GB1576175A - Screenless granular bed filter - Google Patents

Description

(54) SCREENLESS GRANULAR BED FILTER (71) We, THE DUCON COMPANY, INC. a Corporation organised and existing under the laws of the state of New York, United States of America, of 147 E. Second Street, Mineola, New York 11501, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to granular bed filters of which some known filters of this type have at least an inlet screen and in some cases a bed support screen, for example, see British Patent Specification nos. 1,169,638 and 1,375,220.

When the temperature of the gas being filtered is high, such as above 1600"F, and/or contains for example 1.4%, by weight, hydrogen sulfide, the metallurgical requirements prohibit the use of metallic bed support screens or perforated plates. For the same reasons, an inlet screen cannot be used.

This problem is solved by the present invention by providing a granular bed filter lacking an inlet screen and lacking a support screen in a manner whereby the granular bed material is not lost during operation or during backwashing of the granular material which at least in part is subjected to cleaning by fluidization.

The granular bed filter of the present invention comprises a housing having an inlet and an outlet and walls which define a generally U-shaped passageway between the inlet and outlet, one end of the passageway communicating with the inlet and the other end of the passageway communicating with the outlet and having a cross-sectional area greater than that of said one end, and a bed of granular filter material in the bight portion of the passageway, thus filtering dirty gas flowing from the inlet to the outlet.

In the preferred embodiment of the present invention, the size of the granular material at the inlet end of the passageway is smaller than that of the granular material at the outlet end of the passageway.

Two preferred forms of granular bed filter, in accordance with the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a vertical sectional view through a first form of granular bed filter; Figure 2 is a transverse sectional view taken along the line 2-2 in Figure 1; Figure 3 is a perspective view, partially cut away, for illustrating another form of granular bed filter; and Figure 4 is a sectional view taken along the line 4-4 in Figure 3.

Referring to the drawings in detail, wherein like numerals indicate like elements, there is shown in Figure 1 a granular bed filter 10 comprising a housing 12 having an inlet manifold 14 and an outlet manfnifold 16. The inlet manifold 14 is separated from the outlet manifold 16 by a partition wall 18 which divides the interior of the housing 12 in a manner so that the inlet manifold 14 is substantially smaller in cross-sectional area than the outlet manifold 16.

The filter 10 also comprises a plurality of filter chambers having an inlet end communicating with the inlet manifold 14 and an outlet end communicating with the outlet manifold 16. The walls of the housing 10 for defining the filter chambers are preferably prefabricated so as to have the inlet ends of the chambers secured in a cut-out opeining in the partition wall 18. In Figure 1, the housing 12 includes filter chambers 20 and 22 which are identical. Hence, only the filter chamber 22 will be described in detail.

The filter chamber 22 is U-shaped in transverse section, as shown in Figure 1, with a curved top wall 24 and a curved bottom wall 26 interconnected by side walls 28 and 30. The distance between the side walls 28 and 30 is less than the transverse dimensions across the housing 12, as shown in Figure 2.

An end wall 32 interconnects the upper edge of the walls 24,26,28 and 30 at the inlet end thereof. An inlet opening 34 is provided in the bottom wall 26. The filter chamber 22 communicates with the outlet manifold 16 by way of an outlet opening 36. While it is preferred to have the opening 36 at an elevation above the elevation of opening 34, they may be at substantially the same elevation.

The bight portion and a portion of the legs of the filter chamber 22 is filled with a bed of granular material 38. The granular material 38 is preferably a coarse material such as Alundum (Registered Trade Mark) particles having transverse dimensions of approximately one-quarter inch. On the inlet end of the granular material 38, there is provided a thin layer 40 of fine granular material such as that disclosed in the above-mentioned patents.

The cross sectional area of the filter chamber 22 adjacent the outlet opening 36 is substantially greater than that of the filter chamber 22 adjacent the inlet opening 34. In other words, the top and bottom walls 24, 26 diverge at the bight portion towards the outlet opening 36. The purpose of the enlarged cross sectional area adjacent the outlet opening 36 is to reduce the superficial gas velocity thereby compensating for any increase in pressure drop due to the length of the filter path through the granular materials 38 and 40. The layer of granular material 40 is spaced from the elevation of the inlet opening 34 by a distance so that the layer of granular material 40 may be fluidized in the space thereabove without flowing out of the opening 34. With the layer of granular material 40 having a thickness of three inches, the upper surface thereof will be spaced from the lower edge of opening 34 by a distance of approximately seven inches.

