Distributor / authorized representative that deals with supply & delivery of agitators (mixing equipment) to industrial enterprises of Russia
Engineering company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), Russia, has been successfully working with a number of Russian industrial enterprises at the local market for more than 20 years. Since the company’s founding, it has acquired immense engineering experience, market reputation, and has realized more than a hundred large-scale projects at the industrial plants in Russia. Our company is continuously in search of new business partners, who consider Russian market investment-attractive and want to boost their sales in the region, as well as expand their field of activities and enter a new international level.Contents:
We are interested in cooperation with the manufacturers of agitators (mixing equipment), who are looking for an official and reliable distributor to deal with supply & delivery of their equipment to the industrial plants in Russia.
The company’s top management and sales team are well acquainted with the Russian market, its mentality and laws; they also understand industrial specifics of the financial and economic activities of the Russian customers. All our sales managers have a large customer database, extensive experience of successful sales and well-established connections with the potential buyers of your agitators (mixing equipment). This allows our managers to promptly set out the most promising directions for promotion and to ensure a rapid entry of the products into the promising Russian market. Our employees, who are fluent in English and German, are focused on working at the international market with the supplies of foreign equipment.
Our team of experienced engineers, who can handle the most serious technical problems, constantly keeps in touch with the Russian customers, holds meetings and delivers presentations regarding the latest achievements of our manufacturing partners. They point out the engineering challenges and actively communicate with all the departments at Russian plants. That is why the specifics of doing a business in the Russian Federation are well-known to us, and we also know the equipment of the local industrial plants and their up-to-date modernization needs.
Once we become your authorized representative in Russia, our marketing staff will carry out a market research in order to check the demand for agitators (mixing equipment), will submit a market overview for agitators (mixing equipment) that you offer and evaluate the needs for this type of equipment at local plants. Our specialists will also estimate the potential and capacity of this market at local industrial plants. Our IT-team will start developing a website for your products in Russian. Our experts will assess the conformity between your agitators (mixing equipment) and customer needs as well as analyze the common reaction to the new goods in general. We will look into the categories of potential customers, and pick out the largest and the most promising plants.
Upon becoming your authorized agent on the territory of Russia, ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), will obtain certificates, if required, for a batch of the goods, for various types of agitators (mixing equipment) in compliance with Russian standards. We can also arrange the inspection in order to obtain TR TS 010 and TR TS 012 Certificates. These certificates provides permission to operate your equipment at all industrial plants of the EAEU countries (Russia, Kazakhstan, Belarus, Armenia, Kyrgyzstan), including the hazardous industrial facilities. Our company is eager to assist in issuing Technical Passports for agitators (mixing equipment) as per Russian and other EAEU countries’ requirements.
Our engineering company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), collaborates with several Russian design institutes in various industrial segments, which allows us to conduct preliminary design as well as subsequent design works according to the standards, construction rules and regulations that are applicable in Russia and other CIS countries. It also enables us to include your agitators (mixing equipment) into the future projects.
The Company has its own logistics department that can provide packing service, handling as well as the most efficient and cost effective mode of transportation of the goods (incl. over dimensional and overweight goods). The goods can be delivered on DAP or DDP-customer’s warehouse basis in full compliance with all the relevant regulations and requirements that are applicable on the Russian market.
Our company has its own certified specialists who will carry out installation supervision and commissioning of the delivered equipment, as well as further guarantee and post-guarantee maintenance of agitators (mixing equipment). They will also provide necessary training and guidance for the customer’s personnel.
Agitators (mixing equipment). A brief overwiew
Mixing is applied for the production of suspensions, emulsions and mixtures of solids. Also, this process is used in the chemical industry for activation of mass transfer and heat transfer processes. In addition, intensive mixing is required to carry out the majority of continuous chemical processes.
There are several types of mixing and equipment for its handling depending on the aggregate state of mixed materials. Mixing and chemical reaction are processes that can take place both separately and jointly. They can also coincide in time and place. Mixers are used for separate mixing process, and reaction units equipped with agitators are used for simultaneous mixing and chemical transformation.
Several types of mixing (agitation) are distinguished depending on the environment in which the process takes place:
- in the liquid medium;
- in the solid medium;
- in the granular medium;
- in the pasty medium.
