RU59240U1 - DEVICE FOR MEASURING THE CONSUMPTION OF OXYGEN CONTAINING GASES - Google Patents

Abstract

The proposed utility model relates to the field of analytical instrumentation and can be used in instruments for gas analysis, for technological control in industries associated with the manufacture and use of gas mixtures. The purpose of the utility model is to simplify the design and improve the accuracy of measuring the flow of oxygen-containing gases. The proposed device consists of potentiometric and coulometric cells, structurally made on a tube of solid electrolyte composition of 0.85ZrO ₂ + 0,15Y ₂ O ₃ and a heater that creates a constant temperature in the working part of the cells in the range from 900 to 1200 K. The temperature of the working part of the cells measured using a potentiometric solid electrolyte cell as a thermosensitive element and is set to (1008 ± 2) K when two calibration gas mixtures with an oxygen concentration are applied to the input of the device Yes, they more than doubled. To extract moisture from the analyzed gas, a dehydrator filled with phosphoric anhydride is installed at the inlet of the device. Using ambient air with a known oxygen concentration as a comparative medium, maintaining a constant temperature in the working part of the electrodes of solid electrolyte cells and measuring the emf of the potentiometric cell and the pumping current of the coulometric cell, we can calculate the flow rate of the analyzed gas by the formula:

where Q is the flow rate of the analyzed gas, m ³ / s; I is the oxygen pumping current by a coulometric solid electrolyte cell, A; M is the molar mass of oxygen, kg / mol; 4F - the amount of electricity required for the electrochemical transfer of one mole of oxygen, C / mol; E - EMF of a potentiometric solid electrolyte cell, V; R is the molar gas constant, J / (mol · K); T is the operating temperature of the potentiometric solid electrolyte cell, K; With ₀ - the concentration of oxygen in the ambient air, kg / m ³ . The proposed device is illustrated in the drawing.

Description

The utility model relates to the field of analytical instrumentation and can be used in instruments for gas analysis, for technological control in industries associated with the manufacture and use of gas mixtures.

Known electronic soap and film gas flow meter (http://www.boner.ru). The method of measuring gas flow using this flow meter is to measure the transit time of a soap film (bubble) between the control marks of the burette scale, through which the measured gas flow is continuously supplied. Knowing the burette capacity between the control marks of the burette scale and the transit time of the soap film (bubble) between them, the gas flow rate is determined. In order to bring the gas flow to normal conditions of application and introduce amendments in order to eliminate the systematic components of the error, it is necessary to additionally measure the atmospheric pressure and ambient temperature.

The disadvantages of the soap-film gas flow meter include:

- the procedure for measuring flow requires manual operations, which does not allow to automate the measurement process;

- in the calculations it is necessary to introduce a correction factor that takes into account the change in gas volume due to its moistening in the burette of the soap-film flow meter;

- the measurement result is affected by a change in the burette capacity due to the volume of the film of the solution covering the inner surface of the burette.

To measure gas flow rate, flow meters of constant differential pressure are widely used - rotameters (V.P. Tkhorzhevsky, "Automatic analysis of the chemical composition of gas", M., Chemistry, 1969). Structurally, the rotameter consists of a transparent conical tube,

facing a narrow end to the bottom, and a float of a given mass and shape with oblique slots. When the analyzed gas is supplied, the float rotates around its longitudinal axis with a passing gas stream. Due to this, it does not slip along the walls of the tube during the movement of the gas stream. The pressure drop on both sides of the float remains almost constant. With an increase in gas flow, the float rises, and with a decrease, it falls down. Consequently, the position of the float in accordance with the calibration applied on the scale of the rotameter determines the gas flow rate.

Float rotameters have the following disadvantages:

- when working with a rotameter, corrections should be made for changes in density, pressure and temperature;

- low measurement accuracy;

- poor reproducibility.

The closest in technical essence is a device that implements a method of measuring the flow of oxygen-containing gases (RF patent 2242722 IPC G 01 F 1/64).

