RU2753756C1 - Apparatus for conducting mass exchanging and reaction processes in single-phase and multi-phase media - Google Patents

Abstract

FIELD: mixing equipment.

SUBSTANCE: invention relates to chemical, petrochemical, food, pharmaceutical and other industries. The apparatus for conducting mass exchanging and reaction processes in single-phase and multiphase media contains an elongated housing, pumps for feeding the initial components. The cross-section of the housing is made periodically changing along the axis. In this case, the housing consists of identical elements connected in series, including a zone of smooth narrowing, a narrow neck, a zone of smooth expansion, a wide neck. Moreover, swirlers are installed in the zones of smooth narrowing and expansion of the elements.

EFFECT: increased efficiency of meso-and micro-mixing, increased intensity of heat and mass transfer in the apparatus, including at low Reynolds numbers (less than 1000).

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Description

The invention relates to the chemical, petrochemical, food, pharmaceutical and other industries, and can be used for mixing, processing of heterogeneous systems liquid-liquid, liquid-gas, liquid-solid particles, and liquid-gas-solid particles in various technological processes, such as absorption, gas-liquid reactions, emulsification, liquid extraction, solids dissolution (including chemical reaction), leaching, impregnation, etc.

A device for intensifying reaction and mass transfer processes in heterogeneous systems, implemented in an apparatus for dissolving solid particles in a liquid (Axelrud G.A. .155), in which a liquid carrying solid particles moves through a pipe, the area of which is variable along the length of the pipe. In this case, the pipe consists of a plurality of successively connected elements of the same shape, consisting of two parts: one part of each element is a spindle-shaped hollow body, the second is a cylindrical neck. When moving in such a pipe, the liquid constantly changes its speed. Solid particles also periodically change the speed of their movement, sometimes lagging behind the liquid accelerating in a narrow section, then ahead of the liquid decelerating in a wide section. Due to the inertia of solid particles in the pipe, an additional velocity of the relative motion of the phases is created, which contributes to an increase in the mass transfer coefficient. However, such an inertial effect is possible only in the presence of a nonzero density difference between solid or liquid (dispersed phase) and liquid media (continuous phase), and it will be significant if these densities differ significantly. Studies have shown (A.N. Phan, A. Harvey, Development and evaluation of novel designs of continuous mesoscale oscillatory baffled reactors, Chemical Engineering Journal, 159 (2010) 212-219) that the known device has far from optimal geometry. In particular, it was shown that the distribution of the residence time in such an apparatus is rather wide, which leads to a large uneven effect on homogeneous and heterogeneous media in the apparatus. As a result, the product obtained at the outlet of the apparatus can consist of several substances (when carrying out chemical reactions), which is characterized by low selectivity.

In addition, the known invention does not provide for turbulization of the wall layer, which leads to a decrease in the efficiency of heat transfer from the inner surface of the apparatus to the medium being processed.

There is a known method for intensifying reaction and mass transfer processes in heterogeneous systems, which consists in exciting oscillations in a heterogeneous system by passing it through a pipe with a variable cross-section, characterized in that the excitation of oscillations in a heterogeneous system during its movement alternates with the absence of oscillatory effects, and in a heterogeneous system gas is introduced one or more times, as well as an apparatus for implementing the method, consisting of a blower and one or more pipes with a variable cross-section, devices for supplying components and removing products, characterized in that the pipe consists of sections with a periodically varying cross-section, alternating sections with constant cross-section (US Pat. RF 2264847, B01F 5/00, B01J 19/10).

The known method and apparatus can improve efficiency, reduce hydraulic losses, and simplify the design of the apparatus.

The disadvantages of the known apparatus include a relatively wide distribution of the residence time (especially at Reynolds numbers less than 1000), insufficiently high intensity of heat and mass transfer in the wall zone.

