RU2542241C1 - Continuous preparation of multicomponent mixes of loose materials - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method comprises continuous proportioning of components, their loading into mixer at distance from discharging proportional to bulk densities and/or particle sizes, mixing and discharging of finished mix. Loading of components is performed continuously over mixer length, up to drum discharge edge. Entire period of loading key components is divided into three equal intervals. Loading intensity varies depending upon concentration of said key component after loading period of every component is divided in at least three unequal portions. Proposed device comprises continuous mixer, dispensers of components, loaders of components and finished mix discharge assemblies. Proposed device comprises n-1 perforated pipes arranged inside the mixer in its axis and provided with drives. Perforated shells are fitted at the tube to turn thereon. In initial position, all shell holes are aligned with those in tube. Every shell is divided into, at least, three equal parts with independent turnabout tube. Note here that said every part incorporates drive for its specified turn about the tube.

EFFECT: higher quality of mixing.

7 dwg

Description

The proposed technical solution relates to the field of processing bulk materials and can be used for the continuous preparation of multicomponent mixtures in the chemical and other related industries.

A known method of preparing multicomponent mixtures of bulk materials [see A.S. No. 2207900 (Russian Federation), class B01F 3/18, 07/10/2003], including the continuous dosing of components, their loading into the mixer at a distance from the discharge point, proportional to bulk densities and / or particle sizes, mixing and unloading of the finished mixture. The loading of each of the components is carried out continuously along the length of the mixer, up to the discharge edge of the drum. Continuous loading of components along the length of the drum is carried out uniformly. In the descriptive part, a diagram of a device selected as an analogue is presented: a continuous mixer in the form of a drum, component dispensers, components loading units and finished mixture unloading. The mixer is additionally equipped with n-1 perforated pipes installed inside the mixer along its axis, with rotation drives. On the perforated pipe with the possibility of a fixed rotation, perforated shells are installed, and in the initial position all the holes in the shells coincide with the holes in the pipe.

As the results of our studies have shown, the disadvantage of this technical solution is the uneven distribution of particles of key components along the circulation circuit in the cross section of the mixer, in particular, a reduced concentration of key components in the outer layers and layers adjacent to the region of the circulation center, as well as an increased concentration of key components in middle layers of the circulation circuit, which has a negative impact on the quality of the finished mixture.

The prototype adopted a method of preparing multicomponent mixtures of bulk materials and a device for its implementation [see patent No. 2478420 (RF), class B01F 3/18, (RF), 04/10/2013], which includes the continuous dosing of components, their loading into the mixer at a distance from the discharge point, proportional to bulk densities and / or particle sizes, mixing and unloading of the finished mixture, continuous loading of components according to the length of the drum is carried out unevenly, the entire loading period of each key component is divided into at least three equal sections and in accordance with whether the concentration of the key component is increased in the corresponding region of the circulation circuit or reduced, the intensity of the load changes. In the descriptive part, a diagram of a device selected as a prototype is presented: the device contains a continuous mixer, component dispensers, components loading units, and finished mixture unloading. The device is equipped with n-1 perforated pipes installed inside the mixer along its axis, with rotation drives. On a perforated pipe with the possibility of a fixed rotation, perforated shells are installed. In the initial position, all the holes in the shells coincide with the holes in the pipe. Each of the perforated shells is divided into at least three equal parts with independent possibility of rotation relative to the pipe, each of which is equipped with a drive for its fixed rotation relative to the pipe.

Undoubtedly, the prototype allowed to significantly improve the quality of the mixture compared to the analogue, however, experimental studies of the continuous preparation of multicomponent mixtures, one of the key components of which is the carbon nanomaterial of the Taunit family, showed that even slight (about tenths of a percent) quality deviations from the required regulations, significantly reduce the quality of the finished product. Therefore, to solve specific technical problems, for example, in the production of composite materials modified with carbon nanotubes of the Taunit family, a higher uniformity of the mixture is required.

The technical task of the proposed solutions is to improve the quality of the finished mixture.

