RU2362606C2 - Method for surface distillation of fluids - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to physical-chemical technology and is intended to simplify evaporation plant and distiller design, improvement of their efficiency and also elimination of splashes, foam and scale. Method is suitable for rationalisation of available methods for distillation of liquid solutions and desalination of sea water. Method for surface distillation of liquids includes heating of liquid layer, its evaporation from the evaporation surface, steam drain from steam space and steam condensation on condensation surface. Steam flow from steam space is sent to condensation surface in the form of capillary brush, at that every capillary passes through mirror of liquid evaporation. Channels of capillaries on top are opened into steam space, and are submerged with their lower ends into condensate. Heat of phase transition from condensate flowing in channels is returned to mirror of evaporated liquid right through the capillary walls. Technical result from application of suggested method consists in the fact that due to direct contact of heater with steam space and mirror of evaporation, the maximum possible heat discharge is provided in the system, at that foam and scale are not produced. Recuperation of heat of distilled vapors in capillaries is simple and efficient. Due to usage of molecular effects at the interface of phases and mediums, design of evaporator for method implementation is simplified.

EFFECT: simplified design of evaporator for method realisation.

6 dwg, 3 tbl

Description

The invention relates to physicochemical technology and is intended to simplify the design of evaporators and distillers, improve their efficiency, and also to eliminate the spray, foam and scale generated during operation. The method is suitable for rationalizing methods of distillation of liquid solutions and desalination of sea water.

Various methods are known for industrial separation of liquid solutions into separate fractions. The most common of them are evaporation of the solvent (if the useful product is a concentrated precipitate) or its distillation (if the useful product is a liquid). The procedure is typical. The initial solution is heated or brought to bubble boiling, and then through the vapor space, volatile components are distilled from it, removed or cooled to a liquid state in the condenser.

More complex options are known. To reduce the boiling point of the solution, non-condensable gases are pumped out of the vapor space. To increase the efficiency of the process, the heat condensation of the distilled vapors is returned to the technological cycle, heating the initial solution. To increase productivity, due to the development of the evaporation surface, the hot solution is sprayed or stretched into a film. To increase the heat transfer rate, the hot solution is forcedly mixed, sharp steam is blown into it or other coolants are pumped.

A variety of combinations of technological methods implemented in evaporators and industrial distillation plants are counted in dozens of options. The specific choice in each case is determined by the range of tasks facing the designers.

Source of information: E.I. Taubman. Evaporation (Processes and apparatuses of chemical and petrochemical technology). - M.: Chemistry, 1982. - 328 p., Ill. (p. 143-250).

There are known difficulties associated with the operation of evaporators and high-capacity distillers. Energy-efficient devices are characterized by small differences in temperature and pressure, as well as scanty operating costs. Sometimes they even manage to be reduced to zero, using natural resources as energy sources (sunlight, tectonic heat, etc.). A typical example is the well-known solar desalination plant. The irreparable drawback of such structures is their enormous size (hectares of area). The colossal capital cost of their construction does not pay off for decades.

Source of information: I.E. Apeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 89-98).

Evaporating plants and distillers combining compactness with high productivity are invariably characterized by high energy consumption per unit of the finished product. A typical example is emergency rescue desalination plants. Obviously insufficient surface of the heat exchangers (severe savings on weight and overall dimensions are required) leads to unproductive heat losses.

Attempts to achieve the optimal combination of "economy-material-productivity-productivity" of evaporators and distillers, as a rule, lead to highly complicated design solutions. Typical examples of this kind are conventional distillation columns and multi-stage vapor compression distillation plants. This approach is justified by the unity of the created structures. Any enterprise in the chemical industry is unique in its own way.

Another technological extreme is the use of exotic physical principles for the separation of solutions (for example, biological desalination of water, heating liquids to supercritical temperatures, etc.). Scientific research and experiments in these areas last for decades. The economic effect of them is unknown.

In the general case, when designing equipment and technological processes associated with fractional separation of solutions by evaporation, many factors have to be taken into account and combined. The increase in thermal pressure and differential pressure allows you to increase the productivity of the procedure. The reduction in weight and size reduces capital costs. An increase in the heat transfer surface, with a decrease in temperature and pressure differences, provides energy efficiency.

Source of information: E.I. Taubman. Evaporation (Processes and apparatuses of chemical and petrochemical technology). - M.: Chemistry, 1982. - 328 p., Ill. (p. 34-79).

An important problem that greatly complicates the operation of distillation plants is the behavior of the solution. Even relatively weak flows of heat, liquid, and vapor in a mobile medium are accompanied by undesirable side effects, in particular, the formation of strong scale layers on the surface of the heating elements, the formation of foam on the evaporation mirror, and the entrainment of droplets from bursting bubbles with a vapor stream.

There is the concept of threshold evaporator performance. If it is exceeded, bubble boiling becomes so violent that the evaporation mirror disappears. The solution turns into foam, fills the vapor space and can burst into the condenser. The realizable thermal head between the heated bottom and actively evaporating surface layers of the liquid is very small. For example, the vertical temperature drop on a 250 mm thick water layer boiling at atmospheric pressure in an open vessel heated from below does not exceed 0.7 ° C.

Source of information: V.A. Pazukhin, A.Ya. Fisher. Separation and refining of metals in vacuum. - M.: Metallurgy, 1969. - 204 p., Ill. (p. 42-44).

But the typical temperature differences between the liquid solution and the surface of the heater are disproportionately large, usually 10-25 ° C or more. There are two reasons for this. Firstly, a scale of 0.1 mm thick already reduces the heat transfer coefficient through the wall of the brass tube of a typical desalination heat exchanger by 25-30%. In practice, the thickness of the scale layer can reach several millimeters.

Source of information: I.E. Apeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 60-82).

Secondly, the area of direct contact between the solid surface of the heater and boiling liquid gradually decreases with increasing temperature until complete separation by a continuous vapor film. The experimental dependence of the heater-water heat transfer rate on the boundary temperature difference is shown in FIG. The graph has a relatively steep rise, a sharp peak and a sharp decline, reflecting the moment of transition of bubble boiling into film boiling. In the latter case, the direct liquid-surface contact practically disappears, since at the interface between the media a continuous layer of superheated steam is formed.

It is significant how useful thermal pressure in the layer of evaporated liquid is less than useless, at the interface. It is also seen that even a slight increase in temperature difference at the surface of the heater above the limit of 50-53 ° C leads to a catastrophic deterioration in heat transfer. The heat transfer process from convection becomes radiative (at the indicated temperatures it is extremely inefficient). It is completely pointless to heat the walls (heating tubes) of a conventional evaporator with water boiling at atmospheric pressure above + 150 ° С. Energy is wasted in maintaining high pressure in the vapor film.

Source of information: I.V. Radchenko. Molecular physics. - M .: Nauka, 1965 .-- 480 p., Ill. (p. 449).

In light of the foregoing, it is not surprising that the actual energy costs for the distillation of real solutions (for example, desalination of sea water) are ten times higher than the theoretically necessary work of separation of water and salt molecules (heat of solvation). For typical industrial desalination plants and evaporation plants, the useful component in the total energy costs (thermal efficiency) usually does not exceed 3-5%, in rare cases reaching 6-7%.

