RU2545277C1 - Method for separation of inhomogeneous mixtures in centrifugal field - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: method for the separation of inhomogeneous mixtures in a centrifugal field includes spinning of a mixture flow with the formation of progressive rotation for the main flow of a continuous light phase within the whole process, deposition of a disperse heavy phase under effect of the centrifugal field with the formation of a heavy phase layer at the periphery of the spinned flow, off-take of the heavy phase layer with the secondary flow of the continuous light phase with the formation of an off-take flow(s). Thereafter the repeated deposition of the heavy phase is performed under effect of a gravitational field and off-take of the secondary flow of the continuous light phase to the main flow of the continuous light phase. Besides, at the periphery of the spinned flow multiple off-take flows are created; each of these flows is restricted by the limitation of an input cross-section width up to the value not exceeding 1% of the radius of the spinned flow periphery. At that the off-take flows are oriented outwards under an angle not exceeding 45° from the direction of the spinned flow. Then the off-take flows are reduced up to the rate of the heavy phase gravitational settling by smooth extension with an increased deviation in the radial direction from the centre of the spinned flow. At that the progressive rotation of the main flow of the light phase within the whole process is not deviated in the radial direction to the centre of rotation.EFFECT: reduced hydraulic friction and reduced primary and secondary drifts of the heavy phase.7 dwg, 4 tbl, 2 ex

Description

The technical solution was developed for use in the gas and oil industries and can be used in other industries in the separation of heterogeneous mixtures in a centrifugal field.

A known method of separating inhomogeneous mixtures in a centrifugal field, implemented in the device cyclone reverse flow type (V. Straus. Industrial gas purification, publishing house "Chemistry", 1981, pp. 258-261; A. G. Kasatkin. The main processes and apparatuses of chemical Technologies, Khimiya Publishing House, 1971, pp. 237-238, 241-243), - an analogue in which the mixture flow is swirled with the formation of rotational-translational motion of the main flow of the continuous light phase throughout the process, the precipitation of heavy dispersed centrifugal phases th field to form the heavy phase layer in the periphery of the swirling flow, allocating the heavy phase layer with a continuous flow of secondary light phase with the formation of the slip stream, reprecipitation heavy phase under the influence of the gravitational field, the drainage of the secondary flow a continuous light phase in the main flow of the continuous light phase.

The disadvantages of this method are:

- increased energy consumption of the process with increasing hydraulic resistance due to a change in the direction of translational motion of the main stream of the continuous light phase to the opposite with a rotation in the radial direction to the center of rotation, against the action of the centrifugal field;

- reduction of separation efficiency at maximum speeds due to vortex amplification when changing the direction of translational motion of the continuous light phase, which leads to the breakdown of the heavy phase layer along the entire length of the periphery of the swirling flow, its dispersion and ablation with the main flow (primary ablation);

- a decrease in separation efficiency due to the significant volume discharged with the heavy phase layer of the secondary stream of the continuous phase to 10% and its subsequent return to the main stream along the axis of the bypass stream at a speed sufficient to pick up and carry away the heavy phase from the bypass stream (secondary entrainment).

A known method of separating inhomogeneous mixtures in a centrifugal field, implemented in the device is a direct-flow type cyclone (Straus V. Industrial gas purification, Chemistry publishing house, 1981, pp. 251-255; A. Kasatkin. The main processes and apparatuses of chemical technology , publishing house "Chemistry", 1971, pp. 243-244; AS USSR No. 1409312), - a prototype in which the flow of the mixture is twisted with the formation of rotational-translational motion of the main flow of a continuous light phase throughout the process, precipitation is heavy dispersed phase under the influence of cent a reliable field with the formation of a heavy phase layer at the periphery of the swirling flow, the removal of a heavy phase layer with a secondary stream of a continuous light phase with the formation of a bypass stream, reprecipitation of a heavy phase under the influence of a gravitational field, the removal of a secondary stream of a continuous light phase into the main stream of a continuous light phase, in which, for the same sequence of actions, there is no change in the direction of translational motion of the main stream of the continuous light phase to the opposite direction with rotation in the radial direction SRI to the center of rotation, against the action of the centrifugal field and there is no return flow of the secondary continuous light phase along the axis of the slip stream.

