SU1217458A1 - Method of obtaining gaseous mixtures for calibrating gas analyzers - Google Patents

Description

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The invention relates to gas analysis, in particular, to methods for producing exemplary gas mixtures for gas calibration and calibration of gas analyzers. and may find application in industry, scientific research in the metrological assurance of gas-analytical measurements.

The purpose of the invention is to simplify the procedure for the preparation of mixtures over the entire range of concentrations required for calibration, and to increase the accuracy of preparation in the area of low concentrations.

FIG. 1 shows the installation scheme that implements the proposed method; in fig. 2 is a graph of the change in the concentration of the mixture when the analyte gas outflows from the dosing vessel into the diluent gas tray; on . FIG. 3 is a graph of the concentration of the mixture when the diluent gas is discharged from the dosing vessel into the gas to be analyzed.

Installation for the production of gas mixtures, consists of a metering and 1 with a constant internal volume, pneumodrossel 2, switching valve 3.

To dispensing vessel 1 through the reducer 4, the switching valve 3 is connected to a cylinder 5 with compressed gas (analyzed or diluent - c. Depending on the method used) about

The cylinder 6 with another compressed gas through the reducer 7, the flow regulator 8 and the comparative chamber of the analyzer detector 9 are connected to the output of the switching valve 3, which connects to the measuring chamber of the detector 9.

A reference pressure gauge 10 is connected to the dosing vessel 1, and a measuring transducer 11 and a recording device 12 are used to record the pressure.

A recording device 13 is connected to the electrical output of the detector 9. A waste line 14 with a valve 15 is provided for flushing the dosing vessel 1.

In order to obtain gas mixtures according to the first embodiment, a cylinder 5 with the analyzed substance is connected to the inlet of the crane 3: gas and the dosing vessel 1 is purged with gas by opening the valve 15.

21

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a 74582

 Then the valve 15 is closed and after reaching a predetermined gas pressure in the metering vessel 1, the valve 3 is switched to another position at which

5, the analyzed gas enters the diluent gas stream supplied from the cylinder 6 through the flow regulator 8, is withdrawn with it, and the resulting mixture passes through the measuring gas.

10 camera detector 9.

The characteristics of the pneumatic distributor and the volume of the dosing vessel are chosen so that the pressure in it when the gas outflows varies according to an exponential (or close to it) law with a constant time, which satisfies the time conditions for calibrating the analyzer.

In practice, most of all for these

A laminar choke is suitable for 20 targets, which ensures the operation of the dosing vessel as an aperiodic link with a constant time of 10-100 minutes. As the pressure of the analyzed gas decreases as it flows out of the dosing vessel, the concentration of the analyzed -component in the mixture gradually decreases from maximum to zero.

30 In order to obtain gas mixtures according to the second variant, cylinders 5 and 6 are swapped and carried out similar operations.

At the same time as the pressure drops

2, - the diluent gas in the metering vessel, the concentration of the analyzed component in the mixture smoothly increases from zero to maximum, total.

j. The proposed method is based on the following physical laws. The state of gases or vapors, when they are isothermally flowing through the throttling elements, changes

 according to the law

P, Y, PV

(one)

P, V,

initial pressure and volume of gas; pressure and volume of gas in the intermediate stage of expiration.

If the outflow of gas occurs from a vessel of constant volume Y, then the volume of the gas that left the vessel at pressure P is determined from

expressions

. V (pH-v, ... /

Taking into account the pressure to which the outflow occurs, expression (2) is converted to

R-R

(piV-t-vr

year

Where

PJ - pressure of the medium in which

a gas outflow occurs, the Time Differential (i) equation (3), we obtain the dependence

ciVlp.l V,

at pj di

Where

Q, is the instantaneous dosing flow rate;

(ZR

Tt is the rate of change in gas pressure in the metering vessel.

and dosing of the dilution gas analyzed to the constant flow of the mixture is

C (m -; g-V - 4007... (5)

where Qj is the diluent gas flow rate.

For the case of dosing a diluent gas into a constant flow of the gas to be analyzed, equation (5) is converted to

 1 °°

where Q, is the constant flow rate of the gas being analyzed;

Qj instantaneous diluent gas consumption.

To reduce the calibration time of the instrument in the region of low concentrations of the analyzed component, it is possible to use its previously prepared mixtures with a diluent gas.

In this case, to calculate the concentration, you can use the following approximate dependence C (tl, - °° (7)

where K- is the dilution factor of the gas to be analyzed.

The rate of change of pressure (W) in a dispensing vessel may be determined by

i is divided by known methods according to the schedule, taken with the help of a recording device or according to the observations of the indicating device.

5 The resulting curve (or a series of pressure values) is approximated, for example, by an exponent of the form

p,

(eight)

ten

the coefficients of which are found by the least squares method. Then, the dependence of the pressure change on is found. time (speed), the differential 15 the resulting equation.

The speed can also be found directly by graphical differentiation of the curve: by the manual method J or by an automatic differential device, to the input of which a pressure change signal is given.

Thus, having a graph of the rate of change of pressure in a metering vessel of known volume, pkchod and constant flow pressure and the signal curve of the detector of the gas analyzer, which is supplied with a gas 3Q mixture, is obtained a calibration characteristic of the gas analyzer.

Example 1. Source data: the analyzed gas-nitrogen, gas-diluent, helium-helium, volume of disirguing

vessel V, 16 cm, initial pressure of nitrogen in the dosing vessel (excess) P, 2 kgf / cm, flow pressure gels (excess) P

Q 0.01 kgf / cm, Gj flow rate 120 ml / 1 "1N, nitrogen pressure gauge - exemplary manometer, 2.5 kgf / cm, nitrogen concentration gauge in helium - detector of heating material, water content in the Tsvet-100 chromatograph set.

An experimental verification of the method was carried out at the facility comp. 5Q. in accordance with the scheme (Fig. -1).

The pressure drop of nitrogen from the moment of its expiration from the dosing vessel was recorded at certain time intervals, marked c5i

using a stopwatch.

The measurement results are summarized in table. one .

Table 1

Continuation of table 2

71

At the same time, the accuracy of certification of the obtained mixtures with a time varying concentration does not exceed 2% rel.

Calibration mixtures obtained by the proposed method, you can enter the analyzer both continuously and discretely, using a crane-doo, in

Ct (.oS.)

0.2

(f

2

10 12/4 16 IB 20 22. 24 28 26 B of FIG. 2

2174588

mash, sampling from the mixture flow sample of a known volume at specified points in time.

It should be noted that in order to obtain 5 calibration mixtures with a low content of the analyzed component, it is necessary to meter the analyzed gas into a diluent gas.

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Compiled by T. Kruglov Editor N. Volovik Tehred.Gergel Proofreader O. Lugova

Order 1029/10

Circulation 578

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Branch PPP Patent, Uzhgorod, Proektna St., 4

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Claims (1)

METHOD FOR PRODUCING GAS MIXTURES FOR GRADING GAS ANALYZERS by dosing under overpressure and mixing the analyzed gas and diluent gas and indirectly determining the composition of the mixture using the known values of the volumes and pressures of the dosed gases, which is different, in order to simplify the procedure for preparing mixtures. over the entire range of concentrations necessary for calibration, and to increase the accuracy of preparation in the region of low concentrations, the dosing of one of the gases carries out its continuous throttling: m from a vessel of constant volume into the flow of another gas with a known flow rate, and the concentration of the mixture at fixed time intervals is determined by the rate of change of gas pressure in the vessel and the flow rate S of the other gas.