Title of Invention

A METHOD FOR TRANSPORTING SCAVENGING AIR

Abstract

A method of transporting scavenging air for at least one bag filter where during the operation of cleaning the filter bags the scavenging air is supplied via an air filter a device for conveying gas without self-cooling, and at least one tank to at least one bag filter characterized in that outside the period of the operation of cleaning the filter bags a constant amount of scavenging air is circulated via the device for conveying gas through lines outside the device for conveying gas.

Full Text

-1A- This Invention relates to a method for transporting scavenging air. Description This invention relates to a method of transporting scavenging air for at least one bag filter, where during the operation of cleaning the filter bags the scavenging air is supplied via an air filter, a device for conveying gas without self-cooling, and at least one tank to at least one bag filter. Methods of transporting scavenging air for bag filters are known. In bag filters, where during the operating phase the dust-laden gas flows through the filter bags from the inside to the outside, a filter chamber is separated from the raw gas stream for dedusting in predetermined Intervals or In dependence on the pressure loss, and cleaned gas is countercurrently blown through said filter chamber as scavenging air. In the process, the filter bags are deformed. The dust cake separated breaks up and drops into the bunker as agglomerate. In the case of bag filters, where the dust-laden gas flows through the filter bags from the outside to the inside, the dusts precipitated are removed from the filter surface by Introducing an air blast into the interior of the bag via a lance. As a result, the gas flow Is briefly Interrupted, the - 2 - filter bags are puffed up abruptly, the dust cake breaks up and drops into the bunker. The DE-PS 195 23 417 discloses a method of dedusting a raw gas stream and/or sorbing gaseous substances from the raw gas stream. In the bag filter used a rotating arm is disposed above the gas outlet, which arm is rotatably mounted on a shaft. The shaft is put in rotation by means of a drive. In the clean gas chamber a device for supplying purge gas is provided, by means of which purge gas can be supplied to the rotating arm for dedusting the filter bags. When dedusting filter bags by means of scavenging air, there are generally used devices for conveying gas which are in operation also outside the period of the operation of cleaning. In general, air is constantly sucked in through an air filter and discharged to the environment by means of a valve. Due to the constant supply of air, there frequently occurs a condensation of noxious substances in the pipe conduits, which noxious substances damage the entire system of pipe conduits, as the devices used for conveying gas generally have no self-cooling for cost reasons. Moreover, it is disadvantageous that due to the constant sucking in of scavenging air the air filter used is clogged after relatively short operating periods, which leads to a relatively high maintenance effort. It is therefore the object underlying the invention to create a method of transporting scavenging air for at least one bag filter, where a disadvantageous clogging of the air filter and corrosive damages in the pipe conduit systems are largely avoided. The object underlying the invention is solved in that outside the period of the operation of cleaning the filter bags a constant amount of scavenging air is circulated by means of the device for conveying gas through lines outside the device for conveying gas. As a device for conveying gas there are - 3 - used compressors or blowers without self-cooling. The use of rotary piston blowers has turned out to be particularly advantageous. As lines there may for instance be used parts of the pipe conduits through which the scavenging air is supplied to the at least one bag filter. There may, however, also be chosen pipe conduits of other adjacent plants, in which method-related condensation damages may occur. There is circulated a constant amount of scavenging air, where sucking in scavenging air via the air filter is omitted at the same time. It has surprisingly turned out that corrosive damages in the lines outside the device for conveying gas can be avoided, as due to the operation the circulated scavenging air has a higher temperature than the ambient air and is not brought in contact with additional colder scavenging air. A condensation of noxious substances in the pipe conduit system can thus advantageously be avoided. Since outside the period of the operation of cleaning the filter bags a constant sucking in of scavenging air is omitted, there is no clogging of the air filter provided outside the period of the operation of cleaning the filter bags. If a cleaning of the filter bags is required, the circulation of the scavenging air is interrupted, scavenging air is again sucked in via the air filter, and via a tank which serves as reservoir for the scavenging air, the scavenging air is introduced into the bag filter. When the period of the operation of cleaning has passed, the supply of scavenging air into the tank is interrupted and a constant amount of scavenging air is again circulated via the device for conveying gas through lines outside the device for conveying gas. The pipe conduit system may then be connected with a plurality of bag filters, to which scavenging air is supplied as required. A preferred aspect of the invention consists in that outside the device for conveying gas the scavenging air is passed through at least one line through which it is also passed during the operation of cleaning the filter bags. By means of - 4 - this measure it is advantageously achieved that corrosion damages are also avoided in parts of the plant which provide a connection with the bag filter. In accordance with a further preferred aspect of the invention it is provided that the scavenging air is introduced into at least one bag filter when the excess pressure in the tank provided before the respective bag filter is 0.6 to 0.9 bar. When an excess pressure of 0.6 to 0.9 bar is adjusted, dedusting the filter bags is effected in a particularly advantageous manner, as upon switching the circulation of the scavenging air to the direct supply into the at least one bag filter, the dust will drop off the filter bags in greatly agglomerated form, which facilitates a separation in the bunker of the bag filter. When dedusting the filter bags at an excess pressure of 0.6 to 0.9 bar, the dust in the bag filter will thus not again be whirled up. The invention will subsequently be explained in detail and by way of example with reference to the accompanying drawing (Figs. 1,2): Fig. 1 shows a simplified schematic flow diagram of the method of transporting scavenging air for a bag filter. Fig. 2 shows a simplified schematic flow diagram of a known method of transporting scavenging air for a bag filter. Fig. 1 represents a simplified schematic flow diagram of the method of transporting scavenging air 1 for a bag filter 10. The scavenging air 1 is introduced via an air filter 2 and via a line 3 into the device 4 for conveying gas without self-cooling. In the period of the operation of cleaning the filter bags, the scavenging air 1 is discharged from the device 4 for conveying gas and via line 5 and the three-way - 5 - valve 6 reaches a tank 8 which serves as reservoir for scavenging air. As soon as an excess pressure of o.6 to 0.9 bar has been reached in the tank 8, the valve 9 is opened and the scavenging air 1 is advantageously passed through the bag filter 10 for cleaning the filter bags. The scavenging air l leaves the bag filter 10 through line 11. During the period of the operation of cleaning the filter bags, the three-way valve 6 is switched open from line 5 to (b). When dedusting the filter bags has been terminated, the three-way valve 6 is switched over such that line 5 is switched open to (a). The supply of scavenging air 1 via the air filter 2 to the device 4 for conveying gas without self-cooling is interrupted, and the scavenging air 1 already contained in lines 5, 12 outside the device 4 for conveying gas is circulated via the device 4 for conveying gas. The circulated scavenging air 1 has a higher temperature than the ambient air, so that condensation processes in lines 5, 12 are avoided. The pipe conduit system need therefore not be made of stainless steel. While the scavenging air 1 is circulated, the air filter 2 is not in operation, so that there is no further contamination of the air filter 2 during this period. In the flow diagram in accordance with Fig. 1 there is merely represented the arrangement of a bag filter 10. It is, however, also possible to supply the scavenging air 1 contained in line 5 to a plurality of bag filters 10 via a plurality of valves and the respective tanks 8 • Fig. 2 represents a simplified schematic flow diagram of a known method of transporting scavenging air 1 for a bag filter 10 for comparison purposes. Outside the period of the operation of cleaning the filter bags the three-way valve 6 for line 5 is switched open to (a). The device 4 for conveying gas without self-cooling operates with a relatively high power, where new scavenging air 1 is constantly sucked into line 3 via the air filter 2. As a result, the temperature of the scavenging air 1 is reduced, which flows in line 5 pro- - 6 - vided outside the device 4 for conveying gas. In general, this leads to the disadvantageous condensation of noxious substances in line 5. For these reasons, line 5 should be made of stainless steel. Behind the three-way valve 6 a valve 7 is provided, which is opened when a certain pressure is reached, which leads to the fact that the scavenging air 1 is discharged to the environment behind the valve 7, where condensed noxious substances may be entrained. A further disadvantage of this known procedure consists in that discharging the scavenging air 1 via the valve 7 involves a relatively large annoyance caused by noise, so that the valve 7 must be provided with a sound insulation of a relatively expensive construction. Since with this known procedure the air filter 2 is constantly in operation, the same is clogged even after relatively short operating periods, which results in a relatively high maintenance effort. The disadvantages occurring in the known procedure in accordance with Fig. 2 are avoided in the inventive method. -7- WE CLAIM 1. A method of transporting scavenging air (1) for at least one bag filter (10), where during the operation of cleaning the filter bags the scavenging air (1) is supplied via an air filter (2), a device (4) for conveying gas without self-cooling, and at least one tank (8) to at least one bag filter (10), characterized in that outside the period of the operation of cleaning the filter bags a constant amount of scavenging air (1) is circulated via the device (4) for conveying gas through lines (5,12) outside the device (4) for conveying gas. 2. The method as claimed in claim 1, wherein outside the device (4) for conveying gas the scavenging air (1) is passed through at least one line (5), through which it is also passed during the operation of cleaning the filter bags. 3. The method as claimed in claim 1 or 2, wherein the scavenging air (1) is introduced into at least one bag filter (10) when the excess pressure in the tank (8) disposed before the respective bag filter (10) is 0.6 to 0.9 bar. A method of transporting scavenging air for at least one bag filter where during the operation of cleaning the filter bags the scavenging air is supplied via an air filter a device for conveying gas without self-cooling, and at least one tank to at least one bag filter characterized in that outside the period of the operation of cleaning the filter bags a constant amount of scavenging air is circulated via the device for conveying gas through lines outside the device for conveying gas.

