FORM - 2
THE PATENTS ACT, 1970
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13)
SYSTEM AND METHOD FOR PULSE-JET CLEANING
OF BAG FILTERS
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R.D. Aga Road,
Chinchwad, Pune-411 019,
Maharashtra, India.
Inventors: a) VISHWANATH PUNDALIK BHANDARKAR; b) VISHAL DASHRATH WAYAL; c) SURENDRA HABIB
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF DISCLOSURE
The present disclosure relates to a system and method for cleaning dust-laden bag filters. Particularly, the present disclosure relates to a system and method for on-line/off-line pulse-jet cleaning of bag filters.
BACKGROUND
Bag filters are very commonly used in industry for filtering particulate-laden air/gases. Conventionally, the bag filters comprise a housing with an upper clean air chamber and a lower dirty air/filtering chamber. The two chambers are separated by means of a partition known as a tube sheet. The partition has several openings which provide fluid communication between the two chambers and through which filter bags/cartridges are aligned and suspended downwardly into the filtering chamber. The filter cartridges may be held in place by means of a support such as a cage. Particulate-laden air is introduced into the filtering chamber by a fan or blower, whereupon the particulates get collected onto the filter cartridges. The filtered air passes through the filtering media to the interior of the filter cartridge and upwardly out through the openings in the tube sheet into the clean air chamber from where the clean air can be discharged.
During continuous filtering process, particulate cakes onto the filter cartridges, thus reducing the air flow through the filter media, and thereby reducing efficiency of the bag filter. Therefore, the filter cartridges must be cleaned frequently to remove the trapped particulates. Several methods are known for cleaning filter cartridges in bag filters. A typical method is mechanical shaking. In this method, the filter media is shaken so that the dust falls into a hopper located below the filter media. This is an off-line cleaning method and requires frequent shutting down of the bag filter for cleaning. Also, this method is not suitable for sticky dust particles and the mechanical shaking causes wear and tear of the filter cartridges. Another typical method for cleaning filter cartridges

in bag filters is by reverse-air cleaning. In this method air is supplied by a separate fan to dislodge the particulates on the filter media. This is also an off-line method and requires the bag filter to be shut-down for cleaning. Also, the method is not suitable for filter cartridges longer than 6m and for sticky dust. In some cases sonic vibrations are used, which cause the filter to vibrate and thereby dislodge the dust on the filter media. However, this method has poor efficiency and must be used in conjunction with other cleaning techniques.
One desirable, known method for cleaning filter media in bag filters is by using pressurized air. This type of cleaning is called the pulse-jet cleaning in which compressed air is forced downwards into the filter cartridges in a direction that is reverse to the normal flow causing the particulates to dislodge from the filter media. Commonly, a blow pipe extends across the bag filter which has a series of orifices positioned over each of the filter cartridge. The compressed air used for cleaning is high pressure or intermediate pressure, typically between 60 -100 psig. The pulse-jet cleaning method can be used on-line or off-line, for cleaning tall filter cartridges, with the advantage of cleaning only selective filter cartridges at one time. A larger pulse can be created by providing a venturi at the top of each filter cartridge. However, this is avoided as the venturi can cause erratic air flow rate through the filter cartridge resulting in wear and tear of the filter media; also a significant pressure drop can result especially in tall filter cartridges.
Typically, a pulse-jet cleaning system is periodically activated at a constant air pressure. The time period between subsequent activations is selected based on the calculated need for cleaning. The constant air pressure tends to decrease the wear life of the filter media; also, this method is energy expending. Alternatively, a pulse-jet cleaning system is activated based on the differential pressure across the filter media which increases due to particulate build-up on

