DEVICE FOR WET CLEANING OF DUSTY GASES

ABSTRACT

The article discusses the designs and operating principles of wet dust cleaning devices widely used in industry, and as a result of analysing their advantages and disadvantages, a new design of a wet dust cleaning device with a conical contact element has been developed. As a result of theoretical studies, an equation was proposed that calculates the total pressure lost when dusty air is transferred to the device. The effectiveness of cleaning dusty air can be determined depending on the total pressure of the dusty gas supplied to the device.

АННОТАЦИЯ

В статье рассмотрены конструкции и принципы работы устройств мокрой пыле очистки, широко применяемых в промышленности, и в результате анализа их преимуществ и недостатков разработана новая конструкция устройства мокрой пыле очистки с коническим контактным элементом. В результате проведенных теоретических исследований предложено уравнение, рассчитывающее полные давления, теряемые при передаче запыленного воздуха в устройство. Определить эффективность очистки запыленного воздуха можно в зависимости от общего давления запыленного газа, подаваемого в устройство.

Keywords: dust gas, wet method, liquid, contact element, resistance coefficient, pressure, efficiency.

Ключевые слова: пылевой газ, мокрый метод, жидкость, контактный элемент, коэффициент сопротивления, давление, эффективность.

Introduction

As a result of the development of science and technology and the widespread introduction of new technologies in production, the human impact on nature (anthropogenic impact) is accelerating. The interaction between man and nature has become more complicated, and this influence has reached a level comparable to natural factors. Therefore, environmental protection is one of the most urgent problems of the present time. The anthropogenic impact on the biosphere has reached such a level that natural changes have occurred on the earth, and in some regions it has become impossible to live [1,2,3].

Protecting atmospheric air, which is the most important factor for human life, ensuring its quality indicators meet ecological standards is one of today's global problems. Atmospheric air pollution has a harmful effect on humans, plants, animals, and all living beings.

According to data, 67-74% of human health depends on external environment, food and living conditions, 16-18% on genetic and hereditary factors and only 10-15% on health care. Therefore, it is urgent to take measures to avoid poisoning the environment in order to live. The health of our planet means our health [2,3,9]

Currently, 100 billion tons of raw materials are processed and various products are produced worldwide, and more than 2 billion tons of dust gases and toxic substances are released into the environment. Carbon, nitrogen oxides, hydrocarbons and industrial dust are the most polluting elements of atmospheric air. Construction materials, chemical, metallurgical, and food industry enterprises account for the largest share of dusty gases released into the environment.

More efficient and energy-saving methods of wet cleaning of industrial dust gases and the creation of simple and compact devices are being implemented by industry scientists and applied to the production process [10,12].

Devices for wet cleaning of dust gases generated during production processes are widely used in various branches of chemical, building materials production, metallurgy, mining and other industries worldwide. The peculiarity of their use is that the dust particles mixed with the gas and air directed to the cleaning chambers of the device come into contact with the liquid, and the dusty gas is cleaned.

The advantages of wet cleaning of dusty gases include simplicity of construction and relatively low cost, high cleaning efficiency compared to inertial type dry mechanical dust cleaning devices, small overall dimensions compared to fabric and electric filters, with the possibility of use in cleaning high-temperature, high-humidity gases and explosive gases. stands out. In addition, it can be said that there is a high possibility of trapping solid particles from the composition of steam and gaseous components. Due to the ability to capture dust with a size smaller than 1 μm and the possibility of applying it to the process of cleaning dusty gases from dry filters, the scope of use of these devices is increasing.[3,4,5,12,14].

In addition to cleaning dusty gases from these devices, they are also used in cases where it is necessary to cool and moisten gases.

If we analyze the devices used in the industry from the point of view of structural structure and efficiency, the indicator of cleaning various industrial dusts is 97-99%. But we can point out the complexity of the structural structure, the energy spent on them, and the high hydrodynamic and aerodynamic resistance in the apparatus as a general drawback [3,5,12]. We have developed a new structure of the apparatus that creates effective contact between dusty gas and liquid.

Research object

It is recommended dusty gases The scheme of the wet cleaning apparatus is presented in Fig. 1.

1- lower conical slurry bath, 2- upper conical cleaning chamber, 3- conical contact device, 3a-contact device support, 4- water sprinkler nozzle, 5- water distribution pipe, 6- dust gas inlet pipe, 7- purified gas outlet pipe, 8- water tank, 9- water drum, 10- water pipe, 11- water rotameter, 12- sludge discharge pipe, 13- sludge drum, 14- sludge, 15- dusty air driving fan, 16- dusty air drum, 17- Rotameter, 18- powder gas transmission pipe

Figure 1. Schematic of a wet dust cleaning device

The structure of the device is as follows. The device consists of a lower conical slurry bath 1 and an upper truncated conical cleaning chamber 2, inside which a conical contact device 3 is installed. This contact device consists of upper and lower supporting grids, between which fiber material is placed. This device is attached to the support 3a. Nozzles 4 are used to spray water into the cleaning chamber 2, and water is supplied to these nozzles through a distribution tube 5. Pipe 6 is used to introduce dusty gas into the cleaning chamber, and pipe 7 is used to release purified gas from the apparatus. Water is transferred to the cleaning chamber from tank 8 through valve 9 through pipe 10 and water rotameter 11. Sludge 14 formed in the apparatus is poured through the pipe 12 with the help of a slurry drum 13.

