SU1114156A1 - Pulsed neutron method of determining moisture content of materials - Google Patents

Abstract

YMG-1 NEUTRON METHOD FOR DETERMINING THE MATERIAL HUMIDITY, which means that the material under study is irradiated with a pulsed stream of fast neutrons and the temporal distribution of the thermal neutron flux, which is determined by the fact that the beginning of the beginning of the neutron is measured, and the measurement error and extension of the field of application of the method are determined. the onset of the maximum psithoka of thermal neutrons, the temporal distribution of the flux of the superthermal neutrons is recorded and the average residence time is determined neutron in the epithermal region j and the moisture content of the material is found from the expression C, d,) b, l tM (d,) b ,. - (t is the material humidity 5%, where V7 is the time from the start of the neutron – neutron pulse to the maximum of the warm neutrons, t c is the average residence time of the neutron in the epithermal region, i defined by the formula (L 00 (Y t., t (p ( E t) dt /) () dt, ts is the pulse duration of fast neutrons, .b ,, bjfC C (, C2jd4, d2 are constant coefficients for this material, and the ratio of the duration of a pulse of fast neutrons to the time from the beginning of a pulse of fast neutrons to the onset of the maximu1-1a of the thermal neutron flux in the dry rial is chosen not to exceed They are 0.2, O1 and the period of following pulses of fast neutrons is not less than the lifetime of thermal neutrons in the dry material.

Description

The invention relates to the study of the chemical and physical properties of substances, in particular, methods for determining the moisture content using a fast neutron flux, and can be used, for example, in ferrous metallurgy to determine the moisture content of coke, sinter blend, etc.

A known method for determining the moisture content of materials is that the material is irradiated with a pulsed stream of fast neutrons from a neutron generator, then a flux of thermal neutrons in a channel width h is recorded with a temporal pulse analyzer. with. delay ty relative to the start of the neutron pulse. The number of recorded pulses is used to determine the damping factor of the thermal neutron density, the magnitude of which determines the moisture content of the material.

The disadvantage of this method is a significant measurement error associated with the registration of the absolute value of the heat flow of neutrons. The instability of the output of the neutron generator, as well as the instability of the transmission coefficient of the measuring path, affect the number of registered pulses in the channel At, which determines the damping factor, which leads to significant measurement errors.

When measuring the moisture content of large tonnage masses of materials in ferrous metallurgy, such as coke, charge, iron ore concentrates, a limited amount of the investigated ma. The material leads to measurement errors due to the low representativeness of the sample and narrows the scope of application of the method.

These drawbacks are partially eliminated in the method of measuring the moisture content of materials, which is closest to the invention and consists in the fact that the material under study is irradiated with a pulsed fast neutron flux, the temporal distribution of the thermal neutron flux is recorded, and the total distribution time m is determined.

T itx.

.

where u.t is the width of the temporary channel

analyzer, m

Nt, is the sum of the time channels k-occupied by the distribution. Based on the total distribution time T, the humidity is determined.

materials, pre-graduated scale of the total time distribution of T humidity.

The disadvantage of this method is an insignificant error in the measurement of humidity due to the error

t

N.

registration parameters

exactly -i

Its definition is difficult due to the asymptotic behavior of the curve of the temporal distribution of thermal neutron flux.

The disadvantage of this method is also the significant error in measuring the humidity from measuring the content of absorbing elements, for example iron, manganese, chlorine, ъ of the material under study, as well as the dependence of the measurement results on the density of the material being monitored.

The aim of the invention is to reduce the measurement error and expand the scope of application of the method. This goal is achieved by the fact that, in the method of determining the moisture content of materials, that the material under study is irradiated with a pulsed flux of fast neutrons and the temporal distribution of the thermal neutron flux is recorded, the time from the beginning of the neutron pulse to the occurrence of the maximum thermal neutron flux is determined the temporal distribution of the flux of the suprathermal neutrons is recorded, and the average residence time of the neutron in the suprathermal region is determined, and the moisture content of the material is determined from the phase 0, .., WC. , , Ch, WC

(,) () b, l

 with

where W (is the moisture content of the material,%, t is the time from the beginning of the neutron pulse to the onset of the maximum thermal neutron flux t

t .. is the average dwell time of a neutron in the epithermal region, determined by

formula

with

 t0 (E, t) dt

t

H uo;

