Metodos de Ensayo Ash Probe

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Figure 1. Analysis with Ash Probe

in trucks and ,inset, a photo of the

ash probe.

Probing forPerformance

August 2010 | World Coal | 1

Over the past ten years since the first article appeared in WorldCoal, the Ash Probe has become a vi tal tool for many coalproducers and users in over 20 countries around the world.1 Thishand portable instrument provides quick and accurate

measurements of the ash content of coal in piles, trucks or wagons. It worksusing the natural gamma technique, which makes use of the fact that the dirtassociated with mined coal contains significantly higher concentrations ofgamma emitting radioactive material than the coal itself.1 The signal

received in its sensitive gamma detector increases as the dirt (or ash) contentof the coal increases. Through a suitable calibration, the Ash Probe convertsthis gamma signal into an ash reading.

PAUL MICHAEL TAYLOR,

BRETBY GAMMATECH LTD, UK,

PRESENTS TWO CASE STUDIES

DETAILING THE BENEFITS OF

USING A PROBE INSTRUMENT

TO MEASURE THE ASH

CONTENT OF COAL.


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The main part of this articleconcentrates on providing two setsof case studies where the instrumenthas been used to significantlyimprove customer operations.2These studies outline how the sitesfunctioned before the use of the AshProbe and then how they operateusing the information from theinstrument. Details of theperformance of the instrumentsalong with the benefits they provideto their users are described.

Brief descriptionThe Ash Probe comes in two mainparts: the probe and the displayunit. The probe comprises a stainlesssteel tube containing a sensitive

gamma detector at its inner end.This ensures that the detector is

buried suff iciently deep to makecertain that all the signal comesfrom the surrounding coal and notfrom naturally occurring

background radiation. For a detaileddescription, refer to the many earlyarticles about the Ash Probe.1&3Once calibrated, the Ash Probeprovides the ash reading for eachprobing within 1 2 minutes of

operation. Multiple probings aremade to provide a precisemeasurement for the complete pileor truck load being tested. The

display unit provides the averageash content of the pile from all theprobings, complete with its standarderror (or precision) along with thetotal number of probings made.Thus, the instrument informs theuser when the required number ofprobings has been made to achieve agiven level of precision. For pilesthat are homogeneous in ash, thisoccurs after relatively few probingswhereas, for less homogeneous coal,more probings are needed to reachthe same precision. Withconventional sampling and analysis,no such knowledge of thehomogeneity is obtained from thesingle ash sample even though itmay be made up of many

increments. This information canonly be extracted if each individualincrement is separately analysed forash not a practical prospect inmost cases. So not only does theAsh Probe provide a quickmeasurement of ash content, it alsoinforms the user about the ashhomogeneity of the coal and howmany probings are required toobtain a given precision.

Colombian case studyThe first Ash Probe customer inColombia was C.I. Milpa S.A. Thiscompany extracts and processes

coking coal from three mines:San Miguel, Incarsa and La Limpia.Coal is also purchased from about150 suppliers in the area. Before theuse of the Ash Probe, the analysis ofthe ash content of the coals both atthe purchasing stage and during thecoking process was conducted bymanual sampling of the trucks. Thesamples were then sent to thecompanys laboratory forconventional thermo-gravimetricanalysis. This analysis process tookabout 15 hours.

In 2005, C.I. Milpa S.A. took thedecision to buy an Ash Probe and,after verifying the operation of theequipment, it was quickly decidedto purchase four more units.

The main use of the Ash Probes isto measure the ash content of thecoals arriving by truck at the threewashing plants. The trucks carry10 20 t of coal and the averagenumber of trucks/plant ranges from80 150 trucks/day. Coals with ameasured ash content of less than10% bypass the washery and areeither sent directly for export or tothe coking ovens. Coals with an ashcontent of greater than 10% are

organised into different piles forfuture washing depending upontheir ash content. For example, coalswith an ash content from 10 12%,12 14%, and from 14 16%, etc.,are all sent to separate piles. Thisorganisation enables coals with thesame ash grade to be sent to thewashing plant together so that it can

be calibrated for those ash levels ,thus maximising yield.

The time saving benefits aresubstantial, since the process to

obtain ashes in the laboratory takesan average of 15 hours compared tothe 5 10 minutes that it takes toobtain the ash contents by theAsh Probe. This speeds up theentrance of the loaded coal trucks,

because the destination of the coalcan be quickly decided. Significanteconomic savings are obtained whenclean coals are not washed. Thequality of the final product is alsoimproved because no dirty coals are

used directly in the coking or exportprocess.

The Ash Probe is also used toFigure 2. Analysis with the Ash Probe in piles.

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measure the ash content of thewashed products and theinformation is used to control thewashing parameters to ensure aconsistent product quality. A furtherapplication is to determine the ashcontent of the export coals.