Mixing of substances, which are in different aggregate states, is widely used in chemical engineering in order to obtain:
- homogeneous solutions;
- uniform heterogeneous mixtures-emulsions;
- bulk solids.
Aggregate state and physical properties of mixed substances (as well as requirements to resulting mixtures) define methods of mixing and, consequently, type of construction of the mixing device. In any case, mixing equipment is used to produce a homogenous mixture with minimal energy consumption and maximum production factors.
The most common methods of liquid media mixing in the industry are:
- sparge mixing;
- mixing by means of mechanical agitators, which make oscillatory/rotational movement;
- mixing by means of placing of static turbulizing devices in the stream;
- mixing by means of centrifugal /jet pump units.
Regardless of the method, process of liquid mixing represents a multiple movement of its particles relative to each other. The complex fluid motion that occurs during rotation of the agitator consists of three directions:
- radial direction dR (along the radius of rotation);
- tangential direction dT (along a tangent to the circle described by the end of the agitator);
- axial direction dA (along the axis of the shaft).
Proportions of motion elements of mixed substance may vary depending on the type of agitator.
We need to obtain a mixture, components of which are most evenly distributed, by means of mixing two or more substances. It should be noted that the substances in the mixture are mutually distributed, but they are not combined chemically.
At the initial stage of the mixing process components exist separately from each other or slightly mixed. After prolonged mixing occurs intense mutual distribution, which leads to general uniform distribution.
While mixing various mixtures can be obtained: homogeneous and heterogeneous. Homogeneous mixtures are characterized by the fact that therein can be disintegration of components into smallest particles (atoms or molecules) and their uniform distribution in each other.
The following substances belong to homogeneous mixtures:
- saline solutions;
- metal alloys;
- mixtures of gaseous substances and the like.
Heterogeneous mixtures are characterized by the presence of components in the form of droplets or powder with a specific grain size. In such form they are distributed among each other. Heterogeneous mixtures include powders, suspensions, emulsions, aerosol agents, etc.
The mixtures are widely used in the industry:
- for obtaining intermediate and final product by means of mixing two or more components. Thus, mixtures of fats, paints or fertilizers can be obtained;
- for obtaining initial mixtures for chemical reactions;
- for controlling the reaction flow in a mixture, as the rate of any reaction is determined by the size of the area of contact between the reactants.
Methods of mixing are determined by the aggregate state of substances during mixing:
- mixing by agitators, during which two or more fluids are mixed by means of mechanical moving rotating elements (or gaseous, liquid or solid components are dissolved therein);
- mixing with flow separation, during which the gases and liquids are mixed in nozzles, pumps, mixers using fixedly mounted flow dividers;
- kneading (the same as mixing), during which joined substances are in flowable or pasty state;
- dry mixing, where powder substances are mixed (dry or slightly moistened);
- spattering and spraying are methods, during which liquids, droplets or powders of fine fraction are released into the air, forming a mist or dust;
- aeration and fluidization are methods, during which small gas bubbles are formed in a liquid or in a solid powder. In this case maximally intense contact must be achieved between the gas and the substance;
- mechanical mixing, during which liquids mix with each other by means of agitator (or solid substance is distributed or dissolved in a liquid), forming a suspension, solution or emulsion.
Unit with agitator
Such vessels are used in the chemical industry for mixing of substances and reactions in liquid state. Mixing occurs under ambient conditions or at a temperature of maximum 150º. Vessels may be made of alloyed and unalloyed grades of steel, enameled, coated with rubber.
The most important component of such vessel or container is the agitator, i.e. mechanism of its rotation, as well as built-in and mounted devices, such as thermometers, manometers and other measuring devices.
Mixing vessel is a cylindrical container with a bottom and a cover of convex shape, in which there are several holes (necks) equipped with flanges.
The central flange is the bearing flange; on this flange is located lantern with agitator. Sight glasses may be used for visual inspection. Flow dividers, which can also be installed inside a container, are otherwise referred to as flow breakers. Together with agitator they mix components more intensively. The number of used dividers is generally from 2 to 4. The outlet pipe is usually placed in the bottom of the tank. The vessel with agitator is mounted on legs, grips or ring support.
