Process and system for recovering water from the atmosphere

• US 4,146,372 A
• Filed: 03/28/1977
• Issued: 03/27/1979
• Est. Priority Date: 03/29/1976
• Status: Expired due to Term

• Current Assignee: Mittex AG
• Original Assignee: Mittex AG
• Inventors: Hussmann, Peter, Groth, Wilhelm
• Primary Examiner(s): Spitzer, Robert H.
• Application Number:
  US05/781,890
• Time in Patent Office: 729 Days
• Field of Search: 55/31, 55/33, 55/74, 55/80, 55/208, 55/316, 55/387, 165/10, 203/41, 203/49, 203/DIG. 1
• US Class Current: 95/124
• CPC Class Codes: B01D 53/26 Drying gases or vapours
• CPC Class Codes: C02F 1/18 Transportable devices to obtain potable water
• CPC Class Codes: E03B 3/28 from humid air condensing of vapours in general B01D5/00; dehumidification of air for air-conditioning F24F3/14
• CPC Class Codes: Y02A 20/124 Water desalination

Abstract

Water is recovered from air by a process utilizing the differences in the day-time and night temperatures of such air. The process is especially useful in subtropical desert areas. It consists in alternately removing the moisture from the cool night air by adsorption on suitable adsorbing agents and especially on silica gel and by utilizing the hot day-time air and, if desired and available, the radiation energy of the sun for desorption of the water stored in the adsorbing agent and for condensing the desorbed water by means of the cold stored during the night. An especially suitable silica gel is used for adsorption of the water contained in the air. The energy required for operating the plant is produced by passing the recovered water through energy producing installations such as turbines before it is used as drinking water or for irrigation. The process is very economical and, in contrast to seawater desalination processes, does not require additional thermal energy.

Claims

1. A process for recovering water from air, comprising the steps of passing night air at a relatively low first temperature of up to about 20°

C. first through a layer of a substantially non-adsorbing heat sink material of relatively high heat capacity so as to cool said non-adsorbing material to substantially said first temperature;

thereafter passing the night air through a layer of coarsely granulated, shaped, moisture adsorbent material so as to adsorb the moisture content of the night air;

passing ambient day-time air at a second temperature of from about 25°

C. to about 70°

C., which is sufficiently high to displace moisture from the adsorbing material, and at ambient pressure in reverse direction through the layer of adsorbent material having adsorbed thereon the moisture content of the night air, whereby the water adsorbed in the adsorbent layer is at least substantially removed therefrom by said ambient day-time air at ambient pressure;

thereafter passing the moisture-containing day-time air through the layer of cooled, non-adsorbing material and condensing the water removed from the adsorbent layer on the cooled, non-adsorbent material; and

recovering the condensed water from the non-adsorbent material.

2. The process according to claim 1, in which the adsorbent material is a coarsely grained, shaped silica gel particles.

3. The process of claim 2, in which the nonadsorbent materials are stones.

4. The process according to claim 2, in which the silica gel particles are spherically shaped and have a diameter of between about 8 mm and 12 mm.

5. The process according to claim 2, in which the substantially non-adsorbing material comprises substantially non-porous stone material of a high specific weight, the particles of said stone material having a diameter between 100 mm. and 200 mm.

6. The process according to claim 2, wherein said steps of passing air comprise supplying a plurality of individual air streams, by means of a plurality of air supplying means arranged side by side, at a low air velocity.

7. The process according to claim 6, further comprising the step of producing energy by transporting water recovered in said recovery step to a lower elevation.

8. The process according to claim 7, further comprising the step of using said energy for operating said air supplying means.

9. The process according to claim 8, wherein said first temperature is from about 5°

C. to 15°

C. and said second temperature is from about 30°

C. to 60°

C.

10. The process according to claim 2, in which the steps of passing night air are conducted for about 10 hours, followed each time by a rest period of about 2 hours, and said steps of passing day-time air in the opposite direction are conducted for about 10 hours, followed each time by a rest period of about 2 hours.

11. The process according to claim 2, in which the substantially non-adsorbing material comprises natural stone material of a diameter of 100 mm. to 200 mm., said natural stone material being covered by a thin silicone coating.

12. The process according to claim 2, further comprising the step of applying solar radiation to said silica gel during said step of passing ambient daytime air through said layer of silica, whereby the temperature of said ambient air can be raised from about 10°

to 13°

C. to accelerate removal of the adsorbed moisture.

13. The process according to claim 2, in which said moisture adsorbing material comprises a silica gel which permits water adsorption up to 20°

C. and water desorption within the temperature range of about 25°

C. to 70°

C.

14. The process according to claim 2, wherein said silica gel comprises a silicon dioxide content between about 16% and about 24%, a pore diameter of between about 40 and about 50 Angstroem, a wetting heat of between about 15 and about 18 cal./g., a bulk weight between about 460 and about 520 g./cm.³, an adsorption temperature of up to about 40°

C. and a desorption temperature of between about 50°

C. and about 70°

C., and wherein said second temperature is between about 50°

C. and about 70°

C.

