SU1516908A1 - Method of determining concentration of methane in mine atmosphere - Google Patents

Abstract

The invention relates to mining automation and can be used in the construction of sensors determining the concentration of methane in a mine atmosphere for automatic gas protection in coal mines. The aim of the invention is to improve the accuracy of the analysis by simultaneously increasing the rate of change of the output signal when the concentration of methane changes by reducing the influence of dust fluctuations, humidity, pressure and temperature of the mine atmosphere. In the method of analysis of concentration of methane in the mine atmosphere, based on the heating element, the catalytic oxidation of methane over this element and recording the intensity _I I flows electromagnetic radiation OT element C oxidizable HA HEM METAHOM, part of the element isolates RuyuT OT KOHTAKTA C mine atmosphere, preventing the catalytic oxidation METAHA HA THIS FREQUENCY, AND PRESENTLY REGENERATED INTENSITY I _II electromagnetic radiation from an isolated part of the element, which passed through a controlled amount of the mine atmosphere. The element is heated to a temperature of about 580 ° C by passing through it a stable value of current from the current stabilizer. Electromagnetic radiation is recorded in the band 3.19 - 3.59 µm, and the concentration of methane is judged by the ratio of registered intensities I _I / I _II , and I _{I is} measured at a distance L ₁ selected from the conditions BC _m L ₁ * 981, and I _{II are} measured at a distance L ₂ chosen from the condition BC _cp L ₂ = 2, where B is the absorption coefficient of methane, in the specified band, C _m is maximum, and C _cp is the average concentration of methane. 1 il.

Description

The invention relates to mining automation and can be used in the construction of sensors analyzing the concentration of methane in the mine atmosphere for automatic gas protection in coal mines.

The aim of the invention is to improve the accuracy by increasing the rate of change of the output signal when the concentration of methane changes while reducing the effects of fluctuations in dust, humidity, pressure and temperature in the mine atmosphere.

The drawing shows the functional diagram of the device for determining

concentration of methane in the mine atmosphere.

The device consists of a heating element (e.g., thermal catalytic), the non-insulated part 1 of which is in contact with the mine atmosphere, and the isolated part 2 is covered with a gas-impermeable film 3 that is transparent to infrared radiation (for example, from sapphire).

The heating element through the switch 4 is connected to the stabilizer 5 current, to the open part 1 of the heating element adjacent chamber 6 with the analyzed object 7 mine atmosphere.

Chamber 6 is open on the side of part 1, as well as in directions perpendicular to the plane of the drawing. This ensures free access of the mine atmosphere to the chamber and to the open 1 heating element.

Against the open part 1 behind the camera 6, a photodetector 8 is mounted, mounted in a container collimator 9; Against the isolated part 2 of the heating element, an additional photoreceiver 10 is mounted behind the camera 6 mounted in a second container collimator 11,

Before the main photodetector 8, a first bandpass (for example, interference) filter 12 is installed, and a second bandpass filter 13 is installed in front of the additional photodetector IO. The thickness of the monitored volume L before the main photoreceiver 8 is less than the thickness L of the monitored mine atmosphere 10,

The outputs of the photodetectors 8 and 10 through the amplifiers 14 and 15 are connected to the inputs of the ratio meter 16, the output of which is connected to the input of the display and recording unit 17. The heating element of open 1 and closed 2 parts, the switch 4 and the current stabilizer 5 are placed in the housing 18 of the metal mesh IS on the side of the open part 1, the grid 19 is a flame arrester.

The concentration of methane in the mine atmosphere is determined by the following sequence of operations.

Through the open and insulated parts of the heating element, a stable current I is passed through.

0

five

0

0

five

0

five

0

five

heating the element to a temperature of about. Record the intensity I, the flux of infrared radiation in the band 3.19-3.59 µm from the open part of the element with methane oxidized on it. The intensity I ij of the infrared radiation flux in the band 3.19-3.59 µm from the closed part of the heating element heated from the current stabilizer to a temperature of about is recorded. The ratio of the registered intensities 1, / 1 j is determined. By the ratio Ij / I, -, the concentration of methane in the mine atmosphere is judged, Intensity 1 is recorded at a distance Lj from the open part, and the intensity I is recorded at a distance Lj from the isolated part of the heating element, where.

The device works as follows.

Turn on the switch 4, pod1 $ lucha stabilizer 5 current to the heating element. A constant current I passes through a heating element, heating it open 1 and insulated 2 parts to a constant temperature of about 580 ° C,

When the open part 1 is heated to a temperature of 580 C, thermal catalytic combustion (oxidation) of methane occurs on it. The temperature of the open part increases and the resistance of this part of the heating element R increases, the more the methane concentration increases.