Source of information: E.I. Taubman. Evaporation (Processes and apparatuses of chemical and petrochemical technology). - M.: Chemistry, 1982. - 328 p., Ill. (p. 34-36).

Even the very usual fact that a layer of a solution separates heating and evaporation surfaces is a source of operational difficulties. The list of substances actually contained in the distilled liquid is always quite extensive. A solution is considered diluted if its concentration is significantly lower than the level at which crystallization begins and precipitation of at least one mineral component of the mixture into a solid insoluble precipitate.

The solubility values of some natural salts in water are shown in table 1.

No. p / p NAME OF SUBSTANCE Solubility in% by weight of saturated solution 0 ° C + 10 ° С + 20 ° С + 30 ° C + 40 ° C + 50 ° C one Sodium Chloride (NaCl) 26.3 26.3 26,4 26.5 26.7 26.8 2 Sodium Sulfate (Na ₂ SO ₄ ) 4.8 8.3 16.3 29.0 32.8 31.8 3 Potassium Chloride (KCl) 21.9 23.8 25.5 27.1 28.6 30,0 four Potassium bromide (KBr) 34.9 37.3 39.5 41,4 43.0 44.5 5 Potassium Sulfate (K ₂ SO ₄ ) 6.9 8.5 10.0 11.5 12.9 14.2 6 Magnesium Chloride (MgCl ₂ ) 34.6 34.9 35.3 35.8 36.5 37,2 7 Calcium Chloride (CaCl ₂ ) 37.3 39,4 42.7 50.1 53,4 57.8

Source of information: Brief reference book on chemistry; under the editorship of O.D. Kurylenko. - Kiev: Naukova Dumka, 1974. - 985 p., Ill. (p. 799).

Theoretically, natural waters with a salinity of 0.35-0.02% are advantageously evaporated at a temperature of maximum equivalent solubility of the salt mixture. For most aqueous solutions, this point is below + 36-40 ° C. Naturally, in ordinary desalination plants this is not possible. It is necessary to regularly stop the distillation for mechanical cleaning of metal surfaces coated with insoluble mineral peel.

The temperature at the “heater-solution” boundary of traditional distillers always significantly exceeds the temperature of the evaporation mirror. As a result, salts with a negative temperature coefficient of solubility precipitate there (calcium sulfate CaSO ₄ , hemihydrate calcium sulfate 2CaSO ₄ · H ₂ O, calcium carbonate CaCO ₃ , etc.). The fracture of the solubility curve of these substances lies in the vicinity of + 32-40 ° C. Obviously, if distillation of sea water is carried out at a temperature significantly lower than + 50-60 ° C, then the specified precipitate will not appear at all. The solubility curve of calcium sulfate, for example, is shown in figure 2.

Source of information: I.E. Opeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 66).

The main disadvantages of traditional methods of evaporation and distillation, based on the evaporation of the volatile components of liquid solutions, are the irrational organization of the transfer of energy (heat) from the heater to the evaporation mirror and the mass flow motion system.

The useful thermal pressure between the heating and evaporation surfaces is extremely small; the natural convection of the liquid is difficult. As a result, most of the supplied energy is wasted - to overcome harmful thermal resistance. The process is accompanied by the formation of foam and scale; the steam being distilled off contains spray of boiling solution.

Attempts to overcome these shortcomings by reducing the power of heat fluxes lead to unjustified inflating of the geometric dimensions of the equipment, and the artificial forcing of heat and mass transfer processes (pumping out non-condensable gases, mixers, sprayers, etc.) to excessively complicate its design. It is thanks to the options for circumventing one or another specific technological limitation that the types of evaporation chemical plants are so diverse.

A known method of eliminating heat loss due to the physical combination of the surface of the heater and the evaporation mirror. It is more correct to say, due to the direct heating of the liquid from the side of the vapor space by short-wave electromagnetic radiation, for example, sunlight. The beneficial effect is achieved cleanly and extremely cheaply. The distillation process is perfect. Almost all the heat absorbed by the liquid is immediately and directly spent on receiving steam. The formation of foam, scale or brine spray is physically impossible.

The simplicity of the method and its technical efficiency is confirmed by many years of experience in the successful operation of solar desalination plants, solar dryers, etc. equipment. For example, in Los Salinos (Chile), a solar desalination plant of the simplest design, with a total area of 4760 m ² , successfully worked for 36 years (from 1872 to 1908, before the construction of the water supply system). Its average distillate capacity was 4.6 l / day from each square meter of evaporation trays.

An irreparable disadvantage of distillation plants with heating of the evaporation mirror by radiation is the low specific productivity. It is limited by the energy of sunlight (not more than 0.8-1.2 kW / m ² ) and thermal pressure "evaporator-condenser" (usually 10-25 ° C). The maximum temperature of the liquid in the trays rarely exceeds + 50-65 ° С at an air temperature of + 25-35 ° С. Contact heating of the brine through the same surface area manages to transfer 70-120 times more energy.

Attempts have been made to increase the temperature of the evaporation mirror due to the concentration of sunlight on the surface of the solution with a system of mirrors. High pressure steam was obtained. There was no great benefit from this. It turned out that the sizes of the necessary reflectors are approximately equal to the area of simple glazed trays, and such a system is more expensive and more difficult to operate. Surface distillation of water by heating with microwave radiation, etc. currently economically unprofitable.

Source of information: I.E. Opeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 87-98).

A known method of increasing the productivity of low-temperature dryers and distillators due to the mechanical development of the evaporation surface. Quality (energy and steam pressure) are compensated by quantity (area). Contacted liquid heated to a temperature of no more than + 40-50 ° С is stretched by centrifugal forces, wrinkled by vibration, sprayed through nozzles, and transferred in the form of a thin film on a wettable disk near the condenser. The output of the final product for the passage is usually small and one portion of the brine is chased in a circle many times.

Reception allows one to two orders of magnitude, compared with ordinary conditions at equal temperatures, to accelerate the process of evaporation of the liquid. Foam and scale are practically not formed, since the concentration of the evaporated solution changes little during each cycle, and its temperature, on the contrary, drops rapidly. The evaporation zone is usually at a noticeable distance from the heat exchange zone (solid surface of the heater).

Fatal disadvantages of the method are its low specific productivity and implementation complexity. Pumps, sprays, fans and other mechanical devices turn a simple physical process into a sophisticated and expensive technical procedure. The method justifies itself in some specific situations (food production, medicines, etc.), when it is important not to allow strong heating of the evaporated liquid or it is necessary to use at least somehow useful large amount of waste heat.

Source of information: K.P. Shumsky. Vacuum and chemical engineering devices. - M.: Mechanical Engineering, 1974. - 576 p., Ill. (p. 121-211).

A known method of rational organization of contact heat transfer in distillation plants by heating the solution with liquid or gaseous heat carrier. The absence of a solid heat exchange surface excludes the appearance of a continuous layer of scale regardless of the temperature of the heating agent. Relatively uniform (volumetric) heating of the solution eliminates the formation of vapor bubbles on the evaporation mirror, and therefore, the formation of foam and spray in the vapor space. It turns out extremely high (especially in the case of blowing with hot steam) flow of thermal energy "heating agent-liquid". The contact temperature difference between them can harmlessly reach 200-300 ° C. An extreme variant of the method is heating the solution with submerged burners.