Vessels with agitator operating at high pressure
For reactions occurring at a high pressure and in a discontinuous mode of operation the special vessels are applied, which are called autoclaves with agitator.
Its main difference from conventional unit with agitator is that its walls, bottom, walls of flanges and inlets are designed with the use of thicker elements. The vessel operating under high pressure typically has no outlet ports.
Emptying takes place by tipping or suction through the hole (inlet) in the lid. Pasty reaction products are removed with a shovel or scraper. Pressure is supplied to the vessel by pressure pipeline through the discharge tube. High-strength steel (usually stainless steel) is commonly used for the manufacture of such vessels.
Process operations based on mixing
Mixing, as a process, solves a number of different tasks of technological character:
- mixing of two or more components in liquid form;
- dissolution of solid substances in the liquid fraction;
- emulsification (fine distribution of two insoluble liquids in each other);
- suspending (fine distribution of insoluble solids in the liquid).
Mixing is achieved by means of agitation and is the simplest and most widespread technological operation. Redistribution of large fractions of substances takes place on the basis of the heliciform circulation flow around the agitator and vertical flow of the entire contents in the tank. Generated turbulent flows with ripples and twists is formed in the area of flow dividers, and at the ends of the agitator. A whirlpool, in which the components are mixed at the molecular level by means of diffusion, is generated. Transverse movement of the turbulent flow also contributes to the mixing.
Index M, which indicates the degree of uniform distribution in the range from 0 to 1, can be used for evaluation of mixing. At zero agitation the degree of mixing M is 0, and with the ideal uniform distribution - 1. During the mixing process M ratio increases, starting from 0. First, it increases very rapidly and then slows down the increase. And at the end of the mixing time it is close to M = 1.
The required mixing time for achievement of optimal mixing depends on the viscosity of the components, on the type of agitator and on the speed of its rotation. There’s only one regularity: the lower the viscosity of the mixed components and the higher agitator rotation speed, the shorter the mixing process is.
Propeller agitators, disk agitators and agitators with inclined planes have a short mixing time. Spiral agitator is best suited for the viscous media.
The dissolution process assumes the distribution of solid matter in a liquid. In this case, the solid material is disintegrated into atoms, ions or molecules.
The condition for this is such a parameter as the solubility of solid matter in a liquid, which characterizes the process of dissolution. In the case of the addition of a small portion of the substance in the fluid, this substance will be completely dissolved therein. During subsequent addition the dissolution is slower and then the solid substance completely ceases to dissolve. When the amount of the substance in the liquid reaches its maximum, the solution becomes saturated.
The corresponding concentration of the solution is called the saturation concentration. Upon subsequent addition the substance does not dissolve in the fluid; it remains in the liquid as a suspension or settles as residue.
The greater amount of solid matter can be dissolved at higher temperatures, than at lower temperatures. This dependence of the saturation concentration on the temperature is reflected on the saturation-dissolution curve.
Saturation concentration occurs at all points of the curve (i.e., there is an equilibrium of dissolution and crystallization). The rate, at which equilibrium of dissolution is established, increases due to the mixing. As a result of mixing the concentration does not increase.
Dispersion is a thin grinding and mixing of solid, liquid or gaseous substances in a liquid, which does not dissolve these substances. The substance is present in the liquid in the form of ultimate particles. The resulting mixture is called dispersion.
Depending on the aggregate state of substance, the following can be observed in dispersion zone:
- emulsification, when the distributed substance is liquid, and droplets of non-dissolving liquid are finely dispersed in another liquid;
- suspending, when the distributed substance is the solid substance, which does not dissolve in liquid (mixtures formed in this case are called emulsions or suspensions).
Mechanical mixing is performed by agitators, which consist of one or several pairs of blades. Blades are fixed on a shaft, which is rotated by a motor or the transmission (gear train, friction gear or worm gear).
Pneumatic mixing. Sparge mixing of liquids and suspensions
Mixing or circulation in the mixing tank can be carried out by means of injection of air, steam or dissolved gases. This refers to the pneumatic mixing or air mixing.
This method is used when gassing or heating with hot steam is supposed along with mixing. Only liquids with a low viscosity are suitable for pneumatic mixing. Natural circulation is not possible with a higher viscosity.
At the bottom of containers for pneumatic mixing are located perforated discs, nozzles, injectors or conduits, through which gas is supplied.
