Method and apparatus for filtering and cleaning the filter

Claim 2

Method of cleaning a dust filter unit of the kind that comprises a plurality of flexible filter bags that are open to the clean air side and mounted on cages that prevent the filter bags from collapsing, the method comprising: terminating the flow of dust laden air into the filter prior to cleaning the filter, locating a distribution device having a plurality of nozzles so that the nozzles are in communication with the openings of all the filter bags, and cleaning all the filter bags simultaneously, while the flow of dust laden air is terminated, by injecting repetitively pulsed high velocity air jets from the nozzles into the filter bags, said high air velocity jets being formed by repetitive sudden pressurization and then venting of the distribution device having the plurality of nozzles, said high velocity air jets being injected substantially in parallel with the walls of the filter bags and being thin relative to the width of the filter bags so that a considerable part of the length of the jets do not touch the filter bags, the total area of said nozzles being so small that it is the dominating restriction in the system formed by the pulse valve arrangement and said air conveying means.

Claim 3

Method according to claim 1 wherein the time between the jet pulses is so long that there will be almost pressure equalization in the filter bags between the jet pulses.

Claim 4

Method according to claim 1 comprising repetitively pressurizing and venting the distribution device.

Claim 5

Method according to claim 1 wherein the filter bags have a length in their cross section which is larger than 10 times their width, comprising injecting only one pulsed jet into each filter bag.

Claim 6

Method according to claim 1 comprising ejecting the jets substantially perpendicularly to the openings of the filter bags.

Claim 7

Method according to claim 1 comprising injecting the jets into the filter bags such that they have super-sonic speed in the filter bags.

Claim 8

Method according to claim 1 comprising injecting the repetitively pulsed high velocity air jets from expansion nozzles into the filter bags.

Claim 9

A dust filter unit comprising: a housing, a plurality of substantially parallelly arranged filter bags in the housing and dividing the housing into a lower dusty air chamber and an upper clean air chamber, said filter bags being open to the clean air chamber, a plurality of cages in said housing on which respective filter bags are mounted to prevent them from collapsing, an inlet in the housing for admission of dusty air into said dusty air chamber of the housing, an outlet in said housing for exit of clean air from said clean air chamber of the housing, a selectively activatable automatic pulse valve arrangement connectable to a source of pressurized air, an air conveying means connected to said pulse valve arrangement and having a plurality of expansion nozzles directed to inject high velocity jets into the filter bags substantially in parallel with the filter bags, said jets being thin relative to the width of the filter bags, the total area of said nozzles being so small that it is the dominating restriction in the system formed by the pulse valve arrangement and said air conveying means, said pulse valve arrangement including means for repetitively and suddenly pressurizing and alternately venting said air conveying means when activated to produce repetitively pulsed high velocity air jets, and means for terminating the flow of dusty air into said dusty air chamber before the activation of said automatic pulse valve and before said repetitive pressurizing and venting of said air conveying means.

Claim 10

A dust filter unit comprising: a housing, a plurality of substantially parallelly arranged filter bags in the housing and dividing the housing into a lower dusty air chamber and an upper clean air chamber, said filter bags being open to the clean air chamber, a plurality of cages in said housing on which respective filter bags are mounted to prevent them from collapsing, an inlet in the housing for admission of dusty air into said dusty air chamber of the housing, an outlet in said housing for exit of clean air from said clean air chamber of the housing, a selectively activatable automatic pulse valve arrangement connectable to a source of pressurized air, an air conveying means connected to said pulse valve arrangement and having a plurality of expansion nozzles directed to inject high velocity jets into the filter bags substantially in parallel with the filter bags, said jets being thin relative to the width of the filter bags, the total area of said nozzles being so small that it is the dominating restriction in the system formed by the pulse valve arrangement and said air conveying means, said pulse valve arrangement including means for repetitively and suddenly pressurizing and alternately venting said air conveying means when activated to produce repetitively pulsed high velocity air jets, and means for terminating the flow of dusty air into said dusty air chamber before the activation of said automatic pulse valve and before said repetitive pressurizing and venting of said air conveying means.

Claim 11

A dust filter unit according to claim 8 wherein the length of each filter bag in its cross-section is larger than 10 times its width, and comprising a single nozzle for each filter bag.

Claim 12

A dust filter unit according to claim 8 wherein said pulse valve arrangement injects said high velocity jets into the filter bags with a super-sonic speed in the filter bags.

Claim 13

A dust filter unit according to claim 8 wherein said pulse valve arrangement is arranged to provide jets having a time period between jets which is sufficiently long that there will be almost pressure equalization in the filter bags between the jet pulses.

Claim 14

A dust filter unit according to claim 8 wherein said expansion nozzles have a diameter of about 1.7 mm.