FI104154B - Filters for gases - Google Patents

Description

5, 104154

Gas filter

The invention relates to a gas filter of the type set forth in the preamble of claim 1.

Such a gas filter is intended e.g. to be located in the ventilation duct to remove gaseous impurities from the supply air of the space.

Harmful gases are generally removed from the supply air by filters 10, which are located in the ventilation duct and contain granular material with a high specific surface area. Sulfur dioxide, nitrogen oxides, chlorine, hydrogen chloride and ozone, among others, are common gases to be filtered by such filters.

15 In addition to the standard working and living areas, there are a number of special spaces that are subject to remarkably high standards of air cleanliness. Such special modes are, for example, so-called. clean rooms, where components of sensitive electronic devices and / or the devices themselves. Also. equipment operating spaces often need to be protected, even with device-specific filters, to ensure their reliable operation.

Supply air filtration has increased, and will continue to increase substantially, for a variety of vehicles and machinery where filtering of exhaust fumes, in particular, and pollutants for which the vehicle or machine is used (eg application of pesticides on a tractor) is important.

It is generally known to increase the filtering efficiency of the filters by increasing the contact or residence time between the filter material and the air to be filtered, e.g. by increasing the thickness of the filter, i.e. the layer through which the air to be filtered flows. Then there will be '! pressure loss, which is not favorable for the operation of the ventilation system.

A filter is known from French Patent 7232725 (Publication Number 2199479), in which the flow of gas to be purified is intended to pass through a layer of filter material. Such layers may consist of two layers of fibrous material and a granular adsorbent interposed therebetween. In the actual filter structure, these layers may be located in parallel to form a pack or, as shown in Figures 8 and 9 of the publication, spirally wrapped 5 and housed, with the material to be filtered passing axially and outwardly from the center of the spiral.

In addition, European Patent Publication No. 504389 discloses a filter structure in which the material to be filtered is intended to pass through layers of filter material wrapped in spiral from the center to the outside. The filter material is obtained by mixing the granules and the fibers of the adsorbent with each other.

Also in these filters, the flow resistance caused by the material must be taken into account when passing the gas to be purified through the filter material containing adsor-15 bent, with the above problems.

Finnish patent FI-94724 discloses a method for making a gas filter, wherein the filter is formed from overlaid, corrugated and chemisorption-impregnated carrier material layers in which the wavelengths merge with the air flow direction and the layers form separate elongated flow channels. The carrier material is an aluminum sheet with alumina secured to the porous surface on both surfaces. Such a filter does not cause flow resistance: for the air to be filtered, but the contact surface is obtained much more than the same volume as when using granular materials. A filter of the same type is also known, for example, from U.S. Patent No. 4,391,616.

30

It is an object of the invention to provide a new type of filter structure which combines a low flow resistance and a good filtration efficiency due to the large surface area. To accomplish this purpose, the filter according to the invention is essentially characterized in what is described in the characterizing part of claim 1 attached.

3, 104154

At the same time, the filter material forms the walls separating the longitudinal flow channels. In these flow channels, flow occurs between their upstream and downstream ends in the direction of the filter material, i.e. the filter material adsorbs the desired impurities from the gas flowing past it. The planar filter material layer has at least two overlapping layers: a support layer and a porous adsorbent material layer. In addition, the various layers of filter material are separated from their surface by elongated elongated spacers which also contain porous adsorbent material. The filter material layers may be multilayer structures with the support layer in the middle and the adsorbent material layers on one or both sides, or preferably the filter material layer having a layer of adsorbent material disposed between the two porous support layers.

15

The oblong flow channels are thus limited by walls containing adsorbent in perpendicular to the flow direction: areas between the spacers of the filter material layer on opposite sides of the filter material layers and filter 20 in the direction of the material layers on the opposite sides of the aforementioned spacers.

For other preferred embodiments, reference is made to the appended dependent claims and to the description which follows.

The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 is a cross-sectional view of a filter material used in a filter according to the invention; Fig. 2 is a cross-sectional view of a second structure 35 of a filter according to the invention; Fig. 5 illustrates a preferred embodiment of a filter material in cross-section, Fig. 6 illustrates the operating principle of a filter according to the invention in a channel cross-section, and Figs. 7 to 9 illustrate the results of tests performed as a filter.

The filter material layer described in the following description comprises a porous adsorbent material layer held in place by a support layer. The backing layer forms the backing structure of the filter and allows the filter to be made into a permanent structure of the desired shape and thus obtains a porous adsorbent material of relatively low strength properties.

