RU2761207C1 - Film evaporation drum - Google Patents

Abstract

FIELD: physical chemistry.

SUBSTANCE: invention relates to the field of separation of liquid media by evaporation and can be used in the energy, oil and gas, nuclear, chemical, food, pharmacological and other industries for the concentration of liquid solutions, vacuum evaporation, etc. The film evaporation drum contains a cylindrical body with bottoms, a pipe for supplying heating steam to the body and removing secondary steam from the body, a condensate drain pipe from the bottom of the body, an evaporation drum partially filled with evaporated solution and mounted on rotation supports, a drum rotation drive, a pipeline for supplying evaporated solution into the drum cavity, a pipeline for removing concentrate from the bottom of the drum, a device for mechanical cleaning of the evaporative surface of the drum from salt deposits located under the liquid level in the drum. The drum rotation drive is made in the form of a turbine-type pneumatic motor, in which the role of blades is performed by ribs on the outer surface of the drum. The heating steam supply pipe is designed with the possibility of supplying heating steam to the housing tangentially forming the trajectory of rotation of the ribs and is equipped with a constricting device. The conditions for ensuring the rotation speed of the drum provide the possibility of choosing the size of the flow section of the heating steam supply pipe and the geometric parameters of the ribs.

EFFECT: invention provides simplification of the design of the apparatus, high manufacturability of the apparatus and makes it possible to use the kinetic energy of the heating steam entering the apparatus as a driving force for the drum rotation drive.

1 cl, 1 ex, 1 dwg

Description

State of the art

From the prior art, a device for concentrating liquid solutions in rotary film evaporators (film evaporators with a rotary stirrer) is widely known (Udima P.G. Textbook for the course design, installation and operation of heat and mass transfer installations. Film evaporators. M., MPEI, 1985, 52), which consists in the fact that the solution is fed to the inner surface of the heated housing and distributed over it in a thin layer by blades (scrapers) fixed on the central rotating rotor. The rotor blades create vortex structures in the solution layer, intensifying heat exchange processes.

The rotary film evaporator is a stationary heated tube with a rotor located inside it with blades adjacent to the inner surface. The solution fed into the pipe is "smeared" with blades on the surface and flows down in the form of a film to the place of unloading. The concentrated product is removed through the bleed nipple into the collection of the finished product, and the steam obtained from the solution is discharged through the outlet nipple to the condenser. This method is used, for example, to concentrate food products (milk, whey, tomato paste, fruit juices, etc.).

This method makes it possible to effectively carry out the process of concentrating highly mineralized liquids in a continuous mode without the growth of deposits on heated surfaces. The disadvantage of this method is the unresolved problem of droplet-aerosol entrainment, which sharply reduces the degree of purity of condensed solvent vapors, which in turn leads to product loss, the formation of deposits on the heat exchange surfaces of heat exchangers-condensers, also significantly complicates the possibility of using the method for concentrating radiation and chemically hazardous substances. This disadvantage is due to the high circulation rates of solvent vapors, which is created by the blades of an extended rotor in contact with the liquid film, rotating at a high angular velocity, which leads to the exit, together with the solvent vapor flow, of a large number of microparticles of the dissolved substance (aerosols).

In addition, the method is effective only when thin films are formed, which requires "fine tuning" of the rotary film evaporator due to the need to maintain small gaps between the blades of the rotating rotor and the heated inner surface of the housing.

Another analogue, which coincides with the claimed invention in many significant ways, are rotary evaporators of liquid solutions (Laboratory instruments and equipment made of glass and porcelain. Reference edition. M., Chemistry, 1988, p. 211), operating by evaporating the solvent from a thin film of solution formed on the inner surface of the rotating evaporation chamber (rotary evaporation). Their principle of operation is that a certain amount of liquid solution is loaded into an evaporation chamber in the form of a flask through the loading opening, the flask is rotated at an angle to the horizon, while the bottom of the flask is immersed in a hot liquid (water, oil, etc.) ). From the hot liquid, heat is transferred to the solution through the glass wall of the flask, heating it. During rotation, a solution film is formed on the inner surface of the flask, from which the solvent evaporates. The inner cavity of the flask is connected to a condenser made in the form of a tube with flowing cold water, in which solvent vapors are collected for condensation. Since steam turns into liquid on the heat exchange surface of the condenser, a vacuum is created in the inner cavity of the flask, which is compensated by further evaporation from the solution film. During evaporation, heat is removed from the film itself and the adjacent glass wall, which is replenished by periodically immersing the outer surface of the flask wall in hot liquid. After reaching a predetermined level of concentration of the solution, the rotation of the flask is stopped and the concentrated product is unloaded through the same hole through which the solution was loaded.

Due to the formation of a film on the inner surface of the flask, the evaporation area increases, while the vaporization process is intensified. When selecting temperature conditions, a sufficiently high degree of purity of condensed solvent vapors is ensured.

