DE4321192A1 - Apparatus for distilling water in the low-temperature range - Google Patents

Abstract

The apparatus can be used for the desalination of seawater for agricultural purposes. Known "high-tech" distillation processes require primary energy of 30 litres of oil for distilling water. During the day, solar energy is employed. Waste heat from power stations, geothermal energy etc. can be combined. Since only atmospheric pressure and a temperature below 95 DEG C in the interior are employed, and to avoid lime encrustation and corrosion, the apparatus is made of polypropylene. The natural utilisation of gravity, the difference in level from the tank to the heat store, is sufficient for distillation. Solar collectors which comprise glass covering, frame and an absorber are combined with evaporators and heat exchangers to form a wall which is oriented north-south. In addition, mirror foils are irradiated, the angles of which are set by rigging known from sailing ships. The irradiated side is on the east in the morning and is changed at midday to the west. Thermal energy is collected in an energy storage device via a thermosyphon system. Hot water flows to trickle over a sponge, which is only water-permeable at a slight superatmospheric pressure, in Z-shaped flow mats. The droplets forming increase the surface area of evaporation. <IMAGE>

Description

The apparatus can preferably be used for desalination of sea water arid areas of the world. The size and performance let the desalination of sea water for agricultural Use too.

In contrast to the known "high-tech" processes (MSF: R.O .; E.D .; V.C.) the primary energy for distilling 1 m³ of water Value of 30 liters of oil, or only through detours via use of electricity can use solar energy works this device during the day 100% with thermal solar energy. It can, e.g. B. at night, other forms of energy such as, waste heat from Power plants, hot water sources of geothermal energy etc. alone or in Combination can be used. Unlike solar desalination devices, economical from 3 to 100 l dest / d work, this apparatus is only at higher distillation capacities economically. This is the model for this distillation system the sun with which seawater has been desalinated for millions of years.

The device is made of 95% polypropylene (PP). This is possible because of evaporation and subsequent condensation run under atmospheric pressure. PP lets out produce renewable raw materials. It has the property of one wax-like surface, the connections with other materials does not allow. That is, Calcification and corrosion are excluded. The basic material already has a factor in its manufacture  100 less energy than stainless steel, or by the factor 1000 as titanium used at MSF.

The device can be industrially prefabricated as a unit and only assembled to the finished wall at the operator's location. Regardless of the geographical location, the walls are created in a north-south direction. Fig. 1 For energy consumption, the solar collectors are illuminated directly and via mirrors. Since hot water below 95 ° C is sufficient for distillation, an increase in energy of the sun rays is only necessary by a factor of 3-5, so that inexpensive mirror films can be used. In contrast to the production of superheated steam, in which the sun's rays have to be concentrated in order to reach temperatures above 390 ° C. The parabolic mirror troughs used to generate electricity with thermal solar energy can also be used if the apparatus is housed in a tube.

The wall described below offers significant advantages: Natural gravity, a small level difference (NU) is sufficient to operate the system, makes the assembly of individual components into a compact unit inexpensive. The sun's rays are deflected towards the vertical collector surface by means of light mirror foils. In the event of sandstorms, storms or to switch off when waste heat is used, these are pulled in front of the collector. Fig. 2

The operation with the straight walls can be seen from the drawings ( Fig. 1 to 9). On the solar collectors ( 1 ) via sun sails ( 2 ) which consist of mirror foils, the sun's rays ( Fig. 2) are directed onto the solar collectors ( 1 ) in such a way that the energy density is increased on the side irradiated by the sun. The angle of the mirror surface is changed by adjusting the tubes attached to the ends so that the energy arrives at the solar collector ( 1 ) during the day. The mirrors are adjusted, like the sails on sailing ships, with the well-known rigging, roles, docks, shrouds, sheets, etc.

A cross section of the wall is shown on ( Fig. 3). Flat collectors ( 1 ) are mounted in the longitudinal direction on the west and east sides, which are additionally illuminated by the mirror ( 2 ). The heat store in the form of a water tank ( 3 ) is located above the collector so that the system works with gravity. The evaporators ( 4 ), which can consist of several evaporation stages, are attached next to the collectors. The evaporators are connected to the condenser ( 5 ) via windows. The concrete foundation ( 6 ) is integrated in the system and designed as a gutter ( 7 ). It acts as a basin in which the feed and discharge lines ( 8 ), ( 9 ) are also housed.

