Gas separation – Multiple bag type filters in chamber
Reexamination Certificate
1999-06-24
2001-01-30
Simmons, David A. (Department: 1724)
Gas separation
Multiple bag type filters in chamber
C055S376000, C055S377000, C055S378000, C055S379000
Reexamination Certificate
active
06179888
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates generally to the construction of filter bags used in fabric-type dust and particulate collection, and more particularly, to an improved filter bag construction of hybrid construction.
Stringent environmental controls on industrial emissions virtually require many industries to remove particulate matter from dust-laden air and gas streams before the air and gas streams are exhausted into the atmosphere. This removal is typically done by filtration and involves passing the gas, or airstream, through a fabric filter. This filtration is typically accomplished in what is known as a “baghouse” or “dust collector” which is an enclosed area having what is known as a tubesheet with one or more openings formed therein that receive and support elongated filter “bags” that are made of a filter fabric.
The air, or gas stream, is forced into the baghouse where it passes through the filter bags, trapping the particulate matter in the air stream on the bag's surface so as to collect the particulate matter. The filtered air may then be exhausted to the atmosphere or used in another industrial application. After a predetermined time of operation, the particulate matter has accumulated on the filter bags and the bags need to be cleaned.
This cleaning may be accomplished by mechanically shaking the filter bags to dislodge the accumulated particulate matter. Cleaning may also be accomplished by reversing the flow of the air or gas stream which passes through the bag in order to dislodge the accumulated particulate matter. Cleaning may still further be effected by using a pulsed jet of air that is forced through the filter fabric. All of this type of cleaning, as well as the normal operation of the baghouse, subjects the filter fabric of the bags to repeated stretching which eventually may result in the deterioration of the filter bags. The filter bags must be checked periodically and manually replaced at intervals.
Filter bags used in baghouses may be classified into two different types of construction. In the first type of construction, the filter bag is formed from a filter fabric and is stretched over an internal metal cage that supports the bag within the tubesheet opening. A metal collar assembly is required to hold the filter bag and the support cage together and to provide the combined assembly with a flange that engages the tubesheet. U.S. Pat. No. 4,138,234, issued Feb. 6, 1979, describes such a filter bag construction.
As shown in this '234 patent, it can be seen that the metal wire support cage is position inside the filter bag and extends for the entire length. The wire support cage is attached to a collar that has an annular gasket supported thereon. A metal venturi may be also attached to the collar and extend part way into the bag to provide for a smooth transition of the air or gas stream when entering the bag. Certain problems are inherent with this type of filter bag construction. For example, the metal cages are prone to wear out. The metal support cage causes the overall bag assembly to have a rather heavy weight that renders its replacement and removal difficult and requires increased labor. Additionally, the metal support assembly is composed of multiple parts that must be assembled prior to insertion of the filter bag assembly into the baghouse. This assembly requires labor and these parts must also be checked during service and maintenance intervals. This increases the labor cost associated with assembling and servicing these filter bags.
Another type of filter bag assembly construction is described in U.S. Pat. No. 5,632,791, issued May 27, 1997. In this type of construction, a pleated filter bag is used and is supported by an internal plastic support cage. The internal support and the bag are attached to a pliable plastic cap, or annular header portion, that is formed of polyurethane or the like. The polyurethane header member may often be molded, or potted, directly to the filter bag. This header member is formed with a diameter that is slightly less than the diameter of the tubesheet opening. However, this filter bag construction is costly, because each such filter bag assembly has an individual mold for the header member having a specific diameter that matches the tubesheet opening size. This increases the overall cost of the filter bag assemblies in that the cost for each size mold must be considered. Additionally, when the header member is molded to the top end of the pleated filter media, an inadequate seal may result from the molding under elevated temperature operation that would create an opening between the two members through which air or gas could bypass the filter fabric. Still further, the molded header member may tear or rip during installation or removal and may lose strength due to high temperature conditions.
Still further, other filter bag constructions in the prior art utilize a filter bag with a molded header member in consideration with a metal snap band on the inside diameter of the header member. This snap band serves to secure the bag assembly to the tubesheet opening. This snap band must be removed when the filter bag assembly is installed and removed. This is an extra step that increases the labor cost of installation and removal.
The present invention is accordingly directed to an improved filter bag assembly of hybrid material construction that avoids the aforementioned shortcomings.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a filter bag assembly with an improved construction that is simpler and less expensive to manufacture.
Another object of the present invention is to provide a filter bag assembly for use in industrial applications such as in baghouse and tubesheets wherein that has a construction that is easy for installation and removal.
A still further object of the present invention is to provide a filter bag assembly construction wherein the filter bag assembly includes an internal plastic core to support an outer filter fabric in the form of a bag, the outer filter fabric having a polymer collar molded thereto and having a fabric extension in the form of a collar attached to the collar and extending upwardly therefrom, the extension incorporating a snap band therein in retaining the filter bag assembly in place within a tubesheet opening.
Yet another object of the present invention is to provide a filter bag assembly of hybrid construction, the filter bag assembly having an elongated fabric filter body, the filter body having a collar portion attached thereto and defining an exist passage from the interior of the filter body, the assembly further including a flexible, extension portion extending from the collar portion and being formed from a different material from that of the collar portion, the extension portion having a diameter larger than that of the collar portion so that by varying the diameter of the flexible extension portion, a number of filter bag assemblies may be formed having the same sized collar portions but capable of fitting different size tubesheet openings.
A further object of the present invention is to provide an improved filter bag assembly for use in a baghouse wherein the filter bag assembly includes an elongated filter body, a collar portion forming one end of the bag assembly and defining a passage into the interior of the filter body, the assembly further having a fabric extension portion attached to the collar portion and aligned with the filter body portion, the extension portion forming an extension of the collar portion passage and having a diameter greater than the collar portion diameter, the extension portion further including a plurality of bag assembly handling members forward from a fabric and disposed within the extension portion passage.
In accordance with the aforementioned objects, the present invention accomplishes these objects by way of a unique construction in which the filter body portion has an endcap and a collar portion molded to opposite ends. The collar portion has a given d
Filtration Group Incorporated
Hoey Betsey Morrison
Simmons David A.
Vedder Price Kaufman & Kammholz
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