IL81876A

IL81876A - Method and apparatus for watering the ground

Info

Publication number: IL81876A
Application number: IL8187687A
Authority: IL
Original assignee: Japan Gore Tex Inc
Priority date: 1986-03-27
Filing date: 1987-03-12
Publication date: 1995-06-29
Also published as: IL81876A0; DE3776581D1; DE3610548C2; EP0238941B1; ES2028809T3; JPH082221B2; EP0238941A1; JPS62236429A; DE3610548A1

Description

81876/2 METHOD AND APPARATUS FOR WATERING THE GROUND JAPAN GORE -TEX INC.

Mgthod_§nd_aEEa£-itUf3_ o£_Hgt EiDg_thg_QlQUD The invention relates to a method of watering dry ground with freshwater obtained from saltwater, wherein the saltwater is led through vapor-permeable pipes laid in the ground to be watered which give off free water vapor at their outer sides. Furthermore, the invention is concerned with a watering system in accordance with this method .

The watering of dry and salty ground plays a large role in arid and semi-arid hot countries because these types of ground are mainly fertile and can serve for the production of foodstuffs. Freshwater is often not procurable or too costly for watering. Accordingly there is an interest in making the seawater which is available in any desired quantity in many hot countries, in particular of islands or in the costal regions, usable for irrigation purposes,. Salty groundwater or brackish •water (seawater mixed with river water) is frequently also present. Water rich in salt can however only be used for irrigation purposes if it is first converted into freshwater, for example by distillation. Irrigation with saltwater would lead to severe damage to the plants and to the ground becoming salty (infertile) . 1 81876/2 In a known method of obtaining freshwater from seawater for the irrigation of cultured plants which grow in arid zones in spaces surrounded by light-permeable walls (DE-AS 16 32 943) provision is made for vaporising the. saltwater which is guided in a circuit within these spacesr partly by solar radiation or the action of heat, for capturing the condensate and for passing it to the cultured plants to be watered. The disadvantage of this known method is the fact that it can only be carried out in closed spaces which signifies a considerable constructional expense and precludes the irrigation of large area plantations.

Furthermore, a method of obtaining freshwater from seawater for the watering of agricultural plantations is already known (German patent 27 53 311) wherein the seawater which is led in a circuit is vaporised by the effects of heat, is condensed in the same pipe system and is then fed to the earth in liquid form. This known method has first of all the disadvantage that double-walled pipes are necessary which are lined with various materials and provided with openings, with the pipes being expensive and susceptible to breakdown, and secondly the disadvantage that in these known systems the pipes must be exactly levelled.

German Patent No. 3409510 describes a certain type of-a conduit which has a water-permeable upper portion, and a water- impermeab le lower portion. The conduit is embedded underground. Salt water is made to low in the lower portion of the conduit. Vapor which evaporates is absorbed by soil. However, a hydrophobic micro-porous membrane is not used.

USP 3,528,251 discloses a hollow body having pores (perforations) through which water vapor passes into the soil adjacent to the hollow body while preventing penetration of the unevaporated water into the surrounding soil.

However, this hollow body is not made of a hydrophobic microporous material or membrane and the wall of the hollow body prevents vapor and water solution from passing through in most portions but allows vapor and water solution to pass through in some portions. The wall structure is essentially different from that of the hydrophobic microporous material. Particularly, both water vapor and solution can pass through pores (not micropores) formed in the wall of a hollow body.

Moreover, the penetration of water solution into the surrounding soil is prevented by arranging the pores only in the upper portion of the hollow body' and partially filling the follow body with water, i.e., the water level does not come up to the level of' the pores. The penetration of water solution is prevented by controlling the amount of water solution flowing in the hollow body.

Furthermore, the interior of the hollow body can not be filled with heated salt water and the size of the penetrations of the hollow body is much larger than a micron order, more than several millimeters.

The object of the present invention is in contrast to provide a method and an apparatus for moistening dry ground with freshwater obtained from saltwater which does not require any complicated distillation systems or distillation systems which require a lot of space, are expensive to install and consume a lot of - 2b - 81876/. energy, and which permits extensive loss-free watering even of large area regions with a low energy requirement, with the intention that watering of non-flat terrain should in particular also be possible. 3 1 In order to satisfy this object the invention provides a method which is characterised in that the pipes or areal hollow structures consist of hydrophobic, microporous 5 material; and in that the salt water is sent through the pipe or through the areal hollow structure with a temperature elevated relative to the temperature of the earth surrounding the pipe or areal structure such that a notable quantity of vapor passes from the inside to 10 the outside through the wall of the pipe and condenses in the surrounding earth.

