ANALYSIS OF THE DISPERSE COMPOSITION OF DUST OF COTTON CLEANING INDUSTRIES

ABSTRACT

Annotation. The article determines the dispersion composition of dust in the air emitted into the atmosphere after cleaning from a cyclone device used at a cotton gin. A laboratory analysis was carried out to determine the percentage of dust by mass, as well as the median size of the dust emitted to the atmosphere. As a result, it became possible to determine the relative contact surfaces of dust particles. This, in turn, is important for comparison with the relative contact surface of the liquid droplets sprayed onto the device and for the correct choice of the ratio of liquid and gas flow rates.

АННОТАЦИЯ

В статье определен дисперсионный состав пыли в воздухе, выбрасываемой в атмосферу после очистки от циклонного устройства, используемого на хлопкоочистительном заводе. Проведен лабораторный анализ для определения процентного содержания пыли по массе, а также медианного размера пыли, выбрасываемой в атмосферу. В результате появилась возможность определять относительные контактные поверхности пылевых частиц. Это, в свою очередь, важно для сравнения с относительной контактной поверхностью распыляемых на устройство капель жидкости и для правильного выбора соотношения расхода жидкости и газа.

Keywords: cotton, dusty gas, wet method, liquid, dispersion composition, cyclone, percentage, average size.

Ключевые слова: хлопок, запыленный газ, мокрый способ, жидкость, дисперсионный состав, циклон, процентная доля, средний размер.

Introduction

Currently, in the cotton ginning industry, a large amount of dust is generated during the initial processing of cotton. As a result, it causes great damage to the environment. In addition, dust pollution of the air of production buildings has a great impact on the health of workers working there. Currently, single-stage and two-stage dust removal equipment are used in cotton ginning factories to remove dust from the environmental point of view. Dust from cotton ginning plants is sucked by a fan and sent to cyclones, through which it is cleaned and released into the atmosphere. Cleaning efficiency of cyclones in cotton cleaning plants is 60-85% [4]. In cyclones, very small (1.0-10.0 μm) dust particles escape into the atmosphere without being caught. The amount of dust in the air in the production buildings of the cotton ginning plant should not exceed 10 mg/m³. Dusty air released into the atmosphere is 300-350 mg/m³. It can be seen that the concentration of dust in the enterprise is much higher than the norm.

Research object

It is important to determine the dispersion composition of the dust when determining the cleaning efficiency of the dust cleaning device recommended by us and determining the optimal values [1,2,3,5]. For this purpose, samples of dust cleaned by cyclones from the shops of the “Beshariq” cotton cleaning enterprise in Fergana region were analyzed according to the dispersion composition.

Obtained results

Dust samples caught in the process of cleaning dust in a cyclone in a cotton factory were taken out of the cyclone and 500 grams were weighed on a laboratory scale, and cotton fibers were separated into organic compounds (Figure 1).

Figure 1. Dust samples from the cyclone

The dispersion composition and size distribution of these dusts were carried out in two stages: 1- by using a sieve and 2-microscopic laboratory analysis.

In the first step, the dust separated from the cyclone was subjected to 10-step sorting on a RETSCH-DIN-ISO 3310/1 brand sorting laboratory sieve (Fig. 2). The size of sieve meshes was selected up to 850, 600, 425, 250, 125, 100, 75, 53 μm. Based on the obtained results, the dusts were divided into fractions in percentages (Table 1).

Table 1.

Sieve analysis of dust sample

In the second stage, the dusts were crushed for 5 minutes in the laboratory model of the LM-2Е brand sieving device (runner) and were subjected to 7-stage sorting for 5 minutes through the RETSCH-DIN-ISO 3310/1 brand sorting laboratory sieve. The size of the sieve meshes was selected up to 1, 3, 5, 10, 20, 40, 60 μm (Fig. 2).

Figure 2. RETSCH-DIN-ISO 3310/1 sorting sieve laboratory device

Based on the obtained results, the dusts were divided into fractions in percentages. The following are the results of post-crushed laboratory analysis of cotton dust samples (Table 2).

Table 2.

Sieve analysis of dust sample in crashed condition

In the third stage, the method of optical microscopy was used to determine the dispersed composition of dust. The relative error of particle analysis in a biological microscope is ±1.5%. The relative error of the measurements to the average value is ±3.4%.

Figure 3. Overview of the BM-1800 biological microscope

In optical microscopy method, photographs were taken of each of the dust samples from the cyclone device and the crashed dust samples (Figures 4 and 5). A hair fiber was used as a scale to determine the size of the dust samples and fractionated in percentages. The average median size of a hair fiber is 40 μm.     Photography was carried out on a BM-1800 biological microscope (Fig. 3). Photo processing was done based on computer program. The magnification degree of the microscope is up to 400 times, the dimension of  the dust samples was determined  in percentages with comparison  1÷100 μm interval relative to the hair fiber.

Figure 4. Microscopic view of cyclone dust and cotton fiber samples

Figure 5. Microscopic view of dust ejected from the cyclone into the atmosphere

Laboratory analyzes show that dust from cotton raw materials consists of organic and mineral fractions. Organic fractions consist of crushed particles of bush or cotton bolls and short cotton fibers [4].

The mineral fraction of dust consists of soil, sand and other impurities that enter cotton raw materials during harvesting, transportation and storage.

At the beginning of the technological process, during the transportation and weeding of raw cotton, mainly mineral dust is released and pollutes the air, and at the end of the technological process, especially during linting and pressing, organic dust is released. The exhaust air of the pneumatic transport system of cotton raw materials contains 10-20% of the total dust content and 80-90% of mineral dust. According to sieving and microscopic analysis of dust samples from the cyclone, particles smaller than 53 μm make up 3% of the total dust mass. When the dust samples were sieved and analyzed by microscopy, the amount of dust smaller than 10 microns was 51%. It follows that the fraction of dust entering the cyclone with sizes smaller than 10 μm leaves without cleaning.

The cleaning efficiency of wet vacuum cleaners depends on the size of the dust, which has different sizes in the size range. This, in turn, causes difficulties in determining the relative surfaces in contact with liquid droplets, depending on the size of the dust. Therefore, it is desirable to calculate by determining the contact surfaces in relation to the individual dust size.

The results of laboratory analysis determined by the method of sorting dust samples on a sieve and microscopy were processed on the basis of a computer program, regression equations were obtained, and a graph of the change in the percentage of dust was constructed depending on the distribution of the dispersed sizes. (Figure 6).

Figure 6. The graph of the change of the percentage of dust samples depending on the dispersed content

The resulting regression equations look like this:

y = 9,7178e^0,051x                     R² = 0,984773

In the calculations, we assume that the dust samples are spherical and determine the relative (median) diameters of the isolated dust through a horizontal line that makes up 50% of the total dust (see Figure 6). In this case, the values ​​of d_m were determined by drawing a vertical line from the intersection point of the graph drawn for dust samples with a horizontal line. It can be seen from the graph that the median size of dust samples is d_m=10 μm.

Conclusion

The error between the results of the laboratory analysis between the sieving and the microscopy method on the dust samples taken from the cotton factory was ±5%. As a result of laboratory studies, the average median size of dust particles was determined. Depending on these dimensions, the cleaning efficiency of wet dust cleaning devices is determined according to the volume surface diameters of dust and the amount of water supplied in relation to the dust content of 1 m³ of air or gas.

References:

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4. Справочник по первичной обработке хлопка книга 2, Ташкент «Мехнат»-1995  246-247 с.
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