RESISTANCE COEFFICIENTS OF THE APPARATUS WITH CONE MESH WET CLEANING OF DUST GASES

ABSTRACT

The article presents the results of an experimental study conducted on a pilot plant with a mesh cone for wet dust cleaning. In the studies carried out, the local resistances of the devices and the resistance coefficients of the selected three different-sized grids were determined in the absence of splashing of the device with water, at variable gas flow rates. Based on the research results, the values ​​of correction factors for calculating the resistance coefficient of the selected grids were determined. As a result, it was possible to calculate the total pressure loss depending on the total resistance coefficient in the contact devices of the apparatus.

АННОТАЦИЯ

В статье представлены результаты экспериментального исследования, проведенного на опытной установке с сетчатой конусом мокрого пылеочистки. В проведенных исследованиях определены местные сопротивления аппаратов и коэффициенты сопротивления выбранных трех разно размерных сеток в условиях отсутствия забрызгивания устройства водой, при переменных значениях расхода газа. По результатам исследований определены значения поправочных коэффициентов для расчета коэффициента сопротивления выбранных сеток. В результате создано возможности рассчитать суммарные потери давления в зависимости от коэффициента полного сопротивления в контактных устройствах аппарата.

Keywords: dusty gas, gas velocity, flow rate, wet method, liquid, cone mesh, resistance coefficient, correction factor.

Ключевые слова: запыленный газ, скорость газа, расход, мокрый способ, жидкость, конусная сетка, коэффициент сопротивления, поправочный коэффициент.

Introduction

The cheapest and most convenient way to clean dust and toxic gases in gas is the wet cleaning process. The essence of wet cleaning of dusty gases is to combine fine dispersed dust particles by wetting the dust particles. In this case, the contact of dust particles occurs on the surface of a liquid film or liquid droplets. In the implementation of this process, the flow of gas and liquid can move perpendicularly or oppositely [1,7].

If we analyze these devices from the point of view of constructive structure and efficiency, the indicator of cleaning various industrial dusts is 97-99%. But the complexity of the structural structure of these devices, the energy spent on them, and the high hydrodynamic and aerodynamic resistance in the device can be pointed out as a general drawback [1,3,4,7]. In order to eliminate the aforementioned shortcomings and to increase the contact surface between the dusty gases and the liquid supplied to the device, a new design of the dusty gas cleaning device was recommended [3,4]. Below is a diagram of the device (Fig. 1).

Research object

As an object of research, the experimental device of the cone meeting device created at the department of “Technological machines and equipment” of Fergana Polytechnic Institute (Fig. 2) and the formula for calculating the total resistance coefficient lost in the device [3,4], which was created as a result of theoretical research, were used.

1- lower conical sludge bath, 2- upper conical cleaning chamber, 3- conical screen, 3a-screen support, 4-water sprinkling nozzle, 5-water distribution pipe, 6- powder gas inlet pipe, 7- cleaned gas discharge pipe, 8- water tank, 9- water drum, 10-water pipe, 11-water rotameter, 12- sludge discharge pipe, 13- sludge drum, 14- sludge, 15-dust air driving fan, 16- dust air bag, 17 - rotameter, 18- dust gas transfer pipe

Figure 1. Schematic of the device with a cone

Figure 2. Overview of the cone-shaped apparatus

Technical indicators of the device with a cone

The obtained results

To calculate the total pressure lost in the apparatus, it is necessary to determine the local resistance of the apparatus and the coefficients of resistance of metal grids with different hole sizes, which are installed on the metal drum, which is the main working body of the apparatus. Therefore, GOST 3826-82, 12X18N10T stainless steel mats made of square holes of 3 different sizes were selected in experimental studies (Fig. 2, b). Grid dimensions 1. Square hole size a=1.1 mm, wire thickness δ=0,16mm; 2. Square hole size a=1.3 mm, wire thickness δ=0,18 mm; 3. Square hole size a=1.6 mm, wire thickness δ=0,2 mm;

The theoretical total resistance coefficient of the device is equal to the following [3].

