SU1704017A1 - Method of determination of contact strength of frozen coal - Google Patents

Abstract

The invention relates to a technique for testing materials, in particular, to methods for determining the contact strength of frozen coals. The purpose of the invention is to increase productivity in determining the strength of frozen coals in a wide range of humidity. The prepared samples of the coal are immersed in water and allowed to stand for a certain time to ensure the moisture content Wm corresponding to the limiting water capacity of the samples. The samples are then frozen and destroyed by inserting an indenter at a fixed negative temperature, while determining the fracture toughness of the sample. Additionally, the strength of ice P is determined at the same negative temperature. For coal of arbitrary degree of moisture, the strength is determined by the formula: P = VV- [Kn'Pm Ku + W Ku + W 4-1 KY + W -y 'I, Wm / (W4 Wm) - KiHKu + VVKu + VV + \ X PmWm /

Description

The invention relates to test equipment and can be used to determine the strength of the destruction of frozen coals with a high degree of humidity.

The invention can be used to calculate and optimize the operation of machines and devices grinding ground frozen mass.

A known method for determining the strength of destruction of the rock mass is that a non-through hole is made in the rock sample, into which the indenter is inserted, is impacted upon it until a through hole is formed in the sample and the diameter and depth of the well are judged about the strength of the destruction of the rock. (Malt VI. Zaikov VI and Pervov KM Mining machines and automated complexes. M .: Nedra, 1981, p.8).

The disadvantage of this method is its laboriousness and complexity of testing, since it is impossible to determine the strength of a material when its humidity varies over a wide range without multiple tests. The closest in technical essence to the present invention is a method for determining the ultimate strength of rocks (A.N. Ne 1422104, C 01 N 3/32). in which a stepwise increasing load is applied to the test specimen and after each load step a partial discharge is applied to the load equal to the first step, and the strength limit is judged by the voltage at which the deformation increments corresponding to the partial discharge reach a minimum value.

Determination of long-term strength of the frozen mountain mass.

At low temperatures and varying degrees of moisture of the rock mass, the value of the limit of long-term strength, thus determined, is unstable and cannot be used as a starting point for calculating and optimizing the operation of machines and mechanisms that grind frozen mountain mass.

The aim of the invention is to improve the performance in determining the strength of frozen coals in a wide range of humidity.

This goal is achieved by the fact that in the method of determining the contact strength of dead coals, including sample preparation, destruction of this sample by introducing an indenter and registering the breaking force, according to which contact strength is evaluated, the sample is prepared by freezing coal samples with moisture equal to the limiting water content , the destruction of the sample is carried out at a fixed negative temperature, then the strength of ice is determined at the same temperature, and the strength of the frozen coals in This remaining humidity range is determined by the formula:

 one

where W is the mass of frozen moisture in fractions of the mass of the sample;

Рш - sample duration at a fixed temperature and humidity equal to the limiting water capacity;

Wm is the humidity corresponding to the limiting water capacity; „

RL ice strength at a fixed temperature;

Ki is the coefficient depending on the shape of the cross section and the rate of introduction of the indenter;

Ku is the coefficient depending on the properties of the angles.

Preparing the sample by freezing the coal sample with a moisture content equal to the limiting water capacity and destroying the sample at a fixed negative temperature allows one to directly determine the maximum fracture strength of the frozen rock mass. (This was proved experimentally on repeated experiments with different grades of coal at different degrees of watering of the rock mass and negative temperatures in the range from {-) 5 ° С to (-) 40 ° С.

Determination of the strength of the destruction of ice with fixed negative

temperature allows once obtained dependence of the strength of the frozen water on the value of negative temperature to use in the future when determining the characteristics of the rock mass coming from the supplier to the consumer. Since coal is transported mainly in open ponds, in winter time due to accumulated snow in the empty air and rainwater in loaded wagons in the lower layers of the wagons.

a certain amount of ice or rock mass, extremely saturated with gravitational water, and then frozen into a monolith accumulates. As deep and comprehensive studies of the problems of transportation and processing of frozen fuel fed to thermal power plants show (Mikhailov, NM, Combating Difficulties When Wet or Deadly Fuels Enter the Power Plants, M; Gosenergoizdat, 1951,

p.204) (I) and later observations (Pasko V.I. Thermometeorological method for diagnosing machines for crushing hardened solid fuels. Abstracts of VTNR on the introduction of technical diagnostics at TPPs. Gorlovka, 1988, p.34), in most cases fuel is discharged from the lower part of the cars to the receiving lattices of the wagon dumpers in the form of frozen blocks, does not pass through

cells and must be processed by machines and devices. Thus, determining the strength of the destruction of frozen water, wet snow is particularly important.

