slow and expensive test, though ittends to be somewhat indicative of the coal, thusfewer tests are generally sufficient to categorize thecoal.

4. RESEARCH

4.1 Validation of fluidity tests

Fluidity can be highly susceptible to oxidation, andtesting for fluidity is recommended to be undertakenwithin 24 hours of drilling. MGM drill sites are veryremote, and analysis was often taken l0 days or soafter drilling. The data was reviewed to check thevalidity of the fluidity program. A plot was rnadeshowing the Maximum Fluidity (MF) (log l0)against time ( number of days ) between drilling andthe sample being prepared in the IndonesianIaboratory. Note that after preparation the laboratoryfreezes the sample - essentially stopping oxidationand fl uidity deterioration.

The plot of the samples shows a "flat"relationship, indicating no obvious deteriorationwith time. It was concluded that:-

. Field procedures of coal sampling are generallyeffective in keeping the coal santple fresh forfluidity testing.

o That laboratory fluidity results can be used torcflect "fresh" coal.

. No significant batch variations were indicated.

. The very low coefficient probably reflects theknown low repeatability and high laboratoryvariance normally associated with fluiditytestlng.

4.2 Coking properties deterioration

To determine the likely deterioration of fluidity andCSN over time, a 5 ton sample was wet crushed tonominal 50 mm top size and placed in drums tosimulate stock pile conditions. Three types ofdrums representing loose stockpile, compactedstockpile and a control set of drums with loose coalsubmersed in water were tested over 150 days.

A typical hyperbola curve of deterioration wasfound for the fluidity, with negligible differencebctween loose and compacted stockpile densities.Also according to expectations, the coal under waterdeteriorated rnarkedly slower. However CSNshowed no deterioration over 150 days.

These tests indicate MGM coal has relatively good"shelf life", which is seen as a marketing advantage.

5. WHERE TO LOOK

Coals exhibiting coking properties also tend to haverelatively low moisture content, reflecting a higherdiagenisis. This may be due to :-

r Deeper burial

. Confining pressure ( as reflected by folding )

o Proximity to intrusives.

In each case older sediments are more likely to havebeen subject to such influences. Within a coalsequence, the lower seams may tend to exhibitincreased coking properties.

6. WHY LOOK

Export coking coal prices have historically bcen 3 to6 US dollars per ton higher than steaming coal. Thisprice diffdrential is a good commercial incentive toinclude some aspcct of the specialized sampling andtesting suggested here in to look for cokingproperties in Indonesian coal deposits.

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