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The Importance of Sampling for Optimal Coal Analyzer

Performance

Richard Woodward, Thermo Fisher ScientificNational Weighing & Sampling Association

ConferenceSt. Louis, MO

25 February 2009

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Why you DO need a sampling system

Most analyzer purchases are intended to generate an acceptable return on investment

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Why do utilities and coal producers buy analyzers

Improve profitability• Utilities

• Reduced fuel cost by blending• Better boiler operation, hence reduced heat rate and fewer unplanned outages• Better emissions compliance, fewer penalties for exceedance• Improved scrubber efficiency

• Coal producers• Fewer penalties by consistently meeting contract specifications (blending)• Better prep plant efficiency, less over-cleaning• More consistent coal quality leads to better price and/or market share

Peer pressure Panic

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Why you DO need a sampling system

Most analyzer purchases are intended to generate an acceptable return on investmentAlso assume that a higher ROI is preferable to a low ROIVirtually axiomatic that better accuracy leads to better profitability

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Prob

abili

tyThe critical importance of

analyzer and reference system precision—power plant

RMSD = 0.04Setpoint = 0.72

RMSD = 0.03Setpoint = 0.74

Upper limit = 0.8 Seemingly modest differences in accuracy can lead to huge profit differences

• Assume • 5 mtpy clean coal burned• $10/ton cost differential

• 0.6% sulfur• 1.8% sulfur

• Annual savings associated with 0.03% RMSD rather than 0.04% = $833,000

% sulfur

The key is being able to move the target quality setpoint closer to the upper limit.

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The critical importance of analyzer and reference system precision—coal mine

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8 8.5 9 9.5 10 10.5 11 11.5 12% Ash

Prob

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RMSD = 0.50Setpoint = 10.18

RMSD = 0.35Setpoint = 10.42

Upper limit = 11%Seemingly modest differences in accuracy can lead to huge profit differences

• Assume • 4 mtpy clean coal sold• $4/ton cost of coal cleaning• $10/ton variable cost of mining• 70% yield in

cleaning from 25% to 7% ash

• Annual savings associated with 0.35% RMSD rather than 0.50% = $465,000

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Why you DO need a sampling system

We start with the premise that an analyzer purchase is not whimsical, but it is intended to generate an acceptable return on investmentAlso assume that a higher ROI is preferable to a low ROIVirtually axiomatic that better accuracy leads to better profitabilityNeed to convince you that sampling systems ensure better accuracy

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Why you DO need a sampling system

Won’t get as good an initial calibration

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Example of an inadequate, but not atypical, commissioning calibration

As Received Ash

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Analyzer Data

Lab

Dat

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As Received Sulfur

95% Confidence Interval on CalibrationExcel LINEST results

Slope 1.19 -0.07 Intercept

Standard error of Slope 0.239 0.158

Standard Error of Intercept

R2 0.692 0.018Standard Error of Fit

Minimum Maximum

Slope 0.71 1.67

Intercept -0.39 0.25

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Example of an inadequate, but not atypical, commissioning calibration

As Received Ash

0.50

0.55

0.60

0.65

0.70

0.75

0.80

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0.90

0.95

1.00

0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Analyzer Data

Lab

Dat

a

As Received Sulfur

95% Confidence Interval on CalibrationExcel LINEST results

Slope 1.19 -0.07 Intercept

Standard error of Slope 0.239 0.158

Standard Error of Intercept

R2 0.692 0.018Standard Error of Fit

Minimum Maximum

Slope 0.71 1.67

Intercept -0.39 0.25

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Why you DO need a sampling system

Won’t get as good an initial calibrationWon’t keep up with changes in the analysis environment

• Different coal types• Different belt loading conditions (rate of variability, bed depth,

topsize, surcharge angle, new conveyor)

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Yes, PGNAA analyzers measure every part of the cross-section but not uniformly so

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This model is for a Thermo Fisher ECA on a 42-inch belt using MCNP modeling programThe spatial sensitivity is very much influenced by product design, especially the location of sources, detectors, and reflectors

• Sources below the belt experience severe vertical non-uniformity

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Other technologies are much more impacted by coal heterogeneity

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Dual-gamma analyzers “see” only a thin sliver of coalXRF analyzers only “see” the surface of the coalThey are even more in need of regular lab vs. analyzer calibration comparisons

Dual-gamma ash gauge

XRF Analyzer

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Why you DO need a sampling system

Won’t get as good an initial calibrationWon’t keep up with changes in the analysis environment

• Different coal types• Different belt loading conditions (rate of variability, bed depth,

topsize, surcharge angle, new conveyor)Less likely to know when problems have occurredChange in bound moisture (e.g., frozen coal)Change in “ash other”

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Other considerations

Analyzers are not plug and play• Those analyzer owners who exercise diligence in their calibration

maintenance reap the economic rewards• We’ve inaugurated an award for the most accurate analyzer

Factory calibration is important but on-site calibration is the “acid test”

• Factory testing doesn’t fully capture• The lack of homogeneity in the coal• The varying belt loading• The profile on the belt• The belt composition

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Sampling systems can be relatively simple and inexpensive

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Constellation Energy uses a mobile sampling unit

Mobile Sampling

Unit

Primary sampler

Belt analyzer Reject

conveyorSecondary

samplerPower

unitCrusher

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Analyzer of the Year Award Initiated in 2008

A separate award for each parameter

• Sulfur• Ash• Moisture

Based on the lowest one month RMSD throughout the yearAward recognizes not only superior analyzer performance but excellence in sampling and sample preparation as well

Takes good sampling practices to win the award.