DESCRIPTION

FIELD OF THE INVENTION

The present invention refers to an air filter, especially of the type that uses adsorbents such as carbon (chemically activated or not), zeolite or alumina, being particularly suitable for application in laboratory cabinets, such as gas filtration cabinets. The present invention also relates to a laboratory cabinet associated to said filter.

BACKGROUND OF THE INVENTION

Air filters of the indicated type, such as those using active carbon adsorbents from coconut shell, for example, have a large proportion of micropores, being the most suitable for adsorbing gaseous pollutants.

There are currently several types of filters known, which can be combined between them according to the work needs. For example:

- A: General purpose filter, especially suitable for organic vapors such as ketones, ethers, xylene alcohols, etc.

- BE: For inorganic acid fumes such as: H2SO4, HCI , HNO3, as well as volatile sulfur compounds such as H2S, SO3, etc.

- F: For formaldehyde and formalin fumes, and their derivatives. It can also be used for other organic compounds.

- K: For NH3 and amine fumes. It can also be used for other organic compounds.

The adsorption phenomenon initially takes place in a small section of the filter bed, known as the mass transfer zone or ZTM. As the ZTM reaches its capacity limit (saturation) it progressively moves through the thickness of the filter, until it reaches the top. It is then said that the breaking point has been reached, observing a gradual increase in the concentration of the pollutant gas until reaching a total saturation of the filter.

As for the gas filtration cabinets, it should be noted that they do not require a coupled extraction equipment, since they have a filtration system to retain gases and polluting vapors generated inside the cabinet, thus constantly renewing, the air in the laboratory and giving it a number of advantages over conventional extraction hoods: - Pollutants are not released into the environment but are rather retained in the filter.

- They do not require the installation of outdoor exhaust ducts.

- Its small size and weight, as well as the absence of coupling to an evacuation system, expand the possibilities of location and make it possible to replace it in the event of a change of needs.

- The aspirated air is not expelled but recirculated back into the laboratory free of contaminants. This does not increase the consumption of air conditioning to replace the extraction loss.

To obtain maximum filtration efficiency, the following parameters of vital importance should be taken into account in the design and construction of recirculation cabinets with air filters of the indicated type.

Adsorption is a process of physicochemical nature in which molecules of a gas or liquid, called adsorbate, interact and adhere to the surface of a solid, called adsorbent or substrate. This phenomenon is widely used in the purification of liquid or gaseous streams. Gas phase applications include air odor removal, solvent recovery for reuse, respiratory protection, etc.

There are different types of adsorbents such as activated carbon, silica gel, alumina, zeolites and synthetic resins. The most important characteristic of an adsorbent material is its high porosity, which gives it a high specific surface area. Inside this distribution of pores of different sizes, the gaseous molecules are adsorbed and eventually condense and are retained.

Activated carbon, for example, is a carbonized material that has undergone an activation process in order to increase its porosity. Activated carbon has a number of characteristics that make it a highly appreciated adsorbent material:

- The manufacturing process ensures a great development of its active surface.

- It has the physical properties necessary to ensure good mechanical resistance.

- The cost of the manufacturing process and raw material is accessible.

The retention capacity of the activated carbon for a given gas depends on the characteristics of the adsorbent (chemical composition, pore size and distribution, surface area, and particle size), the adsorbate (chemical composition, molecular size, boiling point and polarity), and the adsorbate (chemical composition, molecular size, boiling point and polarity). The concentration of the adsorbate in the liquid phase and the characteristics of the phase (pH, temperature, vapor pressure and humidity).

Today's air filters are usually formed by a casing configured to contain a compact filling of an adsorbent, such as activated carbon. Said housing presents a vacuum side and an extraction side. The suction face has a distribution of suction openings that define a suction area that allows an air flow into the filter. The extraction face has a distribution of extraction openings that define an extraction area that allows airflow to escape from the filter. The suction openings on the suction face are distributed exactly the same and/or symmetrical to the extraction openings on the extraction face, as shown in Figures 1 and 2.