The device works as follows.The dusty gas is supplied to the cleaning chamber of the device by means of a fan 15 through a valve 16 and a rotameter 17 through special transmission pipes 18 and 6. During the movement of the dusty gas from the pipe 6, it rotates on the walls of the apparatus in a test position and its speed decreases. Large-sized dust particles settle into the lower conical slurry bath 1 under the influence of centrifugal force. The dusty gas containing small particles rises to the upper conical cleaning chamber 2. At the same time, water is transferred from the water tank 8 to the cleaning chamber 2 using the pipe 11, and to the nozzles 4 through the distribution pipe 5. Water from nozzles 4 is sprayed along the surface of the truncated conical contact device 3 installed in the cleaning chamber. This contact device contacts the dusty gas with the sprinkled water droplets, and the gas is cleaned of dust. The consumption of sprayed water is controlled by the valve 9 and the rotameter 10. Dusts are absorbed by the fibrous material in the wet contact device and settle by gravity to the bottom slurry bath. The purified gas rises to the top of the conical chamber and is discharged into the atmosphere through the pipe 7. The sludge 14 collected in the lower conical sludge bath of the device is poured through the discharge pipe 12 with the help of a sludge drum 13 and the water is separated by straining.

The consumption of water coming out of the hole of the nozzle 4, which sprinkles water on the truncated conical contact device 3, depends on the resistance coefficient of the hole and is determined by experiments. The number of nozzles 4 is selected based on the level of water spraying on the conical screens and the cleaning efficiency. Conical cleaning chamber 2 and the base diameter and height of the truncated conical contact device are determined depending on the amount of dusty air to be cleaned and the cleaning efficiency of the selected contact device. The ratio of dusty air and water consumption to the device is determined as a result of experiments through cleaning efficiency indicators depending on the resistance coefficients of the cleaning conical contact device. The height of the container 8 installed for transferring water to the device depends on the resistance coefficients of the nozzle,

Research methodology

Theoretical studies were carried out to calculate the apparatus. The calculation scheme of the device is presented in Fig. 2, and the total lost pressure in the device according to sections I–I and II–II can be written as follows, Pa ;[9,10];

,                                                              (1)

in which P₁- is the pressure lost due to internal friction during the transfer of dusty air to the device through the pipe and is determined as follows by the Darcy-Weissbach formula, Pa[11,13];

,                                                      (2)

where l1 is the coefficient of friction with the pipe wall that transmits dusty gas to the device, l1 is the length of the pipe through which dusty gas moves, m; D is the diameter of the base of the conical grid, m; d1 pipe diameter, m; speed of dust and air mixture moving in the pipe, m/s; rar is the density of the dusty air mixture, which is determined according to the following equation [2,3,9,10,12], kg/m3;

                                                             (3)

where  is air density, kg/m³;  dust density, kg/m³; g dust content in air, %.

Figure 2. The calculation scheme of the device

The coefficient of friction l1 depends on the flow regimes of the dusty gas in the pipe and is determined as follows when Re ≤ 2320 for the laminar mode[11,13];

,                                                                           (4)

The flow mode is defined as follows when 2320<Re<4000.

                                                              (5)

For smooth pipes, when 4000<Re<10000, it is defined as follows.

                                                                     (6)

 P₂is the lost pressure during the passage of dusty air through the conical contact device and is determined as follows, Pa;

,                                                                (7)

where ωsm is the movement speed of the dusty air mixture on the surface of the conical contact device, m/s;  is the resistance coefficient of the conical contact device; rar-dust and gas mixture density kg/m³.

The resistance coefficient of the conical contact device is determined as follows.

                                                                   (8)

where  is the resistance coefficient of the base grids; -the coefficient of resistance of the fibrous material laid on the base grids;

The resistance coefficient of the base grids is determined as follows. From Fig. 1 and 2, according to section A-A, it is determined as follows, depending on the total surface of the mesh through which dusty air passes and the diameter of the wire of the mesh and the dimensions of the square hole of the mesh, m2[9];

                                                         (9)

where ∆k is the correction coefficient, determined by experiments, R is the radius of the base of the conical grid, m; r is the radius of the cut part of the conical mesh, m; lc is the average value of the length of the circumference of the mesh base and the length of the circumference of the cut part, m; d mesh wire diameter, m; a mesh square hole dimensions, m.

The optimal values of the sizes of the mesh holes to be installed are determined by experiments with the condition that the fiber material laid on it does not move.

The coefficient of resistance of the fibrous material laid on the base grids xT is defined as follows[6,7,8];.

                                                                 (10)

where  is the correction factor, which is determined by the following equation;

                                                                         (11)

in which - is the resistance coefficient of the fibrous material, which is determined by experiments;  is the relative resistance coefficient of the fibrous material, which is determined as follows [5].

                                                                   (12)  

where  is the relative surface of the fibrous material by mass, m²; It is determined as follows [6,7,8].

                                                                  (13)

The total surface of the mesh square holes on which the -selectable fibrous material is laid, m².

where m is the mass of fibrous material, grams; r-fiber material density,kg/m³, R- fiber material radius, m          

In the pipe that removes the purified air from the device pressure lost due to internal friction P₃ tooIt is determined by the Darcy-Weissbach formula, Pa;

                                                            (14)

in this l₂- coefficient of friction in the pipe releasing the purified air into the atmosphere (the method of calculation is given above), l₂ is the length of the pipe through which the purified air moves, m; d₂ pipe diameter, m; r density of purified air, kg/m³; ω is the velocity of purified air moving in the pipe, m/s.

Now if we put equations (2), (7), (9), (10), (14) into the 1st equation, the equation for calculating the total lost pressure in the device will look like this, Pa;

       (15)Summary

Constructions and principles of operation of wet dust cleaning devices were studied, their achievements and shortcomings were analyzed, and a new design of wet dust cleaning equipment was developed. As a result of theoretical studies, a formula for determining the total pressure lost during the transfer of dusty air to the device was derived. As a result, it was possible to determine the efficiency of dusty air cleaning depending on the total pressure of dusty gas supply to the device.

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