WO2021245661A1

WO2021245661A1 - Air purifier and method of improving indoor air quality

Info

Publication number: WO2021245661A1
Application number: PCT/IL2021/050648
Authority: WO
Inventors: David Itzhak
Original assignee: David Itzhak
Priority date: 2020-06-02
Filing date: 2021-06-01
Publication date: 2021-12-09
Also published as: KR20230042670A

Abstract

An air purifier comprising: an elongated, vertically positioned gas/liquid contactor, bounded by a bottom section, a top section and a lateral surface, with an air inlet opening disposed in the lateral surface and an air outlet opening at the top section, a pipe mounted horizontally in the interior space of the gas/liquid contactor, wherein the pipe is perforated along its length with a plurality of downwardly directed apertures, a demister fitted into the space of the gas/liquid contactor, a pump installed to circulate an aqueous solution through the gas/liquid contactor, wherein a discharge line of the pump is directed to a liquid inlet opening disposed in the lateral surface, to join said perforated pipe, a blower for drawing air stream into the gas/liquid contactor via said laterally disposed air inlet, the air inlet and liquid inlet openings being located at different radial directions with respect to the longitudinal axis of the gas/liquid contactor. A method for improving the quality of indoor air by circulating an aqueous salt solution through the air purifier is also described.

Description

Air purifier and method of improving indoor air quality

Field of the invention

The invention relates to an air purifier used to remove from indoor air particulate matter, chemical pollutants (such as acidic gases) and biological pollutants.

Background of the invention

The major function served by standard air purifiers is the capture of airborne particulate matter with the aid of High Efficiency Particulate Air (HEPA) filters. However, strong demand exists to improve indoor air quality by removal of chemical and biological pollutants. To this end, ultraviolet (e.g. germicidal UV lamp, which can destroy germs, viruses and bacteria) and air ionization-related technologies were incorporated into air purifiers over the past decades. See, for example, US 5,833,740, and commercially available air purifiers such as "XJ-3000 C" of Heaven Fresh Canada Inc.

A different approach to targeting chemical and biological pollutants is to pass the air through a reactive aqueous solution, such that the pollutants are absorbed and/or neutralized owing to interaction with reactive species in the solution. The major challenges involved include identification of a powerful solution effective against a wide array of pollutants and design of an appropriate reactor to enable efficient air/liquid contact and minimize escape of moisture with the outgoing purified air stream.

It has been shown by the present inventor (see US 8,398,917) that concentrated aqueous solutions of alkali halides (brines) act on airborne biological pollutants. Under aeration, certain brines develop enhanced redox potential, e.g., above +200 mV, that is, the brines gain oxidation capacity. In US 8,398,917, more efficient enhancement of the redox potential of the brine was achieved with the aid of electrolysis. The brines were tested in a counterflow packed column, namely, the air was introduced from the bottom and blown up through the column while the solution was sprayed from the top of the column. The brines displayed good disinfecting action.

Sodium chloride solution that was tested in a counterflow packed column of US 8,398,917 was an electrolyzed solution. That is, it was passed through an electrolysis cell, to increase its redox potential. In comparative Example 1 of US 8,398,917 is was shown that absent electrolysis, sodium chloride solution would not acquire satisfactory activity. Likewise, in a latter patent of the present inventor (US 8,603,631) an electrolyzed sodium chloride solution demonstrated good sanitization action when the air/liquid interface was achieved with the aid of a different column design (bubble column). The outgoing air stream released from the bubble column assisted in maintaining good air quality in cooled storage rooms of agricultural and food products (see also EP 2358208).

The potential utility of sodium chloride solution in air purification treatments, revealed in the publications presented above, is restricted by the need to electrolyze the solution. Utilization of non-electrolyzed sodium chloride solution for air cleaning is reported in US 10,456,736, namely, as absorbent solution, mentioning the bacteriocidic effect of such solution. For example, an absorbent solution was loaded into a vessel through which air was bubbled (fed via a tube submerged below the level of the liquid). The purified air existing the vessel was supplied to a face mask affixed to an individual's head. Summary of the invention

We have now found an effective gas/liquid contactor configuration that enables to benefit from the action of e.g., non-electrolyzed aqueous alkali chloride solution on airborne pollutants, namely, to capture particulate matter, remove chemical pollutants such as acidic gases and reduce microbial load. Stated otherwise, suitably formulated aqueous salt solutions (e.g., alkali chloride solution) can serve on its own several purification purposes, such that the air purifier may be configured as HEPA filter-free apparatus, especially suited for improving indoor air quality in middle size rooms (~ 70 cubic meters) and larger spaces (e.g., > 100 cubic meters) .

