Ceramic coated filter medium and internal support

Details Ceramic coated filter medium and internal support Ceramic coated filter medium and internal support

1998-04-17

2001-04-10

Spitzer, Robert H. (Department: 1724)

Gas separation

Flexible or collapsible bag type

With securing or supporting means

C055S302000, C055S496000, C055S523000

Reexamination Certificate

active

06214072

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to elongated bag-like tubular filters (“filter bags”) for filtering particulate material carried in a gas or liquid stream in a filter housing and, more particularly, relates to a ceramic coated filter medium and internal support for use in gas filtration.
2. Related Background Art
Filter bags are typically mounted in filter housings or in a baghouse with supporting frames or cages positioned therein to hold the filter bags in an open, hollow tubular configuration. The bags are open at an outlet end and closed at the other end. Particulate-laden gas or liquid is directed into the baghouse and through the gas-permeable filter bags. The particulate material is filtered and retained on the exterior surface of the filter bags while the filtered gas passes through the filter bag. Periodically, a reverse purge of gas or fluid is directed into the open outlet end of the filter bags for dislodging any trapped particulate material from the bags and thus, cleaning the filter bags. Hence, filter media must be able to withstand not only the normal conditions of gas filtration, but also the periodic cleaning process to which they will be subjected.
The temperatures at which gas filtration is conducted are greatly limited by the properties of the filter media employed. Synthetic filter media typically have insufficient heat resistance beyond approximately 250° C. At temperatures above 250° C., loss of mechanical strength and/or thermal decomposition is observed with such conventional synthetic filter media. For temperatures up to about 300° C., woven or non-woven glass can be used. However, filters of glass fibers are often brittle and do not withstand the mechanical stress associated with typical baghouse operations. For temperatures above 300° C., metallic filter media may be utilized. However, due to their very high price and limited corrosion resistance, the field of application for metallic filter media is very limited. Vacuum formed fiber ceramics or sintered grain ceramics are also available. However, due to the limited filter area per ceramic filter element, substantially more space is required for the total filter, thereby resulting in elevated cost.
Hence, there is great industrial demand for inexpensive, compact filtration equipment operational within a high-temperature range of about 300° C. to about 500° C. or even as high as 700° C. or higher. Glass fibers are an attractive filter media in this temperature range due to their desirable physical and chemical properties and low cost. However, as described previously, the use of glass fiber based filter media is limited by the brittleness of the media which results in fiber breakage due to friction and bending during use.
To reduce friction between the glass fibers, the art has suggested applying various coatings, such as silicon, starch, graphite and PTFE to glass fibers. However, above 300° C., these coatings degrade, thus resulting in the loss of fiber protection and therefore, rapid destruction of the filter media.
Therefore, for economical and process reasons, a need exists for a filter medium operational at temperatures above about 300° C., exhibiting good chemical resistance, long lifetime, a larger filter area per element, and an attractive price.
SUMMARY OF THE INVENTION
In the filter media of the present invention, individual fibers of woven or non-woven glass or mineral are fixed at the fiber crossover points through coating with organic-inorganic or inorganic binders. Breakage at the fiber crossover points is avoided by substantially eliminating movement of the filter medium through the use of a support. The support is desirably dimensionally adjustable (e.g., transversely adjustable) to provide a close fit between the filter medium and the support.
The present invention provides for high-temperature (e.g., above about 300° C. to at least about 500° C. or even as high as about 700° C.) filter media of ceramic coated woven or non-woven glass fibers with optimal filtration properties, such as filter rate and dust-collecting efficiency and without significant pressure drop. This is accomplished by coating the glass fibers with an organic-inorganic or inorganic binder to effect fixation of the fibers at the crossover points. Additionally, through the use of a special support member, breakage of the fixed crossover points, both as a result of the normal conditions of gas filtration and as a result of periodic cleaning processes, is eliminated. Thus, the filter medium of the present invention results in good operation in the temperature range of about 300° C. to at least about 500° C. (or even as high as about 700° C.) and exhibits good chemical resistance, long lifetime, a larger filter area per element (e.g., 1-2 m
2
/element) and an attractive price.
Accordingly, in a first aspect, this invention is directed to a filter comprising a filter bag formed of a filter medium comprising glass fibers, the fibers being fixed to one another at crossover points by a ceramic binder coating. This invention is also directed to such a filter medium wherein the filter medium is fixed on a dimensionally adjustable (i.e., transversely adjustable) support member.
Preferably, the glass fibers suitable for use in the present invention include materials such as glass, ceramic minerals, and a mixture thereof.
In the preferred embodiment of the present invention, the filter medium operates at temperatures up to about 700° C.
In yet another preferred embodiment, the filter medium weighs from about 100 g/m
2
to about 2000 g/m
2
.
Preferably, the binder coating is an organic-inorganic or inorganic substance.
In another preferred embodiment of the present invention, the binder comprises SiO
2
, Al
3
O
3
ZrO
2
, TiO
2
, SiO
2
/TiO
2
, SiO
2
/ZrO
2
, B
2
O
3
/SiO
2
, Na
2
O/B
2
O
3
/SiO
2
or Na
2
O/Al
2
O
3
/B
2
O
3
/SiO
2
composites.
In yet another preferred embodiment, the binder composition is applied to the filter medium by dipping, rolling or spraying.
In the preferred embodiment of the present invention, the support member is dimensionally adjustable by being transversely adjustable. A suitable support member may comprise a cylindrical metal support comprising metal wires, slotted support rings, spacers, and V- or U-shaped rails. For example, the support member may have a circumference which can be fixed in position by spacers guided in parallel or conically arranged V-shaped or U-shaped guiding rails.
This invention is also directed to a method of filtering a gas stream, comprising the steps of providing a support member being transversely adjustable, supporting, by the support member, a filter medium comprising glass fibers, wherein the fibers are fixed to one another at crossover points by a ceramic binder which is applied to the filter medium, and passing a gas stream with particulates therein through the filter medium supported by the support member, wherein the filter medium traps the particulates and removes the particulates from the gas stream.


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