ABSTRACT
Abstract
A process and an apparatus for obtaining pure water from seawater, comprising: a) a raw water is provided that comprises at least one non-volatile component (salt), b) the raw water provided is passed as cooling medium into a heat ex-changer, c) additional heat is supplied to the raw water that is heated in the heat exchanger, d) the raw water from step c) is fed to an evaporation zone, e) a carrier gas suitable for water vapour is provided (air), f) the carrier gas is brought into contact with the raw water in counter current flow in the evaporation zone which contains baffles, wherein the carrier gas takes up water vapour from the raw water, g) the raw water that is obtained in step f) that is enriched with the at least one non-volatile component is taken off from the evaporation zone, h) the water vapour- loaded carrier gas from the evaporation zone is fed to the heat exchanger and is cooled in counter current flow to the raw water, wherein the water vapour present in the carrier gas partially condenses out, i) the carrier gas depleted in water vapour is passed out of the heat exchanger, k) the condensed water vapour is taken off from the heat exchanger as pure water, wherein the evaporation zone is operated substantially adiabatically, and wherein the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
Description
The present invention relates to a water treatment process in which pure water is separated off from raw water that comprises non-volatile unwanted components. The present invention relates in particular to a continuous process for obtaining freshwater from salt water and also to an apparatus for continuously obtaining freshwater from salt water.
Water treatment denotes the targeted modification of water quality. This includes in principle two groups of treatment: removing substances from water (e.g. desalting, removal of iron, softening, sterilization or other purification), on the one hand, and also supplementation of substances and setting parameters of the water (e.g. addition of dissolved ions, setting the pH and/or the conductivity) on the other. Water treatment in this case generally serves for obtaining drinking water or service water (today frequently termed process water). Also, desalted or demineralized water is particularly useful for watering plants. Water treatment for generating drinking water acts to meet legal provisions and provisions of standards (e.g. the German drinking water regulation, DIN 2000). Service water is required in large amounts, for example for power stations (as cooling water and feed water), industrial plants, chemical processes, pharmacy, laundries etc. Frequently, very substantial modifications of the water properties are required in water treatment for generating service water and especially diverse process waters.
A special process for water treatment is water desalination. Desalination of salt water designates obtaining service water or drinking water from salt water, especially from seawater, by reducing the salt content. In particular seawater desalination will become of great importance in the future since the supply of all people with clean water will become ever more difficult owing to lack of or pollution of the existing freshwater. The desalination of seawater is used on ships, submarines, islands and in arid coastal countries. Salt water in this case must have only low contamination. In the oil-rich Gulf States, seawater desalination is the main source of obtaining drinking water. Here the drinking water is obtained in gas- or oil-fired desalination plants. In the near East, also, this energy-intensive form of obtaining drinking water is widespread. Combined-cycle gas- and steam-turbine power plants having an attached multistage flash (MSF) evaporation desalination plant are likewise frequently used. On the Canary Islands and the German deep-sea island Helgoland, drinking water is obtained from salt water by the reverse osmosis process.
Membrane processes such as, e.g., reverse osmosis are established processes of water desalination. Of all of the known processes they theoretically require the lowest specific separation energy and the membranes can be produced very inexpensively even today. However, completely deionized water cannot be produced thereby, since some salt always also permeates the membranes. The membranes are in addition both mechanically and chemically sensitive, and so the salt water used must be pretreated. The pretreatment expenditure can exceed the actual separation expenditure. In addition, the membranes have only a limited lifetime. Although the specific separation expenditure is low, a high level of mechanical energy is required for pumping the water.
The efficiency of generation of this energy from primary energy such as, e.g., solar energy, is low, generally in total less than 20%.
Multiple-effect evaporation processes (also referred to as MEV processes) or multistage flash processes (also referred to as MSF processes) are now the most widespread processes for producing freshwater from salt water. MEV and MSF can also be operated using waste heat at below 100° C. and achieve a comparatively high energy utilization factor. The high energy efficiency is achieved by the multistage operation. Each stage, however, is a separate unit having evaporator and condenser and is operated at a separate pressure level. In the MEV process, the brine vaporizes on the evaporator surface. In this process local oversaturation of the brine occurs and salt precipitates out. The evaporator surface can become encrusted by this scaling as it is called. In the MSF process, scaling is avoided by complex forced circulation evaporation. For this purpose each evaporator stage requires a separate, sometimes very large, pump, which must circulate about 10 times the amount of brine by pumping in relation to the amount of freshwater vaporized. This process therefore requires a comparatively very high mechanical energy.
The dewvaporation process is a multistage evaporation process. A carrier gas is used, wherein the heat of condensation of the freshwater is utilized for the partial evaporation of the brine. The heat transport is solely across heat-exchange surfaces, and so correspondingly large heat-exchange surfaces are required. The expenditure on transport of the carrier gas is considerable.
What is termed the Memstill process is a combination of membrane process and MEV process which makes possible theoretically infinitely many stages. Of the theoretically infinitely many stages, however, owing to the non-suppressible axial backmixing of the vapor and the heat streams, in practice, only few may be implemented. The process exhibits the same disadvantages as the abovementioned membrane processes.
DE 19620214 describes a process for desalinating seawater by means of solar energy. This is a multistage evaporation process in which a carrier gas is used. In the process described, the carrier gas must be transported by means of gas compression. The expenditure for transport of the carrier gas is correspondingly high.
WO 02/087721 describes a device for obtaining freshwater by distilling salt water by means of solar energy. As carrier gas, air is used and circulates through the device owing to the thermal effects. Salt water is likewise transported in circulation through the device. By concentrating the salt in the salt water, considerable impairments owing to encrusting of the heat-exchange surfaces may be expected. In addition, with increasing salt content the water vapor pressure decreases and the separation expenditure increases therewith.
DE 102005046643 describes an apparatus for separating a liquid from impurities dissolved therein with a heater and modules arranged in series, each of the modules consisting of a moisturizer and a demoisturizer. Through each module, a blower circulates a carrier gas flow, so that the heat capacity flows in each module are equal. Regulating the heat capacity flows in such a way is very intricate.
DE 102004005689 describes an evaporation method for purifying contaminated liquids using a heater and several complementary pairs arranged in series, each of these complementary pairs consisting of an evaporation element and a condensation element. One or more of these complementary pairs are arranged in a module having a carrier gas circulation system which is circulated by means of a blower. Each module works at a separate pressure level, the pressure levels in the different modules being staged.