Thus, being the cab motor normally located on the extraction face in the central part of the filter, it is observed that most of the flow passes through the central part of the filter, without going beyond the ends or lateral areas of the filter. As shown in the flow diagrams of Figures 3a - 3c, looking for the path with the lowest load loss.

So today, in commercially used activated carbon filters, a large amount of unused activated carbon is discarded because the breaking point is reached prematurely, usually in the central part of the filter, and not homogeneously. This leads to a replacement of the filter even though much of the activated carbon is still in perfect condition to continue adsorption.

The present invention refers to an air filter specially designed to ensure a greater use of the adsorbent, thus maximizing the efficiency of the filter, extending its useful life and with product retention capacities substantially higher than current. Whose configuration allows:

- directing the air flow through the adsorbent filler to increase the contact area between the adsorbent and the adsorbate;

- decreasing its speed so that the contact time between the filter coating and the flow is much longer, which results in a greater optimization of the adsorbent, that is, significantly increases the residence time of the flow within the bed;

- adapting to the needs of the system in terms of facade speed (known as the speed used to achieve the necessary air barrier between the operator and the pollutant), load loss and engine performance; and

- having a reduced filter manufacturing cost.

DESCRIPTION OF THE INVENTION

The air filter of the present invention comprises at least one housing configured to contain an adsorbent inside, where the housing has:

- a suction face with a distribution of suction openings that define a suction area that allows an air flow into the filter; and

- an extraction face with a distribution of extraction openings that define an extraction area that allows airflow to escape from the filter. The filter is characterized by the suction openings on the suction face being distributed inversely to the extraction openings on the extraction face to redirect the air flow inside the filter.

The suction face therefore has suction openings that allow the air flow to enter through them, arranged between suction separation zones that prevent the passage of air flow. Similarly, the extraction face has extraction openings that allow airflow to escape through these, arranged between extraction separation zones that prevent airflow. Thus, by arranging this combination of openings and separation areas in reverse on one side and the other side of the filter, it is possible to redirect the air flow inside, making better use of the adsorbent.

The inverse distribution of openings means that the air flow is therefore found with roads with greater loss of load when trying to cross the filter perpendicular to it, finding alternately paths in longitudinal direction to the filter that favor its circulation. So the air flow travels further inside the filter.

Therefore, there is an increase in the load loss perpendicular to the filter, which in turn causes a decrease in the air flow output speed. Consequently, this fact directly affects the residence time of the flow within the bed, increasing it considerably. As a result, the contact time between the filter adsorbent coating or filler and the flow is much longer, while circulation is occurring throughout the filter bed, including both the central part and the ends or lateral areas of the filter, which translates into greater optimization, performance and I or use of this adsorbent.

The term “reverse form” is also interpreted as an “opposite” distribution of the openings of one face with respect to the other face.

Preferably the distribution of openings is heterogeneous, defining areas of aspiration and extraction that vary along the length and/or width of the surface of the corresponding suction and extraction faces. Preferably, the suction area of the suction face is equal to the extraction area of the extraction face.

Preferably, the distribution of extraction openings on the extraction face is coincident with the distribution of suction openings on the suction face. So that when these are arranged in reverse in the housing, a distribution of apertures is created symmetrically inverse or opposite of one side with respect to the other, both in the longitudinal direction of the filter and in the transverse direction of the same. In other cases of embodiment, the distribution of extraction openings on the extraction face may not be coincident with the distribution of suction openings on the suction face, so, when these are arranged in reverse in the housing, an asymmetrically inverse or opposite distribution of openings from one side to the other, either in the longitudinal and I or transverse direction of the filter is created.

The distribution of filter openings can be done in different ways, for example; by arranging a greater or lesser number of them, by varying the dimensions and/or shape of them, concentrating them and/or dispersing them in certain areas of the face along and/or width of its surface, etc.