Since a constant current I flows from the current stabilizer 5 into the heating element, the electric power RI released at the open part increases with increasing methane concentration.

Because of the heating of the open part 1, the current stabilizer 5 emits infrared radiation from the open part, the intensity of which is proportional. Because of the thermal catalytic methane burning in the open part 1, infrared radiation is emitted, the intensity 1 of which is proportional to the methane concentration C,

Thus, infrared radiation of intensity 1, -t-i, on path L, is radiated to the main photodetector 8 from the open part 1, through the mine atmosphere, to infrared radiation

the reading is attenuated so that both intensities decrease by the same number of times,

The intensity of the infrared flux to the main photodetector 8 can be represented as

Ii- (I, -H2) k ,, CJ, (I) where k j is the instrument coefficient; b is the absorption coefficient of infrared radiation in a band with a wavelength of 3.39 µm in the middle, for example, a band from 3.19 to 3.59 µm. At the same time, infrared radiation from the open part 1 of the element has a wide continuous spectrum with a maximum occurring at a wavelength of 3.39 µm at 580 ° C and with a decreasing wavelength at the maximum during intensification of methane burning, i.e. when the temperature of the open part increases. Experiments show that the temperature rise from the concentration depends on the size of the open part and on the power P /,. When the element diameter is 3 mm, its length is 2 mm and power W, the temperature of the open part 1 increases with concentration from 0 to 3 vol%; from 580 to 632 ° C, which corresponds to a change in the wavelength in the maximum from 3.39 to 3.2 μm.

Experiments show that intensities 1 and 1 can be approximated with sufficient accuracy by linear functions of the form

1, a, C; (2)

, C, (3)

where a. - free member, numerically

equal to intensity 1, with zero methane concentration; e ,,, the angular coefficients, numerically equal to the increments of the corresponding intensities with a single increase in the concentration of methane. Substituting 1, and I 2 from (2) and (3) in (1) receive

, -bC (e, + eg) JkjexpC-bL, Cj. (4) In the device, the value of L. is chosen such that at the maximum value of the detectable concentration of methane C, the condition

bL, C «0. (5)

When condition (5) is fulfilled, the intensity according to (4) increases over the entire range of increase in methane concentration from to,. With bLj.

908

on the upper part of the range, an inflection is observed, and when an inflection is observed on dependence I., according to (4), it is observed at CjiC concentrations when C, I, and with a further increase in C7C; the intensity Ij according to (4) decreases.

From the current stabilizer 5, the same current I flows into the insulated part of the mine atmosphere. The resistance Rj of part 2 of the element remains constant (Rj const), since there is no methane burning on it, and the heat transfer along the spiral element can be neglected. The power allocated to the isolated part 2 of the element Rjj const remains constant. Because of the heating of the isolated part

0 2 elements by a current stabilizer 5 up to a constant temperature of 580 ° C. Infrared radiation is emitted from this part, the intensity of which is constant is proportional to P, and the maximum intensity corresponds to a wavelength of 3.39 µm.

Thus, an additional photodetector 10 is emitted from the isolated element 2 of the element by infrared radiation of intensity 1, independent of the concentration of methane in the mine atmosphere. On the way, through the mine atmosphere, the intensity 1c is exponentially weakened and

g additional photodetector 10 hits intensity I according to the expression

li (-bL, C), (6) where k is the instrument coefficient.

0 Signals from photocells B and 10, proportional to the intensity m Ij. and I; amplified by amplifiers 14 and 15 and fed to the inputs of the meter 16 ratios, the output of which forms a signal proportional to the ratio I ../ I S 1

Ijl, k, (; a, + C (e, + ei) jexp (-bL, C) vk, lV Cexp (-bLjC) - k, k-; 1-; Ha, (e, + e) (Lj -L;) (7) Ij / Ij signal from the meter output

16 relations, which is a measure of the concentration of methane C, is supplied to the unit

17 indication and registration, where is displayed (in vol.%) Methane content.

five ,

The essence of accuracy

simultaneously increasing the sensitivity and reducing the effects of fluctuations in dust, humidity, pressure and

The temperatures of the mine atmosphere are based on the analysis of formula (7).