Both according to DE 102005046643 and according to DE 102004005689, the operating expense for circulating the carrier gas at a certain pressure level is correspondingly high. Moreover, the technical complexity due to the multi-stage arrangement, the resulting number of modules in contact with saltwater, and the expense for the required heat transfer surface are accordingly high.
The object of the present invention is to provide an improved water treatment process which avoids the disadvantages of the processes known from the prior art. A process shall be provided here that is suitable not only for obtaining drinking water, but also service water for diverse service sectors. The process must not need either complex and expensive salt water pretreatment or a high energy requirement for transporting the streams and shall also be suitable for use in remote regions or in developing countries. A corresponding apparatus must therefore be able to be fabricated using inexpensive materials and nevertheless be reliable in use and insensitive to fouling or scaling.
This object is achieved according to the invention by a continuous process for obtaining pure water from raw water, in which process
a) a raw water is provided that comprises at least one non-volatile component, b) the raw water provided is passed as cooling medium into a heat exchanger, c) additional heat is supplied to the raw water that is heated in the heat exchanger, d) the raw water from step c) is fed to an evaporation zone, e) a carrier gas suitable for water vapor is provided, f) the carrier gas is brought into contact with the raw water in countercurrent flow in the evaporation zone, wherein the carrier gas takes up water vapor from the raw water, g) the raw water that is obtained in step f) that is enriched with the at least one non-volatile component is taken off from the evaporation zone, h) the water vapor-loaded carrier gas from the evaporation zone is fed to the heat exchanger and is cooled in countercurrent flow to the raw water, wherein the water vapor present in the carrier gas partially condenses out, i) the carrier gas depleted in water vapor is passed out of the heat exchanger, k) the condensed water vapor is taken off from the heat exchanger as pure water.
In the process according to the invention, the evaporation zone is operated substantially adiabatically and the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
The process according to the invention serves for the removal from a raw water feed of at least one unwanted contaminant which is non-volatile under the process conditions.
In this case a pure water that is depleted in the unwanted component(s) is obtained. In addition, a raw water enriched with the unwanted component(s) is obtained.
The raw water used according to the invention can comprise at least one non-volatile component in dissolved or non-dissolved form. The non-volatile components present in the raw water can be organic or inorganic substances. The non-volatile components present in the raw water can be liquid or solid under standard conditions (20° C., 1 atm). The non-volatile components are generally distinguished by a very low vapor pressure. Non-dissolved, solid, non-volatile components are preferably present in suspended form in the raw water. Non-dissolved, liquid, non-volatile components are preferably present in dispersed form in the raw water.
Non-volatile components which can be removed by the process according to the invention are, e.g., relatively large solids, floating matter, suspended matter, oils, fats, organic contaminants different from oils and fats, salts, etc. and mixtures thereof.
Since the process according to the invention comprises vaporization of the raw water, it is suitable not only for producing drinking water but also service water for diverse service sectors. Measures that are additionally optionally necessary such as supplementation of dissolved salts in a physiologically compatible amount for treating drinking water are within the expertise of those skilled in the art.
In a special embodiment, the process according to the invention serves for obtaining freshwater from salt water.
A preferred embodiment of the process according to the invention is a continuous process for obtaining freshwater from salt water in which
a) salt water is provided; b) the salt water provided is passed as cooling medium into a heat exchanger; c) heat is additionally supplied to the salt water that is heated in the heat exchanger; d) the salt water of step c) is fed to an evaporation zone; e) a carrier gas suitable for water vapor is provided; f) the carrier gas is brought into contact with the salt water in countercurrent flow in the evaporation zone, wherein the carrier gas takes up water vapor from the salt water; g) the concentrated salt water obtained in step f) is taken off from the evaporation zone; h) the carrier gas loaded with water vapor is fed from the evaporation zone to the heat exchanger and cooled in countercurrent flow to the salt water, wherein the water vapor present in the carrier gas partly condenses out; i) the carrier gas that is depleted in water vapor is passed out of the heat exchanger; k) the condensed water vapor is taken off from the heat exchanger as pure water.
In this embodiment of the novel process too, the evaporation zone is operated substantially adiabatically and the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
Salt water customarily designates a solution of salts in water, e.g. seawater, brackish water, saline river water, or salt-loaded wastewater. The salt content of naturally occurring water such as, for example, in rivers, salt lakes, seas etc., fluctuates just as does the salt content of industrial wastewaters. Waters which are particularly suitable for use in the process according to the invention are brackish water, seawater, industrial wastewater, or mixtures thereof. The salt water used in the process according to the invention has, for example, a salt content of at least 0.5%, preferably at least 1%, particularly preferably at least 3%. Preferably, salt water having a salt content of at most 20% is used, for example having a salt content in the range from 0.1 to 10%, preferably in the range from 2 to 5%.
The salt content of water is reported in the context of the present invention as mass fraction in g/kg of water or in percent. A salt content of 1% is equivalent to 10 g/kg.
Preferably, the salt water used according to the invention comprises at least 1% by weight, based on the total content of salt, of salts of cations and anions. Preferably, the cations are selected from Li + , Na + , K + , NH 4 + , Ca 2+ , Mg 2+ and mixtures thereof. Preferably, the anions are selected from F â , Cl â , Br â , I â , NO 3 â , SO 4 2â , CO<
The present invention relates to a water treatment process in which pure water is separated off from raw water that comprises non-volatile unwanted components. The present invention relates in particular to a continuous process for obtaining freshwater from salt water and also to an apparatus for continuously obtaining freshwater from salt water.
Water treatment denotes the targeted modification of water quality. This includes in principle two groups of treatment: removing substances from water (e.g. desalting, removal of iron, softening, sterilization or other purification), on the one hand, and also supplementation of substances and setting parameters of the water (e.g. addition of dissolved ions, setting the pH and/or the conductivity) on the other. Water treatment in this case generally serves for obtaining drinking water or service water (today frequently termed process water). Also, desalted or demineralized water is particularly useful for watering plants. Water treatment for generating drinking water acts to meet legal provisions and provisions of standards (e.g. the German drinking water regulation, DIN 2000). Service water is required in large amounts, for example for power stations (as cooling water and feed water), industrial plants, chemical processes, pharmacy, laundries etc. Frequently, very substantial modifications of the water properties are required in water treatment for generating service water and especially diverse process waters.