Documents:

00256-cal-1998 abstract.pdf

00256-cal-1998 claims.pdf

00256-cal-1998 correspondence.pdf

00256-cal-1998 description(complete).pdf

00256-cal-1998 drawings.pdf

00256-cal-1998 form-1.pdf

00256-cal-1998 form-2.pdf

00256-cal-1998 form-3.pdf

00256-cal-1998 form-5.pdf

00256-cal-1998 letters patent.pdf

00256-cal-1998 pa.pdf

00256-cal-1998 priority document.pdf

256-cal-1998-granted-abstract.pdf

256-cal-1998-granted-claims.pdf

256-cal-1998-granted-correspondence.pdf

256-cal-1998-granted-description (complete).pdf

256-cal-1998-granted-drawings.pdf

256-cal-1998-granted-examination report.pdf

256-cal-1998-granted-form 1.pdf

256-cal-1998-granted-form 2.pdf

256-cal-1998-granted-form 3.pdf

256-cal-1998-granted-form 5.pdf

256-cal-1998-granted-letter patent.pdf

256-cal-1998-granted-pa.pdf

256-cal-1998-granted-priority document.pdf

256-cal-1998-granted-reply to examination report.pdf

256-cal-1998-granted-specification.pdf

256-cal-1998-granted-translated copy of priority document.pdf