Method and apparatus for washing a plurality of filter elements

A method and apparatus for simultaneously washing a plurality of generally tubular or sock-like filtering elements of a gas filtering apparatus without removing the elements from the apparatus, the filter elements being disposed in a regular array of rows and columns within a housing between an inlet and an outlet thereof. The method includes positioning in the housing a liquid conduit having a plurality of axially spaced spray nozzles for delivering washing liquid along one or more rows of elements and supplying washing liquid to the conduit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to methods and apparatus for cleaning sock-like 
filter elements of a gas filtering apparatus with the filter elements in 
place. 
2. Description of the Prior Art 
In filters for gases, generally tubular or socklike filter elements made of 
woven cloth or needle felts or other natural or synthetic fibers are often 
used as filter media. Over a prolonged period, these filter elements can 
become clogged with solid particles or volatile organic constituents 
resulting in a gradual reduction in the volume flow of gas filtered 
through the system due to decreased permeability of the filter elements. 
As a result, more energy is required to maintain the system's operational 
pressure. 
In order to remedy this situation several solutions have been proposed, 
including the use of polytetrafluoroethylene fibers for producing filter 
elements having "anti-adhesive" characteristics. While 
polytetrafluoroethylene filter elements are somewhat effective, they are 
relatively expensive and demonstrate poor mechanical strength in 
comparison to other fibers such as woven cloth or needle felts. 
Another solution is the use of pneumatic or mechanical cleaning devices to 
clean the filter elements. As described in pending U.S. application Ser. 
No. 571,253, (filed Jan. 16, 1984), pneumatic or mechanical cleaning can 
be carried out periodically with the filter in operation and can 
effectively remove many particulates from the filter elements. However, 
solid particles and even volatile organic constituents can still 
accumulate over a prolonged period despite such cleaning because 
particulates, which generally accumulate on the external surfaces of the 
elements, can work their way into the fibers, reduce the permeability of 
the filters, increase the energy consumption of the filtering apparatus 
and reduce the overall efficiency of the operation. 
Hence, the filter elements must periodically be removed from the apparatus 
and thoroughly washed. These washing operations are usually 
labor-intensive and sacrifice production because of extended periods of 
"down time." In addition, removal of the filter elements can be dangerous 
to health, especially where fine particulates are introduced in the 
breathing air of the technicians servicing the apparatus.

DESCRIPTION OF THE INVENTION 
Accordingly, one object of the present invention is to enable through 
cleaning of filter elements in place, without contaminating the breathing 
air of technicians servicing the unit and without introducing fine 
particulates and other pollutants into the atmosphere. Another object of 
the invention is to achieve cleaning of the filter elements without 
labor-intensive, production-sacrificing costs associated with the methods 
discussed above. 
Still another object of the present invention is to provide a method and 
apparatus for substantially removing the solid particles and/or volatile 
organic constituents that may accumulate on or within the filter elements 
despite mechanical or pneumatic cleaning. 
Yet another object of the present invention is to provide a method and 
apparatus for simultaneously cleaning the exteriors and interiors of the 
filter elements avoiding the additional costs associated with complex 
anti-adhesive organic filtering fibers, and increasing the long term 
operating efficiency of gas filtering apparatus. 
As embodied and broadly described herein, the present invention provides a 
method and apparatus for washing a plurality of generally tubular or 
sock-like filter elements of a gas filtering apparatus without removing 
the elements from regular array of rows and columns in a housing between 
an inlet for dust-laden gas and an outlet for filtered gas. The gas flows 
from the exterior of the elements to the interior of the elements, with 
dust accumulating primarily on the exterior of the elements. The method 
comprises positioning within the filter housing a liquid conduit having a 
plurality of spray nozzles axially spaced on the conduit for delivering a 
plurality of jets of washing liquid along one or more rows of filter 
elements; and supplying washing liquid through the conduit for discharge 
through the nozzles to clean a plurality of filter elements. 
Preferably, the spray of washing liquid from the nozzles is confined to a 
fan-shape having a narrow spray portion for traversing between adjacent 
rows of elements and a wide spray portion expanding in a direction axial 
of the filter elements for washing the exterior surfaces of the filter 
element. 
It may be preferred to align the conduit with a single row of filter 
elements and spray into the interiors thereof. In this embodiment 
extensions may be provided between the conduit and the spray nozzles for 
projecting the nozzle axially of the filter elements. 
In all embodiments, water or other suitable fluids can be used as the 
washing liquid and can be heated to facilitate efficient cleaning. 
Other objects and advantages of the invention will become apparent from 
consideration of the following detailed description taken in connection 
with the accompanying drawings which constitute part of this 
specification. In the drawings, preferred embodiments of the present 
invention are depicted. However, it is to be understood that the invention 
is not limited to the details disclosed but includes all variations and 
modifications within the spirit of the invention and the scope of the 
appended claims. 
