WO2000047306A1

WO2000047306A1 - Aerosol filter media

Info

Publication number: WO2000047306A1
Application number: PCT/US2000/003620
Authority: WO
Inventors: Keith Edward Burgess
Original assignee: Albany International Techniweave, Inc.
Priority date: 1999-02-12
Filing date: 2000-02-11
Publication date: 2000-08-17
Also published as: AU3489200A

Abstract

The present invention is an aerosol filter media having entirely parallel and consistent flow passages through the filter media. The filter media is comprised of filaments that are arranged entirely parallel to each other. That is, the filaments are parallel for the entirety of their length. The filaments are compacted so as to create contact between the filaments along their length and then fixed either by mechanically restraining them or by causing each of the filaments to adhere to its neighbors at points of contact, such as by adhesive bonding or fusion caused by heat or chemical methods.

Description

AEROSOL FILTER MEDIA Field of the Invention

The present invention is directed to media for filtering aerosols. The filter media is comprised of closely spaced, collimated filaments that are arranged parallel to the air flow through the filter.

Background of the Invention

Aerosol filter media usually consist of small randomly arranged filaments or particles that are arranged so as to create small and irregular or tortuous passages for air or other fluid to pass through. Such filters are produced from woven and non woven fabrics. In the process of passing through the filter, the aerosol particles, which are typically small compared to the passages, contact the surfaces of the filaments or particles and remain attached or "filtered" from the air stream. In the case of fibers or filaments, the filaments are mostly parallel to the filter media surface, thus normal to the airflow. The passages that are created are very inconsistent in size and shape and are not optimized for the job that they must do. The primary means of trapping the particles are impaction and interception with very little trapping due to settling or diffusion.

Some patents, such as those directed to cigarette filters, describe filters with a plurality of substantially longitudinally extending strands. U.S. Patent nos. 4,889,143 and 5,025,814 are two such examples. The '143 patent discloses cigarette rods and filters made from a sheet-like material. The '814 patent discloses a filter medium including a plurality of generally longitudinally extending strands provided from a sheetlike material, as opposed to a filamentary material. Neither of these patents disclose that the filaments are maintained parallel to one another.

U.S. Patent no. 3,976,457 describes a filter cell. The gas flows parallel to the filter as it enters and exits the filter cell. Whether the filter fibers are parallel to gas flow is not indicated in this patent. U.S. Patent nos. 4,676,807 and 4,759,782 describe a coalescing filter for removing liquid aerosols from gaseous streams. The gaseous stream enters the cylinder at one end, and is then forced out of the cylinder due to the other end being capped. The gaseous stream enters the filter normal to the filter media, but evidently must deviate from that path in order to exit the filter.

U.S. Patent no. 5,190,571 describes a diesel particulate trap for filtering diesel fuels. The filtering element uses yarn extending in straight lines in a repeating pattern. The yarns have been compacted to form a plurality of fibrous walls that intersect to form tunnels that extend in the axial direction, parallel to the flow. Lofty yarns, that is, yarns with a high void volume, are used in constructing this filter. After compaction, the yarns define a plurality of uniform tunnels which extend through the fiber mass in the direction of the axis of the tubular casing, which in essence, is parallel to the alignment of the fibers.

There are several disadvantages associated with prior art filter media. As noted above, the filter media usually consists of small randomly arranged filaments or particles arranged so as to create small and irregular or tortuous passages for the air to pass through. The passages are very inconsistent in size and shape and thus are not optimized for filtration. The primary means of trapping the particles are impaction and interception of the particles while very little trapping occurs from settling or diffusion. Moreover, if a thicker filter element is desired, if must be produced from a composite of several layers of randomly arranged filaments. In this arrangement, the flow path is circuitous, which may not be the most efficient filter construction. This also increases the time needed to manufacture the filter element.

Summary of the Invention

The present invention is an aerosol filter media having entirely parallel and consistent flow passages through the filter media. The filter media is comprised of filaments that are arranged entirely parallel to each other. That is, the filaments are parallel for the entirety of their length. The filaments are compacted so as to create contact between the filaments along their length and are then fixed either by mechanically restraining them or by causing each of the filaments to adhere to its neighbors at points of contact, such as by adhesive bonding or fusion caused by heat or chemical methods. Inter-fiber friction is also a means of providing the adherence between fibers that provides the structural integrity of the filter element.

The airflow through the filter media of the present invention is parallel to the fibers in passing through the filter from one side of the media to the other. In this unique filter construction, the filter media traps the aerosol particles primarily by settling and by diffusion.

Among the advantages of the present invention is the relative ease and efficiency in which the filter media is constructed. In the present invention, several individual filter elements can be created from one filter construction. That is, after a large filter media is built, it can be sliced into individual elements of desired thickness, with the fiber ends at each side of the cut portions defining the entranceway and exit of the filter elements.

The diffusion mechanism is a result of a maintaining surfaces close to the particles throughout their journey through the media. The cumulative effects of Brownian motion result in the movement of the smaller particle sizes in directions that are independent of the airflow. By having the filament surfaces in close proximity to the particles, this motion will eventually result in particle contact with these surfaces, thus resulting in capture of the particle. The capture of the particle when it contacts a surface is a phenomena common to aerosol particles - capture efficiency is essentially 100%. The diffusion mechanism is most effective for small particle sizes as the larger particles do not exhibit sufficient Brownian movement.

By orienting the filaments normal to the pull of gravity, settling of the particles onto the parallel fibers of the filter media can be effected, particularly with larger particles that are not as subject to Brownian motion. Such particles will fall or settle towards the earth at a speed that is a function of their size, shape and density. By orienting the flow passages parallel to the surface of the earth, the maximum distance that a particle can move before contacting a filament surface is only the maximum vertical distance between filament surfaces in the passage.

By adjusting the length of the fibers, the diameter of the fibers and the fiber volume fraction of the fibers, the efficiency of the media can be designed for capture efficiency of known particles sizes and types.

Additional features of this filter media design are that it can be made from a wide variety of filaments including but not limited to glass, ceramics, plastics and metals, and round, irregular, shapes or hollow fiber types. The fabrication can be accomplished without the generation of dust that would be released during operation - a feature of great importance in applications such as clean rooms. An additional feature is that no small particles or filaments are used in the fabrication and thus can not be released during operation - as contrasted to a conventional glass based paper media. An additional feature is that the possible operating temperature for the filter is a function only of the selection of filament and means of adhering the filaments to each other -this opens the possible temperatures to several thousand degrees if desired. A further feature that can be achieved is the ability to clean and reuse the filter by heat, by solvent purge of by a combination of the two.

Claims

I claim:

1. A filter element for filtering particles out of aerosols comprised of a first end for the entry of an aerosol and a second end for the exit of a filtered gas, and plurality of filaments located between the first and second ends arranged entirely parallel to each other and forming parallel through- filter flow paths.

2. The filter element of claim 1 wherein the fibers are selected from the group consisting of glass fibers, ceramic fibers, plastic fibers and metal fibers.

3. The filter element of claim 1 wherein the fibers have rounded, asymmetrical shapes or are constructed of hollow-type fibers.

4. A method of filtering an aerosol using the filter set forth in claim 1 comprised of the steps of : passing an aerosol through the first end of the filter,

flowing the aerosol through the filter in a direction that is parallel to the arrangement of the fibers of the filter;

passing the filtered aerosol through the second end of the filter.