Abstract:
The invention provides an apparatus and method for treating indoor air, utilizing a container suitable for holding a brine solution thereinside, a porous medium rotatably mounted on, or in, said container such that a section thereof is capable of being immersed in the brine solution held inside it, rotating means mechanically coupled to said porous medium, and air streaming means capable of directing a stream of air to a surface area of said porous medium.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and an apparatus for purifying and humidifying air. More particularly, the invention relates to a method and apparatus for purifying and humidifying contaminated air by contacting a stream of ambient air with a brine solution. 
       BACKGROUND OF THE INVENTION 
       [0002]    Commonly used methods for treating contaminated air are based on filtration, air ionization and sterilization of air by means of ozone or ultraviolet light. 
         [0003]    WO 2007/026363 describes a method for reducing the level of microorganism of indoor air, by contacting a stream of indoor air with a concentrated salt solution, which is preferably halide brine having a Redox (reduction-oxidation) potential in the range between 200 mV and 450 mV. The publication identifies certain brines that are capable of developing such Redox potentials under suitable aeration conditions, and alternatively or in addition, proposes to electrolyze the brine in an electrolytic cell, whereby the Redox potential of the brine is suitably adjusted. WO 2007/026363 also specifically describes a packed column scrubber (in which the air and the brine solution are brought into contact via solid material filling the column) for running the method set forth above in various facilities, including hospitals. 
         [0004]    It has been demonstrated that operating under the preferred treatment regime according to WO 2007/026363, using brines having Redox potentials in the range between 200 and about 450 mV, effectively reduces the level of biological contaminants of indoor air. There exists a need, however, in certain facilities, to periodically sanitize the air, the walls and other surfaces in closed spaces. 
         [0005]    There is still a need for cost effective solutions for purifying air and controlling its humidity in houses and relatively small spaces. 
         [0006]    It is therefore an object of the present invention to provide a simplified method and apparatus for purifying air inside houses and relatively small spaces. 
         [0007]    It is another object of the present invention to provide a method and apparatus for purifying air and adjusting its humidity. 
         [0008]    Other objects and advantages of the invention will become apparent as the description proceeds. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a method and apparatus for treating air by contacting a stream of air with a brine solution contained in a revolving porous medium. In particular, the invention provides a method and apparatus for purifying contaminated air, and optionally also humidifying the purified air, by contacting a stream of ambient air with a brine solution contained in a revolving porous medium. 
         [0010]    In a preferred embodiment of the invention a portion of the porous revolving medium is maintained immersed in a brine solution such that portions of the brine solution are continuously absorbed in its pores and moved thereinside to a treatment zone wherein a stream of ambient air is caused to pass through portions of the porous rotating medium maintained external to (not immersed in) the brine solution. Advantageously, the humidity of the air passed through the porous revolving medium may be controllably altered by adjusting the vapor pressure of the brine solution e.g., by means of a heating element such as a filament, in order to prevent excess absorption of moisture from the environment. Advantageously, whenever the ambient air is too dry moisture may be added to it (up to a level of about 60%) by increasing vapor pressure in order to improve the air conditions. For this purpose the invention further provides means for monitoring the humidity of the purified air, for monitoring and controlling the temperature of the brine solution and for monitoring and adjusting its quantity, concentration, and activity. 
         [0011]    In one aspect the present invention is directed to an apparatus for purifying air comprising a rotatable porous drum (e.g., comprising interconnected pores) mounted for revolution within a container, wherein a section of said drum extends outside of said container, rotating means for rotating (e.g., electrical motor) the rotatable porous drum within the container, and air streaming means for directing a stream of air to a surface area of the section of rotatable porous drum extending outside of said container. 
         [0012]    In operation, the container is filled with a brine solution, such that a portion of the revolving porous drum is immersed in the brine solution. While the porous drum is rotated about its axis, a stream of ambient air is forced to pass through the section of the drum in the treatment zone i.e., which extends outside of the brine solution. The pores of the revolving porous drum are repeatedly filled with fresh brine solution from the container, and the ambient air streamed therethrough contacts the brine solution within the porous drum, whereby the air is treated. 
         [0013]    The apparatus may further comprise humidity sensing means adapted to contact the treated air and means for monitoring (e.g., a temperature sensor) and adjusting (e.g., a heating element) the temperature of a solution maintained inside the container responsive to indications received from said humidity sensing means and from temperature monitoring means installed inside the container. 