The interface between the coarse granular material 38 and the layer 40 of fine granular material is preferably horizontally disposed to assure uniform distribution of the fluidizing, reverse gas flow. During backwashing, the layer 40 of granular material will be fluidized into the space thereabove without any lifting or fluidizing of the coarse granular material 38. The large interface between the materials 38, 40 assures that the reverse flow cleaning gas velocity will be insufficient to fluidize the coarse granular material 38. The interface between the materials 38, 40 extends across the full width and length of the inlet end of the filter chamber 22.

Dirty gas at an elevated temperature with or without highly corrosive components is introduced into the inlet manifold 14. The dirty gas enters each of the filter chambers 20, 22 through a respective inlet opening, is filtered as it passes downwardly through the layer 40 of fine granular material, is further filtered as it passes through the granular material 38, and then exits into the outlet manifold 16. When it is desired to clean the filter beds, backwash gas such as air is introduced into the outlet manifold 16 at a low pressure, such as 80 psi above the normal operating pressure in the manifold 16. The backwash gas flows through the coarse granular material 38 and envelopes any accumulated dust in the interstices between the coarse granular material 38. The backwash gas then passes upwardly through the interface between materials 38, 40 and fluidizes the granular material 40 into the space thereabove but below the elevation of the inlet opening 34. The backwash gas then passes out the inlet opening 34 into the inlet manifold 14. Accumulated contaminants in the layer 40 of granular material are removed therefrom as the material is fluidized.

In Figures 3 and 4, there is illustrated another embodiment of the present invention designated generally as 10'. The filter 10' comprises a housing defined by an outer pipe 42 and an inner pipe 44 coupled together by way of a partition wall 46 which divides the annular space between the pipes so as to define a generally U-shaped passageway between an inlet end 48 and an outlet end 50 with the larger cross sectional area of the passage-way being provided at the outlet end 50 for the reasons discussed above.

Dirty gas is supplied to the inlet end 48 by way of conduit 54.

Clean gas from the outlet end 50 flows into the pipe 44 by way of holes 52. The filter 10' may have a plurality of filter chambers along the length of the pipes 42, 44. The ends of pipe 42 are closed at each end by an end wall whereas the pipe 44 may be open at both ends or may be closed at one end depending upon the desired distribution of the clean air therewithin. The generally U-shaped passageway is filled with the granular material, coarse and fine as described above. The elevation of the fine granular material is spaced below an inlet aperture 56 in accordance with the description set forth above so that the fine granular material is not lost when being backwashed.

When filters 10 and 10' are used with high temperature and/or corrosive gases, the walls of the housings may be made from ceramic or refractory material. Preferably, the walls of the housing exposed to contact with the dirty corrosive gas are made from metal coated on its exposed surface with a thin layer of ceramic in accordance with conventional procedures utilized heretofore for making kitchen sinks, bathtubs, and the like.

As will be apparent from the above description and the illustrations in the drawings, the filter of the present invention is easily fabricated from readily available materials requir ing little machining. For example, the embodiment in Figures 3 and 4 has the advantage of permitting the use of readily available tubes with tube 44 being surrounded by tube 42. The generally U-shaped passageway, divergent at its outlet end, is attained by positioning the tubes so as to be non-concentric. The absence of inlet screens or support screens decreases the cost of the filter while at the same time eliminating a component which is highly subject to corrosion.

WHAT WE CLAIM IS: 1. A granular bed filter comprising a housing having an inlet and an outlet and walls which define a generally U-shaped passageway between the inlet and outlet, one end of the passageway communicating with the inlet and the other end of the passageway communicating with the outlet and having a cross-sectional area greater than that of said one end, and a bed of granular filter material in the bight portion of the passageway.

2. A filter in accordance with claim 1, wherein the granular filter material is in two sizes, most of the filter material being of a coarse size, with a layer of fine granular material overlying the coarse granular material only at said one end of the passageway, and with the top surface of the fine granular material being spaced below an inlet opening of the passageway by a distance sufficient to permit the fine granular material to be fluidized into the space there above during backwashing, without the fine granular material being lost by passing through the inlet opening of the passageway.

