RU2081840C1 - Solar desalination apparatus - Google Patents

Abstract

FIELD: solar-energy engineering, continuous-action solar water desalination equipment. SUBSTANCE: proposed apparatus comprises heat insulating casing having lower darkened panel and plurality of inclined intermediate panels 5 with condensate collectors. Panels are formed with flanged edges in form of trays and they are provided with drainage pipes extending between adjacent panels. Upper cut ends of drainage pipes are disposed in horizontal planes lying over surface of panels and below their flanged edges, while lower cut ends of drainage pipes lie below identical planes of low-lying panels. Salted water admission pipe connected to surface of upper intermediate panel and lower ends of pipes are formed with side outlet openings. Pipes of panels are communicated with collector, to which excess brine is discharged. Upper panel and intermediate panels are made transparent for solar radiation. Intermediate panels are made of heat conductive glass or of glass reinforced with heating elements. Structural arrangement of apparatus ensures optimum level of filling panels with salted water and discharge of excess brine. EFFECT: improved efficiency and reliability in operation; salinization of panels is ruled out; maximum utilization of solar radiation energy. 3 cl, 1 dwg

Description

 The present invention relates to solar engineering, and more specifically to continuous desalination plants.

 The closest in technical essence to the claimed solution is a solar desalination plant containing a heat-insulating casing with a lower heat-absorbing panel, over which a series of convex intermediate panels with condensate collectors are installed at the periphery, pipes for supplying salt water and drainage of desalinated water and a collector for drainage are led to the casing brine. Salt water is supplied through sprinklers located between the panels for even distribution of water, connected to the pipes for supplying salt water.

 This installation implements the regeneration of heat generated by the condensation of water vapor on the lower surface of each subsequent panel used to evaporate salt water from the upper surface of these panels.

 However, this well-known desalination plant due to the adopted method of supplying salt water to each panel through an extensive system of irrigators is inefficient and unreliable in conditions of ensuring a sufficiently large productivity.

 The fact is that in order to achieve a uniform distribution of salt water on the upper surface of the panels, the sprinklers must have a large number of holes located at a distance of at least 100 mm from each other (with a larger distance between the holes uniform spreading of water across the panels is ensured, which will lead to their partial salinization).

4,4 м/сек. Максимальное значение удельного расхода опресняемой воды при обычном для южных широт уровне потока солнечной радиации q_с=750 вт/м² составляет 0,32•10^-3 кг/м²•сек и при площади 10 м² расход воды равен C=3,2•10^-3 кг/сек. Тогда легко определить диаметр отверстий в оросителе

где: μ=0,6 коэффициент расхода для отверстий, ρ = 1000 кг/м³ плотность воды. Подставляя n=64 и W=4,4 м/секунд, найдем d=0,155 мм.For a desalination plant module with an area of 10 m ² (with a side of ≈3.2 m), the number of holes in the sprinkler with two rows of holes will be n = 64. In a desalination plant, for example, with ten panels located at a distance Δ = 100 mm from each other, the height of the column, under the pressure of which water flows out of the holes of the sprinkler placed above the heat-sensitive stove, is h nΔ = 1 m and, therefore, the flow rate of water will be is equal to

4.4 m / s The maximum value of the specific consumption of desalinated water at the usual level of solar radiation flux q _с = 750 W / m ² for southern latitudes is 0.32 • 10 ^-3 kg / m ² • s and with an area of 10 m ^{2 the} water consumption is C = 3, 2 • 10 ^-3 kg / s. Then it is easy to determine the diameter of the holes in the sprinkler

where: μ = 0.6 flow coefficient for holes, ρ = 1000 kg / m ^{3 the} density of water. Substituting n = 64 and W = 4.4 m / s, we find d = 0.155 mm.

Obviously, openings of such a small diameter will quickly clog and the desalination plant will fail. If the holes have a diameter acceptable for operation, for example, d = 0.6 mm, then it will be necessary to increase the flow rate of water supplied to the desalination plant by (0.6 / 0.155) ² = 15 times, which will require a large heat consumption for heating the excess water flow passed through the desalination plant, and indicates the low efficiency of the latter in terms of the output of desalinated water, especially in conditions with a variable solar radiation flux, which takes place in reality.

 An object of the present invention is to increase the efficiency and reliability of a solar desalination plant.

 To achieve this goal in a known installation containing a heat-insulating casing with a heat-absorbing bottom panel and a number of intermediate panels installed above it with condensate collectors, these panels are flanged in the form of baking sheets and equipped with drainage pipes installed between adjacent panels, the upper edges of which are located in horizontal planes lying above the surface of the respective panels and below the edges of the flanges of these panels. In this case, the salt water supply pipe is brought to the surface of the upper intermediate panel, and the drainage tubes of the lower panel are combined into a collector for draining the brine.