Fatal disadvantages of the described method are the high cost of the procedure and the mandatory pollution of the final products with extraneous chemicals. For example, all attempts to use hydrophobic coolants (paraffin and mineral oils) in desalination plants failed. The resulting water could not be drunk.

Source of information: E.I. Taubman. Evaporation (Processes and apparatuses of chemical and petrochemical technology). - M.: Chemistry, 1982. - 328 p., Ill. (p. 230-241).

To solve the problem of optimizing the operation of evaporator and distillation plants, it is necessary and sufficient to find a way to directly combine the solid surface of the heater with the evaporation mirror, which will provide the maximum possible thermal pressure in the absence of foam and scale. The method must operate reliably in a wide range of operating conditions, without agitators, sprays and other mechanical devices. A simple recovery of the heat of condensation of the distilled vapors into additional heating of the initial solution is highly desirable.

The prototype adopted the method of distillation of sea water by thermal diffusion evaporation from the surface of the rotating discs.

Around the horizontal axis, at a speed of 50-60 rpm, rotate disks made of highly heat-conducting stainless materials (copper, brass, etc.). The lower part of the disc is immersed in heated evaporated water filling the pan. The upper part of the discs is placed in the gaps between the flat, internally cooled condensers.

The distance between the surfaces of evaporation and condensation is minimized (from centimeters to several millimeters). The formation of foam and scale discs is completely excluded. Atmospheric air is not removed from the installation. The vapor from the water film covering the discs settles on adjacent cold surfaces, giving off the heat of condensation to the salt water circulating in the evaporator. The resulting distillate flows into the gutters and is discharged from the installation. The loss of fluid is compensated by the influx of fresh salt water. To increase the useful thermal pressure between the installation elements, the salt solution entering the sump is additionally heated, and the pumped through the condensers is cooled. The layout diagram of such an evaporator (scanned image No. 5.13 from page 29 of the information source) is shown in FIG. 3.

Source of information: I.E. Opeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 29-30).

The method is valuable for the disposal of waste steam from a low temperature source (cooling tower). The design has many promising ideas: sublimating the solvent from a thin layer of liquid on a heat-conducting surface, continuously updating this layer, removing the evaporated film from the heater, bringing the condenser and the evaporation mirror closer to the smallest possible distance, eliminating the causes of foam and scale formation. These measures significantly reduce useless heat loss. Compared with solar desalination, the product is more compact.

The obvious disadvantages of the described technical solutions are the excessive complexity of the procedure. The distillation principle eliminates the appearance of foam, but the vapor space still contains splashes of brine, agitated by spinning disks. The evaporation mirror is pulled towards the condenser, although the surface tension of the cold liquid is higher than that of the heated one. The brine film could move on its own. And so on.

A known method of desalination of sea water by osmosis through a steam gap, supported by capillarity, known as the "Hassler steam osmosis method." According to the Hassler method, the osmotic cell is composed of two cellophane membranes mounted on porous plates. The gap performing the function of the diffusion gap between the membranes is filled with a loose hydrophobic material, for example, ground pumice. Through one plate, seawater is supplied to the cell under pressure. Through another plate, the cell is connected to a fresh water reservoir. Compressed air is supplied to the pumice gap. There are no moving parts.

In a working cell, the sea water pressure is higher than the osmosis pressure and air pressure in the gap, and the fresh water pressure is less than the air pressure in the diffusion gap. With a pressure differential between vessels with salt and fresh water of about 50 kg / cm, the daily system capacity for distillate is approximately 20 l / m ² area. The salinity of desalinated sea water is 30-35 g / l, the cell temperature is 20-25 ° C.

Source of information: I.E. Apeltsin; V.A. Klyachko. Desalination of water. - M.: Stroyizdat, 1968 .-- 222 p., Ill. (p. 193).

The Hassler method is based on a witty combination of several molecular physical effects:

Salt water cannot penetrate the gap through the porous slab. Compressed air cannot escape from the gap through liquid-filled capillaries in porous plates, reliably clogged by surface tension. The salt dissolved in sea water is firmly bound to the liquid phase. Water molecules evaporate almost freely and drift through the porous layer between the plates towards lower pressure. The air gap acts as a semi-permeable membrane that transmits water vapor well and does not permeate salt at all.

A directed mass flow appears in the cell, transferring water molecules from the brine to the distillate, and a counter heat flow, which transfers the condensation energy from the distillate to the brine. The installation diagram for demineralization of water, according to the Hassler method is shown in figure 4.

Source of information: M. Tribus. Thermostatics and thermodynamics. Per. from English. - M .: Energy, 1970. - 504 p., Ill. (p. 417-419).

A known method of producing fresh water by capillary condensation. In ancient times, sailors secured pieces of porous elastic materials (dried sponge) on a ship's rigging. The vapor pressure over the concave menisci of the distillate was lower than over a flat sea surface. Moisture condensed in narrow capillary channels. The heat of condensation was carried away by the wind. The fluid accumulating in the pores was almost fresh. Periodically, a wet sponge was squeezed out and hung again in the open air. The resulting water could be drunk.

Source of information: I.V. Radchenko. Molecular physics. - M .: Nauka, 1965 .-- 480 p., Ill. (pg. 403-405).

The effect of condensation of atmospheric moisture in the small pores of an initially dry body is known. So books and hygroscopic powders are moistened, adsorbents lose their activity. With rapid capillary condensation, strong heating of hygroscopic materials is observed. The saturated vapor pressure in microcavities is significantly lower than the equilibrium value even at temperatures above 150-200 ° C. There is no boiling water. The released heat warms the walls of the capillaries. If the air humidity is high, but there is a lot of porous material, then its spoilage and even spontaneous combustion are possible. For this reason, the rules for the safe storage of pressed cotton, ground peat and coal dust are strictly regulated.

Source of information: A.V. Lykov. Theory of drying. - M .: Energy, 1968. - 472 p., Ill. (p. 10-24).

The effect of vigorous absorption of water vapor from atmospheric air by finely porous hydrophobic materials is known. The value of the contact angle of condensate walls of the capillaries to the condensate does not affect the course of the process. The temperature develops up to + 200 ° С and more.

Source of information: E.N. Serapionova. Industrial adsorption of gases and vapors. - M.: Higher School, 1969. - 416 p., Ill. (p. 31-42).

Signs of the prototype, coinciding with the essential features of the claimed invention:

The solvent is evaporated from a continuously updated film layer of a liquid adjacent to a solid heat-conducting surface. The evaporated solution is continuously moved from the heater to the evaporation mirror, which is extremely close combined with the surface of the cooled condenser. The process is conducted at a temperature below the boiling level of the solution, which eliminates the causes of the formation of foam and scale on the disks.

The above methods provide a high thermal head and small intermediate energy losses in the layer of evaporated liquid. The presence of atmospheric air, the relatively low distillation temperature and the low pressure of the condensing liquid vapor practically do not affect the efficiency of the evaporation procedure.

The reasons that impede the receipt of the required technical result for the prototype:

The surface of the disks from which the solution film evaporates is not a heater, but only a heat accumulator, and it’s bad. The heat capacity of copper is ten times less than that of water. The real distance of the heat transfer is determined by the length of the pipeline supplying hot brine to the pan. An equally long path, together with a cooling brine, is overcome by the heat of condensation of the distillate. The total thermal pressure in the system is extremely small. Without a circulation pump, it is not operational.

