SU1620510A1 - Method of melting and/or crystallizing substances - Google Patents

Abstract

The invention relates to the management of thermodynamic fluxes and can be used in the design and optimization of various mass transfer processes, including heat and mass transfer in the liquid phase, melting and / or crystallization. The invention provides control of convective mass transfer, acceleration of processes and reduction of energy consumption. The method involves heating a substance and exposing the liquid phase to vibrations excited by a system of solid bodies with sharp edges. The configuration and direction of oscillations of each solid body is chosen in accordance with the given structure of convection, and the frequency and amplitude from the given dependencies. 3 il. S l

Description

The invention relates to the control of thermodynamic flows and can be used in the development and optimization of various mass transfer processes involving heat and mass transfer in the liquid phase.

The purpose of the invention is to control convective mass transfer, thereby ensuring that the process is accelerated and energy consumption is reduced.

The invention is illustrated in the diagrams showing examples of controlling the heat and mass transfer in the liquid phase by creating predetermined convection structures that allow optimizing the conditions of various mass transfer processes.

FIG. 1 shows the process of melting and evaporation under conditions of lateral heating of an open crucible; Fig. 2 shows the process of mass transfer between the dissolution and crystallization zones in the horizontal layer of the solution; Fig. 3 shows the process of melting the starting material and stirring the melt during its continuous crystallization in a container with lateral heating.

Example 1. FIG. 1, the proposed method is used to optimize the conditions of melting and evaporation of a substance 1 placed in a cylindrical crucible 2, which is mounted on a stand 3 inside a tubular heater 4. Heat and mass transfer during this process is characterized by the fact that the melt has a maximum temperature at the walls of the crucibles, resulting in the melt has a thermogram

Vitation convection, the structure of which is shown by dashed line 5. At the same time, near the walls, the melt movement is directed upwards, and in the center of the crucibles - downwards, and the melt temperature on the surface significantly exceeds the melting temperature, at which the melt is located in the lower part of the crucibles at the interface with the solid substance The conditions of overheating of the melt near the walls may cause its decomposition, and intense evaporation from the surface

Optimization of the conditions of these processes consists in reducing the overheating of the melt. For this, the structure of convection, depicted by line 7, is set, in which the melt moves to the center upwards and downwards along the walls. To create it, a solid body in the form of a disk 8, fixed with the possibility of vertical oscillations, is brought into contact with the surface of the melt (the mounting of the disk in Fig. 1 is not shown). In the specific case of sodium nitrate melting (sound speed of 1500 m / s, viscosity 3.17 mPa-s) in a crucible with a diameter of 65 mm and a height of 60 mm with a disk diameter of 17 mm, the oscillation frequency was equal to 78 Hz, which is less than the limit value of 20000 Hz and the amplitude value is set to 0.9 mm, which ensures the circulation of the melt in the entire volume of the crucibles. The created structure of convection allows the melt overheating to be reduced by 30 ° C with the substance completely melted.

Example 2. In FIG. 2, the proposed method is used to optimize the mass transfer conditions between the dissolution zone 8 and the crystallization zone 9 in the horizontal layer of the solution 10 contained in the vessel 11.

In this process, the rate of mass transfer is limited by the rate of diffusion transfer of the dissolved substance from the dissolution zone to the crystallization zone. Optimization is to increase the rate of transfer of the solute. For this, the structure of convection in solution is defined, which is characterized by a circulation flow extending from one zone to another. To create it, the configuration of a system of solids is chosen

is in the form of a vertical plate 12, i

partially immersed in the solution and

fixed with horizon capability

0

"J Q 5 55

thirty

35

40

45

50

tal oscillations, and a horizontal plate 13 brought into contact with the surface of the solution and fixed with the possibility of vertical oscillations (the fastening of the plates 12 and 13 in Fig. 2 is not shown).

At small oscillation amplitudes, the plate has circulating streams 14-17, and with an increase in the amplitude of oscillations, streams 15 and 16 do not interact and merge into one stream 18, which provides transfer of the solute between zones, and streams 14 and 17 turn into streams 19 and 20 respectively, contributing to the mixing of the solution in the zones. In the particular case of a layer of an aqueous solution of sodium nitrate (speed (sound 1500 m / s, viscosity 1, 1 mPa-s) 100 mm thick with a distance between 250 mm and plate sizes of 50 mm, the oscillation frequency of plate 12 was chosen to be 157 Hz, the plates are 13–168 Hz, which is less than the limiting value of 7000 Hz, and the amplitudes are set to 3.25 and 3.15 mm for plates 12 and 13, respectively, which creates a convection structure with a circulating flow 18. The convection structure created provides multiple acceleration of the process.