the filter media. The differential pressure is monitored by means of a pressure responsive device which communicates with an electronic control circuitry to automatically activate the pulse-jet on reaching a selected upper threshold level. A drawback of the known pulse-jet cleaning systems is that the air flow rate at the entrance of the filter cartridge is higher and decreases along the length of the filter, providing uneven cleaning along the length of the filter cartridge. Also, since a constant air pressure is used even where the air pressure is greater than needed, excess stress is placed on the filtering media causing wear and tear. Also, more energy is consumed. Therefore, there is felt a need for a pulse-jet cleaning system which is highly effective, provides uniform cleaning through the entire length of the filter cartridge, provides controlled air flow rate thereby enhancing life of the filter media, has a simple construction and low operating costs.
OBJECTS
An object of the present invention is to provide a system and method for pulse-jet cleaning of bag filters which is energy efficient, increases the wear life of the filter media and provides uniform cleaning through the entire length of the filter cartridge thus suitable for tall (< 8m) bag filters.
Another object of the present invention is to provide a system and method for pulse-jet cleaning of bag filters which requires low pressure or intermediate pressure air for cleaning, and the flow to different portions of the filter cartridge can be controlled, this conserves energy and increases the bag filter life.
One more object of the present invention is to provide a system and method for pulse-jet cleaning of bag filters which can be used for on-line or off-line cleaning of bag filters.

An additional object of the present invention is to provide a system and method for pulse-jet cleaning of bag filters which has simple construction with fewer components and low operating costs.
SUMMARY
These and other objects and advantages are achieved by a system and method for pulse-jet cleaning of bag filters as disclosed in the present invention.
In accordance with the present invention, there is provided a system for pulse-jet cleaning of filter cartridges in a bag filter having a filtering chamber and a clean air chamber, said system comprising:
■ an air reservoir for supplying compressed air;
■ a pulse valve adapted to regulate the supply of said compressed air;
■ an air supply conduit having a plurality of apertures along the operative longitudinal axis, said plurality of apertures are positioned to correspond to said filter cartridges for conducting said regulated flow of compressed air into said filter cartridges; and
■ wherein each of said plurality of apertures is provided with a dual-jet nozzle, said dual-jet nozzle being adapted to produce a dual-jet pulse, and each jet pulse having different jet velocity and jet angle for penetrating at different sections of said filter cartridge.
Typically, in accordance with the present invention, said air supply conduit has a configuration selected from a group of configurations consisting of uniform cross-section tube, varying cross-section tube, concentric tubes, and combinations thereof.
Preferably, in accordance with the present invention, said dual-jet nozzle has a configuration selected from a group of configurations consisting of concentric

cylindrical nozzle, concentric cylindrical nozzle with serrations, double cylindrical nozzle, convergent nozzle with a cylindrical shroud, double convergent nozzle, cylindrical shroud with convergent sections, double convergent-divergent nozzle, pipe-in-pipe double jet nozzle, and combinations thereof.
Typically, in accordance with the present invention, said dual-jet nozzle is supported on said aperture of said air supply conduit by means of a joint selected from threaded, bolted, hinged and welded.
Preferably, in accordance with the present invention, said dual-jet nozzle is adapted for pulse-jet cleaning of filter cartridges having length between 8m -12m.
In accordance with the present invention, a pressure response device is provided for monitoring differential pressure between said filtering chamber and said clean air chamber. The pulse valve is automatically activated in response to the differential pressure to provide said compressed air to said filter cartridges at a regulated pressure.
Preferably, in accordance with the present invention, said dual-jet nozzle is maintained at a selective distance above said filter cartridge.
In accordance with the present invention, there is provided a method for pulse-jet cleaning of filter cartridges in a bag filter having a filtering chamber and a clean air chamber, said method comprising the steps of:
■ supplying a regulated flow of compressed air from an air reservoir via a pulse valve;

■ conducting said regulated flow of compressed air through an air supply conduit having a plurality of apertures where each aperture directly corresponds to a filter cartridge to provide said regulated flow of compressed air therein, wherein, said aperture is provided with a dual-jet nozzle which splits the regulated flow of compressed air in a dual-jet pulse with each pulse having different jet velocity and jet angle for penetrating at different sections of said filter cartridge to provide uniform pressure differential and therefore uniform cleaning through the length of said filter cartridge.
Preferably, in accordance with the present invention, pressure of said compressed air is in the range of 30 - 50 psig.
Typically, in accordance with the present invention, the method includes the step of monitoring differential pressure between said filtering chamber and said clean air chamber and activating said pulse valve in response to the differential pressure to provide a regulated flow of compressed air.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with the help of the accompanying drawings, in which,
FIGURE 1 illustrates a schematic of the system for pulse-jet cleaning of bag filters particularly showing the air reservoir, pulse valve, air supply conduit and the dual-jet nozzle, in accordance with the present invention;
FIGURES 2A, 2B & 2C illustrate a schematic of the preferred embodiments of the support means for connecting the air supply conduit and the dual-jet nozzle, in accordance with the present invention;