         [0014]    The apparatus may further comprise level measuring means installed in the container, such that readings from said level measuring means may be used to control the level of the solution in the container. For example, whenever the solution level is too high the temperature of the solution may be increased in order to increase the vapor pressure and prevent moisture absorption from the environment. 
         [0015]    In one preferred embodiment the apparatus further comprises a reservoir for holding water, wherein said reservoir is in fluid communication with said container, and means for controlling the flow of water (e.g., valve) from said reservoir to said container. Conveniently, the means for determining the level of the solution contained inside the container and the means for controlling the flow of water from said reservoir are used for adjusting the solution level in the container responsive to indications received from said level determining means. 
         [0016]    The apparatus may further comprise means for measuring a Redox (Reduction-Oxidation) potential of the solution maintained inside the container and for adjusting its activity responsive to indications received from said Redox measuring means. For example, Redox potential may be increased by increasing the speed of the stream of air introduced into the treatment zone, and/or by increasing the speed of rotations of the rotatable porous drum; by means of an automated whisk or mixer device installed in the container and adapted to introduce bubbles into the solution; and/or by introducing air bubbles by means of an air pump. 
         [0017]    The rotatable porous drum may optionally comprise one or more elongated members formed in, or attached on, one or more sides of the porous rotatable drum, wherein each of said elongated members comprises an elongated ditch adapted to collect brine solution in it, and an elongated slit provided in the base, and/or the sides, of said elongated ditch and adapted to discharge brine solution therefrom onto the surface of said porous drum. 
         [0018]    In another aspect the present invention is also directed to a method for treating air, which method comprises rotating a porous drum in a brine solution and forcing a stream of air to pass through a section of said drum which extends from said brine solution into a treatment zone. Preferably, upon heating, the brine solution also serves for humidifying the treated air, in which case water is being fed into said brine solution to prevent possible crystallization of salts within the brine. The method further comprises periodically or continuously measuring the Redox potential of the brine and adjusting the Redox potential of said brine based on the measured value of the Redox potential by introducing Oxigen into the solution by one or more of the following means: increasing the rate of the stream of air introduced into the treatment zone; by increasing the speed of rotations of the rotatable porous drum; by means of an automated whisk or mixer device installed in the container and adapted to introduce air bubbles into the solution; and/or by introducing air bubbles into the solution by means of an air pump. 
         [0019]    The term “brine solution”, as used herein, refers to concentrated solutions wherein the concentration of the salt dissolved therein is preferably not less than 10% (w/w), and preferably not less than 20% (w/w), and up to saturation at the relevant temperature. Compositionally, the concentrated salt solution operative in the present invention is an aqueous solution containing one or more water soluble salts represented by the formulas MX, M 2 X and MX 2 , wherein X is selected from the group consisting of chloride, bromide, iodide, sulfate and nitrate anions, and M indicates a metal cation, which is most preferably selected from the group consisting of lithium, sodium, potassium, calcium, magnesium and zinc, and mixtures thereof. Preferred brine solutions include concentrated solutions of sodium chloride and calcium chloride (with a concentration of not less than 20 wt %, and preferably not less than 30 wt %). Another preferred concentrated salt solution to be used according to the invention comprises a mixture of at least one bromide or iodide salt, in combination with at least one chloride salt of one or more of the following metals: Na + , K + , Mg 2+  and Ca 2+ . An especially preferred solution contains a mixture of bromide and chloride salts dissolved therein in a total concentration of 30 to 40% by weight, with the cationic species being Mg 2+ , Ca 2+ , Na +  and K + . More specifically, the concentrations of the aforementioned ions are as follows: Mg 2+ : 30-50 g/liter; Ca 2+ : 10-20 g/liter; Na + : 30-50 g/liter; K + : 5-10 g/liter; Cl − : 150-240 g/liter; Br − : 3-10 g/liter. An example of such a solution is provided by the Dead Sea brine, which has the following typical (average) mineral composition: Mg 2+ : about 40.6 g/liter; Ca 2+ : about 16.8 g/liter; Na + : about 39.1 g/liter; K + : about 7.26 g/liter; Cl − : about 212.4 g/liter; Br − : about 5.12 g/liter, with the total concentration of salts dissolved therein being 33% by weight. Another preferred concentrated salt solution comprises a mixture of bromide and chloride salts dissolved in water in a total concentration of 30 to 40% by weight, with the cationic species being Mg 2+ , Ca 2+ , Na +  and K + , wherein the concentration of calcium chloride in said solution is effective in reducing the rate of evaporation of water therefrom, and is preferably in the range between 20 and 200 g/liter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements and in which: 
           [0021]      FIG. 1  illustrates a longitudinal-section view of an air purifying apparatus demonstrating the basic principle of the invention; 
           [0022]      FIG. 2  illustrates a longitudinal-section view of a preferred embodiment of the air purifying and humidifying apparatus of the invention; 
           [0023]      FIG. 3  is a three dimensional perspective view of the longitudinal-section view shown in  FIG. 2 ; 
           [0024]      FIG. 4  is a three dimensional longitudinal-section view taken along line X-X in  FIG. 2 ; 
           [0025]      FIGS. 5A and 5B  show an optional embodiment of a revolving drum comprising liquid collecting means, wherein  FIG. 5A  shows a perspective view of the revolving drum and  FIG. 5B  shows a perspective view of the optional liquid collecting means; and 
           [0026]      FIG. 6  is a block diagram schematically illustrating electrical connectivity of a control unit in the apparatus of the invention. 