One of the methods of liquid media mixing consists of passing of dispersed gas phase through them. This process is called sparging, and a device for its implementation is called "sparger". This method is the simplest and is used in cases where one of mixing substances is a gas or air. Sparging is also suitable in the case of heating by the direct steam along with mixing.
Unit for sparging is a tank, with a pipe with multiple holes at the bottom through which gas media is supplied. The upward flow of air carries away the particles of liquid, whereby appears a stream, the speed of which increases with an increase of airspeed. Spargers are equipped with a set of horizontal pipes for uniformity and intensity of mixing.
Tubes are mounted horizontally, so that the air could overcome the same hydraulic resistance at the outlet of the holes of perforated pipes (which is necessary for its uniform distribution). The holes in the tubes must go along a helical path in order to provide intensive mixing of the liquid phase. The diameter of holes is selected as small as possible, which also contributes to a more uniform distribution of the gas phase. Holes are typically 3-6 mm in diameter (in order to avoid clogging).
If the mixed liquid is chemically active or contributes to the destruction of a mechanical agitator, it is advisable to use the sparging. However, during sparging valuable vapors and gases can be carried away from the liquid together with air, causing the occurrence of unwanted processes: oxidation or resinification of the mixed liquid. It is also important to note that the sparging consumes more energy, than mechanical mixing.
Sparge mixing is applied:
- if the gas or some of its components must undergo a chemical reaction with mixed liquid;
- in the process of mass transfer between liquids and gases;
- in the process of mass transfer between liquid and vapor.
Advantages of the sparge mixing include:
- absence of moving parts;
- simplicity of the device;
- the ease of maintaining of suspension solid phase in the suspended state.
Power consumption for the sparge mixing
In conditions of free sparging gas stream passes through perforated grids and splits into bubbles at the outlet of the holes. Bubbles push fluid forward and sideways, pulling its nearer layers by the action of the tangential dilution and the voltage, which occurs outside the bubble. External hydrostatic pressure decreases and the bubble rises. The bubble grows in size and loses its spherical shape, its trajectory becomes vertical.
All of the abovementioned processes in conjunction with the merger of bubbles provide the growth of the intensity of mixing from bottom to top. Once the gas bubbles enter into the free space of the unit, the liquid lowers down. Thus, mixing and circulation of liquids are energy transfer (amount of motion) from gas to liquid. The most preferred type of sparge mixers represents devices with large height of the liquid layer. The amount of work, transferred by gas of the mixed liquid, is calculated using the formula:
L = p1 · VF · ln(p1/p0)
p1 – pressure of sparging gas at the outlet of the sparger
p0 – final gas pressure at the outlet of mixed layer
VF - sparging gas flow
Selection of the pipe diameter plays a great role in the sparging device. The larger the tube diameter, the lower the turbulence (but circulation is more intense). The optimal ratio of these factors provides a high intensity during mixing.
Mixing of substance flow by stationary turbulizers
Artificial turbulence of flow is used for mixing of gases and liquids in pipelines. For this purpose, static parts that provide a change of direction and flow are installed rate inside the pipeline:
- manger bulkheads and diaphragms with displaced holes;
- screw inserts;
- injection mixers.
Use of manger bulkheads and diaphragms with displaced holes provides multiple constriction and expansion of the flow, as a result of which the flow direction changes. Screw inserts with alternation of helical turn direction (left and right) twist the flow repeatedly and in different directions. Injection mixers are used in conjunction with screw inserts.
Circulation mixing of fluids
The circulation of substance in the closed loop can provide effective mixing. This process is realized by means of a centrifugal or jet pump, which acts as a local turbulator.
The mixing by liquid circulation is carried out in two ways. Thus, in large machines operating with liquid, components of which are of different density, lower layers are absorbed by the centrifugal pump. Heavier layer passes through the pump and are supplied through the discharge nozzle into the circulation pipe leading to the free surface of the liquid level in the unit through the sprinkler. Fluid circulation in a mixed volume increases in process of increase of productivity of the pump.
Classification (types) of agitators. Mechanism of their rotation
The content of the vessel is mixed in it by special devices - agitators. The viscosity of mixed material, the purpose of the mixing process and mixing duration determine the choice of agitator.