FIGURES 3A, 3B, 3C & 3D illustrate a schematic of the preferred embodiments of the air supply conduit, in accordance with the present invention;
FIGURE 4A - 41 illustrate a schematic of the preferred embodiments of the dual-jet nozzle, in accordance with the present invention;
FIGURE 5 illustrates the preferred alignment of the system for pulse-jet cleaning on a bag filter, in accordance with the present invention; and
FIGURE 6 illustrates a schematic of the preferred dual-jet flow profile in accordance with the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the accompanying drawings which only exemplify the invention and in no way limit its scope and ambit. The description provided is purely by way of example and illustration.
The present invention envisages a system and method for pulse-jet cleaning of filter cartridges in a bag filter. The system of the present invention uses a dual-jet nozzle which generates multiple jets of air that penetrate at different sections of the filter cartridge to provide effective cleaning. This allows uniform cleaning through the entire length of the filter cartridge and thus can be used for effectively cleaning tall bag filters which is greater than 8 m long, however, the present invention is more suitable for tall bag filters of length up to 12m. The pressure of the compressed air is low to intermediate pressure, typically between 30 - 50 psig, and the pressure is regulated depending upon the amount of cleaning needed. This reduces the energy consumption and enhances wear

life of the filter media. The system of the present invention can be used for online or off-line cleaning.
Referring to FIG. 1, there is illustrated the system for pulse-jet cleaning of filter cartridges in a bag filter in accordance with the present invention. The system, generally represented by numeral 100 in FIG.1, comprises an air reservoir 102 in operative communication with a compressor (not shown) for receiving compressed air via an inlet 104. A pulse valve 106 is provided in operative communication with the air reservoir 102 for regulating the flow of compressed air from the air reservoir 102. On activation of the pulse valve 106, a regulated flow of compressed air, typically having a pressure between 30 - 50 psig, flows into an air supply conduit 110 via an outlet 108 from the air reservoir 102. Multiple outlets with respective pulse valves can also be provided. The various preferred configurations of the air supply conduit 110 are illustrated in FIG. 3 A - 3D. The air supply conduit 110 can have a configuration selected from: a uniform cross-section cylindrical tube as represented by numeral 110A in FIG. 3A, a tapering cross-section cylindrical tube as represented by numeral 110B in FIG. 3B, concentric cylindrical tubes or pipe-in-pipe arrangement as represented by numeral HOC in FIG. 3C, a step-type arrangement as represented by numeral 110D in FIG. 3D, or combinations thereof. The air supply conduit 110 can be supported on both ends by means of saddle supports 138 & 140 as shown in FIG. 3A.
The air supply conduit 110 comprises a plurality of apertures 120 lined along the operative longitudinal axis. The plurality of apertures 120 are positioned equidistant from each other. These apertures 120 can have uniform or varying cross-sections. The compressed air flow conducted through the air supply conduit 110 is uniform distributed through each of the aperture 120. In case of the pipe-in-pipe configuration 110C, the inner tube and the outer tube each have

a plurality of apertures 120, where the apertures on the inner tube correspond with the apertures on the outer tube to define a flow path. A typical baghouse filter can have up to 20 apertures in a row.
The plurality of apertures 120 are positioned such as to correspond with filter cartridges of a baghouse filter for conducting the regulated flow of compressed air therein. The baghouse filter typically comprises a filtering chamber and a clean air chamber; the two chambers are divided by a tube sheet. This tube sheet has a plurality of openings through which filter bags/cartridges are suspended downwards. A tube sheet 122 and a filter cartridge 124 are shown in FIG. 5. The filter cartridge 124 can be woven or non-woven and of any shape and size, however the present invention is more suitable for non-woven and cylindrical filter cartridges with enclosed bottoms. The filter cartridge 124 is supported in a cage structure 126. The air supply conduit 110 is positioned such that aperture 120 is aligned above the filter cartridge 124.
The aperture 120 is provided with a specially designed dual-jet nozzle 112. The dual-jet nozzle 112 is adapted to split the regulated flow of compressed air in a dual-jet pulse with each jet pulse having different jet velocity and jet angle for penetrating the different sections of the filter cartridge, thereby providing uniform pressure differential and therefore uniform cleaning through the entire length of the filter cartridge. The dual-jet nozzle 112 is joined on the aperture 120 of the air supply conduit 110. The joint is typically a threaded, bolted, hinged or welded joint. The various embodiments for supporting the dual-jet nozzle 112 in the aperture 120 of the air supply conduit 110 are shown in FIG. 2A - 2C, where FIG. 2A shows a welded joint 114, FIG. 2B shows a threaded joint 116, and FIG. 2C shows a bolted joint 118.

