EFFECT OF LIGHT LIQUID VELOCITIES ON HEAVY LIQUID DROPLET CRUSHING IN A BUBBLING EXTRACTOR

ABSTRACT

In the article, the crushing of heavy liquid into droplets depending on the hole sizes of the heavy liquid discharge pipe and the light liquid concentration in the experimental device of the bubble extractor in the state where gas is not supplied to the mixing zones is studied. Compared to a single drop the volumetric surface diameters of the droplets were determined. As a result, by studying the crushing of heavy liquid into droplets and their size distribution when gas is introduced into the apparatus, it is possible to determine the degree of crushing of heavy liquid into droplets at liquid and gas velocities. Because the degree of crushing is important in determining the efficiency of mass transfer

АННОТАЦИЯ

В статье исследовано дробление тяжелой жидкости на капли в зависимости от размеров отверстий патрубке отвода тяжелой жидкости и скорости легкой жидкости в случае отсутствия подачи газа в зоны смешения в экспериментальном установке барботажного экстрактора. Для каждого режима определено дробление капель и их распределение по размерам и объемно-поверхностного диаметра капель относительно отдельных капель. В результате, изучая дробление тяжелой жидкости на капли и распределение их по размерам при вводе газа в аппарат, можно определить степень дробления тяжелой жидкости на капли при скоростях жидкости и газа. Это играет важную роль в определении эффективности массообмена

Keywords: gas velocity, liquid velocity, mixing zone, droplet diameter, distribution, proportion, volume surface diameter, mixing time, surface tension, viscosity, density.

Ключевые слова: скорость газа, скорость жидкости, зона смешения, диаметр капель, распределение, доля, объемный диаметр поверхности, время перемешивания, поверхностное натяжение, вязкость, плотность.

Introduction

"Scientific research is being carried out to create new designs of highly efficient extractors, to increase the contact surface of liquid phases and to speed up the mixing process for performing extraction processes in the "liquid-liquid" system. In this regard, the use of compressed gas energy, which is chemically inert to liquids, the improvement of drop crushing mechanisms and mass exchange models according to the physico-chemical properties of liquid phases, the reduction and stability of extractant consumption in the device stages, the reduction of the number of stages, high-performance metal and energy-efficient, compact, special attention is being paid to the creation of new types of extractors capable of extracting different liquids [1,4,7].

Research object

Based on the above requirements, we invented a new construction of a multi-stage filter bubble extractor[2,3]. Below is the construction and principle of operation of the invented apparatus [2].

The structure of the extractor is as follows. The extractor body 1 is divided into separate mixing and settling stages by means of barriers 2. Mixing devices are made of inner 3 and outer 4 concentric nozzles, and the barrier is installed in 2. The nozzles 3 are installed on the barriers 2 in such a way that their lower parts 5 protrude from under the barriers 2 and serve as gas distribution nozzles through the holes 6 on the side walls. Also, heavy liquid discharge pipes 7 are installed on the barrier 2. Holes 8 are opened in the lower parts of these pipes. The upper part of the pipe 7 is closed with a cap 9. The cap 9 has a lower 10 and an upper hole 11. Gas pipelines 12 are installed on barrier 2. The top of these pipes is closed, and holes 13 are opened on its side walls for the release of inert gas. through these holes, the nozzles of the inert gas mixing devices go to the annular channel between 3 and 4. A special hole 14 is opened along the diameter from the lower part of the center of the hole 13, which is opened in the pipelines 4 that transmit gas to the ring channel, and a cover (filter) 15 made of fiber material that absorbs heavy liquid is installed in it. Slots 16 are formed in order to ensure the flow of the heavy liquid, which has been quenched, to the next step when the pipes 4 are installed on the barriers 2. Metal meshes 17 and 18 are installed in the upper part of the central section of the holes in the gas distribution nozzle 5 and the holes in the tubes 12 installed in the barriers 2 to further crush the bubbles coming out of these holes. A special hole 14 is opened along the diameter from the lower part of the center of the hole 13, which is opened in the pipelines 4 that transmit gas to the ring channel, and a cover (filter) 15 made of fiber material that absorbs heavy liquid is installed in it. Slots 16 are formed in order to ensure the flow of the heavy liquid, which has been quenched, to the next step when the pipes 4 are installed on the barriers 2. Metal meshes 17 and 18 are installed in the upper part of the central section of the holes in the gas distribution nozzle 5 and the holes in the tubes 12 installed in the barriers 2 to further crush the bubbles coming out of these holes. A special hole 14 is opened along the diameter from the lower part of the center of the hole 13, which is opened in the pipelines 4 that transmit gas to the ring channel, and a cover (filter) 15 made of fiber material that absorbs heavy liquid is installed in it. Slots 16 are formed in order to ensure the flow of the heavy liquid, which has been quenched, to the next step when the pipes 4 are installed on the barriers 2. Metal meshes 17 and 18 are installed in the upper part of the central section of the holes in the gas distribution nozzle 5 and the holes in the tubes 12 installed in the barriers 2 to further crush the bubbles coming out of these holes.