15. The process according to claim 2, wherein said silica gel comprises silicon dioxide content between about 16% and about 24%, a pore diameter of between about 50 and about 60 Angstroem, a wetting heat of between about 12 and about 15 cal./g., a bulk weight between about 300 and about 460 g./cm.³, an adsorption temperature of up to about 30°

C. and a desorption temperature of between about 40°

C. and about 60°

C., and wherein said second temperature is between about 40°

C. and about 60°

C.

16. The process according to claim 2, wherein said silica gel comprises silicon dioxide content between about 16% and about 24%, a pore diameter of between about 60 and about 70 Angstroem, a wetting heat of between about 10 and about 12 cal./g., a bulk weight between about 250 and about 350 g./cm.³, an adsorption temperature of up to about 20°

C. and a desorption temperature of between about 30°

C. and about 50°

C., and wherein said second temperature is between about 30°

C. and about 50°

C.

17. The process according to claim 16, wherein said silica gel is further characterized by the ability to adsorb up to 80% of its weight of water at a temperature between about 0°

C. and about 20°

C. and by a desorption effectiveness of from about 95% to about 98% at a temperature between about 50°

C. and about 55°

C.

18. The process according to claim 2, wherein said silica gel comprises a silicon dioxide content between about 16% and about 24%, a pore diameter between about 40 and 70 Angstroem, a wetting heat of between about 10 and 18 cal./g. a bulk weight between about 250 and 420 g./cm.³, an adsorption temperature of up to about 40°

C. and a desorption temperature between about 30° and

70°

C., said silica gel having been produced by a process comprising the steps of precipitating a silicic acid-containing starting material and acid reactant to first form an unstable silicic acid containing sol as an intermediate product, subsequently gelling the sol, washing the gel to remove the salts, and drying the gel, wherein the improvements comprise carrying out the precipitation process in two steps, wherein in the first step a first silicic acid-containing starting material with a silicon dioxide content between about 20% and about 32% by weight is introduced in such a fine distribution and at such a high discharge velocity into the acid reactant, while being subjected to high speed agitation, until a pH-value of the acid reactant between about 1.5 and about 1.8 is attained, that instantaneous reaction between the acid and the silicic acid-containing starting material takes place without any precipitation of silicic acid, and wherein in the second precipitation step a second silicic acid-containing starting material having a silicon dioxide content between about 8% and about 14% by weight is introduced into the acid reactant until a pH-value of between about 2.6 and about 3.5 is attained, thereby producing a sol having a silicon dioxide content of about 14% to about 18% by weight, and carrying out the washing step by washing with a washing liquid of a pH between about 7 and about 12.

19. The process according to claim 2, wherein said night air is passed through a plurality of layers of silica gel particles, the particles in each layer having a pore size different from the particles in the other layers, and wherein said day-time air is passed through the same plurality of layers in the direction opposite to the direction in which the night air is passed through said layers.

20. The process according to claim 19, wherein said plurality of layers are arranged in order to increasing values of adsorption temperature in the direction of night air flow.

21. The process according to claim 2, further comprising the step of passing said day-time air through a solar-powered heating device prior to passing the daytime air through the layer of silica gel.

22. The process according to claim 2, wherein the step of displacing moisture from said silica gel consists essentially of passing said ambient day-time air through the layer of the silica gel particles.

23. A system for recovering water from air by adsorption during the night and desorption during the day-time, said system comprising a structural unit having an air penetrable intermediate bottom, at least one layer of a substantially non-adsorbing heat sink material having a high heat capacity placed on said bottom, a layer of an adsorbent material being provided on top of said non-adsorbing layer said adsorbent material being capable of adsorbing moisture at a temperature up to about 20°

C. at ambient pressure and being capable of desorbing moisture at a temperature between about 25°

C. and about 70°

C., first means for passing night air at a relatively low first temperature into said structural unit and through said layer of heat sink material and through said layer of absorbent material, respectively, second means for passing ambient daytime air at a second temperature higher than said first temperature and sufficient to cause desorption of water from said adsorbent material into said structural unit and through said layer of adsorbent material and through said layer of heat sink material, respectively, and means associated with said layer of heat sink material for recovery therefrom water which has condensed out of said day-time air.

24. The system according to claim 23, in which the construction unit has a width between 100 m. and 200 m. and a length up to 15 km.

25. The system according to claim 23, in which the non-adsorbing material is in the form of shaped concrete spheres or natural stones of a high specific density and a low porosity, the particles of said non-adsorbing material having a diameter between 100 mm. and 200 mm.

26. The system according to claim 23, in which the non-adsorbing material is substantially non-porous and consists of natural stones selected from the group consisting of basalt and silicate stones, said stones being provided with a thin silicone coating to close any pores therein.

