RU2747022C1 - Thermogravimetric method for evaluating the quality of shealing of mines - Google Patents

Abstract

FIELD: mine working safety.SUBSTANCE: invention relates to safety measures in the development of deposits of combustible minerals and can be used to assess the explosiveness of deposits of a mixture of coal and inert shale dust. The thermogravimetric method includes taking samples of mine dust, followed by determining the percentage of inert (shale) dust in the mixture of additives and comparing it with the mine dusting rate. The dust sample is placed in the receiving container of the thermal balance. Simultaneous isothermal heating is carried out at the temperature of thermal decomposition. The changes in the mass of the sample are recorded by periodic weighing. The content of incombustible additives of shale dust is determined by the characteristic points of the obtained thermoanalytical dependences.EFFECT: technical result is to increase the efficiency and accuracy of quality control of the mine workings dusting.1 cl, 2 dwg, 1 tbl

Description

The invention relates to mining, namely to safety in the development of deposits of combustible minerals, and can be used in assessing the explosiveness of deposits of a mixture of coal and inert shale dust, applied as a preventive measure in mine workings, developing seams, hazardous by explosions of coal dust.

The dust of most grades of coal, with the exception of anthracite, is classified as hazardous for explosions and dusting or inertization is used as a preventive anti-explosion measure. In this case, coal dust settled in the mine is mixed with non-combustible dust based on limestone (dolomite) with hydrophobic additives in accordance with GOST R 51569-2000 (Inert dust). Inert dust has an additional name - shale dust, and the process of mixing it with coal dust to neutralize the explosive properties is called shale dusting.

Shale dust explosion protection is provided for by the current regulations: Safety Rules (approved by Rostechnadzor Order No. 449 dated October 31, 2016), Instructions on dust control and dust explosion protection. Initially, for each coal seam, the norm of dusting is determined by normative means - the minimum allowable content of non-combustible particles in the mixture, at which the dust will not be explosive (N). After the operation of polishing, the quality control of the work is carried out, which is reduced to determining the actually obtained content of non-combustible (shale) dust in the mixture (N _fact .). The conclusion about the quality of polishing is made on the basis of a comparison of the actual value N _fact and the required N, while the ratio N _fact ≥ N must be fulfilled.

Known methods for quality control of neutralization of the explosive properties of dust (or the quality of flanching), based on 3 physical principles of measurements: optical, radioisotope and chemical.

There is a known method of quality control of the dusting of mine workings by the content of inert dust (USSR author's certificate No. 420790, class E21F 5/00, published 03/25/1974, BI No. 11). The essence of the method lies in the fact that the selected dust sample is placed on the substrate and a beam of light is directed at it, and the reflected flow is captured using a photocell and the converted signal is analyzed in the measuring unit. The parameters of the light beam reflected by the dust depend on the ratios in the sample of inert (light) and coal (dark) dust.

The disadvantage of this method is the complexity of the design, the need to adjust the device for each grade of coal and each coal seam. Industrial devices based on the optical principle of operation: CDEM-1000 (USA), FotoPylox (Poland). In the Russian Federation, devices based on the optical measurement principle have not found industrial application.

A known method for determining the content of incombustible substances in a mixture of coal and inert dust (USSR author's certificate No. 1711049, class G01N 23/22, published on February 7, 1992, BI No. 5).

The method includes irradiation of the investigated and two calibration samples with beta radiation, registration of backscattered beta radiation and determination of the content of incombustible substances from the obtained data. An equivalent measure of the mass fraction of non-combustible substances made from a homogeneous solid material is used as one of the calibration samples. The other is a sample of inert dust, used to polish a given mine.

The main disadvantage of the known radioisotope method is its low accuracy, especially when working with wet dust (up to ± 20%). When working with devices based on this principle, great difficulties arise in metrological support, as well as the need to use special modes of operation and disposal of radioactive materials. These devices have not found practical application in the coal industry.

A known method for assessing the quality of preventive treatment of coal dust deposits (RF patent No. 2249816, IPC G01N 31/00 (2000.01), published on April 10, 2005, bull. No. 10), based on chemical reactions of decomposition of substances with acid and adopted as a prototype of the proposed method.

The essence of the method consists in placing a selected dust sample in a sealed vessel (flask) and exposing it to citric acid, which enters into a chemical reaction with the limestone component of the sample with the release of carbon dioxide while processing the sample with ethyl alcohol, and the content of incombustible particles in the sample is determined by the amount of released carbon dioxide.

The disadvantages of the chemical method are:

- the presence of a period of uncertainty during which the flask with the acid and the sampler placed in it must be inserted directly into the instrument. During this period, the reaction of chemical decomposition of limestone has already begun, and measurements are not yet carried out. The duration of this period is not defined, which affects the accuracy of measurements;

- the complexity of the design, providing for the presence of sealing devices (thread or sleeve made of elastic material) between the chamber and the channel, the presence of a gas flow sensor, as well as the presence of chemicals (hydrochloric or citric acid, ethyl alcohol) in a removable vessel;

- the need to replace flasks and chemicals for each measurement.

A thermogravimetric method for assessing the quality of mine workings dusting is proposed, based on studies of the processes of thermal decomposition of limestone-coal mixtures in various ratios from 0% coal dust to 100% coal dust in the mixture.

The methods of thermal analysis have been sufficiently developed, there is commercially available equipment (thermal balances), the high accuracy of their results has been practically proven ¹ ( ¹ Wendlandt U. Thermal methods of analysis. - M .: Mir, 1978. - 526 p.). Basic terms, characteristics and characteristic points of thermal analysis processes are defined in GOST R 53293-2009.