Aqueous solutions for use in the air purifier of the invention contain one or more salts of alkali and alkaline earth metals dissolved in water, e.g., halides (such as chlorides and bromides), nitrates (such as sodium nitrate, potassium nitrate and magnesium nitrate), water soluble carbonates and sulfates (that is, alkali carbonates and alkali sulfates; amongst the alkaline earth compounds, magnesium sulfate exhibits good solubility in water and can be used in the invention) . Suitable solutions can be prepared by dissolving in water a single salt or a blend of salts, e.g., two or more alkali/alkaline earth halides, either as individual salts, or in the form of a suitable double salt of the formula MiCl- M₂CI₂ (H₂O)_n (Mi and M₂ indicate the alkali and alkaline earth metals, respectively; e.g., carnallite, a mineral consisting of a hydrated mixed chloride of potassium and magnesium), or by dissolving alkali carbonate in water, e.g., Na₂C0₃," carbonate solutions can also be obtained by the reaction of the corresponding alkali bicarbonate and alkali hydroxide (namely, NaHCCq + NaOH Na2CC>3 +H2O). For the sake of simplicity, the operation of the air purifier is largely described herein in reference to a sodium chloride solution; this solution, however, can be replaced by one the alternatives set forth above. The concentration of the salt dissolved in the aqueous solution is generally at least 10% by weight, e.g., at least 15% by weight.

The air purifier of the invention is designed to enable circulation of alkali chloride solution held in a gas/liquid contactor. The solution is introduced laterally into an elongated, vertically positioned gas/liquid contactor, and is distributed in the interior of the reactor so as to achieve good contact with an indoor air stream, fed laterally into the gas/liquid contactor and forced to travel through the "mixing zone". The liquid and air streams both enter the gas/liquid contactor through its lateral surface, but from two different radial directions (with respect to the longitudinal axis of the gas/liquid contactor).

In one variant of the invention, circulation of the aqueous alkali chloride solution includes diverging the liquid stream supplied from a pump to the gas/liquid contactor into a main liquid stream and a secondary liquid stream. The main liquid stream is introduced radially via the lateral surface of the reactor, and the solution is sprayed so as to form a liquid curtain, as explained in detail below. The incoming indoor air stream is laterally fed to the reactor and is forced to move in the direction of, and cross through, the liquid curtain (the terms "air/liquid contactor" and "reactor" are used herein interchangeably). The role of secondary liquid stream is to maintain the temperature of the circulated solution slightly below ambience. To this end, the secondary liquid stream is cooled, e.g., passed through a chiller to remove heat absorbed by the circulated solution due to the operation of the pump. On exiting the chiller, the secondary liquid stream is guided directly to the reactor, or is joined with the main liquid stream before it enters the reactor. Solution entrained in the air blown up through the reactor (in droplet form) is captured by a demister fitted at the top of the air/liquid contactor. The preferred demister of the invention possesses unique geometry, consisting of a plurality of disc sectors or disc segments arranged spatially so as to force the air to move transversally to the longitudinal axis of the gas/liquid contactor, thereby to minimize escape of moisture by the purified air released from the reactor, as shown below. Purified air is released either directly to the room or directed to an air-conditioning system.

Owing to the intense air/liquid contact created, the concentrated alkali chloride solution can act on airborne biological pollutants to generate outgoing air stream with reduced microbial load and improve indoor air quality with respect to other parameters as well. Experimental work reported below indicates that with the aid of an air purifier operating in a fashion described above, it is possible to keep good indoor air quality by: capturing particulate matter (reduce levels of PM 2.5; i.e., particulate matter of less than 2.5 microns, namely, "fine" particles) . absorbing acidic gases such CO2, SO2 and NO2 as well as other chemical pollutants; and reducing microbial load.