Reference will now be made in detail to the present preferred embodiments 
of the invention, examples of which are illustrated in the accompanying 
drawings. 
A method and apparatus are provided for washing a plurality of generally 
tubular or sock-like filter elements of a gas filtering apparatus, the 
filter elements being disposed in a regular array of rows and columns 
within a housing between an inlet for dust-laden gas and an outlet for 
filtered gas. 
The method includes the steps of positioning in the housing a liquid 
conduit having a plurality of spray nozzles axially spaced apart on the 
conduit for delivering a plurality of jets of washing liquid along one or 
more rows of elements and supplying washing liquid through the conduit for 
discharge through the nozzles to wash the filter elements. 
As embodied in FIG. 1, filter elements 1 are generally tubular or socklike 
and are arranged in a regular array of rows and columns which depend from 
orifice plate 2 in housing 3. Dust-laden gas 4 enters housing 3 through 
inlet 5 and filtered gas 6 exits through outlet 7. The gas flows through 
the exterior surface 8 of filter elements 1 and out the open end 9 of the 
elements 1, with dust accumulating primarily on the exterior surface 8 of 
elements 1. 
As depicted in FIGS. 1 and 2, liquid conduit 10 having a plurality of spray 
nozzles 11 axially spaced on the conduit is positioned within housing 3 
such that each nozzle 11 delivers a jet of washing liquid between 
substantially adjacent rows of filter elements 1, or between one row of 
filter elements and a wall of housing 3. Nozzles 11 are spaced at a 
distance substantially equal to space between adjacent rows of elements 1. 
Washing liquid is supplied through conduit 10 and discharged substantially 
horizontally across housing 3 for cleaning the exterior or upstream 
surface of elements 1 from a single position of conduit 10. Preferably, 
conduit 10 is disposed on inlet side of housing 3. 
In the embodiment of FIGS. 1 and 2, nozzles 11 shape the jets of a washing 
liquid into a fan-shape having a narrow, horizontally confined, linear 
portion 12 for traversing between rows of elements 1 and a vertically 
broad portion 13 which expands in a direction axial of the filter elements 
to insure cleaning along the axial length of elements 1. In this way, the 
plurality of fan-shaped jets of washing liquid can intensively wet and 
flush all the filter elements 1. 
In the embodiment of FIGS. 1 and 2, conduit 10 can be vertically moveable 
during washing of filter elements 1. 
Referring now to FIG. 3, a second embodiment of the present invention is 
depicted. Conduit 14 having a plurality of axially spaced apart spray 
nozzles 15 is positioned within housing 3 for delivering washing liquid to 
the interior of filter elements 1. In this embodiment, the washing liquid 
flows in a direction opposite to the gas flow through the housing. The 
washing liquid can wash both surfaces of elements 1 as it passes through 
the elements. 
Spray nozzles 15 preferably depend from conduit 14 on extensions 16 which 
extend into the interiors of filter elements 1. 
Conduit 14 is mounted within housing 3 for movement both horizontally and 
vertically. During washing of one row of elements 1, conduit 14 can be 
moved vertically thereby moving nozzle 15 on extensions 16 axially of 
elements 1. This permits complete washing of the full length of the 
elements. After one row has been washed, conduit 14 is moved horizontally 
to line up with another row of elements. Alternatively, a separate conduit 
can be provided for each row of elements 1. 
In all of the depicted embodiments, washing liquid from the cleaning 
operation can be drained from housing 3 through dust funnels 17 or removed 
by other conventional means. 
After cleaning, the filter elements are dried by passing air heated to 
about 100.degree. C. through the filter for a period of approximately 1 
hour. Adequate drying can also be obtained if the filter is not used for a 
relatively long time after washing. 
In both embodiments, the washing units are preferably designed in such a 
way that all the filter elements of at least one row or column can be 
cleaned at the same time. Water is used as the washing liquid in the case 
of water-soluble products. Tests have shown that the washing time is 
shortened by higher water temperatures; thus, the washing liquid may be 
heated. Water containing suitable additives or any other cleaning liquid 
can also be used. Washing from the dust-laden air side and from the clean 
air side can be carried out simultaneously and also successively. In many 
cases, washing of the type shown in FIGS. 1 and 2 or in FIG. 3 is 
sufficient. However, the cleaning effect can be intensified by switching 
on a conventional pneumatic or mechanical cleaning system during the 
washing of the filter elements in accordance with the invention. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is, therefore, to be 
understood, that within the scope of the pended claims, the invention may 
be practiced otherwise than as specifically described. 
In gas-filtering apparatus of the type in which this invention is useful, 
the filter element (such as a tube) surrounds a supporting basket which is 
fastened to a perforated plate located between dusty air to be filtered 
and the clean, filtered air regions. The filter element is surrounded on 
the outside by dusty air, which penetrates through the filter element to 
its inside, while depositing the entrained dust particles on the outside. 
