HYDRODYNAMICS OF CONVEX-CONCAVE PLATE COLUMN FOR COTTON OIL MISCELLANEOUS DISTILLATION

ABSTRACT

The article presents the structural characteristics of the new type of convex-concave plates used in the processes of mass exchange. Also, the bubble mode of the liquid in the wave-like motion, the mode of intermediate transition from the bubble mode to the flow mode, and flow hydrodynamic modes characterizing the rise of the liquid level in the direction of the flow are presented.

АННОТАЦИЯ

В статье представлены конструктивные особенности выпукло-вогнутых пластин нового типа, используемых в процессах массообмена. Также представлены пузырьковый режим жидкости при волнообразном движении, режим промежуточного перехода от пузырькового режима к проточному и гидродинамические режимы течения, характеризующие подъем уровня жидкости в направлении течения.

Keywords: plate of convex-concave type, body, angle of inclination of body, hydrodynamic regime, angle of rise of flow.

Ключевые слова: пластина выпукло-вогнутого типа, тело, угол наклона тела, гидродинамический режим, угол подъема потока.

The total volume of products produced by oil industry enterprises is almost 40% of the gross food products produced in the republic. For this reason, in order to increase the range of products with guaranteed quality and low cost, the problem of introducing effective technologies that allow saving material and energy resources and compact and intensive technological equipment to food industry enterprises is considered urgent[1].

In the improvement and development of mass exchange devices, issues such as obtaining more products per volume unit of the device, reducing the hydraulic resistance corresponding to one separation step, and reducing the relative metal consumption of the device are aimed at.

To solve the problem, several concave and convex plates are placed in a row, the liquid phase moves from the top of the device to the bottom, from the body wall to the center and from the center to the body wall, which increases the contact surface between the phases on the plate due to the installation of central and peripheral pouring pipes, vapor the phase is installed from the bottom of the device through the holes in the form of coins on the plates, preventing the vapor phase from leaving the liquid phase falling pipe, and installing the plates at an angle of 3-5° prevents the liquid from spilling out of the holes when the vapor phase flow decreases [2,3 ].

The degree of openness and location of the contact element, which changes the level of steam exposure to the liquid stream on the plate, allows changing the cross-sectional surface of the steam stream coming out of it. In the liquid-vapor system, the edges of the particles are raised to provide an intensive bubbling process around the contact element [4,5].

The composition (arrangement) of plates in the column consists of a body, a concave plate, a central pouring pipe, a bubble plate, an edge (small) pouring pipe, a spill (pouring) barrier, and particles. The raw material is supplied in liquid-gas form from the upper part of the column body, the distillate is removed from the upper part of the column, and the cube residue is removed from the lower part. The liquid phase moves along the plate and falls through the pouring pipe to the pouring barrier, from where it flows to the plate below. The vapor phase passes through the contact elements of the plate and contacts the liquid phase on the plate. Due to the formation of intensive bubbling in the vapor-liquid system, it provides a high-level process of substance exchange.

The device works as follows: in the vapor (gas)-liquid system, raw materials are fed to the column to separate the light volatile components of the liquid phase. The liquid phase moves from the body wall towards the center because the concave plate of the receiver has an inclined angle of ∠3-5°. During movement, the liquid comes into intensive contact with the vapor phase coming out between the contact elements of the plate - coins. Coins in a concave plate are circular, spaced at a certain distance from each other, the open side of the coin is opened at an angle of ∠15° from the body wall to the center. The liquid falling from the spill barrier to the convex plate after the central discharge pipe moves from the center towards the casing wall and through the peripheral discharge pipe, passing through the spill barrier that prevents the vapor phase from escaping through the discharge pipes, falls into the lower plate. The coins in the convex type plate are also circular, at a certain distance from each other, the open side of the coin is opened at an angle of ∠15° from the center to the body wall, not from the body wall to the center. The liquid, purified from light volatile components, is removed from the bottom of the device as a cubic residue. Light volatile components separated from the raw material are removed from the top of the device in the form of distillate[6-9].

Figure 1.  Convex-concave plates:  а)  convex plate ; б)  concave plate

In industrial production plants, the method of processing material exchange processes in plate-type devices is common, and in recent decades there has been an increasing demand for devices that are easy to manufacture and use, with small volume, high performance, without internal moving elements, and high efficiency that can be easily integrated into existing production lines. plate-type devices have great prospects. In the oil extraction plant, we proposed to carry out the final distillation process in a convex-concave plate still, which speeds up mass transfer processes due to intensive mixing.

