Principles of Operation

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Principles of Operation

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Prompt Gamma Neutron Activation Analysis, What is it?

Elemental Analysis Technique

Bulk Analysis Method• Penetrating Technology

Non-Destructive Analysis Tool

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The PGNAA Process

Neutron source 252Cf emits neutrons.

Thermal neutrons are absorbed and cause gamma ray emissions

Each element reacts differently When the gamma ray strikes

the NaI crystal a photon of light is emitted.

Gamma ray detection system converts counts into an energy spectrum

High speed digital electronics and sophisticated software convert the spectra into elemental composition

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PGNAA Detection

Pulse Processor

(DSP)

Electronics enclosure

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Typical PGNAA Gamma Ray Spectrum for Coal

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Method of Spectral Analysis

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× 1 × 0.25× 1× 2

+ ++

S Si Fe C

The measured spectrum

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Parameters Measured

PGNAA measurements

S

Ash

Moisture

Heating Value

Ash ConstituentsSiO2

Al2O3

Fe3O4

CaO

TiO2

K2O

Na2O

Cl

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Calibration is critical to good performance

Thermo uses high purity chemicals to calibrate the analyzers in the factory before they are shipped to the field.

• This is critical as it insures that there are no correlations between elements in the calibration.

• This is not possible to do if calibration is done in the field with coals.• The value of the factory calibration is that the analyzer will perform

properly with any mixture of coal seams. The calibration uses every element normally seen in coal.

• With out information on all the elemental data, the result would be less accuracy.

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How are the analysis calculated?

PGNAA measures the weight (in kg) of the elements of interest in the sample. (S, Si, Al, Fe, Ca, K & Ti)

The elemental weight of the ash oxide elements are converted to the weight of the oxides in the ash.

• Eg. Ca + ½ O2 → CaO therefore 1kg Ca = 1.39919kg CaO

The kg are then each divided by the analyzed sample weight to get the % weights.

The percent as received ash is then calculated• AR Ash = (sum of six oxides)/(1 - % other as a percentage of ash)

• Other is the sum of SO3 + MgO + Na2O + P2O5 + Undetermined

• In situations where the Na2O content is great enough (0.20% of coal), it is

used in the ash calculation above.

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Calibration Ranges

Ultimate Range

S 0-6%

C 30-80%

H 3-8.5%

N 0.4-1.7%

Cl 0-0.5%

Moisture* 0-35%

Ash** 3-38.5%

Ash Oxides Range % Coal

SiO2 0-21%

Al2O3 0-16%

Fe2O3 0-6.5%

CaO 0-16%

K2O 0-1.1%

TiO2 0-1.0%

Na2O 0-1.0%

* Moisture is determined from Moisture Gauge** Ash is determined from the sum of ash oxides

No correlations exist between components

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Moisture Measurement

Thermo uses microwave moisture gauges to measure the free moisture in the coal.

Total moisture is the sum of the free moisture plus the bound moisture for the coal being analyzed.

Moisture measurements are needed to:• Determine the dry analysis values (PGNAA measures as received)• To calculate the heat content of the coal

• To calculate the emissions potential as a function of heat content

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CV and emission calculations

CV is calculated based on the moisture ash free CV (MAF CV) of the coals being analyzed.

Lbs SO2/million Btu (in USA)

Or any empirical formula the customer uses to measure performance.

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AshARMoistureCVMAFCV

BtuAR

SulfurAR

Btumillion

SOlbs %000,202

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Information on Coal input by the customer

The following coal parameters need to be input by the customer.• Other Ash oxides• MAF CV• Bound Moisture

COBOS Thermo’s coal blending software package will weight average these values to allow the correct constants to be applied to the analysis results.

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Analysis differences between PGNAA and Dual-gamma analysis technologies

Dual-gamma ash gaugeMeasures average Atomic Number

Detector

Am & either Ba or Cs Source

PGNAA much less affected by composition differences within the cross-sectional profile of coal on the conveyor

PGNAA elemental gaugeMeasures Elements that make up the ash

Cf Source

NaI Detector

neutrons

gamma rays