RU2326373C1 - Measuring cell of sodium analyser - Google Patents

Abstract

FIELD: measuring devices.

SUBSTANCE: measuring cell of a sodium analyser consists of three serially connected flowing chambers. In the first chamber along the flow of the medium, a temperature sensor is mounted. In the second chamber there is a test electrode and the main electrode is in the third chamber. The first chamber has two channels, linking it to sources of the controlled media and an alkaline reagent. The chamber is divided horizontally using a partition wall with a central opening on two parts, the upper part on which is mounted a temperature sensor and has input channels. On the lower part of the channel there is an electroconductivity sensor. The input channel, linked to the medium, is located near the upper filling level of the liquid in the upper part of the chamber. The axis of the given channel is at a tangent to the wall of the chamber. The output section of the second input channel is located over the horizontal partition wall, lower than the output section of the first input channel.

EFFECT: lower inertia, increased accuracy and stability of measurements.

1 dwg

Description

The invention relates to the field of measurement technology, and more particularly to devices designed to measure the activity of sodium ions.

The measuring cells in potentiometric analyzers are designed to supply controlled water (the so-called sample) to the electrode system of the device. They provide isolation of the flowing fluid from contact with ambient air, the supply of the necessary additional reagents and eliminate the possible interelectrode effect.

They find the greatest application in the power industry when controlling clean waters having an electrical conductivity of 1 μS / cm or less. Among the most common instruments are pH meters and sodium analyzers (pNa meters).

A specificity of sodium analyzers is the need to supply an additional alkalizing reagent, which, by lowering the concentration of hydrogen ions to the required level, allows selective measurement of the activity of sodium ions.

Measurement of low sodium concentrations (less than 5 μg / dm) requires the supply of such an amount of alkalizing reagent that it essentially becomes the dominant component of the solution and determines all its properties. For example, for a given lower limit of the sodium measurement range of 2 μg / dm ^{3, the} concentration of a typical alkalizing reagent, ammonia, should be at least 150 mg / dm. In this case, the electrical conductivity of the resulting solution will be 110 μS / cm.

As a rule, the alkalizing reagent is supplied in the form of a mixture of its vapors with air, which eliminates the introduction of undesirable impurities into the controlled water. In existing instrument designs, the mixing of such a vapor-air mixture and controlled water is carried out in a special separate device - a mixer. The mixer is a chamber having two inlets - for controlled water and steam-air mixture, and one outlet. There are mixers operating in the mode of a water-jet pump, when the flowing water creates a vacuum and captures the vapor-air mixture with an alkalizing reagent. A variant of the mixer with forced supply of steam-air mixture. From the mixer output, controlled water with air bubbles is supplied through a connecting tube to one of the chambers of the measuring cell, in which either a temperature sensor or an indicator (sodium) electrode is installed.

The measuring cell of the sodium analyzer is known, which is part of the device "Ionomeric analyzer type pNa - 205.1", commercially available from the Gomel plant of measuring devices (see the attached sample from the device passport 5M2.840.098 PS, 1990), which is a three-chamber design with series connected by the flow of the medium through flow chambers, in the first of which a temperature sensor is installed, in the second - an indicator electrode, and in the third - a reference electrode. The inlet of the first flow chamber is connected to the outlet of the mixer, made in the form of an injector operating on the principle of a water-jet pump, the active nozzle of which is connected to a source of a controlled medium, and the nozzle of the mixing chamber to a source of alkalizing reagent.

This measuring cell is the closest in combination of essential features to the claimed one and is selected as the closest analogue.

As experience shows, such a mixture of an alkalizing reagent and a controlled liquid has a significant drawback. In the connecting tube, through which the alkalized mixture is supplied from the mixer to the measuring cell, the phenomenon is periodically observed when air bubbles stop there for a while and then spontaneously all at once are dumped into the measuring cell. Changes in the cross sections of the tube and the supply pipes make it possible in some cases to reduce the likelihood of such a phenomenon, but do not completely exclude it. The cleanliness of the surface of the connecting tube, the composition of the controlled fluid, and temperature are, apparently, factors determining the existence of such a phenomenon.

This phenomenon causes fluctuations in the concentration of alkalizing reagent, and in some cases a disruption of the water-jet pump. Conductivity measurements show that there are significant fluctuations in the electrical conductivity of the resulting solution, which can be up to 20%. The corresponding fluctuations in the concentration of hydrogen ions (at an average pH = 10.5) reach 25%.

Such heterogeneous concentration of alkalizing reagent in the solution can adversely affect the metrological characteristics of the sodium analyzer due to the fact that the concentration of hydrogen ions can periodically exceed a predetermined limit level and the sodium electrode will begin to respond to their presence.

Fluctuations in the concentration of the alkalizing reagent have a negative effect on the reference electrode, due to the fact that the reagent to one degree or another penetrates the potential-forming system of the electrode and shifts its potential.

An obvious solution to this technical problem could be to increase the average concentration of alkalizing reagent to such an extent that its minimum value (taking into account possible fluctuations) does not fall below a certain predetermined level. But such a solution is highly undesirable, since the consumption of alkalizing reagent is already quite large and, accordingly, the operating costs for servicing the device are high. So, for the above example, the flow rate of ammonia (with a flow of controlled water of 100 ml / min) is 0.9 l / h. At the same time, 1 liter of ammonia solution (with a maximum concentration of 30%) is enough for 14 days at an optimal flow rate.

Another possible solution is to increase the volume of the chamber in which saturation with an alkalizing reagent takes place. Obviously, in this case, the response time of the device will increase due to the appearance of an additional buffer volume. This decision is also associated with an increase in the size of the structure.

