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№ 2(131)
февраль, 2025 г.
PAPERS IN ENGLISH
CHEMICAL ENGINEERING
EXPERIMENTAL STUDY OF THE EFFECT OF TECHNOLOGICAL INDICATORS ON THE DURABILITY OF COAL BRIQUETTES
Khakimov Akmaljon
PhD in Technical Sciences, Associate Professor, Fergana Polytechnic Institute, Republic of Uzbekistan, Fergana E-mail: [email protected]
Azizjon Isomidinov
PhD in Technical Sciences, Associate Professor, Fergana Polytechnic Institute, Republic of Uzbekistan, Fergana E-mail: asisomidinov@ferpi. uz
ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ТЕХНОЛОГИЧЕСКИХ ПАРАМЕТРОВ НА ПРОЧНОСТЬ УГОЛЬНЫХ БРИКЕТОВ
Хакимов Акмалжон Ахмедович
PhD, доцент,
Ферганский политехнический институт, Республика Узбекистан, г. Фергана.
Исомидинов Азизжон Саломидинович
PhD, доцент,
Ферганский политехнический институт, Республика Узбекистан, г. Фергана
ABSTRACT
In this research work, the effect of various technological parameters on the strength of briquettes during the bri-quetting process by adding a binder of coal fines was investigated. As an object of research, small lumps of coal from Angren coal mines and a variable pitch screw press device for pressing it were selected. Experimental studies in the following limits of variable parameters liquid content 10^20 %, nozzle diameter 20; 25 and 30 mm; the compression force of the pressing screw is 1.8; 2.4 and 3 kN and the diameter of the working chamber was 120 mm. Based on the experimental results, it was determined that 10-12 % moisture is considered optimal for briquetting.
АННОТАЦИЯ
В данном исследовании изучалось влияние различных технологических параметров на прочность брикетов в процессе брикетирования угольных частиц с добавлением связующего вещества. Объектом исследования выбраны угольные брикеты, добываемые на угольных шахтах Ангрена, и пресс-устройство с переменным шагом шнека для их прессования. Экспериментальные исследования показали, что используются следующие пределы варьируемых параметров: содержание жидкости 10^20 %, диаметр мундштука 20; 25 и 30 мм; Сила сжатия прижимного винта составляет 1,8; Также были испытаны 2,4 и 3 кН и диаметр рабочей камеры 120 мм. На основании результатов эксперимента установлено, что оптимальной для брикетирования является влажность 10-12 %.
Keywords: briquette, moisture, strength, adhesion, granulometric content, screw press, compression force, pressing pressure.
Ключевые слова: брикет, влажность, прочность, адгезия, гранулометрический состав, шнековый пресс, усилие прессования, давление прессования.
Библиографическое описание: Khakimov A., Isomidinov A. EXPERIMENTAL STUDY OF THE EFFECT OF TECHNOLOGICAL INDICATORS ON THE DURABILITY OF COAL BRIQUETTES // Universum: технические науки : электрон. научн. журн. 2025. 2(131). URL: https://7universum.com/ru/tech/archive/item/19259
Materials and methods
Introduction
It is known that the granulometric composition of coal and the distribution of grains of different sizes should correspond to its maximum compressibility, which ensures the greatest strength of the bonds between the binder and the grains and the high strength of the briquettes. Therefore, the principle of selecting mixtures of particles of different sizes for the optimal mass density is based on the theory of the most dense pressing of the grains. An incorrectly selected sieve or inattention to the process will require filling the space between the coal grains with a mixture of the binder or its small coal grains, the necessary bonding between the coal grains will be disrupted, which will make it impossible to obtain briquettes of the required strength. Preliminary studies on determining the granulometric composition of coal and studying its effect on the mechanical properties of the resulting briquettes have shown that increasing the pressure allows, in particular, to obtain briquettes from the smallest coal (coal class 01, 2.5 mm). The reason for this is that when briquetting finely divided coal, the interacting surface decreases, but the active contact surfaces with the binder increase to the maximum, the role of the so-called active centres on the solid surface increases, adsorption interactions at the coal boundary increase, the solid and liquid phases increase, and the distribution of binders into pores and cracks continues more effectively, which leads to an increase in strength [1,2].
