DE102007047319A1 - Process and plant for recovering water from air - Google Patents

Abstract

In the extraction of water from air, the air is brought into contact with sulfuric acid of a concentration> = 60 wt .-%, so that water condenses on the surface of the acid. The dilute sulfuric acid is concentrated to a concentration> = 60 wt .-%, wherein the liberated steam is condensed by cooling. The condensate obtained is removed.

Description

The The invention relates to the recovery of water from gas, in particular Ambient air.

Water scarcity is a growing problem in many areas of the world Water is seen as a renewable resource in some parts of the world may be due to pollution or insufficient Water infrastructure of constantly growing demand is not be followed. Water scarcity is increasing Risk to the global industry, which, for example, in mining to do so is to recycle as much water as possible. this leads to however, to a deteriorated quality of the again and again circulated water, its salt and pollutant content increases by evaporation.

usual Water extraction methods set the availability of Raw water in water-bearing layers or seawater ahead. The plants for the treatment of the water should hereby regardless of the technology as close as possible at the raw water source to the line or pump costs minimize. The high salt content of the seawater also leads excessive stress on the lines and therefore high maintenance costs.

In front desalination of raw water must be purified and separated from solids, immiscible liquids, poorly soluble Salts etc are released as accumulations of these materials desalination areas significantly impair efficiency. In addition, the life of desalination plants without adequate pretreatment of raw water reduces what the Operating times shortened and the maintenance further elevated.

The currently most commonly used method desalination of seawater is the distillation / condensation, which is used in more than 70% of all desalination plants. In the high-temperature distillation is over with temperatures 95 ° C worked. Mechanical systems work at temperatures below the boiling point and use different methods for the evaporation of raw water.

moreover are membrane techniques such as electrodialysis or reverse osmosis known. Electrodialysis is an electrochemically driven Membrane process in which ion exchange membranes in combination be used with an electrical potential difference to ionic Species of uncharged solvents or impurities separate. Will in such electrodialysis the polarity regularly reversed so that the ions in the flow contrary direction, become the anions returned through the membrane and support a break-up of deposits on the surface of the membrane.

at The reverse osmosis becomes the solution (seawater) to overcome of the osmotic pressure under high pressure through a semipermeable Membrane pressed. This acts like a filter and leaves only certain ions and molecules through. Thus receives a separation of the original solution. Through the membrane filter can be salts, bacteria, viruses, lime and detain toxins such as heavy metals.

at However, these known methods become significant waste streams produced. Thus, in the pretreatment, the solids and the to precipitate added chemicals flakes by clarification must be removed from the raw water. The sewage sludge is drained and dumped. Besides the solid waste In the filter cleaning, liquid wastes can also be generated. Upon evaporation in the distillation / condensation system drops a concentrated brine that controls the salinity of groundwater can increase if a discharge into the sea not possible is. Membrane desalination is the most efficient method for the production of drinking water, but this is the most pre-treatment waste generated. In addition, a low concentrated brine fall and the spent membrane modules.

It has also been proposed to extract water from the air. That's how it describes DE 197 34 887 C2 a device for recovering water from the air by means of a hygroscopic absorbent material which is intermittently charged with moist air and exposed to a heat source. The air passes through a container containing a highly porous carrier, for example silica gel, whose pores are impregnated with a selective water absorption material such as calcium chloride, lithium bromide or sodium sulfate.

At the time of the DE 10 2004 026 334 A1 known device is water from atmospheric air with the aid of a flowable adsorbent or absorbent, in particular a brine solution with a hygroskopi won salt.

Air drying processes are also known in which the drying of the air takes place by absorption on solid or liquid absorbents. That's how it describes DE 100 14 792 A1 Air drying in fuel tank ventilation systems using vapor permeation membranes and sorbents. As liquid absorbents lithium chloride solutions, sulfuric acid and glycols are proposed. The regeneration during operation of the absorption dryers takes place in the temperature or pressure swing process or by replacement of the used materials.

task The invention is the economic extraction of water without allow large waste streams.

