SSince its introduction in 2000, ThermoElectron has sold almost 30 units of itsGamma-Metrics Coal Quality Manager(CQM). Last year, the product’s range ofapplication was broadened significantly bythe introduction of two new variations. Thefirst of these permits real-time analysis ofauger sample increments. The second vari-ation allows the owner to use the devicealternately, either as a process streamanalyser or a discrete sample analyser.

Auger sample online analysis

Auger samplers have long been popularwith coal producers and some utilities. Theprimary purpose of these sampling systemshas been, frankly, to keep the supplier hon-est. Subjecting each incoming truck to sam-pling and subsequent analysis also pro-vides a tangible means of measuring aggre-gate coal quality to determine paymentrequired for contracts that pay per Btu/lbor that penalise for excursions in sulphur,ash or moisture. Despite the fact that theauger sampling process is quick, withtrucks often arriving every three minutes insome operations, the potential to take

advantage of each physical sample isalmost always squandered. Usually, thesample increment is merely deposited in asample can (following crushing and sec-ondary sampling) and aggregated with allthe other increments for that supplier orthat seam. Ultimately, a single analysis isperformed on the composite of dozens ofindividual increments.

In the early 1990’s, Cyprus Coal (Figure1) and Fola Coal tried to marry auger sampling with onlinecoal analysis, combin-ing an auger samplerwith a Gamma-Metrics 1812C coalanalyser. The conceptwas sound, but thechallenge associatedwith separating theanalysis of one incre-ment from the incre-ment immediately fol-lowing it was formi-dable. The chute of the1812C had to remainfull for reasons of

safety and detector stability, and the abilityto know the exact boundary between suc-cessive increments was virtually impossi-ble. Furthermore, the analysis technology,Prompt Gamma Neutron ActivationAnalysis (PGNAA), is one in which thegamma rays entering the detector comefrom as much as 9 in. above and below theplane of the neutron source and the gammaray detector. This meant that 18 vertical in.of coal (in an 18 X 12 in. chute) went

Reprinted from World Coal • May 2005

Analyse coal!

Richard Woodward,

Thermo Electron Corp., outlines

recent developments in coal analysis.

Figure 1. An early attempt at combining auger sampling with online analysis.

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unanalysed (in fact, it was deliberatelyrejected) as the boundary between succes-sive increments. If the auger incrementwere, say, 250 lb, approximately 50% of thecoal would not be analysed. Thus, the goalof analysing each auger increment wascompromised by the physics of PGNAAand the geometry of the Gamma-Metrics1812C.

Enter the Gamma-Metrics CQM coalanalyser, which was developed in 2000(Figure 2). This analyser has an analysis

zone with a 55% smaller cross-section,meaning that the fraction of coal goingunanalysed could shrink by the same 55%for an equal-sized auger increment.Furthermore, controlling the level in theCQM’s input hopper was made far simplerthan the challenge presented by the 1812C.The standard Gamma-Metrics CQM hop-per was made smaller in one dimension tominimise the time delay between arrival ofthe auger increment in the input hopperand its transport into the analysis zone.

Moreover, it was possible to create a gapbetween increments to eliminate any‘crossover’ effects. Figure 3 shows thedesign change in the input hopper.

The first such auger application of theGamma-Metrics CQM was sold last year toLongyu Power in China. This analyser wascommissioned early this year. Figure 4shows the overall installation, while Figure5 clearly shows the ‘reduced size’ inputhopper for the CQM.

Combination process and

sample analyser

The Gamma-Metrics CQM was popularupon its launch. Occasionally a buyerwould express an interest in having ananalyser that performed two tasks. Theinstrument would be used to monitor andcontrol the process most of the time, but atother times the goal would be to run dis-crete samples into the analyser to get aquick indication of the coal’s quality.

Last year a new model of the CQM,dubbed the ‘Duplex,’ merged these ideas.The concept of using the analyser in twoways was not new, since Gamma-Metrics(now known as Thermo Electron Corp.)had always calibrated its analysers in theplant by using coal samples in rectangularblocks inserted into the analysis zone.Furthermore, two or three reference stan-dards accompanied every analysershipped. These reference standards wereused to check the consistency of theanalyser onsite and to help calibrate duringneutron source replenishment. The onlydifference was that the reference standardswere static, unchanging chemistry. Inessence, the user wanted a box to place thesample into.

Other coal sample analysers have beendeveloped in the past, including theGamma-Metrics FastLab. These analysersworked well on occasion, but the relativelysmall sample size (4 - 5 kg) often requiredextensive sample preparation, a task theuser was trying to avoid with the use of asample analyser.

The design challenge was two-fold. Thesample container had to be small enough tobe lifted by a single person. It also had to besuccessively placed in two different positionsand precisely inside the tunnel, to allow den-sity and moisture measurement, followedimmediately thereafter by elemental analy-sis. The resulting dimensions of the samplecontainer are 24 in. x 10.5 in. x 9 in. (60 cm x27 cm x 23 cm), which, when filled with sam-ple, weighs approximately 65 lb (30 kg).

Reprinted from World Coal • May 2005

Figure 2. Thermo Electron’s Gamma-Metrics CQM Analyser.

Figure 3. Hopper assembly on CQM frame with tunnel liners and sample conveyor belt.