However, in this method, the disadvantages of the previous separation method are not completely eliminated:

- an increase in the energy consumption of the process with an increase in hydraulic resistance due to a change in the direction of translational motion of the main flow of the continuous phase with the envelope of the outlet flow of a circular shape in the radial direction to the center of rotation, against the action of the centrifugal field;

- decrease in separation efficiency at maximum speeds due to vortex amplification when the main stream flows around the continuous light phase of the annular discharge flow, which leads to the breakdown of the heavy phase layer from the surface of the flow part in the zone in front of the discharge flow, its dispersion and ablation with the main flow (primary ablation) ;

- reduction of separation efficiency due to a significant volume of the secondary stream of the continuous light phase removed with the layer of the heavy phase to 10% and its subsequent return to the main stream at a speed sufficient to pick up and carry away the heavy phase from the gravitational deposition zone (secondary ablation).

The technical result consists in reducing the hydraulic resistance and reducing the primary and secondary ablation of the heavy phase.

The technical result is achieved by the fact that in the method for separating inhomogeneous mixtures, including swirling the flow of the mixture with the formation of rotational-translational motion of the main flow of the continuous light phase throughout the process, the precipitation of the dispersed heavy phase under the influence of a centrifugal field with the formation of a layer of the heavy phase at the periphery of the swirling stream, abstraction of a layer of a heavy phase with a secondary stream of a continuous light phase with the formation of the bypass stream (s), re-deposition of the heavy phase under the influence of gravitational field, the diversion of the secondary stream of a continuous light phase into the main stream of a continuous light phase, numerous exhaust flows are formed on the entire periphery of the swirling stream, each of which is throttled by restricting the width of the inlet section to a value not exceeding 1% of the radius of the periphery of the swirling stream, while they are directed outward at an angle not exceeding 45 ° from the direction of the swirling flow, then they are reduced to the rate of gravitational deposition of the heavy phase by smooth expansion with increasing msya deviation in the radial direction from the center of rotation of the swirling flow, thus the translational motion of the main flow continuous light phase throughout the process does not deflect in a radial direction toward the center of rotation.

The formation of numerous by-pass flows on the entire periphery of the swirling flow, their throttling by limiting the width of the inlet section to a value not exceeding 1% of the radius of the periphery of the swirling flow, while their direction outward at an angle not exceeding 45 ° from the direction of the swirling flow, then their reduction up to the rate of gravitational deposition of the heavy phase by smooth expansion with increasing deviation in the radial direction from the center of rotation of the swirling flow, it was possible to increase the effective separation during reduction of secondary entrainment due to the limitation of the volume of the secondary stream of the continuous light phase entering the by-pass flows, during the expansion of which its speed decreases to the rate of gravitational deposition of the heavy phase, and allowed to reduce the hydraulic resistance due to a slight deviation of the by-pass flows from the direction of the swirling flow with subsequent increasing deviation in the radial direction to reduce the length of the bypass stream.

The absence of a deviation of the translational motion of the main flow of the continuous light phase in the radial direction to the center of rotation throughout the process allowed to increase the separation efficiency, while reducing the primary ablation, by eliminating the formation of intense vortices, leading to the disruption and pickup of the heavy phase from the surface of the flow part.

The movement of the formed main flow of the continuous phase in the separation process without changing its direction allowed to reduce the hydraulic resistance.

The author knows methods or devices that implement methods for separating inhomogeneous mixtures in a centrifugal field, in which the outlet flows at the periphery of the swirl flow are formed by a porous structure or expanded metal mesh, but these methods do not provide the claimed technical result.

The author does not know how to separate inhomogeneous mixtures in a centrifugal field, in which the technical result would be achieved in a similar way.

The implementation of the method is illustrated by drawings:

- Figure 1 - separation scheme of heterogeneous mixtures in a centrifugal field;

- Figure 2 is a diagram of an elementary section of the bypass stream;

- Figure 3 is a diagram of the longitudinal direct by-pass flows;

- Figure 4 is a diagram of a longitudinal circular bypass flows;

- Figure 5 is a diagram of a longitudinal spiral bypass flows;

- Fig.6 - dependence of the pressure drop on the air flow during the test without water supply;

- Fig.7 - field of vectors of hydrodynamic calculation.

Figure 1 presents: inlet flow of the mixture 1; rotational-translational motion of the main stream of continuous light phase 2; the direction of centrifugal deposition of the dispersed heavy phase 3; heavy phase layer 4; the periphery of the swirling flow 5; branch flows 6; elementary section 7 of the discharge stream 6; direction of gravitational deposition of the heavy phase 9; heavy phase collection zone 10; secondary stream of continuous light phase 11; continuous light phase yield 12.