The extractor works as intended. Light liquid (LL) enters the manifold 3 through the gas distribution nozzle 5. Heavy liquid (HL) flows through the holes 8 of the pipes 7 to the same nozzles. The mixture of liquid phases moving together from bottom to top in the pipe 3 enters the gas distribution nozzle 5 in the form of a bubbling inert gas bubble through the holes 6, and rises to the top in the metal mesh 17 with small holes installed above the hole, and the liquid phases are further crushed and intensively mixed. After mixing the liquids, this part of the gas is collected in the gas cushion under the barrier 2.

At the same time, the rest of the inert gas, the gas bubbles coming out of the holes 13 opened in the gas transmission pipes 12, are further crushed in the small-sized metal mesh 18 installed on top of these holes, and are discharged into the ring channels between the 3 and 4 nozzles. This part of the inert gas in the form of a bubble moving from the bottom to the top in the annular channels passes through the stream of the liquid mixture moving from the top to the bottom. In this transition, it rapidly mixes the flow of liquid phases and accumulates in the gas cushion under the barrier 2 s. In the process of the light liquid flowing through the hole 14 formed in the lower part of the nozzle 4 and the fibrous material (filter) 15 covered with it, the heavy phase drops with small particles that join it are caught in the fibrous material (filter) and as a result of their mutual integration, they turn into large drops and begin to sink under the influence of gravity and inertial forces. The light liquid, which is purified from the heavy liquid, continues to move to the top. Drops of heavy liquid settle in the lower part of the annular channel formed by nozzles 3 and 4 and flow out through the slits 16 in the lower part of nozzle 4 and form a homogeneous layer on the barrier 2. Such installation of the pipe 4 on the barriers 2 ensures the maximum use of the volume of the annular channel, the passage of light liquid only through the holes 14 and the fibrous material (filter) 15 covered with them. The slots 16 in its lower part ensure the movement of heavy liquids only. The size and number of holes 6 in the gas distribution nozzle 5 are determined depending on the value of the gas cushion formed under the barrier 2. The sizes of the holes 13, which transmit gas to the ring channel, are determined by the condition of equal distribution of inert gas according to the pressure difference between the two holes. The size of the holes of the metal grid 17 is selected up to 4 times the size of the holes 6, and the size of the holes of the metal grid 18 is selected up to 2 times the size of the holes 13. It takes into account the stable flow of the liquid phases in the internal bubble tube and the ring channel. The sizes of the holes 13, which transmit gas to the ring channel, are determined by the condition of equal distribution of inert gas according to the pressure difference between the two holes. The size of the holes of the metal grid 17 is selected up to 4 times the size of the holes 6, and the size of the holes of the metal grid 18 is selected up to 2 times the size of the holes 13. It takes into account the stable flow of the liquid phases in the internal bubble tube and the ring channel. The sizes of the holes 13, which transmit gas to the ring channel, are determined by the condition of equal distribution of inert gas according to the pressure difference between the two holes. The size of the holes of the metal grid 17 is selected up to 4 times the size of the holes 6, and the size of the holes of the metal grid 18 is selected up to 2 times the size of the holes 13. It takes into account the stable flow of the liquid phases in the internal bubble tube and the ring channel.

For experimental studies, a pilot device of this inventive multi-prong bubble extractor was constructed (Fig. 2). In this device, the processes of crushing heavy liquid into droplets are being studied experimentally.

The results obtained

Experimental studies "Farg‘onaazot" JSC in butylacetate liquid and model liquids. The purpose of the experimental study is to study the process of crushing into droplets at variable liquid velocities during the flow of heavy liquid through the holes of the discharge pipe without gassing the mixing zones of the apparatus [5,6,8,9,10].

The droplet sizes of water droplets during extraction washing of butylacetate liquid with water in the experimental device and the droplet sizes of model liquids selected as heavy liquids were filmed and photographed using a video camera. A mixture of carbon tetrachloride + benzene was taken as the model liquid selected as heavy liquid. The density of the mixture was created at ρ_d =1120 kg/m³. The density was determined using a hydrometer in laboratory conditions. The physical and chemical properties of industrial and model fluids are presented in Table 1. The mixture of selected model liquids was colored with a chemical substance "Dithizone" powder (1,5-diphenylthiocorbazone S12N2N4S) that gives color for clear visibility in video footage and pictures [4,5].

