RU2602412C1 - Method of calibrating and checking radioisotope density meters for suspensions by samples-imitations - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to automatic control of composition of substances and can be used in potassium industry for calibrating radioisotope density meters for suspensions, using a source Na₂₂ radiation by samples suspensions-imitations and for checking correctness of density meters readings in operation. Method of calibrating and checking radioisotope density meters for suspensions by samples-imitations includes formation of a number of samples, the density of which is within a given range, irradiation of samples by a source of the density meter and registration of radiation by a detector. Herewith the samples-imitations used are represented by a combined solution of calcium chloride and caesium chloride, the composition of which is calculated separately for the solution of calcium chloride and the caesium chloride one provided the maximum density of the solution to avoid crystallization at the lowest temperature limit. Ratio of calcium chloride and caesium chloride in samples-imitations is calculated so, that molecular weight of the sample-imitation is closest to the molecular weight of the controlled suspension. On the basis of calculated values samples-imitations are prepared and used for calibration of the radioisotope density meters.

EFFECT: technical result is higher accuracy of calibrating radioisotope density meters within the range of measurements of 1,200-1,600 kg/m³ with maintaining properties of samples-imitations at the lowest temperature limit allowed during their storage and transportation, providing safety for human health, explosion and fire safety during preparation of the samples-imitations.

3 cl

Description

The invention relates to the field of automatic control of the composition of substances and can be used in the potash industry for calibrating densitometers of suspensions using a Na ₂₂ radiation source, using simulated suspension simulators and verifying the accuracy of densitometers during operation.

A known method of graduation (calibration) and calibration of densitometers (Instrumentation and automation. Volume 2, book 2. M .: Mechanical engineering, 1964. S. 277). Calibration (calibration) is carried out in static conditions using a set of liquids, the density of which is measured by laboratory devices. The disadvantages of the method include the lack of qualification of the properties of liquids in the accuracy of simulating a controlled technological environment - the nature of the interaction of radiation with a controlled environment and a simulating liquid is not taken into account, which does not allow to achieve high calibration accuracy.

A known method and means of verification of radioisotope densitometers using simulators of a controlled environment (GOST 8.368-79 "Density meters of radioisotope liquid media and pulps. Methods and means of verification. Appendix 1. Methods of preparation of liquid simulators of a controlled environment. Appendix 2. General guidelines for the construction of transition dependence" ) The essence of the method is that the measuring section of the pipeline is filled with a liquid simulator of a controlled environment, the readings of the densitometer are determined, the density of the simulator is determined with a standard densimeter, the error of the discrepancies between the readings of the densitometer and the density of the simulator is determined. Alcohol solutions of bromoform (tribromomethane - CHBr ₃ ) are used as a simulator. The disadvantages include the need for accurate density measurement using exemplary means, bromoform is a danger to humans - it has a narcotic effect, irritates the skin and respiratory tract, and causes liver diseases.

Known methods of calibration (calibration) and verification of vibration densitometers (Zhukov Yu.P. Vibration densitometers. M: Energoatomizdat, 1991, section 5.3. Calibration and calibration of vibration densitometers). Liquids are used for calibration and calibration: petroleum ether, gasoline, benzene (650-860 g / dm ³ ), water-alcohol solutions (870-950 g / dm ³ ), sulfuric-wine solutions (960-1010 g / dm ³ ) , sulfur-aqueous solutions (960-1830 g / dm ³ ), Thule solutions (1840-2000 g / dm ³ ). The disadvantage is that hydrogen sulfide solutions and Thule solutions, used as simulators of suspensions with high density, have highly aggressive properties and are extremely dangerous for human health.

A known method of calibration and calibration of radioisotope densitometers (Zaretsky LI Methods of calibration and calibration of radioisotope densitometers. - Devices and control systems. 1976, No. 10, p. 23-24). The densitometer includes a nozzle for a controlled environment, a radiation source and detector, a cassette installed between the source and the nozzle, and an output frequency converter. The method consists in the following: water is poured into the pipe, a certified plate is placed in the cassette, the pulse frequency is measured; the plate is removed, and the nozzle is filled with a controlled liquid, the concentration is gradually increased and adjusted to equal frequencies in the liquid and the plate; a liquid sample is taken, density is measured; the density of the liquid is assigned to the density of the plate. In the future, the plate (solid simulator) is used for calibration and calibration of densitometers. This method is suitable for densitometers with a narrow beam of gamma rays (with radiation collimation) from powerful sources with the cesium-137 or cobalt-60 isotope. The source of Na _{22 is} low-power, a wide beam of radiation is used. For him, the dependence of gamma-ray scattering (attenuation in a controlled medium) on the density for a suspension and a solid simulator in the form of plates is not the same, which reduces the accuracy of calibration and verification.

