Film drum evaporator

Abstract

Film drum evaporator. The invention relates to the separation of liquid media by evaporation, applicable in liquid solution concentration and desalination plants. The evaporator comprises a cylindrical body with ends, a heated steam supply pipe, a secondary steam discharge pipe, and a condensate discharge pipe from the lower part of the body. The drum, partially filled with the solution to be evaporated, is mounted on bearing supports and equipped with a rotation drive. One pipe supplies the solution to be evaporated into the drum cavity, while another pipe discharges the concentrate from the bottom of the drum. A device located below the liquid level in the drum ensures continuous mechanical cleaning of salt deposits from the evaporation surface.To reduce metal consumption, the drum wall thickness is decreased by means of stiffening rings distributed along its entire length. Some of these rings serve as support bushings for a series of bearing supports, evenly distributing the load along the drum's length. This configuration increases drum productivity by reducing wall thickness while simultaneously increasing the drum's diameter and length with a limited number of bearing supports. The evaporator is designed for the separation of liquid media by evaporation in the nuclear, chemical, food, pharmaceutical, energy, oil, and gas industries, among others.

Description

Title of the invention: Film drum evaporator Technical field of the invention

[0001] The invention relates to the field of separation of liquid media by evaporation and can be used in desalination plants, as well as in the nuclear, chemical, food, pharmaceutical, energy, oil, gas and other industrial sectors for the concentration of liquid solutions, vacuum evaporation, etc. Prior art

[0002] A device for concentrating liquid solutions in rotary film evaporators (film evaporators with rotary scrapers) is known from the prior art, in which the solution is introduced onto the inner surface of the heated body and distributed into a thin layer by blades (scrapers) fixed on a rotating central rotor. This device is described in a book by Uduma PG, "Manual of the course on the design, assembly and operation of heat and mass transfer systems. Film evaporators.", Moscow, MEI, 1985, on page 52 (Y^tiMa HL YneÔHoe nocoône no Kypcy npoeKTnpoBanne, MOHTa» n 3KcnjiyaTau,ns TenjiOMaccooÔMeHHtix ycTanoBOK. ÎLueHOUHbie ncnapnTejin. M., M3H, 1985, CTp. 52). The rotor blades create vortex structures in the solution layer, intensifying heat transfer processes.

[0003] The rotary film evaporator consists of a fixed heated tube with a bladed rotor inside, the blades of which are in contact with the inner surface. The solution introduced into the tube is spread by the blades over the surface and flows as a film towards the discharge point. The concentrated product is removed through a drain fitting into a finished product collector, and the vapor obtained from the solution is discharged through an outlet fitting to a condenser. This method is used, for example, for the concentration of food products (milk, whey, tomato paste, fruit juice, etc.).

[0004] This method makes it possible to carry out efficiently the process of concentrating highly mineralized liquids continuously without accumulation of deposits on the heated surfaces.

[0005] However, a drawback of this method is the unresolved problem of droplet and aerosol entrainment, which significantly reduces the purity of the condensed solvent vapors. This leads to product loss, the formation of deposits on the heat exchange surfaces of the condenser-exchangers, and considerably complicates the use of this method for substance concentration. These methods are radiologically and chemically hazardous. This drawback stems from the high circulation speeds of solvent vapors, generated by the rotor blades in contact with the liquid film, which rotates at high angular velocity. This carries with it a large quantity of microparticles of the dissolved substance (aerosols). Furthermore, the method is only effective for forming thin films, requiring precise adjustment of the rotary film evaporator due to the need to maintain small gaps between the rotating rotor blades and the heated inner surface of the housing.

[0006] Another analogue, corresponding to the claimed invention in many essential aspects, is the rotary evaporator for liquid solutions, operating by evaporating the solvent from a thin film of solution formed on the inner surface of the rotary evaporation chamber. This device is described in a book entitled "Laboratory Apparatus and Equipment in Glass and Porcelain." Reference edition, Moscow, Khimiya, 1988, on page 211. (JlaôopaTopHtie npnôopti h oôopyÆOBaHne H3 CTeKjia h (]jap(])opa. CnpaBOHHoe wmaHue. M., Xhmhs, 1988, CTp. 211). Its operating principle is as follows: a certain quantity of liquid solution is introduced into the evaporation chamber, which is shaped like a flask, through a loading opening. The flask is then rotated at an angle to the horizontal, with its lower part immersed in a hot liquid (water, oil, etc.).The heat from the hot liquid is transferred to the solution through the glass wall of the flask, heating it. During rotation, a film of solution forms on the inner surface of the flask, from which the solvent evaporates. The inner cavity of the flask is connected to a condenser, constructed as a tube with circulating cold water, where the solvent vapors are collected for condensation. As the vapor condenses 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 continuous evaporation from the solution film. During evaporation, heat is removed from the film and the adjacent glass wall, and this is compensated by periodically immersing the outer surface of the flask in the hot liquid.Once the desired concentration level is reached, the rotation of the flask is stopped and the concentrated product is discharged through the same opening used for loading the solution.