The technical result of the invention is to reduce inertia, improving the accuracy and stability of measurements of the sodium analyzer.

The specified technical result is achieved in that in the measuring cell of the sodium analyzer containing three series-connected flow chambers, in the first of which a temperature sensor is installed in the medium flow, in the second is an indicator electrode, and in the third is a reference electrode, the first flow chamber being connected to the source of the controlled medium through the first inlet channel, and the source of alkalizing reagent, according to the invention, in the first flow chamber a second inlet channel is communicated from the source lump of alkalizing reagent, the first flow chamber is divided by a horizontal partition with a central hole into two parts, in the upper of which a temperature sensor is installed and the specified input channels are made, and in the lower part there is a conductivity sensor and an output channel is made communicating with the second flow chamber, the inlet section of the first inlet channel is located near the upper level of liquid filling the upper part of the first flow chamber, the axis of the specified channel is oriented tangentially relative to the chamber wall, the channel itself has a tapered portion at the inlet into the chamber, and the output section of the second inlet disposed above the horizontal baffle below the outlet section of the first input channel.

Improving the accuracy and stability of measurements of the sodium analyzer is provided by reducing the level of fluctuations in the concentration of alkalizing reagent. Reduced inertia of measurements is achieved by more efficient mixing of the alkalizing reagent in a controlled environment, which allows to reduce the buffer volume of the flow chamber.

The invention, characterized by the above set of essential features, at the filing date of the application is not known in the Russian Federation and abroad and meets the requirements of the criterion of "novelty."

The invention can be implemented industrially using well-known technical means, technologies and materials and meets the requirements of the criterion of "industrial applicability".

The applicant has not identified technical solutions that have features that match the set of distinctive features of the proposed device and ensure the achievement of the claimed technical result, in connection with which we can conclude that the invention meets the patentability condition "inventive step".

The invention is illustrated in the drawing, which shows the proposed measuring cell, General view.

The measuring cell of the sodium analyzer contains series-connected flow chambers, in the first 1 of which a temperature sensor 2 is installed in the medium flow, in the second 3 is an indicator electrode 4, and in the third 5 is a reference electrode 6, and the flow chamber 1 is connected to a source of a controlled medium ( not shown) through the first input channel 7.

In the flow chamber 1, a second inlet channel 8 is made, in communication with a source of alkalizing reagent (not shown). The chamber 1 is divided by a horizontal partition 9 with a central hole 10 into two parts, the upper one of which has a temperature sensor 2 and the specified input channels 7 and 8. The input channel 11 is installed in the lower part of the chamber 1 and the output channel 12 is made, communicating with the second flow chamber 3.

The input section of the input channel 7 is located near the upper level of liquid filling the upper part of the flow chamber 1, while the axis of the channel 7 is oriented tangentially relative to the wall of the camera 1, and the channel 7 has a tapering section at the entrance to the chamber 1. The output section of the input channel 8 is located above the horizontal the partition 9 below the output section of the input channel 7.

The work of the proposed measuring cell is as follows. Controlled water enters the flow chamber 1 through the inlet channel 7. Due to the presence in the channel 7 of a tapering section located at the entrance to the chamber 1, the water acquires acceleration and exits from the channel 7 into the chamber at an increased speed. The tangential location of the axis of the channel 7 relative to the wall of the chamber 1 leads to the rotation of the water accumulating in the chamber 1. A horizontal partition 9 with a central opening 10 and an output channel 12 located at the bottom of the chamber 1 forms a funnel-shaped configuration of the flow passing from top to bottom. Through the second inlet channel 8, located below the inlet channel 7 at the partition 9, an air-steam mixture with an alkalizing reagent enters. The bubbles of the air-steam mixture pass through a layer of water separating the inlet channels 7 and 8, saturating the water with an alkalizing reagent. Due to the orthogonal movement of water and mixture bubbles, as well as due to mixing in a rotating stream, the alkalizing reagent is evenly distributed over the mass of liquid. Measurements show that fluctuations in electrical conductivity, and hence the concentration of alkalizing reagent, are reduced by no less than an order of magnitude.

The conductivity sensor 11, located in the lower part of the chamber 1, allows not only to control the degree of saturation of the fluid flowing through it with an alkalizing reagent, but also to realize automatic dosing of this reagent and a variant of the device using a pH electrode as a reference electrode.

Improving the accuracy and stability of measurements of the sodium analyzer is provided by reducing the level of fluctuations in the concentration of alkalizing reagent, adversely affecting the operation of the reference 6 and measuring 4 (sodium) electrodes. The decrease in the inertia of the measurements is achieved by more efficient mixing of the alkalizing reagent in a controlled environment, allowing to reduce the buffer volume of the flow chamber 1.

Claims (1)

The measuring cell of the sodium analyzer, containing three series-connected flow chambers, the first of which has a temperature sensor installed in the medium flow, the indicator electrode in the second, and the reference electrode in the third, the first flow chamber connected to the source of the controlled medium through the first input channel, and a source of alkalizing reagent, characterized in that in the first flow chamber there is a second inlet channel in communication with the source of alkalizing reagent, the first flow chamber divided by a horizontal partition with a central hole into two parts, in the upper part a temperature sensor is installed and the specified input channels are made, and the conductivity sensor is installed in the lower part and the output channel is made, which communicates with the second flow chamber, and the input section of the first input channel is located near the upper level of liquid filling the upper part of the first flow chamber, the axis of the specified channel is oriented tangentially relative to the chamber wall, the channel itself has a tapering portion inlet chamber and the outlet section of the second inlet disposed above the horizontal baffle below the outlet section of the first input channel.