3. A filter in accordance with claim 1 or 2, wherein the housing comprises inner and outer non-concentric tubes with a partition extending between the tubes, the passageway being defined by the internal diameter of the outer tube and the outer diameter of the inner tube.

4. A filter in accordance with any one of claims 1-3, wherein the housing includes a plurality of passageways disposed one above the other, an inlet manifold communicating withe the inlet and of each passageway, and an outlet manifild communicating with the outlet end of each passageway.

5. A filter in accordance with any of claims 1-4 wherein the or each generally U-shaped passageway is defined by spaced upper and lower walls which are imperforate in the area juxtaposed the granular filter material.

6. A filter in accordance with claim 3, wherein the inner tube is provided with holes communicating with the outlet.

7. A method of filtering gas to remove contaminants therefrom, using a granular bed filter in accordance with claim 1, comprising passing the gas through the generally U-shaped passageway whose bight portion contains the bed of granular filter material, the velocity of the gas reducing as it exits from the bed of filter material before exiting through the outlet.

8. A method in accordance with claim 7, including using granular material of at least two sizes, the smaller size granular material being a minor portion of the total granular material and being located at the inlet end of the passageway and substantially below the elevation of the inlet to the passageway so as to provide sufficient space thereabove for fluidizing the smaller size granular material without loss of the smaller size granular material through the inlet during backwashing.

9. A method in accordance with claim 7 or 8 including using imperforate portions of spaced non-concentric curved wall portions to define the generally U-shaped passageway.

10. Apparatus according to claim 1 substantially as hereinbefore described.

11. A method of filtering gas according to claim 7 substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. ing little machining. For example, the embodiment in Figures 3 and 4 has the advantage of permitting the use of readily available tubes with tube 44 being surrounded by tube 42. The generally U-shaped passageway, divergent at its outlet end, is attained by positioning the tubes so as to be non-concentric. The absence of inlet screens or support screens decreases the cost of the filter while at the same time eliminating a component which is highly subject to corrosion. WHAT WE CLAIM IS:

1. A granular bed filter comprising a housing having an inlet and an outlet and walls which define a generally U-shaped passageway between the inlet and outlet, one end of the passageway communicating with the inlet and the other end of the passageway communicating with the outlet and having a cross-sectional area greater than that of said one end, and a bed of granular filter material in the bight portion of the passageway.

2. A filter in accordance with claim 1, wherein the granular filter material is in two sizes, most of the filter material being of a coarse size, with a layer of fine granular material overlying the coarse granular material only at said one end of the passageway, and with the top surface of the fine granular material being spaced below an inlet opening of the passageway by a distance sufficient to permit the fine granular material to be fluidized into the space there above during backwashing, without the fine granular material being lost by passing through the inlet opening of the passageway.

3. A filter in accordance with claim 1 or 2, wherein the housing comprises inner and outer non-concentric tubes with a partition extending between the tubes, the passageway being defined by the internal diameter of the outer tube and the outer diameter of the inner tube.

4. A filter in accordance with any one of claims 1-3, wherein the housing includes a plurality of passageways disposed one above the other, an inlet manifold communicating withe the inlet and of each passageway, and an outlet manifild communicating with the outlet end of each passageway.

5. A filter in accordance with any of claims 1-4 wherein the or each generally U-shaped passageway is defined by spaced upper and lower walls which are imperforate in the area juxtaposed the granular filter material.

6. A filter in accordance with claim 3, wherein the inner tube is provided with holes communicating with the outlet.

7. A method of filtering gas to remove contaminants therefrom, using a granular bed filter in accordance with claim 1, comprising passing the gas through the generally U-shaped passageway whose bight portion contains the bed of granular filter material, the velocity of the gas reducing as it exits from the bed of filter material before exiting through the outlet.

8. A method in accordance with claim 7, including using granular material of at least two sizes, the smaller size granular material being a minor portion of the total granular material and being located at the inlet end of the passageway and substantially below the elevation of the inlet to the passageway so as to provide sufficient space thereabove for fluidizing the smaller size granular material without loss of the smaller size granular material through the inlet during backwashing.

9. A method in accordance with claim 7 or 8 including using imperforate portions of spaced non-concentric curved wall portions to define the generally U-shaped passageway.

10. Apparatus according to claim 1 substantially as hereinbefore described.

11. A method of filtering gas according to claim 7 substantially as hereinbefore described.