The performance of the Ash Probeis checked by taking manualsamplings and conducting therespective analysis in the laboratory.Figure 3 shows a graph of 54Ash Probe ash readings against thecomparison laboratory sampleanalyses. It can be seen that the biasis insignificant. The standarddeviation of the differences is 0.7%ash. In general, this level ofperformance is typical.

Once C.I. Milpa S.A. had becomefamiliar with using the Ash Probesin its plants, it could see significantapplications for these instruments inSouth America. It suggested

becoming Bretby Gammatechsrepresentative in the region and thiswas quickly accepted. Since 2005,the company has been selling BretbyGammatech equipment withsignificant success. It now hascustomers who are amongst the

most important players in thecoking coal and coke markets inColombia.

There are also Ash Probesproviding a quick ash measurementof the coal arriving at power plants,cement plants and steel millsthroughout Colombia. Moreover,there are several Ash Probes in useat the large steam coal mine atCerrejon. To date, over 50Ash Probes have been sold to 16different companies in Colombia,

with many repeat sales.

Stockton mineThree coal seams are extracted atStockton mine, about 2 km east ofHazleton, Pennsylvania, US. TheMammoth seam has the lowestinherent ash and it is the primaryseam mined with the highest yield.The washing plant is rated at 150tph of raw coal feed. Up to 1200 tpdare processed with clean coal

production of up to about 500 tpd.Coal is washed at gravities from 1.72to 1.82, depending on the coal seam

being processed. Quality also variessomewhat within the Mammothseam. To adjust gravity toaccommodate changing raw coal, itis vital to know the ash of the cleancoal on a real-time basis. This allowsgravity adjustment to maintain the

desired clean coal ash content.Washed anthracite is sold to steel

plants and utility market customers.Steel producers require a typical ashof 9.5%, while the utility marketaccepts coal in the 8 10% ashrange. The lower ash content coal is

Figure 3. Performance of the Ash Probe at Incarsa mine.

Table 1. Results of the comparisons between the Ash Probe and the laboratory ashes

Date Product Ash Probe % Lab ash % Difference %

11 March 2009 Nut 8.30 8.40 -0.10

Pea 7.90 8.32 -0.42

Buck 8.20 8.71 -0.51

Rice 9.50 9.88 -0.38

22 April 2009 Nut 8.20 8.89 -0.69

Pea 8.90 7.46 1.44

Buck 8.90 8.87 0.03

Rice 9.30 10.78 -1.48

7 May 2009 Nut 8.50 9.23 -0.73

Pea 10.00 9.59 0.41

Buck 10.30 9.18 1.12

Rice 10.60 11.18 -0.58

3 June 2009 Nut 8.40 9.73 -1.33

Pea 9.50 10.00 -0.50

Buck 9.60 9.33 0.27

Rice 10.60 11.71 -1.11

23 June 2009 Nut 8.40 8.70 -0.30

Pea 9.50 9.40 0.10

Buck 9.60 9.80 -0.20

Rice 10.60 10.10 0.50

14 July 2009 Nut 8.50 8.54 -0.04

Pea 9.10 8.78 0.32

Buck 9.90 9.83 0.07

Rice 10.00 10.47 -0.47

August 2010 | World Coal |


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well received by the utility andallows for a higher market price,albeit at lower yield values. Thetypical gain in price does not makeup for the loss in saleable tonnageand therefore revenue caused byproducing cleaner coal using lowerseparation gravity values. This is agood reason to use the Ash Probe.Typical daily volume shippedduring the heating season is about

20 truck loads, or 400+ t. Dailyshipments can increase to 30+ truckloads when industrial shipments areincluded during the heating season(October to February).

Before acquiring the Ash Probe,daily samples of clean coal weregathered and delivered to anindependent laboratory for analysis.Ash results were available thefollowing morning. The laboratoryreport was used to adjust gravitiesfor the current day operation.

Because of the delay in receivingash results, gravity adjustments tolower or increase ash would bedelayed by a full day, resulting insub-optimal control of the washingplant, especially during periods ofvariable raw coal feed. A method ofreducing the time delay wasrequired.

The UK owner of the mine,Atlantic Coal plc., was aware of the

beneficial uses of the Ash Probe

from colleagues in South Waleswhere Ash Probes have been inroutine operation for more than a

decade. It recommended theapplication to Stockton. TheAsh Probe was purchased in

January 2009 and commissioned bythe manufacturer towards the end ofFebruary 2009.

By early March the customergained confidence in the results andthe probe started to be used insteadof the independent laboratory forthe routine analysis of the buck,

rice, peas and nuts. Every fewweeks, as a check on performance,samples taken from around theprobe were delivered to thelaboratory and the ash resultscompared with the Ash Probereadings. The results of thesecomparisons are shown in Table 1.