Can be identified four groups of agitators, which differ by blade structure:
- propeller agitators have helical blades;
- vane agitators have flat blades;
- there are also special agitators and turbine agitators.
Operation of agitators generally depends on the power consumption and mixing efficiency. The actual operating conditions of agitators can be reflected by common regularities and formulas.
From the standpoint of hydrodynamics mixing can be described as an external wrapping of bodies by liquid flow. If any solid body is slowly moving in a viscous fluid, it will overcome only the frictional forces with the formation of the boundary layer. The flow pressure is transmitted through the boundary layer. The inertial force acquires special significance with the increase in speed. In this case, the boundary layer is removed from the solid surface, thus creating vortices. When the flat plate moves in the liquid and forms vortices, it looks like operation of agitators blades in identical hydrodynamic conditions.
The speed at the blade edges is usually highest (Brunelli Equation), but the pressure is less than in the liquid before the plate. The force of the agitator shaft overcomes the differential pressure on the blade from the flow.
The influence of gravity during a wave formation on the liquid surface is not usually taken into account, as the blades are usually deeply immersed into the liquid. At the same time Froude number can be eliminated from the equation. Typical values of criteria vary depending on the motion of the fluid during the mixing.
Parameter of starting power
At start the inertial forces of the fluid are overcome. This is required in order to bring liquid from a standstill, as well as to overcome the occurring frictional force.
NStart = NI · NF
For the calculation of the power of agitators the resistance in the unit must be taken into account, for example, on the walls of the partitions, in coils, etc. This additional resistance increases energy consumption during mixing. For example, in the presence of the coil the power can be increased in two and more times.
It is important to note that:
- high-speed agitators (such as a propeller, disc or with inclined plates) are suitable for mixing of fluid substances;
- slower mixing with the use of such agitators as the anchor, gate, cross, impeller, circular and counter-current agitator is suitable for environments with medium viscosity;
- spiral agitators with slow speed of rotation or impellers with an average speed of rotation are the most suitable for high viscosity substances.
Main parts of the agitator
The main component of the agitator is the mechanism of its rotation, which consists of the drive unit with the engine and gearbox and the lamp parts: a bearing assembly, seals and joints. The engine is a key element of the drive unit and is usually selected as an asynchronous three-phase squirrel cage motor. It meets the requirements for the drives, is structurally simple, reliable and does not require frequent maintenance. As the asynchronous motor, it has a constant number of revolutions and moves to other rotation rates by means of changing of poles. Electronic frequency change results in a smooth speed control.
The motor can run on the gear train, belt transmission or a combination consisting of both gears. The required rotational speed of the agitator and the installation height determine the structure of the drive unit.
The drive mechanism with belt drive and the motor placed on the side provides the minimum mounting height. This drive has a smooth start-up and slippage under all overloads. Gear drives have a fixed number of revolutions. If the engine is placed above the gearbox, a considerable installation height will be required.
Various couplings are used as coupling: rigid couplings, flexible couplings, flange couplings or disc couplings on the joints. Roller bearings are used as a support, and the cuff or conventional gland packing (with sealing fluid) is selected as a shaft seal.
Flow hydraulics in the unit with agitator
During mixing flows are superimposed on each other in a tank with agitator. They move in the horizontal and vertical directions. Any agitator can create horizontal flows of varying degrees around it.
During rotation of the agitator liquid in the vicinity of its axis is involved in rotational flow and thrown outward by centrifugal forces. The fluid moves along a spiral from the center of rotation to the walls of the tank. It swirls at the flow divider and is discharged either up or down from the vertical flow. Further vertical direction of the fluid flow depends on the type of the selected agitator.
Where there is a radial agitator (frame, disc), the liquid flows radially from the agitator to the walls of the tank.
Depression occurs near the agitator axis due to the fluid flow in the radial direction. Because of this, there is a suction of fluid at the top and at the bottom. In this way, vertical flow occurs in the tank with agitator, liquid circulates vertically. Part of the contents of the tank involved in rotation (plus swirls in the area of the flow divider and disks of agitator) is superimposed on the flow.
Axial agitators (propeller, spiral) provide a b flow in the vertical direction.