Accordingly, one aspect of the invention is an air purifier comprising :

An elongated, vertically positioned gas/liquid contactor, bounded by a bottom section, a top section and a lateral surface (preferably cylindrical), with an air inlet opening disposed in the lateral surface and an air outlet opening at the top section, a pipe mounted horizontally, preferably along a diameter, in the interior (e.g., cylindrical) space of the gas/liquid contactor, wherein the pipe is perforated along its length with a plurality of downwardly directed apertures, a demister fitted into the interior (e.g., cylindrical) space of the gas/liquid contactor, a pump installed to circulate an aqueous solution through the gas/liquid contactor, wherein a discharge line of the pump is directed to a liquid inlet opening disposed in the lateral surface, to join said perforated pipe, a blower for drawing air stream into the gas/liquid contactor via said laterally disposed air inlet opening, the air inlet and liquid inlet openings being located at different radial directions with respect to the longitudinal (e.g. axial) axis of the gas/liquid contactor.

Another aspect of the invention is a method of improving the quality of indoor air, to reduce levels of particulate matter and/or chemical pollutants and/or biological pollutants, the method comprising: circulating an aqueous salt solution (e.g., comprising one or more water-soluble salts selected from alkali and alkaline earth halides, nitrates, carbonates and sulfates) held in an elongated, vertically positioned gas/liquid contactor, wherein the circulation includes introducing the solution into the interior of the gas/liquid contactor along a direction perpendicular to the longitudinal axis of the gas/liquid contactor, above the surface level of the solution reservoir, spraying the solution downwards, and optionally cooling the solution, for example, by cooling a portion of the circulated solution to deliver a cooled solution stream to the solution reservoir in the gas/liquid contactor; drawing indoor air into said gas/liquid contactor and releasing purified air stream from the top of the gas/liquid contactor, wherein the incoming air stream is laterally fed to the gas/liquid contactor, above the surface level of the solution reservoir, directed to the surface level of the solution, forced to pass through the sprayed solution, wherein the moving air with entrained liquid flows through a plurality of spaces arranged transverse to the longitudinal axis of the gas/liquid contactor, accessing said transverse spaces via passages located adjacent to, or bounded by, sections of the inner walls of the gas/liquid contactor so as to increase the path the air travels through said transverse spaces.

Detailed description of the invention

A preferred design of an air purifier of the invention is illustrated in Figures 1A and IB, which provide isometric and side of views the apparatus, respectively. Figure 1C is a top view of the apparatus. The elongated air/liquid contactor (1) shown in these drawings possess a cylindrical symmetry, and the description that follows focuses on such symmetry. However, other reactor geometries may be considered as well, e.g., a tower-like design having square or rectangular cross- section, with the understanding that the geometry of the reactor should enable liquid and air streams to be introduced through the lateral surface of the reactor along radial directions that are essentially perpendicular to one another. This requirement implies that in case of a cylindrical gas/liquid contractor (1), the liquid and air inlet openings are preferably oriented about 90° apart on the lateral surface (though at different heights, as explained below).

Turning now to the drawings, the air purifier includes a vertically positioned, preferably cylindrically shaped, air/liquid contactor (1), with frustoconical top section (2) that ends with outlet opening (3) through which the purified air is released. The lowermost section of the reactor is also frustoconical in shape (4), to facilitate drainage.

For example, to treat indoor air in 2500-3000 cubic feet sized space (about 70 to 100 cubic meters), the height and diameter of reactor (1) are adjusted in the ranges from 50 to 90 cm (e.g., 60 to 80 cm) and 30 to 50 cm (e.g., 35 to 45 cm), respectively. Reactor (1) is generally made of stainless steel (for example stainless steel 316) or plastic materials such as poly (vinyl chloride), polyethylene and polypropylene.

Reactor (1) accommodates the aqueous alkali chloride solution, which occupies approximately from about one third to one half of the interior of reactor (1) (e.g., from 30 to 45% of the interior of reactor (1)). For example, reactor (1) with the dimensions set out above is charged with 25 to 30 liters of the alkali chloride solution.