The design spoils the excess of moving parts. Even with a disk radius of 0.5 meters and a rotation speed of 60 rpm, their edges cut water at a speed of more than 3 m / s, raising fountains of spray. Drops of agitated brine fall into the vapor space and distillate. Although the principle of thermal diffusion distillation, as such, eliminates the appearance of foam.

The flow of water molecules through the vapor space is organized irrationally. The rapid movement of the evaporation mirror relative to the condenser excites vortices that interfere with the flow of the distillate. Most of the mechanical power of the engine is spent on overcoming hydraulic and aerodynamic drags (in fact, heating the air and brine).

A variety of molecular phenomena that can facilitate the operation of the distillation plant are completely ignored. For example, the evaporation mirror is forcibly pulled toward the condenser, although the brine film could well have moved there independently. The surface tension of an intensely cooled liquid is noticeably higher than that of a heated one. Air vortices from spinning disks prevent the evaporator from being brought closer to the condenser at an optimum distance of about 1 mm for gas diffusion.

The principle of recovery of condensation heat is the same as in traditional desalination plants. The brine is heated through a conventional steam line, on the surface of which scale can settle. This eliminates the effect of promising technical solutions contained in the prototype. The performance of the described distillation method is obviously low.

The technical result of the application of the proposed method.

Optimization of the operation of evaporator and distillation plants due to the direct combination of the heated surface with the solution evaporation mirror, which ensures the maximum possible thermal pressure in the system, in the absence of foam and scale. Expanding the range of operating modes of the specified equipment, without the use of mixers, spray guns and other mechanical devices with moving parts. Simple and effective recovery of the heat of condensation of distilled vapors into direct heating of the surface of the initial liquid. Simplification of the design and reduction in the size of contact heat exchangers through the use of molecular effects at the interface between phases and media.

The technical result is achieved as follows:

The evaporation mirror of the distilled liquid is heated.

The resulting steam is sent from the vapor space to the condensation surface and there is precipitated in the form of a liquid phase.

The steam flow is directed to the condensation surface, designed as internal channels of the capillary brush.

Each capillary passes through the free surface of the evaporation mirror of the distilled liquid.

The capillary channels from above are open in the vapor space, and the lower ends are immersed in liquid condensate.

The heat of the phase transition from the condensate draining through the channels is returned to the mirror of the evaporated liquid directly through the walls of the capillaries.

The essential features of the claimed invention:

According to the prototype:

1. The distillation process is concentrated at the free surface of the liquid.

2. The liquid vapor is removed from its heated surface.

3. The heated surface of the liquid is combined with the evaporation mirror.

4. The resulting vapor is deposited in liquid form on the surface of the condensation.

Unlike the prototype:

5. The steam stream is directed to the condensation surface in the form of a brush of capillaries passing through the evaporation mirror of the distilled liquid.

6. Steam is condensed in the internal channels of the capillaries, open at the top into the vapor space, and immersed in the condensate with the lower ends.

7. The heat of the phase transition of the condensing vapor, due to the temperature difference on the inner and outer walls of the capillaries, is immediately returned to the evaporated liquid.

8. The heat of the phase transition of the condensate draining to the internal channels is returned to the liquid evaporation mirror via the shortest path, directly through the walls of the capillaries.

The influence of the essential features of the claimed invention on the resulting technical effect:

1. The performance of distillation (evaporation, evaporation) is determined by the flow of thermal energy in the heater chain, evaporation mirror, vapor space, condensation surface. In the case of recovery, a return condenser-evaporation mirror heat flow should be added to the listed units. In the “evaporator-condenser” section, the heat flux takes the form of a vapor flux transferring the latent heat of the phase transition. The relationship between the overall dimensions of the installation and the output of the final product determines the density of the heat flux through the media (W / m ² ) and the second flow of molecules through the cross section of the steam line (kg / m ² ).

Obviously, reducing the thickness of the intermediate barriers, increasing temperature drops and increasing the area of heat exchangers favorably affect the course of the procedure. Possible options. Low thermal pressure is often compensated by a developed surface of evaporation (condensation). Less common are attempts to achieve the same, reducing the thickness of thermal transitions. These include the selected prototype of the invention.

The prospects of the last intake can be judged by the well-known fact: from each square meter of the free surface of the water at + 20 ° С, about 0.2 kg of steam evaporates every second and condenses back. With a negligible temperature difference (fraction of a degree) and an insignificant thickness of the liquid-vapor boundary layer (microns), the energy flux to each side is huge - 0.45 MW / m ² . The combination of evaporation and condensation surfaces, with automatic heat recovery, makes the natural liquid-vapor boundary a demonstration model of an ideal desalination plant.

Source of information: I.V. Radchenko. Molecular physics. - M .: Nauka, 1965 .-- 480 p., Ill. (p. 401).

For comparison, in known technical devices, with bubble boiling of water under atmospheric pressure, the maximum possible heat flux through the surface of the cooler (evaporator) is 0.9 MW / m ² . Actually, this value does not exceed 0.2-0.3 MW / m ² . The temperature difference required to achieve it is measured in tens of degrees.

Source of information: G.N.Dulnev. Heat and mass transfer in electronic equipment. - M .: Higher school, 1984. - 247 p., Ill. (p. 85-91).

Thus, by concentrating the distillation process near the surface of the liquid solution (no further than 1-2 mm), it is easy to obtain a high heat flux density even at room temperature. The closer the neighboring areas of evaporation and condensation, the higher the actual heat pressure between them and the more economical the whole process.

In the technical literature, it is rightly pointed out that the overall performance of distillers at low temperature is small due to the low pressure of saturated vapor above the evaporation mirror. The condensate yield is negligible. Typical values for the adiabatic distillation of sea water at + 20 ° C are 3.5-25.0 liters per day (0.04-0.29 grams per second) per square meter of surface.

The steam properties in the far zone correspond to known tabular data. At a brine temperature of + 110 ° C (common in industrial distillers), its flow reaches 500-3500 kg / m ² per hour (0.14-1.0 kg / m ² per second), and the pressure is 100 kPa. At room temperature, the pressure of water vapor above the brine of the same concentration is 50 times less - about 2-3 kPa. However, the real gain from this difference is small. When boiling violently, water sprays a brine. It is necessary to increase the height of the vapor space to 0.7-1.0 m, limit the steam flow rate to 7-9 m / s, set up grids for catching drops, and build giant steam pipelines. This tens and hundreds of times reduces the actual thermal head.

Low temperature has its advantages. In the absence of brine boiling, the evaporator and condenser can be moved side by side. Bubbles and sprays that can reach the distillate with a stream of steam, in this case, no. And the pressure of saturated steam above the free surface of the liquid (contrary to popular references) depends not only on temperature, but also on the distance to it. The dependence is sharply nonlinear. The experimental graph for fresh water at a temperature of + 10 ° C is shown in Fig.5.

Source of information: A.V. Lykov. Theory of drying. - M .: Energy, 1968. - 472 p., Ill. (p. 171).

