Principles of Operation
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Transcript of 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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DataProcessing
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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