RU2732709C1 - Method for preparation of flocculant solution and apparatus for implementation thereof - Google Patents

Abstract

FIELD: treatment of water, industrial and household waste water.

SUBSTANCE: invention is intended for processes of preparation of solutions of flocculants during preparation of water for drinking purposes, purification of waste water, condensation of slurries of ore dressing enterprises, at coal beneficiation, extraction of valuable minerals. Method for preparing a solution of a flocculant comprises feeding a dry flocculant into a container pre-filled with water, where dissolution is carried out in three steps - rapid mixing, slow mixing and aging, according to the invention all steps are carried out in one container, wherein the dry flocculant is subjected to rapid mixing with water, then formed concentrate is directed into zone of slow mixing in the same vessel, which is combined with aging zone, from where it is removed in form of ready solution. Device for implementing the method includes a dissolution vessel, mixing devices, for rapid mixing - rotor-stator mixing device, rotor and stator surfaces contain a certain number of holes for passage of liquid, for slow mixing - a mixing device of conical mixer type, comprising a hub installed on a rotating vertical shaft, on which blades with a disk are fixed, wherein blades have a curved shape, wherein both mixing devices are installed in one dissolution vessel, mixing device of conical mixer type is installed coaxially to capacity for dissolution, and mixing device of rotor-stator type - with eccentricity, rotation frequency of rotor in mixing device of rotor-stator type is set in range from 1400 to 3000 rpm, and gap between rotor and stator is set in range from 100 mcm to 2000 mcm.

EFFECT: invention provides fast and complete dissolution of dry flocculants due to improved quality of mixing and prevention of lumps, higher efficiency per unit volume of apparatus, simplification of the plant design for flocculant preparation, mobility (easier transportation, assembly and installation), reduction of overall dimensions of the plant.

2 cl, 2 dwg, 2 tbl

Description

The invention is intended for the processes of preparation of solutions of flocculants in the preparation of water for drinking purposes, wastewater treatment, thickening of sludge from mining and processing enterprises, during coal preparation, extraction of valuable minerals.

The vast majority of flocculants are supplied in solid form, in powder form. This is due to cost savings in transportation, easier methods of storage and storage of dry substances. (Frolov V.S., Udovitskiy V.I.Preparation of powdery flocculants at coal preparation enterprises of Kuzbass // Mining information and analytical bulletin (scientific and technical journal) , 2009.) Currently, a method is used (Tager A.A., Physicochemistry of polymers .-3rd ed., Revised., M .: Chemistry, 1978) preparation of solutions from dry particles of a flocculant, consisting of three stages, each of which is carried out in a separate container: wetting of the flocculant particles (using a high-speed mixer), dissolution granules (a slow-speed mixer is used at this stage), ripening. The main problems when preparing a solution from a powder are:

1) adhesion of granules and the formation of flocculant lumps floating on the surface of the liquid and not captured by the circulation currents of the liquid formed by the mixer; As a result, these lumps do not dissolve in the liquid properly, and the factories are forced to increase the flocculant loading volume by 2-3 times higher than the norm to achieve the specified concentration of the flocculant in the solution. Undissolved flocculant granules often later fall on the surfaces of equipment, including heat exchange ones, forming a dense crust on them, which leads to a decrease in heating efficiency.

2) a rather long period of solution preparation, associated primarily with the need for long-term stirring with a high-speed mixer at the wetting stage, as well as a low degree of solution turbulence at the dissolution stage (blade mixers of classical types are characterized by a high degree of shear stresses at the end of the blades and in order to avoid rupture of polymer chains use rather low rotation speeds of mixing devices); this leads to a decrease in the productivity of the device manufactured according to the known method.

The patent (RF Patent No. 2613952, 03/05/2014.) Describes a method for dissolving a polymer based on the separation of lumps by passing through a sieve with a specific cell. The disadvantage of this method is the danger of clogging the filter, as well as a rather complex design of the installation, in which it is necessary to use an additional pump for circulating the flocculant.

A known method of preparing a flocculant based on heating a liquid (RF Patent No. 2114789, 04 11 1996.). The method consists in the fact that the flocculant is loaded into the solvent at 35 - 55 ° C, after which the temperature of the solvent is increased and, with stirring, the flocculant is dissolved at 50 - 75 ° C. The invention makes it possible to reduce the preparation time of the flocculant and to increase the completeness of its dissolution and the efficiency of its action. However, this method is associated with high energy costs and is economically justified only for the preparation of small batches of solution.