The vertical solar collector ( 1 ) is shown in detail in Fig. 4. It consists of the frame ( 10 ), the glass cover ( 11 ), a honeycomb-like insulation ( 12 ), the absorber ( 13 ) and the insulation ( 14 ). The absorbers ( 13 ) consist of PP double-wall sheets, for which a separate profile was developed. Fig. 5

The problem of sealing the web double plates ( 15 ) with the distributors ( 16 ) was solved by extruding the pipes ( 18 ) between three webs ( 17 ). The now full material webs ( 19 ) act as a frame and can now be welded. The thin wall thicknesses of the webs ( 17 ) are sealed with keder hoses ( 20 ) which are inserted into the grooves ( 21 ). The spaces ( 22 ) are filled with plastic material. Backfilled by the previous corona treatment, the process is similar to gluing. Fig. 6 Real permanent gluing is not yet possible with PP.

Another possibility of gluing arises by vapor deposition of a metal layer ( 23 ). On the side of the absorber facing the light, this acts as a selective layer and increases the power when converting UV to IR rays. Insulation ( 14 ) behind the absorber is not absolutely necessary. A simple plate that separates the collector ( 1 ) and evaporator ( 3 ) is sufficient as the rear wall.

The solar energy converted into thermal energy via the solar collectors is collected in the energy store ( 3 ) as hot water. The water heating circuit works as a thermosiphon without pumps. The water heated by the sun opens into the storage tank ( 3 ) ( 24 ) at the end of the absorber plate ( 13 ). The absorber plate is provided with a slot ( 25 ) at the bottom of the memory, above which a deflector plate ( 26 ) is attached. The thermosiphon is created in that the cool water is drawn into the slot ( 25 ) on the shadow side and sinks downward through the absorber ( 13 ) due to gravity. Under the catch basin ( 7 ), the water is piped into the absorber on the sunny side. As a result of the heating, the water becomes lighter and flows back into the tank ( 3 ), ( 24 ) at the top until the contents of the tank reach a uniform temperature or are removed for trickling. Since the desalination walls face north-south, the east wall heats in the mornings. At noon, when the sun has reached its highest level, both sides of the wall are in the shade, the sun sails (mirrors) ( 2 ) are converted from east to west radiation. As soon as the west wall is heated, the water begins to circulate in the opposite direction.

When the distillation temperature is reached, a thermostatic valve Fig. 8 ( 27 ) (known from the cooling circuit in motor vehicles) opens. It is the only part in the system that comes into contact with water and is not made of PP! The hot water flows into the distributor ( 28 ). The distributor ( 28 ) consists of a PP tube, which is provided on the inside with a sponge ( 29 ), which has the property of allowing water to pass only at a slight excess pressure. The tube is provided with a slot ( 30 ) or holes at the bottom. The low overpressure is achieved by opening the thermostatic valve ( 27 ) and is caused by the fact that the water level in the raw water tank is higher by the dimension (NU) to the upper point of the water tower. The evaporator ( 4 ) begins under the distributor pipe.

The distillation is achieved by evaporation of the water on the surface of the evaporator mats ( 28 ) into the air and the subsequent condensation on the heat exchanger plates ( 29 ) in the condenser. Fig. 7

The system is self-contained so that air cannot escape. The hot water seeps into the evaporator mats ( 28 ) made of PP flow and is trickled by gravity through a Z-shaped arrangement ( 30 ). Fig. 8 The again and again forming drops ( 31 ) fall to the connecting web ( 32 ) to trickle again. The surface of the flow mats, plus the surface of the drops, cause part of the water to evaporate and the larger part to cool down (cooling tower principle).

The hot air rises and changes through the opening ( 33 ) into the condenser room ( 5 ). The cooled water in the evaporator drips onto the bottom of the system in the catch basin ( 7 ) and is removed from the system.

Flat double web plates made of PP ( 35 ) are fitted in the condenser chamber ( 5 ) and are filled from below with the cool raw water from the water tower. At the dew point, the moist air releases the condensate onto the outer surface of the double wall plates ( 35 ) and flows into the collectors ( 36 ) and from there, as a product, out of the system. The air was cooled by the cooling process on the heat exchanger. It returns to the evaporator ( 4 ) via a further opening ( 37 ). That is, the air remains in the system and is saturated as warm, with a moisture about 10 times higher than the cold.