       
    
    
       [0027]    It should be noted that the embodiments exemplified in the Figs. are not intended to be in scale and are in diagram form to facilitate ease of understanding and description. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    With reference to  FIG. 1 , air purifying and humidifying apparatus  1  of the invention is generally comprised of an open container  5  suitable for holding a volume of brine solution  9 , a revolving porous drum  2  rotatably mounted on, or above, open container  5  by means of a rotatable shaft  2   p , such that a portion  2   g  of revolving porous drum  2  is immersed inside brine solution  9  contained inside open container  5 , rotating means  2   e  mechanically connected to rotatable shaft  2   p , and air streaming means  4  capable of directing a stream of ambient air  4   a  onto a surface area  2   h  of revolving porous drum  2  in the treatment zone  1   z  i.e., external to open container  5 . Upper part of revolving porous drum  2  is preferably enclosed within a cover  8  adapted to fit over it with close proximity, while not contacting it, such that substantial portions of ambient air stream  4   a  are forced to pass through a portion of revolving porous drum  2  in the treatment zone  1   z . Cover  8  should comprise a rear opening  8   a  facing surface area  2   h  of revolving porous drum  2  for introducing the stream of ambient air  4   a  into apparatus  1 , and a front opening(s)  8   b  for discharging a stream of treated air  4   b  leaving apparatus  1 . 
         [0029]      FIGS. 2 to 4  show longitudinal-section side, and three-dimensional perspective, views of an air purifying and humidifying apparatus  10  according to a preferred embodiment of the invention. Apparatus  10  is generally comprised of an open container  15  made of chemically resistant material such as, but not limited to, stainless alloys (such as austenitic, ferritic and martensitic stainless steels, mild steel, carbon steel, titanium alloys, nickel-based super alloys and cobalt alloys) or suitable plastics (such as PVC, CPVC, polyethylene, polypropylene, polybutylene, PVDF, Teflon and polyester), configured for holding a volume (e.g., 10 to 15 liters) of brine solution (e.g., Dead Sea brine), a revolving porous drum  12  rotatably mounted on, or above, open container  15  by means of rotatable shaft  12   p , such that a portion of revolving porous drum  12  is maintained inside open container  15 . Electrical motor  12   e  (e.g., a 220V/400-900 mA engine), mechanically linked to rotatable shaft  12   p  (e.g., made from plastic or metallic material, such as, but not limited to, stainless steel), is employed for rotating (e.g., 2 to 6 RPM) revolving porous drum  12  inside apparatus  10 . An electrical fan  14  (e.g., a 300 to 1200 WAT engine, such as QC 20 or QC 25 manufactured by Dynair), comprising electrical motor  14   e  and rotatable fan  14   f , is used for directing a stream (e.g., 100 to 200 m 3 /hr) of ambient air onto a surface area of revolving porous drum  12  external to open container  15 . 
         [0030]    Apparatus  10  is enclosed in housing  18  adapted to fit over the portion of revolving porous drum  12  external to open container  15 , such that significant portions of the ambient air streamed by fan  14  are forced to pass through revolving porous drum  12  (i.e., thereby housing  18  implements the functionality of cover  8  shown in  FIG. 1 ). Housing  18  should comprise at least two air openings: i) air inlet opening(s) which may comprise rear opening(s)  18   a , side opening(s)  18   s , and/or bottom opening(s)  18   d , for introducing ambient air streams into apparatus  10 ; and i) front opening(s)  18   b  for discharging treated air from the apparatus. In operation, open container  15  is filled with a brine solution and revolving porous drum  12  is rotated about rotatable shaft  12   p  by electrical motor  12   e , such that its active surface area is continuously wetted with fresh brine solution. The portions of the streams of ambient air driven by fan  14  which pass through revolving porous drum  12  contact the brine solution filling its active surface, thereby discharging a stream of treated air from apparatus  10  due to the activity of the brine solution and due to removal of solid particles (e.g., dust, soot) and liquid droplets by the brine solution. 