The device consists of potentiometric and coulometric solid electrolyte cells, made in the form of tubes of solid electrolyte composition of 0.85ZrO ₂ + 0.15CaO. On the inner and outer surfaces of the tubes, platinum metal electrodes are applied by incineration. The tubes are placed in a heater to warm the working part of the cells to a temperature of 900-1200 K, providing oxygen-ionic conductivity of the electrolyte. The ends of the tubes are fixed in the installation nodes and sealed from the access of oxygen from the ambient air to the internal electrodes of the cells. The installation nodes are interconnected by a gas path in the form of a stainless steel tube. Temperature measurement is carried out by a thermocouple installed at the external electrodes of the cells. Thermocouple and heater

connected to a temperature controller, through which the set temperature is maintained.

To measure the flow, the flow of the analyzed gas is first directed to a potentiometric solid electrolyte cell, the temperature of which is kept constant, the electromotive force of this cell is measured, after which the analyzed gas is sent to the coulometric solid electrolyte cell, oxygen is completely removed from the analyzed gas by pumping under the applied voltage to the electrodes of the coulometric solid electrolyte cells.

By measuring the electromotive force of the potentiometric solid electrolyte cell, the oxygen pumping current by the coulometric solid electrolyte cell from the known absolute temperature of the potentiometric solid electrolyte cell and the oxygen concentration in the ambient air, the flow rate of the analyzed gas is calculated.

The device in question has the disadvantages of:

- complex design of the installation of a thermocouple in the area of the electrodes of the cells;

- the accuracy of the measurement of gas flow depends on the moisture content in the analyzed gas;

- complex hardware design, consisting of potentiometric and coulometric solid electrolyte cells made in the form of test tubes.

The purpose of the proposed utility model is to simplify the design, improve the accuracy of measuring the flow of oxygen-containing gases.

This goal is achieved in that the device has a potentiometric and coulometric solid electrolyte cells, structurally placed on one solid electrolyte tube, and on

a dehydrator is installed at the inlet of the gas path to extract moisture from the analyzed gas.

The figure shows a drawing of the proposed device.

The flow of the analyzed gas, the flow rate of which must be measured, enters the fitting 1 "GAS INPUT", structurally combined with a dehydrator 2, filled with a hygroscopic substance - phosphoric anhydride. Next, the dried gas through a ceramic tube 3 enters the working part of the potentiometric solid electrolyte cell 4 (PTEJ), washing the working electrode 5 of the cell. The outer electrode 6 PTEJ is comparative and is in contact with ambient air. Due to the difference in the oxygen concentration in the analyzed gas and the ambient air, an electromotive force (EMF) arises on the PTEJ electrodes, the value of which is determined by the Nernst equation:

where E is the EMF of the potentiometric solid electrolyte cell;

T is the operating temperature of the potentiometric solid electrolyte cell;

R is the molar gas constant;

4F - the amount of electricity needed for the electrochemical transfer of one mole of oxygen;

С ₀ and С _x - oxygen concentration in the ambient air and in the analyzed gas, respectively.

Then, the analyzed gas passes through the working part of the coulometric solid electrolyte cell 7 (CTEC), contacts the working electrode 8 of the CTEC and then through the hole in the installation unit and the gas fitting 9 “GAS OUT” leaves out into the ambient air. The outer electrode of 10 CTEY is also washed by atmospheric air.

The internal electrodes of PTEI and KTEY are connected to contacts 11 and 12, and the outer ones to contacts 13 and 14, respectively.

Under the action of a voltage applied to the CTEY electrodes from an external DC source, oxygen is pumped out from the analyzed gas into the ambient air. At the same time, an oxygen pumping current is set in the electric circuit, the value of which is measured by an external current-measuring device connected to contacts 12 and 14. In this case, the oxygen concentration in the analyzed gas in accordance with the Faraday law is determined from the equation:

where I is the oxygen pumping current;

M is the molar mass of oxygen;

Q is the flow rate of the analyzed gas.

Based on equations (1) and (2), we can write

Solving equation (3) with respect to Q, we obtain:

From equation (4) it follows that at a constant temperature of the solid electrolyte and a known concentration of oxygen in the ambient air, it is possible to measure the flow rate of the analyzed gas with sufficient accuracy by measuring the pumping current of the CTEC and the EMF of the PTEC.