(ice, descent from water or wet snow), as well as the strength of the destruction of the rock mass, wetted to the state of maximum water compatibility. The latter term, according to the author, will be the most

suitable as gravitational water, the volume of the mountain mass, taking into account all types of moisture. Since the specific gravity of the solid component of the rock mass is higher than that of water, the limit of its content is determined by

the lower layer, filled with water of the rock mass, to the upper layer, in which there are particles of coal. As discussed above, samples of rock mass with humidity corresponding to the limiting water capacity,

most closely corresponds to the maximum strength of the studied rock mass than other typical types of moisture.

wire no (time-consuming) tests, with sufficient accuracy for practical purposes, quickly determine the strength characteristics of the rock mass in the entire range of changes in the content of freezing moisture in it by simple calculations, the error does not exceed 3% compared to the traditional method of testing: by repeating them repeatedly and processing.

In the technique known method for determining the strength of destruction of the frozen fuel on the cement machine (I). However, the conditions of destruction on a cement machine correspond more to the conditions of separation of the frozen fuel when it is unloaded from the cars than the processing by mechanisms on the receiving gratings of car dumpers (force of compression damage). It also proposes a formula characterizing the dependence of the breaking force on the humidity and cooling temperature, but it is not possible to calculate the strength of mass destruction during wetting more than the maximum water capacity (for example, the strength of lumps consisting mainly of frozen water and compacted snow).

Figure 1 shows the dependence of the destructive effort of coal samples of the Cherepovets Ust-Don promprodukt product at a temperature of (-) 12 ° C and (-) 22 ° C and changes in the frozen moisture in the samples from 0 to 1.

Figure 2 shows the dependence of the measurement of the mass component of coal on the amount of water in the sample.

The dots indicate the results obtained experimentally, the solid line shows the calculated dependence, and two points from the experimental data P and, cm, determined from the total moisture W taking into account the safe humidity WeCW 0) and its proportional decrease in the sample with a decrease in the mass component of coal in the sample with an increase in the component water in n, robe (Fig. 2).

The method is carried out as follows.

Prepare several batches of a certain sample, place them in waterproof cups and pour water to a level well above the level of coal in the cup. The sample is held in water for a certain time (for example, the time the cars with coal are in transit). The sample is stirred 2-3 times during the holding time. Water above the coal level is removed. The moisture left in the coal corresponds to the limiting water capacity.

Then freeze the sample in the refrigerating chamber. In the refrigerating chamber, the sample is destroyed (6-8 samples), registering the force at which they are destroyed. The freezing and destruction of water or snow is carried out in the same way as the accompanying transportation of coal in wagons (using previously obtained data).

The obtained values of Pt and Pg substitute the B formula and plot the change in the strength of destruction P at a change in the moisture content of the freezing point in the WCM sample from 0 to 1.

Example. Prepare 8 batches of coal brand Cherepovets-Ust-Don industrial product (W 8.9 A 44.6) entering the Kurakhovskaya GRES. Sample taken after the sampler. Piece size from 3 mm to O. The total weight of one sample of wet fuel is about 50 g. Exposure in water for 2 hours. Freeze in the refrigerator MMM-52 for 3 hours to (-) 12 ° C. A cylindrical D indicator of 11.28 mm is used to destroy, record the force of destruction by samples using a DOSM-3-1 Nfc 613 dynamometer. Weigh weights on an analytical balance, dry in a drying cabinet and determine the total moisture content. The results are tabulated. The strength of ice is determined in a similar manner. According to the described method, the value of safe humidity W6 (W6 0.07) is determined.

Process test results. The curve P (W) is constructed according to the proposed formula with the help of the MK-61 microcalculator. (Ki 1.9; Ku 1).

As can be seen from the above example, it takes about 10 times less time to find the dependence P (W) than the traditional method. Taking into account the reuse of data on the strength of the destruction of ice at a fixed negative temperature, the essence of the method is reduced to registering the effort to destroy the whole and one point P (Wni) and to calculate.

The economic effect of the introduction of this method can be obtained in the aggregate, when it is used to optimize the operation of cutting systems of frozen solid fuel on the grids of receiving hoppers of car dumpers: the value of which can reach 40,000 rubles / year when two four-support car dumpers operate at one power plant.

destructive force, which measures the contact strength, characterized in that, in order to increase productivity in determining the strength of frozen coals in a wide range of humidity, the sample is prepared by freezing a sample of coal with a moisture equal to the maximum water capacity, the sample is destroyed at a fixed negative temperature then determine the strength of the ice at the same temperature, and the strength of the frozen coals throughout the rest of the humidity range of the determinant

KH-PmWn y +

p w

Yy (ky-fw -1) d, j; ky-fw- -1). Ki-pm-wn v + w

+ WG

 14-wj; y + + o

where W is the mass of frozen moisture in fractions of the mass of the sample;

RSH is the strength of the sample at a fixed temperature and humidity equal to the limiting water capacity:

Wrn is the humidity corresponding to the maximum water capacity;

Rl - ice strength at a fixed temperature;

Ki is the coefficient depending on the shape of the cross section and the rate of introduction of the indenter;

Ku is the coefficient depending on the properties of coal.

W,

0.5 Fi2.1

.0 We

0.5

Oh and //

f.OIV