The closest to the proposed method is the method implemented in the installation for the preparation of a flocculant company Prominent (Samsonova S. P. "Examples of optimization of the reagent economy" Water treatment. Water treatment. Water supply, July 2015). The plant body includes three sections connected by overflow pockets into a single hydraulic system: a wetting section, a dissolving section and a maturation section. During the preparation process, the solution sequentially passes through all sections. Water is supplied to the wetting section and at the same time granular flocculant is supplied from the hopper by the dispenser. Dissolution of the flocculant is ensured by a low-speed, paddle-type stirrer with an electric drive. The next cooking cycle starts after the level in the maturation section has dropped. At the same time, the water with the dissolved powder is forced through the overflow pocket into the maturation section, which is also equipped with a low-speed electric stirrer. A similar device is also described in the description of the utility model to the patent (RF Patent No. 157545, 07 09 2015). The disadvantages of the known installation are the rather high manufacturing cost and large overall dimensions of the equipment associated with the arrangement of several compartments for the passage of the solution, as well as the excessively long duration of the process.

The closest technical solution to the proposed apparatus is a device (prototype) (RF Patent No. 212554, C02F 1/52, B01F 15/04, B01J 4/02, publ. 27.01.1999) for preparing a flocculant, containing a dispenser, a reactor vessel with a mechanical an agitator for preparing a working solution of a flocculant of a given concentration and a supply capacity of a working solution of a flocculant for supplying the coagulation process with water purified from sludge according to the established technology, in which the loading container is made in the form of a sealed vessel with a lid, designed for an excess pressure within 0.1 MPa, for at the top of which there is a nozzle for air supply and a pressure regulator in the form of a check valve, and at the bottom on the bottom there are removable dies by means of a threaded connection, which are made with through slots no more than 0.5 mm wide with the possibility of pushing pasty viscous flocculant through these slots in the form of a continuous films under the influence of excess air pressure in the upper th part of the vessel, while the bottom of the intake container with spinnerets is placed inside the reactor vessel below the upper water level in the reactor and tangential to the plane of the upper blade of the reactor stirrer, which, when rotating, breaks the flocculant film squeezed out of the intake container into particles, followed by their dissolution in water with stirring ...

The disadvantage of this technical solution is the structural complexity and frequency of operation, due to the presence of a periodically sealed container for the concentrated flocculant and opening a controlled valve to transfer the flocculant from the reactor vessel to the settler, as well as insufficient uniformity of the resulting flocculant.

Thus, the main problem when using the known method and device is the formation of lumps due to insufficient rapid dissolution, the forced increase in the consumption of dry flocculant, the increase in the duration of the process.

The objective of the present invention is to ensure rapid and complete dissolution of dry flocculants by improving the quality of mixing and preventing the formation of lumps, increasing productivity per unit volume of the apparatus, reducing energy costs, simplifying the design of the installation for preparing a flocculant, ensuring mobility (easier transportation, assembly and installation) , reducing the overall dimensions and weight of the installation.

The solution to this problem is achieved by the fact that in the method for preparing a solution of a flocculant, which consists in the fact that a dry flocculant is fed into a container pre-filled with water, where dissolution is carried out in three stages - rapid mixing, slow stirring and aging, according to the invention, all stages are carried out in one container, while the dry flocculant is subjected to rapid mixing with water, then the resulting concentrate is directed to the slow mixing zone in the same container, which is combined with the ripening zone, from where it is discharged in the form of a ready-made solution.

The solution to this problem is also achieved by the fact that in the device for preparing a solution of a flocculant for implementing the method, including a container for dissolution, mixing devices, according to the invention, a stirring device of the "rotor-stator" type is used for rapid mixing, the surfaces of the rotor and stator contain a certain number of holes for the passage of liquid, for slow mixing, a mixing device of the conical mixer type is used, containing a hub mounted on a rotating vertical shaft, on which blades with a disk are fixed, and the blades have a curved shape, while both mixing devices are installed in the same dissolution tank, a conical mixing device the mixer is installed coaxially with the dissolution vessel, and the rotor-stator mixing device is with eccentricity, the rotor speed in the rotor-stator mixing device is set in the range from 1400 to 3000 rpm, and the gap between the rotor and stator are set in the range from 100 μm to 2000 μm.

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

FIG. 1 shows a general diagram of the proposed apparatus, FIG. 2 is a general view of a conical mixer.

In the housing 1 of the apparatus there is a mixing device 2 of the "rotor-stator" type for rapid mixing, as well as a mixing device of the 3 type of a conical mixer for slow mixing, while both mixing devices 2 and 3 are installed in the same dissolution vessel - housing 1. The mixing device 3 is preferably mounted coaxially with the housing 1, and the mixing device 2 is eccentric. To supply the dry flocculant powder inside the housing of the rotor-stator type mixing device 2, a dispenser 4 and a funnel 5 are provided. The gap between the rotor and the stator of the rotor-stator type mixing device 2 is set in the range from 100 μm to 2000 μm.