Agitator of propeller type has a width of blades of approximately 30% of the diameter of the tank. Its filler is sucked along the agitator axis down, turns back at the bottom and rise again along the tank perimeter.
The diameter of the spiral agitator is 90% of the diameter of the tank. Here the liquid rises along a spiral circle and falls along the agitators shaft. Axial agitators create a weak vortex flow around an axis. Mixing comes due to the vertical flow.
Some agitators (with inclined plates, impeller, counter-current) have mixed flow: radial-axial flow.
Low-speed mechanical agitators include vane, sheet, anchor and anchor-vane agitators.
Vane agitators are agitators of the simplest type with flat blades, which are made of flat and angular steel. They are installed perpendicular or at an angle.
Vane agitators represent shaft on which is mounted a series of vertical blades of rectangular shape. The standard dimensions are:
H/D = 0.8-1.3; d/D = 0.7-0.9; b/D = 0.06-0.1; h1/D = 0.1; h2/d = 2; h3/D = 0.3.
Н – height of liquid in the unit
D – diameter of the unit
d – diameter of the agitator
b – height of the blade
h1 – distance from the bottom of the unit to the agitator
h2 – height of vertical plates
h3 – distance between agitators
In the devices that are characterized by a large height, several pairs of blades are attached to the shaft. These blades are turned to each other at an angle of 90°, the distance between them ranges from 0.3 to 0.8 d. In such devices the liquid mainly moves radially. Rotating blades engage it in motion, and the free surface of the liquid acquires the shape, which is close to the rotational paraboloid. The axial component of the liquid motion is insignificant.
The following measures are used for the elimination of excessive depth of the vortex:
- the circumferential velocity at the ends of the rotating blades does not exceed 1 m/s;
- installation of 2-4 flat vertical edges along the perimeter of the unit.
|Type of agitator||d/D||b/d||h1/D||e/D||f/D|
|Sheet||0.5||0.9 – 1.0||0.1||-||-|
|Anchor||0.9 – 0.98||0.5 – 0.9||0.01 – 0.05||0.06||-|
|Anchor-vane||0.9 – 0.98||0.5 – 0.9||0.01 – 0.05||0.06||0.15|
Frame agitators equipped with blades of horizontal and vertical type are commonly used in order to improve the mixing process.
The lower horizontal blade of such agitators has a radius of curvature which corresponds to the radius of curvature of the bottom of the unit.
Additional vertical flows appear, if the flat blade is located at a certain angle in the direction of its axis of rotation. Their direction depends on the inclination angle of blades.
Agitator is equipped with several pairs of blades, which are inclined in opposite directions, for the creation of crossflows and provision of intensive mixing. Also for this purpose deflector plates may be mounted on the walls of the agitator.
Vane agitators have a low rotational speed: 20-80 rpm. Under certain conditions the rate may be increased. Successful dissolution and suspending of greater range of materials is possible if the vane agitator is equipped with inclined blades and the machine is equipped with deflector plates.
Vane agitators are relatively simple in design concept and are characterized by relatively low cost, required for their manufacture.
Sheet agitators represent blade-mixing devices, characterized by a large blade height. These devices are always used in devices equipped with deflector plates because they transmit the rotation of a large volume of fluid. The intensity of the mixing process can be enhanced by making holes in the blades. Sheet agitators are used for low viscosity liquids (50 Pa·s) and are not able to stir the slurry.
In anchor agitator mixed media mainly performs tangential motion. Devices of this type operate with substances with a viscosity, which is greater or equal to 100 Pa·s. Deflector plates of the anchor agitator are located above the agitator. Their peripheral speed corresponds to the speed of sheet and does not exceed 1 m/s.
Anchor agitators are used when it is necessary to remove the residue from the bottom or walls of the vessel in the process of mixing in order to improve heat exchange between the medium and the wall.
Planetary agitators are used for intensive mixing of the liquid in the tank of large diameter. Planetary agitator rotates around its axis but also moves along a circle, the center of which coincides with the axis of the unit. Movement of a blade agitator is complex and provides intensive mixing of the liquid. Number of shafts in an agitator determines its type. It can be single, double or triple.
At the lower end of the shaft is placed fixed carrier (3). The carrier is freely rotatable on the other end of the shaft in its bearing (4). In turn, the bearing is rigidly connected with a toothed wheel (5) which is geared with the wheel (2). Blades (6) are mounted at the same shaft.