Suitable solutions are prepared by dissolving in water from 200 to 400 g/Liter of alkali chloride, such as sodium chloride and/or potassium chloride and/or lithium chloride, and optionally alkaline earth chloride such as magnesium chloride. Preferred concentration range is from 25 to 35 wt.% of alkali chloride in water. A suitable source of salts worth mentioning is the double salt of the formula KC1-MgCl2, namely, the hydrated mineral known by the name carnallite. The pH of the solution may be adjusted to the alkaline range by addition of a small amount of alkali hydroxide, e.g., to reach pH of 8 to 11, to minimize the corrosive character of the circulated alkali chloride solutions. 150 to 300 g/Liter Na2CC>3 solution can also be used.

The circulation of the aqueous solution is achieved by pump ( 5 ) . The pump, its discharge line ( 5d) and suction line ( 5s ) are best seen in the top view provided by Figure 1C. A suitable fluid pump (e.g., centrifugal) pump supplies flow rates of 30 to 90 liter/min, for example, PQm 60 manufactured by Pedrollo, Italy. The liquid stream ( 5d) discharged from pump ( 5 ) , diverges into a main stream (6) and a secondary stream (8), i.e., an upper branch (consisting of conduit 6) and lower branch (conduit 8). Generally, the ratio of diameters of conduits 6 and 8 is from 5:1 to 3:1. For example, one inch (25.4 mm) diameter conduit

(6) for delivering the main stream and 2/8-3/8 inch (6.4-9.5 mm) diameter conduit (8) for delivering the secondary stream.

The main liquid stream flows to reactor (1) via conduit (6), which enters the lateral surface of the reactor in a radial direction, at a point above the level of the aqueous solution held in the reactor, where it joins pipe ( 7 ) mounted horizontally along a diameter in the cylindrical space of the gas/liquid contactor. Pipe ( 7 ) is positioned about 20 to 30 cm above the liquid level in reactor (1).

Pipe ( 7 ) is illustrated in Figure 2, where, for ease of illustration, it is oriented vertically, with the apertures projecting from the plane of the paper. The diameter of pipe

( 7 ) is about 1.5 to 3.0 cm. Pipe ( 7 ) is perforated along its length with a plurality of evenly spaced apart apertures. Pipe ( 7 ) is mounted in reactor (1), such that the apertures are directed downwards. In the preferred embodiment shown in Figure 2, the apertures are evenly distributed along the length of the pipe in two parallel rows. The diameter of each aperture is from 1.5 to 2.5 mm, and the center-to center distance between two adjacent apertures in the same row may be from 15 to 20 mm. The rows are oriented about 15-25° apart along the perimeter of pipe ( 7 ) . Owing to this unique design of liquid feed into the reactor, the aqueous solution is sprayed from pipe ( 7 ) in the form of plurality of adjacent jets pointing downwards, so as to create a liquid curtain extending from pipe ( 7 ) to the surface of the liquid held in reactor (1). The secondary liquid stream (8) is passed through a cooling unit ( 9 ) , with a compressor (of 250-300 watt) to deliver cooling capacity of 90 to 150 watt. The temperature of the cooled stream is adjusted to keep a constant level of the liquid reservoir in the gas/liquid reactor, by maintaining reservoir temperature at about 4-5 degrees below ambience. In the embodiment illustrated in Figures 1A, IB and 1C, the secondary stream exiting the chiller ( 9 ) is guided to the conduit (6), where it joins the main liquid stream. However, it is generally more convenient to separately feed the secondary, cooled stream directly to reactor (1).

Accordingly, in one variant of the invention, the air purifier further comprises a chiller, wherein a line for delivering the aqueous stream from the pump diverges into a main line and a secondary line, such that the main line joins the perforated pipe (that is mounted horizontally inside the gas/liquid contactor) via the laterally disposed liquid inlet opening, and the secondary line is passed through said chiller and is guided to supply a cooled liquid stream, that exits the chiller, to the gas/liquid contactor.