 The intermediate panels are made transparent to solar radiation and absorbing infrared radiation, for example, from heat-conducting glass or from glass reinforced by heat-conducting elements, for example, copper, and the lower ends of the salt water supply pipe and the drainage tubes of the intermediate panels are provided with lateral outlet openings.

 This installation allows you to maximize the use of solar radiation energy for desalination of salt water, to provide an optimal level of filling pan trays with water and drain excess brine, eliminating the possibility of salinization of the panels.

 Connecting the installation cavity to the vacuum pump allows to increase the rate of water evaporation and condensation of its vapor.

 The installation of an electromagnetic flowmeter sensor on the drain pipe of the collector makes it possible to implement reliable regulation of the supply of salt water in high-capacity desalination plants consisting of a number of modules.

 The proposed technical solution improves the efficiency and reliability of the solar desalination plant.

 The essence of the proposed device is illustrated in the drawing, which shows a longitudinal section of a desalination plant.

 The installation consists of an upper inclined panel 1, which is transparent to solar radiation and absorbing infrared radiation, made, for example, of glass, a lower blackened heat-absorbing panel 2, absorbing solar radiation, a heat-insulating layer 3, a heat-insulating casing 4, and a series of intermediate inclined panels 5 (only shown in the drawing two of them), transparent to solar radiation, made of heat-conducting glass, or glass reinforced with heat-conducting (for example, copper) elements 6. Panels 2 and 5 are made with an end small mouths 7 in the form of baking trays and are equipped with vertical drainage tubes 8 installed between adjacent panels. The installation comprises a branched water supply pipe 9 located above the upper panel 5, condensate collectors 10 mounted obliquely at the lower edge of the panels 1 and 5, and heating elements 11 (for example, electric heating) located under the panel 2. The inclination of the collectors is not shown.

 The bottom panel 2 with its flanging 7 is adjacent to the casing 4 of the installation. Between the flanges 7 of the intermediate panels 5 and the casing 4, a gap is left for the free passage of water vapor.

 The upper edge of the drainage tubes 8 is located in horizontal planes lying an amount h above the surface of the corresponding panel 2 and 5 and lower than the height H of the cutouts 7 of these panels. The lower ends of the water supply pipe 9 and the drainage tubes 8 are located below the planes in which the upper edges of the drainage tubes 8 of the adjacent underlying panels 2 and 5 lie, and are provided with side openings 12 for water to enter the unit and flow through the tubes 8. Minimum height h, onto which the drainage tubes 8 protrude above the surface of the panels 5 (taking into account their inclination), is selected so that when these panels are filled with water, they cover all their surfaces with a margin of about 5-10 mm.

 Draining tubes 8 of panel 2 are connected to a common collector 13 for discharging excess brine. On the drain pipe 14 there is a section 15 of non-magnetic material (for example, polyethylene), on which the sensor 16 of the electromagnetic flow meter is installed. Next, the drain pipe 14 is connected to the pump 17.

 The internal cavity of the desalination plant is connected via a pipe 18 to a vacuum pump (not shown).

 The device operates as follows.

 Salt water enters the installation through the pipe 9 and is distributed through the panels 5 and 2, flowing through the pipe 8.

 Solar radiation, passing through the transparent upper 1 and intermediate panels 5, is absorbed by the lower panel 2 and heats it. The bottom panel 2 gives off a layer of water 19 poured on its surface, which leads to its heating and evaporation.

 Water vapor condenses on the lower surface of the overlying intermediate panel 5 and gives it the heat released during condensation of water. In addition, this panel is heated by infrared radiation from the bottom panel 2 and thermal conductivity through the vapor layer between the panels.

 Through this intermediate panel 5, heat is transferred through a layer of salt water 19 poured on its surface to the surface through heat conduction increased with glass-reinforcing heat-conducting elements 6, which leads to its heating and evaporation, and heat removal from the bottom surface of the panel 5 improves the conditions for condensation of water vapor.

 The desalinated water condensed on the lower surface of the intermediate inclined panel 5 flows into the condensate collector 10, from where it passes through the connecting collectors 10 to a storage tank (not shown in the drawing) and then discharged to the consumer.

 The considered process is repeated many times on subsequent intermediate 5 and upper 1 panels.

 Unlike intermediate 5, the top panel 1 has no reinforcing elements in order to reduce heat loss from the desalination plant to the environment.

 The installation of intermediate panels reinforced with heat-conducting elements dramatically increases the surface of the evaporation of salt water and provides the regeneration of heat released during condensation of water vapor, which together allows to increase the efficiency and productivity of the desalination plant.