The proposed thermogravimetric method differs from the previously known methods:

- the lack of optical sensors with a system for recognizing the intensity of the reflected light;

- absence of radioactive materials in measuring devices;

- lack of chemical reagents and containers for carrying out chemical reactions;

- no need to seal the sample to capture and measure the volume of evolved gas during chemical decomposition of the sample, the absence of a gas flow sensor, as well as the absence of a period of uncertainty - the time for installing a removable test tube with a reagent and a sample into the device when the chemical reaction has already begun, and measurements are not yet taken ;

- lack of consumables or replaceable materials.

The main advantage of the proposed method is the high accuracy of the assessment, the ability to carry it out in a short time and safety for the maintenance personnel due to the absence of hazardous radioisotope or chemical materials. The measurement accuracy does not depend on the degree of coal metamorphism, moisture content and ash content of the sample. Thermoanalytical dependences used in the method make it possible to determine a number of additional parameters (for example, the numerical determination of the moisture content of the sample), which significantly clarifies the process of classifying the dust sample as non-hazardous due to explosions.

The essence of the proposed method lies in the fact that in the thermogravimetric method for assessing the quality of mine workings flanching, including sampling mine dust, followed by determining the percentage of inert (shale) dust in the mixture of additives and comparing it with the mine flaking rate, the dust sample is placed in the receiving tank of the thermal balance and simultaneous isothermal heating is carried out at a temperature above the critical one and the change in the sample mass is recorded by periodic weighing, and the content of incombustible additives of shale dust is determined by the characteristic points of the thermoanalytical dependences.

When using the thermogravimetric method, samples are taken of coal dust deposited in the workings. The sample contains a coal-limestone mixture (hereinafter referred to as a mixture). The sample is placed in a thermogravimetric unit consisting of a heating element and a balance (thermal balance). On a thermal balance in the process of heating the sample, moisture is removed at the first stage, followed by the stage of thermal decomposition of the coal components of the mixture (release of volatiles from coal) and at the final stage, thermal decomposition of CaCO ₃ limestone into quicklime CaO and carbon dioxide CO ₂ (release of volatiles from CaCO ₃ ). During the thermal decomposition of the mixture, the mass of the sample, initially taken as 100%, decreases. The moment of time at which the mass stops decreasing is considered the time of complete thermal decomposition of the mixture T, sec. This time is different for different content of limestone in the mixture and ranges from 1 to 5 minutes in an isothermal heating mode with a temperature above the critical in relation to limestone. The studies have shown that the percentage of limestone in the sample is determined with high accuracy by the time of thermal decomposition T.

The technical result of the proposed thermogravimetric method is to increase the efficiency and accuracy of quality control of the mine workings dusting.

The essence of the invention is illustrated by an example of its implementation and graphic images (Fig. 1 and Fig. 2), which show two main stages: determination of T _meas - the time of complete thermal decomposition of the sample (Fig. 1) by the characteristic point of thermoanalytical dependences (hereinafter - the time of thermal destruction) and assessment of the content of carbonate dust in the selected sample by the time T _meas (Fig. 2).

Example.

For each test sample of dust during thermogravimetric analysis (according to GOST R 53293-2009), characteristic thermoanalytical curves are plotted: TG curve (or function of weight loss over time) and DTG curve (or function of rate of weight loss).

FIG. 1 shows thermoanalytical dependences for 3 mixtures of coal and limestone dust:

sample No. 1 - 100% limestone (curves TG and DTG, respectively 1 and 1 ');

sample No. 2 - 67% limestone and 33% coal (curves 2 and 2 ');

sample No. 3 - 50% limestone and 50% coal (curves 3 and 3 ').

At the top of FIG. 1, TG curves numbered 1, 2, 3 have characteristic points A, B, C, denoting the time of thermal destruction when the decrease in the mass of the sample stopped. When moving along the arrows to the abscissa axis, the time values T _x are obtained, where the subscript ("x") corresponds to the content of shale dust in the sample: T ₁₀₀ ; T ₆₇ , T ₅₀ . Located at the bottom of FIG. 1 DTG curves (1 ', 2', 3 ') make it possible to clarify the end of the thermal decomposition process.

As seen in FIG. 1, the higher the CaCO ₃ content, the longer the process of thermal decomposition of the limestone-coal mixture takes, therefore the following expression takes place:

In the general case, the dependence of the value of the actual content of incombustible components in the dust sample ² is experimentally determined ( ² In the general case, a correction is introduced for the natural ash content and moisture content of the sample) as a function of time T:

The values of function (2) are experimentally determined with a step of 5-10% (Table 1) or in the form of an approximated functional dependence (Fig. 2).

According to the proposed method, after placing the sample in a thermobalance dust and application of the desired mode is determined by the heating time T thermodestruction _edited (for the example in FIG. 2 T _MOD = 160 sec). Next, referring to FIG. 2, when moving along the arrow, N _fact is calculated - the content of shale dust in the sample under study.

In the example of FIG. 2 N _fact = 61.5%.

The feasibility of the proposed method is demonstrated by the immediate results shown in FIG. 1 and FIG. 2, made for mixtures of shale dust (shale dust produced in accordance with GOST R 51569-2000) and coal dust of power-generating coal grade "D" of Kuzbass mines.

The implementation of the method will be in demand for all coal mines, hazardous for gas and coal dust explosions.

Claims (1)

Thermogravimetric method for assessing the quality of mine workings shale formation, including sampling of mine dust with the subsequent determination of the percentage of inert - shale - dust in the mixture of additives and comparison with the mine shale dusting rate, characterized in that the dust sample is placed in the receiving tank of a thermal balance and isothermal heating at a temperature thermal decomposition of the sample and fixing the change in the weight of the sample by periodic weighing, and the percentage of incombustible additives of shale dust is determined based on the time of complete thermal decomposition of the mixture of coal-inert dust.

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