Table 1.

Physico-chemical properties of liquids

Experiments were conducted in the following order. In the first stage of the experiment, the gas transfer holes to the internal and external mixing zones of the device were closed. The light phase was supplied to the device with a consumption of Q_s=0.23,0.27,0.31 m³/h (Q_s=0.04 m³/h step). In these liquid flows, the liquid velocity in the internal mixing zone was w_sⁱ=0.051, 0.075, 0.11 m/s. Mixing time was t_mesh=22,18,14 seconds. The proportion of light and heavy liquids supplied to the device was selected for each experiment in the ratio of 3:1, Q=0.07, 0.9, 0.1 m³/h. These heavy liquid wastes were discharged through holes d=1.0, d=1.5, d=2 mm in the heavy liquid discharge pipe. At each fluid velocities, the process of crushing the heavy liquid flowing through the holes into droplets was studied. The process of crushing the heavy liquid into droplets was filmed and photographed using a Sanon EOS 700 D video camera. A 1 mm diameter wire was placed as a scale in the outer mixing zone to determine the droplet sizes by comparison. Five photographs were taken to determine droplet sizes at each fluid velocity. At each stage of the experiments, the droplet sizes for the selected modes were determined at intervals through photographs. Examples of the resulting photographs are shown in Figure 3. At each stage of the experiments, the droplet sizes for the selected modes were determined at intervals through photographs. Examples of the resulting photographs are shown in Figure 3. At each stage of the experiments, the droplet sizes for the selected modes were determined at intervals through photographs. Examples of the resulting photographs are shown in Figure 3.

Figure 3. A method for determining the sizes of dispersed phase droplets by modes

225÷270 droplet sizes were determined from the photographs taken for each stage of the experiments, and percentage values ​​were found for their intervals. It was processed with the aid of a computer and graphs of the droplet size distribution were constructed (Figures 4, 5, 6).

Figure 4. Size distribution graph of crushed droplets

Figure 5. Size distribution graph of crushed droplets

Figure 6. Size distribution graph of crushed droplets

The next task was to determine the average volume-surface diameter of the droplets during the change of the liquid speed without supplying gas to the apparatus.

Average volume-surface diameter of the dropletcan be determined based on the following equation[4.5], µm;

                                   (1)

where d_max is the maximum diameter of the droplet in the emulsion, µm; a and b are constant coefficients, b=0.725, and "a" can be found from the following equation[4.5];

                                           (2)

where d₅₀ - 50%, is the droplet diameter corresponding to the relative share which is determined by the following equation, µm;

                              (3)

where d₉₀ and d₁₀, droplet diameter corresponding to 90% and 10%, µm.

Based on the results of experimental research, we determine the volume-surface diameters of drops depending on water consumption modes and hole sizes.

For line 1 in Figure 4;

d₉₀ = 5900 μm, d₅₀ =3050 μm, d₁₀ = 950 μm.

When these values ​​are put into equation (3), we get;

We determine the distribution parameter.

And  d_v.s will be:

where d_max is the maximum diameter of the droplet in the emulsion, µm; a and b are constant coefficients, b= 0.725, "α" is the distribution parameter, calculated above.

According to the results of the experiment, all calculations on lines 4, 5, 6 were carried out in this way and are presented in Table 2.

Table 2.

Distribution of droplet sizes by modes

The experimental values ​​obtained during the determination of the volume-surface diameters of the drops depending on the gas consumption were processed with the help of a computer and a graph was constructed (Fig. 7).

1- d=1 mm; 2- d=1.5 mm; 3- d=2 mm;

Figure 7. The graph of changes in the volumetric surface diameter of droplets depending on the consumption of liquid

The resulting regression equations are as follows.

y = -11375x + 5431.9              R² = 0.9986

y = -8687.5x + 5174                R² = 0.9769

y = -2875x + 4197.2                R² = 0.9919

Summary

In the article, the crushing of heavy liquid into droplets depending on the hole sizes and light liquid concentrations of the heavy liquid discharge pipe in the state of no gas supply to the mixing zones in the experimental device of the bubble extractor was studied. For each regime, droplet crushing and size distribution were determined. Volumetric surface diameters of droplets relative to individual droplets were determined. As a result, an opportunity was created to determine the level of crushing of heavy liquid into drops at liquid and gas velocities by studying the crushing of heavy liquid into droplets and size distribution when gas is applied to the apparatus. Because the crushing level is important in determining the efficiency of mass transfer.

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