A special process for water treatment is water desalination. Desalination of salt water designates obtaining service water or drinking water from salt water, especially from seawater, by reducing the salt content. In particular seawater desalination will become of great importance in the future since the supply of all people with clean water will become ever more difficult owing to lack of or pollution of the existing freshwater. The desalination of seawater is used on ships, submarines, islands and in arid coastal countries. Salt water in this case must have only low contamination. In the oil-rich Gulf States, seawater desalination is the main source of obtaining drinking water. Here the drinking water is obtained in gas- or oil-fired desalination plants. In the near East, also, this energy-intensive form of obtaining drinking water is widespread. Combined-cycle gas- and steam-turbine power plants having an attached multistage flash (MSF) evaporation desalination plant are likewise frequently used. On the Canary Islands and the German deep-sea island Helgoland, drinking water is obtained from salt water by the reverse osmosis process.
Membrane processes such as, e.g., reverse osmosis are established processes of water desalination. Of all of the known processes they theoretically require the lowest specific separation energy and the membranes can be produced very inexpensively even today. However, completely deionized water cannot be produced thereby, since some salt always also permeates the membranes. The membranes are in addition both mechanically and chemically sensitive, and so the salt water used must be pretreated. The pretreatment expenditure can exceed the actual separation expenditure. In addition, the membranes have only a limited lifetime. Although the specific separation expenditure is low, a high level of mechanical energy is required for pumping the water.
The efficiency of generation of this energy from primary energy such as, e.g., solar energy, is low, generally in total less than 20%.
Multiple-effect evaporation processes (also referred to as MEV processes) or multistage flash processes (also referred to as MSF processes) are now the most widespread processes for producing freshwater from salt water. MEV and MSF can also be operated using waste heat at below 100° C. and achieve a comparatively high energy utilization factor. The high energy efficiency is achieved by the multistage operation. Each stage, however, is a separate unit having evaporator and condenser and is operated at a separate pressure level. In the MEV process, the brine vaporizes on the evaporator surface. In this process local oversaturation of the brine occurs and salt precipitates out. The evaporator surface can become encrusted by this scaling as it is called. In the MSF process, scaling is avoided by complex forced circulation evaporation. For this purpose each evaporator stage requires a separate, sometimes very large, pump, which must circulate about 10 times the amount of brine by pumping in relation to the amount of freshwater vaporized. This process therefore requires a comparatively very high mechanical energy.
The dewvaporation process is a multistage evaporation process. A carrier gas is used, wherein the heat of condensation of the freshwater is utilized for the partial evaporation of the brine. The heat transport is solely across heat-exchange surfaces, and so correspondingly large heat-exchange surfaces are required. The expenditure on transport of the carrier gas is considerable.
What is termed the Memstill process is a combination of membrane process and MEV process which makes possible theoretically infinitely many stages. Of the theoretically infinitely many stages, however, owing to the non-suppressible axial backmixing of the vapor and the heat streams, in practice, only few may be implemented. The process exhibits the same disadvantages as the abovementioned membrane processes.
DE 19620214 describes a process for desalinating seawater by means of solar energy. This is a multistage evaporation process in which a carrier gas is used. In the process described, the carrier gas must be transported by means of gas compression. The expenditure for transport of the carrier gas is correspondingly high.
WO 02/087721 describes a device for obtaining freshwater by distilling salt water by means of solar energy. As carrier gas, air is used and circulates through the device owing to the thermal effects. Salt water is likewise transported in circulation through the device. By concentrating the salt in the salt water, considerable impairments owing to encrusting of the heat-exchange surfaces may be expected. In addition, with increasing salt content the water vapor pressure decreases and the separation expenditure increases therewith.
DE 102005046643 describes an apparatus for separating a liquid from impurities dissolved therein with a heater and modules arranged in series, each of the modules consisting of a moisturizer and a demoisturizer. Through each module, a blower circulates a carrier gas flow, so that the heat capacity flows in each module are equal. Regulating the heat capacity flows in such a way is very intricate.
DE 102004005689 describes an evaporation method for purifying contaminated liquids using a heater and several complementary pairs arranged in series, each of these complementary pairs consisting of an evaporation element and a condensation element. One or more of these complementary pairs are arranged in a module having a carrier gas circulation system which is circulated by means of a blower. Each module works at a separate pressure level, the pressure levels in the different modules being staged.
Both according to DE 102005046643 and according to DE 102004005689, the operating expense for circulating the carrier gas at a certain pressure level is correspondingly high. Moreover, the technical complexity due to the multi-stage arrangement, the resulting number of modules in contact with saltwater, and the expense for the required heat transfer surface are accordingly high.
The object of the present invention is to provide an improved water treatment process which avoids the disadvantages of the processes known from the prior art. A process shall be provided here that is suitable not only for obtaining drinking water, but also service water for diverse service sectors. The process must not need either complex and expensive salt water pretreatment or a high energy requirement for transporting the streams and shall also be suitable for use in remote regions or in developing countries. A corresponding apparatus must therefore be able to be fabricated using inexpensive materials and nevertheless be reliable in use and insensitive to fouling or scaling.
This object is achieved according to the invention by a continuous process for obtaining pure water from raw water, in which process
a) a raw water is provided that comprises at least one non-volatile component, b) the raw water provided is passed as cooling medium into a heat exchanger, c) additional heat is supplied to the raw water that is heated in the heat exchanger, d) the raw water from step c) is fed to an evaporation zone, e) a carrier gas suitable for water vapor is provided, f) the carrier gas is brought into contact with the raw water in countercurrent flow in the evaporation zone, wherein the carrier gas takes up water vapor from the raw water, g) the raw water that is obtained in step f) that is enriched with the at least one non-volatile component is taken off from the evaporation zone, h) the water vapor-loaded carrier gas from the evaporation zone is fed to the heat exchanger and is cooled in countercurrent flow to the raw water, wherein the water vapor present in the carrier gas partially condenses out, i) the carrier gas depleted in water vapor is passed out of the heat exchanger, k) the condensed water vapor is taken off from the heat exchanger as pure water.
In the process according to the invention, the evaporation zone is operated substantially adiabatically and the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
The process according to the invention serves for the removal from a raw water feed of at least one unwanted contaminant which is non-volatile under the process conditions.
In this case a pure water that is depleted in the unwanted component(s) is obtained. In addition, a raw water enriched with the unwanted component(s) is obtained.