In order to keep the pressure differential, the flow volume, and the 
filtering efficiency constant, it is known to clean the elements during 
operation, for example by means of short-term compressed air pulses from a 
compressed air line through a jet injector into the tube interior. In this 
manner, a brief pressure excess is developed on the inside of the tube, 
which inflates it and causes air to pass in reverse (from inside to 
outside) thus dislodging accumulated dust particles. An alternate method 
of cleaning the filter elements during operation, is disclosed in U.S. 
Pat. No. 4,082,523, and includes striking the filter element from inside 
and then subjecting it to an exterior compressed air impulse. 
Since none of the above cleaning during operation is entirely successful, 
components deposit on the filter medium which can only be removed by 
washing. This more thorough cleaning, also known as regeneration, is the 
purpose of this invention. In the present invention, regeneration of the 
filter elements can be accomplished without the expensive disassembly of 
the filter elements and support baskets. 
Thus, the present invention comprises: 
(1) a first assembly of spray nozzles, which preferably are stationary, and 
which spray cleaning liquid in fan-shaped patterns between the rows of 
filter elements and against their exteriors, as shown in FIGS. 1 and 2; 
and 
(2) a second assembly of spray nozzles, which preferably are mobile, in 
that they can be raised and lowered as well as moved from row to row of 
filter elements, and which spray cleaning liquid in a conical 360.degree. 
pattern inside each of the filter elements, as shown in FIG. 3. 
The fan-shaped spray pattern of the first assembly may be at an angle of up 
to 240.degree. in a plane passing between each row of elements, and 
obviously should be narrow in its perpendicular plane, so that it impinges 
upon the exteriors of each row of filters tangentially. The fan-shape 
plane is shown in FIG. 1 and the perpendicular narrow plane is shown in 
FIG. 2. Incidentally, the first assembly is also useful for extinguishing 
a fire inside the filter apparatus, with either manual operation or 
automatic operation using a temperature sensor and control set for 
predetermined limits. 
The second assembly of spray jets for the inside of the filters, as shown 
in FIG. 3, has two directions of mobility. The first mobility direction is 
verically up and down, whereby the second assembly spray nozzles are 
inserted into the filter elements by lowering the entire conduit 
14--extension 16--spray nozzle 15 assembly into the elements when they are 
to be cleaned. The entire inside length of the filter element may thus be 
subjected to the cleaning liquid spray. The second mobility direction is 
horizontally back and forth, whereby the second assembly, when it is 
outside the filter elements, may be moved from one row of filter elements 
to the next, so that successive rows may be cleaned using only one second 
assembly. Variations of the second assembly include utilizing a plurality 
of parallel conduits 14, with attached extensions 16 and spray nozzles 15, 
whereby more than one row of filter elements may be internally spray 
washed simultaneously. In a further variation a mass array of second 
assembly spray nozzles may be used, one such nozzle located over each 
filter element and mounted for only vertical motion. Such a mass assembly 
could also be stationary mounted, provided that the position of the 
nozzles 15 and extensions 16 do not interfere with the filtering 
operation. 
Specific means for moving either assembly of spray nozzles (when the 
particular assembly is mobile) are not critical and do not form a part of 
this invention. 
Thus, the entire first assembly may be guided for vertical motion by a 
track using manual or powered means. The first assembly may also be moved 
by rotating liquid conduit 10 along it's axis, to adjust th direction of 
spray. However, as indicated above, the first assembly is preferably 
stationary. 
The second assembly may be moved vertically manually or by any power means, 
such as an electric motor. Similarly, the second assembly may be moved 
horizontally manually or by any power means, such as an electric motor. 
The second assembly may be suspended and moved by any suitable means, such 
as a gantry crane, semigantry crane, counterbalanced hammerhead crane, 
overhead traveling crane, or the like. The means for suspending and/or 
moving the first or second assembly is not critical to this invention, and 
therefore are not shown in the drawings. 
An additional drawing is now presented (FIGS. 4 and 5), which is merely a 
composite of original FIGS. 1 and 3, and which illustrates both the first 
assembly and the second assembly, as employed simultaneously, for cleaning 
both the inside of the filters and the outside of the filters, at the same 
time. The identification of the elements is the same as in FIGS. 1 and 3. 
The jet vertical portion (i.e. fan-shaped spray) 13 is shown behind the 
filter elements 1, rather than in front of the filter elements 1 as shown 
in FIG. 1, to avoid any confusion with the spray from nozzles 15. For the 
same reason, the spray 13 has been depicted with fewer radiating lines. 
This does not imply any change in the nature, force, or direction of spray 
13 between FIGS. 1 and 4.