The solution of the technical problem is achieved by the fact that:

in a method for the continuous preparation of multicomponent mixtures of bulk materials, which includes continuous dosing of components, loading them into the mixer at a distance from the discharge point, proportional to bulk densities and / or particle sizes, mixing and unloading the finished mixture, loading each component continuously along the length of the mixer , up to the discharge edge of the drum, continuous loading of components along the length of the drum is carried out unevenly, unlike the prototype, the entire loading period of each the radial component is divided into at least three unequal sections, and the boundaries of the sections pass at the points of transition of the concentration of the key component from increased to low and / or from low to high compared to a given concentration and in accordance with whether in the corresponding region of the circulation circuit the concentration of the key component is increased or decreased, the loading intensity changes, which for any section j is determined by the dependence

where q _cp is the loading intensity of this key component, calculated for the case of continuous uniform loading of the component; deviation of the load intensity in any section j

where m is the number of the first sublayer in the plot; k is the number of the last sublayer in the plot; With _ass - a given concentration; C _i is the concentration of the key component in the i-th sublayer of the circulation circuit; V _i is the volume of the i-th sublayer, and the loading time of the key component in the j-th partition is determined by the dependence

where r is the number of sublayers in the j-th section of the partition; l is the number of sublayers of the circulation circuit; τ _zag - the total duration of the loading of the key component.

For the practical implementation of the proposed method, a device for preparing an n-component mixture described in the prototype can be used. It includes a continuous mixer, component dispensers, components loading and unloading units, and is additionally equipped with n-1 perforated pipes installed inside the mixer along its axis with rotation drives. On the perforated pipe with the possibility of fixed rotation, perforated shells are installed, holes in the shell have characteristic dimensions: d ₁ - along the pipe axis and d ₂ - on the circumference, and are divided into M groups, in each of which d _{1 is the} same and equal to the diameter of the holes in the perforated pipe, ad ₂ changes and is equal

where i is the serial number of the hole in the group, which varies from 1 to n ₀ / M; n ₀ is the number of holes in one cross section of the pipe, is selected as a multiple of M; the distance between the centers of the holes in the cross section of the pipe is greater than or equal to (n ₀ / M) d ₁ , and in the initial position all the holes in the shells coincide with the holes in the pipe, in contrast to the known solutions, each of the perforated shells is divided into at least three parts with independent possibility of rotation relative to the pipe, each of which is equipped with a drive of its fixed rotation relative to the pipe. In contrast to the variant described in the prototype, the length of the shells of each part should not be the same.

A device for implementing this method is shown in figure 1. Figure 2 shows a cross section of a mixer AA. The design includes a mixer 1, with loading units 2-4, an unloading unit for the finished mixture 5, dispensers 6-8 for the continuous supply of components A, B and C, respectively, perforated pipes 9 and 10 with rotation drives 11 and 12.

As a mixer, a continuous drum mixer can be used, in which there is a circulating nature of the movement in cross sections along its length.

The device operates as follows: the main component A is introduced into the mixer using the loading unit. Key components with the help of load nodes 3 and 4 are introduced into the perforated pipes so that they are filled with appropriate bulk materials. Perforation on the pipe 9 for feeding the key component most prone to segregation into the drum does not start from the beginning of the pipe, but at a certain distance from the discharge point. In particular, component C was started to be loaded in cross section when the residence time of the two main components of the mixture corresponded to the estimated time of entry of this component. In this case, the loading of key components into the mixer is carried out through perforation holes in the pipes. The diameter of the holes is selected so that through them a well-defined, required by the requirements for the finished mixture, loading of key components into the mixer, as a result of rotation of the pipes by the actuators 11 and 12, is produced.

Figure 3 shows a cross section of a pipe 13 with a perforated shell 14 mounted on it. The holes on the shell are arranged so that, in the case shown in this figure, unloading of bulk material through all the holes of the pipe is possible. When the shell is rotated relative to the pipe by a certain angle counterclockwise, one hole of the pipe, two, etc. until the holes in the pipe are completely blocked. Due to the fact that a number of such shells are installed on the pipe, it is possible that in certain sections of the pipe both full and partial overlapping of the holes is possible to carry out the necessary regulations for loading key components.

The figure 4 shows one of the perforated pipes 13 with three shells 15-17 located on its perforated section. The rods 18-20 are rigidly attached to the shells. Their free ends pass through a disk with annular grooves 21 located near the loading edge of the pipe. A thread is threaded at the free ends of the rods, and they are fixed with nuts 22 relative to the disk 21, thereby fixing the shells 15-17 on the outer surface of the perforated pipe.