[0007] By forming a film on the inner surface of the flask, the evaporation surface area is increased, thereby intensifying the vaporization process. By adjusting the temperature regimes, a sufficiently high degree of purity of the condensed solvent vapors is ensured. These evaporators are used in the chemical, petrochemical, pharmaceutical, medical, and food industries, and allow the distillation of thermally unstable substances under mild temperature conditions, as well as the distillation of mixtures of high-boiling-point substances that cannot be separated by ordinary distillation, degassing liquids, evaporating liquids, distilling easily foaming substances, etc.

[0008] One drawback of this method is the intermittent nature of the process, due to the need to stop the flask's rotation to discharge the concentrated product and load a new portion of solution. During evaporation, the solution level in the flask gradually decreases, thus reducing the film surface area, which leads to a decrease in evaporation efficiency and, ultimately, a drop in process productivity. Furthermore, a deposit forms on the inner surface of the flask, which is removed by periodic washing, increasing the volume of secondary waste. Disposal of this waste incurs additional costs and complicates the process, especially when concentrating radiologically and chemically hazardous substances. Another disadvantage is the low thermal conductivity of the flask glass, which limits evaporation efficiency.

[0009] The closest analogue, corresponding to the claimed invention by the greatest number of essential features, is the film evaporation drum (patent RU2828541C1), which comprises a cylindrical body with bottoms, a pipe supplying heated steam to the body and a pipe for draining secondary steam from the body, a pipe for draining condensate from the lower part of the body, an evaporator drum partially filled with the solution to be evaporated and mounted on rotating supports, a drum rotation drive, a pipe for supplying the solution to be evaporated into the cavity of the drum, a pipe for draining the concentrate from the lowest point of the drum, a device for mechanically cleaning the evaporation surface of the drum of salt deposits, located below the level of the liquid in the drum, rigid rings on the outer surface of the drum, associated with the roller supports.The drum's rotation is driven by a rotary drive. The rotation speed, the solution level inside the drum, and the heat input used for evaporation are experimentally determined to ensure the discharge of the concentrated product as a liquid with the required concentration. Discharge is achieved through a concentrated product discharge and collection system. The required cleanliness of the drum's inner surface during the concentration process is maintained by a deposit cleaning device, positioned below the solution level for greater cleaning efficiency.The drum rotation supports are made in the form of roller supports evenly distributed throughout the body along the entire length of the drum, which allows the load of the drum's weight to be distributed and the thickness of the heat transfer wall to be reduced, thus increasing the efficiency of heat transfer and, consequently, the productivity of the device without changing the overall dimensions.

[0010] One disadvantage of this installation is that increasing the diameter of the drum while reducing the thickness of the drum wall to decrease thermal resistance requires a large number of roller supports, which complicates the design of the evaporator, its assembly and maintenance, and also reduces resilience in case of destruction or breakage of the bearings, thus increasing the manufacturing cost.

[0011] The claimed evaporator eliminates the aforementioned disadvantages and, by simplifying the design, improves performance while increasing the reliability and lifespan of the installation. Brief summary of the invention

[0012] The invention relates to the creation of horizontal drum-type film evaporation devices, equipped with an annular steam heating space and minimal energy consumption. These devices are technologically advanced in terms of manufacturing and operation, guaranteeing maximum evaporation productivity. They eliminate restrictions on drum length and wall thickness, in accordance with the stability requirements of cylindrical bodies under external pressure.

[0013] The solution for achieving maximum evaporator productivity relies on optimal load distribution on the bearing supports and improved stability of the cylindrical body under external pressure. The load comes from the weight of the solution-filled drum, which is equipped with an internal device for mechanically cleaning the evaporation surface of salt deposits (for example, a heavy rolling rod with a scraping spiral).