A solid electrolyte of composition 0.85ZrO ₂ + 0.15Y ₂ O _{3 is} used as the material for the manufacture of cells; the electrodes are made by the method of incineration from finely dispersed platinum. A tube of solid electrolyte 15 is placed in the heater 16 for heating from an external temperature controller of the working part of the cells to a temperature of 900 to 1200 K, which provides oxygen-ionic conductivity of the solid electrolyte. AT

PTEJA 5 and 6 electrodes are used as a thermosensitive element, to which a high frequency voltage of 20 kHz from an external generator is supplied. The separation of temperature signals (AC voltage) and concentration (DC voltage) is carried out by the input device of the temperature controller.

The ends of the solid electrolyte tube are fixed in the mounting nodes 17 and 18 and are sealed from access of oxygen from the ambient air to the internal electrodes of the cells.

To confirm the industrial applicability of the utility model, an example of its specific implementation is given, which does not exhaust the essence of the proposed solution.

The device operates as follows. Using a heater 16, the working area of the PTFE is heated to a constant temperature in the range from 900 to 1200 K. For accurate temperature setting (1008 ± 2), a test gas mixture (CBC) oxygen-nitrogen with a volume fraction of oxygen is alternately supplied to the GAS INPUT fitting. 1.0 and 10.0% and each time the emf of PTEJ is measured. From these data, the operating temperature is calculated by the formula:

where T is the operating temperature of PTEJ, K;

E ₁ and E ₂ - EMF PTEI when applying the first and second ASG, respectively, In;

C ₁ and C ₂ - volume fraction of oxygen in the first and second ASG, respectively,%.

Using the temperature controller, the operating temperature is set (1008 ± 2) K. If, after the first adjustment, the temperature is lower or higher, the procedure for setting the operating temperature is repeated until the result is obtained with the necessary accuracy.

The temperature of the CTEC also takes on a value close to 1008 K, because electrodes PTEJ and CTEJ are in the same temperature zone.

To take measurements of the flow rate of the analyzed gas, a fine-adjustment variable throttle is connected to the GAS INPUT fitting, with the help of which the gas flow rate is established through PTEJ and KTEY. A 0.6 V DC source and a current meter are connected in series to terminals 12 and 14 of the CTEC, with the source "-" connected to the internal electrode (terminal 12) and a "+" to the external electrode (terminal 14). With such a polarity of the source, oxygen is pumped out from the analyzed gas.

By measuring the oxygen pumping current by the coulometric cell I, the EMF of the potentiometric cell E using formula (4), we calculate the flow rate of the analyzed gas.

Made a sample of the proposed device. Nitrogen and argon with an oxygen content of 1 and 3.1 · 10 ^-3 % were used as the test gas. The measurements were carried out in ambient air.

The experimental work was reduced to a comparison of the costs determined by the proposed device and using a gas-counter GSB-400. whose error is ± 0.5%.

The results obtained when measuring gas flow from 50 to 300 cm ³ / min have good convergence, not worse than 1%.

The application of the proposed device will automate the process of measuring gas flow, which is not achieved by known devices, since the means used for these purposes require manual operations.

Claims (1)

A device for measuring the flow rate of oxygen-containing gases, containing a heater, potentiometric and coulometric solid electrolyte cells, characterized in that a dehydrator filled with phosphoric anhydride is installed at the input of the device, and potentiometric and coulometric solid electrolyte cells are structurally made on a tube of solid electrolyte of the composition 0.85ZrO ₂ +0 , 15Y ₂ O ₃ , and the temperature of the electrodes of the potentiometric solid electrolyte cell is set equal to (1008 ± 2) K by applying three alternately two calibration gas mixtures with an oxygen concentration that differs by more than two times, and the flow rate of the analyzed gas is calculated by the formula:

where Q is the flow rate of the analyzed gas, m ³ / s; I is the oxygen pumping current by a coulometric solid electrolyte cell, A; M is the molar mass of oxygen, kg / mol; 4F - the amount of electricity required for the electrochemical transfer of one mole of oxygen, C / mol; E - EMF of a potentiometric solid electrolyte cell, V; R is the molar gas constant, J / (mol · K); T is the operating temperature of the potentiometric solid electrolyte cell, K; With _{0 the} concentration of oxygen in the ambient air, kg / m ³ , the operating temperature is maintained using a potentiometric solid electrolyte cell as a thermally sensitive element of the electrodes.