Preferably, the suction area of the suction face decreases from a first longitudinal end to a second longitudinal end of the filter. At the same time, the extraction area of the extraction face decreases in reverse from the second longitudinal end to the first longitudinal end of the filter.

Therefore, when the air flow falls on the suction face, a greater part of it enters the filter through the area with a larger suction area, redirecting its circulation once inside it to exit through the area that has a greater extraction area, located at the opposite end.

Preferably, the air flow is redirected inside the filter, increasing its horizontal path through the filter to stay longer inside the filter and pass through both the central and lateral part of the adsorbent bed.

Preferably, the suction face is divided into:

- a first half of aspiration that concentrates a larger aspiration area, e.g. between 55% and 60% of the total aspiration area; and

- a second half of aspiration that concentrates a smaller aspiration area, for example, between 40 and 45% of the total aspiration area.

Preferably, the extraction face is divided into:

- a first half of extraction that concentrates a larger extraction area, for example, between 55 and 60% of the total extraction area; and

- a second extraction half that concentrates a smaller suction area, for example, between 40 and 45% of the total suction area.

In each of these first suction and extraction halves, the suction area or extraction area represents a passage area of between 65 and 75%, for example, 70% of the total area of each of these first halves, representing the separation zones that prevent the flow of air the remaining percentage. In each of these second suction and extraction halves, the suction area or extraction area represents a passage area of between 50% and 60%, for example 54%, of the total area of each second half, representing the separation zones that prevent the flow of air the remaining percentage.

Preferably, the housing is formed by two half bodies, where each of them comprises the suction face or the extraction face, facing each other and joined perimetrally. This union is preferably a thermal union or with addition of material, such as polypropylene, for better compatibility. Preferably, the adsorbent is then filled to this junction, using the side holes to introduce the adsorbent particles. The housing is preferably waterproof.

The filter of the present invention can take different shapes and measures, being preferably rectangular or square.

According to one embodiment, the enclosure comprises a length of 300 to 500 mm long, a width of 100 to 300 mm and a height of 100 to 200 mm. Said dimensions may be larger or smaller, depending on other embodiments.

According to an embodiment, the housing wall comprises a 2 to 8 mm thickness, and preferably 5 mm. Said dimensions may be larger or smaller, depending on other embodiments.

Preferably, the housing is made of propylene.

Suction openings and/or extraction openings can be made in different ways.

According to a first case, the suction openings and/or the extraction openings are formed as holes, each of them preferably having a diameter of 1 to 3 mm, and preferably 2 mm. Said dimensions may be larger or smaller, depending on other embodiments.

Preferably, these holes are distributed in groups on the surface of the suction and extraction faces. Each group concentrates a greater or lesser number of holes, thus creating different suction and extraction areas along the surface of each of these faces. The groups of holes are distributed inversely on one side relative to the other. Preferably the holes are distributed in each group forming rows and columns, or in staggered formation. As an example, the holes are distributed in four groups on the surface of one side of the housing, and inversely on the other side, where:

- The first group has 7 rows of 38 holes of 2 mm each, forming a total dimensions of 30 mm in height and 152 mm in width approx.

- The second group has 10 rows of 38 holes of 2 mm each, forming a total dimensions of 40 mm in height and 152 in width approx., separated about 30 mm from the first group.

- The third group has 12 rows of 38 holes of 2 mm each, forming a total dimensions of 50 mm in height and 152 in width approx., separated about 30 mm from the second group.

- The fourth group has 30 rows of 38 holes of 2 mm each, forming a total dimensions of 120 mm in height and 152 in width approx., separated about 30 mm from the third group.

According to a second case of embodiment, the suction openings and/or the extraction openings are formed as open grids or openings, preferably placing a pre-filter blanket G4 (for coarse particles), in order to avoid both the release of the particles from the adsorbent filler and the dust that may come from it.

Preferably, the filter is formed by a plurality of housings joined laterally, each of them being formed as a cartridge.