The invention makes use here of the membrane hoses known for distillation purposes which operate in accordance *5 with the principle of cross-membrane distillation (in German Transmembran-Distillation) . The basic thought of the invention is thus to be seen in the fact that no special distillation apparatus is provided which first makes freshwater from saltwater, with the freshwater 20 then being supplied to the plantations to be watered. Instead, on the contrary, the earth surrounding the pipes or areal hollow structures is incorporated into the distillation system, in that the condensation of the water vapor which emerges outwardly through the pipes or 25 hollow structures first takes place within the earth. In this way the freshwater required for watering of the plant roots is generated in situ so that no freshwater losses occur during transport, due to seepage into the ground, or reverse flow in the pipes as occurs in the ° method of German patent 27 53 311.

No gas phase is formed, within the pipes or areal hollow structures of the invention. The pipes and hollow structures are completely filled with the saltwater, in 5 particular seawater. The vapor phase occurs at the inner entry, as seen radially, into the microporous walls of the pipes or areal hollow structures and extends in a 4 radial direction up to the regions of the earth where the condensation temperature is reached.

Decisive for the manner of operation of the method of the invention is thus the presence of a specific temperature difference between the inner region of the pipes and the condensation zone in the earth.

The special advantage of the method of the invention thus lies in the fact that the watering not only takes place with freshwater but rather indeed with distilled water.

For ground with high pH values, which can be brought about by sodium or calcium carbonates a significant reduction of the pH value and also a washing-out of the salt occurs as a result of the use of the method of the invention. Moreover, bacteria are prevented from emerging from the interior of the pipe through the microporous pipes or areal hollow structures. It is thus impossible for plant diseases for example to be propagated via the pipe system used for watering.

As heat is generated in the earth on condensation of the water vapor emerging through the pipes or hollow structures, and as a temperature balance gradually takes place between the saltwater and the earth, the invention envisages, in accordance with a preferred embodiment, that the pipe or the areal hollow structure is flowed through by saltwater heated to a predetermined temperature only for a certain time until the temperature difference between the saltwater located in the pipe or areal hollow structure and the ground has been reduced by condensation. During a subsequent rest period the pipe system and the surrounding ground cool down, so that during a renewed throughflow phase the required temperature difference is again present. The 5 time spacing between the two phases depends on the temperature conditions and thermal conductivity values of the system.

A particular advantage of the method of the invention lies in the comparatively small degree of expense and complexity of the apparatus and in the low pump power that is required, the opportunity is thus presented of operating this system as a whole by solar energy.

As the solar energy is only available during the day, whereas the ground to be watered reaches the lowest temperature at night, the method of the invention is made particularly efficient if the saltwater which is heated during. the day by solar energy is stored in an insulated supply vessel; and if the introduction of the heated saltwater into the pipes or the areal hollow structures takes place during the night hours, preferably close to morning, when the earth surrounding the pipes or areal hollow structures has reached the lowest temperature of the day-night cycle.

Sufficient condensation speed can be achieved in the earth when the temperature difference between the saltwater which is supplied and the earth amounts to at least 3°C and preferably 20 to 30°C.

The preferred watering apparatus for carrying out the method of the invention is characterised in that microporous hydrophobic pipes or areal hollow structures are laid in the region of the roots of the plants to be watered or directly below them, substantially parallel to the surface of the ground and are connected to saltwater supply and discharge lines which are preferably thermally insulated. 6 Provision is preferably made for the pipes or areal hollow structures to be laid at a depth from 10 to 50 cm and preferably of approximately 30 cm. In selecting the correct depth of the pipe networks the growth of the roots of the plants to be watered must be taken into account on the one hand, and on the other hand, the fact that the pipe system located in the ground must not be damaged during ground preparation by means of a plough or other agricultural apparatus.

Full area-watering can be achieved when the pipes are laid parallel to one another at the spacing of the plants so that the watering of each row of plants is ensured.

In a further embodiment the pipes are laid in ring-like manner in the root regions of the plants, for example bushes or trees. In so far as one is using an areal hollow structure the construction should be such, in accordance with the invention, that the areal hollow structure only consists of hydrophobic icroporous material at the top and is closed at the bottom by an impermeable foil. In this way one ensures that water vapor only emerges in the direction towards the root area. When using an areal hollow structure attention must be paid to it having the characteristic stiffness required to accommodate the ground pressures. This can optionally be achieved by inbuilt stiffening structures. In practice the pipe or the areal hollow structures can consist of microporous polypropelene, PVDF, PTFE or the like.

