RU2265205C1 - Device for detecting micro-admixtures in gas - Google Patents

Abstract

FIELD: gas-analyzers.

SUBSTANCE: device has gas carrier line, containing flow activator and serially connected converter of admixtures to condensation cores, detector, means for increasing size of condensation cores, photo-electric measuring device. Device is additionally provided with gas-chromatographic column, admixture concentrator, pump for taking samples from atmosphere, flow switcher, dosage meter of support concentration of detected admixture and microprocessor unit for controlling operations concerning analysis and information processing. Switch can enable concentrator either in line of gas carrier before the column, or in sample-taking pump line, and dosage meter is mounted in gas carrier line prior to switch and contains thermostatted shell, provided with lid with calibrated opening, positioned under cap of absorbing material, connected to rod, made with possible reciprocal movement. Inside the shell some admixture is positioned on inert carrier, and between shell and lid polymer film is hermetically pressed, providing diffusion of admixture substance in carrier gas line.

EFFECT: higher precision, higher efficiency, higher trustworthiness, higher reliability, broader functional capabilities.

2 dwg

Description

The invention relates to techniques for the analysis of gas impurities, in particular to aerosol gas analyzers, in which the impurity is converted into condensation nuclei and the subsequent enlargement of condensation nuclei in a supersaturated vapor, and can be used to monitor atmospheric pollution, including highly toxic, for example, toxic substances.

A device is known for determining microimpurities of aromatic and unsaturated hydrocarbons in a gas, including a desiccant, a filter, a flow meter, an impurity converter into condensation nuclei (IAC) sequentially connected in the course of the analyzed stream (UV irradiation with sensitization by mercury vapor) and a condensation nucleus counter type Wilson's camera according to US patent No. 2684008 (1954) (author B.Vonnegnt), which combines the functions of a device for enlarging I. in a supersaturated water vapor (supersaturation is created by adiabatic expansion) and an aerosol photometer to measure the light scattering of the formed fog, the readings of which are associated with the concentration of impurities at the entrance to the device [G.F.Skala, US Pat. USA No. 3102192, cl. 250-833 (1963), claimed 09/30/60].

The disadvantage of this device is the low sensitivity of determining the target components, inferior to the sensitivity of conventional chromatographic detectors (detection limit at the level of 10 ^-6 vol. Fraction or 5 · 10 ^-3 mg / l).

This drawback is due to the fact that only particles consisting of a large number of molecules formed as a result of coagulation of the primary photolysis products can be enlarged in the supersaturated water vapor used in this device.

Another disadvantage is the low selectivity of determining the target components, which limits the applicability of the device for analysis of atmospheric air (such conventional impurities in the atmosphere of industrial cities as SO ₂ , H ₂ S, NO, which form ionic radiation under UV irradiation, interfere with the determination).

Closest to the proposed technical essence and the achieved result is the device presented in the description of the invention to the patent of the Russian Federation No. 792095 with a priority of 12/22/78, "Method for the determination of organometallic impurities in gases", cl. G 01 N 15/00. This device contains a flow inducer, an aerosol filter, and an impurity to condensation core converter installed in series with one another, two devices for developing and enlarging ya. in supersaturated vapors, and a photoelectric nephelometer for measuring light scattering of the obtained aerosol, which is proportional to the concentration of impurities at the entrance to the device.

This device is taken as a prototype of the invention. The use of special "developing" substances and an original method of converting impurities into condensation nuclei made it possible to increase the sensitivity of the determination of organometallic compounds to the level of 10 ^-12 -10 ^-8 mg / l.

A significant drawback of this device is the low selectivity of determining the majority of classes of chemical compounds, as a rule, which does not allow determining the target component in atmospheric air, since ordinary atmospheric impurities give either a false signal (H ₂ S, SO ₂ , NO, H ₂ O) or ( i) affect the signal value of the target component (hydrocarbons, CO, H ₂ O), thereby leading to a large measurement error.

