FI94724C - Method of making a gas filter - Google Patents

Description

! 94724

Method of making a gas filter

The invention relates to a method for manufacturing a gas filter / which can be placed in a ventilation duct and which contains a material which removes gases from the filter air by chemisorption.

Harmful gases are generally removed from the supply air by means of filters placed in the ventilation duct 10 and containing a granular material, which may be alumina or silica impregnated with a chemisorption material. Such filters are intended to prevent gases from entering spaces where they may be harmful, and such gases include e.g. sulfur dioxide, nitrogen oxides, chlorine and hydrogen chloride. The need for filtration of these substances is important and will probably increase e.g. in the following areas: 20 - ventilation filters, especially if recirculated air return air is used for ventilation. 30 - control of odor nuisances in offices and living spaces.

For example, sulfur dioxide, nitrogen oxides, hydrogen sulfide, hydrochloric acid, or ozone cause corrosion on metal-35 surfaces, such as computer circuit board junctions, already at concentrations of 0.03 to 0.01 ppm. These are lower than the concentrations known to be harmful in the working air.

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In industrial sites and busy areas, the concentrations of sulfur dioxide, nitrogen oxides and ozone in the ambient air, in particular, exceed the concentrations required for the proper functioning of sensitive electronic-5 devices. Therefore, the so-called clean rooms, where the components and equipment in question are manufactured, most often require a very efficient filtration unit for gaseous nuisances. Under the conditions of use, the fine electronic devices 10 must also be protected, for example, by device-specific filter units in order to ensure their reliable operation.

The installation of supply air filters has started and will be installed in vehicles and work machines. In these, the filtration of gaseous components is also often as important as the filtration of particulate pollutants (eg filtration of exhaust gases in trucks and filtration of pesticides in tractors).

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The filtration efficiency of normal filters can be increased by increasing the contact time between the filter material and the gas to be filtered, i.e. the residence time. This is done by increasing the thickness of the filter, i.e. 25 the thickness of the layer through which the air to be filtered: flows. In this case, the problem becomes an increasing pressure drop, which is not advantageous for the operation of the ventilation system.

The object of the invention is to eliminate the above-mentioned drawbacks and to provide a method for manufacturing a filter which can enhance filtration based on chemisorption without increasing the pressure drop. To achieve this object, the method according to the invention is mainly characterized in that the layers of corrugated porous carrier material, in which the longitudinal direction of the waves coincides with the air flow direction, are superimposed to form 3 to 94724 separate elongate flow cells. the resulting solution is absorbed into the filter material by passing the solution through flow paths.

The chemisorption agent can thus be placed in the filter in a simple and economical manner.

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Em. the cell does not cause a flow resistance to the air to be filtered, but a much larger contact surface is obtained compared to the same volume as in the flow direction of the air to be treated with the granular materials by means of numerous elongate narrow flow cells.

According to a preferred embodiment, the solution is passed through the flow cells by placing one end of the flow channel 20 in the solution so that the ends of the flow cells come below the solution surface and allowing the substance to spread longitudinally of the cells due to capillary action.

According to a preferred embodiment, the combination of a flexible base plate and a flexible corrugated plate is obtained by wrapping a cylindrical body with a structure known per se.

According to another preferred embodiment, the filter is formed by successively placing separate filter pieces in which different solutions have been impregnated.

The invention will now be described in more detail with reference to the accompanying drawings, in which 4-94724 Fig. 1 shows a filter according to the invention in perspective, Fig. 2 shows the filter of Fig. 1 directly from the air flow direction, Fig. 3 shows a method of manufacturing a filter, Fig. 4 shows a filter placement in a ventilation duct , Figure 5 shows experiments performed as a filter according to the invention in the filtration of sulfur dioxide, and Figure 6 shows an experiment performed as a filter according to the invention in the filtration of nitrogen dioxide.

Figure 1 shows a filter according to the invention in perspective. The filter is of the same type of construction as, for example, the rotating body described in U.S. Pat. No. 4,391,616, the purpose of which is to remove moisture from the air flowing through it. The body 1 forming the filter 25 comprises elongate flow cells 2. The cells are formed by superimposing layers containing a corrugated surface material having a porous surface, whereby the cells 2 are formed at the waves of the corrugated material. The bottoms and ridges of the waves 30 run in the flow direction of the filter, creating parallel flow cells running through them throughout the filter, which together form a filter flow channel.

The body shown in Figures 1 and 2 is formed as shown in U.S. Patent 4,391,616 by wrapping the superimposed straight flexible plate 4 and the corrugated flexible plate 3 into a cylindrical body, 5 to 94724, each side of the corrugated plate always having a straight plate, the individual cells 2 being bounded between the individual wave of the corrugated plate 3 and the straight plate 4. The manufacturing method is illustrated 5 in Fig. 3. The corrugated plate 3 may be a thin crimped (creped) aluminum plate to which a porous surface-providing alumina is attached to both surfaces. The straight plate 4 can also be a thin aluminum plate, on both surfaces of which alumina is attached in the same way, the inner walls of the cells 2 formed by the surfaces of the above-mentioned superimposed plates 3 and 4 being structured so as to have a large surface area. Of course, other large surface area porous plate-like materials can also be used.

