JPH04114709A - Method of manufacturing filter element - Google Patents

Abstract

PURPOSE: To enhance the resistivity against corrosions by high temperature gases by vacuum-forming a fire-resistant ceramic fiber together with an aqueous slurry of a ceramic binder and thermally treating the formed part to obtain a skeletal member, which is then fired at a high temperature after coated with alumina gel. CONSTITUTION: When the filter element (10) is prepared, a fire-resistant ceramic fiber with its diameter of 2 to 3 μ and length of 5 to 10 mm is pulled into a mold together with an aqueous slurry of a ceramic binder for vacuum-molding a part, which is then thermally treated for drying the binder to form a skelton member of the fire-resistant ceramic fiber. The skeletal member has an average pore dimension of larger than 40 μ. The skelton member is then coated with a material selected from alumina gel, colloidal alumina and colloidal silica to reduce the average pore diameter to be 30 to 40 μ. The skeletal member is heated at a temperature of about 925 to 1,260 deg.C for drying the coated material and for enhancing its resistivity against corrosions by high temperature gases. Its durability is thus enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates generally to filters for removing particles from hot gas streams, such as flue gases, and more particularly to new and improved filter elements and methods of making the same. Regarding.

BACKGROUND OF THE INVENTION The use of ceramic filter elements to filter hot flue gases and the like is well known. The use of such filter elements is shown, for example, in US Pat. No. 4,713,174. A method for manufacturing ceramic filter elements by molding is disclosed in U.S. Pat. No. 4,629,483.
It is shown in the number. Although such filter elements are well formed, they suffer from high manufacturing costs, are heavy, and are very brittle and prone to breakage.

This reduces manufacturing costs and at the same time provides a lighter weight, stronger and more durable filter element with at least a similar function to hitherto known ceramic filter elements. It was desired to improve the method of manufacturing certain filter elements.

SUMMARY OF THE INVENTION The present invention provides a new and improved method of manufacturing a high temperature filter element and a new and improved filter element for use in filtering hot gases. When manufacturing a filter element by the method of the present invention, initially the skeletal morphology of the filter element is approximately 1
A large number of short SiO fibers are made with 0% binder to provide a tangled mat-like framework morphology with an average pore size of about 10-200 microns. The desired large number of congratulatory fibers is typically vacuum formed on a mandrel into the desired shape, such as a nine-inch tube (or tube).The pore size of this fiber form is too large for most filter applications. is not suitable but provides a fairly uniform base.

The mat-like fiber configuration is then contacted with alpha alumina gel or colloidal aluminum to reduce the average pore size to an acceptable level and strengthen the element. The matte form is contacted and coated by submerging it entirely in liquid alpha alumina or colloidal aluminum to provide a filter element with pore sizes evenly distributed throughout the form. However, if it is desired that the filter element have an outer surface with an average pore size less than the average pore size of the interior of the element, alpha alumina or colloidal aluminum may be applied by spraying, brushing, rollers, etc. may be applied only to the outer surface of the matte base by a suitable method. This fiber mat-like form is then first submerged in a bath of liquid alpha alumina or colloidal aluminum to uniformly coat the interior fibers, and then the upstream and/or downstream faces of this skeletal form are further coated with additional alpha alumina. It is also possible to provide a less porous filter coat on one or both sides.

EXAMPLE Referring to FIG. 1, a hollow cylindrical filter element 10 is shown. The element 10 is closed at the bottom by an integral circular end wall 12 and is provided with an integral outer annular flange 14 at the top.

Such a shape has a temperature of 1600'F (approximately 870°C P
It is common in ceramic filtration tubes used in high temperature applications such as flue gas filtration. Third
The figure shows another filter element 10' in which the underside 16 of the flange 14' is arched to increase the resistance of the filter element to crushing at the connection between the flange 14' and the cylindrical body of the filter element. ing.

Filter element 10 comprises a skeletal base of refractory ceramic fibers (1) mixed or watted and bonded together with a suitable high temperature binder such as colloidal alumina or colloidal silica.
or has a form. This mat-like form or base is preferably formed by a vacuum forming operation in which a water-based colloidal alumina or silica slurry binder and short random lengths of ceramic fibers are drawn by vacuum into a mold or mandrel. The vacuum formed part is then heat treated to dry the binder and bond the fibers together.

Mat-like skeletal morphology is not suitable for use as a gas filter for two reasons. First, at high surface velocities some fibers are pulled from the downstream face of the filter element and contaminate the filtered gas. Second, during the removal of filter cake from upstream of the filter element in a standard backflow operation where gas is blown in opposite directions through the filter element, some fibers near the upstream face of the filter element This is because it sticks to the filter cake and is torn off from the filter element together with the cake.

According to one aspect of the invention, both the upstream and downstream surfaces of the matte configuration are coated with a layer of ceramic fibers adjacent to each other with a thin layer of alpha alumina or silica. Alpha alumina and silica have temperatures of about 1600°F (about 870°F).
It is known to withstand temperatures as high as ℃). This surface coating of the fibers has been found to greatly strengthen the element and at the same time solidify the ceramic fibers into the filter element. Additionally, alpha alumina or silica coatings reduce the average pore size of the filter element to a more acceptable level. For example, the initial vacuum formed matte fiber form has an average pore size of about 10-200 microns, and after the fiber is coated with alpha alumina or silica, the average pore size is about 5-200 microns. 100 microns, preferably 30 to 40
Becomes a micron.

The amount of alpha alumina or silica applied to the matte fiber form is inversely proportional to the desired average pore size of the surface coating making up the filter layer.

This refractory fiber is alumina-silica and, if very pure, would have the following composition:

AN 203 --- 48.2% Si
O------------48,2
%--1, 1% TIO2 Fe203 -0.5% However, purer aluminum oxide fibers with the following composition may also be used.

A, Q203--------------
97%S i02 −−−−−−−−−−
The 3% binder is colloidal alumina or colloidal silica. If colloidal silica is used with less pure alumina-silica fibers, the framework morphology has the following composition:

Ag2O3 30.5% S l 02 B7.7% T L
02 1.1%Fe2O30,
5% Preferably at 1700'F after the skeletal form is coated with alpha alumina or colloidal silica.
Dry at temperatures of ~2300'F. At this high temperature, the coating transforms into a mulberry wood phase, increasing its resistance to corrosive attack by mud gases during use of the filter element.

Although the invention has been described with respect to specific embodiments, those skilled in the art will be able to make many changes without departing from the spirit and scope of the invention. It is therefore intended that the appended claims cover all changes and improvements falling within the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional elevational view of a filter element embodying the present invention, FIG. 2 is a view taken along the arrow 2-2 in FIG. 1 and shows the overall device shown in FIG. 1, and FIG. FIG. 3 is a cutaway view of another filter element. Explanation of symbols

Claims (2)

[Claims] (1) A method of manufacturing a filter element, comprising: drawing refractory ceramic fibers, each having a diameter of 2-3 microns and a length of 5-10 mm, into a mold with a ceramic binder in an aqueous slurry and heat-treating the vacuum-formed part. drying the binder to form a refractory ceramic fiber skeletal member, the skeletal member having an average pore size greater than 40 microns, the skeletal member selected from the group consisting of alumina gel, colloidal alumina, and colloidal silica. coating the fibers with a material and reducing the average pore size of the framework member to 30-40 microns;
heating the coating to a temperature of about 1260[deg.] C. to dry the coating and increase its resistance to corrosion by hot gases. (2) The step of heating the coated member is approximately 230
2. The method of claim 1, comprising converting said coating to a mullite phase conducted at a temperature of 0 DEG F. (about 1260 DEG C.).