 The flow rate of salt water supplied from above to the desalination plant through a branch pipe 9 is controlled so that it is 20-25% higher than the total flow rate of water evaporated in it. Most of the flow rate of water supplied to the first intermediate panel 5 from above, through the drainage tubes 8, flows to the underlying intermediate panel. The flow of water through the drainage tube 8 is repeated on the subsequent underlying intermediate panels 5.

 Since the number of drainage tubes 8 can be selected relatively small (one or two tubes per square meter of the panel area), and the outflow of water from the side holes 12 in these tubes occurs under very low pressure, these holes have a quite acceptable diameter of 1.5- 2 mm, and therefore eliminates the risk of clogging.

 The height of the flanges H is somewhat (for example, 20-25 mm) greater than the minimum height h at which the drainage tubes protrude above the panel surface. The height h is chosen so that when the panel is filled with salt water to the upper edge of the drainage tubes 8, this ensures full coverage with water (with a margin, for example, 5-10 mm) of the entire surface of the panel.

 Horizontal streams of water flowing from the side openings 12 at the ends of the branched inlet pipe 9 from the drainage tubes 8 enhance the convective mixing in the layers of water 19 poured on the surface of the intermediate and lower panels, and reduce their thermal resistance, improving the conditions of water evaporation, i.e. . contribute to improving the efficiency of desalination plants.

 The excess, compared with the exit of the evaporated water, the flow of salt water entering the bottom panel 2, through the drainage tubes 8 is supplied to the collector 13 and then through the drain pipe 14 with the help of the pump 17 is removed from the desalination plant.

 The presence of a constant stream of salt water through the installation is recorded according to the readings of the electromagnetic flow meter, it is regulated by the water supply through the pipe 9 using, for example, an electrically controlled valve (not shown).

 The choice for measuring the flow rate of the brine, which is an electrolyte, namely an electromagnetic flow meter is determined by the fact that such a flow meter makes it easy to carry out remote flow measurement, which is essential when creating a desalination plant with a large total capacity, consisting of separate modules.

 The use of panels 5 with flanging 7, equipped with drainage tubes 8, in combination with adjusting the flow rate of salt water supplied to the desalination plant according to the readings of an electromagnetic flow meter eliminates the possibility of salinization of the surface of these panels (by automatically maintaining the optimum level of water poured onto them and draining the brine), and Thus, it increases the reliability of the desalination plant.

 Through the pipe 18, the internal cavity of the desalination plant is evacuated, which ensures an increase in the rate of evaporation of water and condensation of its vapor and an increase in the efficiency of the installation. Moreover, the presence of a gap between the casing 4 and flanging 7 of the panels 5 excludes the possibility of a pressure gradient along the installation height and creates the conditions for normal water flow through the drainage tubes 8 of the panels 5.

 When the intensity of solar radiation falls below a certain level, the heating elements 11 located under the bottom panel 2 are turned on, and the process of heating and evaporation of salt water continues continuously, but when using for this purpose not only solar energy, but mainly the heat generated by these elements .

 When the intensity of solar radiation exceeds the specified level, the heating elements are turned off. Thus, the continuous operation of the desalination plant is realized under conditions of a strong decrease in the intensity of solar radiation (cloudiness, evening and night time).

 The proposed desalination plant design, in which solar energy is supplied from above, minimizes unproductive heat losses and creates a reliable, efficient installation of large total capacity by integrating individual modules into a common system.

Claims (3)

 1. A solar desalination plant containing a heat-insulating casing with a transparent upper and blackened lower panels, a series of consecutive inclined intermediate panels with condensate collectors installed on the periphery of the panels, connected to the casing of the pipe for supplying salt water and drainage of desalinated water and a collector for removing excess brine, above the last one characterized in that the lower and intermediate panels are flanged in the form of baking sheets with a gap between the flanging of the intermediate panels and the casing of the installation and bzheny defined between adjacent panels draining tubes, an upper edge which is disposed in horizontal planes lying above the surface of the respective panel and the lower edge of the flange of these panels, the salt water feed pipe is brought to the upper surface of the intermediate panel and the bottom panel draining pipe connected to a manifold.  2. Installation according to claim 1, characterized in that the intermediate panels are transparent for solar radiation from heat-conducting glass or from glass reinforced with highly heat-conducting elements, such as copper.  3. Installation according to claim 1, characterized in that the lower ends of the salt water supply pipe and the drainage tubes of the intermediate panels are made with lateral outlet openings located below the planes in which the upper edge of the drainage tubes of the underlying panels lies.