The raw water used according to the invention can comprise at least one non-volatile component in dissolved or non-dissolved form. The non-volatile components present in the raw water can be organic or inorganic substances. The non-volatile components present in the raw water can be liquid or solid under standard conditions (20° C., 1 atm). The non-volatile components are generally distinguished by a very low vapor pressure. Non-dissolved, solid, non-volatile components are preferably present in suspended form in the raw water. Non-dissolved, liquid, non-volatile components are preferably present in dispersed form in the raw water.
Non-volatile components which can be removed by the process according to the invention are, e.g., relatively large solids, floating matter, suspended matter, oils, fats, organic contaminants different from oils and fats, salts, etc. and mixtures thereof.
Since the process according to the invention comprises vaporization of the raw water, it is suitable not only for producing drinking water but also service water for diverse service sectors. Measures that are additionally optionally necessary such as supplementation of dissolved salts in a physiologically compatible amount for treating drinking water are within the expertise of those skilled in the art.
In a special embodiment, the process according to the invention serves for obtaining freshwater from salt water.
A preferred embodiment of the process according to the invention is a continuous process for obtaining freshwater from salt water in which
a) salt water is provided; b) the salt water provided is passed as cooling medium into a heat exchanger; c) heat is additionally supplied to the salt water that is heated in the heat exchanger; d) the salt water of step c) is fed to an evaporation zone; e) a carrier gas suitable for water vapor is provided; f) the carrier gas is brought into contact with the salt water in countercurrent flow in the evaporation zone, wherein the carrier gas takes up water vapor from the salt water; g) the concentrated salt water obtained in step f) is taken off from the evaporation zone; h) the carrier gas loaded with water vapor is fed from the evaporation zone to the heat exchanger and cooled in countercurrent flow to the salt water, wherein the water vapor present in the carrier gas partly condenses out; i) the carrier gas that is depleted in water vapor is passed out of the heat exchanger; k) the condensed water vapor is taken off from the heat exchanger as pure water.
In this embodiment of the novel process too, the evaporation zone is operated substantially adiabatically and the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
Salt water customarily designates a solution of salts in water, e.g. seawater, brackish water, saline river water, or salt-loaded wastewater. The salt content of naturally occurring water such as, for example, in rivers, salt lakes, seas etc., fluctuates just as does the salt content of industrial wastewaters. Waters which are particularly suitable for use in the process according to the invention are brackish water, seawater, industrial wastewater, or mixtures thereof. The salt water used in the process according to the invention has, for example, a salt content of at least 0.5%, preferably at least 1%, particularly preferably at least 3%. Preferably, salt water having a salt content of at most 20% is used, for example having a salt content in the range from 0.1 to 10%, preferably in the range from 2 to 5%.
The salt content of water is reported in the context of the present invention as mass fraction in g/kg of water or in percent. A salt content of 1% is equivalent to 10 g/kg.
Preferably, the salt water used according to the invention comprises at least 1% by weight, based on the total content of salt, of salts of cations and anions. Preferably, the cations are selected from Li + , Na + , K + , NH 4 + , Ca 2+ , Mg 2+ and mixtures thereof. Preferably, the anions are selected from F â , Cl â , Br â , I â , NO 3 â , SO 4 2â , CO 3 2â and mixtures thereof. Particularly preferably, the salt water used according to the invention comprises at least 50% by weight, especially at least 75% by weight, and in particular at least 90% by weight of NaCl. The salt water used according to the invention can, if desired, comprise salts of divalent, trivalent and/or higher-valent cations and/or anions. These include, in particular, the fractions of customary ions present in the water used. In the provision of salt water for the process according to the invention, optionally a pretreatment of the salt water may be provided. This can be a mechanical prepurification in which the salt water is freed from solids before entry into the heat exchanger. Solids can be removed from the salt water, for example, by means of filtration or in a hydrocyclone. Also, a chemical and/or biological pretreatment can be performed in order to decrease or avoid, for example, the growth of algae, germs etc.
Freshwater, in contrast to salt water, is that fraction of the freely available water on the earth, that is to say not bound, e.g. in plants, in which no salts are dissolved, or salts are dissolved only to a slight extent. Low-salt water having a salt content of less than 0.1%, regardless of its physical state of matter, is described as freshwater.
Freshwater, in the context of the present invention, shall comprise not only process water but also drinking water. Process water (also termed service water or utility water) is water which serves for a specific technical, commercial, agricultural or domestic application. Process water, in contrast to drinking water, is not intended for human consumption, but, however, should correspond to a certain minimum hygiene. In any case it must meet the technological requirements of the respective process. Process water is a type of service water necessary for operating or maintaining an industrial process. Frequently, the salt content of the freshwater used is critical in these applications. Drinking water, in contrast, demands high quality requirements such that it is suitable for human consumption, in particular for drinking and for preparing foods. A certain salt content is required in use as drinking water.
The freshwater obtained according to the invention preferably comprises a salt content of at most 0.1%, preferably in the range from 0.01 to 0.05%. The residual salt content is due, e.g., to droplets entrained from the salt water in the course of the evaporation (step f)).
The carrier gas used in the process according to the invention takes up water vapor by means of temperature elevation and releases it subsequently by reduction in temperature. The carrier gas enriched or saturated with water vapor is hereinafter also termed vapors. All substances and mixtures of substances that are gaseous under the operating conditions of the process according to the invention are in principle suitable as carrier gas. These include, e.g., air, carbon dioxide and nitrogen, and also mixtures thereof. In a preferred embodiment of the process according to the invention, the carrier gas is air. The water content of the carrier gas provided preferably does not exceed 70% by volume. It is for example in the range from 10% by volume to 45% by volume, preferably in the range from 20% by volume to 35% by volume.
In steps b) and h), for condensing pure water, especially freshwater, a suitable countercurrent flow heat exchanger is used. Heat exchangers that are suitable for the process according to the invention in which one medium is a liquid and the other medium is a gas can vary very greatly with respect to the heat capacity per unit volume of the media. Generallyâon a volume basisâmore gas than liquid must flow through the heat exchanger. In a suitable embodiment, therefore, the raw water, especially the salt water, is conducted as liquid cooling medium in tubes. In an equally suitable embodiment, the exchange surface on the gas side is provided with surface-enlarging structures, such as, e.g., cooling fins or sheets. The heat exchanger is, for example, a tubular heat exchanger, tube-bundle heat exchanger, plate heat exchanger or micro heat exchanger. The heat exchanger is preferably made of a readily available material such as, for example, steel, corrosion-resistant metal alloys, coated materials, plastics, or combinations thereof.