An analysis of these comparisonsreveals that the standard deviationof the differences between the probeash contents and the laboratory ashvalues is 0.69% ash. This compares

well with the standard deviation of0.61% ash obtained during thecalibration. There is also a verysmall bias of -0.190.02% ash.Of course, these results include theinevitable sampling and analysiserror by the independent laboratory.It can be seen that there has been nocalibration drift throughout the fourmonth period.

A study has been undertaken toassess whether the mine has derived

any benefit in terms of productconsistency as a result of using theAsh Probe. The daily ashes for each

product have been grouped intomonthly sets for a period of fourmonths both before and after theAsh Probe was commissioned andused. The standard deviation ofeach monthly set has beendetermined and plotted as a s tacked

bar chart, as shown in Figure 4.There are two sets of data for March:data from the conventionallaboratory and the Ash Probe data.All the data before February arederived from the conventionallaboratory ashes and the data fromApril onwards are derived from theprobe ash contents (laboratory ashvalues were limited after March).Since the Ash Probe started to beused in early March, there has been

a significant improvement in theconsistency of all four products.

Recent communication with themine has revealed that since theAsh Probe started to be used it hasnever produced out of specificationcoal.4 Moreover, it is gaining new

business based upon the quality andconsistency of its product. InApril 2010, it used the probe to pre-sample an undeterminable coal type

before i t was excavated. From doing

this it found that the material wasgood quality barley coal. Back in the1950s, when the property wastunnel mined, rice and barley weredumped back into the tunnels to useas fill because there was no marketfor fine coal in those days. By usingthe probe they realised its actualpotential and, rather than bypassingit, they mined it.

The author does not have thefinancial details of the supplycontracts so it is difficult to provide

a detailed account of the financialbenefits accrued to the mine by thisimprovement in productconsistency. Suffice to say theimpact should be significant. Interms of savings in externallaboratory costs, the case is clear.Since March 2009, there has been anaverage reduction of US$ 700/weekin the invoices from theindependent laboratory. Thepayback period on this saving alone

is well under one year.The Ash Probe has allowed real

time testing of clean coal ash. The

Figure 4. Improvement in the consistency of the products after use of the Ash Probe at

Stockton mine.

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total test time is less than one hour.Results are available immediatelyand used to make any necessaryadjustments in gravity to ensureproduct ash specifications. Thefrequency of washed coal testingusing the Ash Probe is dependenton changes in raw coal feed. Whenthe raw coal feed is homogeneous, asingle daily test is completed. Whenraw coal feed is more variable,either within the seam or because of

blending of seams, tests are donemore frequently to ensure washinggravities are properly set for thedesired ash.

ConclusionsThis article has provided detailed

accounts of Ash Probe userexperience in Colombia and the US.These accounts have providedinformation on the results of long-term performance tests and detailsof the considerable benefits derived

by the users of the Ash Probe. Apart

from the reduction in time delays ingaining accurate ash results, the

benefits from using the probe rangefrom financial savings in samplingand analysis costs to improvedconsistency in saleable product. Thislatter benefit is possible because therapid results from the Ash Probeallow plant operators to adjustwashing densities quickly in orderto maximise yield at a given ashcontent or blend coals moreaccurately in real time.

The long-term tests at Incarsamine and Stockton mine haveshown the Ash Probe to perform towithin 0.7% ash of the conventionalsamples. Use of the probe atStockton mine has enabled a very

significant reduction in the day-to-day variability of its products, whileat the same time enabling areduction sampling and analysiscosts such that, on this basis alone,the Ash Probe will pay for itself insignificantly less than a year.

AcknowledgementsThe author would like to thankMartha Parra and German Padilla ofC. I. MILPA S.A. for providing all thedetailed Colombian data, as well asGreg Kuenzel of Atlantic Coal andRay Petrilla, Steve Brobst, Corey Brobstand Steve Ciarimboli of Coal Contractors

(2001) Inc. for providing all theinformation for the Stockton case study.

ReferencesTAYLOR, P.M., An All-NaturalTechnology, World Coal, Volume 9 ,No. 1, January 2000.

TAYLOR, P.M., Natural Gamma Comesof Age for the Quick Measurement of theAsh Content of Coal in Piles, Wagonsand Trucks: Some Case Histories,XVI International Coal PreparationCongress, Lexington, Kentucky,Society for Mining, Metallurgy andExploration, 2010.

TAYLOR, P.M., Quick Ash Measurementof Coal Piles is Possible with theAsh Probe, XIV International CoalPreparation Congress, South AfricanInstitute of Mining & Metallurgy,2002.

Personal communication withSteve Ciarimboli, Stockton mine,May 2010.

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August 2010 | World Coal |

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Metodos de Ensayo Ash Probe