The parameters of the column and convex and concave plates in the conducted experiments are presented in Table 1.

Table 1.

The parameters of the column and convex and concave plates in the conducted experiments

For coin plates, as well as other types of plates, several hydrodynamic operating modes are established. In slotted plates similar to sieve plates, at low velocities of steam, liquid spills out between the plates. Spilling of liquid from the tank slot stops when the vapor velocity in the tank slot is equal to 6.5 ÷ 7.5 m/s. (This speed is called the first critical speed.) The experiments where this speed was determined were carried out in the air-water system when the irrigation density for the liquid was 10.8-36 m³/m²·s. In this case, the slot construction did not significantly affect the value of the critical speed, which determined the lower limit of the working zone of the plate. At small velocities of steam in the slot, the plate works unstable. When the speed on the plate exceeds the first critical speed, the wave-bubble mode of operation is established. In this mode, the wave-like movement of the liquid from the receiving barrier to the spill zone is observed, and uniform bubbling is observed over the entire area of the plate. In this case, a significant slope of the liquid level towards the spillway is observed. This mode of plate work is little different from sieve plate work. When the speed is further increased, the liquid level in the plate becomes equal, at a certain speed called the second critical speed, the liquid level is parallel to the plane of the plate, such a regime is called an intermediate regime. For this mode, the vapor velocity varies depending on the density of the liquid irrigation. In the intermediate mode, the liquid level in the plate remains horizontal, the bubbling process occurs in the plates, but the direction of the vapor flow, which attracts the liquid, is shown.

Figure 2. Convex-concave plate column device:

body 1, concave plate 2, central pouring pipe 3, convex plate 4, peripheral (small) pouring pipe 5, spill (pouring) barrier 6. Designation of flows: I-raw material, II-distillate, III-cubic residue, IV-water vapor.

When the steam velocity in the slots is further increased, the intermediate regime switches to the flow regime. A characteristic difference of the flow regime is the rise of the liquid level in the direction of the liquid flow. This phenomenon is triggered by the vapor stream attracted by the liquid, as well as by the impingement of the vapor-liquid stream on the column wall. The greater the height of the vapor-liquid mixture layer in the spill zone, the greater the vapor velocity in the cracks. At certain vapor velocities in the slits, some of the liquid breaks away from the plate and moves over the plate, increasing the liquid blowout. A further increase in speed will cause the column to jam.

The general view of the plate column device of the convex-concave type is shown in Fig. 2. From the upper convex plate, the liquid phase moves through the marginal (small) pouring pipe (5) from the wall of the case (1) to the central pipe (3) and contacts the gas phase passing between the coins (7). In turn, the liquid from the central pipe moves towards the column wall and comes into contact with the gas passing between the coins of the concave plate, resulting in the process of mass exchange. Contact elements (7) (coins) are formed in the form of a circle by stamping the metal sheet from which the plate is made. In addition, placing the contact elements close to the column body causes a part of the liquid flow that does not participate in the process of mass exchange to participate in the process and prevents the formation of a wall effect.

The working mode of the coin plate is the flow mode. In this case, the upper limit of the speed on the plates is determined by the permissible value of the liquid flow. If the permissible value of flyaway is taken as ε=0.1 (kg liquid)⁄(kg vapor), then the limiting velocity can be found by an empirical formula, the form of the equation depends on the characteristic properties of the plate. Below are the flight and limit speeds of the coin disc. The scheme of the main hydrodynamic regimes of the coin plate is shown in Fig. 1.

а)                                                           б)                                                      в)

Figure 3.  Hydrodynamic regimes of a coin plate: a) bubbling; b) intermediate; c) flowing

Fig. 3.a shows the scheme of the bubbling mode of liquid in wave-like motion. 3. Fig. b shows the intermediate transition mode from the bubbling mode to the flow mode. Figure 3.b shows the horizontal level of the liquid, so that the liquid level drops to the point of discharge. Figure 3.v shows the flow regime that characterizes the rise of the liquid level in the direction of the flow. This mode of operation is the optimal mode for increasing the contact surface of the phases.

In the proposed convexo-concave type distiller, the mistelle with high concentration moves downwards from the top of the apparatus. A concave plate is installed from the top of the column, and then the plates are arranged in a concave-convex order. Open water vapor rising in the opposite direction to the flow is intensively treated with extraction oil, passing through the slits in the plate. This allows maximum use of a small device and accelerates heat and matter exchange processes.

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