Since the exchange surface facing the gas only comes into contact with vaporized pure water, and therefore somewhat non-critical for possible corrosion, this exchange surface can comprise inexpensive materials, e.g. tin plate, or materials as are used for commercially available air coolers. This applies especially to a desalination process in which the exchange surface facing the gas only comes into contact with desalinated water.
For the region of the heat exchanger which comes into contact with the corrosive raw water, especially salt water, generally corrosion-resistant materials are used. Such materials are known to those skilled in the art. These materials include metals, such as stainless steels, bronzes etc. Preferably, for the heat exchanger, a non-corrosion-resistant but inexpensive metal is used and the regions of the heat exchanger that are contacted by salt water are coated, for example with a corrosion-resistant plastic, or oxides or ceramics. The coating is expediently chosen in such a manner that it has a thermal resistance as low as possible and in addition is resistant to deposits, scaling and fouling.
Alternatively thereto, it is also possible to use a non-corrosion-resistant, but cheap, material in the heat exchanger which is then replaced in relatively short intervals.
The selection, dimensioning, and design of suitable heat exchangers are known to those skilled in the art.
All feed and return tubes can comprise a readily available material such as, for example, steel, corrosion-resistant metal alloys, coated materials, plastics or combinations thereof. Preferably, the tubes are made of plastic.
The additional heat supply in step c) can be performed in any desired manner that is suitable for heating raw water, especially salt water. In this operation, in the context of the process according to the invention, generally the raw water is not heated to a temperature above the boiling point of the raw water used. In order to make the process particularly efficient, preferably waste heat from other processes and/or solar heating is used. In a special embodiment, a raw water reservoir, especially a salt water reservoir, is provided, in which the heat input takes place and which can simultaneously serve as heat store.
In step d), the raw water is fed to an evaporation zone. An evaporation zone, in the context of the present invention, is taken to mean a zone in which water is transferred from the raw water to the carrier gas stream. The water is converted into the gaseous state in this case below its boiling temperature. The evaporation zone can be disposed within a region of a component, within an entire component, or within two or more components. In a preferred embodiment, the evaporation zone is situated in a separate component or within a region of a component. The evaporation zone can be situated in a reactor, for example a tower reactor, a column, a mass transfer apparatus, a saturator, or another suitable device.
According to the invention, the evaporation zone is operated substantially adiabatically. âAdiabaticâ is taken to mean heat-insulated in thermodynamics. An adiabatic change of state is a thermodynamic process in which a system is converted from one state to another without exchanging thermal energy with its surroundings. âOperated substantially adiabaticallyâ is therefore taken to mean, in the context of the present invention, that no heat, or only a negligibly small amount of heat, is exchanged between the evaporation zone and the surroundings. Effects such as solar irradiation on the device, heat radiation of the device to the environment, etc., are generally negligible. If the temperature effects and/or the climatic effects of the environment on the evaporation zone are not negligible, the device can be appropriately insulated in the region of the evaporation zone in order to make possible a substantially adiabatic mode of operation. The heat input required for the vaporization process proceeds according to the invention outside the evaporation zone into the raw water.
According to the invention, the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the heat exchanger.
âNatural convectionâ here, and hereinafter, is taken to mean the physical effect by which a fluid, in particular a gas, owing to the density difference, is transported from a warm region to a cold region (density gradient). The density difference is maintained by heating or warming in one region and cooling in another region (temperature gradient). Under the influence of gravitation, zones of lower density ascend against the gravitation field within the gas (buoyancy) whereas zones of higher density descend. If heat is supplied in the bottom region, a continuous flow is generated; the gas is heated, expands, and ascends. The resultant differential pressure is termed âdriving pressureâ or âactive pressureâ. Natural convection is utilized predominantly in connection with gases, for example carrier gases, and in particular air. A typical example is a flame, such as a candle flame or a lighter flame. Due to the convection of the ascending gas, the combustion air descends according to the arising vacuum. Starting from the flame inner core towards the periphery, a steep temperature gradient is generated, so that the flue gases ascend, suck in and entrain the surrounding air. Above the flame, even though the effect continues, it wears off rapidly since no further temperature gradient is generated. In this way, a natural chimney or a stack, that is without defined boundaries, sucking in air vertically from the bottom and horizontally from all sides and conveying it vertically upward.
If a gas flows over or around a fluid, in addition to heat transfer, mass transfer takes place. If the vapor pressure of the gas is below its saturation vapor pressure, i.e. if the gas is not saturated, part of the fluid diffuses into the gas phase. A difference in temperature is not essential but nevertheless beneficial. Even if the gas has the same temperature as the fluid or higher, the fluid will be cooled on losing evaporation heat. Natural convection can also take place in that the mass transfer causes a change in the density of the gas causing the gas to ascend or descend, even if the temperature difference is too small to cause buoyancy. In this case, mass and heat transfer interfere with one another both following similar rules, what is also known as analogy among heat and mass transfer.
In the process according to the invention the effect of natural convection of the gas owing to the temperature gradient is additionally reinforced by the differing water vapor content in the carrier gas. Since water vapor generally has a lower density than the carrier gas, the moist carrier gas is lighter than the dry carrier gas. The moist carrier gas therefore naturally flows upwards, whereas the dry carrier gas descends. In the process according to the invention, the carrier gas is transported solely by the effects of the density differences. Warm and/or moist air has a lower density than cold and/or dry air. Thereby, a lift is generated for the warm moist air and a reduced pressure is generated which is compensated for by an inflow of cold dry air.
The functioning of stacks in firing technology is based thereon, for example. The stack effect or chimney effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers due to buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The greater the thermal difference and the height of the structure, the greater is the buoyancy force and thus the stack effect. To ascertain a sufficient buoyancy force despite of heat losses at the inner walls, the dimensioning of the chimney has to be considered in terms of height and inner width.
To support the natural convection of the gas stream or in order to make the process still more efficient, residual dehumidification of the carrier gas after it has passed out of the condensation zone or of the countercurrent flow heat exchanger can be provided subsequent to step i).
Advantageously, no mechanical energy for transporting the carrier gas stream need be supplied to the process according to the invention. Optionally, however, an input of mechanical energy can additionally be provided, for example using a fan, for supporting the gas flow, e.g. on startup or in the event of unfavorable climatic conditions.