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To ensure the sample was positionedproperly, first for density and moisturemeasurement, and subsequently for ele-mental analysis, the company designed anextension to the Gamma-Metrics CQM atthe open end of the analysis tunnel (Figure6). This extension consists of a platformalong with a laser range finder. The laser

measures how deep into the tunnel thesample container has progressed, as it istransported by the conveyor in the oppositedirection top than that followed by normalsample stream flows. The position deter-mined by the laser is sent electronically tothe belt drive motor control. The CQMslowly scans the sample through the first

position where moisture and density aremeasured; this process takes approximatelyone minute. Then the conveyor moves backin the opposite direction until it reaches theelemental analysis zone, where it stops. Theelemental analysis time can be selected bythe user, but 10 minutes is typical. Whenthe analysis is complete, the conveyor auto-matically transports the sample containerto the tunnel opening where the user canremove it.

The first to apply this model of theGamma-Metrics CQM is a West Virginiacoal producer. While normally monitoringthe prep plant product, it will at other timesbe using the analyser to do prep plant cir-cuit diagnostics on its deister tables and tocheck train quality halfway through thebatch.

New utility applications

In the years 2000 - 2002, coal analyser pur-chases were made primarily by coal pro-ducers. In the two and a half years since,there has been a decided rise in utility inter-est in online analysis. The reasons for thisinvolve the following factors:

� Increasing coal costs have drivenpower plants to find ways to eke outadditional improvement in heat rateby avoiding outages and deratesthrough improved ash fusion control.

� Changing local and regional require-ments on emission limits are sparkinga greater use of low sulphur coals,which often lead to precise blendingrequirements.

In the past year and a half, three differ-ent coal analyser users have presentedpapers at major conferences describing thebenefits derived from using either theGamma-Metrics CQM or the Gamma-Metrics ECA (an over-the-belt analyser) toimprove their operations.

PacifiCorp Hunter plant As detailed in a 2003 Coal-Gen paper,PacifiCorp was suffering an increase inoutages and derates at the Hunter plant,which were caused by a shift in coal sup-pliers, precipitated by the closure of anearby mine. The lost generation wastraced to increased slagging, which inturn was related to lower ash fusion tem-peratures from one of the new coal sup-pliers. In 2002, PacifiCorp installed aGamma-Metrics CQM on a conveyor sup-plying a storage barn whose coal servedas the bunker feed for the plant. Since ashfusion in this case was closely correlated

Reprinted from World Coal • May 2005

Figure 4. Auger sampling system, including the Gamma-Metrics CQM, at Luoyang Longyu power plant,China.

Figure 5. This side view of Gamma-Metrics CQM coal analyser shows the sloped backside of the input hopper, which minimises the volumetric delay to reach the analysis zone.

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with iron and calcium,the CQM, as an elemen-tal analyser, was able toestimate ash fusiononline Consequently,the plant was able toadjust the blend of twodifferent coals to ensurethat the ash softeningtemperature remainedabove the danger pointof 2200 ˚F. The plantwas able to recover itslost generation capacityand quickly paid for itsanalyser investment.

Trans Alta Centralia Generation This plant in Washington (Figure 7) pri-marily burns local sub-bituminous coal.In 1990, Centralia Mining installed aGamma-Metrics 1812C coal analyser toimprove the consistency of the coal froman adjacent mine. In 1999, the local emis-sion requirements changed, whichresulted in the addition of an FGD scrub-ber system two years later.

In 2003, the plant installed twoGamma-Metrics ECA’s (Figure 8), one oneach of the belts feeding the plant, to beused in conjunction with GE’s OvationDCS control system, GE-Energy Services’Coal Logic software and Thermo’sGamma-Metrics COBOS blending soft-ware. This sophisticated combination ofsensors, electronics and software sys-tems has brought about some impressiveresults:

� A three-fold reduction in coal quali-ty variability (in terms of lbsSO2/MMBtu) has enabled the plantto operate the scrubbers at higherSO2 levels and consistently at orabove design capacity.

� The gypsum produced by the scrub-ber is consistently saleable for wall-board manufacture.

� The amount of low sulphur coalrequired for blending has been dras-tically reduced, offset by an increasein local mine production. Mine pro-duction has also become more effi-cient, as single seam mining is nowpossible.

Conectiv B.L. England plant A recent renewal of the fuel permit forthis coal-fired plant in New Jersey led theplant to purchase an analyser in late 2003to control the blending of anAppalachian bituminous coal with a PRBsub-bituminous coal. The Gamma-Metrics ECA analyser became part of itscompliance plan submitted to the NewJersey Department of EnvironmentalProtection.

Since its installation in January lastyear, this analyser has allowed the plantto stay below its emissions limits andsimultaneously minimise the amount ofPRB coal in the blend. This keeps the fuelcost in check and maintains the designslag viscosity factor. The analyser is alsoused as a constant monitor to alert theplant of any potential problems in theupcoming burn. _______________________�

Reprinted from World Coal • May 2005

Figure 7. Trans Alta Centralia plant.

Figure 6. Laser light table and sample container for CQM’s discrete sample analysis mode.

Figure 8. Gamma-Metrics ECA analyser at Centralia.

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