During the condensation, the heat energy supplied for evaporation is released to the cool raw water. The preheated raw water flows from the heat exchanger plates ( 35 ) in the middle into the storage tank ( 3 ).

calculation

The direct solar radiation (R), plus that of the mirror, provides a usable energy of approx. 1500 W / m² at the absorber ( 13 ) with a factor of 3. (In comparison flat collectors for hot water generation max. 600 W / m²). Thermal energy losses only occur on the glass side, because the back of the absorber opens into the evaporator ( 3 ) in which the energy is required. The energy consumption takes place in the heat exchanger, in which the cooling water is heated by the condensation. With a wall height of 4.5 meters, an output of 6,600 watts per running meter of wall can be expected in the energy calculation. By installing one collector in each of the east and west walls, the solar radiation is extended to 12 hours / day as with mechanical tracking.

12 hours × 6,600 watts = 79.2 KWH / d * running meter

The energy recovery in this system is in one stage Air cycle approx. 66% of the energy supplied. The condensation Heat = the heat of evaporation. The energy supply = the energy dissipation out of the system.

The mass flow of air caused by the different moisture content is easy at the top and heavy at the bottom Condensation amount in 12 hours. To be as constant as possible Mass flows of air, in evaporation and condensation to get the device in different height chambers divided that allow multiple independent air circuits, without changing the course of the water.  

Evaporators and condensers are made of water-permeable plates divided. Then there are further openings for air exchange required above and below the plate, depending on how many Levels are desired. Although on the condenser or on the evaporator nothing is changed, is with higher energy recovery too count. The recovery is added to the preliminary stage for each stage another 66%. That is, from the collector power in the example 79 KWH / d become 79 + 52 + 34 + 23 = 188 KWH / d through heat recovery Distillation can be used.

At 700 KWH enthalpy, which is required for 1 m³ of water to evaporate 3.7 running meters of wall are required.

Compared to reverse osmosis R.O. (7.5 KWH electrical) is the Energy use is still significantly higher, but will be the energy production costs (Power plant efficiency) to environmental pollution added, it is already possible with this device today cheaper than with any other type of desalination plant Desalinate sea water. In 1990, 10% of CO₂ emissions came at the expense of water desalination.

2. Procedure with the same film levels

The distillation wall can be used instead of the previously described chamber principle (one chamber each for evaporation and for condensation) also a modified desalination system according to the MSF Process used by the University of Nanci, Prof. P. Le Goff was introduced in Cannes in 1987.  

Brief description

An aluminum plate is covered with solar paint at the front provided and glued with gauze bandages on the back. The plate is aimed at the sun, the angle of attack resulting from it shows how long water flows in the gauze bandage without dripping down. (Image attached from Desalination 67 (1987) 43-52)

Under the illuminated plate, more plates are attached, who use the condensation energy the water in the under the gauze bandage glued to the plate evaporates again.

The disadvantages of the system are 1. water distribution, because each stage needs its own distribution and 2. in the use of energy the brine, because of the heat due to the metal plates only a synchronous system is possible.

Mirror tube method

The following apparatus is also with the double wall plates and PP flow mats installed in the collector wall with the heat accumulator. After the solar collector is an evaporator mat in Z shape attached the over the distribution plate from the top of the store is supplied. An additional convection takes place over the Absorber rear wall. Because heat only flows from warm to cold neither condensation nor evaporation in the space. The The capacitor plate is filled with cold raw water from below flows into the middle of the heat accumulator. The evaporator mat will supplied from the distribution plate, which is in the middle of the store flows. The capacitor plate opens into the storage tank at the bottom.  

This arrangement causes stratification of the heat in the store on, which leads to different trickle temperatures are on the evaporator mats. In addition, the channels still divided in height so that there are a variety of chambers forms, each with its own air cycle. With the Flow of cooling water through the condenser plates from bottom to bottom the desired countercurrent effect occurs above, which is a good one Heat recovery can be expected.

variant

It is also possible to use parabolic mirror tubs. The Walls must then be curved. The whole apparatus will expediently housed in a tube. The pipe will (morning and afternoon) with the parabolic mirror tubs pivoted. The angle is based on when a drop of the raw water into the distillate. The evaporator mats are not attached in a Z-shape, but straight. By turning the Rohres automatically results in a step memory, whose advantages can be used like this. This distillation tube can be up to two-stage wall without solar collectors, that takes advantage of the space under the mirrors.

One advantage of the pipe is the inexpensive manufacture Complete with standard parabolic mirror tubs are offered on the market with tracking controls.  

epilogue

In 1989, 11 million CBM / d, 10% of the oil extracted worldwide. Today 15 million CBM Desalinated water. Projections of population growth have a desalination requirement of 30 million CBM / d in 10 years expect. At some point in between the next energy crisis which also wakes up the last opponent of solar energy. It stays only the question: "Solar desalination with lots of junk or after the simplest possible methods and materials that grow back. " The attached lecture at the Dechema Annual Meeting 1993: "Series production of solar water desalination plants" has been added as prior art. The bibliography at the end of the remarks can the examination and search procedure be helpful.  