Propeller agitators are actively used for liquids with a viscosity of less than 10 Pa·s. The peripheral speed of such devices is 10 m/s. The blades are the main working elements; their number can be from 2 to 6 pieces. They are attached to the sleeve and can change the slope. Externally propeller agitator looks like a marine propeller or aircraft propeller. The agitator is fixed on a shaft, which is connected to the electric motor. During rotation the agitator produces radial and axial motion of the medium, whereby the circulating flows are formed. An important characteristic of the stirring device is the volume of the circulating liquid per unit time (pumping effect, Vm). This figure depends on the viscosity of the material and decreases with its increase.
High-speed mechanical agitators
Vortex in the central part of the device, which arises in the course of rotation of the substance, can be eliminated by means of deflector plates. The pumping effect and axial motion of the fluid can be significantly increased by placing the agitator inside a coaxial cylinder (the result is something like an axial pump).
The standard sizes of propeller agitators include:
d/D = 0.15-0.4; s/d = 1-2; h2/D = 0.8-1.6; h1/d = 1.2-2.0.
D – diameter of the unit
d – diameter of the agitator
h1 – distance from the bottom of the unit to the agitator
h2 – height of vertical plates
s – step of the helical line
Several propellers are mounted on the shaft in case of high altitude of the volume of mixed substance. Particularly intensive mixing through the countermovement of two streams (intake stream and discharged stream) occurs in the interval between the propellers.
Agitators of this type are widely used to provide intensive circulation during the mixing of liquids.
The screw diameter is from 1/3 to 1/4 of the diameter of the unit, used for mixing. There are two types of screws: right screw with clockwise rotation and the left screw with counterclockwise rotation. Pitch of the screw can be constant or variable.
The screw (propeller) with variable pitch promotes intense mixing during its rotation, but only in the zone of action of the screw. It is better to use agitators, equipped with propellers with constant pitch, while stirring the liquid in full volume. These propellers (in the form of marine propeller) vigorously mix liquid due to different rates of fluid jets and the different directions of motion at the time of impact with the bottom of the vessel or the free surface.
Propeller may be installed in the diffuser (glass of the cylindrical form) in order to improve fluid flow. Diffusers are used in devices with pipes or coils, and also in devices with the large height to diameter ratio.
Propeller agitators, which have several screws and a diffuser in the form of a coil, are used throughout the height of the liquid distribution for more intensive mixing process. The turns of the coil are in close contact with each other. Temperature regime of mixing can be easily adjusted by using such diffuser.
Rotation speed of propeller agitators can reach 400 - 1750 rpm. Upon mixing of viscous fluids (500 cps or more), liquids with slurries and liquids forming foam the agitator must rotate at a speed of 150 - 400 rpm. Propeller agitators can be used in processes of mixing of liquids with viscosity of up to 4000 cps, but the efficiency of such mixing will be low.
These agitators are usually mounted in the units of small volume, because the propeller dimensions are relatively small. And propellers are installed in the volumetric units obliquely to the axis of the unit (an angle of 10 - 15 º) in order to accelerate and intensify the mixing process.
Propeller agitators are simple in design concept, cheap in manufacturing, high-speed and consume small amount of power during operation.
In the chemical industry these agitators are used for mixing of low-viscosity fluids during the preparation of emulsions, as well as for resuspension of residues of solutions containing not more than 10% of solid phase.
Viscous liquids should be mixed by ribbon impellers because they clean the vessel walls from adhering mass during rotation.
For creation of emulsions a separate unit consisting of a set of disks must be used with perforated holes, which are mounted on the rod and perform oscillations. The edges of adjacent holes are bent in opposite directions. Thus, as a result of oscillations liquid is mixed and crushed into small droplets repeatedly passing through the holes in the two directions.
Propeller agitators are used:
- for mixing and formation of low-viscosity emulsions;
- in the process of dissolution and chemical conversion;
- for obtaining fine suspensions (solid particles with the size of not more than 0.5 mm and with the concentration of 8-10%);
- for dispersion of gases in liquids.