These The object is achieved with the invention essentially by a method for the recovery of water from gas, in particular air, dissolved, in which the air is in contact with sulfuric acid of a concentration ≥ 60 Wt .-% is brought, leaving water at the surface the acid is condensed and absorbed, the so diluted sulfuric acid to a concentration ≥ 60 Wt .-% is concentrated, wherein the liberated vapor by Cooling is condensed and wherein the condensate is discharged becomes.

The Water is thus extracted with the invention from the ambient air, so that no raw water needs to be made available. In addition, in contrast to the desalting process large waste streams. Rather, it is even possible To recover water from waste gases from chemical or metallurgical processes.

According to one preferred embodiment of the invention, the air is in contact with sulfuric acid of (origin) concentration of 65 brought to 80 wt .-% and in particular about 70 to 75 wt .-%, wherein the Air preferably in countercurrent to drooling sulfuric acid through a drying tower (eg packed tower) to be led.

To recover the water from the acid, it is concentrated to its original concentration. The concentration of the dilute sulfuric acid is carried out according to the invention by vacuum evaporation, wherein at the above concentrations, a low or technical vacuum in the range of 10 to 90000 N / m ² , preferably 100 to 10,000 N / m ² , more preferably 2000 to 2500 N / m ² is provided.

It may also be provided that part of the diluted Sulfuric acid fed to a sulfuric acid plant so that there to the sulfuric acid dilution required water supply can be reduced. Likewise, this can dilute sulfuric acid in whole or in part other Attachments are fed to such a sulfuric acid directly or for dilution or concentration. This sulfuric acid can be added to other parts of the system before delivery also be prepurified.

According to one Another embodiment of the invention, the gas, in particular Air, passed through a humidifier, before it is brought into contact with the sulfuric acid. ambient air is in most cases below its saturation state before, so they add in the humidifier can be moistened. This part of the water evaporates in the air flow, while cooling the water he follows. This cool water can then be used for condensation the water vapor from the vacuum unit can be used.

In A continuation of the inventive concept is with this moistening possible, contaminated To clean water. For this purpose, the gas, preferably air, before moistening also be cleaned to reduce contamination of the water.

According to the invention a partial flow of the condensate is branched off after the condenser and be supplied to the humidifying, so on an external water supply can be dispensed with.

In a further development of the concept of the invention, the moist gas can come from a plant in which moist gas is generated. Examples include the drying of biomass, leaching residues and crystallization products, drying and / or calcination of aluminum hydroxide or other dehydrating substances, combustion of biomass, hydrocarbons, hydrogen or other hydrogen-containing materials. Furthermore, this process, after a first step for water recovery from these gases, z. B. by condensation after EP 1 063 472 or AU 2005 237179 , to the more complete Extraction of water from the exhaust gas can be used.

The The invention also includes a plant for recovering water Gas, in particular air, for carrying out the above-described Method is suitable and a drying tower in which air is concentrated through Sulfuric acid, an evaporator, to dilute the water condensed out of the air Sulfuric acid is supplied, and a capacitor, condensed in the water vapor removed from the evaporator is, has.

at In one embodiment of the invention, the drying tower is a moistening device upstream, in which humidifies the air by means of cooling water becomes. in development of this invention is the water outlet the humidifier with the water inlet of the capacitor connected to the water for cooling and condensation to use the emerging from the evaporator water vapor.

Further developments, Advantages and applications of the invention result also from the following description of an embodiment and the drawing. All are described and / or illustrated illustrated features alone or in any combination the subject of the invention, regardless of its summary in the claims or their dependency.

It demonstrate:

1 a diagram of the water content of air over sulfuric acid at 40 ° C as a function of the acid concentration,

2 a graph of H ₂ SO ₄ vapor pressure over sulfuric acid at 40 ° C, depending on the acid concentration, and

3 schematically a flow diagram of the method according to the invention.