A known method of graduating radioisotope densitometers (RU 2442889 C1). The method is intended for the calibration of radioisotope densitometers of drilling and cement slurries and consists in the fact that an emitter and a detector are installed on the pipeline, the density of equivalents of the solutions are produced, the equivalents are calibrated using standard samples of the solutions, the equivalents are used on the disconnected tubular element with position fixation, the density equivalents are made from solid materials, in shape and size corresponding to the internal cross section of the tubular element in the sensing zone detector performance. The disadvantage of this method is that it includes an intermediate operation between a sample solution (a liquid simulator of a controlled solution) and a densitometer in the form of creating and using a solid density equivalent (solid simulator). The use of a solid simulator, as in the previous example, does not allow to achieve high calibration accuracy. The operation can only be used to verify the performance of the densitometer during episodic monitoring.

A known method of calibration (calibration) of radioisotope densitometers (SU 1400253 A1) is a prototype, which includes the formation of a number of samples whose density is in a given range, irradiating the samples with a densitometer source and registering reflected radiation with a detector, determining the range of relative values of the coefficients of Compton and photoelectric interaction, choosing components whose composition provides a ratio of these components. In accordance with the calculations, a composition is selected consisting of paraffin, iron oxide, silicon oxide and perlite sand. With regard to the task of controlling the density of potassium suspensions, one can note the disadvantages: the invention records the reflected radiation, it requires registration of the attenuation of radiation when passing through the suspension, a complex calculation mechanism for the ratio of Compton scattering and photoabsorption, the calculations are given for reflected radiation, the selected composition does not reflect the true composition potassium suspensions.

The objective of the invention is: to improve the calibration accuracy of radioisotope densitometers of potassium suspensions using simulator samples in the measurement range from 1200 to 1600 kg / m ³ while maintaining the properties of simulators at the lower temperature limit allowed during storage and transportation, for example 5 ° C, ensuring safe properties for human health, explosion safety and fire safety during the preparation of simulators.

The solution to the problem is as follows.

Calibration and verification of radioisotope densitometers of suspensions of potash dressing plants with Na ₂₂ radiation sources, including the formation of a number of samples whose density is in a given range from 1200 to 1600 kg / m ³ , irradiating the samples with a densitometer source and detecting radiation with a detector, is performed using simulator samples in in the form of a joint solution of calcium chloride and cesium chloride. The relationship (similarity) between the controlled suspension and the sample-simulator is preliminarily established - coefficient K _{P of the} ratio of the density of the suspension D _С to the density of the sample-simulator D _О. For each type of suspension and for each control point (i - point) of the range, the coefficient K _{Pi is} determined separately _{for the} ratio of the densities of the suspension - D _Сi to the density of the simulator sample - D _Оi . The density of the sample D _{Оi is} calculated during preparation and, if necessary, clarified, is measured using a high accuracy hydrometer. The coefficient K _{Pi is} set according to the frequency signal of the density meter detector as follows. A sample simulator with a density D _{Оi is} placed in the measuring channel of the densitometer, and the frequency - F _{Оi is measured} . The simulator sample is removed. A suspension is placed in the measuring channel, the frequency - F _{Сi is measured} . The density of the suspension is selected until the condition: F _Сi = F _Оi . A sample of the suspension is _taken and the density of the suspension — D _Ci — is _{measured by} weight or bulk-weight (pycnometric) method. Produce K _Pi coefficient calculation according to the formula: K _{Pi Ci} = D / D _Oi. The values of D _Оi and K _Пi are entered in the certificate of calibration of the density meter according to simulator samples.

Improving the calibration accuracy in comparison with the known compositions of the simulator samples is achieved by the fact that the elemental composition of the simulator samples in the calcium solution: Ca, O, H, O is close to the basic elemental composition of the potassium suspension: K, Cl, Na, Ca, H, O, and cesium in chemical properties is in the same (1st) group with potassium and sodium.

The composition of the simulator samples is calculated in such a way that their properties are preserved (the absence of salt crystallization from solution) at the lower temperature limit necessary for storage and movement, for example, 5 ° C. The calculation is made for the separate preparation of a solution of CaCl ₂ and a solution of CsCl. To calculate the CaCl ₂ solution and with a maximum take CsCl density does not lead to crystallization at lower limit temperature. The volume of the CaCl ₂ solution is calculated according to the formula (1) and the weight of the CaCl ₂ sample according to the formula (2) for a given volume at the temperature of the subsequent calibration, the volume of the CsCl solution is calculated according to the formula (3) and the mass of the CsCl sample according to the formula (4), the sample calculation water according to the formula (5). Prepare a solution with the calculated parameters. The calculated density is assigned to the density value of the simulator sample - D _Оi .