The various preferred configurations of the dual-jet nozzle 112 are illustrated in FIG. 4A - 41. The dual-jet nozzle 112 can have a configuration selected from: concentric cylindrical nozzle as shown in FIG. 4B, concentric cylindrical nozzle with serrations as shown in FIG. 4A, convergent cylindrical nozzle as shown in FIG. 4C, convergent nozzle with a cylindrical shroud as shown in FIG. 4D, cylindrical shroud with convergent sections as shown in FIG. 4E, convergent-divergent type nozzle as shown in FIG. 4F, bi-cylindrical tubes/pipes as shown in FIG. 4G, pipe-in-pipe double jet nozzle as shown in FIG. 4H, convergent-divergent type nozzle with an enlarged throat as shown in FIG. 41, or combinations thereof. A preferred embodiment of the dual-jet nozzle 112 is the concentric cylindrical nozzle of FIG. 4B, where a portion of the inner cylinder 144 protrudes outwards beyond the outer cylinder 142.
A dual-jet flow profile for concentric cylindrical nozzle of FIG. 4B is shown in FIG. 6. The dual-jet nozzle 112 is maintained at a selective distance above the filter cartridge 124 to direct the compressed air effectively into the filter cartridge 124 without any drift. The relative distance between the dual-jet nozzle 112 and the filter cartridge 124 is critical. The jet angle enlarges as the dual-jet nozzle 112 is moved away from the filter cartridge 124, and too large a gap may cause certain portion of the jet to impinge on the tube sheet 122 instead of entering the filter cartridge 124, thereby resulting in wastage. If the dual-jet nozzle 112 is maintained very near to the filter cartridge 124, then a suction is created at the top portion of the filter cartridge 124 which results in improper bag cleaning. An optimum distance between the dual-jet nozzle 112 and the filter cartridge 124 for the concentric dual-jet nozzle of FIG. 4B is between 75 -150 mm.
The dual jet nozzle 112, in particular configured in the form of concentric cylinders as shown in FIG. 4B, with the inner nozzle slightly protruding from

the outer nozzle, have varying jet angles so as to optimally clean the entire length of the filter cartridge 124. A pressure response device (not shown) monitors differential pressure between the filtering chamber and the clean air chamber of the baghouse filter. The pressure response device is in operative communication with a electronic control circuitry to communicate the data, the circuitry in-turn actuates the pulse valve 106. The pulse valve 106 is automatically activated in response to the differential pressure level to provide compressed air 128 to the filter cartridge 124 at a regulated pressure. On passing through the dual-jet nozzle 112, the compressed air flow 130 is split into a dual-jet pulse. A first jet pulse 134 emanating from the inner cylinder 144 is narrow, typically having an angle between 2-5 deg, and has a higher velocity. A second jet pulse 132 emanating from between the outer cylinder 142 and the inner cylinder 144 is wider, typically having an angle between 25 - 30 deg, and has a lower velocity. The first jet pulse penetrates into the lower section of the filter cartridge 124 thereby dislodging the particulates trapped in the lower section, and the second jet pulse penetrates into the upper section of the filter cartridge 124 dislodging the particulates trapped in the upper section. The dislodged particulates drop to the bottom of the baghouse and are collected in a hopper (not shown). The hopper is periodically cleaned by providing sensing means which monitor the level of dust collected in the hopper and control means which operate a lock device for discharging the dust. The jet velocity and jet angle can be varied by varying the pressure of the compressed air or by changing the nozzle type or dimension, filter inlet or both. The jet pulse 132 & 134 create suction pressure that draws secondary air 136 from the vicinity. The secondary air 136 further aids in cleaning the filter cartridge 124.
TECHNICAL ADVANTAGES
A system and method for pulse-jet cleaning of bag filters, as described in the present invention has several technical advantages including but not limited to