According to a preferred embodiment example, the filter has a rectangular configuration consisting of four housings. As an example, each of these housings or cartridges has the following characteristics:

Weight: 600g approximately;

External dimensions in mm: 390 x 182 x 55;

Material: Polypropylene of 5 mm thickness;

Maximum adsorbent load: 2kg approximately.

No. of carbon mesh: 6x12 mesh (from 3.35 mm to 1 ,68mm particle size).

The filter presents a waterproof feature.

Preferably, the adsorbent used by the filter of the present invention in any of its embodiments is active carbon, zeolite or alumina.

Preferably, the air filter of the present invention is an air filter for laboratory cabinets, such as gas filtration cabinets. The present invention also has as its object a laboratory cabinet, such as a gas filtration cabinet, comprising one or more air filters according to any of the embodiments described above. Preferably, the gas filtration cabinet is a gas filtration ductless fume hood.

SUMMARY OF THE DRAWINGS

Then, a series of drawings are briefly described, which help to better understand the invention and that are expressly related to two embodiments of this invention that are presented as nonlimiting examples of it.

Figure 1 represents a perspective view of a conventional air filter.

Figure 2 represents a longitudinal section of a conventional air filter.

Figures 3a - 3c represent a sequence of flow diagrams in a laboratory cabinet equipped with a conventional filter, at different heights after passing through the filter.

Figure 4 represents a perspective view of the air filter of the present invention showing the suction face, according to a first case of embodiment.

Figure 5 represents a perspective view of the air filter of the present invention showing the extraction face, according to a first embodiment case.

Figure 6 represents a longitudinal section of the air filter of the present invention, according to a first case of embodiment.

Figure 7 represents a frontal view of the air filter of the present invention showing the suction face, according to a first case of embodiment.

Figure 8 represents a front view of the air filter of the present invention showing the extraction face, according to a first case of embodiment.

Figure 9 represents a view of the “Z” detail of Figure 4.

Figure 10 represents a perspective view of the air filter of the present invention, according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

Figures 1 and 2 represent a perspective view and a longitudinal section of a conventional air filter (T). This filter (T) is formed by a housing (2’) configured to contain inside a compact filling of an adsorbent (O’), such as activated carbon. The housing (2’) presents a vacuum side (3’) and an extraction side (4’). The suction face (3’) has a distribution of suction openings (3T) that allows an air flow (F’) to enter the filter (T). The extraction face (4’) has a distribution of extraction openings (4T) that allows the air flow (F’) to escape from the filter (1). As can be seen, the suction openings (3T) of the suction face (3’) are distributed exactly the same and symmetrical to the extraction openings (4T) of the extraction face (4’).

Thus, being the engine of the cab located on the extraction face (4’) in the central part of the filter (T), it is observed how most of the flow (F’) passes through the central part of the filter (T), without passing through the ends or lateral areas of the filter. So that the adsorbent (C’) fills much earlier in the central part of the filter (T) than in the rest of the areas. This involves the replacement of the filter (T) even though much of the adsorbent (C’) around that central part is still in perfect condition to continue with the adsorption functions. So in the filter (T) of the Figs. 1 and 2 A large amount of rarely used adsorbent (C) is discarded because the breaking point is reached prematurely in the central part of the filter (T). That is, in a non-homogeneous way.

Figures 3a - 3c represent a sequence of flow diagrams in a laboratory cabinet equipped with a conventional filter (T), at different heights (h: 90cm, h: 85cm, h: 82 cm) after its passage through the filter (T). The abscissa and ordinate axes reflect the length and width of the filter (T) respectively, so as a whole they represent the filter surface (T). The shades of gray reflect the airflow velocity (F’), measured in meters per second, in each area of the filter (T).

As you can see, the areas of higher speed are in the central part of the filter (T), being much smaller around it. This shows that most of the air flow (F’) passes through the central part of the filter (T), without passing through the lateral ends and/or the most perimetral area of the filter (T).