Settlement formulas:

The formula for calculating the volume of a solution of calcium chloride - V _Ca :

$$V_{Ca}=\left(D_{Cs}-D_p\right)\cdot V_p/\left(D_{Cs}-D_{Ca}\right),\left(\text{one}\right)$$

where D _Cs is the density of a solution of cesium chloride at a limiting temperature;

D _p - the density of the solution of the sample simulator;

V _p - the total volume of the solution;

D _Ca is the density of a solution of calcium chloride at a limiting temperature.

The formula for calculating the weight of a sample of calcium chloride - M _Ca :

$$M_{Ca}=D_{Ca}\cdot C_{Ca}\cdot V_{Ca},\left(\text{2}\right)$$

where C _Ca is the mass fraction of calcium chloride in a solution of calcium chloride.

The formula for calculating the volume of cesium chloride is V _Cs :

$$V_{Cs}=V_p-V_{Ca}.\left(\text{3}\right)$$

The formula for calculating the weight of a sample of cesium chloride - M _Cs :

$$M_{Cs}=D_{Cs}\cdot C_{Cs}\cdot V_{Cs},\left(\text{four}\right)$$

where C _Cs - mass fraction of cesium chloride in a solution of cesium chloride.

The formula for calculating the mass of a sample of water - M _in :

$$M_{\mathrm{at}}=V_p\cdot D_p-M_{Ca}-M_{Cs}.\left(\text{5}\right)$$

Improving the calibration accuracy is also achieved by the fact that the simulator samples are prepared in such a way that the molecular weight of the simulator sample most closely matches the molecular weight of the controlled suspension. This correspondence corresponds to the nature of the absorption of radiation when passing through a suspension and through a simulator sample and contributes to an increase in calibration accuracy. Calculation of the molecular weight of the suspension and the simulator is performed according to formulas (6), (7), respectively.

The formula for calculating the molecular weight of the suspension is M _ms :

$$M_{m\mathrm{from}}=\Sigma {\mathrm{FROM}}_m\cdot C_{\mathrm{to}mi}\cdot M_{m\mathrm{to}mi}+\Sigma C_{\mathrm{well}}\cdot C_{\mathrm{to}\mathrm{well}i}\cdot M_{m\mathrm{to}\mathrm{well}i},\left(\text{6}\right)$$

where C _m is the mass fraction of the solid phase in suspension, fractions of a unit;

C _kmi - mass fraction of the i-th component in the solid phase of the suspension, fractions of a unit;

M _µmi is the molecular weight of the i-th component in the solid phase of the suspension, g-mol (g-m).

The formula for calculating the molecular weight of the simulator is M _mo :

$$M_{m\mathrm{about}}=\Sigma C_{\mathrm{to}\mathrm{about}i}\cdot M_{m\mathrm{to}\mathrm{about}i},\left(\text{7}\right)$$

where C _koi is the mass fraction of the i-th component in the simulator sample, fractions of a unit;

M _MCI - molecular weight of the i-th component of the simulator sample, gm

The solution of calcium chloride and cesium chloride is explosion and fire safe and safe for human health, since the elements Ca and Cs themselves do not have explosion and fire hazard properties, and also do not adversely affect human health.

The use of simulator samples to verify the accuracy of the testimony is as follows. In case of doubt about the correctness of the readings of the densitometer, the emitter and detector are removed from the pipe and installed in the same way on the simulator. If the D _{Оi value} of the simulator is confirmed, the measuring part of the densitometer meets the requirements of the densitometer, a possible cause of pipe overgrowing or wear. It is necessary to carry out routine work to eliminate overgrowing. In case of wear, re-calibration is necessary. If the value of D _Оi of the simulator is not confirmed, for example, due to aging of the source (half-life of 2.6 years), it is necessary, in particular, to replace the source and calibrate the density meter.

An example of calculating the composition of a sample simulator

Initial data: temperature of the simulator at which calibration is performed, 20 ° C; the estimated volume of the simulator Vp = 1000 cm ³ ; the density of the simulator solution Dp = 1.4 g / cm ³ (average value of the measurement range); the lower limit of the temperature at which the properties of the simulator are maintained, 5 ° C; the density of the solution of calcium chloride corresponding to the specified temperature with a safety margin, D _Ca = 1.38 g / cm ³ ; mass fraction of calcium chloride in a solution of calcium chloride C _Ca = 0.37; the density of the cesium chloride solution corresponding to the indicated temperature with a safety margin of D _Cs = 1.8 g / cm ³ ; mass fraction of cesium chloride in a solution of cesium chloride C _Cs = 0.606.