Stirring device 2 of the "rotor-stator" type is used to wet the powder with water by rapid stirring. For distribution in the volume of the container due to slow mixing, a mixing device 3 (conical mixer) is used, containing a hub 7 mounted on a rotating vertical shaft 6, on which blades 8 with a disk 9 are fixed, and the blades 8 have a curved shape (Fig. 2).

A feature of the mixing device 2 is the presence of two elements symmetrical about the common axis of rotation - a high-speed rotor located on the drive shaft and a stationary stator rigidly fixed to the body of the apparatus or combined with it (Edward L. Paul, Victor A. Atiemo-Obeng, Suzanne M . Kresta, Handbook of industrial mixing: science and practice, Canada: A John Wiley & Sons, Inc., Publ., 2004.). The radial clearance between the rotor and the stator is set in the range from 100 μm to 2000 μm. Smaller clearance values provide a higher level of shear stress, but also higher complexity and cost of manufacture; large clearance values correspond to lower shear stresses, but this simplifies the design of the device and reduces the cost of its manufacture and assembly. Gap values less than 100 microns lead to an unnecessary complication of the structure, an increase in the cost of its manufacture, an increase in the requirements for the accuracy of manufacturing seats, for bearings, and for the rigidity of elements. Gap values greater than 2000 μm (2 mm) lead to a decrease in the level of shear stresses in the gap between the rotor and stator, and therefore to a decrease in the efficiency of rapid mixing. The surfaces of the rotor and stator contain a certain number of holes for fluid passage. When the rotor rotates, there are instantaneous positions in which part of the stator holes are open for the passage of liquid, and the other part is blocked by the rotor. For open holes, the hydraulic resistance to the flow is the smallest and the speed of fluid passage through them is maximum. At the moment of overlapping of these holes in the zone between the rotor and the stator due to the rapid rarefaction and subsequent recovery of speed, mechanisms of explosive boiling and cavitation are initiated. These mechanisms proceed in a rather severe mode due to the extremely short duration of energy transformation between subsequent overlap of the holes. Due to the small clearance between the rotor and stator, the lateral speed gradients are extremely high. In this zone of the mixer, the greatest energy dissipation is observed, but it is here that the strongest destructive effect on the dispersed phase is observed (R. Sh. Abiev, Theoretical Foundations of Energy and Resource Saving in Chemical Technology: Textbook, SPb: SPbSTI (TU), 2006. ).

The proposed apparatus works as follows.

The body 1 of the apparatus is filled with water to a predetermined level, which must ensure the immersion of the working part of the rotor and the stator of the mixing device 2 of the "rotor-stator" type.

The drives of both mixing devices 2 and 3 are switched on, while the rotor speed in the mixing device 2 of the "rotor-stator" type is set in the range from 1400 to 3000 rpm, and the rotation frequency of the mixing device 3 is set in the range of optimal frequencies (from 22 to 140 rpm); these values are determined experimentally. Experiments have shown that lower rotational speeds do not allow achieving sufficient mixing efficiency, and higher rotational speeds lead to a significant increase in energy consumption, as well as to the destruction of swollen flocculant particles.

Powder of dry flocculant is fed into the housing of a mixing device 2 of the "rotor-stator" type using a dispenser 4 through a funnel 5.

When the surface of the blades of the mixing device 3 interacts with the liquid in the apparatus, rotational movement is transmitted to it, a complex velocity field with three components arises in the apparatus: circumferential, radial and axial. The peripheral speed is an order of magnitude or more higher than the other two components of speed. As a result of the rotational movement in the apparatus, centrifugal forces of inertia arise, generating radial movement. Near the walls, the rotational motion significantly dies out, partially passing into the meridional (axial) one, which contributes to the creation of meridional circulation and the rise of particles from the bottom of the apparatus, i.e. weighing them (suspension).

When flocculant particles enter the central part of the mixing device 2 as a result of the action of centrifugal forces, they are transported together with the liquid flow from the central part of the mixing device 2 to the peripheral part. Due to the complex of factors acting on the particles in the mixing device 2: high shear stresses, pressure pulsations, cavitation effects, almost instantaneous swelling and primary dissolution of flocculant particles in water is achieved. The swollen particles fall further into the total volume of the apparatus, where, due to the circulation created by the stirring device 3, they are captured by currents of liquid and are fairly evenly distributed over the volume of the body 1 of the apparatus; during the circulation, the particles mature. At the same time, the level of shear stresses created by the mixing device 3 (conical mixer) is quite low, which makes it possible to prevent excessive deformation of the swollen particles and their destruction.

