RU2310825C1 - Method for preparation of steam-gas mixtures for calibration of gas analyzers - Google Patents

Abstract

FIELD: methods for preparing steam-gas mixtures of substances in mass concentration units, possible use for metrological provision (attestation, verification and graduation) of gas analyzers.

SUBSTANCE: in the method for preparation of steam-gas mixture for calibrating gas-analyzers in mass units of concentration of the component being analyzed, comprising injection of given amount of the component being analyzed into preliminarily vacuumized hermetic vessel, mixing thereof with diluting gas and forcing resulting mixture towards the gas analyzer being calibrated, a bottle of known capacity is connected to hermetic vessel with possible isolation from it, which bottle is preliminarily vacuumized and its mass is measured, value of pressure is computed, which ensures achievement of given mass concentration of the component being analyzed at a temperature which equals environment temperature in accordance to the formula:

where P_n - pressure, ensuring achievement of given mass concentration of the component being analyzed, kPa;

- given mass concentration of the component being analyzed, g/m; T - environment temperature, °K; M - molecular mass of the component being analyzed; K - coefficient, which includes the universal gas constant and a numeric value which leads to required dimension of pressure (K=8,3·10^-3m³·kPa/°K·grammolecule), resulting combined volume of vessel and bottle is vacuumized, component being analyzed is injected into it until achievement of computed pressure at temperature which equals temperature of environment, after that the bottle is isolated and disconnected from hermetic vessel, bottle mass is measured and effective value of mass concentration C_M is derived from formula

where C_M - mass concentration of the substance being analyzed, g/m³; M_k - mass of bottle with the substance being analyzed, g; M₀ - mass of vacuumized bottle, g; V - bottle capacity, m³.

EFFECT: increased precision of preparation of steam-gas mixture in mass units of substance concentration during calibration of gas analyzers, expanded range of concentrations of mixture components.

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Description

The invention relates to methods for preparing gas-vapor mixtures of substances in mass concentration units and can be used for graduation of gas analyzers, the determination of the concentration of which is based mainly on the absorption of radiation, measurement of thermal conductivity, thermal effect of the reaction and diffusion.

A known method of preparing a mixture in a glass container of known volume with a magnetic stirrer inside, the implementation of which is based on placing gas of known concentration in a bottle, constant flow of diluent gas through the capillary without the analyzed component in an amount corresponding to the amount of gas displaced. The concentration of the determined component in the bottle decreases in accordance with the exponential law of dilution, provided that it is fully mixed. (Drugov Yu.S. et al. Methods of analysis of air pollution. - M.: Chemistry, 1984 - 384 p., Sludge (p.119)).

The disadvantages of this method is the significant error in the preparation of the mixture due to the inability to determine with high accuracy the degree of dilution of the analyzed component in the tank, the inability to graduate on gas-vapor mixtures obtained from substances having a liquid state of aggregation under normal conditions, and also due to dynamically changing concentration time, this method is not applicable for graduation of gas analyzers with a large delay in readings.

The closest technical solution, selected as a prototype, is a method of preparing a mixture and calibrating gas analyzers, based on the static method of preparing a mixture in a glass or metal container. (Y. Vanya. Analyzers of gases and liquids. - M.: Energy, 1970 - 552 p., Sludge (p. 491)).

The essence of the method for preparing the mixture for calibrating gas analyzers is that a calculated amount of liquid or gas is introduced into a previously evacuated container of known volume, for example with a syringe, then its volume is supplemented with a diluent gas until atmospheric pressure is reached in the vessel. Thus, the concentration specified by the calculation is established.

Mixing the mixture in a vessel is carried out by shaking glass or aluminum balls or using a mixer with a mercury shutter. The displacement of the prepared mixture into the cavity with a gas analyzer is carried out by supplying a liquid with low vapor pressure or an inflated rubber balloon placed inside.

The main disadvantages of this method is the large error in setting the concentration of substances, due to the use of calculation formulas for the ideal state of the gas, a small range of concentrations of the prepared mixtures due to the impossibility of dosing microvolumes of evaporated substances.

The technical result of the invention is to increase the accuracy of preparation of a gas-vapor mixture in mass units of the concentration of substances during the calibration of gas analyzers and expand the range of concentrations of the components of the mixture.

The specified result is achieved by the fact that in the known method of preparing a gas-vapor mixture for calibrating gas analyzers in mass units of the concentration of the analyzed component, which consists in introducing a predetermined amount of the analyzed component into a previously evacuated sealed container, mixing it with a diluent gas and displacing the resulting mixture with a calibrated gas analyzer, according to the invention to a sealed container is connected with the possibility of isolating from it a flask of known capacity, otorrhea previously evacuated and its mass was measured, calculated pressure value that ensures the achievement of a given weight concentration of the analyte at a temperature of ambient temperature, according to the formula

,

,

Where

R _p - pressure, ensuring the achievement of a given mass concentration of the analyzed component, kPa;

- задаваемая массовая концентрация анализируемого компонента, г/м³;

- set mass concentration of the analyzed component, g / m ³ ;

T is the ambient temperature, K;

M is the molecular weight of the analyzed component;

K is the coefficient, which includes the universal gas constant and a numerical value, leading to the required pressure dimension (K = 8, 3 · 10 ^-3 m ³ · kPa / K · mol),

the resulting combined volume of the container and the flask is evacuated, the analyzed component is introduced into it until the calculated pressure is reached at a temperature equal to the ambient temperature, after which the flask is isolated and disconnected from the sealed container, the mass of the flask is measured and the actual mass concentration C _{m is} determined by the formula

,

,

where C _m is the mass concentration of the analyte, g / m ³ ;

M _to - the mass of the flask with the analyte, g;

M _about - the mass of the evacuated flask, g;

V is the capacity of the flask, m ³ .