In step g), the concentrated raw water obtained in step f) is taken off from the evaporation zone. The raw water taken off in step g) is generally warmer than the provided raw water, by a maximum of 25° C., preferably by a maximum of 15° C., and in particular by a maximum of 5° C. Therefore, it can be drained directly into a receiving body of water or a corresponding treatment device. If the concentrated raw water is at least 10° C., preferably at least 20° C., and in particular at least 30° C., warmer than the raw water provided, pre-heating of the provided raw water before entry into the heat exchanger in step b) can be provided using the concentrated raw water from step g). For this purpose, a heat exchanger suitable for raw water streams, especially salt water streams, or any other suitable device, can be used.
In a preferred embodiment of the process according to the invention, the evaporation zone has internals that enlarge the mass transfer area.
Internals which can be used for increasing the mass transfer area are, in principle, all internals that are suitable for use in mass transfer apparatuses, for example for absorption, distillation, drying. These can be both ordered packings and also dumped beds. They can be regularly or irregularly, coated or uncoated. Industrially produced ordered packings or dumped beds of metal, plastic or ceramics, dumped beds of stones or other natural materials, or combinations thereof, can be used. In a suitable embodiment, the internals are made of a biogenic material, in particular of plant origin such as branches, straw, brushwood and the like. Preferably, the internals are water-wettable. Likewise preferably, the internals have a high specific surface area. Equally preferably, the internals have a low pressure drop. Particularly preferably, internals are made of plastic. In a suitable design, plastic fibers are used, for example in the form of a braided fabric, laid fabric, woven fabric, loop-formingly knitted fabric or loop-drawingly knitted fabric. Fabrics which are particularly suitable are loop-drawingly knitted fabrics of water-wettable plastic fibers, since loop-drawingly knitted fabrics not only have a high specific surface area but also a low pressure drop.
The internals can either occupy parts of the cross section or the entire cross section of the evaporation zone perpendicularly to the main direction of flow of the carrier gas stream. In this case they decrease the cross section available for the gas and liquid passage, preferably by 1% to 50%. The selection and dimensioning of suitable internals is known to those skilled in the art. In the case of large cross sections, the most uniform distribution possible of the heated raw water onto the internals enlarging the mass transfer area is of importance.
The internals are preferably selected in such a manner that the mass transfer area is dimensioned to be at least large enough that the evaporation zone corresponds to a mass transfer apparatus having more than one theoretical equilibrium stage.
Using the model of the theoretical equilibrium stage (also called ideal equilibrium stage, theoretical separation plate or ideal separation plate), in process engineering, thermal separation processes, mixing processes of gas and liquid streams, distillations and many other processes are described. The equilibrium stage model can be used not only for describing cocurrent flow apparatuses but also countercurrent flow apparatuses. It characterizes the action of a thermal apparatus by the number of equilibrium stages describing it. This number of equilibrium stages is not a pure apparatus factor but depends, in particular, on the material system, the thermodynamic state, and the mass streams in the apparatus. The theoretical equilibrium stage is characterized in that the mass streams that leave the stage are in thermodynamic equilibrium. This means, for example for an absorber, that the gas and the liquid which leave a stage each have the same temperature and the same pressure. The calculation of such (theoretical) equilibrium stages is familiar to those skilled in the art and can be carried out for example by computer using programs such as ASPEN or Chemasim (simulation software developed by BASF SE).
In a suitable embodiment of the process according to the invention, in step f), the carrier gas and the raw water are brought to mass transfer in the evaporation zone by spraying, injecting, or instilling the raw water into the carrier gas. In the embodiment as a desalination process, in step f), the carrier gas and the salt water are brought to mass transfer in the evaporation zone preferably by injecting or instilling the salt water into the carrier gas.
An enlargement of the mass transfer area can be achieved also by this measure. Internals in the evaporation zone can then be optionally dispensed with. The evaporation zone, however, can additionally have internals in this embodiment also.
If the pure water obtained according to the invention (i.e. in the case of a desalination process, the freshwater) must be desalted as far as possible for further use, for example having a salt content of at most 0.01%, optionally a demister can be provided before entry of the loaded carrier gas into the heat exchanger for condensation in step h).
In a suitable embodiment of the process according to the invention, the carrier gas, after it leaves the heat exchanger (step i)), is passed back into the evaporation zone (step f)). In this embodiment, the carrier gas is conducted in a closed circuit in which the carrier gas circulates between a warm zone having a heat source and a cold zone having a heat sink owing to the difference in density.
In this case, under the influence of gravitation, zones of lower density ascend against the gravitation field within the gas (buoyancy) whereas zones of higher density descend. If heat is supplied in the bottom region, a continuous flow is generated; the gas is heated, expands, and ascends. Reaching the top, it is cooled, contracts, and descends to be heated in the bottom region again.
The convection effect can be still enforced, if the descending carrier gas and the ascending carrier gas are spatially separated. A particularly suitable embodiment of the process is shown in FIG. 2 . This spatial separation can be put into practice by, for example, heating the carrier gas at the lower end of a first tube and cooling it at the upper end of a second tube. In this case, the tubes can be arranged horizontally and in particular as tube-in-tube.
In a preferred embodiment of the process according to the invention, for the supply of heat in step c), solar heating is utilized.
Solar heating, in the context of the present invention, denotes the conversion of solar energy into thermal energy, i.e. heat for heating the raw water used in the process according to the invention is obtained from the solar irradiation. Both the passive utilization and also the active utilization of solar energy are possible. In the case of passive utilization, the sun heats the raw water directly, such as, for example, in the case of a solar pond. Active utilization occurs when absorber surfaces collect the solar energy and transfer it to a heat store, such as, for example, by means of a solar collector.
A solar collector in the context of the present invention is a thermal solar collector, i.e. a device for collecting the energy present in sunlight. Such a solar collector uses the âtrappedâ solar energy to heat a transfer medium, also termed a heat carrier. In this case virtually the entire radiation spectrum of sunlight is utilized at relatively high efficiency. A central component of the solar collector is a solar absorber which converts the light energy of the sun into heat and gives it off to a heat carrier or a solar transmitter that allows the light radiation to pass through but not the heat resulting therefrom. Using the heat carrier, the heat is removed and is subsequently used directly or stored.