Ambient air usually has a water content of 15 to 30 g H ₂ O / Nm ₃ . When this ambient air is brought into contact with concentrated acid, water vapor condenses on the acid surface at which the saturated water vapor pressure is lower than the water vapor partial pressure in the gas volume and is absorbed by the acid. The residual water content of the air after sufficient contact with the acid theoretically corresponds to the partial pressure of the water vapor over the acid at the prevailing temperature and concentration. Out 1 shows that at acid concentrations above 60 wt .-%, a significant drying effect is achieved, in which only a water content <10 g / Nm ³ remains in the air.

The recovery of the water from the acid is carried out by concentrating the acid to its original concentration. As it turned out 2 results in acid concentrations of less than 75 wt .-% H ₂ SO _4, the acidity of the gas phase due to the low H ₂ SO ₄ vapor pressure is negligible. At an acid concentration below 75 wt .-% H ₂ SO ₄ thus essentially only water is evaporated.

From the into the 1 and 2 As shown, the acid concentration for optimum recovery of water from the ambient air is in the range of 65 to 75% by weight. If a higher acid concentration is selected, which would extract more water from the air, this would result in the vapors produced in the evaporator being too high in impurities, in particular sulfur trioxide (SO ₃ ), and additional air purification would have to be provided.

The concentration of sulfuric acid is carried out according to the invention by vacuum evaporation. The dilute sulfuric acid is kept at boiling temperature by indirect heating under vacuum. A concentration of the acid to 70 wt .-% at 70 ° C requires a vacuum of about 2200 N / m ² , which is to be regarded as a low or technical vacuum and therefore can be provided with reasonable effort.

The in the evaporation resulting vapors are in one Cooling system condenses, leaving aside negligible Amounts of inert gases desorbed from the acid no exhaust gas streams attack. The concentrated acid becomes the drying tower returned, while the steam condensate for further use and treatment is discharged.

The energy required for water evaporation is usually provided in the form of low-pressure steam. But since the heat of condensation is transferred directly into the acid and heat losses ver are negligible, it is possible to keep the amount of heat that must be supplied from the outside much smaller than in the conventional method. In fact, the vacuum generating unit consumes the majority of the energy. By using multi-stage evaporators and / or reducing the applied vacuum, the amount of steam required or hot water can be significantly reduced.

The Efficiency of the plant is achieved by using a combined saturation / cooling tower further improved upstream of the drying tower. The supplied air, which in most cases below is present in the saturation state, passes through a wasserberegnete Cell before entering the drying tower. Part of the water evaporates into the air stream, causing the water to cool becomes. The cold water is then used to control the water vapor to condense out of the vacuum unit.

It would also be possible instead of a conventional one Cooling tower with closed cycle to use exhaust gases passed through the plant and then discharged become. The exhaust gas that passes through the saturator, evaporates water into the acid, which eventually is recovered as pure condensate.

The Combination with the saturation / cooling tower reduced the air flow required per tonne of water produced.

In 3 a flow diagram of the method is shown.

Via an air supply line 1 ambient air is a cooling tower 2 fed, in which they by cooling water, through a pipe 3 fed and passed in countercurrent to the air, preferably is moistened to saturation. At the same time thereby a cooling of the cooling water is achieved.

The top of the cooling tower 2 escaping air is through a pipe 4 a drying tower filled with suitable packing (s) 5 supplied below, in which the air with sulfuric acid of a concentration of about 70 wt .-%, via a conduit 6 is fed, is sprinkled. In this case, a large part of the water contained in the air is absorbed by the sulfuric acid and dilutes it. The dried air is via a discharge line 7 from the drying tower 5 dissipated.

The sulfuric acid diluted by the water condensed from the air is passed through a pipe 8th a vacuum evaporator 9 supplied, in which at a low vacuum of, for example, 2200 N / m ² essentially only water is driven out of the sulfuric acid and evaporated until the sulfuric acid is concentrated again to its original concentration of about 70 wt .-%.

The water vapor is via a pipe 10 a capacitor 11 in which he is using the over the line 12 from the cooling tower 2 withdrawn and recirculated cooling water is condensed.