Thus, in the proposed device, the proposed method is implemented: dissolution is carried out in three stages - fast mixing, slow mixing and aging, and all stages are carried out in one container 1, while the dry flocculant is rapidly mixed with water using a mixing device 2, then the resulting the concentrate is directed to the zone of slow mixing by means of a mixing device 3 in the same container 1, which is combined with the ripening zone, from where it is taken out in the form of a finished solution. The slow mixing zone is a zone that includes a volume adjacent to the mixing device 3, as well as a zone of circulating currents passing through this volume (the so-called "active" mixing zone). The rest of the space in tank 1 (where the mixing intensity is relatively low) is the ripening zone.

The technical result of the proposed invention is to ensure rapid and complete dissolution of dry flocculants by improving the quality of mixing and preventing the formation of lumps, increasing the productivity of the process, simplifying the design of the installation for preparing the flocculant, ensuring mobility (easier transportation, assembly and installation), and reducing the overall dimensions of the installation.

Ensuring fast and complete dissolution of dry flocculants is achieved by combining in one apparatus a uniform feed of particles supplied by a dispenser, creating a high level of shear stresses in a rotor-stator stirrer, and then a low level of shear stresses in the apparatus due to the use of a conical agitator, which generally leads to improved mixing quality and prevention of lump formation.

The increase in the productivity of the process is achieved by organizing a continuous process, combining all stages of the process in one apparatus.

The simplification of the design of the installation for the preparation of the flocculant is due to the reduction in the number of units used, and the provision of mobility (easier transportation, assembly and installation) is due to the use of two monoblock mixing devices that can be easily mounted in an apparatus of almost any geometry.

Reducing the overall dimensions of the apparatus is achieved through the transition from a three-section design of the apparatus to a single-section design. As the body 1 can be used containers in the form of a cube or parallelepiped, produced in series, as well as shells of a cylindrical or spherical shape.

In essence, it can be considered that the volume of the mixing device 2 of the "rotor-stator" type is the primary treatment zone (rapid mixing zone) located inside the main body of the apparatus, and the rest of the volume of the apparatus, where mixing is provided by the mixing device 3 of the conical mixer type, is the zone secondary processing (slow mixing zone). At the same time, due to the absence of additional shells, the metal consumption of the equipment decreases and its dimensions are reduced.

An example of a specific implementation 1 (basic version - according to the invention-prototype).

For the preparation and dosing of the flocculant, a three-section UPF 1000 unit is used, the characteristics of which are shown in Table 1.

The body of the UPF 1000 unit for flocculant preparation includes three sections connected by overflow pockets into a single hydraulic system: a dissolving section, a maturing section and a ready solution section.

During the preparation process, the solution sequentially passes through all sections. Water is supplied to the dissolution section and at the same time granular flocculant is supplied from the hopper by a screw feeder. The mixing of the flocculant with water is ensured by a low-speed electric stirrer. After filling the dissolution section, the supply of water and flocculant is stopped.

The next cooking cycle begins after the level drops in the ready-to-mix section. At the same time, water with dissolved flocculant is forced through the overflow pocket into the maturation section, also equipped with an electric slow-speed stirrer. From the second section, the already matured solution through the overflow pocket is displaced into the section of the finished solution, from where it is taken.

The main disadvantages of this installation are its cumbersomeness and high clogging of the screw feeder, which in turn leads to the ingress of adhered polymer lumps into the mixing chamber. This increases the dissolution time of the flocculant several times, and also seriously affects the quality of the finished solution.

In addition, the average residence time in the known device with a capacity for the ready-made solution of 1000 l / h is 4.15 hours, and the power consumption is 1.6 kW.

An example of a specific implementation 2 (according to the proposed invention).

The device according to the invention is a one-section device for preparing and dispensing a flocculant, made according to the claims, i.e. it combines the stages of wetting and dissolution. The body 1 of the apparatus is a eurocube made, for example, of high density polyethylene (HDPE) (it is possible to manufacture it from polypropylene (PP), stainless steel or other materials). A steel frame is attached to the top of the cube, which allows placing the main low-speed hyperbolic mixer 3 in the center of the housing 1, as well as an eccentrically located mixer 2 of the "rotor-stator" type with a funnel 5 and a dispenser 4, as shown in Fig. 1.