Figure 1 shows a layer of material used in the filter according to the invention as part of the structure 20. The material layer is a filter material which forms a substantially uniform layer 1. The layer is formed of three sub-layers, i.e. two gauze nonwoven backing layers 1a which form the outer surfaces of the layer and a sandwich adsorbent material 1 sandwiched therebetween.

Fig. 1 further shows elongated, separate and substantially parallel strips disposed on top of the layer. These strips may be of the same structure as the material forming the layer 1, whereby they may have been cut into narrower strips from the wider planar material used for the layer 1 and placed over the layer 1. The strips thus form elongate protrusions in the material layer 1, which act as spacers 2 to keep the overlapping layers 1 separated.

5, 104154

Figure 2 shows one possible filter, or filter cell, to be constructed by means of filter material. The layers 1 of the material of Fig. 1, on which separate strips are disposed, are superimposed, thereby producing elongated parallel flow channels 3 parallel to the layers of the layers. The individual channels 3 are delimited by spacers 2 separating the layers 1. and, on the other hand, layers of filter material 1. Thus, all walls of the flow passage 3 are of filter material, i.e. they contain porous adsorbent material.

In the resulting cell, air flows in channels 3, the walls of which pass through gaseous substances to be filtered off. All wall surfaces of the channels are porous because at the uniform layers of filter material they consist of a porous support layer 1a and at spacers 2 directly from the porous adsorbent material.

15

The rectangular rectangular cell shown in Figure 2 is easy to shape, for example, by cutting to the desired shape determined by the application.

It is also possible to provide a similar type of frost structure by pleating a continuous planar material such that successive portions of the same material form parallel overlapping layers 1 in the cell. Figure 3 illustrates this principle in which the protrusions of the material layer 1 overlap each other pleating, whereby these protuberances are naturally sufficiently sparse on the surface of the material layer. The smooth surfaces on one side are similarly facing each other.

Figure 4 shows another alternative in which the basic design principle is the same as in Figure 2. Here, the filter cell is formed by winding the same planar filter material on a roll, whereby the overlapping layers of filter material 1 consist of successive, intermittent interconnected portions of the same material. Also, such a material may initially be similar to Figure 1, whereby the strips on its surface form a spiral cross-section of a strip perpendicular to the passageways 3, thus forming a spacer 2 as described above. Such a filter mesh can also be shaped at its ends, for example, by cutting to the desired shape.

Before the formation of the cell, the spacers 2 may be secured to the surface of the layer 1 by any suitable means, for example by utilizing the fibers of the support layer 1a in the layers 1 and / or spacers 2, which may be heat-binding fibers. Bonding can also be used. Pullοί 0 a bulky cell, ie a pack or roll, can be mechanically retained, for example, by placing it in a suitable housing.

Figure 5 shows an advantageous constructional variant of the material layer 1. When the protrusions acting as spacers 2 in FIG. The image structure may be practically fabricated by passing an adsorbent particle layer 1b between two support layers 1a by a so-called multi-layer stripping method, followed by passing the resulting multi-layer structure between two pressing surfaces, such as a roll, having grooves to provide the desired shape. For this mechanical shaping step, the topsheet I on which the protrusions are formed may be wider than the topsheet on the opposite side because it undergoes narrowing in width.

Although Figure 5 illustrates the availability of approximately rectangular, rectangular or trapezoidal cross-sections, it is possible to select another shape, for example wavy, by choosing a pressing surface to perform the shaping. However, with known filter materials made of corrugated carrier material, there is a difference here that the thickness of the material layer 1 varies due to the bumps and there is more porous adsorbent material in the thickness direction than between them.

Figure 6 shows a schematic side view of the filter. The flow channels 3 pass through the entire filter cell 35 7 104154 substantially parallel, with their open ends open to the gas inlet A and the end open to the gas outlet B. The layers of filter material 1 and the strips thereon form flow channels facing their main flow direction. walls that receive impurities from the filter gas flowing through the ducts. The housing in which the filter cell is located is designated by reference numeral 4.

There are several options for layers of filter material. A large adsorption surface is obtained on the walls by placing separate adsorbent particles between two porous support layers 1a. These support layers preferably consist of interconnected fibers between which gas can penetrate the adsorbent. Such a layer of non-woven material may be of non-woven fabric, i.e. gauze. The fibers of the fiber layer may be, for example, synthetic fibers, such as thermoplastic thermoplastic fibers.

On the other hand, there are many alternatives to the porous adsorbent material. The porous adsorbent material layer 1b may be provided by separate adsorbent particles which may be in principle any known granular or fibrous material, for example activated carbon. It is also contemplated that a larger structure of porous fibers, such as fabric, nonwovens, or knit, which is one or more superimposed on the layer of adsorbent material, may be contemplated. 25 These structures can also be activated carbon. Naturally, the adsorbent can be selected according to the gas to be removed, and the adsorption can then be effected by physical sorption or chemisorption, whereupon a corresponding chemical is absorbed into the adsorbent material. Of course, adsorbent bent, whether as discrete particles or as a larger porous structure, should not be packed in layer 1b too tightly to allow gas to pass between the particles, and this is particularly important for fibrous materials. when using particles.