27. The system according to claim 23, further comprising an upper roofing on said structural unit comprising a roof permeable to the rays of the sun, whereby the temperature of the day-time air passing through the adsorbent material layer is increased by solar radiation.

28. The system according to claim 27, in which the roof permeable to the rays of the sun comprises a material selected from the group consisting of glass, polyacrylic plastic, and polyester.

29. The system according to claim 23, in which the structural unit consists of a plurality of separate building elements of like construction being arranged so as to provide passages between said building elements.

30. The system according to claim 23, further comprising a web of a filter fabric pivotally provided underneath the intermediate bottom carrying the non-adsorbing material layer, and a plurality of brushing devices with rotating brushes capable of being raised or lowered and travelling along said web of filter fabric provided in operative relationship underneath said web.

31. The system according to claim 23, wherein said second air passing means comprises openings for admitting air into the space above the adsorbent material layer, filters pivotably connected over said openings and air supplying means arranged behind said filters.

32. The system according to claim 31, wherein said first air passing means comprises a plurality of low-speed blowers located below said heat sink layer and said second air passing means comprises a plurality of low-speed blowers located above said layer of adsorbent.

33. The system according to claim 31, further comprising means for transporting water from said heat sink layer to a position at least 200 m. lower in altitude and means located at said lower position for converting the water pressure head into energy.

34. The system according to claim 33, further comprising means for supplying said blowers with energy produced by said conversion means.

35. The system according to claim 34, wherein said conversion means is the sole source of mechanically-produced energy in said system.

36. The system according to claim 23, wherein the absorbent is a coarsely grained, shaped silca gel.

37. The system according to claim 36, wherein said silica gel comprises generally spherically shaped particles having a diameter between about 8 mm and 12 mm.

38. The system according to claim 37, wherein said silica gel comprises silicon dioxide content between about 16% and about 24%, a pore diameter of between about 40 and about 50 Angstroem, a wetting heat of between about 15 and about 18 cal./g., a bulk weight between about 460 and about 520 g./cm.³, an adsorption temperature of up to about 40°

and a desorption temperature of between about 50°

C. and about 70°

C.

39. The system according to claim 37, wherein said silica gel comprises silicon dioxide content between about 16% and about 24%, a pore diameter of between about 50 and about 60 Angstroem, a wetting heat of between about 12 and about 15 cal./g., a bulk weight between about 300 and about 460 g./cm.³, an adsorption temperature of up to about 30°

and a desorption temperature of between about 40°

C. and about 60°

C.

40. The system according to claim 37, wherein said silica gel comprises a silicon dioxide content between about 16% and about 24%, a pore diameter of between about 60 and about 70 Angstroem, a wetting heat of between about 10 and about 12 cal./g., a bulk weight between about 250 and about 350 g./cm.³, an adsorption temperature of up to about 20°

and a desorption temperature of between about 30°

C. and about 50°

C.

41. The system according to claim 40, wherein said silica gel is further characterized by the ability to adsorb up to 80% of its weight of water at a temperature between about 0°

C. and about 20°

C. and by a desorption effectiveness of from about 95% to about 98% at a temperature between about 50°

C. and about 55°

C.

42. The system according to claim 37, wherein said silica gel comprises a silicon dioxide content between about 16% and about 24%, a pore diameter between about 40 and 70 Angstroem, a wetting heat of between about 10 and 18 cal./g. a bulk weight between about 250 and 420 g./cm.³, an adsorption temperature of up to about 40°

C. and a desorption temperature between about 30° and

70°

C., said silica gel having been produced by a process comprising the steps of precipitating a silicic acid containing starting material and acid reactant to first form an unstable silicic acid containing sol as an intermediate product, subsequently gelling the sol, washing the gel to remove the salts, and drying the gel, wherein the improvements comprise carrying out the precipitation process in two steps, wherein in the first step a first silicic acid-containing starting material with a silicon dioxide content between about 20% and about 32% by weight is introduced in such a fine distribution and at such a high discharge velocity into the acid reactant, while being subjected to high speed agitation, until a pH-value of the acid reactant between about 1.5 and about 1.8 is attained, that instantaneous reaction between the acid and the silicic acid-containing starting material takes place without any precipitation of silicic acid, and wherein in the second precipitation step a second silicic acid-containing starting material having a silicon dioxide content between about 8% and about 14% by weight is introduced into the acid reactant until a pH-value of between about 2.6 and about 3.5 is attained, thereby producing a sol having a silicon dioxide content of about 14% to about 18% by weight, and carrying out the washing step by washing with a washing liquid of a pH between about 7 and about 12.

43. The system according to claim 36, comprising a plurality of layers of silica gel particles, the particles in each layer having a pore size different from the particles in the other layers.

44. The system according to claim 43, wherein said layers of silica gel are arranged in order of increasing values of adsorption temperature from the lowermost layer to the uppermost layer.