These evaporators are used in the chemical, petrochemical, chemical-pharmaceutical, medical and food industries, and allow the distillation of thermally unstable substances under mild temperature conditions, the distillation of a mixture of high-boiling substances that cannot be separated by conventional distillation, the degassing of liquids, the evaporation of liquids, the distillation of easily foaming substances, etc.

The disadvantage of this method is that the concentration process is periodic, which is caused by the need to stop the rotation of the flask to unload the concentrated product and load a new portion of the solution. In the process of evaporation, the level of the solution in the flask gradually decreases, and, consequently, the surface of the film decreases, which leads to a decrease in the evaporation efficiency and, ultimately, to a decrease in the productivity of the process. In addition, a sedimentary deposit forms on the inner surface of the flask, which is removed by periodic washing, which increases the volume of secondary waste, the disposal of which requires additional costs and complicates the process, especially when concentrating radiation and chemically hazardous substances.

The closest analogue, which coincides with the claimed invention in terms of the greatest number of essential features, is an evaporator for concentrating liquid solutions (US Pat. a cavity, a tube for removing one stripped off solution and a device for cleaning its inner surface. The rotation of the drum is carried out by a rotation drive. The rotation speed, the level of the solution inside the drum, and the heat power expended on the evaporation of the solvent are selected experimentally from the condition of ensuring the discharge of the concentrated product in the form of a liquid with the required concentration. Unloading is provided by a concentrated product unloading and collection system. The required cleanliness of the inner surface of the drum during the concentration process is maintained by a device for cleaning deposits, placed under the level of the solution to obtain a greater cleaning efficiency.

The disadvantage of this installation is that to ensure the rotation of the drum, it is necessary to use an external, usually electromechanical rotation drive, which causes additional equipment (motor, gearbox, shaft seal unit, etc.), increases the cost of maintenance and repairs and creates difficulties ensuring the tightness of the evaporator, especially when evaporating radioactive solutions.

The inventive device BPI allows you to eliminate the indicated disadvantages and, with a significant simplification of the design, to provide the required quality indicators of the concentrated product and condensed solvent vapors in continuous operation without reducing productivity in a wide range of changes in the concentration of solutions, while the operation does not require repair and maintenance of the drum rotation drive.

The essence of the invention

The invention is aimed at creating effective horizontal evaporators for film evaporation of a drum structure without an external rotation drive, with a steam heating jacket and a minimum power consumption, technologically advanced in manufacture and operation, providing a minimum droplet-aerosol entrainment in the secondary steam at a high degree of concentration of solutions.

Task Solving the drum rotation due to the kinetic energy supplied to the heating jacket steam is achieved in that the horizontal evaporator "reel of film evaporation" (BPI), comprising a cylindrical body with a bottom, and at least one detachable flange, pipe supplying the heating steam to the body and the secondary steam outlet from the body, the condensate outlet from the bottom of the body, the evaporating drum partially filled with the evaporated liquid, mounted on the rotation supports, the pipeline for supplying the evaporated solution to the drum cavity and the concentrate withdrawal pipeline from the bottom point of the drum, the device for mechanical cleaning the evaporating surface of the drum from salt deposits, located under the liquid level, the drum rotation drive is made in the form of a turbine-type pneumatic motor, in which the role of blades is played by the ribs on the drum surface, and the heating steam is supplied to the body tangentially forming the traces torii of rotation of edges.

The design of the BPI makes it possible to use the kinetic energy of the steam flow entering the apparatus to drive the evaporation drum in rotation. In this case, the drum rotation drive can be made in the form of a turbine-type pneumatic engine, in which the ribs on the outer surface of the drum act as blades, and the steam medium is supplied to the apparatus body tangentially generating the rib rotation trajectory. The rotational speed of the evaporator drum is determined by:

- mechanical resistance of the drum bearing supports;

- hydraulic resistance to drum rotation from the side of the moving stream of the evaporated solution in the lower part of the drum cavity;

- mechanical resistance to drum rotation from the side of the device for cleaning the inner surface of the drum from salt deposits;

- torque when the steam flow acts on the drum blades in the form of ribs on the outer surface with tangential steam injection into the apparatus body.

In the latter case, in the presence of an adjustable restriction device in the inlet pipe, it is possible to significantly change the heating steam injection rate, thereby changing the effect on the blades and, consequently, on the drum rotation speed.

The stated complex of design solutions allows you to achieve the goals and provides:

- a significant simplification of the design of the film evaporator, associated with the rejection of the use of an electromechanical or any other external rotation drive due to the possibility of using the kinetic energy of the heating steam flow entering the BPI as the driving force of the turbine-type rotation drive;

- the possibility of creating a simple evaporator with vapor recompression based on the BPI, when the secondary steam from the evaporator, compressed in a gas blower or a Roots pump, is directly used as heating steam for the same apparatus. In this case, there is no need for a source of heating steam, a heat exchanger-condenser for condensing steam with a cooling liquid system, sealing the drum rotation shaft, etc .;

- compactness, simplicity and manufacturability of the BPI design;

- low energy consumption during the operation of the device;

- the ability to control the speed of rotation of the drum;

- minimal drip-aerosol entrainment;

- Favorable conditions for ensuring tightness in the BPI due to the absence of movable joints in the body when supplying and removing working media;

- the ability to ensure complete tightness of the shaft with the environment when using a turbine-type pneumatic motor as a drive for rotating the drum.