The reason for this drawback is the versatility of the conversion processes and the manifestation of condensation nuclei with respect to different types of substrate.

With rare exceptions, this drawback cannot be eliminated in the framework of the prototype device.

Another disadvantage is the impossibility of simultaneously determining several substances in the analyzed gas stream.

Another disadvantage of the prototype device is the poor reproducibility of the analysis results, which depends on the accuracy of maintaining many parameters, including the values of four different temperatures of the device elements, humidity and degree of purification of the carrier gas (air is used), the intensity of the conversion factor, and the sensitivity of the photodetector aerosol photometer etc. All of these parameters are difficult to maintain constant for a long time.

The objective of the invention is to create a device that allows automatic monitoring of the atmosphere for pollution of highly toxic substances and their mixtures.

The technical result consists in a significant increase in the sensitivity and selectivity of determining the target components compared to the prototype, an increase in the reproducibility and accuracy of measurements, in the possibility of simultaneous determination of several substances in one sample, as well as in complete automation of the measurement process.

The specified technical result is achieved by the fact that the proposed device, which includes a carrier gas line containing a flow inducer and series-connected impurity to condensation core converter, a developer, condensation core enlarger and a photoelectric nephelometer, is additionally equipped with a gas chromatographic column, impurity concentrator, and a sampling pump from atmosphere, a flow switch, a dispenser of the reference concentration of the detected impurity and a microprocessor to control the analysis and processing of information, the switch allows you to turn on the concentrator either in the carrier gas line in front of the column, or to the sampling pump, and the dispenser is installed in the carrier gas line in front of the switch and contains a thermostated cartridge equipped with a cover with a calibrated hole located under the cap of the sorbent material, connected to the rod, made with the possibility of reciprocating movement, while inside the cartridge is placed an impurity substance on an inert carrier, and between the cartridge and the cover The polymer film is tightly pressed, which ensures the diffusion of the impurity substance into the carrier gas line.

The difference between the proposed device and the prototype lies in the fact that it is equipped with a gas chromatographic column installed in front of the converter, an impurity concentrator, a pump for sampling from the atmosphere, a flow switch for connecting the concentrator either to the carrier gas line in front of the column, or to a sampling pump, microprocessor for management of information analysis and processing operations, as well as a dispenser of the reference concentration of the detected impurity installed in the carrier gas line in front of the flow switch, comprising a thermostatically controlled cartridge, equipped with a cover with a calibrated hole, located under a cap of sorbent material, connected to a rod made with the possibility of reciprocating movement, while inside the cartridge there is an impurity substance on an inert carrier, and a polymer film is sealed between the cartridge and the cover, providing diffusion of the impurity substance into the carrier gas line, as a result of which the sensitivity and selectivity of determining the target mponentov increases the accuracy and reproducibility of measurements, it becomes possible to determine several substances in a sample, as well as fully automated measurement process.

The invention is illustrated by drawings. Figure 1 shows the connection diagram of the elements of the device, where the designations are:

1, 17, 19 - rotameters;

2 - pump for sampling from the atmosphere;

3, 13, 16, 22 - filters for air purification from gas and aerosol impurities;

4 - stream switch;

5 - aerosol filter;

6 - gas chromatographic column with a thermostat;

7 - converter of gas impurities to condensation nuclei;

UK - block two-stage enlargement of the condensation nuclei, including the developer 8 and enlarger 9;

10 - photoelectric nephelometer;

11 - power supply unit;

12 - block UROI (control of operating modes and information processing): microprocessor;

14 - stimulator of the flow of carrier gas (air);

15 - air pressure stabilizer;

18 - desiccant;

20 - air flow stabilizer;

21 - hub;

23 - dispenser reference concentration of the detected impurities.

- carrier gas line;

- • - • - sampling line from the atmosphere;

--- power supply, control and information transmission lines.