Of course, it is also possible to use other types of structures, for example those in which the body 1 does not consist of two plates wrapped in a cylindrical body 20, but consists of stacked separate sheets or stacked sheets, resulting in similar flow cells due to corrugated sheets.

25 The filter cell shown in Figures 1 and 2 is attached to the surface of the cell walls by impregnating a chemical that reacts with the gas to be removed from the air to be treated. Such a chemisorption coating can be provided to the walls 30 by means of a solution in which the chemisorption agent is dissolved. It is most practical to apply the substance by passing said solution through the flow cells 2, whereby the substance adheres to the porous walls having a large surface area as the solution is impregnated on their surface. Since the flow cells 2 form thin capillaries passing through the body 1, the easiest way to impregnate is to immerse the other end of the filter in the impregnation, whereby the capillary forces absorb 6 to 94724 solution through the cells 2. After evaporation of the solvent, the filter is ready for use.

Figure 4 shows the possibility of assembling the filter 5 from several cylindrical bodies 1 shown in Figures 1 and 2. Due to the round shape of the bodies it is easy to place them in the tubular ventilation duct 5, in which case only the outer surfaces of the bodies 1 and the inner surfaces of the duct 5 need to be sealed. Each of the two bodies 1 shown in Figure 4 may contain its own chemisorption material, whereby the bodies can be used to remove different gases from the same air flow through the duct 5. The pieces 1 can also be placed in the ventilation duct 15 so that they can be easily replaced.

The following is an example of the use of the invention.

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The filter according to the invention was made of a material used for automotive catalysts. The base material of the filter was a thin aluminum plate (straight plate 4) and a crimped (creped) aluminum plate 25 (corrugated plate 3) on top of it. Fine porous alumina was attached to the surface of these. The plates were rolled together into a tight cylinder. Numerous narrow capillaries were then formed in the longitudinal direction of the cylinder. Depending on the density of the second aluminum plate 30, capillaries of different sizes were obtained. Materials were tested that yielded 500 to 1,300 capillaries! per square inch, 77.5 to 200 capillaries / cm 2. The finished bodies were 3.4 cm in diameter, 9 cm in length and had about 1100 capillaries / Kap-35 pale. The body had a volume of about 80 ml and a weight of 65-70 g. The bodies were impregnated with different chemicals by immersing one end of the body in the impregnation liquid, whereby capillary forces absorb the liquid through the body.

7 94724

Potassium permanganate, potassium iodide, sodium hydroxide, metal oxides and potassium carbonate were tested as impregnating agents. The pieces were weighed before and after impregnation and drying.

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The pieces were tightly glued between two metal filter holders, each with side branches for sampling. Separation degree measurements were made with different body / gas combinations as a function of contact. If the contact time of 0.3 seconds reached almost 100% prediction, a load test was performed as a filter.

The concentration of gas entering the filter was adjusted to 1 ppm in all load tests and the concentration after the filter was measured with a continuous gas analyzer. The gas contact time with the body was adjusted to 0.3 seconds.

20 As with commercial filtration materials, filters impregnated with various chemicals initially had a sulfur dioxide separation rate of almost 100%. Figure 5 shows the permeation concentration of sulfur dioxide as a function of loading time for filters impregnated with different chemicals. The designation Ά1203 means an unimpregnated filter in which the filtration has taken place by adsorption on the pores of alumina.

Depending on the chemical, 30 different amounts of material could be impregnated into the pieces. The reaction equations for sulfur dioxide include potassium carbonate, sodium hydroxide and potassium perm-! with the garnet, it was calculated how much the filtered sulfur dioxide had consumed the impregnating agent. As a result, about half of the chemical impregnated in the body 35 had been consumed with a permeation of about 5% and a contact time of 0.3 seconds.

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Finding an impregnating agent suitable for nitrogen dioxide filtration proved difficult. Only the potassium iodide impregnated body proved to be so effective that a loading test was performed. Figure 6 shows the results of that experiment.

The following impregnating agents proved to be the most effective in terms of filtration capacity for the studied gases: 10 - for sulfur dioxide potassium carbonate - for hydrogen sulphide copper - silver - chromium salts for nitrogen dioxide potassium iodide - a filter with a circular cross-section can be placed directly in the circular ventilation duct.

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Filters can, of course, be made with different diameters and different lengths depending on the size of the ventilation duct and the desired capacity.

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Claims (4)

9 94724 A method of manufacturing a gas filter which can be placed in a ventilation duct and which contains a material which removes gases from the filter air by chemisorption, characterized in that layers of corrugated porous carrier material in which the longitudinal direction of the waves coincides with the flow direction (2), which together form a filter flow channel, after which the solution causing the chemisorption is absorbed into the filter material by passing the solution through the flow cells (2). 15 A method according to claim 1, characterized in that the solution is passed through the cells (2) by placing one end of the flow channel in the solution so that the ends of the flow cells (2) are below the solution surface 20 and allowing the solution to spread longitudinally due to capillary action. Method according to Claim 1 or 2, characterized in that the combination of the flexible base plate (4) and the flexible corrugated plate (3) is wrapped together into a cylindrical filter body (1). Method according to one of the preceding claims, characterized in that the filter is formed by successively placing separate filter pieces (1) in which different solutions have been impregnated. 10 - 94724