Figure 2 additionally presents: the input section 13 of the elementary section 7 of the discharge stream 6; the projection 18 of the elementary section 7 on the surface of the longitudinal section of the swirling stream; the projection 19 of the elementary section 7 on the surface of the cross section of the swirling stream; input section width h; the vector of the axial component of the flow motion V _a ; the vector of the tangential component of the flow motion V _τ ; the vector of the radial component of the flow motion V _r ; the motion vector of the swirling stream near the periphery of the stream V _sn ; motion vector of the discharge flow in the inlet section V _op ; angle α between the directions of swirling and by-pass flows.

Figure 3, 4, 5, 7 additionally presents the periphery of the longitudinal bypass stream 17.

Figure 6 presents: the dashed line is the proposed method, the solid line is the analogue.

The method of separation of heterogeneous mixtures in a centrifugal field is as follows.

At the entrance to the process, the flow of the heterogeneous mixture 1 (Fig. 1) is twisted with the formation of rotational-translational motion of the main flow of the continuous light phase 2 throughout the process. An inhomogeneous mixture consists of a main stream of a continuous light phase and a dispersed heavy phase. Under the influence of a centrifugal field, the dispersed heavy phase 3 is precipitated and a concentrated layer of the heavy phase 4 is formed on the periphery of the swirling flow 5. The spin speed is selected based on the required separation quality and the corresponding minimum particle mass of the dispersed phase. In the case of a liquid heavy phase, the formed layer is a liquid film. As you move the main stream of the continuous light phase 2 is purified from the dispersed heavy phase. The motion energy of the main stream of the continuous phase 2 is transferred to the layer of the heavy phase 4, which has the same direction of rotational-translational motion, but a lower speed.

Under the influence of a centrifugal field, the layer of the heavy phase 4 is withdrawn, forming on the entire periphery of the swirling stream 5 numerous bypass streams 6. The bypass streams consist of a heavy phase and a secondary stream of a continuous light phase.

Since the bypass flows can have a different shape, when summarizing the description of their properties, it is convenient to consider the elementary section 7 (figure 2) of the bypass stream. The properties of the elementary sections are identical for all elementary sections with the same dimensions. The elementary section in question has a square inlet section 13. The shape of the elementary section is not limited to the one presented. The motion vector of the outlet flow V _op at the input of the elementary section is directed outside the swirling flow 2 at an angle α not exceeding 45 ° to the motion vector of the swirling flow V _z near the periphery, immediately before the outlet. Vector V _zp is the resulting vectors of the axial V _a and tangential V _τ components, and the vector V _op is the resulting vectors of the axial V _a , tangential V _τ and radial V _r components of the flow motion. Conventionally, the vectors V _op and V _{zp are} depicted emanating from one point, and the vectors V _zp , V _a and V _τ lie in the plane of the input section 13.

Point outflows are formed from single elementary sections 7, and longitudinal outflows are formed from a plurality of elementary sections combined along lines on the periphery of swirling flow 5. When elementary sections are located along generatrices, circles or spiral lines on the periphery of swirling flow, longitudinal straight lines are formed (Fig. 3), longitudinal annular (figure 4) or longitudinal spiral by-pass flows, respectively (figure 5). The greatest effect is obtained during the formation of spiral branch flows 6 with the longitudinal edges of the input sections of these flows located transversely, perpendicular to the trajectory of the swirling stream.

The width h of the inlet section 13 of the elementary section of the bypass stream is limited to a value not exceeding 1% of the radius of the periphery of the swirling stream 5 to limit the volume of the secondary stream of the continuous light phase entering the bypass streams. The preferred value of the width h is several times smaller than the average thickness of the layer of the heavy phase 4. Thus, carry out the gradual removal of the layer of the heavy phase with a minimum amount of light phase of the secondary stream. In the case of a solid heavy phase, the width h cannot exceed the maximum size of the dispersed particles. In the case of a liquid heavy phase, at sections of the periphery 5 of the swirling flow completely covered by a liquid film (heavy phase layer 4) of the inlet cross sections of the branch flows 6, the secondary stream of the light phase does not enter the branch flows.

As the main flow of the continuous light phase 2 advances, the layer of heavy phase 4 is withdrawn gradually, decreasing its thickness. After the heavy phase layer is completely removed, only the secondary stream of the continuous light phase is directed into the bypass flows along the periphery of the swirling stream, determined taking into account fluctuations in the amount of the dispersed phase in the mixture.