To justify the correctness of the selected method of the mixing process, numerical experiments were carried out with the calculation of the concentration and quality of the mixture according to mathematical models of the process of mixing dispersed materials that differ in particle size [Pershin V.F., Selivanov Yu.T. Modeling the process of mixing bulk materials in continuous circulation mixers // Theor. basics of chem. Technology, 2003, vol. 37, No. 6, pp. 629-635] and real experiments on existing laboratory facilities.

Due to the fact that the separation into different components of multicomponent mixtures, one of the key components of which is the carbon nanomaterial of the Taunit family, for further analysis of the composition, is a very difficult technical problem, in the future, when conducting experiments, the following components were used as mixture components: glass balls with a diameter of d = 0.8 mm - the main component; glass balls with d = 0.4 mm and silica sand d = 0.2 mm are key components.

For calculations, a layer-by-layer model of the process of preparing multicomponent mixtures in a continuous drum mixer was used [Pershin V.F. The model of the process of mixing bulk material in the cross section of a smooth rotating drum // Theor. basics of chem. technology, 1989, t. 23, No. 3, S. 370-377].

When moving in the cross section of a smooth rotating drum of a polydisperse material, a segregation effect is observed. The essence of this effect is that particles of a certain size are concentrated in certain areas of the mixer. The speed of particles moving towards their final distribution depends on the ratio of particle sizes. In the case under consideration, the smallest particles of quartz sand had the greatest segregation tendency. Particles of glass balls with a size of d = 0.4 mm will be called less prone to segregation, and particles of glass balls with d = 0.8 mm will be called the main component. The quality of the mixture was evaluated by the inhomogeneity coefficients VS1 and VS2 [see A.S. No. 2207900 (Russian Federation), class B01F 3/18, 07/10/03].

When sampling after the experiment and mathematical modeling of the mixing process, the circulation circuit formed by the mixed components in cross section is divided into sublayers.

Figure 5 shows the structure of the distribution of key components in the sublayers of the circulation circuit with uniform and continuous loading of key components, i.e. corresponding to the option selected as an analogue. It is obvious that in different zones of the circulation circuit there is an increased or decreased content of key components. Moreover, in the general case, the width of these zones, corresponding to a different number of sublayers, is not the same. From this we can conclude that when dividing the loading period of each key component into at least three equal sections, in accordance with the option described in the prototype, it is impossible to achieve a uniform distribution over the sublayers of the circulation circuit. In the case of dividing the loading period into unequal sections, with the boundaries of the sections passing at the points of transition of the concentration of the key component from high to low and / or from low to high compared to the specified concentration, it is possible to achieve complete coincidence of periods of high or low intensity of loading with zones of high or low content of key components.

Consider the dependencies that allow you to calculate the load intensity of any one key component when dividing the load period into unequal sections. Let the average loading intensity of this key component calculated for the case of continuous uniform loading of the component, i.e. for the variant corresponding to the analogue is equal to q _cp . The loading time for this key component is τ _zag . Then the total amount of the key component loaded into the mixture will be equal to

Let the entire loading period be divided into three unequal sections with the loading intensity q ₁ , q ₂ , q ₃ , as shown in Figure 5. The loading duration in each of the sections, corresponding to the number of sublayers with a reduced or increased content of the key component, is τ ₁ , τ ₂ , τ ₃ .

Then

The intensity of the load in the first section

Deviation of the load intensity from the average value for the first section

In the upper boundary of the sum 5 is the number of sublayers corresponding to the first section (in figure 5 is indicated by the number I); With _ass - the concentration of the key component that meets the requirements of the customer; C _i is the concentration of the key component in the i-th sublayer of the circulation circuit; V _i is the volume of the i-th sublayer.

The deviation of the load intensity from the average value for the second section (in figure 5 is indicated by the number II)

The deviation of the load intensity from the average value for the third section (in figure 5 is indicated by the number III)

In the general case of division into sections, the deviation of the loading intensity in any section is determined by dependence (2).

It should be noted that the deviation in intensity can have both positive and negative values, depending on whether the concentration of the key component in this area is increased or decreased compared to the requirements.

The intensity of the load is determined from the expression (1). The loading time of the key component in the jth section of the partition is determined by dependence (3).

The dependencies that allow you to calculate the load intensity for other key components are similar.