It should be noted that a cooling method involving a secondary stream that is passed through a chiller positioned externally to the gas/liquid contactor and returned to the gas/liquid contactor to mix with the major portion of the solution, is just optional. A cooling coil (that is connected to a cooling system) can be inserted into the gas/liquid contactor, below the surface level of the solution, to keep the temperature of the solution at about 10 to 20°C.

Indoor air is drawn into reactor (1) by a device used to move air, e.g., a blower (10), operating to generate airflow of 1500 - 2500 cubic meter/hour. The air flows via 60-80 mm diameter conduit (11) and enters the lateral face of the gas/liquid contactor through an opening (12) located ~18 to 20 cm above the surface level of the liquid (that is, about ~2-5 cm (e.g. ~3 cm) below the plane where conduit (7) lies). It is noted that the air inlet and liquid inlet openings (12, 13, respectively) are located at different radial directions (with respect the axial axis of reactor (1)). Conduit (11) extends into the interior of the reactor in a non-radial direction, created by cylindrical section (14) which is oriented in an angle of least 30 to 80° relative to the radially oriented portion of pipe (11a) that reaches the lateral surface of reactor (1) at opening (12), such that the incoming air stream is forced to flow downwards, in the direction of the liquid surface .

A demister (15) is fitted in the upper zone of the gas/liquid contactor (1), that is, in the space above the plane through which the diametrically oriented pipe (7) is positioned and below the frustoconical section (2). A preferred demister configuration consists of two or more, for example four, vertically spaced apart disc sectors as shown in Figure 3A and 3B, or disc segments (not shown).

By the term "disc sector" is meant a part of a disc bounded by a central angle and a corresponding arc, wherein preferably 180°£ £250°. For example, in Figure 3A, a=200°.

By the term "disc segment" is meant a part of a disc bounded by an arc and its chord (the segment connecting two points of a circumference of a circle), wherein the corresponding central angle b that lies on the chord is preferably in the range from 50°< b <70°, such that the area of the disc is reduced by about 15 to 25% compared to the area of the full disc. The thickness of the disc sectors/disc segments is from 1 to 2 mm, and they are generally made of stainless steel (e.g., 316) or polymers such as poly(vinyl chloride), polyethylene and polypropylene .

In the specific design shown in Figures 3A and 3B, the demister consists of four disc sectors/disc segments, of equal radius [designated (17(1), 17(2), 17(3) and 17(4)] which corresponds to the radius of the cylindrical space of reactor (1). Adjacent disc sectors/disc segments are spaced about 2 to 4 cm apart (vertical distance). Demister (15) is coaxially and concentrically mounted in the cylindrical space of reactor (1), more precisely, in the section just below the frustoconical top part (2) of the reactor, with the aid of a vertically extending rod (16), to enable easy removal of the entire demister (the arc of the lowermost disc sector/disc segment (17(1)) lies on a thin rim provided along the circumference of the inner wall of reactor (1)).

The arcs of the disc sectors/disc segments are essentially contiguous with the inner wall of reactor (1). The moving air, that is, the mist consisting of air/solution, travels through the spaces between the disc sectors/disc segments, advancing upward via the access created by the "missing" piece of the disc. Adjacent disc sectors/disc segments are spatially oriented with respect to one another such that their arcs lie on essentially diametrically opposed walls of reactor (1), or, stated otherwise, with the "missing" piece of disc n being atop of, and beneath, the solid surface of disc n-1 and disc n+1, respectively. The arc of the lowermost disc sector/disc segment (17(1)) is positioned above air income opening (12).

The spatial arrangement of the disc sectors/disc segments 17(1), 17(2), 17(3) and 17(4) creates large surface area for solution vapors to condense, thereby minimizing escape of moisture. Our results indicate that with the aid of such demister and the cooled secondary stream supplied to reactor (1), escape of solution is avoided and liquid level in reactor (1) is fairly constant over long operation time, suppressing crystallization of the salts from the concentrated/nearly saturated circulating solution.