In the direction of travel, the by-pass flow gradually expands and slows down to the gravitational deposition rate of the heavy phase with increasing deviation in the radial direction from the center of rotation of the swirling flow to provide a larger expansion angle, reduce the length of the by-pass flow and a more uniform distribution of velocities in the output section. The specified radial direction is clearly shown on the projections of the elementary section 6 (figure 2) on the surface of the longitudinal 18 and transverse 19 cross-sections of the swirling flow.

The movement of the longitudinal by-pass flows of various shapes can be considered with the components of the movement in the input section 13 (figure 2) - V _a , V _τ and V _r . The increase in the radial component of the movement V _r occurs in direct by-pass flows (Figs. 3, 7) due to a decrease in the tangential component of the motion V _τ , in the ring by-pass flows (Fig. 4) due to a decrease in the axial component of the motion V _a , and in spiral by-pass flows (Fig. 5) by reducing the tangential V _τ and axial V _a components of motion.

At the exit of the bypass flows 6, under the influence of the gravitational field, the heavy phase 9 is precipitated (FIG. 1) and collected in zone 10. The gravitational deposition rate is selected based on the required separation quality and the corresponding minimum particle mass of the dispersed phase. In the case of a liquid heavy phase, the liquid film (heavy phase layer 14) is directed along the periphery of the swirling main stream 5, passing to the periphery 17 of the bypass stream (Fig.7), and then through it to the collection zone of the heavy phase 10.

The secondary stream of the continuous light phase 11 exiting the by-pass streams is directed to the main stream of the continuous light phase 2 to the outlet of the purified stream of the continuous light phase 12. The direction of the secondary stream from the gravitational deposition zone of the heavy phase 9 is not limited to that shown in Figure 1 — the secondary stream can be directed to recirculation to the inlet of the mixture 1 or to any point in the stream, outside the process under consideration, with less pressure.

Throughout the process, the translational movement of the swirling main flow of the continuous light phase is not radially deflected to the center of rotation, which allows you to maintain the lowest possible pressure drop during the separation process, thus ensuring that no large eddies form on the periphery of the swirling flow. The main flow of the continuous light phase may have a small radial component of the direction of motion, but its sharp change in the direction of the center of rotation, which is present in the analogues, is excluded.

The location in space of the axis of rotation of the swirling flow is not limited to the example shown in figure 1 with the direction of movement of the main stream from the bottom up. With a different orientation of the axis, the location of the collection zone of the heavy phase 10 and the removal of the secondary stream 11 are corrected. The shape of the periphery of the swirling flow is not limited to the cylindrical shape shown in Figure 1, and can be with straight or curved generators.

Example 1

The proposed separation method was formed in the process of improving the method implemented in a device such as a centrifugal separation element (USSR AS No. 1409312) - an analogue used in the gas industry for several decades.

To carry out comparative tests of the proposed method and analogue, devices with identical swirlers and with geometric parameters of the flow part (periphery of the swirling flow) were taken: inner diameter 100 mm, height 300 mm.

The geometric parameters of the bypass flows of the proposed method: quantity - 6 pcs., Evenly distributed over the cylindrical surface of the flowing part; the shape of the by-pass flows corresponds to a variant of the direct longitudinal by-pass flows (Fig. 3); the width of the inlet section of the outlet flow is 0.5 mm.

Technological parameters of the pilot work: continuous medium - air; dispersed medium - water; outlet pressure - atmospheric; temperature + 30 ° С.

The dependence of the pressure drop in the process on air flow during the test without water supply is shown in Fig.6, where the dashed line shows the proposed method, and the solid line is the analogue.

The pressure drop of the proposed method compared with the analogue is less by 12-33%.

Tests of the device that implements the proposed method, and the analogue with the water supply was carried out sequentially with air flow rates close to 4, 6, 8, 10, 12 m ³ / min. Tests with water supply were carried out with a multiple exceeding the usual liquid content in the gas for typical processes of using direct-flow centrifugal elements to determine the maximum possible water concentrations. At each air flow rate, the water flow rate increased gradually from zero to the maximum Q _max , which is determined either by the start of flowing from the outlet cross section of the main stream, with the release of about 600 g / min of water, or, in the absence of flowing, is the maximum possible water flow at the test bench 1.0-1.4 m ³ / hour.