                                                          (1)

where ξ_к is the coefficient of internal friction when transferring dusty air to the device through a pipe, defined as follows [5,6,7].

                                                            (2)

where λ₁ is the coefficient of friction with the pipe wall introducing dust gas into the device, l- is the length of the pipe through which dust gas is moving, m; D-section cone base diameter, m; d-is the diameter of the truncated part of the cone.

ξ_с - is the resistance coefficient of the drum mesh and is determined as follows. From Fig. 1 and 2, the total resistance coefficient of the truncated conical grid on the A-A section is determined as follows depending on the total surface of the grid through which dusty air passes and the diameter of the wire of the grid and the dimensions of the square holes of the grid [3,4] m²;

                                  (3)

where ∆k is the correction coefficient, determined through experiments, R- is the radius of the base of the conical grid, m; r-radius of the cut part of the conical mesh, m; l_c - the average value of the length of the circle of the base of the mesh and the length of the circle of the cut part, m; δ -grid wire diameter, m; a- mesh square hole dimensions, m.

ξ_ch - when dusty air is discharged from the device through a pipe, the coefficient of internal friction is defined as follows [5,6,7].

                                                   (4)

where λ₂ is the coefficient of friction in the pipe for releasing the purified air from the device; l- is the length of the pipe through which the purified air moves, m; d-pipe diameter, m;

If we add the values of formulas 2, 3, 4 -to the above-mentioned formula 1, it will look like this.

                          (5)

Through this equation, the total resistance coefficients of the apparatus are determined.

At the initial stage of the experiments, a damper (moving barrier) was installed on the gas suction part of the fan that transmits the dust gas to the apparatus. The damper was changed in the range of 30÷90⁰ (with 15⁰ steps) and the gas velocities coming out of the fan and the corresponding gas consumption were determined.

According to it, when Shiber is opened to 30⁰, Q_g=170m³/h, when opened to 45⁰, Q_g=340m³/h, when opened to 60⁰, Q_g=510m³/h, when opened to 75⁰, Q_g=680m³/h, when opened to 90⁰, Q_g=850m³/h. In the next course of experiments, a fan was installed in the apparatus body, and the above-determined gas consumption was given as Q=170÷850 m³/h (with a step of 170 m³/h), and the gas consumption was determined by the gas velocities coming out of the apparatus.

 In this case, Shiber was Q_g=107m³/h when opened to 30⁰, Q_g=220m³/h when opened to 45⁰, Q_g=318m³/h when opened to 60⁰, Q_g =438m³/h when opened to 75⁰, Q_g =512m³/h when opened to 90⁰. The local resistance coefficient of the device was determined from the difference in gas consumption. Anemometer VA06-TROTEC brand electronic device was used to determine these differences at all stages of experiments. The average local resistance coefficient of the device was x=0.6. At the next stage of the experiments, cones with a square hole size a=1,1; 1,3; 1,6 mm were installed in the apparatus body in a row (Fig. 2b)

Q=170÷850 m³/hour (with a step of 170 m³/hour) was supplied to each gas drum installed in the apparatus. Experimental studies were carried out separately for each cone grid. In the experiments, the gas density was chosen at ρ_g=1,29 kg/m³ (for air). According to the results, the resistance coefficient ξ_с =2,6 when the mesh square hole size is a=1,1mm, the thickness of the mesh wire is δ=0,16mm; ξ_с = 2.5 when the hole size is a=1,3mm, the mesh wire thickness is δ=0,18mm; hole size a=1,6mm, mesh wire thickness δ =0,2mm ξ_с=2,2.

These determined resistance coefficients are the overall resistance coefficient of the apparatus, plus the local resistance coefficients of the apparatus. If we subtract the local resistances from these values, the grid resistance coefficients are derived. The local resistance coefficient is determined as follows.