Settlement procedure

Calculation of the volume of a solution of calcium chloride according to the formula (1):

V _Ca = (1.8-1.4) 1000 / (1.8-1.38) = 952.4 cm ³

Calculation of the mass of a sample of calcium chloride according to the formula (2):

M _Ca = 1.38 · 0.37 · 952.4 = 486.3 g

Calculation of the volume of cesium chloride according to the formula (3):

V _Cs = 1000-952.4 = 47.6 cm ³

Calculation of the mass of a sample of cesium chloride according to the formula (4):

M _Cs = 1.8 · 0.606 · 47.6 = 51.9 g

Calculation of the mass of a sample of water by the formula (5):

M _in = 1000 · 1.4-486.3-51.9 = 861.8 g

Having prepared a solution with calculated weights, we obtain a simulator sample with an estimated density of 1.4 g / cm ³ . If it is necessary to clarify the calculated density, the density of the solution is measured using a hydrometer or by the volume-weight method. The calculated or measured density D _{Оi is} assigned to the ith sample-simulator of the suspension along with the coefficient K _Pi . The simulator is identified by the number according to which the density meter is calibrated or the readings are checked during operation.

An example of calculating the molecular weight of a suspension and a simulator sample. As an example, a KCl suspension of a crystallizer from a galurgic potash concentration plant was taken. The initial data on the suspension: the density of the suspension is 1.4 g / cm ³ ; the mass fraction of the solid phase in the suspension is 0.31, the mass fraction of the liquid phase is 0.69; mass fraction of components in the liquid phase: KCl - 0.20; NaCl - 0.17; H ₂ O - 0.63; molecular weight of components, gm: KCl - 74.6; NaCl - 58.5; water - 18. Initial data for the sample simulator: density - 1.4 g / cm ³ ; mass fraction of calcium chloride - 0.347; mass fraction of cesium chloride - 0,037; mass fraction of water - 0.616; molecular weight of the components, gm: calcium chloride - 111; cesium chloride - 168.5; water - 18.

The calculation of the molecular weight of the suspension according to the formula (6):

M _ms = 0.31 · 74.6 + 0.69 (0.2 · 74.6 + 0.17 · 58.5 + 0.63 · 18) = 48.1 gm.

The calculation of the molecular weight of the sample simulator according to the formula (7):

M _mo = 0.347 · 111 + 0.037 · 168.5 + 0.616 · 18 = 55.8 g-m.

Calculations show that the simulator sample with a molecular weight of 48.1 gm is closer to the molecular weight of the suspension of 55.8 gm (deviation: (55.8-48.1) · 100: 48.1 = 16.0 %) compared with the fact that if a single-component solution of cesium chloride with a molecular weight of 75.8 g-m is taken as a simulator (deviation: (75.8-48.1) · 100: 48.1 = 58.5%) , which confirms the possibility of increasing the accuracy of calibration.

Claims (3)

1. A method for calibrating and checking radioisotope densitometers of suspensions using simulator samples, including the formation of a number of samples whose density is in a given range, irradiating the samples with a densitometer source and detecting radiation with a detector, characterized in that a calcium chloride joint solution and cesium chloride. 2. The method according to p. 1, characterized in that the calculation of the composition for the preparation of simulator samples is carried out separately for solutions of calcium chloride and cesium chloride under the condition of a maximum density of solutions that do not lead to crystallization at a lower temperature limit, according to the following relationships:
formula for calculating the volume of calcium chloride:
_{V Ca = (D Cs -D p} ) · V p / (D Cs -D Ca),
where D _Cs is the density of a solution of cesium chloride at a limiting temperature;
D _p is the density of the solution of the sample simulator;
V _p is the total volume of the solution;
D _Ca is the density of the solution of calcium chloride at the limiting temperature;
formula for calculating the weight of a sample of calcium chloride:
M _Ca = D _Ca · C _Ca · V _Ca ,
where C _Ca is the mass fraction of calcium chloride in a solution of calcium chloride;
formula for calculating the volume of cesium chloride:
V _Cs = V _p -V _Ca ;
formula for calculating the weight of a sample of cesium chloride:
M _Cs = D _Cs · C _Cs · V _Cs ,
where C _Cs is the mass fraction of cesium chloride in a solution of cesium chloride;
formula for calculating the weight of a sample of water:
M _{a = V p · D p -M Ca} -M Cs,
and in accordance with the calculated values produce the preparation of simulator samples. 3. The method according to p. 1, characterized in that the ratio of calcium chloride and cesium chloride in the sample simulators is calculated so that the molecular weight of the sample simulator most closely matches the molecular weight of the controlled suspension.