Table 1 The ablation of water with air at the maximum flow rate Q _{max of the} proposed method Interval of air consumption, m ³ / min Q _max , m ³ / hour Water entrainment 4-6 1,2 No more than 0,05% 6-10 1.4 No more than 1% 10-12 1.4 No more than 3%

table 2 Water entrainment with air at maximum water flow rates Q _max analogue Interval of air consumption, m ³ / min Q _max , m ³ / hour Water entrainment 4-6 0.6 More than 10%
Accumulation of water in the lower zone of the flowing part, periodic fountain emissions 6-10 0.4 More than 10%
Constant gushing 10-12 1,0 High-speed fog, pulsating fine emissions

The proposed method in terms of the maximum content of the dispersed phase at the inlet and entrainment of the dispersed phase at the outlet significantly exceeds the analogue. Moreover, the proposed method does not have the following significant disadvantages of the analogue: the accumulation of the heavy phase in the lower zone of the flow part at reduced flow rates with periodic emissions, since in the new method the selection of the heavy phase is performed over the entire surface of the flow part; the formation of a finer dispersed phase and fog at higher flow rates, since the new method does not have obstacles that dramatically change the translational motion of the main flow, which leads to the formation of intense vortices and flow oscillations. The absence of these disadvantages expands the range of normal operation of the new method.

Example 2

To assess the influence of the transverse size of the input section of the outlet flow of the proposed method, computer simulation was performed in a specialized computer program for hydrodynamic calculations.

To carry out the calculation, a model was adopted with the geometric parameters of the flow part that are identical with the parameters of the tested devices: inner diameter 100 mm, height 300 mm.

The geometric parameters of the bypass stream of the proposed method: the length of the sector occupied by the bypass stream on the circumference of the cross section of the flowing part involves the placement of 36 pcs. such by-pass flows along the entire perimeter of the specified circle; the shape of the by-pass flows corresponds to a variant of the direct longitudinal by-pass flows (Fig. 3); the width of the inlet section of the discharge flow is made in 5 versions - 0.25; 0.5; 1.0; 2.0; 4.0 mm.

Technological parameters of the calculation: medium - air; outlet pressure - atmospheric; temperature + 30 ° С.

Figure 7 presents the field of vectors of hydrodynamic calculation. The sizes of the arrows of the vectors are proportional to the velocities in the cross section of the device. In the bypass stream, the speed is noticeably lower than the speed of the swirling stream at the periphery.

The numerical results of the hydrodynamic calculation are as follows.

Table 3 The drop in the velocity of the discharge flow at the speed of the main flow at the periphery of the flow part of 7.3 m / s Outflow Parameters The cross-sectional size of the inlet section of the outlet flow 4.00 mm 2.00 mm 1.00 mm 0.50 mm 0.25 mm The speed at the outlet of the bypass stream, m / s 5.97 4.60 2,36 0.83 0.22 Speed drop eighteen% 38% 68% 89% 97% Pressure drop, Pa 13.7 24.0 34.6 37.0 38.5

Table 4 The drop in the velocity of the discharge flow at a velocity of the main flow at the periphery of the flowing part of 15.1 m / s Outflow Parameters The cross-sectional size of the inlet section of the outlet flow 4.00 mm 2.00 mm 1.00 mm 0.50 mm 0.25 mm The speed at the outlet of the bypass stream, m / s 12.87 9.84 5.30 2.05 0.94 Speed drop 13% 34% 49% 86% 94% Pressure drop, Pa 46.0 93.6 140.5 153.0 152.5

A significant drop in the velocity of the discharge flow is observed when the inlet section is less than 1% of the radius of the cylindrical surface of the flow part (the periphery of the swirling flow). The flow rate decreases to the rate of gravitational deposition of the heavy phase.

Claims (1)

A method for separating inhomogeneous mixtures, including swirling the mixture flow with the formation of rotational-translational motion of the main flow of the continuous light phase throughout the process, the precipitation of the dispersed heavy phase under the influence of a centrifugal field with the formation of a heavy phase layer at the periphery of the swirling flow, removal of the heavy phase layer with the secondary flow continuous light phase with the formation of the diversion flow (s), reprecipitation of the heavy phase under the influence of the gravitational field, secondary discharge flow of a continuous light phase into the main stream of a continuous light phase, characterized in that on the entire periphery of the swirl flow, numerous bypass flows are formed, each of which is throttled by limiting the width of the input section to a value not exceeding 1% of the radius of the periphery of the swirl flow, while directed outward at an angle not exceeding 45 ° from the direction of the swirling flow, then reduced to the rate of gravitational deposition of the heavy phase by smooth expansion with increasing deviation in rad nom direction from the center of rotation of the swirling flow, thus the translational motion of the main flow continuous light phase throughout the process does not deflect in a radial direction toward the center of rotation.

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