Known apparatus of cylindrical shape with a screw insert located along the wall of the apparatus along its entire length, and the winding step was made 1.5 times the inner diameter of the apparatus (prototype) (AN Phan, A. Harvey, Development and evaluation of novel designs of continuous mesoscale oscillatory baffled reactors, Chemical Engineering Journal, 159 (2010) 212-219). Studies have shown that an apparatus with this geometry can significantly reduce the irregularity of the residence time, especially when operating in the oscillation mode. The disadvantages of this device include the impact on the treated medium mainly in the near-wall zone, while in the core of the flow (far from the walls) the intensity of the impact is not so great. This leads to the fact that when using this device in the mode of continuous supply of media with a fixed flow rate, the distribution of the residence time becomes quite wide.

The objective of the present invention is to increase the mixing efficiency at macro-, meso- and minimum-scale levels, to increase the intensity of heat and mass transfer in the apparatus, including at low Reynolds numbers.

The task is achieved by the fact that in the proposed apparatus for carrying out mass exchange and reaction processes in single-phase and multiphase media, containing an elongated body, pumps for supplying the initial components, according to the invention, the cross-section of the body is made periodically changing along the axis, while the body consists of sequentially connected identical elements, including a zone of smooth tapering, a narrow throat, a zone of smooth expansion, a wide throat, and in the zones of smooth tapering and expansion of the elements, swirlers are installed.

The claimed device makes it possible to reduce the unevenness of the stay (narrowing the distribution curve of the residence time in the apparatus, i.e. to improve the macro-mixing), to increase the efficiency of meso- and micro-mixing, and, as a result, to increase the intensity of heat and mass transfer in the apparatus, including at low numbers Reynolds (less than 1000).

The claimed technical solution is new, has an inventive step and is industrially applicable.

The proposed device can be manufactured in various versions: with the connection of elements by welding, using flanges, threaded couplings, yoke couplings, smooth couplings or in other ways.

FIG. 1 shows an assembled elongated body, including several series-connected identical elements, FIG. 2 - a housing element in a welded design with a swirler installed in it, in Fig. 3 and 4 - a housing element in a flange design, with a swirler installed in it (in Fig. 3 - with two short swirlers, in Fig. 4 - with one long swirler).

FIG. 1 shows the proposed device containing a body 1 in an elongated shape, pumps for supplying the initial components (not shown in Fig. 1 conventionally), while the cross section of the body 1 is made periodically changing along the axis, the body consists of a number of series-connected identical elements 2, including a zone 3 of smooth tapering, a narrow throat 4, a zone of 5 smooth expansion, a wide throat 6, and in the zones of smooth tapering and expansion there are swirlers 7. The number of elements 2 is determined by a specific process and is usually from three to ten; its more precise value is subject to determination by experimental or calculation methods.

In the embodiment shown in FIG. 1, 3 and 4, the elements 2 are connected to each other by means of flanges 8. In the embodiment shown in FIG. 2, the elements 2 are connected by welding.

Swirlers 7 can be made in the form of rosette devices, similar to those used, for example, in direct-flow cyclones, or in the form of a wire wound in the form of a cylindrical-conical helical spiral from a wire, as shown in Fig. 1-4. The second option is preferable because it is less costly, has less resistance and is less prone to overgrowth.

When connecting elements 2 by welding (Fig. 2), elements 2 can be made of two parts 2a and 2b, connected by welding (Fig. 2), and a swirler 7 is installed in the cavity formed when parts 2a and 2b are connected In this case, parts 2a and 2b are a part of the body with a narrow neck 4, a zone 5 of smooth expansion, a wide neck 6.

Elements 2, connected to each other by welding, can also be made in the form, including a wide neck 6, a smooth tapering zone 3, a narrow neck 4, a smooth expansion zone 5, a wide neck 6, i.e. elements 2 on both sides are joined to each other by wide necks 6 (as shown in Fig. 2), or narrow necks 4. The swirler 7 can be made in the form of two separate parts 7a and 7b (as shown in Fig. 3), but it is preferable making the swirler 7 in the form of a single piece (as shown in Fig. 4). The swirler 7 can be fixed relative to the body 1 due to the friction force, which arises, in turn, due to the elastic forces caused by the compression of the wire wound in the form of a cylindrical-conical helical spiral, of which the swirler is made 7. Other methods of fastening the swirler 7 are also possible, for example, when by welding to the inner surface of the housing 1.