When used as separate adsorbent particles, they remain well within the wall because they are located between the support layers 1b and hold by the support layers, allowing them to be relatively loose relative to one another, which increases the filtration surface. This is a good 8,104,154 way to bind a just granular adsorbent to a filter material. However, it is possible to place the adsorbent particles on opposite surfaces of the backing layer or only on one surface, whereby they can be bonded to this backing layer, e.g. with special binder fibers. If the 5 porous layer of adsorbent material is on only one surface, the backing layer is porous, allowing the gases to be removed to pass from the flow passage 3 through the backing layer to the other side of the adsorbent layer. If, on the other hand, the porous adsorbent material layer 1b is on both surfaces of the support layer 1a, the tu-10 layer 1a may also be closed without the possibility of gas flow. Particularly in the form of staple fibers, the separate adsorbent particles or the larger porous structures formed of the fibers can thus be attached to the surface of the support layer 1a.

Also, in the embodiment where the porous adsorbent material layer 1b is outermost in the multilayer structure, the spacers can be formed according to the principle described above either from separate adsorbent material material strips or from thicker elongated regions of the same layer 1b.

20

The invention is not limited to the above alternatives, but may be varied within the scope of the inventive idea of the claims. Although it has been stated above that the separate strips that form the spacers separating the layers in the finished filter can be cut from the same filter material which forms the layers themselves, they can also be formed as separate bodies containing adsorbent particles. They may then be e.g. elongate bodies in which the adsorbent is enclosed within a porous support layer, e.g. a fibrous web, which surrounds the adsorbent in all directions perpendicular to the longitudinal direction of the body 30. These spacers may also comprise a porous adsorbent material in a different structure than the porous adsorbent material layer 1b.

The granular adsorbent used may have a grain size ranging from coarse to fine-35 no. Similarly, the fiber size of the adsorbent may vary in size. The thickness of the layers 1 of the filter material, i.e. the walls of the flow passages 3, may vary, and most commonly may be 1 to 10 mm. With small fiber lengths and adsorbent particle size, 1 mm thick materials can be obtained, and on the other hand, some material choices may have a layer thickness of 1 cm.

The material layer may also comprise parts other than the materials of the backing layer 1a and the porous adsorbent material, for example, particularly the adsorbent particles may contain binders, in particular binder fibers, used to solidify the layers of the adsorbent particles and bind them to other layers. The proportion of binders should be low so that the adsorption surface is not unduly reduced by their action.

It is also possible that there are more than three layers of the filter material layer 1, for example, so that the support layers 1a and the adsorbent layers 1b alternate in the same layer 1.

15

The invention is illustrated by the following non-limiting example.

Gas Filter Cell Permeability and Capacity Measurements 20 1. Gas Filter Cell Structure

The gas filter cell tested is constructed of a three-layer material with activated carbon granules 25 (diameter about 1 mm) between two synthetic fiber layers. The material is not optimized for the cellular application. The material information provided by the material manufacturer is as follows:

Total surface weight (g / m2) 480 30 Activated carbon surface weight (g / m2) 350

Thickness [mm] 1.35

From the resulting 1.35 mm thick material, strips (spacers) of 3-4 mm width were cut, which were glued to a planar surface of the same material, leaving grooves 3 to 4 mm wide between them (Figure 1). The material prepared in the above manner was wrapped in a spiral cell (35 mm) and 32 mm (Fig. 4) with a diameter of 1 ° 104154 (Figure 4), which formed 52 flow channels.

2. Measurement methods 5 2.1. the ozone load

The cell was placed in a 35 mm steel cylinder. A steel cylinder blade was inserted between two aluminum conical holders with 10 arms for sampling. Dry compressed air was supplied to the filter with a mass flow controller, to which ozone was added with a Thermo Environmental Instruments Inc 165 ozone generator. The total air flow was 24 l / min and the pressure drop in the cell was 25 Pa. The ozone concentration before and after the filter cell was measured with an Environnement SA 0341M ozone analyzer based on UV light adsorption. The change in ozone concentration was recorded on a data logger. The air supplied to the cell had an ozone concentration of 0.112-0.120 ppm and a temperature of 20-22 ° C. The residence time calculated from the filter front face was 0.077 s.

