RU2398623C1 - Method of mixing loose materials and unit to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: set of inventions relates to processing of loose materials and can be used in chemical, pharmaceutical and food industries. Proposed method comprises simultaneous loading of components over the entire length of the mixer, mixing of components and mix unloading. To facilitate starting the engine, process is initiated at minimum intensities of "piston" and displacement motions. Then to reduce mixing internal and increase mix quality, concentration of components is quickly leveled axially and maximum "piston" and displacement motions of loose material particles are activated at definite periods of connective and diffusion mixing. To reduce mix unloading time without loss in homogeneity, mix is imparted directed shift motion, in significant flow, toward unloading assembly. Process control is performed via control of vane turn angles with respect to shaft rotational direction. Proposed unit comprises work members representing flat vanes made up of two parts: outer and inner with independent variation of their turn angles.

EFFECT: reduced mixing and unloading intervals, higher quality of mix.

2 cl, 2 dwg

Description

The proposed technical solutions relate to the field of processing bulk materials and can be used in the chemical, food, pharmaceutical industries.

A known method of producing a multicomponent mixture in feed production by simultaneous dosing of all components [see Prince Technology of flour, cereals and animal feed / G.A. Egorov, E.M. Melnikov, B.M. Maksimchuk. - M .: Kolos, 1984, p.339]. Its disadvantage is the simultaneous dosing through a variety of loading nodes of a large number of components, which leads to long-term alignment of their concentrations in the axial direction.

The well-known mixing of bulk materials [see Prince Technological equipment for grain storage and processing enterprises / Ed. A.Ya.Sokolova. - M .: Kolos, 1984, p.207]. This method is characterized by the fact that all components are loaded into the mixer through the load nodes, followed by a working process in which the working body repeatedly moves the components inside the mixer. Due to the circulation, the components are evenly distributed throughout the reaction volume, after which the mixture is unloaded. The disadvantages of this technical solution are the following:

1. The loading of components is carried out through various nodes located along the length of the mixer, which leads to the cost of time for uniform distribution and alignment of their concentrations in the axial direction.

2. The use of a fixed spatial position of the working bodies, in particular the blades, does not allow to control the mixing process through the use of various types of particle movement, to facilitate the start of the engine at the start of the mixing process, and to organize quick unloading of the mixture through the unloading unit.

A known mixer with adjusting the spatial position of the mixing blades and a spring with adjustable compression force, due to which the optimal elasticity of the mixing blades is established depending on the volumetric weight of the mixed materials and their granulometry [see RF patent 94007464, A1 B01F 15/00. Mixer / L.R. Gurevich, G.V. Khokhlachev, A.Ya. Starozhitsky, V. S. Shchukin (RF), 01.27.1996]. The disadvantage of this mixer is the lack of directional, controlled changes in the spatial position of the blades.

A mixer with the ability to automatically control the position of the blade depending on the physico-mechanical properties, viscosity of the materials used and the degree of filling of the mixer was taken as a prototype of the mixer [see A.S. No. 1502068 (USSR), class B01F 7/04, 08/23/89]. The disadvantage of this installation is that there is no possibility of organizing rapid alignment of component concentrations in the axial direction along the length of the mixer due to the strict orientation of the blades in the rows of the working bodies and the fast directed discharge of the mixture in a large flow through the unloading unit.

An object of the invention is to reduce the time of mixing and unloading, improving the quality of the mixture.

The solution to this problem is achieved by the fact that the loading of components is carried out simultaneously through various loading nodes located along the length of the mixer. When starting the engine provides a minimum load on the working bodies of the mixer. Changing the rotation angles of the blades provides a quick alignment of the concentrations of the starting components in the axial direction due to two oppositely directed flows and intensifies the processes of convective and diffusion mixing due to the combination of various types of particle transport of the material (“piston” and shear). Unloading is provided by moving the entire volume of the mixture in a large flow without losing its uniformity through the unloading unit.

Mixing in plants of this type is ensured by the circulation of the material in two directions: axial and radial. The main influence on the mixing time is exerted by the axial movement of the components.

Figure 1 shows a General view of the mixing installation, figure 2 - kinetic curves of the mixing process.

