US 3807149 A
An exchanger for removing moisture from a gas comprising a fibrous carrier in sheet form preferably arranged in layers and provided with passageways extending from end to end of the exchanger and supplied with two moisture absorbing substances, viz. a water soluble salt and crystalline zeolite, arranged in two separate zones in the direction of travel of the gas through the passageways.
Description (OCR text may contain errors)
United States Patent 1191 Norback 1 Apr. 30, 1974  MOISTURE EXCHANGER FOR GASEOUS 3,306,006 2/1967 Urban 55/31 x MEDIA 3,312,041 4/1967 Hill 55/30 3,001,607 /1961 Eng et a1 55/30 Inventor: Per Gunnar Norback, g 2,926,502 1/1960 Munters 61 a1. 62/94 Sweden 3,231,409 1/1966 Munters 261/28 x 3,307,617 3/1967 Munters 165/10  Asslgnee: Aktiebolaget Carl M n e 3,377,225 4 1968 Munters 156/210 lndustrivagen, Sollentuna, Sweden Filed: June 4, 1971 Appl. No.: 150,189
Foreign Application Priority Data June 8, 1970 Sweden 7930/70 US. Cl. ..-55/388, 55/389 Int. Cl B0ld 53/04, BOld 53/18 Field of Search 55/29, 30, 31, 35, 316,
References Cited UNITED STATES PATENTS 10/1970 Thijssen 55/30 X 12/1964 Eastwood et al. 55/30' Primary Examiner--Samih N. Zaharna Assistant Examiner-R. Burks v Attorney, Agent, or Firm-Shlesinger, Fitzsimmons and Shlesinger ABSTRACT 8 Claims, No Drawings MOISTURE EXCHANGER FOR GASEOUS MEDIA This invention relates to a moisture exchanger for gaseous media which comprises an exchanger body composed by a carrier for a moisture absorbing or hygroscopic material and formed with channels extending from end to end for the passage of the media. Preferably, the carrier has the shape of thin layers or foils, such as paper of cellulose or asbestos. Also plastic substances or glass fibres may come into consideration. The layer material shall primarily be fibrous, i.e., composed of, or covered with, fine fibres or threads.
The channels or passageways extending from end to end in the exchanger body can be formed by making every second layer plane and every interposed second layer corrugated with the corrugations extending in mutually parallel relationship or possibly also by forming the layers to. a honeycomb pattern or providing them with widenings or other spacer elements, ensuring that the layers are spaced from one another. The layers may be wound up spirally to form a cylindrical body. If the layers abut against one another, they can be interconnected at the places of contact.
In order to obtain a compactbody which per unit volume contains a large surface exposed to the media passing through the channels it is advantageous to keep the medium spacing between the layers as small as from 0.5 to 1.0 mm, up to 1.5 mms. In the embodiment with alternately plane and corrugated sheets abutting against one another, the spacing between the plane layers should thus be twice said values. Exchanger bodies or inserts of this type are disclosed, e.g., in the U.S. Pat. Nos. 3,231,409, 3,377,225 and 3,307,617, to which patents reference is made for fuller explanation of the structure of the moisture exchanger in consideration. if the moisture exchanger is of .the regenerative type it has a casing to which are connected inlets and outlets for, respectively, the gas, such as air, which is to be desiccated and a gas, such as air, which is heated and serves to remove the moisture taken up by the exchanger body. in this case the channels or passageways of the exchanger body are caused alternately to communicate with inlets and outlets, respectively, for the air to be conditioned and for the regenerating gas. The exchanger body may be rotatable in which case it moves with low speed between a dewatering'zone and a regenerating zone of the moisture exchanger. It is, however, conceivable also .that the exchanger body is stationary while a reversal of the flow of the two media is brought about by means of valves or the like. The moisture exchanger can also be used for ventilation of a room or space in which case both consumed room air on its way out, and fresh air on its way into, the room or space, exchange both heat and moisture within the exchanger. Thus, the moisture exchanger can produce simultaneously with the desiccation also the heat exchange between two media. As an alternativethe moisture exchanger may form part of an air conditioning system as is shown, e.g., in the U.S. Pat. No. 2,926,502.
if the carrier in itself hasa moisture absorbing'capacity which at'all events is insignificant, itis caused to take up a particular, moisture absorbing material. it is known to use for this purpose finally powdered silica gel. It is also known to impregnate the carrier with a hygroscopic salt such as lithium chloride, lithium bromide or calcium chloride. Such a salt is capable of absorbing a great quantity of moisture in, relation to its own weight, thus if the salt e.g., is contained in an amount equal to 10 percent by weight in a carrier of asbestos paper, the amount of moisture which can be absorbed can equal from between 25 and 50 up to 100 percent of the weight of the carrier. in return, such salts have no particular great capacity of deep desiccation. Thus, lithium chloride is capable of desiccating air down to a relative moisture content of l to 2 percent, but on the other hand is capable of absorbing steam from the air at very high vapour pressures.