These measurements (requiring the manufacture of special microscopic sensors and sophisticated experimental methods) were carried out in the USSR more than 50 years ago. In the available literature, information about them is almost absent.

Source of information: NF Dokuchaev, abstract of the dissertation “Application of thermohygrometric methods to the study of the evaporation process”, M .; 1951 year.

It is known that over an open surface of a liquid in free space there always exists a noticeable layer of dense vapor. The pressure there varies, from a low partial level (at a distance of the order of a meter) to atmospheric and higher. With very dusty air, this border is visible in lateral lighting as a dust-free zone (0.5-1 mm thick) between the liquid and the atmosphere, the so-called “black layer”.

Source of information: A.I. Pirumov. Dust removal of air. - M.: Stroyizdat, 1981. - 296 p., Ill. (p. 53).

With a close combination of the evaporation and condensation surfaces (no further than 1.0-2.0 mm), it is possible at + 10-40 ° C, without mechanical devices, to have the intensity of the evaporation mirror as in the far zone of conventional industrial distillers. This effect removes the overall limitations on the creation of distillation plants without bubble boiling of the solution.

2. Long-term contact of a limited volume of the distilled solution with the solid surface of the heater is inevitably accompanied by either a solid precipitate (scale) or overheating of the liquid to a vapor state and a decrease in the area of direct heat transfer. These disadvantages are easily eliminated if the solution is continuously mixed. Then its temperature and concentration differ little from the state of the bulk phase. Although it is a thin boundary layer that is difficult to set in motion.

3. It is known that the thermal conductivity of solutions, compared with metal, is negligible. Convection, due to the difference in densities of hot and cold liquids, is also small. Steam boiling allows you to accelerate convective heat transfer at the border, but it provokes the loss of scale. The ideal solution is to artificially create a thin layer of solution along the surface of the heater, in the direction of the intensive evaporation zone. In the prototype, this is produced by rotating disks. The result is no foam and scale, the hot boundary layer is effectively updated, its evaporation is extremely facilitated due to molecular effects.

In aqueous solutions of inorganic electrolytes, the surface layer is always enriched with solvent molecules. Salt ions are hydrated and squeezed in depth, and pure water, as a kind of surface-active substance, is concentrated at the interface. In the absence of steam boiling and film flow of the liquid, this significantly accelerates the distillation of sea water. Chemical separation of the solution, due to molecular forces, occurs already at the stage of its heating.

Source of information: ED Shchukin et al. Colloid chemistry, textbook for high schools. - M .: Higher school, 2004 .-- 445 p., Ill. (p. 80-83).

4. The best option for arranging the solid surface of the steam space heater and the mirror of the evaporated liquid is their direct physical contact in one plane. Regularly located heating elements that pierce the liquid-vapor interface eliminate the useless loss of heat pressure. The hot solution film itself, without interference, flows onto the evaporation mirror. Closed steam bubbles near the heater do not occur even at the highest temperature. The result - the liquid does not boil, although it evaporates extremely quickly.

A similar effect from the crushing of an evaporation mirror is known in metallurgy. Ultrafast cooling of steel (up to 600-1200 ° С / s) is obtained by its drop spraying with aqueous solutions of salts. The heat flux density at the interface between the media in this case reaches 4.2-7.5 MW / m ² or more.

Source of information: Yu.P. Solntsev et al. Metallurgy and metal technology. - M.: Metallurgy, 1988 .-- 512 p., Ill. (p. 158-164).

5. The closer the evaporation mirror and the condensation surface, the less interference with the steam flow and the size of the distillation unit. To reduce the gap to a thickness of a dense vapor layer (1.0-2.0 mm) in the prototype does not allow mutual sliding of the surfaces. Instead of the ordered movement of molecules near spinning disks, chaotic gas vortices are obtained. The mutual immobility of the areas of the free surface of the liquid eliminates this problem. This arrangement gives maximum benefit in the case of contact recovery of condensation energy.

In terms of efficiency, the operation mode of the distillation unit strives for a natural analogue - the free surface of water. Even at room temperature range. Especially when the evaporation and condensation zones are sufficiently small, they alternate evenly and do not protrude beyond the dense vapor layer above the liquid mirror.

Naturally, the neighboring areas of evaporation and condensation, at the closest approach, cannot physically come into contact. Moreover, it is necessary to prevent the return flow of steam from the distillate to the solution (advantageous from the standpoint of thermodynamics). Cells of the liquid surface should be separated by a material barrier, and the desired difference in saturated vapor pressure above them should be maintained artificially, for example, due to the temperature difference on the sides of the partition. The latter is feasible if the heating elements are combined with capillary condensers - tubes open into the vapor space with a thin internal channel.

The saturated vapor pressure above the concave meniscus of condensation at the same temperature is always lower than above a flat evaporation surface. Consequently, the steam will condense itself in the capillary and create a local heating zone there. With the timely removal of the accumulating liquid, this is a non-stop process, the speed of which is limited only by the density of the heat flux through the walls of the capillary. The condenser tube automatically turns into a heater.

When the diameter of the channel of the capillary is in the range of 0.4-0.1 mm, the temperature difference between its outer and inner surfaces can reach several degrees or more. This is quite a lot, given the scale factor. The heat flux through the steel wall of the steam boiler 1 cm thick (temperature difference 150 ° C) is equal to the heat flux through the same wall area (0.1 mm thick) of steel capillaries at a temperature difference of 1.5 ° C. Frequent bristles of capillary tubes penetrating the evaporation mirror allow compact folding of the heat exchange surface. The condensation heat recovery unit is simple and efficient.

6. The process of surface distillation is extremely sensitive to the absolute value and temperature differences in the system. Any specific combination of chemical composition and concentration of the solution, vapor pressure, and other process parameters corresponds to some optimal temperature regime. The method of establishing it does not matter. Both direct heating and cooling of reagents and indirect methods are acceptable - fast or slow update of the evaporated solution, vacuum pumping of the vapor space, etc.

Especially precisely the requirements for the minimum and maximum temperatures of the individual elements of the installation should be observed during cold distillation with the recovery of the energy of vaporization. The productivity of the process is maximized when the internal capillary channels are perfectly wetted and their external walls repel liquid. For this, the saturated vapor pressure above the concave surface of the tubes should be noticeably lower than above the evaporation mirror, and the pressure above the outer surface of the tubes should slightly exceed it. The effect depends on the correct combination of capillary geometry and the surface tension of the solution with the distillate.

7. A feature of the surface distillation of a liquid is the widespread use of macroscopic molecular effects at the interface between a liquid and its saturated vapor.

Due to the mosaic nature of the working area and the small overall dimensions of its elements, it is impossible to organize mechanical or convection mixing of the solution. Therefore, the transport of the film of the solution from the heater to the place of evaporation is carried out due to its own surface tension force. At a short distance not exceeding a few millimeters, it is convenient and extremely effective.

It is known that the thermal conductivity of liquids is 2-3 orders of magnitude worse than that of metals. Convection helps poorly. For example, at the most rapid boiling of water, the rate of rise of vapor bubbles (with a diameter of 2-3 mm and larger) does not exceed 30 cm / s. If the heat flux density is increased beyond the permissible limit, a foam cap rises above the evaporation mirror.

Source of information: V.G. Levich. Physicochemical hydrodynamics. - M.: Publ. physical mat. literature, 1959. - 700 p., ill. (p. 434-450).