2.2. Cyclohexane and ozone load

A second cell prepared as described in Chapter 1 was loaded with a mixture of cyclohexane and ozone. Cyclohexane was produced by bubbling cyclohexane in two successive gas scrubbing bottles, followed by mixing with gas filter-purified air (40-60% RH and 20-24 ° C). Ozone was produced by a Red03x Plus ozone generator. Air was drawn through the cell at 25 l / min using a sampling pump. The entire flow of air through the cell passed through the measuring chamber of the Miran 1A Infrared Gas Analyzer. Cyclohexane concentration was measured with Miran. Ozone concentration was measured with Environnement SA 0341M ozone analyzer. The air supplied to the cell had a cyclohexane content of 7.5 ppm and an ozone content of 0.5 ppm. The residence time calculated from the filter front face was 0.074 s.

* 11 104154 2.3. Tolueenikuormitus

The ozone and cyclohexane-loaded filter cells were both successively placed in the same steel cylinder with a gap of about 5 5 mm between them. Hot air (temperature over 80 ° C) was passed through the cells to regenerate the cells. After regeneration, the cells were loaded with toluene. Toluene was produced by bubbling toluene in a vessel in a water bath. The toluene produced was introduced into an air stream from which 18.5 l / min was passed through the cell by means of a sampling pump. The entire flow of air through the cell 10 passed through the Miran 1A measuring chamber. Miraniil was measured for toluene content. The concentration of toluene before the cell was 20-22 ppm. The residence time calculated from the filter face was 0.20 s.

The toluene loading was also carried out with commercial cylindrical activated carbon granules (4 mm in diameter and approximately 5 mm in length). The granules were placed in a box having a face size of 430 * 170 mm and a depth of 80 mm. The face surfaces had perforated plates. The air flow through the filter was 35 l / s and the pressure drop was 160 Pa. The concentration of toluene before the cell was 20-22 ppm. The dwell time from the filter face was 0.17 s.

3. Results

The results of cell permeability and load measurements are shown in Figures 7 through 25, of which Figure 7 illustrates the change in cell permeability under ozone load, Figure 8 the change in cell permeability under cyclohexane and ozone load, and Figure 9 the change in cell permeability under toluene load. The figures show the change in cell permeability as a function of time. In cyclohexane and ozone loads, ozone permeability was measured only at the beginning of the load.

4. Conclusions

The measurement results of the filter cell are promising, considering that the material used is not optimized for the intended use. The permeability of the filter cell can be significantly reduced by extending the residence time in the filter. The dwell time can be selected by selecting 12 104154 cell lengths, head area and airflow. Increasing the length of the cell increases the pressure drop, but because of the low pressure loss of the cell in the tests performed, this is possible.

Claims (10)

A gas filter, in particular for ventilation, in which there are elongated flow channels (3), which are formed at least in part by attaching to each other material layers (1), between which the flow channels (3) are formed so that their inlet ends are open The gas inlet portion (A) and outlet ends are open to the gas outlet portion (B), the gas flow between the inlet ends and the outlet ends within the channels (3) being arranged in the direction of the plane of the material layer (1) and in the layers are adsorbed. which contaminants are adsorbed from the flow occurring within the channels (3), wherein at least one support layer (1a) and a porous adsorbent material layer (1b) which the support layer (1a) pours into the site, characterized in that the channels (3) are formed between porous adsorbent material containing spacers (2), which constitute elevations in said material layer (1) and pour them separately at the channels (3), and the channels are enclosed in each pour of porous walls through which there is flow communication with the porous adsorbent material surrounding the channels of each pour. Filter according to claim 1, characterized in that the adsorbent material layer (1b) is placed between two porous support layers (1a). 3. Filter according to claim 1 or 2, characterized in that the support layer (1a) is a fiber-resistant layer, such as a fibrous web. 25. 4. Filter according to any of the preceding claims, characterized in that the separate pouring layers (2) of the material layers (1) consist of thicker elongated areas of the adsorbent material layer (1b). Filter according to any of the preceding claims 1 to 3, characterized in that the separate layers (1) of the material layers (1) are separate strips of material layers (1) located between the layers (1). Filter according to claim 5, characterized in that the spacers (2) consist of strips of the same planar material which constitute the material layers (1). 16 104154 Filter according to any of the preceding claims, characterized in that the porous adsorbent material layer (1b) consists of separate adsorbent particles, such as granular or fibrous elements. 5 Filter according to any of the preceding claims 1 to 7, characterized in that the porous adsorbent material is activated carbon. Filter according to any of the preceding claims, characterized in that it consists of superposed parallel layers of material (1), which are a compact structure. Filter according to any of the preceding claims 1 to 8, characterized in that it is formed by winding a planar material into a helical shape in a cross-section perpendicular to the flow channels (3). r