[0014] Improving the stability of the cylindrical body, necessary due to external pressure and the corresponding increase in temperature difference between the outside and inside of the drum (which depends on the pressure dependence of the liquid's boiling point), is achieved by equipping the drums with stiffening rings on their outer face. Some of these rings are connected to mechanical bearings. This reduces the number of bearing supports while maintaining the drum's stability against crushing under external pressure, thereby lowering construction costs and decreasing the probability of failure of the drum film evaporator due to mechanical damage or bearing failures.

[0015] The optimization of the load distribution due to external pressure is achieved by a uniform distribution of stiffening rings along the entire length of the drum. The stiffening rings are arranged on the body along the entire length of the drum, which makes it possible to reduce the wall thickness of the shell, thus decreasing the resistance thermal conductivity during heat transfer. The maximum distance between adjacent stiffness rings is determined by the following relationship: [Math 1] T _H Q 1 77^ d™ f — \ 2 “>WHERE - U. J m (P^P^ ( dm ) AND - modulus of elasticity of the drum material at the design temperature, MP a; dm - average diameter of the drum, mm; P ext - external pressure on the drum, MPa; Pint - internal pressure in the drum, MPa; 5 - drum wall thickness, mm; c - total increase in wall thickness, mm.

[0016] The distance between the bearing supports is determined by the permissible deflection of the thin-walled drum under its own weight and the available power margin in terms of drum torque.

[0017] The formula presented for determining the optimal distance between the stiffening rings conforms to the standards for calculating the stability of cylindrical bodies under external pressure IIHA3 T-7-002-86 (Standards for calculating the resistance of equipment and piping in nuclear installations PNAE G-7-002-86).

[0018] The proposed set of constructive solutions makes it possible to achieve the stated objectives and ensures: a. the removal of restrictions on the length and diameter of drum evaporators, which increases evaporator productivity; b. reducing the required number of bearing supports, which reduces construction costs and increases resilience to failures; c. the reduction in the thickness of the drum wall, which considerably reduces the thermal resistance of the heat transfer wall and increases the efficiency of evaporation; d. an optimized solution to the problem of drum bending under its own weight, which reduces not only cyclic loads, but also the torque required to rotate the drum. Brief description of the figures

[0019] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which: a. [Fig. 1] shows the arrangement of the stiffening rings on the outer surface of the drum (1), including those acting as the stiffening rings (2). b. [Fig.2] presents a longitudinal section of the DFE, its cross-section in the bearing area, carried out in accordance with the invention and the isometric drawing of the bearing support. Detailed description of the figures

[0020] The following description refers to the accompanying drawings, which present, by way of non-limiting example, show a variant embodiment of the invention.

[0021] [Fig.1] shows the arrangement of the stiffening rings on the outer surface of the drum (1), including those acting as the stiffening rings (2).

[0022] The drum film evaporator (DFE) shown in [Fig. 2] is a hermetically sealed horizontal cylindrical body (3) with flanged ends and an evaporator drum (1) located inside on bearing supports (4), rotated by a geared motor (5). [Fig. 2] shows a longitudinal section of the DFE and its cross-section in the bearing area, made according to the invention. The design of the DFE ensures a hermetic connection between the steam outlet pipe rotating around the axis of the drum (6) and the fixed pipe (7), intended for the discharge of secondary steam from the DFE. The pipe (6) is equipped with a removable flanged cover (8). Through this cover, a tube (9) for supplying the solution to be evaporated, equipped with a float valve (10), and a concentrate sampling tube (11) pass into the cavity of the drum (1).

[0023] The drum is partially filled with the solution to be evaporated (12), the level of which is constantly maintained by a float valve (10). To ensure the mechanical cleaning of the heating surface of salt deposits, a rod with a spiral (13) rolls during the rotation of the drum. Due to the screw effect of the spiral, and the impossibility of moving in the axial direction, it moves the salt deposits towards the discharge zone, where the evaporated product is collected by the tube (11). The condensate of the heating steam flows towards the lower part of the body and is discharged through the tube (14) equipped with a thermodynamic condensate drain.

[0024] The design of the bearing supports (4), associated with the flanges, some of which are stiffening rings (2), ensures a uniform distribution of the drum's weight load over its entire length, which practically eliminates the drum's bending under its own weight.

[0025] The ceramic bearing-based rollers (15) are fixed between two perforated structures (16) and (17) located in the body (3). The outer diameter of these structures allows the roller supports (4) to be placed inside the body (3), while their inner diameter allows the drum (1) with the flanges (2) to be placed on the roller supports (4). The structural elements (16) and (17) that hold the rollers (15) are spaced apart and fixed to each other by means of fasteners (18).