The situation completely changes when the distillation system is entirely concentrated at the interface between phases and media. The surface tension of liquids is temperature dependent. Pure water, for example, at 0 ° C has a surface tension of 75.64 mN / m, and at + 20 ° C it is only 72.75 mN / m. If this difference is entirely applied to the thinnest layer of a substance (3-7 molecular layers), which does not have a strong bond with adjacent materials, then the speed it acquires is quite significant. A film of water, on the border with air, with a surface temperature gradient of 1 ° C / cm, is pulled to the cold side at a speed of about 1-2 cm / s. With a typical thermal pressure of 2-2.5 ° C / mm, at the wall of the heating element, the film flow rate of water can be expected to be no less than 0.2-0.25 m / s. There are no closed bubbles and no foam.

Source of information: V.G. Levich. Physicochemical hydrodynamics. - M.: Publ. physical mat. literature, 1959. - 700 p., ill. (p. 382-388).

In this case, the evaporation mirror at the boundary with the vapor space is covered with a frequent (2-3 mm pitch) funnel matrix around poorly wettable heated rods. The surface tension force continuously draws a film of a hot solution from them, dragging along part of the liquid. Solvent molecules are volatilized. The concentrated solution drops down, since its specific gravity is rapidly increasing. The mass transfer rate noticeably exceeds normal values.

The cumulative technical effect of the application of the method:

Firstly, overall dimensions of technological equipment are extremely reduced. The use of molecular effects eliminates heat exchangers, steam lines, vacuum pumps and mixers. This streamlines the familiar manufacturing process.

Secondly, the range of temperatures and pressures available for the distillation of liquids is expanded without sacrificing performance.

Thirdly, due to the rational layout of the elements of the working area, the recovery of steam condensation energy is greatly facilitated, accordingly, the necessary energy costs are reduced.

Fourth, the formation of foam and scale is completely eliminated.

An example embodiment of the invention.

Continuous adiabatic water distiller.

The most fully demonstrate the properties and advantages of the proposed method allows its use in a well-known technical field, for example, for adiabatic distillation of sea water.

If we direct the natural steam flow rising from its surface to a capillary condenser passing through the same surface, we can close the “distillate-brine” heat flux along the shortest path, not further than a few millimeters from the interface between phases and media. The heat of solvation will be compensated by cooling the flow of the effluent, and all energy costs will be reduced to pumping it. The layout of such a system is schematically shown in Fig.6.

Description of the design and operation of the desalination plant.

The central node of the capillary desalination unit is a flat pan 1. It is filled with running sea water. On top of the tray cover a transparent casing 2 to protect the capillary holes from dust and debris. The evaporation mirror of sea water 3 through the steam space under the casing is connected to the condensation surface in the form of a capillary brush. Each capillary 4 is installed so that, passing through a layer of sea water, it exits with the upper open end into the vapor space (slightly rising above the evaporation mirror), and connects with the lower open end to distilled water. The side walls of the capillary are used as a heat exchange surface with brine.

Through the inlet pipe 5 into the pan serves sea water of natural temperature. From a flat evaporation mirror, the steam stream 6 is directed into the channel of the capillary. There it condenses on a cylindrical meniscus 7 and a hemispherical meniscus 8. The excess of sea water is removed through the overflow pipe 9. The heat of vapor condensation through the walls of the capillary is transferred to the water washing them from the outside. The surface tension force continuously draws a hot liquid film from the boundary zone of contact with the capillary wall directly onto the cold surface of the evaporation mirror.

The depth of the seawater flow in the pan is set close to the length of the steam condensation section inside the capillary (from its upper cut to the meniscus). The height of the distillate column H, at zero condensation rate, is itself determined by the Juren formula. In normal operation, the desalination plant is more than the static level by ΔН. This increase is not constant, depending on the temperature and the rate of steam condensation. The value ΔН creates an additional hydrostatic head, partially compensating for the hydraulic resistance to the flow of the current distillate.

The performance of the capillary desalination plant is set by moving the adjusting plate 10, where the distillate flows. The level of its free surface in the plate is rigidly fixed using the overflow pipe 12. Moving the plate up and down, relative to the expansion pipe 13, control the current position of the hemispherical meniscus in the channel of the capillary.

For this design of the desalination plant and the selected diameter of the capillaries (medical needle of standard 24G1, R _VNUT = 0.17 mm), certain limitations of the operating conditions are significant. The optimum temperature of the distilled water should be in the range of + 5-15 ° C, and the final weight content of the substances dissolved in it should not exceed 10%. Thus, sea water with a natural salinity of 17-35 g / l can evaporate about 3-4 times.

Watermaker operates continuously. The flow of seawater passing through it at natural temperature and salinity is automatically divided into two parts - a more concentrated brine and a completely fresh distillate. Operating costs come down to maintaining the operation of the water supply pumps and pipelines.

To reduce the flow resistance of the distillate, the length of the capillary, constantly filled with water, is limited by the necessary minimum sufficient for the operation of the system. It should be not less than the temperature drift of the meniscus (5 mm) and not much more than the adjustment range of movement of the hemispherical meniscus. Tentatively, 10-20 mm.

Theoretical basis of the principle of desalination.

The pressure of water vapor above a flat surface of distilled water and salt solution differs by Δp (Pa), pressure depression. A similar pressure depression is observed over the curved surface of the water in the capillary. At a temperature of + 20 ± 15 ° C they are comparable. The first is usually measured, the second is calculated by the Laplace formula:

;

;

Here Δр is the pressure depression over the curved surface (Pa);

δ is the surface tension of the liquid (N / m);

R ₁ and R ₂ - the main radii of curvature of the surface (m).

The vapor pressure above the menisci of the distillate in a typical capillary (a steel medical needle of standard 24G1, R _VNUT = 0.17 mm) above a flat mirror of the distillate and one stripped off seawater are shown in table 2.

T (° C) δ distill. (mn / m) Above the menisci in the capillary (Pa) Water and sat. NaCl brine (Pa) cylinder scope depression distillate brine depression 5 74.92 423.8 0.3 864.2 864.5 651.7 212.8 6 74.78 491.1 51.23 879.8 931.0 704.9 226.1 7 74.64 558.4 119.4 878.1 997.5 758.1 239.4 8 74.50 625.8 187.5 876.5 1064.0 811.3 252.7 9 74.36 706.4 269.0 874.8 1143.8 864.5 279.3 10 74.22 787.0 350,4 873.2 1223.6 917.7 305.9 eleven 74.07 867.7 432.0 871.4 1303,4 984.2 319.2 12 73.93 961.6 526.7 869.8 1396.5 1050.7 345.8 13 73.78 1055.6 621.6 868.0 1489.6 1130.5 359.1 fourteen 73.64 1162.8 729.6 866.3 1596.0 1210.3 385.7 fifteen 73.49 1270.1 837.8 864.6 1702.4 1290.1 412.3 16 73.34 1377.4 946.0 862.8 1808.8 1369.9 438.9