As dust increases, the values of a ,, ,, f and e simultaneously decrease, and the value of b increases. Decreases a, e lead to a decrease, and an increase in b leads to an increase in the right side of equation (7). Due to this, there is a reduction in the effect of dust fluctuations. Physically, this is explained by simultaneous decreases in the intensities I and I, according to (2) and (3), an increase in (4) and an increase in b in (6), i.e. an increase in dustiness leads to a deterioration of methane burning in the open part of the cell, to a decrease in the temperature of the open part 1, to an increase in the absorption of infrared radiation on paths I: and 1 to the photodetectors 8 and 10. Similar patterns are observed with increasing humidity and pressure mine atmosphere. As the temperature of the mine atmosphere increases, the intensity of methane burning in the open part 1 increases (because of which the intensities 1 and Ij increase), and the absorption coefficient b decreases simultaneously, while the a, e and e, j increase and the drive decreases b; to a weak dependence of the ratio Ij / Lj on temperature.

Dependence (71 can be represented as

Ij / 1, (k3 + k, C) exptbC (L -, - L J, where s bjk jI Y; a, const and k, k, kjl «(e i + ei) const.

The lengths of the infrared radiation paths L and L through the mine atmosphere are selected during alignment of the device.

The selection process L j. carried out as follows. Increase the concentration of methane from 0.8 C, and follow the change in intensity Ij. If with increasing С from 0.8 С to С „intensity 1 decreases, then decreases. lj to increase 1. If with increasing C from 0.8 ° C to C, the intensity Ij increases from I to 1.05 1, then the distance L is increased to ensure an increase of 5% with an increase in concentration from 0.8 C to C, i.e. from 2.4 to 3 vol.%. Thus, the numerator in O) is increased, i.e. an increase in intensity of 1 by 18.3 rel.% with an increase in

five

0

five

0

five

0

five

0

five

methane content by 1 abs.% by volume. The distance L is selected so that when the average concentration of methane is 1.5%, the value is 2. This ensures a decrease in intensity I I with an increase in concentration from 0.8 C to C „by 5%, i.e. a decrease in intensity I- by 8.3 rel.% with an increase in methane content by 1 abs.% by volume. Such an adjustment of the device results in a sensitivity of 1.105, a 10.5% increase in the ratio of 1 ,, / Ij with an increase in the methane content of 1 absD by volume. Under these conditions, minimum aggregate values are also observed. Neither fluctuations of dust content, pressure and temperature of the mine atmosphere are affected. So with an increase in the dust content of the mine atmosphere by 10%, i.e. from 300 to 330 mg / m, the ratio j decreases only by 1.3%, i.e. by 0.12% for methane. With an increase in relative humidity from 0.8 to 0.9, i.e. by 10% at 35 ° C, the ratio J) decreases by 1%, i.e. less than 0.1% methane. Increasing the pressure by 10% of the nominal results in a reduction of the ratio by 0.5%, i.e. less than 0.05% in methane readings. An increase in temperature from 35 to 45 C leads to an increase in the ratio Ij / 1- by 0.12%, i.e. to changes in performance less than 0.012% by volume in methane. The L 1 and L 1 values during adjustment are L, 60 mm mm with the passband width of the filters 12 and 13 from 13.9 to 3.59 µm.

After alignment, the device is calibrated, the drive is in one-to-one correspondence with the readings of block 17, and the masking and registration (proportional to the ratio I / T -) with methane concentration C. Graduation can be carried out by any known method, for example, using the least squares method on gas calibration mixtures.

Claims (1)

Invention Formula The method for determining the concentration of methane in the mine atmosphere by catalytic oxidation of methane on the heated ale, nte, and recording the intensity of optical radiation from this element, is different in that, in order to improve the accuracy by increasing the speed changes in the output signal when the methane concentration changes while reducing the effects of fluctuations in dustiness, humidity, pressure and temperature; the element is heated to 580 ° C with a stabilized electric current; optical radiation intensity is measured in a band of 3.19-3.59 µm from two parts of the element, one of which is isolated from the mine atmosphere, and the intensity I, of the optical Radiation from the non-insulated section is recorded at a distance L ,, cnipn- divisible from the ratio bl., and intensity I i from isolate (cfg11) ha - at the distance LI determined by the ratio, where b is the absorption coefficient of the meter radiation in the specified lane. C, is the maximum h of the given concentration of metpna, C (. P is the average concentration of methane, and the concentration of methane is judged by the ratio of I g / T li Compiled by D, Pakhomov Editor N. Bobkova Tehred M. Morgental Proofreader M. Pojo Order 7828 Circulation 789 VNIIPI State Committee for Inventions and Discoveries at the State Committee for Science and Technology CdС 113035, Moscow, Ж-35, Raushsk nab., I / 5 Subscription