Figure 2 shows a drawing of a dispenser reference concentration of the detected impurities, where the numbers indicate:

24 - a movable rod;

25 - case;

26 - a sleeve with an annular groove into which a cap of sorbent material 27 is glued;

28 - polymer film;

29 - output fitting of the carrier gas;

30 - cartridge cover with calibrated hole;

31 - cartridge;

32 - massive copper body;

33 - cooling radiators;

34 - thermal batteries;

35 - inert carrier with a defined impurity;

36 - inlet fitting of the carrier gas.

Figure 3 shows the printout of a computer file corresponding to the analysis cycle of atmospheric air containing an admixture of a toxic substance: soman. In a large central window, chromatograms of desorption products from the concentrator are displayed. The lower curve corresponds to the reference signal from the dispenser (for safety reasons, the soman simulator was used in the dispenser: diethylethylphosphonate); upper - a signal from the atmosphere; 1-dimethylformamide (technological impurity), 2 - soman. In the upper left window, the concentration of the target component (soman) is displayed in units of the MPC of the working area; in the other two upper windows - the current operation and device operation mode; in the windows on the right are the set and actual temperatures of the elements of the device.

The device operates according to the following algorithm:

1. Turn on the flow inducer (14) (compressor or mains air).

2. Turn on the power. In this case, the “Preparation” mode is automatically activated. In this mode, the carrier gas (air) from the inducer (14) through the cleaning and drying system (16, 18, 22), stabilization and measurement (15, 19, 20) is supplied to the dispenser (23) in the closed state (Figure 2 ), passing through the inlet fitting (36), the annular gap in the sleeve (26) and the outlet fitting (29). In this position, the stationary flow of diffusion of the impurity substance (35) through the film (28) and the hole in the cover (30) of the cartridge (31) is carried out by removing the substance from the outer surface of the film to the cap of the sorbent material (27). In order to maintain a constant temperature, the cartridge case (31) is screwed into a massive copper body (32), thermostatically controlled by means of thermal batteries (34) with cooling radiators (33). Then, the carrier gas through the flow switch (4, position I) enters the concentrator (21) and then the gas chromatographic column (6), converter (7), developer (8), enlarger (9) and nephelometer (10). Using the microprocessor (12) during the preparation mode, the set temperatures of the following elements are set: columns (6), converter (7) (if a thermal converter is used), evaporators and developer refrigerators (8) and enlarger (9), dispenser (23). In this mode, air containing only traces of the stationary liquid phase from the column enters the converter (7). The background concentration of condensation nuclei is formed in the converter, which are then enlarged in devices (8) and (9) (the so-called condensation devices KUST), forming an aerosol. A nephelometer (10) captures the photocurrent of light scattering of this aerosol (background signal).

3. After a predetermined preparation time (usually 20 minutes), the device switches to automatic selection mode itself, and the following sequence of operations is performed:

3a - control heating of the concentrator to clean it from accidental contamination.

3b - sampling at the concentrator of a sample of the reference concentration from the dispenser (23).

To do this, for a given time using the electric drive and the rod (24, Figure 2), the sorbent cap (27) rises, freeing the surface of the film (28). Air from the inlet fitting (36) captures the impurity vapors diffused through the film and delivers them through the outlet fitting (29) and switch (4, position I) to the concentrator (21).

The amount of substance M ₁ adsorbed in the concentrator is:

where f is the diffusion flow of the dispenser, mg / min;

t ₁ - the accumulation of impurities from the dispenser, min

3c - desorption of the impurity accumulated from the batcher, and gas chromatographic analysis of the desorbed sample.

As a result of short-term heating of the concentrator at the command of the processor, a compact zone of desorbed impurity vapors is formed behind the concentrator in the carrier gas stream, which, through the switch (4, position I), enter the input of the GC column. After a certain time, the impurity substance leaves the column in the form of a peak, which is fixed on the curve of the time dependence of the aerosol light scattering photocurrent in the nephelometer (10).

The processor "counts" the peak area S ₁ in a given "window" of time and remembers its value.

3g - sampling from the atmosphere.