Continuation of table 2 17 73.19 1498.0 1067.4 861.1 1928.5 1463.0 465.5 eighteen 73.05 1631.8 1202,1 859.4 2061.5 1556.1 505.4 19 72.90 1765.7 1336.8 857.6 2194.5 1649.2 545.3 twenty 72.75 1899.5 1471.6 855.9 2327.5 1755.6 571.9 21 72.59 2060.1 1633.1 854.0 2487.1 1875.3 611.8 22 72.44 2207.3 1781.2 852.2 2633,4 1995,0 638.4 23 72.28 2381.1 1955.9 850.3 2806.3 2114.7 691.6 24 72.13 2554.9 2130.6 848.6 2979.2 2247.7 731.5 25 71.97 2742.0 2318.7 846.7 3165,4 2380.7 784.7 26 71.82 2929.1 2506.7 844.9 3351.6 2527.0 824.6 27 71.66 3129.6 2708.0 843.1 3551.1 2686.6 864.5 28 71.50 3343.3 2922.7 841.2 3763.9 2846,2 917.7 29th 71.35 3570.3 3150.6 839.4 3990.0 3019.1 970.9 thirty 71.18 3810.7 3392,0 837.4 4229.4 3192,0 1037,4 31 71.03 4064.3 3646,4 835.6 4482.1 3364.9 1117.2 32 70.88 4331.2 3914.2 833.9 4748,1 3564.4 1183.7 33 70.73 4598,0 4182.0 832.1 5014.1 3777.2 1236.9 34 70.56 4891.6 4476.6 830.1 5306.7 3990.0 1316.7 35 70.38 5210,0 4796,0 828.0 5624.0 4218.0 1406.0

Information sources:

Calculation of saturated vapor pressure in a capillary - according to the Laplace formula; I.T. Goronovsky and others. A quick reference to chemistry; Kiev: Naukova Dumka. 1974.- 985 p., Ill. (p. 772, Surface tension of water); Yu.Yu. Lurie. Handbook of analytical chemistry; Chemistry, - M., 1971, 496 p., Ill. (p. 141, Water vapor pressure above the distillate); Chemistry Handbook, Second Edition, Volume III, ed. P. B. Nikolsky. - M .: Chemistry, 1964 .-- 1008 p., Ill. (p. 345, Vapors of water over salt solutions).

The table shows that if you take a saturated salt solution as raw material, then raising the temperature inside the capillary above + 15 ° C is pointless - the conditions of internal wetting of the channel are violated. Moreover, the maximum temperature difference (ΔТ) between cold brine and hot distillate cannot exceed 6 ° C, even theoretically.

Actually, you should expect a thermal difference of about 3 ° C, corresponding to the minimum possible system performance. However, there is a way out - the abundance of available sea water with a weight concentration of salt of not more than 35 g / kg allows to obtain much higher productivity due to the continuous discharge of weak brine into the environment (sea). At the same time, the danger of scale formation disappears.

The vapor pressure of water (kPa) over the distillate (control line) and sodium chloride solutions of various concentrations are summarized in table 3.

T (° C) The weight concentration of an aqueous solution of sodium chloride (distillate) 50 g / kg 100 g / kg 150 g / kg 200 g / kg 250 g / kg 0 0.6105 0.5852 0.5719 0.5453 0.5054 0.4655 10 1,2278 1,1837 1,1438 1,0906 1,0241 0.9443 twenty 2,338 2,261 2.1812 2,0881 1,9684 1.8088 thirty 4,242 4,1097 3.9634 3,7905 3,5644 3,2851 40 7,375 7.1288 6.8761 6.5835 6.1978 5,719

Continuation of table 3 fifty 12.33 11,930 11,491 11,012 10,387 9.6026 60 19.92 19,258 18,580 17,782 16,758 15,534 70 31.16 30,111 29,034 27,784 26,267 24,352 80 47.34 45.752 44,156 42,294 39,966 37,094 90 70.10 67,697 65,303 62,510 59,198 55,062 one hundred 101.32 97,888 94,430 90,440 85,519 79,667 110 143.3 138.32 133.40 127.81 121.16 112.92

Source of information: Handbook of a chemist, second edition, III volume, ed. P. B. Nikolsky. - M .: Chemistry, 1964 .-- 1008 p., Ill. (p. 345).

It can be seen that the vapor pressure above water with a salinity of 50-100 g / kg at low temperatures is almost equal to the pressure above pure distillate. The difference does not exceed a few percent. The conditions for the complete wetting of the internal channel of the capillary and its working capacity are maintained up to the threshold of + 40-50 ° С. It is also seen that the pressure depression in the capillary decreases with increasing temperature and it is advantageous to distill in the thermal range below + 15 ° С. The theoretical maximum (ΔT) in this case is approximately equal to 10 ° C.

The found values make it possible to find the magnitude of the condensation meniscus stroke in the channel of the vertical capillary tube of medical standard 24G1 (R _VNUT = 0.17 mm) by the difference in capillary rise at the minimum and maximum temperature according to the Juren formula:

;

;

Here: H - the height of the capillary rise of the liquid (m);

R is the radius of the capillary channel (mm);

δ is the surface tension of the liquid (mN / m);

g - acceleration of gravity (9.87 m / s ² );

ρ is the density of the liquid (kg / m ³ ).

At ordinary temperatures, the capillary rise of the condensate can range from 0.09 m (at 5 ° C) to 0.085 m (at 35 ° C). The thermal drift of the meniscus is 5 millimeters. The sum of the length of the vapor condensation zone and the meniscus drift margin determines the minimum capillary length.

The normal movement of the hot brine film, from the external capillary machine to the evaporation mirror, requires deliberately poor wetting of the heating surface with sea water. This is facilitated by the increased temperature of the walls of the capillaries, the reduced pressure of saturated steam above the brine, and the noticeable curvature of the outer walls of the capillaries.

In the case of desalination of ordinary sea water (without organic impurities), all of the above is guaranteed. On the other hand, in conditions of a small temperature difference at the heater-solution interface, a large heat transfer area is useful. It is advisable to make the condenser tubes thicker. The search for the optimum for each particular case requires practical experiments.

Desalination calculation.

1. Set the composition and maximum concentration of brine. For example, a solution of sodium chloride evaporated to a concentration of 50 g / l.

2. Set (learn from the directory) the maximum deviations of the temperature of the source of sea water and its salinity. For example, the Pacific Ocean, temperate latitudes, from + 5 ° С to + 15 ° С, water salinity 35 g / l.

3. Take for reference the performance of the evaporation mirror desalination without heating. The second flow of water molecules from a unit surface to vacuum at a temperature of + 15 ° C is 0.16-0.2 kg / m ² .

4. Determine the maximum operating temperature of the evaporation mirror under given conditions. In this case (according to claim 2) it is + 15 ° С.

5. Determine the minimum temperature difference between the flat brine mirror and the cylindrical meniscus of condensate on the wet walls of the capillary. According to table 2: ΔT _MIN = 19-15 = 4 ° C.

6. Determine the minimum pressure difference between the flat brine mirror and the hemispherical meniscus of condensate in the depth of the capillary. According to table 2:

ΔP _MIN = 1.702-1.337 = 0.365 kPa.

7. Determine the maximum temperature difference between the flat mirror of the brine and the cylindrical meniscus of condensate on the wet walls of the capillary. According to table 2: ΔТ _MAX = 11-5 = 6 ° C.