         [0031]    In one preferred embodiment of the invention apparatus  10  further comprises a water reservoir  13  installed inside housing  18  and adapted to fit over, and in close proximity to, the portion of revolving porous drum  12  external to open container  15  (i.e., bottom section of water reservoir  13  is made round corresponding to roundness of revolving porous drum  12 ), without contacting it. This configuration drives significant portions of the streams of ambient air introduced into apparatus  10  by fan  14  through revolving porous drum  12 . Water reservoir  13  communicates with open container  15  by means of pipe system  16  adapted for controllably discharging volumes of water from water reservoir  13  into open container by means of valve  16   v  (shown in  FIG. 4 ). Since water reservoir  18  is mounted above open container  15  water can be streamed through pipe system  16  by force of gravity. Water reservoir  13  may be filled with water via opening  13   o  provided at its upper wall, wherein said opening  13   o  may be accessed via a respective opening provided in housing  18 , by removing the sealing lid  13   c.    
         [0032]    Revolving porous drum  12  is preferably made from a spongy or fibrous material, such as, but not limited to, polyethylene, polypropylene, foamed polystyrene, polybutylene, or spongy metals (e.g., austenitic stainless steel). The diameter of revolving porous drum  12  may generally be in range of 40 to 55 cm, and its thickness may generally be in range of 2 to 4 cm. The rate of ambient air introduced into apparatus  10  may generally be in the range 100 to 200 m 3 /hr. 
         [0033]    In a preferred embodiment of the invention open container  15  comprises a heating element  17 , preferably mounted on its bottom wall, for heating the brine solution maintained thereinside. Heating element  17  is preferably an electrical heating element capable of producing heat powers of about 100 to 300 WAT, employed for heating the brine solution and increase vapor pressure whenever there is a need to increase the humidity in the stream of treated air discharged from apparatus  10 . Heating element  17  may be further employed for reducing the level of brine solution in open container  15 , whenever it is determined that the level of brine has been increased due to absorption of moisture from the stream of ambient air passed through apparatus  10 , which may result in an overflow of the solution. 
         [0034]    Open container  15  may further comprise one or more level determining means  19  (e.g., electrodes) for providing indications responsive to the level of the brine solution maintained thereinside, and RedOx electrodes (reduction-oxidation electrodes—not shown) for providing indications regarding the activity of the brine solution. Removable waist disposal vessel  15   d  is preferably attached to an opening  15   o  provided in the bottom wall of open container  15  for receiving waist precipitants obtained thereinside. The bottom wall of open container  15  is preferably curved for facilitating the drainage of the precipitants into opening  15   o.    
         [0035]    With reference to  FIG. 6 , the operation of apparatus  10  is preferably managed by means of a control unit  60  (e.g., a programmable microcontroller such as DSP33FJ256 of Microchip Technology Inc), electrically linked to fan  14 , electrical motor  12   e , to heating element  17 , to level determining means  19 , to valve  16   v , to RedOx electrodes  66 , and to a humidity sensor  63  (e.g., SHT1x or SHT7x of Sensirion). Humidity sensor  63  may be placed on housing  18  of apparatus  10 , or inside housing  18  near one of the air inlet openings, or nearby (e.g., on a nearby wall), such that it is brought in contact with the ambient air. Fan  14  and electrical motor  12   e  are preferably adapted to operate responsive to control signals received from control unit  60 , which is preferably also capable of setting a desired speed of rotations of said fan  14  and electrical motor  12   e.    
         [0036]    For example, control unit  60  may be adapted to increase the speed of rotations of electrical motor  12   e  (i.e., for increasing the speed of rotations of drum  12 ), or of electrical motor  14   e  (for increasing the rate of ambient air introduced into the device), responsive to readings received from the RedOx electrodes indicating low RedOx levels (e.g., less then 200 mV), for increasing the oxidation levels in the brine. Additionally or alternatively, the apparatus may further comprise an automatic whisk or mixer device installed in the container (not shown), and/or an air pump (not shown) adapted to introduce air bubbles into the brine solution, for increasing the oxidation levels of the solution. 