Another kind of moisture absorbing substances are the so-called molecular sieves which may consist of synthetically produced crystalline, metallic aluminum silicates which have been activated for adsorption by removal of their water of hydration.- Such molecular sieves obtain a very fine porousity and have a great affinity to water. The pores of the molecular sieve have high equal size molecular dimensions which afford to them a high adsorbing capacity within 'a limited range of the relative moisture of the gas. v
The molecular sieves consist of crystalline zeolites which have the basic formula Mz/ o Al Q -xsiO vHQO wIiere M i'QZtitJnEfikYn'ifie'"valeiie. in spite of some similarity in composition, they differ thoroughly from the gel-type amorphous aluminumsilicates, commonly referred to as zeolites, and used for making water soft. The last-mentioned material does not exhibit any selectivity based on molecular size.
As examples of zeolites which to advantage can be used for desiccation, those types may be mentioned which commercially have the denominations 4A and 13X, PQYLafilld the fqllo s ne q Type 13X: Na [(AlO (SiO 276F1 0 The sodium ions in type 4A can be replaced by six calcium ions.
A moisture adsorbing substance of the kind now described can also be defined as a solid fine powder of crystalline aluminium silicates based on alkali metals or alkali-earth metals, the water of hydration of which has been removed. They may consist of natural or synthetic zeolites or molecular sieves.
The material can be admixed as a powder into the fibre pulp suspension of which the carrier, such as the cellulose or asbestos paper, is manufactured or the mate rial can be supplied to the finished paper after the exchanger body has been built up. The quantity of material may amount from 10 to 25 up to percent and even more of the weight of the carrier.
According to the invention, the carrier of the exchanger body is supplied with moisture absorbing substances of both kinds'mentioned above, i.e., firstly a water soluble salt and secondly a solid material of the type of zeolite or molecular sieve. The secondmentioned material has in this connection the particular effect of having the capcity of desiccating a gas such as air'to a very low relative moisture content such as less than 0.1 percent. In return, when compared with the saltthe molecular sieve has a limited capacity only of adsorbing moisture and according to the invention the two components constitute complements to one another in a'particularly advantageous manner. Generally speaking, the salt has to manage the preliminary coarse desiccation of the air whereas the other material effects the final desiccation to a very low moisture content. The two components can be distributed evenly over the entire exchanger body, even if it is particularly advantageous to subdivide the same into two zones, a first zone which is initially met bythe gas or air to be desiccated and which is impregnated with the salt whereas a second zone at the outlet side of the channels or passageways is impregnated with the molecular sieve or the like means. The first zone may have a greater extension in the direction-of flow of gas to be desiccated through the channels or passageways of the exchanger body than the secondzone. It is also possible to provide two exchanger bodies in a series or adjacent one another of which the first body to be passed by the air to be dried is impregnated with the salt and the second one with the other material or molecular sieve. The two exchanger bodies may be rotated with different speeds.
When layers having a thickness of one or some few tenths of a millimeter consist of cellulose or'asbestos.
fibres it is important that their mechanical strength, especially in moist condition, is improved which can be accomplished as is evident from the patents referred to above by means of one or several water-soluble components such as water glass and calcium chloride which together result in an unsoluble deposit on the fibre structure. The asbestos paper contains organic constituents to obtain required joining of the asbestos fibres. These constituents are removed after the exchanger body has been built up by burning away said constituents as is evident from the US. Pat. No. 3,231,409.
Obviously, the invention is not limited to the specific examples described above but may be varied in the widest sense within the scope of the basic idea thereof.
1. A moisture exchanger for gaseous media which comprises a carrier for moisture absorbing material formed with channels extending from end to end for the passage of the media, said material consisting of two components, firstly, a water-soluble salt, and secondly, a water-insoluble, solid molecular sieve, said salt having the greater absorbing capacity with respect to the quantity of moisture, and said sieve being of such nature as to possess the capacity of desiccating the media to a lower relative moisture content than said salt.
2. A moisture exchanger as claimed in claim 1, wherein the salt at least in its major portion is located in a zone of the exchanger body which is initially passed by the gas to be desiccated whereas the molecular sieve at least in its major portion is located in a zone at the outlet side of the exchanger body for said gas.
3. A moisture exchanger for gaseous media comprisa fibrous carrier for moisture absorbing material in sheet form arranged in layers and having a plurality of channels extending from end to end of the carrier for passageway therethrough of the media,
said material being of two kinds, namely, a water soluble salt and a molecular sieve, the sheets being arranged so that the media pass over the salt-carrying sheets before passing over the sieve-carrying sheets.
4. A moisture exchanger as claimed in claim 3, wherein every second layer of the carrier is plane and every interposed layer is corrugated, the corrugations being parallel to one another and forming with the plane layers the passageways for the media.
5. A moisture exchanger as claimed in claim 3, wherein the salt is lithium chloride, and the molecular sieve is a crystalline aluminum silicate, activated by removal-of its water of hydration.
6. A moisture exchanger as claimed in claim 5,
.wherein the crystalline aluminum silicate is in powder form admixed into the fibres of the carrier sheets, and is selected from the group consisting of crystalline alluminum silicates of alkali metals and alkali earth metals.
. 7. A moisture exchanger as claimed in claim 3, wherein the salt is disposed in the carrier in a first zone through which the media first contacts the carrier, and the molecular sieve is disposed in the carrier in a second zone through which the media subsequently contacts the carrier, and said first zone has greater extent in the direction of flow of the media than said second zone.
8. A moisture exchanger as claimed in claim 3, wherein the salt carrying sheets and the molecular sieve sheets are disposed on separately rotatable bodies which rotate at different speeds.