8. Determine the maximum pressure difference between the flat brine mirror and the hemispherical meniscus of condensate in the depth of the capillary. According to table 2:

ΔP _MAX = 0.864-0.432 = 0.432 kPa.

9. The approximate length of the steam condensation section inside the capillary (active heat transfer length) is set, for example, 20 mm.

10. Set the distribution of thermal pressure over the thickness of the capillary wall and the boundary layers of the liquid. In the absence of reference data on the thermal flow of the surface salt water film, it is assumed that half of the total thermal resistance falls on the metal. Then the temperature drops between the inner channel and the outer surface of the capillary will be:

ΔТ _MIN = 2 ° С; ΔT _max = 3 ° C.

11. Determine the thermal conductivity of the material of the capillary λ. In this case, for medical grade 30X13 stainless steel, λ = 45 (W / (m · ° K)). Source of information: Physical quantities; Directory; under the editorship of I.S. Grigoriev. - M.: Energoatomizdat, 1991 .-- 1232 p., Ill. (p. 349).

12. Determine the thermal power P (W) transmitted to the brine through the wall of a single capillary, according to the standard formula:

Source of information: G.N.Dulnev. Heat and mass transfer in electronic equipment. - M .: Higher school, 1984. - 247 p., Ill. (p. 30-32).

Here:

λ is the coefficient of thermal conductivity of the wall material (W / (m · ° K));

L _CIL - active capillary length (m);

r _OUT - external radius of the capillary (mm);

r _VNUT - the inner radius of the capillary (mm);

ΔТ - temperature difference between the walls of the capillary (° K);

In this case, for a 24G1 caliber capillary (R _VNUT = 0.17 mm):

L _C = 0.02 m; r _OUT = 0.55 / 2 = 0.275 mm; r _VNUT = 0.17 mm; ΔТ _MIN = 2 ° K;

ΔТ _MAX = 3 ° K; λ = 45 (W / (m ° K));

Result: P _MIN = 23.5 W; P _MAX = 35.3 watts.

13. Determine the mass productivity of a single capillary in terms of heat transfer. The energy of water evaporation at + 5 ° C is 2.5 kJ / g, and at + 15 ° C, respectively, 2.47 kJ / g. Result:

m _MIN = 23.5 W / 2.47 kJ / g = 9.5 mg / s;

m _MAX = 35.3 W / 2.5 kJ / g = 14.1 mg / s.

14. Determine the hydrostatic pressure Δp (Pa) created in the capillary channel by a water column of height ΔH, according to the standard formula:

Δp = ρgh

Here: ρ is the fluid density (kg / m ³ );

g is the acceleration of gravity (m / s ² );

h is the height of the liquid column (m);

In this case: ρ = 1000 kg / m ³ ; g = 9.81 m / s ² ; h _MIN = 0.01 m;

Result: Δp = 98.1 Pa.

15. Check the second flow of the distillate V _C (m ³ / s) through the channel of the needle from the syringe caliber 24G1 (R _VNUT = 0.17 mm) according to the formula:

;

;

Source of information: L.M. Batuner, M.E. Pozin. Mathematical methods in chemical engineering. - L .: State Scientific and Technical Publishing House of Chemical Literature, 1963. - 640 p., Ill. (p. 161).

Here:

R is the radius of the capillary channel (m);

L is the length of the liquid-filled capillary channel (m);

η is the viscosity of the liquid (Pa · s);

Δp is the hydrostatic pressure of the fluid inside the capillary (Pa).

In this case: R = 1.7 · 10 ^-4 m; L = 0.01 m; Δp = 98.1 Pa; ultimate viscosity of distilled water at + 5 ° С η _MAX = 1,518 · 10 ^-3 Pa · s.

Result: V _C = 2.12 · 10 ^-9 m ³ / s or m _C = 2.12 mg / s.

16. Take into account that the static pressure created by the distillate column in the capillary channel is insufficient for its possible productivity (4-7 times less than necessary) and should be amplified by the pressure of the distillate column in the expansion pipe. From this, the necessary course of vertical movement of the adjusting plate is found - 0.04-0.07 m. With a margin, this stroke is taken to be 0.1 m.

17. Determine the length of the expansion pipe as the sum of the maximum capillary lift of the distillate (0.09 m) and the estimated vertical stroke of the adjusting plate (0.1 m). Result: at least 0.19 m.

18. Determine the technological limitations of the density of installation of capillaries in an automated production environment. The process of manufacturing a capacitor is similar to drilling and assembling printed circuit boards. Standard mounting pitch 2.5 mm. Conclusion: on 1 m ² brine mirrors on average there will be no more than 160,000 capillaries.

19. Design constraints are set for the size of a single capillary capacitor unit. Obviously, for the normal operation of the overflow limiter, the level of the brine should be a radially symmetric disk with a central hole. It is assumed that for convenient routine maintenance (visual inspection, manual replacement, cleaning of capillaries, etc.), its diameter does not exceed 200 mm.

20. Set the number of capillaries in a single block. For example, N = 3300 pcs.

21. Determine the theoretically possible minimum and maximum performance of the indicated block of the capillary capacitor: M _MIN = m _MIN × N = 9.5 · 10 ^-3 g / s × 3300 = 31.35 g / s = 112.9 l / h;

M _MAX = m _MAX × N = 14.1-10 ^-3 g / s × 3300 = 46.5 g / s = 167.5 l / h.

22. For control, determine the steam productivity of an even water mirror, equal in size to the capillary block (disk with a radius R = 0.1 m at + 20 ° C), only due to the internal heat capacity of water: M _K = 200 g / s × π × 0.1 ² = 6.28 g / s = 22.62 l / h.

Conclusion: the unit capacity is in the range of 20-160 l / h.

23. Determine the consumer properties of the distillation plant in comparison with the prototype, solar desalination plants (3.5-4.6 l / m ² per day) and the similar in general idea "Hasler method" (20 l / m ² per day): Productivity, estimated - 20-160 l / h or 0.48-3.84 t / day. Operating costs - round-the-clock operation of an electric pump with a capacity of 50-100 watts for pumping distillate (about $ 1.0 per day).

In the presence of particularly thin capillaries with an inner channel diameter of less than 0.1 mm, it becomes technically feasible to additionally heat the free surface of the distilled liquid with light, radiation or a contact method, for example, a semi-immersed spiral into it through which an electric current passes. The formation of foam and scale near the wall of such a heater, for the reasons described above, is physically impossible.

Conclusions: The prototype is overly complex. The Hassler method is simpler, but requires the operation of compressors, to create a pressure difference between salt and fresh water of about 50 kg / cm ² . Solar desalination plants are bulky.

The benefits of the proposed distillation method are obvious. The specific productivity of the structure can be increased by reducing the diameter of the capillaries, pumping out non-condensable gases and using other well-known technical methods.

Claims (1)

A method of surface distillation of liquids, including heating its vaporization mirror, removing steam from the vapor space and condensing the steam on the condensation surface, characterized in that the steam flow from the steam space is directed to the surface in the form of a capillary brush, with each capillary passing through the evaporation mirror, channels the capillaries are open at the top into the vapor space and immersed in the condensate with the lower ends, and the heat of the phase transition from the condensate draining through the channels is returned directly to the mirror of the evaporated liquid o through the walls of the capillaries.

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