According to the tests carried out for the conventional filter (T) of the Figs. 3a - 3c, this filter (T) is saturated much earlier, because the central part comes to fill faster than the parts further away from it.

According to AFNOR NFX 15-211 , the test methodology consists of maintaining 200 ppm of isopropanol at all times in the volume of a cabinet by means of controlled evaporation thanks to a peristaltic pump that supplies the precise flow to achieve this concentration in the environment. The experiment is considered to have come to an end when 1% of the allowed TLV (environmental limit value) is detected at the exit of the cabinet (TLV of isopropanol is 200ppm, therefore, the experiment ends when at the exit 2ppm is detected). The concentration at the outlet is measured just at the outlet of the cabinet using a PID (Photoionization Detector) calibrated for organic compounds. The obtained results are summarized in the following tables:

Thus, according to the tests carried out on the conventional filter (T), it is saturated between 273 and 303 minutes.

Figures 4 and 5 respectively represent a perspective view from the suction face (4) and a perspective view from the extraction face (3) of the air filter (1) of the present invention, according to a first case of embodiment.

As can be seen, the air filter (1) of the present invention comprises a housing (2) configured to contain inside an adsorbent (C), where said housing (2) features:

- a suction face (3) with a distribution of suction openings (31) defining a suction area (A31) allowing an air flow (F) into the filter (1); and an extraction face (4) with a distribution of extraction openings (41) defining an extraction area (A41) that allows airflow (F) to escape from the filter (1);

The filter (1) is characterized by the suction openings (31) on the suction face (3) being distributed inversely to the extraction openings (41) on the extraction face (4) to redirect the air flow (F) inside the filter (1). For a clearer view of this reverse distribution, the suction openings (31) in Figure 5 have been represented using hidden lines.

The suction face (3) therefore has suction openings (31) that allow the airflow (F) to enter through these, arranged between suction separation zones (32) that prevent the air flow (F) from passing. Similarly, the extraction face (4) has extraction openings (41) that allow the airflow (F) to escape through these, arranged between extraction separation zones (42) that prevent the airflow (F) from passing. Thus, by arranging this combination of openings (31 , 41) and separation zones (32, 42) in reverse on one side and the other side of the filter (1), it is possible to redirect the air flow (F) inside, making better use of the adsorbent (C).

The adsorbent (C) is filled using the side holes (5), which allow the adsorbent particles to be introduced. The housing (2) is preferably waterproof.

As shown in Figure 6, the inverse distribution of openings (31 , 41) makes the air flow (F) meet with roads of greater loss of load when trying to cross the filter (1) perpendicular to it, alternatively finding paths in longitudinal direction to the filter (1) that favor its circulation. So the air flow (F) makes a longer travel inside the filter (1).

Thus, when the air flow (F) falls on the suction face (3), a greater part of the air flow enters the filter (1) through the area with the largest suction area (A31). Redirecting its circulation once inside it to exit through the area that has a greater extraction area (A41), located at the opposite end.

The air flow (F) is redirected inside the filter (1) increasing its horizontal travel (RH) through the filter (1) to stay longer inside the filter and pass both the central and lateral part of the adsorbent bed.

Figures 7 and 8 respectively represent a frontal view of the suction face (3) and a frontal view of the extraction face (4), according to a first embodiment case. As can be seen, the distribution of openings (31 , 41) is heterogeneous, defining areas of aspiration (A31) and extraction (A41) that vary along the surface of the corresponding suction (3) and extraction (4) faces. The suction area (A31) of the suction face (3) is equal to the extraction area (A41) of the extraction face (4). The distribution of extraction apertures (31) on the extraction face (3) is coincident with the distribution of suction openings (41) on the suction face (4), so that when these are arranged in reverse in the housing (2) a distribution of openings (31 , 41) is created symmetrically inverse or opposite of one face with respect to the other, both in the longitudinal direction of the filter (1) and in the transverse direction of the filter.