                                                   (6)

                                               (7)

a=1,1mm, when the mesh wire thickness is δ=0,16 mm; ξ_с=ξ_gen- ξ_м=2,6-0,6=2

a=1,3mm, when the mesh wire thickness is δ=0,18mm; ξ_с= ξ_gen- ξ_м=2,5-0,6=1,9

a=1,6mm, when the mesh wire thickness is δ=0,2 mm ξ_с= ξ_gen- ξ_м=2,2-0,6=1,6

The obtained experimental results were processed on the basis of a computer program and a graph of dependence was built (Fig. 4).

Figure 3. Graph of variation of resistance coefficient ξ_gen and ξ_с depending on Σδ/Σa (in the case of no liquid spraying)
A view of the resulting regression equation: 1. y = 20,388x - 0,9395 R² = 0,9881
 2. y = 20,388x - 0,3395 R² = 0,9881

Based on experimental studies, research was conducted to determine the values of the correction coefficient Δк depending on the resistance coefficient of the recommended grids. Relative resistance coefficients of selected grids were determined. Below is the calculation method.

1- calculation of a truncated conical grid. Wire thickness- ,Hole size .

First of all, we take a square shape with sides of 10 sm by 10 sm as a sample.

Figure 4. Graphic image

                                                     8)

; ; ;

 .

There are 95 check boxes in total where:

- the side surface of the truncated cone surrounded by mesh,

-10 cm. a surface covered with wires at a distance of 10 cm, a surface covered with wires at a distance of 10 cm

 -10 cm and a surface covered with empty cells,

 - the total thickness of the wires on one side of the isolated mesh sample, - the total thickness of the wires on the other side of the isolated mesh sample, - the surface covered by the wire in the isolated sample, - the sum of the areas of the empty cells in the isolated sample.

To find the total area covered by wire in the net, we multiply 95 pieces by -(that is, the size of the surface of 10 cm by 10 cm):

                                                             (9)

.

To find the surface occupied by the total empty cells, we subtract the total surface covered by  wire from the  surfaces:

That is: .

So: ; ; .

Here: - Cut is the surface occupied by the total number of empty cells in the mesh wrapped around the side surface of the cone (wireless part).

- The total surface covered with a wire mesh wrapped around the side surface of a truncated cone.

 - the side surface of a truncated cone surrounded by mesh.

We find the coefficient of relative resistance of the set:

                                                    10)

Here - is the relative resistance coefficient of the grid, - we determine the total surface covered by the wire in the mesh wrapped around the side surface of the truncated cone by the ratio of  - the total free cells in the mesh wrapped around the side surface of the truncated cone by the ratio of the surface (non-wired part):

We determine the correction coefficient .

                                              (11)

To do this, we divide the experimental resistance coefficient ξ by the relative resistance coefficient ξ_n.

The correction factors for subsequent grid sizes were also determined in the same way. The size of the square hole of the mesh is a=1,3mm. The thickness of the mesh wire is δ =0,18 mm. when ΔК =5,1. The size of the square hole of the mesh is a=1,6mm. When the thickness of the mesh wire is δ=0.2 mm, the correction factor is equal to ΔК =5. For selected grid sizes, it is recommended to take the correction factor in the range ΔК=(5-5.1).

To simplify calculations, the coefficient of local resistance in the inlet and outlet pipe of dusty air to the device was ξ_м=0.6. In that case, formula 5, which calculates the total resistance of the device, will look like this.

                                   (12) 

Summary

As a result of experimental studies, the local resistances of the arrarat and the resistance coefficients of the selected three different sizes of grids were determined in the condition that the device was not sprinkled with water, at step variable values of gas consumption. According to the results of the study, the values ​​of the correction coefficients for calculating the resistance coefficient of the selected grids were determined. As a result, it is possible to calculate the total lost pressure depending on the total resistance coefficient in the contact devices of the apparatus.

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