It was found that the strength of composites made of coal particles with a particle size of 2.5-5.0 mm is approximately 3 times lower than the strength of briquettes made of coal with a particle size of 0-1.25 mm with the same briquetting parameters. This is due to the fact that during pressing, large coal particles disperse and additional non-wetting surfaces appear that do not bind. It is not logical to use samples made of coal dust only, despite the high pressure, because the briquetting process involves labour-intensive pressing and sorting operations, so for further studies, we used the optimal coal. In this case, the particle size is less than 2.5 mm [3].
Thus, we can say that brown coals, regardless of their source, contain up to 60 % fines. It is necessary to obtain high-quality briquettes from them by adding local binders with optimal geometric dimensions. At the same time, it is important to study their chemical composition and physical and mechanical properties in advance [4,5].
The briquetting process is not only a mechanical but also a chemical-technological process, because the mechanical strength, energy efficiency, porosity and other indicators of the obtained briquettes depend on many chemical compounds.
To date, the role of moisture in the briquetting process of various types and compositions of coal has been studied in detail [6]. However, these technological parameters are not sufficient to select the optimal conditions for carrying out this process [7].
The moisture content of coal, which is one of the important factors for the production of briquettes, determines the mechanical properties of the resulting briquettes. Moisture forms a hydrated film on the surface of coal grains, which affects the strength of the bond between the binder and the coal. The analysis of numerous studies [8,9,10] has shown that high humidity forms a liquid film on the surface of coal briquettes, which prevents the binder from adhering tightly to the coal, at the same time, the wetting of the internal structure of the coal by the binder decreases, and thereby its mechanical strength decreases, the quality of the resulting briquettes deteriorates, in addition, when the hot binder comes into contact with the coal, the moisture on the surface of the coal evaporates intensively, which reduces the cooling and wetting ability of the binder. The optimal values of briquette moisture were determined by us depending on the value of the compressive force applied to the samples, i.e. at the minimum and maximum pressing force [11].
Based on the above, the influence of various technological parameters on briquette durability was studied. As a research object, small pieces of coal from Angren coal mines and a variable pitch screw press device for pressing it were selected. Figure 1 shows an overview of a variable pitch screw press.
Experimental studies in the following limits of variable parameters liquid content 10^20 %, nozzle diameter 20; 25 and 30 mm; The compressive force of the pressing screw was selected as 1.8; 2.4 and 3 kN and the working chamber diameter was 120 mm. When conducting the research, the humidity and temperature of the external environment (taking into account that the experimental research was conducted in May and June, the average external temperature was selected as 30o for the conditions of the Fergana region of the Republic of Uzbekistan, and the air humidity was 18.7 %) were taken into account. The experimental research was conducted in two stages.
LATR TAYANCH RAMA
Figure 1. Overview of the briquetting device
Results and discussion
Initially, 5 mm coal particles obtained from the Angren coalfields were mixed with 10,11,12.....20 % water
to prepare a mass, and coal briquettes (not less than 5 kg of briquettes for each percentage of added water) for different values of the variable parameters were bri-quetted in a variable pitch screw press. In the test work, briquettes from 30 samples taken separately for the case of press force 1.8; 2.4 and 3 kN const were dried under natural conditions and the moisture content of each sample was determined. Measured in a UT-377A moisture meter. Sample briquettes were checked for durability in two different ways.