Turbine agitators are also high-speed and consist of a set of vertical rectangular blades mounted radially on a horizontal disc or hub. During the rotation of the wheel in the center is created depression, and on the periphery is created the excess pressure. Fluid dropped to the walls of the unit diverges into two streams: the upper and the lower. These streams are absorbed by the central part of the wheel. Thus, there are two circulating flows, which enhance mixing of the liquid. The higher is the viscosity of the substance, the less intense is the mixing process.
Turbine agitators are equipped with deflector plates. If necessary, the impeller can be installed inside the coaxial pipe, or blades can be placed at an angle of 45 °C to the shaft axis. This type of agitators is used for substances, viscosity index of which does not exceed 100 Pa·s (in case of a higher viscosity it is necessary to use blades curved helically or circumferentially).
The standard sizes of turbine agitators include:
d/D = 0.7-0.35; b/d = 0.2-0.3; d/b = 1.0; h1/D = 0.5-1.0
D – diameter of the unit
d – diameter of the agitator
b – height of the blade
h1 – distance from the bottom of the unit to the agitator
s – step of the helical line
Turbine agitators are actively used for dispersing of liquids and gases in liquids, as well as for mixing of substances with a viscosity higher than 10 Pa·s.
Several turbine agitators must be installed on the shaft in the case when ratio of the height of the liquid layer in the unit to the diameter of the unit is more than two (H/D>2). For liquids characterized by a high level of viscosity are applied:
- screw devices (μ=500 Pa·s; d/D=0.65; s/d=1.4);
- ribbon-blade units (μ=3000 Pa·s; d/D=0.94; s/d=1.1, where s is a step of helical line at a belt width b= 0.1d).
As a rule, turbine agitator includes several small turbines (centrifugal wheels) fixed on the shaft of vertical type. Each turbine may have 6-16 blades or more. During rotation the turbine of closed type sucks liquid through the central hole. Thereafter, the liquid is pulled by centrifugal force through internal channels.
The liquid in the turbine agitators smoothly changes its direction: from vertical to radial. There is a loss of kinetic energy of the flow (although small). The stream of liquid leaves the wheel at high speed, spreading across multiple lines and causing a b mixing of full volume of liquid.
Cost of turbine agitators exceeds the cost of propeller agitators. They are used instead of propeller agitators when mixed liquids have a high viscosity index or the mixing vessel has a specific shape. For example, the height of the vessel is too small and does not allow establishing a propeller agitator.
Agitators of turbine type are used:
- for mixing of fluids with a maximum viscosity parameter of 200 poise;
- for b mixing and for dispersing large amounts of liquids (up to 6 cubic meters);
- for mixing of suspensions with solid coarse particles of 25 mm (maximum);
- for stirring of residues, which contain 60% of the solid phase (maximum).
They are used together:
- with guiding unit (for dispersing);
- with a sparger (at interactions of gases and liquids).
Agitators of special designs are used along with agitators of standard design.
It is advisable to use drum agitators to prepare emulsions or suspensions, as well as for the reaction between the gas and the liquid. Such drum agitators are equipped with blades, designed as a squirrel cage.
Agitators of this type perfectly mix liquid in the following proportions:
- the ratio of drum diameter to the height: 2:3;
- the ratio of drum diameter to the diameter of the vessel: from 1:4 to 1:6.
For the preparation of emulsion or suspension must be selected tenfold filling height of the vessel in relation to the value of the drum diameter. The process of mixing of gas and liquid requires much greater height of the vessel.
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- Описание процесса смешения. Методы перемешивания. Мешалки
- Mischern (Mischwerke)
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Upon becoming the official distributer of agitators (mixing equipment), our company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), carries out the following: finds the buyers of your products on the market, conducts technical and commercial negotiations with the customers regarding the supplies of your equipment, concludes contracts. Should a bidding take place, we will collect and prepare all the documents required for the participation, conclude all the necessary contracts for the supply of your equipment, as well as register the goods (agitators (mixing equipment)) and conduct customs clearance procedures. We will also register a certificate of transaction (Passport of Deal) required for all foreign trade contracts in the foreign currency control department of the authorized Russian bank so that currency transaction could be effected. If required, our company will implement an equipment spacing project in order to integrate your equipment into the existing or newly built production plant.
We are convinced that our company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), will become your reliable, qualified and efficient partner & distributor in Russia.
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