The mixing installation comprises a cylindrical housing 1, inside of which a hollow shaft 2 is located, equipped with a drive 3 (figure 1). On the shaft 2 radially along the helix there are working bodies — movable blades 4 made in the form of flat plates and consisting of two parts: outer I and inner II. The mixer is equipped with a mechanism for independently changing the rotation angles α of both parts of the blades 4, made in the form of rods 5, 6 installed in the shaft cavity 2, the outer ends of which are connected to devices 7, 8, which provide their reverse movement in the guide bushings 9, 10. Turning the outer part I and the inner part II of the blades 4 is carried out by means of gears 11, 12, mounted on the axes 13, 14, freely rotating in the sleeves 15. The installation has nodes for loading components 16 and a node for unloading the mixture 17.

The method is implemented as follows.

The components are loaded simultaneously through nodes 16 located along the mixer (Fig. 1). The movement of the material in the axial direction in the reaction volume of the mixer is created due to a corresponding change in the angles of rotation of the blades: the outer I and inner II parts of the blades 4 are rotated in opposite directions at different angles α, which provides two axial flows of material movement: the outer one near the housing 1 and the inner one near shaft 2, between which there is an exchange of particles, intensifying radial mixing.

To reduce starting loads on the working bodies, both parts of the blades 4 are installed at an angle α = 90 ° to the axis of rotation of the shaft (figure 1). The gap between the blades and the cylindrical body is minimal and uniform, eliminating the possibility of jamming of the material, which leads to engine overload at the time of starting.

Comprehensive studies of the process of mixing bulk materials in a paddle mixer with working bodies made in the form of flat plates [see Improvement of calculation methods and designs of paddle mixers: Diss. for a job. student step. Cand. tech. Sciences / OVV Demin - Tambov, 2003. - 210 S.], showed that when the angle of rotation of the blades in the range 0 ° ... φ _Art. (φ _article - the angle of friction of the bulk material on the surface of the working body) the main axial movement of particles is carried out by blocks at a distance from the blade. Because This process is similar in its mechanism to the movement of the piston, the considered movement of particles of bulk material is conventionally called "piston". When the angle of rotation of the blades in the range of φ _Art. ... 90 ° in front of the blade flows of particles of granular material are formed, uniformly distributed from the zone of motion of the blade to the adjacent zone. As a result, the movement of particles occurs due to shear processes, and therefore this type of movement is called shear. In the range of α _to ... 90 ° (where α _to is the critical angle of rotation of the blade), the energy consumption for the process of moving particles decreases due to an increase in the proportion of movement of the material in the direction of rotation of the blades, sliding layers of material relative to the surface of the working bodies.

After starting the engine after 5 ... 10 seconds, the rotation angles of the blades are set equal: the outer part I - α = α _k ; inner part II - α = (180 ° -α _k ). A simultaneous and rapid movement of particles by two flows along the axis of rotation of the shaft in opposite directions is created until the concentration of the initial components is evenly distributed along the length of the mixer. The process lasts 10 ... 20 s depending on the physicomechanical properties of the materials used (at shaft rotation frequencies n = 20 ... 40 min ^-1 ). The value of the critical angle of rotation of the blades α _k is determined experimentally and is 50 ... 70 ° depending on the materials being processed mixtures.

Mixing in a mixer of bulk materials consists of the following simultaneously proceeding elementary processes [see Prince Technological equipment for grain storage and processing enterprises / Ed. A.Ya.Sokolova. - M.: Kolos, 1984, p.206, Makarov Yu.I. Apparatus for mixing bulk materials - M .: Mechanical Engineering, 1973, p.85]:

1. Moving a group of adjacent particles from one place in the mixture to another by introducing, sliding layers (the process of convective mixing).

2. Redistribution of component particles through a freshly formed interface (diffusion mixing process).

3. The concentration of particles having the same mass in the corresponding places of the mixer under the influence of gravitational or inertial forces (segregation process).

At the initial stage, mixing occurs at the level of macroscopic volumes due to the convective separation of the components (section I of the curve of the graph of the dependence of the heterogeneity coefficient on the mixing time t V _c = f (t) (Fig. 2)). To intensify the process of transfer of components after their uniform distribution along the length of the mixer, an angle of rotation of both parts of the blades 4 is set equal to 0 ⁰ . The maximum intensity of the "piston" movement of particles is achieved (section I, figure 2). The process proceeds at high speed and continues for 0.1 ... 0.3 of the total mixing time. Then the redistribution of particles occurs at the level of microvolumes due to diffusion mixing (section II, figure 2). To intensify it, the shear movement of particles is activated, for which the rotation angle of the blades is set from the range of optimal values (α _opt = 40 ... 50 °): the outer part of the I blades by an angle α = α _opt ; inner part II at an angle α = (180 ° -α _opt ). An optimal combination of quantitative indicators of the shear movement of particles under the influence of the scapula and energy costs for this process is created. Mutual exchange of particles occurs in the radial direction between two oppositely directed axial flows, which also intensifies mixing processes and reduces the time of redistribution of particles. In the subsequent manifestation of segregation and mixing are balanced (section III, figure 2) and you want to unload the finished mixture.