When assembling the body 1, the elements 2 are connected by welding or using flanges 8, between which gaskets are installed, while the flanges 8 are connected using fasteners (gaskets and fasteners are not shown in Fig. 1 conventionally).

The proposed apparatus works as follows.

The solutions of the initial media are fed by pumps (not shown in Fig. 1 conventionally) to the inlet of the apparatus body (shown by arrows in Fig. 1) at predetermined flow rates. As the solutions move along the axis of the apparatus, the solutions experience the action of several factors: 1) a periodic change in the cross-sectional area along the movement (along the streamlines), due to the presence of zones 3 of smooth narrowing, narrow necks 4, zones 5 of smooth expansion, wide necks 6, leading to the appearance of pulsations when the mixed solutions move along the axis of the apparatus; 2) swirling flows, created and maintained along each of the elements 2 by means of swirlers 7; 3) near-wall turbulization of the flow caused by the flow around the wire from which the swirlers are made 7.

Due to the superposition of these three factors in the proposed device, conditions are created to achieve the desired technical result.

The solution to the problem of the proposed invention is achieved as follows:

1) an increase in the uniformity of the residence time in the apparatus is achieved due to a significant improvement in macro-, meso- and micro-mixing;

2) increasing the efficiency of mixing, namely, achieving a predetermined high level of macro-, meso- and micro-mixing with reduced energy consumption;

3) an increase in the intensity of heat and mass transfer in the apparatus, including at low Reynolds numbers - as a result of an improvement in the hydrodynamic situation in the apparatus, namely, mixing conditions at all levels.

It is customary to distinguish three levels (scales) of mixing - macro mixing, meso mixing and micro mixing (Baldyga, J., Bourne, JR, 1986. Transport phenomena and hydrodynamics of complex flows. In: Cheremisinoff, NP (Ed.), Encyclopedia of Fluid Mechanics, vol 1. Gulf Publishing Company, Houston, TX, p. 145; Baldyga, J., Bourne, JR Interactions between mixing on various scales in stirred tank reactors // Chem. Eng. Sci. 1992, 47, 1839).

Macro-mixing corresponds to the scale of the apparatus as a whole. It determines the conditions for the transfer of matter by large-scale convection throughout the volume of the flow in the reactor, i.e. the average speed of movement of macrovolumes. The main characteristic of macro-mixing is the residence time distribution curve. In essence, the residence time characterizes the duration of the presence of the macrovolumes of the liquid from the point of entry into the apparatus to the point of exit from it. At the same time, it is precisely this motion that is responsible for the transfer of macrovolumes of liquid from zones without mixing to zones with a high rate of energy dissipation. A simple example is circulating flow in a reactor with a propeller or turbine stirrer.

Meso-mixing takes place at an intermediate level and is responsible for large-scale turbulent transfer between the energy-carrying flow introduced into the apparatus and its environment. A fast chemical reaction usually takes place in the vicinity of the injection point (zone of "feed", input of the "fresh" stream), which forms a "cloud" (clot, English: plume, blob) with a high concentration of the product around the injected stream. This cloud is an intermediate scale between the micromixing level and the size of the reactor. The spatial evolution of a cloud can be identified as a process of turbulent diffusion. Another aspect of meso-mixing relates to the inertial-convective process of disintegration of large vortices, and is characterized by an almost complete absence of the influence of molecular diffusion. On the other hand, inertial-convective mixing influences micro-mixing processes. A complete understanding and accurate description of inertial-convective mixing is still lacking. The kinetic energy of turbulence k, the scale of the length of turbulent fluctuations L, and their combination, expressed by the coefficient of turbulent diffusion D _t, are used as quantitative characteristics of meso mixing. At the same time, meso-mixing also depends on specific conditions, such as the pipe diameter, the ratio of the feed rates and the average speed of the medium in the apparatus.