These distinguishing features, together with the known ones, are essential for achieving a technical result, since connecting the flask will allow you to set equal mass concentrations of the substance in the container and in the flask, which will allow using the direct static method (weighting) to determine the mass concentration as a reference, possessing high accuracy and reliability. Preparation of the mass concentration of a gaseous substance by its pressure in the tank will allow you to set the necessary points in the concentration range, and weighing the measuring flask will accurately determine its value. Entering and determining the concentration of the component, taking into account the pressure created inside the tank, compared to just entering the pre-calculated amount of the substance, will allow more accurately setting the concentration of the component in a wide range of its values (from 2 to 2000 g / m ³ depending on the substance).

The method is implemented as follows. To prepare a vapor-gas mixture of n-pentane (C ₅ H ₁₂ molecular weight M = 72) with atmospheric air in mass units of the concentration of the analyzed component (n-pentane) 500 g / m ³ , necessary for the calibration of IR gas analyzers (SKZ-PB-01 ) in mass units of the concentration of oil vapor in the air, take a flask 1 of known capacity equal to V = 1.0783 · 10 ^-3 m ³ , vacuum it and weigh it on an analytical balance (for example, SARTORIUS L310 with a resolution of 0.1 mg), determine the mass , M ₀ = 218.999 grams. Connect flask 1 to a sealed container 2. Measure the ambient temperature, T = 295 K. Calculate the pressure of the analyzed component to obtain a mass concentration of 500 g / m ^{3 of the} medium according to the formula

,

,

where R _p - pressure of the analyzed component, kPa;

- задаваемая массовая концентрация анализируемого компонента, г/м;

- set mass concentration of the analyzed component, g / m;

T is the ambient temperature, K;

M is the molecular weight of the analyzed component;

K is the coefficient, which includes the universal gas constant and a numerical value, leading to the required pressure dimension (K = 8, 3 · 10 ^-3 m ³ · kPa / K · mol).

Having determined P _n = 17.0 kPa, the combined volume of the vessel 2 and flask 1 is evacuated to the minimum pressure created by the vacuum pump 3 (for example, 2НВР-5ДМ with an achievable vacuum of 10 ^-5 Pa). Opening the fine adjustment valve 4, the component is supplied from the cylinder 5 to the calculated pressure P _p , which is monitored by the gauge 6 (for example, the VO-1227 gauge, accuracy class 0.25), while controlling and maintaining the equality of ambient temperatures and the analyzed component by thermometer 7 (for example, a mercury thermometer ТН - 0.2) in a container 2, by adjusting the input rate of the component, or by placing a sealed container 2 in a thermostatically controlled volume of water. Close the shut-off valve 8, disconnect the flask 1 with the pairs of the analyte from the container 2 and weigh it on an analytical balance, determining the mass M _k = 219.5287 grams, after which the true value of the mass concentration C _m = 491.2 g / m ^{3 is} determined, calculated by the formula

,

,

Where

C _m - mass concentration of the analyte, g / m ³ ;

M _to - the mass of the flask with the analyte, g;

M _about - the mass of the evacuated flask, g;

V is the capacity of the flask, m ³ .

After determining the mass concentration, opening the valve 9, a diluent gas, air, is added to the container through the pipe 10 until atmospheric pressure is reached. After mixing due to diffusion or by mechanical means (circulation of the mixture in a closed bypass line 11 with a fan 12), compressed air is fed into the rubber bottle 13 and the mixture is forced out through the pipe 10 to the sensitive element of the gas analyzer to set or correct its readings.

Using this method, it is possible to prepare a wide range of mixtures of gaseous and liquid individual or complex substances, obtaining the mass value of their concentration.

The proposed technical solution is new, because from publicly available information there is no known method for preparing gas-vapor mixtures with the task of mass concentration by direct weighing.

The proposed technical solution is industrially applicable, since standard equipment, devices, and materials that are widely used in the field of measurement technology can be used for its implementation.

Claims (1)

A method of preparing a gas-vapor mixture for calibrating gas analyzers in mass units of the concentration of the analyzed component, which consists in introducing a predetermined amount of the analyzed component into a previously evacuated sealed container, mixing it with a diluent gas and displacing the resulting mixture in a calibrated gas analyzer, characterized in that it is connected to the sealed container the possibility of isolating from it a flask of known capacity, which is pre-evacuated and its mass is measured Is calculated pressure value that ensures the achievement of a given weight concentration of the analyte at a temperature of ambient temperature according to the formula:

where R _p - pressure, ensuring the achievement of a given mass concentration of the analyzed component, kPa; With ³ _m - the set mass concentration of the analyzed component, g / m ³ ; T is the ambient temperature, K; M is the molecular weight of the analyzed component; K is the coefficient, which includes the universal gas constant and a numerical value, leading to the required pressure dimension (K = 8, 3 · 10 ^-3 m ³ · kPa / K · mol), the resulting combined volume of the container and flask are vacuumized, introduced into the analyzed component until the calculated pressure is reached at a temperature equal to the ambient temperature, after which the flask is isolated and disconnected from the sealed container, the mass of the flask is measured and the actual mass concentration C _{m is} determined by the formula:

where C _m is the mass concentration of the analyte, g / m ³ ; M _to - the mass of the flask with the analyte, g; M _about - the mass of the evacuated flask, g; V is the capacity of the flask, m ³ .