Accordingly, another aspect of the invention is a method wherein the gas/liquid contactor is cylindrically shaped and wherein the moving air with entrained liquid flows through spaces defined by a set of disc sectors or disc segments mounted in the gas/liquid contactor with vertical spacings between said disc sectors or disc segments, the arcs of said disc sectors or disc segments being contiguous with the inner wall of gas/liquid contactor, wherein adjacent disc sectors or disc segments are spatially oriented with respect to one another such that their arcs lie on essentially diametrically opposed walls of the gas/liquid contactor, thereby creating the passages for the flow of the moving air.

Brief description of the drawings

Figures 1A, IB and 1C are isometric, side and top views, respectively, of one preferred design of the air purifier of the invention.

Figure 2 shows a pipe mounted inside the air purifier, to deliver the circulated aqueous salt solution.

Figures 3a and 3B show a demister used in the air purifier. Figure 4 shows PM 10 levels versus time plot, measured in a study reported in Example 1.

Figure 5 shows PM 2.5 levels versus time plot, measured in a study reported in Example 1.

Figure 6 shows SO2 levels versus time plot, measured in a study reported in Example 1.

Figure 7 shows NO2 levels versus time plot, measured in a study reported in Example 1. Figure 8 shows CO2 levels versus time plot, measured in a study reported in Example 1.

Figure 9 shows ozone levels versus time plot, measured in a study reported in Example 1.

Figures 10 shows lead levels versus time plot, measured in a study reported in Example 1.

Figures 11 and 12 show the level of biological load (bacterial count and yeast and mould counts in CFU/plate units, respectively) versus time plot, measured in a study reported in Example 1.

Examples

Example 1

The goal of the study was to evaluate the efficiency of the apparatus of the invention (similar to the one shown in Figure 1, but without the chiller) in maintaining good air quality in 2400 cubic feet sized room (~ 70 m³; medium size living room). The apparatus was placed in Room 1.

For the purpose of comparison, a commercial air purifier, equipped with HEPA filter and active carbon, was placed in Room 2. A third room served as control (Room 3). The environment, that is, the open area in the vicinity of the three rooms, is designated in the study Room 0.

Experimental protocol and methods

The test lasted over fourteen days. During the first 48 hours, all three rooms were kept open to allow air exchange with the environment. The rooms were closed, and the air purifiers placed in Room 1 and Room 2 were turned on and allowed to operate continuously for the next twelve days.

During operation of the air purifier of the invention in Room 1, indoor air was blown up through the gas/liquid contactor (1) at a flow rate of 1500 m³/hour. Twenty-five liters of 30 wt.% sodium chloride solution was circulated with the aid of pump PQm 60 manufactured by Pedrollo, Italy, at a flow rate of 50 liter/min.

The quality of the indoor air was evaluated periodically over the test period. Levels of particulate matter and chemical pollutants were measured once daily (at the morning of each day, starting from day 1 to day 14). Measurements of biological pollutants began on the third day (three samples were taken on that day, at morning, afternoon and evening hours); next biological samplings were carried out on the even days of the fourteen days test period, once daily.

Particulate matter of smaller than 10 microns (PMio) and 2.5 microns (PM2.5) were measured by digital indoor air quality meter from Perfect Prime.

SO2 levels were measured by the method set out in IS:5182(P-2) 2001. Briefly, SO2 is collected from the air by a solution of potassium tetrachloromercurate. The oxidation-resistant HgCl2SC>3² complex thus formed is made to react with formaldehyde and pararosaniline hydrochloride to produce intensely colored solution. The absorbance of the resultant solution is measured spectrophotometrically at 560nm wavelength .

NO2 levels were measured by the method set out in IS:5182(P-6) 2006. NO2 is collected by bubbling air through a solution of sodium hydroxide (NaOH) and sodium arsenite (NaAs0₂₎ . The nitric ion formed is reacted with a solution reagent comprising phosphoric acid, sulfanilamide and N-(l- naphthyl)ethylendiamine dihydrochloride. The absorbance of the resultant colored solution is measured spectrophotometrically at 560nm wavelength.

CO₂ levels were measured by online meter for carbon dioxide from Lutron Electronic Enterprise Ltd.

