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Dr.Sci.Tech. Pak Y.N., Cand.Tech.Sci. Pak D.Y.,
Blochshitsyna A.Ì., Nikitina A.V.
Karaganda State
Technical University, Kazakhstan
Application of instrumental
nuclear-physical method
for quality control of solid fuel
Coal
as an object of nuclear-physical control is a complex compound including
organic matter and multicomponent mixture of mineral impurities. More than 95 percents of all coal mineral
matter is accounted for by aluminium, silicium, calcium and iron compounds.
The
most integral coal characteristics connected with ultimate composition is its
effective atomic number Zeff.
Effective atomic number and ash-content A
relation defines methodical capabilities of low-energy scattered gamma radiation method.
Photoabsorption
coefficients regularly raise with element`s atomic number increasing in case of
gamma radiant energy is higher than iron K-level absorption energy (7.11 keV).
This regularity is broken when gamma radiant energy is lower than iron Ek.
Iron is comparable with aluminium in attenuation properties by reason of
photoabsorption coefficient`s
stick-slip behavior. Due to this the heaviest ash-forming element is
calcium that has photoabsorption coefficient almost 3.5 times higher aluminium
has. Taking into account that alumosolicates form considerable proportion of
coal`s mineral matter in most deposites the relative stability of
gamma-absorbing properties of coal mineral matter under iron content
fluctuation may be expected. In this case coal can be represented as a three-component
compound that consists of carbon and mineral matter in the form of
alumosilicates and calcium.
The
intensity value of scattered gamma-quantums is ambiguously connected with basic
qualitative parameter of coal –
ash-content. The reason of ambiguity is difference between constituent of ash in interaction coefficient
(alumosilicates and calcium) and non-correlated redistribution of ash
composition and ash-content.
The
method essence of which is a measurement of secondary gamma emission integral
intensity including gamma radiation scattered by the coal and roentgen
fluorescent radiation of calcium finds
application in the practice of coal rapid-analysis. Compensative principle is
reached by the qualitively back changing
of scattered and fluorescent radiation intensities under the
calcium-content fluctuation. Secondary radiation is proposed to attenuate
additionally by the filter made from the light element to enhance compensative
effect and to reach larger unambiguity of the results.
Design
and experimental researches defined complex regularities between integral
intensity changing and thickness of the attenuating filter, coal`s ash-content
and calcium concentration. Inversion zone indicative about independence of
integral intensity from calcium composition`s
fluctuations is observed under setting a certain thickness of filter.
The condition of inversion`s origination is equality of absolute increments of
fluorescent and scattered radiation`s intensity that has opposite
sightings under calcium fluctuation in
coal.
Fluorescent
radiation of calcium has prevailing role more to the left of curves` crossing
point in pre-inverse zone. Scattered gamma-radiation has dominating role in
post-inverse zone (more to the right of crossing point).
It needs a prior
information about ash-content and its fluctuation to do accurate quality
control of coal by secondary emission`s integral intensity. This information
helps to select optimal thickness of the attenuating filter.
Provided
that insignificant ash-content`s dispersion suggested integral method of
compensation of variable calcium composition by attenuating the secondary
emission gives satisfactory accurate result. Analyzing raw coals with
fluctuation ash-content and material composition it is necessary to have a
hardware-methodical information about calcium with following correction of measured secondary emission`s
integral intensity.
Statistical
analysis of multifactorial measurements` results defined close interconnections
between secondary emission`s integral intensity and calcium composition in coal
and its ash-content that are
approximated by empiric equation:
Nis = a0 – a1 ×
À + a2
× m – a3 ×A·m, (1)
where
a0, a1....
a3 – contants determined on model coal mixtures of learned composition.
Thus it is clear that the problem of
coal`s ash-content determination of variable composition according to the
expression (1) comes to on-line test of calcium composition by means of indivisible hardware-methodical complex.
Information
sources
1. Starchik L.P., Pak Y.N. Nuclear-physical
methods for quality control of solid
fuel. – M.: Nedra, 1985. P.224.
2. Klempner K.S., Vasilyev A.G.
Physical methods of ash-content control in coal. - M.: Nedra, 1978. P.174.
3. Pak Y.N. Increasing of
radioisotope analysis` accuracy of ash-content in coal.- Plant laboratory. – 1980. #8. P. 74-76.
4. Storm E., Israel H. Interaction
cross-section of gamma radiation.- M.: Atomizdat, 1973. P. 254