Example 3. FIG. 3, the proposed method has been used to optimize the melting processes of the initial substance and the mixing of the melt 21 in the rectangular container 22, when it moves downwardly relative to the heater 23, the crystals grow 24. The initial heat and mass transfer process in the melt is characterized by the presence of a circulation flow of thermogravitational convection, whose structure shown by dashed line 25. This flow, directed down the center of the container 4, causes a rapid vertical movement of the original substance, continuously entering the surface of the melt, which leads to a violation of the stationarity of the crystallization conditions due to insufficient heating of the starting material and mixing of the melt

Optimization of the conditions of mass transfer processes in this case consists in providing heating of the melted source material mainly in the upper part of the melt layer and improving the mixing of the melt in the whole volume. For this purpose, the structure of convection in the melt is defined, which is characterized by the presence of vertically interacting but not pouring circulation streams. To create it, the configuration of the solid body system is selected as horizontal rectangular plates in contact with the surface of the melt, and parallel to them is a rectangular cross-section bar 26 immersed in the melt between them, all bodies can make vertical oscillations.

At small amplitudes, oscillations in this system occur in the form of circuits Schun fluxes of the type of the indicated flux 27, which, as the amplitudes of the oscillations increase, increase and interact, leading to a predetermined structure of convection with circulating fluxes shown by lines 28-31. This convection structure provides for the melting and heating of the source material during its circulation in stream 28 and the mixing of the melt in the whole volume due to the interaction of the flows 28-31, weakening the influence of the melting process on the crystallization process.

R case of continuous crystallization of sodium nitrate in a container with a side of 100 mm with a width of plates 32 and 33 and a beam of 26-20 mm, a beam height of 30 mm, a melt layer height of 100 mm, a distance between the plates 32 and 33 20 mm, distance from the surface melt to the beam 26–30 mm, the oscillation frequencies of the plates 32 and 33 are chosen to be 157 Hz, and the beam to 26–73 Hz, which is less than the limiting value — 12000 Hz; and the amplitude values are set to 0.3 mm for the plates 32 and 33, and for the beam - 1.2 mm, which ensures the interaction of circulation flows and the complete suppression of thermogravity constant convection. The created structure of convection makes it possible to stabilize the conditions of continuous crystallization.

The configuration and direction of oscillations of each solid body in all examples is chosen in accordance with the given structure of convection, cos

given in re: ultata of formation at the edge of bodies of vortices and their interaction. The oscillation frequency is set from

f C / 4L,

and the amplitude of the dependence

A (D-d) / (3fC-y2ff), where C

T -

A dud

R

0

| U

- sound velocity in the liquid phase, m / s;

maximum size of solid, mm; amplitude, mm; distances in the direction from the sharp edge of the body and the edge of the vortex, respectively; oscillation frequency, Hz; viscosity of the liquid phase, mPas.

five

0

Using the proposed method of controlling the heat and mass transfer in the liquid phase makes it possible to optimize the conditions of various mass transfer processes by creating a given convection structure, on which the spatial distribution of mass and heat flux significantly depends. As the analysis and experimental studies show, using the proposed method achieves a positive technical and economic effect, expressed in the intensification of mass transfer processes, improving the quality of the output product, and resource saving.

Claims (1)

Claim 0 A method of melting and / or crystalline substances, which includes heating when vibrations induced by a system of solids with sharp edges are applied to the liquid phase, so that, in order to control convective mass transfer , ensuring due to this acceleration of the process and reduction of energy consumption, the configuration and direction of oscillations of each solid body is chosen in accordance with the predetermined structure of convection created by the formation of vortices at the edge of the bodies 5 and their interaction, while the oscillation frequency f (Hz) azhdogo body set of conditions f C / (4L), five 0 and the amplitude of oscillation - from the dependence A (D-d) / (3fay-25), where C is the speed of sound in the liquid phase, m / s; L is the maximum size of a solid body, mm; A and d R - amplitude, mm; - distance in the direction of oscillations from the sharp edge of the body and the border of the vortex to the border of the liquid phase, respectively, mm; viscosity of the liquid phase, mPa-s. FIG. one t FIG. 2 13 A   t 172 ° . / And 25 22 21 FIG. 3