For supplying heat by means of solar heating, in the context of the present invention, solar absorbers, solar transmitters, heat exchangers, solar collectors, solar ponds and also other devices that are suitable for transferring heat radiation to the raw water provided, especially salt water, can be used, such as, for example, flexible tubes, tubes, etc. and suitable combinations thereof. These devices can be made, for example, of glass, plastic, metal, and/or suitable combinations thereof.
In a preferred embodiment, a salt water reservoir is used. The salt water reservoir can be a natural salt water lake or an artificially constructed pond which can act at the same time as heat store, e.g. for night operation. The salt water provided in this case takes over the function of the heat carrier. The salt water reservoir can be open, partially or entirely covered by a solar transmitter, or can be bridged by a solar transmitter.
The solar transmitter has the task of permitting the irradiation of the sunâeven at a low angle of irradiationâas completely as possible into the interior of the collector and as far as possible to prevent the escape of heat in the form of evaporation, convection, and radiation. The solar transmitter is therefore a medium substantially permeable to solar rays. It can comprise, for example, glass, such as, for example, simple glass, which can also have an antireflection coating, or plastic, such as, for example, polyethylene (PE), polypropylene (PP), PE/PP copolymers, PET, polycarbonate or ethylene/propylene-diene monomer-terpolymers (EPDM) or a combination thereof. The solar transmitter can be continuous, such as, for example, a film, a screen, etc., or can comprise a plurality of elements such as, for example, panels etc. It can be structured or planar. The solar transmitter can be transparent, partially transparent, or non-transparent, completely or in regions.
Expediently, the solar transmitter should have an insulating action with respect to heat conduction, and should reflect the heat radiation of the raw water, especially the salt water. Suitable solar transmitters are known to those skilled in the art and are commercially available.
Optionally, the raw water reservoir (especially salt water reservoir) can be insulated from the environment in order to keep heat losses as low as possible. Expediently, the bottom of the reservoir is of dark color, in particular black, the radiation/absorption being as close to a black body as possible. Suitable heat insulation must be taken into account before constructing the raw water reservoir.
The raw water reservoir can expediently combine the functions of a solar collector and a heat store. The water at the bottom is more salty and therefore denser than at the surface. If solar radiation is absorbed in the lower layers, these heat up further, for example up to 85 to 90° C. Owing to the density gradient existing due to the differing salt content, the heated water cannot ascend, convection does not take place, and the heat is stored in the lower water layer. The stored heat can be available for 24 hours a day, with an appropriate design.
In a particularly preferred embodiment of the process according to the invention, a salt water reservoir having a solar transmitter is used and the vapors from the saturator are passed between the surface of the salt water in the salt water reservoir and the solar transmitter before they enter the heat exchanger for condensation. In this embodiment of the process according to the invention, steps c) and f) are in part carried out in parallel in the same device. In this case the salt water reservoir and the gas layer thereabove below the solar transmitter form a part of the evaporation zone.
In an alternative preferred embodiment of the process according to the invention, for the supply of heat in step c), waste heat from other processes is utilized. For this purpose, particularly preferably, a heat exchanger is used in which a suitable heat carrier from another process acts as heating medium which heats further the already preheated salt water. The heat carrier can be, for example, warm wastewater, heat carrier oil, steam such as, for example, saturated steam or superheated steam, or another medium suitable for such an application. The design of such heat carriers is familiar to those skilled in the art.
In principle it is also possible to combine waste heat from other processes and solar heating for supplying heat in step c), and so both forms of energy supply are employed simultaneously and/or alternately.
In a further preferred embodiment of the process according to the invention, the carrier gas is brought into contact with the raw water, especially the salt water, in step f) in two or more than two evaporation zones. In this case the carrier gas and the raw water are brought into contact in countercurrent flow in at least one evaporation zone. In a special embodiment, the carrier gas is saturated in two stages: in a first stage the carrier gas and the raw water are brought into contact in countercurrent flow in the first evaporation zone; and in a second stage the vapors from the saturator are conducted between the surface of the raw water in the raw water reservoir and the solar transmitter before the vapors are passed into the heat exchanger for condensation. In this embodiment, the raw water reservoir and the gas layer thereabove below the solar transmitter form the second evaporation zone.
In a suitable embodiment of the process according to the invention, the pure water obtained in step k) (freshwater) is subjected to one or more treatment steps in order to obtain drinking water.
Drinking water is freshwater having a high degree of purity such that it is suitable for human consumption, in particular for drinking and for food preparation. Drinking water must not contain pathogenic microorganisms and should have a minimum concentration of minerals. The water treatment depends on the quality of the raw water, in the present case of the freshwater obtained after the process according to the invention. The treatment processes depend on the substances present in the raw water or freshwater which are to be removed and on the substances lacking in the raw water or freshwater which are to be added. The customary chemical and/or physical treatment methods suitable for obtaining drinking water are known to those skilled in the art.
The present invention further relates to an apparatus for continuously obtaining pure water from raw water comprising
a device for feeding the raw water into the apparatus; a heat exchanger in which a water vapor-comprising carrier gas and the raw water are conducted in countercurrent flow, wherein at least some of the water vapor present in the carrier gas condenses out and the salt water raw water is heated; a device for heat supply in which the raw water that is already heated in the heat exchanger is further heated; an evaporation zone in which the raw water from the device for heat supply and the carrier gas are brought into contact, wherein the carrier gas is enriched with water vapor and is provided as water vapor-comprising carrier gas for introduction into the heat exchanger; an outlet device for the concentrated raw water from the evaporation zone; a take-off device for the condensed pure water from the heat exchanger.
According to the invention, the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the condensation zone.
The present invention relates especially to an apparatus for continuously obtaining freshwater from salt water comprising the following components:
a device for feeding the salt water into the apparatus, a heat exchanger in which a water vapor-comprising carrier gas and the salt water are conducted in countercurrent flow, wherein at least some of the water vapor present in the carrier gas condenses out and the salt water is heated, a device for heat supply in which the salt water that is already heated in the heat exchanger is further heated, an evaporation zone in which the salt water from the device for heat supply and the carrier gas are brought into contact, wherein the carrier gas is enriched with water vapor and is provided as water vapor-comprising carrier gas for introduction into the heat exchanger, an outlet device for the concentrated salt water from the evaporation zone, and a take-off device for the condensed freshwater from the heat exchanger.
In this embodiment of the novel device, too, the carrier gas is transported by means of natural convection through the evaporation zone and thereafter through the condensation zone.