Description of drawings

The following description refers to the accompanying drawings, which show, by way of a non-limiting example, an embodiment of the invention and in which Figure 1 shows a longitudinal sectional diagram of a film evaporation drum (FIB) and its cross-section in the tangential heating steam inlet region, made in accordance with the invention.

Presented in figure 1 drum of film evaporation (BPI) is a cylindrical horizontal sealed housing (1) with bottoms (2) on flange connections and located inside the evaporation drum (3) on bearing supports (4) and (5). The design of the support (5) provides a hermetic connection of the drum (6) rotating around the axis of the steam outlet pipe and the stationary pipe (7) designed to remove the secondary steam from the BPI. The branch pipe (7) is equipped with a removable cover on the flange connection (8). Through this cover, a tube for feeding the evaporated solution (9), equipped with a float valve (10) and a tube for collecting the concentrate (11), pass into the cavity of the drum (3).

The drum is partially filled with a solution to be evaporated (12), the level of which is constantly maintained by a float valve (10). To ensure the cleaning of the heating surface from deposits, a rod with a spiral winding (13), which rolls when the drum rotates, is used, which, due to the screw effect of winding, if it is impossible to move in the axial direction, moves the salt sediment towards the unloading side, where the evaporated product is taken through the tube ( eleven).

The drum is driven into rotation using a turbine-type pneumatic motor, in which the ribs (14) on the end surface (15) of the drum act as blades, and the working medium (heating steam) is supplied through a branch pipe (16) on the housing (1) located tangent to the generatrix of the trajectory of rotation of the ribs. The above sketch of the cross section A-A shows the relative position of the blades (ribs 14) and the heating steam supply pipe (16). The same section schematically shows an adjustable restriction device (17), which allows you to change the speed of steam at the inlet to the housing and, accordingly, to regulate the amount of flow pressure on the ribs (14), while changing the torque and rotation speed of the drum.

Evaporation of the solution in the BPI is as follows. Heating steam flowing through the tangent pipe (16) enters the space between the sealed casing (1) and the evaporator drum (3). On the outer surface of the drum (3), heating steam condenses and the condensate drains into the lower part of the housing (1), from where it is discharged through a pipe (18) equipped with a thermodynamic condensate drain (19). When heat is transferred by heating steam to the drum (3), secondary steam is formed in its cavity, which is removed from the sealed housing (1) through the branch pipe (7).

In start-up mode, it is necessary to remove non-condensable gases from the heating jacket. To do this, after starting the installation, keep the valve for blowing off the steam-gas mixture (20) open for some time. After removing the non-condensable gases, it is closed.

As an example of a specific embodiment of an evaporator for concentrating liquid solutions, the case of evaporation of liquid radioactive waste with a salt concentration (in mass fractions) of 0.005-0.01 kg / kg in a film evaporation drum 6 m long, 500 mm in diameter and with a wall thickness of 6 mm is considered ... The secondary pressure inside the drum is 85 kPa. Heating steam with a flow rate of 290 kg / h, a pressure of 150 kPa and a temperature of 112 ° C, steam is fed through the restriction device of the inlet pipe to the heating jacket of the apparatus body. The maximum steam velocity in a narrow section is 120 m / s. The steam flow acts on the drum blades with a force of 180 N, while creating a drum torque of 45 N × m. This is enough for a drum partially filled with liquid (with a wound rod rolling inside to clean the surface from deposits) rotated at a frequency of ~ 8 rpm. During the period of one revolution, the liquid film, ~ 50 µm thick, will decrease by about 7 µm due to evaporation. This is an insignificant and quite acceptable change in the thickness of the evaporation film with a large margin of its drying; therefore, the rotation speed of the drum can be considered acceptable.

Claims (1)

A film evaporation drum containing a cylindrical body with bottoms, a pipe for supplying heating steam to the body and removing secondary steam from the body, a pipe for draining condensate from the bottom of the body, an evaporator drum partially filled with an evaporated solution and mounted on rotation supports, a drum rotation drive, a pipeline for supplying the evaporated solution to the drum cavity, the concentrate outlet pipeline from the bottom point of the drum, a device located under the liquid level in the drum for mechanical cleaning of the evaporating surface of the drum from salt deposits, characterized in that the drum rotation drive is made in the form of a turbine-type pneumatic engine, in which the role of the blades, ribs are made on the outer surface of the drum, the heating steam supply pipe is made with the possibility of supplying heating steam to the body of the tangentially generating trajectory of rotation of the ribs and is equipped with a narrowing device, and the conditions for ensuring the drum rotation speed are made with the possibility the choice of the size of the flow area of the heating steam supply pipe and the geometric parameters of the ribs.

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