It is particularly advantageous if water-impermeable foils are laid beneath the pipes or areal hollow structures. With this arrangement it is particular expedient for the foils to be laid at a distance from 10 to 50 cm and in particular approximately 30 cm beneath 7 , the pipes. This construction prevents freshwater which may eventually be formed in excess sinking into deeper ground regions. On the other hand, the rising of salt-rich groundwater which may eventually be present is effectively avoided.

If necessary the surface of the ground can also be covered in accordance with the invention with a foil which has openings for the emergence of the plants.

The two-phase watering of the invention can preferably be effected so that the total pipe network is subdivided into various watering regions with only one watering section being supplied with heated saltwater at a particular time. The cyclic change-over to the remaining watering sections then takes place subsequently.

The saltwater fed through the pipes or hollow structures of the invention can be fed back in a circuit to the input of the pipe network when it is not too concentrated or, for example, discharged back into the sea .

The invention will now be described in the following by way of example and with reference to the drawings which show: Fig. 1 a very schematic illustration of the principle of a watering apparatus in accordance with the invention, Fig. 2 a plan view of a pipe system laid in the ground of a watering apparatus in accordance with the invention, Fig. 3 a section on the line III-III of Fig. 2 to an enlarged scale. 8 Fig. 4 a schematic perspective view of a pipe system of a watering apparatus in accordance with the invention for the watering of trees, and Fig. 5 a schematic perspective view of an areal hollow structure used for the watering apparatus of the invention.

As seen in Fig. 1 saltwater 12 is sucked by means of a suction pump 15 through a suction duct 23 which opens into the saltwater 12 of a sea 22 and is pumped through a solar collector 24 into a thermally insulated supply container 14. The solar collector 24 is heated by solar radiation indicated by arrows and heats the saltwater 12 which flows through it to a temperature between 40 and 80°C.

The pump 15 is driven by an electric motor 25 which is supplied with electrical energy by photoelectric solar elements 26 which likewise receive the solar radiation indicated by arrows. The electrical energy generated by the solar elements 26 is also used to charge accumulators 27 which are housed with the other parts of the full installation in a building 38.

While the heated saltwater 12 is introduced at the top into the supply container 14 an extraction «duc't 28 is located in the lower region of the supply container 14 which is connected via a valve 29 which can be selectively opened or shut, and via a pressure pump 15' driven by an electric motor 33, to a change-over distribution valve 10. The change-over distribution valve 10 has two outputs each of which is connected to a saltwater supply duct 19 laid in the earth 13, which is also shown in Fig. 2. 9 Microporous hydrophobic pipes 11 having a length of 1 to 2 m branch off from the saltwater supply conduit 19 laid parallel to the earth's surface 17 (Fig. 3)r at intervals of 1 to 2 m perpendicular to its longitudinal axis, and open into a saltwater discharge line 20 laid in the earth 13 parallel to the saltwater supply line 19. The lines 19, 20 should be thermally insulated.

A return conduit 30 is in each case connected to the end of the saltwater discharge conduit 20 remote from the supply side of the saltwater supply conduit 19, and is led via a valve 31 back to the supply container 14. A discharge conduit 32 which is only indicated in broken lines and which leads back into the sea 22 branches off from the valve 31.

The electric motor 33 which drives the pump 15' is connected via an electric cable 34, which is only indicated in broken lines, to the accumulators 27.

The ideal depth arrangement of the microporous hydrophobic pipes 11 can be seen from Fig. 3. The pipes 11 are laid either in the region of the roots 18 of a plant 16 set into the surface 17 of the earth or directly below the region of the roots 18.

At a distance of 10 to 20 cm beneath the pipes 11 the earth 13 is sealed off downwardly and upwardly by a water-impermeable foil 37.

The manner of operation of the described watering apparatus is as follows: During the hours of daylight the pump 15 continuously feeds saltwater 12 into the solar collector 24 from which it passes into the supply container 14 after being 10 heated to 40 to 80°C until the latter is completely filled.

At the same time the accumulators 27 are charged up via the solar elements 26. ^ During the hours of night the valve29 is open so that the saltwater 12 can enter, depending on the position of the change-over distribution valve 10, from the supply container 14 into the microporous hydrophobic pipes 11 of the one or other watering section or bed 8 or 9.