Micro-mixing, the last stage of mixing in traditional apparatus, consists of visco-convective deformation of the elements of the liquid, which accelerates the breakdown of liquid aggregates up to the diffusion scale [Baldyga, J., Bourne, JR, 1989. Simplification of micro-mixing calculations: I. Derivation and application of a new model. Chem. Eng. J. 42, 83-92]. The selectivity of the reactions ultimately depends on micromixing, i.e. on how the reagents are mixed at the molecular level [Baldyga J., Bourne JR Turbulent Mixing and Chemical Reactions. Wiley, Chichester, 1999]. This mechanism entails the involvement (English: "engulfment") and deformation of vortices of the Kolmogorov scale λ _k and is the limiting process in the reduction of local concentration gradients. Quantitative characteristics are the micro-mixing time associated with the rate of energy dissipation ε [Baldyga J., Bourne JR Turbulent Mixing and Chemical Reactions. Wiley, Chichester, 1999]: the higher the ε, the better the micromixing and the higher the selectivity of fast reactions.

The basic version is illustrated by the following example (example 1)

EXAMPLE 1. Dispersion of oil droplets in water (emulsification) and liquid extraction in a known device.

Dispersion of drops of sunflower oil in water was carried out in a known device (US Pat. RF 2264847) at room temperature. The diameter of the narrow neck was 10 mm, the wide neck was 20 mm, the number of elements connected in series was 10; the total volume of the apparatus is 180 ml. At a water flow rate of 0.7 m3 / h and an oil flow rate of 0.007 m3 / h, the average oil droplet size was 180 μm. The residence time of the mixture in the reactor was 0.926 s. The same device was used to study the mass transfer during the extraction of succinic acid from n-butanol droplets into water. It was revealed in the experiments that no more than 7.2% of succinic acid passes into the aqueous phase, which is due to an insufficiently high coefficient of mass transfer from the droplet surface and an insufficiently developed phase contact surface.

Thus, the known device makes it possible to obtain relatively small droplets, but the level of mixing is not high enough to ensure intensive mass transfer.

The proposed option is illustrated by the following example (example 2)

EXAMPLE 2. Dispersion of oil droplets in water (emulsification) and liquid extraction in the proposed device.

The processes of emulsification and extraction, described in example 1, were carried out in the proposed device (see Fig. 1), made according to the claims with a narrow neck diameter of 10 mm and a wide neck diameter of 20 mm. In the zones of smooth contraction and expansion of the apparatus, swirlers are inserted, made in the form of conical helical springs wound from wire (steel 12X18H10T), as shown in Fig. 1 and FIG. 4.

Water and oil were supplied at the same flow rates as in example 1. The resulting oil droplets had an average size of 80 μm, which is 2.25 times higher than in the known device.

The process of extraction of succinic acid was carried out according to the method described in example 1. Experiments have shown that 52% of succinic acid passes into the aqueous phase, which is 7.36 times higher than in the base version.

Thus, the coefficient of mass transfer in the proposed device with the specified parameters increased by 3.27 times compared with the known analogues.

Similar experiments were carried out at a water flow rate of 0.006 m ³ / h and an oil flow rate of 6⋅10 ^-5 m ³ / h, while the average size of oil droplets was 280 μm (1.7 times less than for the basic version), and the share of succinic acid transferred was 74% (5.4 times higher than for the baseline variant).

This result confirms an improvement in the mixing efficiency at macro-, meso- and minimum-scale levels, an increase in the intensity of mass transfer in the apparatus, including at low Reynolds numbers.

Taking into account the analogy of the processes of energy and matter transfer, one can expect an intensification of heat transfer from the walls to the core of the flow.

Thus, the use of the proposed device allows for an increase in the mixing efficiency at macro-, meso- and minimum-scale levels, an increase in the intensity of heat and mass transfer in the apparatus, including at low Reynolds numbers.

Claims (1)

An apparatus for carrying out mass transfer and reaction processes in single-phase and multiphase media, containing an elongated body, pumps for supplying initial components, characterized in that the cross-section of the body is made periodically changing along the axis, and the body consists of series-connected identical elements including a smooth narrowing zone , a narrow throat, a zone of smooth expansion, a wide throat, and swirlers are installed in the zones of smooth narrowing and expansion of the elements.

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