In the acid cycle can also be a in 3 Not shown cleaning device for the sulfuric acid are turned on to free the sulfuric acid from dissolved or particulate impurities.

The condensate thus obtained is via a line 13 deducted. A partial flow of the condensate can via a line 14 the cooling tower 2 be supplied to assist the humidification and saturation of the ambient air.

example

Process data: Ambient pressure: 101.3 kN / m ² Air supply: 1.5 MNm ³ / h Air temperature: 25 ° C Relative humidity: 61% Water content: 16 g H ₂ O / Nm ³ air

The acid dilution and water condensation leads to a significant heat release in the dry zone. The temperature of the acid leaving the drying tower is thus a function of the acid flow through the tower. Acid flow, a: 650 m ³ / h Acid concentration, a: 70% by weight Acid flow, from: 678 m ³ / h Acid concentration, from: 68.6% by weight

If a tower efficiency of 95% is assumed, the air leaves the drying tower with a residual water content of 2.3 g / Nm ³ .

The The amount of water generated by such a system is to 500 t / d.

A comparison with the specific costs for conventional technologies shows: technology specific costs Raw water supply + brine removal two-stage reverse osmosis EUR 1.21 EUR 0.02 / m ³ Multiple Flash EUR 1.04 EUR 0.02 / m ³ More effect distillation EUR 0.93 EUR 0.02 / m ³ water condensation EUR 1.24 N / A

It shows that the water condensation according to the invention Method with the conventional methods in competition can occur.

1

Air supply line

2

cooling tower

3

management

4

management

5

drying tower

6

management

7

withdrawal line

8th

management

9

vacuum evaporator

10

management

11

capacitor

12

management

13

management

14

management

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19734887 C2 [0009]
• DE 102004026334 A1 [0010]
• DE 10014792 A1 [0011]
• - EP 1063472 [0021]
• - AU 2005237179 [0021]

Claims (13)

Process for recovering water from gas, in particular Air, the gas being in contact with sulfuric acid Concentration ≥ 60 weight percent is brought, so that Water vapor condenses on the surface of the acid, wherein the dilute sulfuric acid to a Concentration ≥ 60 weight percent is concentrated, wherein the liberated vapor condenses by cooling and wherein the condensate is discharged. Method according to claim 1, characterized in that that the gas is in contact with sulfuric acid of a concentration from 65 to 75 weight percent is brought. Method according to claim 1 or 2, characterized that the gas in countercurrent to drooping sulfuric acid is passed through a drying tower. Method according to one of the preceding claims, characterized in that the dilute sulfuric acid concentrated to a concentration of 65 to 75 weight percent becomes. Method according to one of the preceding claims, characterized in that the dilute sulfuric acid is concentrated by evaporation. A method according to claim 5, characterized in that the evaporation takes place at reduced pressure, in particular at a pressure of 2000 to 2500 N / m ² . Method according to one of the preceding claims, characterized in that the dilute sulfuric acid at least partially supplied to a sulfuric acid plant becomes. Method according to one of the preceding claims, characterized in that the gas through a humidifier is led before with the sulfuric acid is brought into contact. Method according to one of the preceding claims, characterized in that water from the moistening device is used for condensation of the steam. Method according to claim 8 or 9, characterized that a partial flow of the condensate is diverted to the condenser and the humidifying device is supplied. Plant for the production of water from gas, in particular from air, and for carrying out a process according to one of the preceding claims, comprising a drying tower ( 5 ), in which the gas is passed through concentrated sulfuric acid, an evaporator ( 9 ) to which the sulfuric acid diluted by the water condensed from the gas is fed, and a condenser ( 11 ), in which condensed water vapor is condensed from the evaporator. Plant according to claim 11, characterized in that the drying tower ( 5 ) a humidifying device ( 2 ) upstream, in which the gas is moistened by means of cooling water Plant according to claim 11 or 12, characterized in that the water outlet of the humidifying device ( 2 ) with the water inlet of the condenser ( 11 ) connected is.