SU1679318A1 - Method for determining ash content of coal - Google Patents

Abstract

The invention relates to methods for determining the ash content of coal by radiometric methods. The purpose of the invention is to improve the accuracy of determination. Calibration samples are taken with known values of ash, and several samples with different effective atomic number and density are prepared for each value of ash. the density of the calibration and test samples, build a calibration graph. The ash content of the test sample is determined by the values of its effective atomic number ra and density 2 silt

Description

The invention relates to methods for determining the ash content of coal by radiometric methods.

The purpose of the invention is to improve the accuracy of determination.

FIG. 1 shows a calibration graph showing the relationship between sample density, its effective atomic number, and ash content; Fig. 2 shows graphs showing regions (ellipses) of the scattering of the effective atomic number and density of two coal samples having different ash contents.

FIG. Figure 2 shows the ellipses of scattering (the internal ellipse corresponds to one standard deviation, and the external to two) of the effective atomic number and density for two samples of Donetsk coal with an ash content of AI 20% and Ar 22%. In the first sample, the effective atomic number fluctuates within 7.560-7.639, and in the second sample - 7.611-7.690 (with a confidence probability of 0.95). The sample density at ash content of 20% fluctuates within 0.920-1.2575 g / cm, the sample density of 22% zonality is 0.953-1 305 g / cm3. The average atomic number of the sample ash 20% is 7,600, and its density is 1.100 g / cm3. with an ash content of 22%, the average atomic number is 7.650, and the average density is 1.133 g / cm3

Atomic number and density fluctuations are limited to ellipses, they are subject to normal probability density. This is explained by the fact that each of the fluctuations is caused by many reasons comparable in influence, the density changes due to fluctuations in size, fracture, humidity and content Atomic number changes due to the redistribution of heavy and light elements in coal ash (aluminum, silicon, and sulfur content are redistributed

oh h

S 00

00

calcium, nitrogen, phosphorus, iron, manganese, titanium and other elements).

It can be seen from the graphs (Fig. 2) that it is impossible to distinguish samples with ash contents of 20% and 22% in the range of atomic number changes of 7.611-7.639, as well as in the range of density changes of 0.953-1.275 g / cm3. These samples can be distinguished by the average atomic number only with a probability of 0.57. Thus, when measuring the ash content in density, there will be 340 errors for each thousand measurements, in order to distinguish one sample from another with ash content differing by 2%. If, however, the ash content is measured by atomic number, then there will be 311 errors for every thousand measurements.

The ellipses for the two standard deviations do not intersect (Fig. 2). These ellipses intersect at a confidence probability of 0.965. Therefore, if the ash content is measured by atomic number and density simultaneously, there will be 35 errors for every thousand measurements. The number of errors in the measurement of ash content by density and atomic number is simultaneously reduced by nine times as compared to the measurement of ash content by atomic number and reduced by 12.3 times as compared to the measurement of ash content by density.

The method is carried out as follows.

Calibration coal samples are prepared with known ash values A |. In this case, for each value of ash content, a certain amount of K samples are prepared, having different effective atomic number and density values.

For each calibration sample, the values of effective atomic Zij number and density p (1K) are determined. For each value of ash content I, the average values of the effective atomic number Zj and p are determined.

3-K-12 Z ,,:

j i (1)

/ 5 1 Ј d,

eleven

Based on the obtained values of Zi, p and known values of AI, a calibration graph is constructed (Fig. 1). The values of the effective atomic number Z and density p are determined in a controlled volume of coal with unknown ash content. Then, the ash content of the test sample is determined from these data using a calibration graph. To do this, determine the distance from the point (Z, p) to each calibration point in the coordinates (ZO p) and find the two shortest distances. If the point with coordinates (Z / e) is closest to the points (Zi, p i) and (Zi-c, p n-i), as shown in FIG. 1, the distances from the measured point to the nearest calibration points are

, (Z-Z,) 24/3-pi) 2 1/21/9 (2)

and 1n-1 - (Z-Zi + i) 2 + {p-p m) (3)

Unknown ash content is determined from

expressions

r2

An-2 (AilH.i + An.ili) h (li + ln-ir (4)

FIG. 1 shows five calibration points of ash content on the 20p plane: 5 point with coordinates (gMin, D min) corresponds to the minimum value of the ash content, etc. point with coordinates (Z |. р) - ash content AI, point with coordinates (Zi + i, / 01 + 1) - ash content Аts-i, point with coordinates 0 (Еmax, р max) - the maximum possible value of ash content of the controlled volume MAh AMAKcd.

The ash values in the calibration points are set so that they evenly fill the range of possible changes in the ash content from to Amax. Usually, for any kind of dependence (Z), five points are enough.

If the measurement result (Z, p) does not fall on the smooth curve connecting

.one

calibration points, the ash content A is determined in the same way as the ash content Ad, according to the formula (4).

The values li and li-i are determined, like li and li + i, by formulas (2) and (3).

five

0

five

The method was tested in the determination of ash samples of coal. The controlled volume of coal is irradiated with a flux of gamma quanta with an energy of 60 keV from the americium source - 241. At the same time, gamma radiation back scattered by coal is detected by two detectors. The first detector is installed closer to the source in a geometry that provides inversion (independence) to density. The signal from the first NI detector is inversely proportional to the effective atom number Z of the monitored coal volume and NI decreases linearly with increasing Z. The second detector is set farther from the source in a geometry that provides a decrease in the N2 signal with increasing Z or p. Geometry is chosen so that

the contribution of gamma quanta coherently scattered by carbon to the intensity detected by the second detector is as great as possible, as evidenced by low sensitivity to Z or / e const In this case, the N2 signal decreases slightly with increasing g (for each percent Z increase, the Na signal decreases by about 0.3 %) and strongly (approximately linearly) decreases with increasing p (for each percent increase in p, the N2 signal decreases by about 2.5%). In the coordinates (N, 0), the method is calibrated, for example, similarly to FIG. 1, replacing in FIG. 1 Z with NI and p with N2. After graduation, the coal volume is set with an unknown ash content Ad and the signals NI and N2 are measured. Then, according to formula (4), taking into account formulas (2) and (3), the ash content of the controlled volume of coal is determined. It is 25%.

The standard deviations of the results of determining the ash content of the coal according to the known and proposed methods are 2.4 and 0.25 rel.%, Respectively.

Claims (1)

Claim method for determining coal ash content, including sampling calibration samples with a known ash content and determining the effective atomic number of calibration and radiometric samples under investigation, characterized in that, in order to improve the accuracy of the determination, several calibration samples are taken for each ash content when preparing calibration samples , having different values of the effective atomic number and density, determine the density of the calibration and test samples, and the ash content of the samples eduemoy sample was determined using the calibration curve according to its density and effective atomic number. 2n /  Uw & /. / It Z, Z Zt- ,; T-MOW, FI.1 BUT 7,560 16007,611 2№ 7,650 Phie