the realization of: the system provides uniform cleaning through the entire length of the filter cartridge thus suitable for tall (< 8m) bag filters; the system requires low pressure or intermediate pressure air for cleaning, and the flow to different portions of the filter cartridge can be controlled, this conserves energy and increases the wear life of the filter media; the system can be used for on-line or off-line cleaning of bag filters; and the system has a simple construction with fewer components and low operating costs.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a

statement in the specification specific to the contrary. Wherever a range of values is specified, a value up to 10% below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the invention.
In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

WE CLAIM,
1. A system (100) for pulse-jet cleaning of filter cartridges in a bag filter
having a filtering chamber and a clean air chamber, said system
comprising:
■ an air reservoir (102) for supplying compressed air;
■ a pulse valve (106) adapted to regulate the supply of said compressed air;
■ an air supply conduit (110) having a plurality of apertures (120) along the operative longitudinal axis, said plurality of apertures are positioned to correspond to said filter cartridges (124) for conducting said regulated flow of compressed air into said filter cartridges; and
■ wherein each of said plurality of apertures (120) is provided with a dual-jet nozzle (112), said dual-jet nozzle being adapted to produce a dual-jet pulse, and each jet pulse having different jet velocity and jet angle for penetrating at different sections of said filter cartridge (124).
2. The system as claimed in claim 1, wherein said air supply conduit (110)
has a configuration selected from a group of configurations consisting of
uniform cross-section tube, varying cross-section tube, concentric tubes,
and combinations thereof.
3. The system as claimed in claim 1, wherein said dual-jet nozzle (112) has a
configuration selected from a group of configurations consisting of
concentric cylindrical nozzle, concentric cylindrical nozzle with serrations,
double cylindrical nozzle, convergent nozzle with a cylindrical shroud,
double convergent nozzle, cylindrical shroud with convergent sections,
double convergent-divergent nozzle, pipe-in-pipe double jet nozzle, and
combinations thereof.

4. The system as claimed in claim 1, wherein said dual-jet nozzle (112) is supported on said aperture (120) of said air supply conduit (110) by means of a joint selected from threaded, bolted, hinged and welded.
5. The system as claimed in claim 1, wherein said dual-jet nozzle (112) is adapted for pulse-jet cleaning of filter cartridges having length between 8m -12m.
6. The system as claimed in claim 1, wherein a pressure response device is provided for monitoring differential pressure between said filtering chamber and said clean air chamber.
7. The system as claimed in claim 6, wherein said pulse valve (106) is automatically activated in response to the differential pressure to provide said compressed air to said filter cartridges (124) at a regulated pressure.
8. The system as claimed in claim 1, wherein said dual-jet nozzle (112) is maintained at a selective distance above said filter cartridge (124).
9. A method for pulse-jet cleaning of filter cartridges in a bag filter having a
filtering chamber and a clean air chamber, said method comprising the
steps of:
■ supplying a regulated flow of compressed air from an air reservoir via a pulse valve;
■ conducting said regulated flow of compressed air through an air supply conduit having a plurality of apertures where each aperture directly corresponds to a filter cartridge to provide said regulated flow of compressed air therein, wherein, said aperture is provided with a

dual-jet nozzle which splits the regulated flow of compressed air in a dual-jet pulse with each pulse having different jet velocity and jet angle for penetrating at different sections of said filter cartridge to provide uniform pressure differential and therefore uniform cleaning through the length of said filter cartridge.
10. The method as claimed in claim 9, wherein pressure of said compressed air is in the range of 30 - 50 psig.
11. The method as claimed in claim 9, which includes the step of monitoring differential pressure between said filtering chamber and said clean air chamber and activating said pulse valve in response to the differential pressure to provide a regulated flow of compressed air.