O3 levels were measured by the method set out in IS:5182 (P-9) 1974. The absorbent used to collect O3 consists of potassium iodide solution (pH buffer of 6.8). Iodide is reduced to elemental iodine. The absorbance of the resultant colored solution is measured spectrophotometrically at 352nm wavelength . Pb levels were measured by the method set out in IS:5182(P-22) 2004. Particulate Pb and vaporous Pb are measured separately by the procedure. The procedure employs a sampling train with a pump, or source of suction, and a flow regulator. The sampling train is fitted with 0.45 pm membrane and activated carbon. Air is passed through the sampling train at a flow rate of 1 to 1.5 L/min for eight hours. Particulate lead is solubilized in nitric acid/perchloric acid solution and the dissolved lead is determined by ICP-MS.

Biological pollutants were measured by exposing agar- containing petri dishes to the air. Microorganism grown on the agar medium are determined by incubation of the agar plates and then counting the number of colonies developed.

Results

The results are presented graphically, showing plots of pollutants levels versus time. The measured concentrations of the chemical pollutants are expressed either in pg/m³ or ppm units. For biological pollutants, CFU/plate units are used.

Figure 4 and 5 show the levels of the particulate matter (PMio and PM2.5, respectively) plotted against time. Figures 6 to 10 show SO2, NO2, CO2, ozone and lead levels against time plots. Figure 11 and 12 report total bacterial count and total yeast and mould count, respectively.

Each of the appended graphs depicts four plots, corresponding to measurements taken in Room 0 (environment; blue, uppermost curve), Room 1 (where the apparatus of the invention operated; orange, usually lowermost curve), Room 2 (where a commercial, competitor air purifier was used; grey curve) and Room 3 (the control, treatment-free room; yellow curve). The results indicate that the HEPA-free air purifier of the invention kept consistently low levels of particulate matter and chemical pollutants and reduced the microbial load effectively in Room 1, at least equally as good as, and in fact slightly better than, the HEPA/activated carbon filter- based commercial air purifier which operated in Room 2.

Example 2

The goal of the study was to evaluate the efficiency of an apparatus of the invention in reducing microbial load in 800 m³ hall accommodating a few dozens of people during day time. The configuration of the apparatus was similar to the one shown in Figure 1, but stainless steel cooling coil was mounted inside the gas/liquid contactor below the surface level of the liquid, connected to a chiller operating at lkW output.

Experimental protocol and methods

The test lasted over three days. During operation of the air purifier of the invention in the hall, indoor air was blown up through the gas/liquid contactor (1) at a flow rate of 600 m³/hour. 30 liters of 30 wt .% carnallite solution was circulated with the aid of pump PQm 60 manufactured by

Pedrollo, Italy, at a flow rate of 50 liter/min. A constant temperature of ~20°C was kept throughout the test period.

Air samples were collected by a centrifugal air sampler before the experiment begun (to), and then from time to time until the end of the three days test period (16 hours, t24 hours and t72 _hours) to determine the level of microbial contamination. Air (a volume of 500 Liter) was extracted by the sampler and directed to an agar strip. Microorganism in the air deposit onto the agar. The agar strips were removed from the sampler and incubated for 48 hours, following which the colonies were counted . Results

At the beginning of the experiment (to), the initial bacterial load was estimated to be 120 CFU per cubic meter. A steady reduction in bacterial counts was noted during the three days test period, as follows: te hours = 50 CFU/m³ t₂₄ hours = 20 CFU/m³ t₇₂ hours = 11 CFU/m³.

The results show that continuous operation of the air purifier, with circulation of a carnallite solution, improved the quality of indoor environment in a closed space accommodating people, achieving bacterial removal rates of about 90% (i.e., from 120 CFU/m³ down to 11 CFU/m³.

Claims

1) An air purifier comprising: an elongated, vertically positioned gas/liquid contactor, bounded by a bottom section, a top section and a lateral surface, with an air inlet opening disposed in the lateral surface and an air outlet opening at the top section, a pipe mounted horizontally in the interior space of the gas/liquid contactor, wherein the pipe is perforated along its length with a plurality of downwardly directed apertures, a demister fitted into the space of the gas/liquid contactor, a pump installed to circulate an aqueous solution through the gas/liquid contactor, wherein a discharge line of the pump is directed to a liquid inlet opening disposed in the lateral surface, to join said perforated pipe, a blower for drawing air stream into the gas/liquid contactor via said laterally disposed air inlet, the air inlet and liquid inlet openings being located at different radial directions with respect to the longitudinal axis of the gas/liquid contactor.