An experimental verification of the indicated methods for carrying out mixing processes corresponded to the conditions for conducting numerical experiments. In this case, a drum mixer with a diameter of 0.3 meters and a length of 1 meter was used. The concentration of key components in the mixture for each of them was 5%. The state of the mixture was evaluated only for cases corresponding to the best distribution of each key component in the cross section of the drum, calculated according to the mathematical model of the process. The experimental points characterizing the state of the mixture are indicated for quartz sand - o, and for glass balls - □.

Figure 6 shows graphs characterizing the change in the qualitative composition of the mixture in the case of uniform and continuous loading of key components, up to the discharge edge of the drum, i.e. according to the method selected as an analogue. The start time for loading the first and second key components, as can be seen from the graphs, does not match. The duration of the process in this case increases, however, the best quality of the finished mixture for both key components is achieved simultaneously, and the heterogeneity coefficients do not exceed 2-3%.

An analysis of the quality of the distribution of key components among the sublayers of the circulation circuit shows that zones of increased or decreased concentration are observed in various groups of sublayers. Moreover, in the general case, these zones for different key components do not coincide. This is due to the fact that the volumes of the sublayers decrease as they move from the outer surface of the drum to the center of circulation. The rate of progress of key components in the region of the center of circulation is also affected by their number in adjacent sublayers. From the analysis of the above it follows that with a targeted change in the intensity of the supply of key components to various zones of the mixer, the quality of the finished mixture can be improved. The range of variation in the feed rate is negligible and does not exceed plus or minus 8%.

The figure 7 shows graphs characterizing the change in the qualitative composition of the mixture in the case of non-uniform continuous loading of key components along the length of the drum, i.e. by the method selected as a prototype. The entire loading period of each key component was divided into at least three equal sections, and in accordance with whether the concentration of the key component was increased or decreased in the corresponding region of the circulation circuit, the loading intensity changed. The best quality of the finished mixture for both key components is achieved simultaneously, and the heterogeneity coefficients do not exceed 1.85%.

Graphs characterizing the change in the qualitative composition of the mixture in the case of non-uniform continuous loading of key components along the length of the drum, when the entire loading period of each key component was divided into at least three unequal sections and in accordance with whether the concentration of the key component was increased in the corresponding region of the circulation circuit or reduced, the download intensity changed, similar to the graphs shown in figure 7. However, in this case, it is possible to achieve higher quality mixtures, and the heterogeneity coefficients do not exceed 1.4%. Thus, in comparison with the prototype, the uniformity of the mixture when using the proposed method is improved by at least 20%.

Equally important is the reduction in the range of variation in the quality of the mixture in individual samples. If in the case of obtaining mixtures corresponding to the prototype method, in some samples, the heterogeneity coefficients were slightly higher or lower than the average values, then in the case of the proposed method, the number of such samples was significantly lower.

Thus, as shown above, the results of numerical and field experiments, the proposed method is able to achieve this goal - improving the quality of the mixture.

Claims (1)

The method of continuous preparation of multicomponent mixtures of bulk materials, including continuous dosing of components, loading them into the mixer at a distance from the discharge point proportional to bulk densities and / or particle sizes, mixing and unloading the finished mixture, loading of each component is carried out continuously along the length of the mixer, up to to the discharge edge of the drum, continuous loading of components along the length of the drum is carried out unevenly, characterized in that the entire loading period of each key of the component is divided into at least three unequal sections, with the boundaries of the sections passing at the points of transition of the concentration of the key component from increased to low and / or from low to high compared to a given concentration and in accordance with whether there is a circulation loop in the corresponding region the concentration of the key component increased or decreased, the loading intensity changes, which for any section j is determined by the dependence
q _j = q _cp -Δq _j ,
where q _cp is the loading intensity of this key component, calculated for the case of continuous uniform loading of the component; deviation of the load intensity in any section j
$$\Delta q_j=\left({\displaystyle \sum _{i=m}^k{V}_i{C}_i-C_{s\mathrm{but}d}{\displaystyle \sum _{i=m}^k{V}_i}}\right)/{\displaystyle \sum _{i=m}^k{V}_i}$$

,
where m is the number of the first sublayer in the plot; k is the number of the last sublayer in the plot; With _ass - a given concentration; C _i is the concentration of the key component in the i-th sublayer of the circulation circuit; V _i is the volume of the i-th sublayer, and the loading time of the key component in the j-th partition is determined by the dependence
τ _j = r / l * τ _zag ,
where r is the number of sublayers in the j-th section of the partition; l is the number of sublayers of the circulation circuit; τ _zag - the total duration of the loading of the key component.

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