To ensure natural convection of the carrier gas, the gas loading factor F is preferably in the range of from 0.1 to 10 Pa 1/2 . This corresponds to a Reynolds number in the range 10â¦Reâ¦10 9 . Even more preferably, the gas loading factor F is in the range of from 0.5 to 5 Pa 1/2 . This corresponds to a Reynolds number in the range 10 3 â¦Reâ¦10 8 . In particular, the gas loading factor F is in the range of from 1 to 3 Pa 1/2 . This corresponds to a Reynolds number in the range 5*10 4 â¦Reâ¦5*10 6 .
The gas loading factor F or F-factor is a characteristic factor expedient for the dimensioning of mass transfer units, such as reactors, columns, trays, pipes and the like. F is defined as in formula (I):
F=w G *(Ï G ) 1/2 ââ(I)
with
w G =V G /A ââ(II)
in which
F is the gas loading factor in [Pa 1/2 ]
w G is the medium velocity of the loaded carrier gas in [m/s]
Ï G is the density of the loaded carrier gas in [kg/m 3 ]
V G is the volume flow of the loaded carrier gas in [m 3 /s]
A is the cross section surface of the evaporation zone in [m 2 ].
According to formula (III), the Re number can also be calculated:
Re =( w G *Ï G *D )/η G ââ(III)
in which
Re is the Reynolds number in [â]
w G is the medium velocity of the loaded carrier gas in [m/s]
Ï G is the median density of the loaded carrier gas in [kg/m 3 ]
η G is the median viscosity of the loaded carrier gas in [Pa*s]
D is the diameter of the evaporation zone in [m].
Further explanation of the F-factor can be found e.g. in Klaus Sattler, âThermische Trennverfahrenâ, VCH Weinheim, 1995, pages 20 seq. The dimensioning of mass transfer units is generally known to the person skilled in the art.
Hereinafter, raw water designates especially salt water and pure water designates especially freshwater.
The device for feeding the raw water into the apparatus comprises a feed line from a preexisting natural or artificially constructed body of water and a suitable transport means, for example a pump or a transport screw such as, e.g., an Archimedean screw. The water body can be flowing water, e.g. a river or canal, or static water, e.g. a lake or a collecting tank. It can be an above-ground water body, such as an inland water body or a sea, or else a subterranean water body.
The feed line is essentially a pipe. Depending on the type of the pump, further fittings, e.g. shut-off valves or throttling units, need to be provided on the feed line. In addition, a mechanical prepurification stage such as, for example, a strainer, a filter, a membrane, a screen, a hydrocyclone, another mechanical separator for removing solids, or a combination thereof is generally required. Optionally, chemical and/or biological prepurification can also be provided. In particular, treatment with active ingredients can be provided that reduce biological growth, for e
CLAIMS
Claims ( 18 )
1 . A continuous process for obtaining a pure water from a raw water, the process comprising:
passing the raw water comprising a non-volatile component into a heat exchanger as a cooling medium, supplying additional heat to the raw water, subsequently feeding the raw water to an evaporation zone, contacting a carrier gas suitable for water vapor with the raw water in countercurrent flow in the evaporation zone to add water vapor from the raw water to the carrier gas, and to obtain a water vapor-loaded carrier gas, subsequently removing the raw water from the evaporation zone, feeding the water vapor-loaded carrier gas to the heat exchanger and cooling the water vapor-loaded carrier gas in countercurrent flow to the raw water, thereby partially condensing out the water vapor in the carrier gas, to obtain a carrier gas depleted in water vapor and a condensed water vapor, passing the carrier gas depleted in water vapor out of the heat exchanger, removing the condensed water vapor is from the heat exchanger as the pure water, wherein the supplying additional heat comprises solar heating, the supplying additional heat is in a salt water reservoir that can simultaneously serve as a heat store, contacting a carrier gas with the raw water in the evaporation zone is substantially adiabatically, and the passing the carrier gas through the evaporation zone and the passing the carrier gas through the heat exchanger are both by natural convection.
2 . The process of claim 1 , wherein the raw water is salt water and the pure water is freshwater.
3 . The process of claim 1 , wherein the evaporation zone comprises internals enlarging the mass transfer area.
4 . The process of claim 1 , wherein the carrier gas is air.
5 . The process of claim 1 , further comprising:
passing the carrier gas back into the evaporation zone after it leaves the heat exchanger.
6 - 7 . (canceled)
8 . The process of claim 1 ,
wherein contacting the carrier gas with the raw water comprises contacting the carrier gas and the raw water in two evaporation zones, and in one evaporation zone, the carrier gas and the raw water are in countercurrent flow.
9 . The process of claim 1 , further comprising:
treating the pure water to obtain drinking water.
10 . An apparatus for continuously obtaining a pure water from a raw water, the apparatus comprising:
a device configured to feed the raw water into the apparatus; a heat exchanger configured to conduct a water vapor-comprising carrier gas and the raw water in countercurrent flow, suitable for condensing at least some water vapor present in the carrier gas, and configured to heat the raw water; a salt water reservoir as a device for heat supply, configured to further heat the raw water after heating in the heat exchanger; an evaporation zone configured to contact the raw water from the device for heat supply and the carrier gas, to enrich the carrier gas with water vapor, and to provide the carrier gas as water vapor-comprising carrier gas into the heat exchanger; an outlet device configured to let out a concentrated raw water from the evaporation zone; a take-off device configured to remove the pure water from the heat exchanger, wherein the apparatus is configured to transport the carrier gas by natural convection through the evaporation zone and thereafter through a condensation zone.
11 . The apparatus of claim 10 , wherein a gas loading factor F is from 0.1 to 10 Pa 1/2 .
12 . The apparatus of claim 11 , wherein the gas loading factor F is from 0.5 to 5 Pa 1/2 .
13 . (canceled)
14 . The apparatus of claim 10 , wherein the device for heat supply is configured to heat by a process comprising solar heating.
15 . The apparatus of claim 10 , wherein the evaporation zone is a saturator with internals.
16 . (canceled)
17 . The apparatus of claim 10 , further comprising:
a solar transmitter separating at least some of the salt water reservoir from the open atmosphere.
18 . A drinking water or a service water, comprising:
pure water obtained by a process comprising the process of claim 1 .
19 . The apparatus of claim 10 , wherein the salt water reservoir is a natural lake or an artificially constructed pond.
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