2) An air purifier according to claim 1, wherein the gas/liquid contactor is cylindrically shaped, and the horizontally mounted pipe lies along a diameter of the internal space of the gas/liquid contactor.

3) An air purifier according to claim 1 or 2, further comprising a chiller, wherein a line for delivering the aqueous stream from the pump diverges into a main line and a secondary line, such that the main line joins said perforated pipe via the laterally disposed liquid inlet opening, and the secondary line is passed through said chiller and is guided to supply a cooled liquid stream, that exits the chiller, to the gas/liquid contactor. 4) An air purifier according to claim 2 or 3, wherein the demister consists of two or more vertically spaced apart disc sectors or disc segments, the arcs of said disc sectors or disc segments being contiguous with the inner wall of the cylindrical gas/liquid contactor.

5) An air purifier according to claim 4, wherein adjacent disc sectors or disc segments are spatially oriented with respect to one another such that their arcs lie on essentially diametrically opposed walls of the cylindrical gas/liquid contactor.

6) An air purifier according to any one of the preceding claims, wherein a conduit delivering the indoor air stream ends with a section that extends into the interior of the reactor in a non-radial direction, creating an angle from 30 to 80° relative to radially oriented portion of the conduit that reaches the lateral surface of the gas/liquid contactor.

7) An air purifier according to any one of the preceding claims, wherein the gas/liquid contactor accommodates an aqueous solution comprising alkali chloride at concentration of 200 to 400 g/Liter, wherein said solution is optionally slightly alkaline.

8) A method of improving the quality of indoor air, to reduce levels of particulate matter and/or chemical pollutants and/or biological pollutants, the method comprising: circulating an aqueous salt solution held in an elongated, vertically positioned gas/liquid contactor, wherein the circulation includes introducing the solution into the interior of the gas/liquid contactor along a direction perpendicular to the longitudinal axis of the gas/liquid contactor, above the surface level of the solution reservoir, spraying the solution downwards, and optionally cooling a portion of the circulated solution to deliver a cooled solution stream to the solution reservoir in the gas/liquid contactor; drawing indoor air into said gas/liquid contactor and releasing purified air stream from the top of the gas/liquid contactor, wherein the incoming air stream is laterally fed to the gas/liquid contactor, above the surface level of the solution reservoir, directed to the surface level of the solution, forced to pass through the sprayed solution, wherein the moving air with entrained liquid flows in an upward direction through a plurality of spaces arranged transverse to the longitudinal axis of the gas/liquid contactor, accessing said transverse spaces via passages located adjacent to, or bounded by, sections of the inner walls of the gas/liquid contactor so as to increase the path the air travels through said transverse spaces.

9) A method according to claim 8, wherein the gas/liquid contactor is cylindrically shaped and wherein the moving air with entrained liquid flows through spaces defined by a set of disc sectors or disc segments mounted in the gas/liquid contactor with vertical spacings between said disc sectors or disc segments, the arcs of said disc sectors or disc segments being contiguous with the inner wall of gas/liquid contactor, wherein adjacent disc sectors or disc segments are spatially oriented with respect to one another such that their arcs lie on essentially diametrically opposed walls of the gas/liquid contactor, thereby creating the passages for the flow of the moving air.

10) A method according to claim 8 or 9, wherein the solution comprises from 200 to 400 g/liter alkali chloride and is optionally slightly alkaline. 11) A method according to claim 10, wherein the solution comprises sodium chloride.

12) A method according to claim 8 or 9, wherein the solution comprises from 200 to 400 g/liter a mixture of alkali chloride and alkaline earth metal chloride and is optionally slightly alkaline.

13) A method according to claim 12, wherein the solution comprises potassium chloride and magnesium chloride.

14) A method according to any one of claims 8 to 13, wherein the quality of the indoor air is improved by reducing the levels of particulate matter and/or acidic gases and/or microbial load.