Contents of the drawings

Fig. 1 Structure of a solar desalination plant

Fig. 2 Structure of the mirror system

Fig. 3 section of the wall from east to west

Fig. 4 solar collector

Fig. 5 double-wall sheet profile

Fig. 6 web double plate connection

Fig. 7 water storage

Fig. 8 memory detail with water distributor

Fig. 9 evaporator and condenser

Claims (21)

1. Apparatus for distilling water at temperatures below 100 ° C, preferably used for the desalination of sea and brackish water in water-poor, therefore sunny climate zones, characterized in that the apparatus consists entirely of radiation energy converters and energy collectors, (solar collectors) energy storage, flat evaporators, flat plate heat exchangers and piping, which are made of food-safe plastics, preferably polypropylene. 2. Apparatus according to claim 1, characterized in that the Apparatus to several lined up a wall results in Set up north-south, using mirrors with solar energy is supplied. 3. Apparatus according to claim 1 and 2, characterized in that the Mirrors are made of mirrored foils that vary depending on Position of the sun over pulleys the sun's rays on the wall distribute, the mirror surface being many times larger Energy conversion area is. 4. Apparatus according to claim 1 to 3, characterized in that the longitudinal walls on both sides made of vertical solar collectors exist, the mode of operation of the thermosiphon system corresponds.   5. Apparatus according to claim 1 to 4, characterized in that the thermosiphon system by the arrangement of the memory in the upper part arises, in the highest place, the Open the absorber plates directly. 6. Apparatus according to claim 1 to 5, characterized in that the absorbers consist of double-wall sheets, below in the memory are opened with a slot, whereby the flow direction of the Water is changed when the one irradiated by the sun Area changes. 7. Apparatus according to claim 1 to 6, characterized in that the Illumination of the solar collectors by parabolic mirror channels takes place, which run in north-south direction and at the angle of attack are adjustable. 8. Apparatus according to claim 1 to 7, characterized in that the foils made of mirrored plastics, in the angles of attack, Sun against the wall, with shrouds, pods and taljen are to be adjusted so that they make optimal use of solar energy cause. 9. Apparatus according to claim 1 to 8, characterized in that Housing, absorber, connecting pipes, heat exchangers, evaporator mats and gutters made of polypropylene and therefore neither calcify nor corrode. 10. Apparatus according to claim 1 to 9, characterized in that the Units that are largely automatically produced can be assembled later at the operator location.   11. Apparatus according to claim 1 to 10, characterized in that the wall in the morning on the east side and in the afternoon on the West side is illuminated, making the energy yield optimal becomes. 12. Apparatus according to claim 1 to 11, characterized in that the construction of the wall in the order, outside the solar panels, then the evaporators and in the middle the heat exchangers, which eliminates the need for rear insulation on the collector, thereby direct energy use. 13. Apparatus according to claim 1 to 12, characterized in that a thermostatic valve is sufficient to control the system if the water level of the reservoir is higher. 14. Apparatus according to claim 1 to 13, characterized in that the water distribution in the sprinkling mat by one Sponge takes place, the water only with a slight overpressure lets through. 15. Apparatus according to claim 1 to 14, characterized in that the sponge is housed in a tube, the wall of which is provided with a slot or holes, the route of which one avoids direct contact with the flow mats. 16. Apparatus according to claim 1 to 15, characterized in that the water to evaporate over a flow mat, which is Layers are layered, sprinkled.   17. Apparatus according to claim 1 to 16, characterized in that through unobstructed straight channels, next to the Z-shaped mats Laminar air circulation in the evaporator and in the heat exchanger supports the natural air circulation. 18. Apparatus according to claim 1 to 17, characterized in that through partitions and opening windows, before and after the separation, any number of air circuits arise, though the watercourse is not changed. 19. Apparatus according to claim 1 to 18, characterized in that a multi-stage evaporation system by setting up several air circuits that arises in heat recovery Performance increases to the single-stage system. 20. Apparatus according to claim 1 to 19, characterized in that alternatively, the evaporators with the condensers do not pass through a middle wall are separated and thus a direct mass transfer takes place. 21. Apparatus according to claim 1 to 19, characterized in that the fittings are made in a tube that is twisted Storage can be a stratified storage.