The cooking process begins with pre-filling the working volume of the device with water to the required level. Then the main slow-speed hyperbolic mixer 3 and mixer 2 of the "rotor-stator" type are started. Powder in dry form is fed into the funnel 5 by means of the dispenser 4, which, passing through the mixer chamber 2, is wetted with water and enters the main working volume of the apparatus.

After the supplied powder passes through the mixer 2 of the "rotor-stator" type, the speed of movement of the particles in the liquid (as the kinetic energy of the liquid jets flowing out of the mixer 2 dissipates) sharply decreases, and then the stage of complete dissolution of the polymer particles in the liquid occurs, carried out with the help of the main hyperbolic mixer 3, which evenly distributes the powder over the entire working volume of the apparatus and maintains it in suspension.

Compared to a three-section device, this unit has smaller dimensions and weight (1.68 m ³ , which is 2.47 times less than the volume of the prototype device), as well as less power consumption (1.1 kW, which is 1.455 times less than for the prototype device), coupled with greater efficiency in the use of volume (residence time is reduced by 2.47 times for a given performance). Obviously, due to the simplified design of the proposed installation, its mobility is ensured due to simpler transportation, assembly and installation.

Mixer 2 of the "rotor-stator" type guarantees the absence of polymer lumps at the outlet of the mixing chamber, and the hyperbolic mixer 3, which does not create dangerous shear stresses, allows the flocculant to be mixed at higher speeds, which helps to reduce the time of complete polymer dissolution.

The value of the maximum allowable clearance between the rotor and stator is selected according to the following recommendations. The minimum clearance between rotor and stator is 100 µm. Smaller values of the gap are technologically difficult to implement, and it is difficult to ensure the operability of the mixer 2. The larger this gap, the less requirements are imposed on the quality and cost of manufacturing the mixer. However, an increase in the gap also leads to a drop in the efficiency of the rotor-stator mixer and an increase in useful power losses. the values of the created shear stresses decrease. Therefore, the gap should not exceed 2000 µm.

Experiments have shown that when the rotor speed of the "rotor-stator" type mixer is selected, the operating efficiency decreases in the range from 1400 to 3000 rpm: at a speed below 1400 rpm, the mixing quality deteriorates, flocculant lumps appear in the solution; at a speed of more than 3000 rpm, the level of shear stresses in the liquid increases excessively, which leads to the destruction of the swollen particles of the flocculant.

Thus, the use of the invention makes it possible to ensure fast and complete dissolution of dry flocculants by improving the quality of mixing and preventing the formation of lumps, to increase productivity per unit volume of the apparatus, to reduce energy costs, to simplify the design of an installation for preparing a flocculant, to provide mobility (easier transportation, assembly and installation), to reduce the overall dimensions of the unit.

Method of preparation of flocculant solution

and apparatus for its implementation

Table 1. Main characteristics of the UPF 1000 installation (according to the known technical solution)

Productivity for the ready-made solution, l / hour Overall dimensions (L × W × H), mm power, kWt Weight (transport / working), kg Body material 1000 2000 × 1250 × 1660 1.6 290/1790 Stainless steel

Table 2. Main characteristics of a one-section installation for the preparation and dosing of flocculant (according to the proposed invention)

Productivity for the ready-made solution, l / hour Overall dimensions (L × W × H), mm power, kWt Weight (transport /
working), kg Body material 1000 1200 × 1000 × 1400 1.1 150/1150 HDPE, PP, stainless steel

Claims (2)

1. A method of preparing a solution of a flocculant, which consists in the fact that the dry flocculant is fed into a container pre-filled with water, where dissolution is carried out in three stages - rapid mixing, slow stirring and aging, characterized in that all stages are carried out in one container, while dry flocculant is subjected to rapid mixing with water, then the resulting concentrate is sent to the slow mixing zone in the same container, which is combined with the ripening zone, from where it is discharged in the form of a finished solution. 2. A device for preparing a solution of a flocculant for implementing the method according to claim 1, including a container for dissolution, stirring devices, characterized in that a stirring device of the "rotor-stator" type is used for rapid stirring, the surfaces of the rotor and stator contain a certain number of holes for the passage of liquid , for slow mixing, a mixing device of the conical mixer type is used, containing a hub mounted on a rotating vertical shaft, on which blades with a disk are fixed, and the blades have a curved shape, while both mixing devices are installed in one dissolution vessel, a mixing device of the conical mixer type is installed coaxially with the dissolution tank, and the rotor-stator mixing device is eccentric, the rotor speed in the rotor-stator mixing device is set in the range from 1400 to 3000 rpm, and the gap between the rotor and stator is set in the range from 100 to 2000 microns.

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