The unloading of the finished mixture is organized by its directed movement in a large flow to the unloading unit 17 in the axial direction (Fig. 1) by changing the angle of rotation of the blades: the inner part II and the outer part I of the blades by the same angles α = (180 ° -α _to ). Maximum shear rate reduces unloading time without loss of mixture uniformity.

при снижении коэффициента неоднородности смеси

Активизация сдвигового перемещения частиц сокращает время второго диффузионного периода процесса смешивания (участок II, фиг.2). Суммарное время названных процессов - время смесеприготовления уменьшается

при улучшении качества получаемой смеси

Экспериментальное смешивание с модельными материалами показало уменьшение суммарного времени процесса смешивания и времени выгрузки на 15…20%.Process control realized by the design of the single-shaft paddle mixer, ensures rapid and uniform distribution of the starting components of the reaction volume of the mixer when the simultaneous loading through various nodes and timely activation "piston" and the shift displacement reduces mixing time (t _smesh) (Figure 2, curve And), directed movement by a large flow reduces the time of unloading the mixture (t _vygr ) while improving the quality of the mixture in comparison with the mixing realized in known paddle mixers with a fixed location of the blades (figure 2, curve F). The directional movement of the material by two opposite axial flows at the beginning of the mixing process allows for uniform distribution of the starting components along the mixer in less time. The maximum intensity of the "piston" movement of particles in the first period of the mixing process (section I, figure 2), reduces the time of the convective mixing process

with a decrease in the coefficient of heterogeneity of the mixture

Activation of the shear movement of particles reduces the time of the second diffusion period of the mixing process (section II, figure 2). The total time of these processes - the time of mixing is reduced

while improving the quality of the resulting mixture

Experimental mixing with model materials showed a decrease in the total mixing process time and unloading time by 15 ... 20%.

The blades on the periphery are rounded. The radius of rounding is determined from the condition of a uniform gap between the edge of the blade and the wall of the cylindrical body of the mixer for the position of the blade corresponding to the moment of starting the engine.

The rounding radius will be determined by the formula:

r = R-δ,

where r is the radius of the rounding of the blades, m;

δ = (0.001 ... 0.002) m - the necessary clearance between the blade edge and the wall of the mixer body, m

R is the inner radius of the cylindrical body of the mixer, m

The volume of particles of bulk material moving along two oppositely directed axial flows depends on the fill factor of the mixer. The volume of material moved in axial flows during the movement of the inner part II and the outer part I of the blades 4 (Fig. 1) should be the same to ensure uniform distribution along the length, which is taken into account when calculating the geometric parameters of the blades. The fill factor is recommended 0.3 ... 0.6, depending on the physico-mechanical properties of the mixed materials. Considering the insignificant shaft rotation speed of the proposed installation (n = 20 ... 40 min ^-1 ), this coefficient, as experiments show, can be increased to 0.8 ... 0.9.

The width of the zone of motion of the scapula taking into account this method will be determined by the formula:

,

,

where L is the length of the mixer, m;

n is the number of rows of blades;

α _to - the critical angle of rotation of the scapula.

Claims (2)

1. A method of mixing powdered and fine-grained bulk materials in a mixing installation, including the simultaneous loading of components through various nodes, mixing them by organizing a “piston” and shear movement of particles of the mixture components and unloading the mixture, characterized in that at the beginning of the mixing process provide quick alignment concentrations of components in the axial direction due to the organization of shear movement of material along two oppositely directed flows, intensify the period convective and diffusive mixing by rotating the parts of the blades in opposite directions to a different angle at unloading mixture organize its movement in the direction of directional flow due to discharge node identical angles of rotation of parts of the blades. 2. Installation for preparing a mixture of bulk materials, comprising a housing in which a shaft with a drive and blades is installed, made with the possibility of changing the angle of rotation of the blades, characterized in that the blades are made of two parts: external and internal, with the possibility of independently changing their rotation angles relative to the axis of rotation of the shaft.

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