[0026] To protect the body (3) of the DFE against bending, it can be installed on a rigid support (19), made in the form of a frame of metal profiles.

[0027] The evaporation of the solution in the DFE proceeds as follows. The heating steam entering through the inlet pipe (20) enters the space between the hermetic body (3) and the evaporator drum (1). Condensation of the heating steam occurs on the outer surface of the drum (1), and the condensate flows to the lower part of the body (3), from where it is discharged through the tube (14) equipped with a thermodynamic condensate drain. During the heat transfer from the heating steam to the outer surface of the drum (1), secondary steam forms in its cavity by film evaporation, and this is discharged from the hermetic body through the pipe (21).

[0028] During start-up, it is necessary to remove non-condensable gases from the heating steam chamber. To do this, after the system has started, the steam-gas mixture purge valve (22) is kept open for a certain time. After the non-condensable gases have been removed, it is closed.

[0029] As an example of a specific embodiment of the DFE for the concentration of liquid solutions, we consider the case of bearing supports in the form of roller bearings for a drum of diameter d. The supports are uniformly distributed over the entire length of the drum in the body of the DFE of diameter D at a distance L ([Fig.2]).

[0030] As a specific example of the "drum film evaporator" evaporation plant, a 21-meter-long 12X18H10T stainless steel drum with an outer diameter of 520 mm and a wall thickness of 2.5 mm is considered. The total wall thickness increase is 0.4 mm. The inner diameter of the drum body is 650 mm. The stiffening rings in the form of flanges on the drum are 10 mm wide, and the outer diameter of the flanges is 550 mm. The width of the perforated structures for the roller supports is 8 mm. The bearings used are 6300-ZrO2-VKE ceramic bearings with an outer diameter of 35 mm and a width of 11 mm.

[0031] To determine the optimal distance between the stiffening rings, we consider a heating steam pressure of 150 kPa at a temperature of 111.4°C, and a secondary steam pressure of 90 kPa at a temperature of 96.7°C. The calculation is carried out in accordance with the stability standards for cylindrical bodies under external pressure, specified in External Standard IIHA3 F-7-002-86 (Standards for the design of the strength of equipment and piping in nuclear installations (PNAE G-7-002-86)).

[0032] For 12X18H9T grade steel, the modulus of elasticity at the design temperature of 107.1°C is 195 GPa. Using this value, the maximum distance between adjacent stiffening rings was calculated in accordance with applicable standards: [Math 2] 517 5 / ' 5-0 4 \ Lmax = 0.91 • 195000 ■ (iïTj ) = 1605 mm

[0033] For a minimum yield strength RTp0,2 of 196 MPa for the chosen steel, the critical pressure [Pa] is 0.07 MPa, which is less than the maximum pressure differential on the drum shell of 0.06 MPa. Thus, the distance between the stiffening rings of the evaporator drum L1 is 1500 mm, and their total number is 15. To prevent drum deflection, a reduced number of roller supports is required; therefore, every other stiffening ring is used as a support flange, resulting in 7 rings with a distance L2 between the roller supports of 3000 mm.

Claims

Demands

1. A drum film evaporator, comprising a cylindrical body with ends, piping for supplying heated steam to the body and for discharging secondary steam from the body, piping for discharging condensate from the lower part of the body, an evaporation drum partially filled with the solution to be evaporated and mounted on rotating supports, a drum rotation drive, piping for supplying the solution to be evaporated into the drum cavity, piping for discharging the concentrate from the lowest point, located below the liquid level in the drum, a device for mechanically cleaning the evaporative surface of the drum of salt deposits, support flanges uniformly distributed along the entire length of the drum body, coupled with bearing supports, characterized in that the outer face of the drum is equipped with stiffening rings along the entire length of the drum,a part of which is made in the form of support edges coupled with bearing supports, the maximum distance between the stiffening rings being determined by the following ratio: [Math 3] Lmin = 0.91EV~KT~ ( ¥ ) 2 5°ù ET - modulus of elasticity of the drum material at the design temperature, MPa, dm - mean diameter of the drum, mm; P ext - external pressure on the drum, MPa; Pint - internal pressure in the drum, MPa; 5 - thickness of the drum wall, mm; c - total increase in wall thickness, mm.,

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