j (E t) dt

t

where t is the pulse duration of fast neutrons. b (, b ,,, c, Cj, c, dp dg, constant coefficients for this material, and the ratio of the duration of the impulse of fast neutrons to the time from starting a pulse of fast neutrons until the maximum thermal neutron flux in the dry material is chosen not exceeding 0 , 2, and the fast neutron pulse pulse period is not less than the life time of thermal neutrons in a dry material. The essence of the invention is illustrated by the following dependencies: Fig. 1 is a graph of the temporal distribution of the thermal neutron flux at different humid values. TI and determination of the total distribution time T of the prototype; Fig. graph of temporal distributions of fast neutron pulses F, flux of epithermal N neutrons and flux FG of thermal neutrons Reducing the measurement error of humidity in this method compared to the prototype is achieved by defining the position of the maximum thermal neutron flux and the average residence time of neutrons in the epithermal region is performed with greater accuracy than the total time of distribution of neutrons, due to the fact that this time depends um on the chemical composition of the material (absorbing elements) has assimpatichesky the curve, and is also sensitive to pulsed neutron source output change. The expansion of the area of application of the method as compared with the prototype is the possibility of measuring the humidity in materials with different contents of abnormally absorbable elements, for example iron, manganese, chlorine. To weaken the dependence of the moisture measurement on the containing / absorbing elements, it is necessary to measure the parameters of the neutron fluxes at short deceleration times. Such parameters are the time t-j from the beginning of the neutron pulse to the onset of the thermal neutron flux maximum and the average time t c of the neutrons in the thermal region. 6 To determine the moisture content of materials in this method, preliminary experimental dependences of f (w, |)) iTa material samples are obtained with known values of moisture content (w) and material density, in the required range of their measurement. According to the experimental data, the analytic functions f (w, p) I (w, p) are approximated, and the moisture content of the material is determined from the expression: W F (t, t), which is found by solving the system of equations: tM f.p). H According to the results of experiments, depending on humidity w. The densities p of coke are defined as -b W 1 m (t b, p) 3. - d, -CiW tH () 1 + d. Excluded from the system of equations (1) 0 WPi gain. wCo (t .. - (, 1. -t a, bj -, c) Determining the values of t for a material with arbitrary humidity and lottery and substituting these values for formula (2), one can determine the moisture content of the material w. The process of measuring and determining the affection by For example, for samples of material with known moisture and density values, the tj values are determined by the belt density distribution of thermal and epithermal neutrons, and the least squares method determines the dependences of t and t on the affection and density of the material, i.e. the limits are the coefficients a, b, c, a, bg, ci and dj In system 1. The values of the coefficients are substituted into formula (2) .., The measurements are made on the test material. From the obtained values of tfj n, the humidity of the material is determined by formula (2).

The method can be implemented, for example, on equipment implemented by industry.

The radiation source is a pulsed generator of fast neutron IGN-A with a duration of 10 neutron pulses and a frequency of 400 Hz. The average neutron yield was 5) i10 neutrons / s. A detector based on the SNM18-1 slow neutron counters, covered with a cadmium shield, is used to record the flux of epithermal neutrons. The registration of thermal neutrons is defined as the difference between the readings of the SNM-18-1 counter without a screen and the readings of the same counter with a screen of cadmium. The material under study (small coke with different humidity) is placed in an iron box with dimensions 80X80 X50 cm, a neutron generator and detectors are placed in cylindrical channels inside the material.

. . . /,

The time t dz from the beginning of the neutron pulse to the onset of the maximum is determined from the smoothed spectra of neutron heat spectra with an accuracy of 0, 1 MKS. The smoothing of the spectra was performed by a polynomial of the 2nd degree using a computer, for example, SM-1.

The average residence time t of neutrons in the epithermal region is determined by the formula oo

21F -f

H

Ri;

where „1 is the value of the flux of neutrons above neutrons at time t; |, t. - neutron duration

momentum.

According to the results of experiments of the least quadrant methods, the following equations were obtained:

-O t (89.1-77.38) 1 + 37.5

-O.

t .. (27.6 - 238) 1

+ 26

U

From equation (2), the moisture values for experimental materials with different humidity and density are determined.

The advantage of the method is that the measured humidity value does not depend on the density of the measured material due to the fact that two parameters of the slow neutron flux are measured, one of which is used to correct the moisture rolling of the density of the material. This advantage is very effective in industrial production and allows determination of the moisture content of a material with different density values. Thus, for example, in blast furnace production, the method can be effectively used for: measuring the moisture content of coke in bins, where the bulk density varies in the range of 0.4-0.6 g / cm, depending on the grain and humidity, which allows to improve the process conditions process and quality of pig iron produced.

Claims (2)

PULSED NEUTRON METHOD FOR DETERMINING THE HUMIDITY OF MATERIALS, which consists in irradiating the test material with a pulsed fast neutron flux and recording the temporal distribution of the thermal neutron flux, characterized in that, in order to reduce the measurement error and expand the scope of the method, the start time of the neutron pulse to the onset of the maximum flux of thermal neutrons, record the temporary 2 distribution of the epithermal neutron flux and determine the average neutron residence time in the epithermal region, and the moisture content of the material is found from the expression, X - (t _K - d ₂ ) b ₁ 1 ^ ² · = c, where w is the moisture content of the material,%, * t is the time from the beginning of the neutron pulse to the onset of the maximum flux of thermal neutrons, t c is the average residence time of neut rock in the epithermal areas defined by the formula OO (y? t _H = f tty (Е t) dt / I <? (E ^ t) dt, t £ is the pulse duration of fast neutrons,. b ₍ , b ₂ , s, s ₍ , s _g , d _o d ₂ are constant coefficients for this material, and the ratio of the fast neutron pulse duration to the time from the beginning of the fast neutron pulse to the onset of the maximum thermal neutron flux in the dry material is chosen not exceeding 0.2, and the repetition period of fast neutron pulses is not less than the lifetime of thermal neutrons in dry material. 1114156 A1