The switch (4) switches to position II and immediately turns on the pump (2), with which air from the atmosphere through the filter (5) enters the concentrator (21). At the end of the set time, the pump turns off and the switch (4) returns to position I.

3d - analysis of samples from the atmosphere.

Similarly, 3c, the concentrator is briefly heated and the chromatogram is recorded. In the same "window", the processor considers the peak area of the analyzed impurity S ₁ and calculates the mass of the substance M ₂ :

as well as its concentration of C in the atmosphere:

where C is the concentration, mg / l;

V is the sampling rate from the atmosphere, l / min;

t ₂ - sampling time from the atmosphere, min.

Combining (1), (2) and (3), we have

moreover, the value of the diffusion flux Φ of the dispenser is constant at a given temperature, determined by calibration by an independent method, and entered into the processor memory.

At the end of the analysis cycle, its result is displayed on the built-in display, and more detailed information on the analysis conditions using various communication lines (RS232; Ethernet, etc.) can be transferred to a personal computer. An example of a computer file thus obtained is shown in FIG. 3.

Next, the processor repeats the analysis cycles from the atmosphere (operations 3d and 3d). At certain intervals (usually once per hour), the processor gives a command to calibrate the device (operations 3b and 3c).

Comparative characteristics of the proposed device and the prototype device for some examples are shown in the table.

It should be noted that in measurements using the prototype device, the relative error can reach several times (if you do not carry out the often laborious calibration of the device using a multi-stage impurity diluent). In the proposed method, the measurement error does not exceed 20%, while calibration from an external source is carried out no more than once a year.

Thus, in comparison with the prototype, the proposed device allows to increase the sensitivity, selectivity and accuracy of determination of various, including highly toxic compounds in a gas, to determine several compounds in one sample at once, to fully automate the analysis process, which in turn allows constant automatic monitoring of the atmosphere harmful production.

Solved problem of analysis (target component) Impurities that interfere with the determination of the target component in concentrations at the MPC level of the working area Detection limit, mg / l The influence of other impurities Prototype (RF patent 792095) The proposed method Definition of soman in clean air - 10 ^-5 10 ^-8 Determination of soman in the atmosphere of a production room
Acid gases (Cl ₂ , HCl, SO ₂ , H ₂ S, NO)
Solvent vapors, including chlorine ≫10 ^-5 10 ^-8 Interfere

Interfere Do not interfere

Do not interfere Determination of trinitrotoluene in clean air - 10 ^-7 10 ^-8 Determination of trinitrotoluene in atmospheric air
Water vapor ≫10 ^-7 10 ^-8 Interfere Do not interfere Acid Gases Interfere Do not interfere Hydrocarbons (vapors of motor fuels) Interfere Do not interfere Car exhaust Interfere Do not interfere Household odors (perfumes, food, etc.). Interfere Do not interfere Simultaneous separate determination of organic derivatives of tin and lead in atmospheric air - impossible Tetraethyltin - 10 ^-9 ; Tetra-n-propyltin - 10 ^-9 ; Tetraethyl lead - 10 ^-10 ;
Acid gases, hydrocarbons, CO, NH ₃ do not interfere with the determination

Claims (1)

A device for determining microimpurities in a gas, including a carrier gas line containing a flow rate driver and a series-connected impurity to condensation core converter, a developer, a condensation core enlarger and a photoelectric nephelometer, characterized in that it is equipped with a gas chromatographic column installed in front of the converter, an impurity concentrator, a pump for sampling from the atmosphere, a flow switch to turn on the concentrator either in the carrier gas line in front of the column or to the sampling an washer, a microprocessor to control information analysis and processing operations, as well as a dispenser of the reference concentration of the detected impurity installed in the carrier gas line in front of the flow switch, containing a thermostated cartridge, equipped with a cover with a calibrated hole and located under a cap made of sorbent material connected to a rod made with the possibility of reciprocating movement, while inside the cartridge is placed an impurity substance on an inert carrier, and between the cartridge and the cover ermetichno biased polymer film providing diffusion substance impurities in the carrier gas line.

Images