The suction area (A31) of the suction face (3) decreases from a first longitudinal end (1 Li) to a second longitudinal end (I L2) of the filter (1). At the same time the extraction area (A41) of the extraction face (4) decreases in reverse from the second longitudinal end (I L2) to the first longitudinal end (1 Li) of the filter (1).

The suction face (3) is divided into:

- a first half of aspiration (31a) which concentrates a larger aspiration area (A31), e.g. 55% to 60% of the total aspiration area (A31); and

- a second half of aspiration (31 b) which concentrates a smaller aspiration area (A31), for example, between 40% and 45% of the total aspiration area (A31).

The extraction face (4) is divided into:

- a first half extraction (41a) which concentrates a larger extraction area (A41), e.g. 55 to 60% of the total extraction area (A41); and

- a second extraction half (41 b) which concentrates a smaller suction area (A41), for example, between 40% and 45% of the total suction area (A41).

In each of these first halves of suction (31a) and extraction (41a), the suction area (A31) or extraction area (A41) represents a passage area of 65 to 75%, for example, 70% of the total area of each of these first halves (31a, 41a), representing the separation zones (32, 42) that prevent the flow (F) of air from passing the remaining percentage.

In each of these second halves of suction (31 b) and extraction (41b), the suction area (A31) or extraction area (A41) represents a passage area of 50 to 60%, for example 54%. Of the total area of each of these second halves (31b, 41b), representing the separation zones (32, 42) that prevent the passage of the flow (F) of air the remaining percentage.

The filter (1) in this example is rectangular, with a housing (2) comprising a length (L) from 300 to 500 mm long and a width (W) from 100 to 300 mm, Figs. 7 and 8, as well as a height (H) of 100 to 200 mm and a thickness (E) of 2 to 8 mm, Fig. 6. As shown in detail" Z" of Figure 9, the suction openings (31) and/or the extraction openings (41) are formed as open grids or openings, also placing a pre-filter blanket G4 (for coarse particles) In order to avoid both the detachment of the particles from the adsorbent filler (C) and the dust that may come from it.

According to the tests carried out for the filter (1) of the present invention, corresponding to the Figs. 4 to 9, this filter (1) is saturated much later than the conventional filter, thus guaranteeing a greater use of the adsorbent, thus maximizing the efficiency of the filter, extending its useful life and with a greater adsorption capacity.

The test methodology also consists, according to AFNOR NFX 15-211 , in maintaining 200 ppm of isopropanol at all times in the volume of a cabinet by means of controlled evaporation thanks to a peristaltic pump that supplies the precise flow to achieve this concentration in the environment. The experiment is considered to have come to an end when 1% of the allowed TLV (environmental limit value) is detected at the exit of the cabinet (TLV of isopropanol is 200ppm, therefore, the experiment ends when at the exit 2ppm is detected). The concentration at the outlet is measured just at the outlet of the cabinet using a PID (Photoionization Detector) calibrated for organic compounds. The obtained results are summarized in the following tables:

Thus, according to the tests carried out on the filter (1) of the present invention, it is saturated about 420 minutes for a standard load of adsorbent (C), and about 521 minutes for a maximum load of adsorbent (C). That is, it is saturated much later than a conventional filter with the same standard load.

Figure 10 shows a perspective view of the air filter (1) of the present invention, according to a second embodiment. In this case, the filter (1) consists of a plurality of housings (2) joined laterally, each forming as a cartridge.

Specifically, the filter (1) has a rectangular watertight configuration consisting of four housings (2), each of which has the following characteristics:

Weight: 600g approximately;

External dimensions in mm: 390 x 182 x 55;

Material: Polypropylene of 5 mm thickness;

Maximum adsorbent load: 2kg approximately.

No. of carbon mesh: 6x12 mesh (from 3.35 mm to 1 ,68mm particle size).

Each housing (2) consists of two half-bodies (2a, 2b), each comprising the suction face (3) or extraction face (4), facing each other and joined by the perimeter. This union is preferably a thermal union or with addition of material, such as polypropylene, for better compatibility.