Initially, the strength was tested according to the requirements of GOST 21289-2018 and ISO 1213-1 [12]. The essence of this method is to drop briquettes loaded into a container with an opening bottom from a certain height onto a metal plate at least 4 times from a height of 1.5 m under certain conditions and determine the impact resistance, measured as a percentage of the mass of the resulting briquettes. For the experiments, a rectangular laboratory sieve with dimensions of 750x600 mm, a side height of 200 mm, and a P25-5 mesh according to GOST 3306 [13] was prepared (the lower part of the sieve was equipped with a container with two opening shelves measuring 300x250x250 mm for testing briquettes by dropping them). A pre-weighed sample of at least 5 kg of whole briquettes was placed in a sieve with a bottom opening and dropped onto a metal plate from a height of 1.5 m. All briquettes on the plate, including any individual pieces that fell off the edge
of the plate, were collected and placed back into the container, and the dropping process was repeated. After the fourth drop, the test briquette pieces were collected and sieved on a laboratory sieve until the product under the grate stopped separating.
The test results were calculated according to the following formula, %;
ПМС — '
•100
(1)
Where, m is the mass of the product on the sieve with a particle size of 25 mm or larger after the test, kg;
M- mass of tested briquettes, kg.
The results of each obtained experiment were calculated according to the formula (1) and the total amount range was determined.
In the second method, a laboratory model of the VP-300 durability testing machine was used for durability testing. Experiments were conducted in the following sequence. Initially, the briquette products produced in different variable parameters for the experiment were checked according to the procedure. Figure 2 illustrates the process of testing the robustness of a single unit.
Experiments were conducted in the following sequence. Initially, the briquette products produced for the experiment with different variable parameters were checked according to the procedure in the laboratory model of the VP-300 durability testing machine. Figure 2 illustrates the process of testing the robustness of a single unit.
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№ 2(131)
февраль, 2025 г.
Figure 2. Briquette durability testing process on VP-300 durability testing machine
The results of each experiment were repeated 5 times, and the arithmetic mean values were selected and compared with the values determined in the first method, and a correlation graph was constructed. Figure
3 shows the dependence of briquette strength on compressive strength versus charge moisture content.
1-1.8 kN-const; 2-2.4 kN-const; 3-3.2 kN-const; Figure 3. Dependence of briquette strength on compaction moisture content
Figure 3 shows that with increasing coal moisture content, the mechanical strength of the resulting briquette decreases, which is clearly observed when the coal moisture content is 10-12 %. As a result of the breakdown of the adsorption contact between the phases that occurs when the initial coal moisture content increases from 10 % to 20 %, the adhesion process between coal and the binder slows down, which, in turn, leads to a decrease in strength. In addition, the bonding of moisture and coal powder also depends on external
forces. For example, an increase in the pressing force on the tested object increases the strength. The amount of water in the mass has almost no effect. However, the energy consumed in the process increases. Based on this, it was found in experiments that 10-12 % moisture is considered optimal for briquetting.
The graphical relationships presented in Figure 3 can be expressed by the following empirical equations determined by the least squares method [14, 15].
When 1-1.8 kN-const;
y = -0,0023x2 - 0,0086x + 8,4989 R2 = 0,9974
(2)
When 2-2.4 kN-const;
y = -0,0022x2 - 0,0084x + 8,3078 R2 = 0,9989
(3)
When 3-3.2 kN-const;
y = -0,0022x2 - 0,0082x + 8,121 R2 = 0,9981
(4)
The graph in Figure 3 shows that the error coefficient between theoretical and experimental studies is not significantly large and meets the technical requirements for research work, i.e. the error coefficient between theoretical and experimental values does not exceed 2 %, and the polynomial linear correlation value in the graph is not less than P2=0.99. This indicator indicates that the experiments were carried out correctly.
Conclusions
Technological indicators form a correlation relationship with the parameters of the obtained coal briquettes, in particular, the moisture content of the
briquetted coal particles, the strength of the obtained briquette, the pressure in the press, the strength of the resulting briquette, and other indicators. For example, an increase in humidity during the production of coal briquettes sharply reduces the strength correlation line. This, in turn, leads to a violation of the mechanism of bonding between moisture and coal particles in the internal structure of the briquette. A decrease in humidity also has a negative effect on the bonding mechanism. As found in the research work, the moisture content of the coal class 0-1, 2.5 mm, in the range of 10-12 %, causes the briquette strength to be 7-8 Pa. This, in turn, satisfies the established technological regulations.
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