         [0037]    The control unit may be adapted to increase the vapor pressure by activating the heating element  17  for discharging vapors with the stream of treated air discharged from apparatus  10 , responsive to readings received from level determining means  19  indicating that the level of the brine solution in open container  15  exceeds an acceptable level (e.g., due to absorption of moisture from the ambient air streamed through apparatus  10 ). 
         [0038]    Control unit  60  may be further adapted to alter the state of valve  16   v  according to indications received from level determining means  19  for streaming water from water reservoir  13 , whenever the level of the brine solution in open container  15  is below an acceptable level. Water reservoir  13  preferably also comprises level determining means  13   e  (shown in  FIG. 2 ), which may be also linked to control unit  60  for allowing it to issue alerts whenever the level of water maintained therein is too low. For this purpose control unit  60  may be linked to speakers, LEDs and/or display means, or other visual/audio output means, suitable for issuing alert indications. Similarly, control unit  60  may be adapted to issue alert indications responsive to RedOx readings indicating too low oxidation levels (e.g., less than 100 mV). A turbidity sensing means (e.g., photodiode—not shown) linked to the control unit may be installed inside open container  15 , or waist disposal vessel  15   d , near opening  15   o , to allow control until  60  to issue visual/audio indications to the operator for replacing the waist disposal vessel  15   d  whenever it is filled with precipitants. 
         [0039]    As described hereinabove, apparatus  10  may be used as a humidifier by employing heating element  17  for heating the brine solution in open container  15 . This functionality is preferably managed responsive to indicating signals received by control unit  60  from humidity sensor  63 . For example, control unit  60  may be adapted to activate heating element  17  whenever it is determined according to signals received from humidity sensor  63  that the air humidity is less than 50%. Furthermore, control unit  60  may be further adapted to change the state of valve  16   v  before, or during, activation of heating element  17 , for streaming a volume of water from water reservoir  13  into open container  15 . 
         [0040]    A suitable set-up for measuring the Redox potential of the brine solution comprises a measuring electrode made of an inert metal or alloy (a platinum electrode) and a reference electrode (such as Ag/AgCl or calomel). Suitable electrodes are commercially available. The Redox potentials reported herein are measured using Pt/Ag/AgCl electrodes, thus indicating the electrochemical potential which is developed between Pt electrode exposed to the brine and a standard silver-silver chloride electrode. 
         [0041]    In one optional embodiment of the invention revolving porous drum  12  may optionally include liquid collecting means for increasing the amount of brine solution contained in its pores during operation.  FIG. 5A  shows an optional embodiment of revolving porous drum  12  comprising liquid collecting means  12   c  attached to one of its sides. Liquid collecting means  12   c  are preferably arced shaped elements attached on revolving porous drum  12  to a round base  12   b  attached over rotatable shaft  12   p . A number of (e.g., about 6 to 10) collecting means  12   c  are preferably evenly distributed with more or less equal angles therebetween forming a structure similar to that of a wind mill. In this configuration, revolving porous drum  12  is rotated in the direction (indicated by arrow  12   w ) which introduces the inner arcs  12   i  of collecting means  12   c  first into open container. 
         [0042]    As best seen in  FIG. 5B , showing a perspective view of liquid collecting means  12   c , a canal (ditch)  12   f  is formed in collecting means  12   c , said canal  12   f  is formed in the side of inner arc  12   i  of collecting means  12   c . An elongated slot  12   y , communicating with canal  12   f , is formed in the outer arc  12   o  of collecting means  12   c , more or less centrally along its length. Similar slot ( 12   o ) may be may be also provided in one, or both, sides of collecting means  12   c . Advantageously, elongated slot  12   y  is formed near the side of collecting means  12   c  attached to revolving porous drum  12 , such that the brine solution obtained in canal  12   f  whenever it is rotated through the brine solution maintained in open container  15  is discharged from canal  12   f  through elongated slot  12   y  over a surface area of revolving porous drum  12 , when said collecting means  12   c  is rotated out of the brine solution. 
         [0043]    Experiments carried out with an apparatus of the invention using a spongy drum having a diameter of about 50 cm and thickness of about 2.5 cm, and a dead sea brine, showed that it is capable of reducing the amount of contaminants in the air by more than %50. 
         [0044]    It is noted that the apparatus of the invention may be used in a wide range of applications requiring treatment of contaminated air. For example, the invention may be used for treating air in hospitals departments and particularly patients&#39; rooms, in elderly care units (retirement houses) refrigerating facilities (devices and rooms), healthcare facilities, kinder gardens, and private houses. The invention may be also a benefit for people suffering from breathing difficulties (e.g., asthma) and those suffering from airborne allergens. 
         [0045]    The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.