Gas and liquid contact apparatus – Contact devices – Porous mass
Reexamination Certificate
2000-12-07
2002-11-05
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Porous mass
C261S107000
Reexamination Certificate
active
06474628
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device for humidifying air and to a method for air humidification using this device.
The use of air with a defined humidity is desirable or required in many cases, for example in air-conditioning technology or in medicine. Air from compressed-air lines or cylinders is generally too dry, while atmospheric air exhibits considerable fluctuations in terms of its humidity and, moreover, its composition often fails to satisfy requirements.
Various methods are used to humidify air. In most cases, water is sprayed or vaporized. For example, a conventional method uses, for example, an open water reservoir, from which liquid is pumped out and sprayed into the flow of air. The water which is not taken up by the flow of air flows back into the reservoir. The microorganisms introduced multiply in this water reservoir and can only be controlled by the use of chemicals. Therefore, in many situations the humidified air is undesirably polluted with chemicals. To counteract the microorganisms, methods have been developed according to which the humidification water was heated. However, it has emerged that even dead microorganisms or their cell constituents may impair the respiratory tract of humans. Therefore, alternative methods have been developed which envisage water vapor being introduced into the air to be humidified. In these methods, the water is heated to boiling point and only the vapor phase is used for the humidification. A drawback of these methods is the long mixing paths required in order to achieve uniform humidification. Finally, it is known for water to be sprayed directly into the room which is to be air-conditioned. This, however, requires an optimum distribution of a very large number of nozzles in order to achieve uniform humidity throughout the room. Moreover, this system cannot be integrated into an existing air-conditioning unit without further measures.
It is known, for example from EP 0 370 540 A1 and U.S. Pat. No. 5,348,691, to sterilize water by filtration using membranes. According to the methods described in those documents, dry air from a blower is passed through a membrane contactor, the membrane contactor separating the liquid phase, i.e. water, from the air and exposing the airflow to a large area of water in a very small space. The water molecules evaporate from the water surface and pass into the airflow. The membranes employed are hydrophilic and hydrophobic membranes, preferably in capillary form. For the generally large airstreams, it is necessary to provide a large membrane area combined with a low loss of flow pressure. With both flat and hollow fiber membranes, this leads to very short modules with very large end faces, i.e. inlet surfaces. To achieve the required low pressure losses, the flow channels have to be relatively large or the hollow fiber diameters must not be too small. However, this entails the drawback that it is impossible to achieve a high packing density. In addition, large-scale production of modules of this nature has not yet been tried and will certainly entail a very complex method.
SUMMARY OF THE INVENTION
The present invention is therefore based on the technnical problem of providing an air humidifier which overcomes the abovementioned drawbacks, in particular provides a large contact area between water and air combined, at the same time, with low losses of flow pressure.
The present invention solves this technical problem by providing an air humidifier, comprising a membrane contactor, in which the membrane contactor has at least one tube membrane embedded in a hydrophilic, porous body. In a particularly preferred embodiment of the invention, the hydrophilic, porous body is a body made from a ceramic material, referred to below as a ceramic body. The body may consist exclusively of the ceramic material or may contain substantial amounts, preferably more than 50% by weight, based on the weight of the body, of this material. According to the invention, it is possible, for example, to use coarse ceramic filters such as are used for filtering molten metals. In another preferred embodiment of the invention, the hydrophilic, porous body is made from a polymer, i.e. consists of this polymer or contains substantial amounts, preferably an amount of more than 50% by weight, based on the weight of the body, of this polymer. Naturally, it is also possible to use hydrophilic, porous bodies made from other materials, provided that these materials are able to ensure that the water is dispersed over a large surface area. According to the invention, organic or inorganic woven fabrics or woven-fabric-like structures consisting of or containing substantial proportions, preferably more than 50% by weight (based on the weight of the body), of porous filament material, may also be used as the only or principal constituent of the body. The body should be hydrophilic and have a porous structure, i.e. a structure of increased surface area. In addition, it is necessary for the hydrophilic, porous body to be sufficiently strong and rigid for the incoming flow of air not to cause any compression and therefore any significant change in the pore structure and flow velocities. Therefore, bodies which are used according to the invention preferably have a self-supporting, non-compressible structure.
In a preferred embodiment of the present invention, the diameter of the pores in the hydrophilic, porous body is less than or equal to 5 mm.
In connection with the present invention, a membrane contactor is understood as meaning the unit according to the invention comprising at least one tube membrane and hydrophilic, porous body. The function of a membrane contactor is to sterilize the water by means of the at least one tube membrane contained therein, while the hydrophilic, porous body serves as an area-enlarging contact means between air and sterile water. The membrane contactor according to the invention may be fitted, in conventional air humidifiers, in the form of a module individually or in series or parallel with other modules and the water supply. The use of the membrane contactor according to the present invention in an air humidifier is possible wherever humidified, sterile air is required, for example in air-conditioning units, be they stationary, for example in building, or in mobile units, such as vehicles, in room air humidifiers, sterile working areas, operating theaters, laboratories, for the production of medicaments or sterile appliances or for storing valuable cultural materials, such as books, or in storage and exhibition areas, museums, etc.
In the context of the present invention, a membrane is understood as meaning a technical membrane, particularly preferably a thin, film-like, microporous separating layer. A porous membrane of this nature may have a foam-like mesh structure. According to the invention, it is equally possible to use homogenous membranes and membranes of asymmetric structure, for example comprising a supporting layer and a separating layer.
The membrane according to the invention is therefore preferably a membrane filter which particularly preferably may be produced, for example, from ceramic or polymeric material, for example cellulose derivatives, polyamides, polyvinyl chloride, polysulfone and/or teflon and consists of this material or contains substantial proportions of this material, in particular more than 50% by weight. The membranes are preferably 50 to 250 &mgr;m thick.
The membranes according to the invention are designed as tube membranes.
According to the invention, it is also possible to combine capillary membranes or hollow fiber membranes to form bundles of flexible tubular bodies and to integrate these bundles in the hydrophilic body.
In a particularly preferred embodiment, the invention provides for the at least one tube membrane to be a ceramic tube membrane or a polymeric filtration membrane, in particular a microfiltration membrane. Naturally, it is also possible to use other tube membranes, provided that they are of substantially tubular form a
Stroh Norbert
Walitza Eckehard
Bushey C. Scott
Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung
Ostrolenk Faber Gerb & Soffen, LLP
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