During this operation the water continuously evaporates due to its higher temperature relative to the temperature of the earth 13, and enters into the earth 13 as water vapor through the walls of the pipe 11, which is indicated in Figs. 1 and 3 by arrows. In the colder earth 13 the water vapor condenses so that distilled water is produced which is taken up by the roots 18 of the plants 16.

The saltwater forced by the pump 15* driven by the accumulators 27 through the pipes 11 is led, depending on the position of the valve 31, either back into the container or back into the sea 22, depending on the concentration of the saltwater. The illustration in Fig. 1 is to be understood purely schematically. A special supply container is advantageously provided for the returned concentrated saltwater from which the (now cooled) concentrated water can likewise be pumped during the day through a solar connector into the supply container which is available for the watering during the next night. In Fig. 1 only two beds 8, 9 are shown. In actual fact a large number of beds will be cyclically watered one after the other using one plant, for which purpose the change-over distribution valve 10 has correspondingly many switch positions. 11 The temperature of the warm saltwater stored in the supply vessel 14 should amount to at least 40°C. A higher temperature of for example 70 to 80°C can be considered when the pipes 11 are laid so deeply below the plant 16 that plant damaging heating of the roots 18 need not be feared.

Fig. 4 shows how larger plants can also be watered by laying the pipes 11 in ring-like manner around trees 16·.

As seen in Fig. 5 an areal (two-dimensional) hollow structure 11' is laid in the earth in place of the pipes 11 with the lower side of the hollow structure 11* consisting of a vapor and water-impermeable foil 21, while the upper side consists of a microporous hydrophobic material through which the water vapor formed from the saltwater 12 can pass. In order to prevent the areal hollow structure being compressed by the ground pressure, webs 35 are provided in its interior which ensure an adequate hollow space for the passage of the saltwater. The webs can either be arranged only in intervals or can have bores 36 for the transverse passage of the saltwater.

The operation of the watering apparatus during the night preferably takes place discontinuously in the sense that the pipes 11 or the hollow structures 11' of one portion (for example 8, 9) are flowed through by heated saltwater until the temperature difference between the saltwater and the earth has reached a predetermined value of for example 5°C. The change-over distribution valve 10 is then switched over to another watering section where the earth 13 still has a low temperature, or has again reached a low temperature which ensures the required temperature gradient.

With the described method a certain automatic control takes place in that on heating up of the earth by the heat of condensation the passage of vapor through the wall of the pipes 11 or the hollow structures II1 is reduced which in turn reduces the generation of heat of condensation. The temperature difference between the saltwater 12 and the earth 13 thus again increases and once again vapor can pass in larger quantities through the walls of the pipes 11 or hollow structures 11'.

The watering system of the invention can also be particularly advantageously used on slopes because the freshwater in the region around the pipes 11 or hollow structures 11' is first only present in vapor form so that problems of increasing hydrostatic pressure in the lower region of the slopes does not occur.

The surface of the earth can, in accordance with the invention optionally also be covered with a foil which has openings for the emergence of the plants 16.

The porous pipes 11 can optionally be surrounded by a liquid-permeable, coarse-pored mechanical protective sheath 7. - 13 - 8187(

Claims

1. Method for underground watering of plants by means of salt water by arranging a water solution-impermeable, hollow body comprising a hydrophobic, microporous vapor- permeable, water solution-impermeable membrane, underground and totally filling the interior thereof with heated salt water.

2. Method according to claim 1, characterised in that the hollow body is a tube. i

3. Method according to claim 1, characterised in that the hollow body is a flat hollow structure.

4. Method according to claim 3 , characterised in that the flat hollow structure consists of the microporous hydrophobic membrane only at its top and is closed by an impermeable sheet at its bottom.

5. Method according to any one of claims 1 to 4, characterised in that the hollow body is disposed at a depth of 10 to 50 cm, preferably about 30 cm, in the ground.

6. Method according to any of claims 1 to 5, characterised in that water impermeable sheets are disposed at a vertical distance below the hollow body.

7. Method according to any of claims 1 to 6, characterised in that the hollow body is surrounded by a coarsely porous mechanical protective cover.

8. Method according to any of claims 1 to 6, characterised in that the hollow body comprises microporous polypropy- J lene, polyvinylidefluoride or polytetrafluoroethylene. Dt. Yitzhak Hess