Title of Invention	A METHOD FOR REGULATING THE PRESSURE IN BAG HOUSE FILTERS
Abstract	A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, wherein bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned, characterised in that each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber and the method comprising the steps of: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and, if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to the preset value.

Title of Invention

A METHOD FOR REGULATING THE PRESSURE IN BAG HOUSE FILTERS

Abstract

A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, wherein bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned, characterised in that each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber and the method comprising the steps of: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and, if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to the preset value.

Full Text	Method for regulating reverse-air in bag filters The present invention relates to a method for regulating reverse-air pressure in bag filters. The term "bag filters" as used herein includes all types of filters where the gas to be cleaned of solid particles passes through a filtering cloth. In these kinds of filters, the filter cloth is usually in the form of cylinder-shaped bags. The uncleaned gas is passed through the cloth in the filtering bags either by passing uncleaned gas into the bags and out through the filtering cloth whereby solid particles are retained on the inside of the filtering cloth, or, alternatively, by passing uncleaned gas through the filtering cloth from the outside of the bags whereby solid particles are retained on the outside of the filtering bags. In this specification, gas filters of the kind where uncleaned gas is passed into the filtering bags will be described, but it should be understood that the comments will also apply to all other types of bag filter. Bag filters usually comprises a plurality of chambers where each chamber comprises a plurality of normally vertically arranged filtering bags. Uncleaned gas is passed into the bag and passes through the filtering cloth in the walls of the bag, while the solid particles are retained inside the bags. When the filter has been in operation for some time the solid particles must be removed from the bags. This is done by disconnecting the supply of uncleaned gas to the chamber to be cleaned, and the bags in the disconnected chamber are then cleaned by supplying cleaning gas in the opposite direction of the direction of the uncleaned gas. This method is called reverse-air cleaning. The particulate material contained in the chamber which is being cleaned will fall into a closed-bottom hopper situated below the chamber and is then transported through valves or the like to a storage silo by means of pneumatic transport or by some other means of transportation such as chain conveyers of other ways of mechanical transportation. The reverse-air method for cleaning chambers uses a suction fan which is connected to the chamber to be cleaned after the supply of uncleaned gas to this chamber has been disconnected. The duration of running the suction fan for each chamber is relatively short, normally between 10 and 15 seconds. In conventional methods for regulating the pressure provided by the suction fan, the suction fan is set at a fixed value regardless of which of the chambers is to be cleaned. This is effected by keeping the conductor rail of the suction fan in a fixed position or by running the suction fan at a fixed number of revolutions per minute. Those approaches, however, have a number of drawbacks and disadvantages. There is often a substantial physical distance between the chambers which are located closest to the suction fan and the chambers which are located furthest from the suction fan. As the settings for the suction fan is fixed the pressure provided by the suction fan will vary from chamber to chamber due to the different pressure drops in the pipes from the suction fan to each chamber. Further, new filtering bags will have a lower pressure drop than filtering bags which have been in operation for some time, and this will give a lower cleaning pressure in chambers having new filtering bags t ban in chambers having filtering bags which have been in use for some time. After some time in operation, it may al so be necessary to close some of the bags in one or more chambers due to leakages in the bags and in such cases, where the number of bags in one or more chambers are fewer than normal, the pressure in these chambers will increase when the suction fan is operated with a fixed regulation. If the pressure in one or more chambers during the reverse -air cleaning becomes too high, there will be an increased risk of damage to the bags, for instance by destroying the connection between the bags and metal rings which are used r to hold the bags open during the reverse-air cleaning. The consumption of filtering gas can thus become high and the maintenance costs for the bag house filter will be increased. On the other hand, if the reverse-air pressure becomes too low in one or more of the chambers, the cleaning of the filter bags will not be adequate. It is therefore an object of the present invention to provide a method which solves the above mentioned problems which exist in bag house filters which use a common suction fan for reverse-air cleaning. According to the present invention, there is provided a method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, in which bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned and in which each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber, the method comprising: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and, if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to the preset value. Preferably, the pressure in each of the chambers during the reverse-air cleaning is measured by a pressure transmitter arranged in each chamber. Alternatively, the pressure in each of the chambers during the reverse-air cleaning is measured by means of one common pressure transmitter which is connected to all of the chambers by means of pipes and where one chamber at a time can be connected to the common pressure transmitter by opening and closing valves in the pipes. The preset values for the reverse-air pressure can be set individually for each chamber. It is, however, preferred to use the same preset value for the reverse-air pressure in all of the chambers. By the method according to the present invention it will always be possible to obtain a substantially constant reverse-air pressure in each chamber corresponding to the preset pressure value. Even if one or more filtering bags in one chamber have to be closed, the reverse-air pressure in this chamber will not increase, but will be kept at the preset value. It is thus possible to avoid the reverse-air pressure in a chamber becoming so high that the remaining filtering bags are damaged or destroyed. The invention also extends to apparatus suitable for carrying out the method of the invention. The invention may be carried into practice in various ways and some embodiments will now be described by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows a bag house filter where the reverse-air pressure is regulated according to a first embodiment of the method of the present invention; and Figure 2 shows a bag house filter where the reverse-air pressure is regulated according to a second embodiment of the method of the present invention. Figure 1 shows a vertical section through a bag house filter comprising three chambers. The filter building is indicated by reference number 1. For simplicity, three chambers 2,3,4 are shown, each containing one filtering bag 5,6,7. Each of the chambers 2,3,4 is equipped with a bottom hopper 8,9,10. The filtering bags 5,6,7 are suspended from the filtering building 1 at their upper ends and their open lower ends are connected to the bottom hoppers 8,9,10. The chamber 4 is shown in a disconnected state for the installment of a new filtering bag 7. Gas which is to be cleaned is supplied through a main fan 2 8 to the chamber 2,3,4 via pipes 11,12,13 to the bottom hoppers 8,9,10. The pipes 11,12,13 are equipped with valves 14,15,16 for opening and closing the supply of uncleaned gas to the bottom hoppers 8,9,10, The valve 14 is open while the valves 15 and 16 are in the closed position . Uncleaned gas is thus supplied through the pipe 11 to the bottom hopper 28 for the chamber 2 and flows upwards through the filter in bag 5, then passes through the cloth in the filtering bag 5 and into the bag house building 1. Particles contained in the uncleaned gas are retained on the inside of the filtering bag 5. A reverse-air suction fan 17 is connected to the bottom hoppers 8,9,10 via pipes 18,19,20. The pipes 18,10,20 are equipped with valves 21,22,23 for opening and closing the pipes 18,19,20. The outlet end of the suction fan 17 is connected to the pipe for uncleaned gas. The valves 21 and 23 are in the closed position and the valve 2 2 is in open position. This means that chamber 3 is being cleaned. During the cleaning, air is sucked from the outside of the filtering bag 6, through the bottom hopper 9 and via the suction fan 17 into the pipe for uncleaned gas. Solid particles retained on the inside of the filtering bag 6 will fall down into the bottom hopper 9 during the reverse-air cleaning and are removed therefore through valves or chain conveyers in a conventional way. In accordance with the present invention, pressure transmitters 24,25,26 are arranged in each chamber 2,3,4 for measuring the pressure during the cleaning of the chambers. The pressure measured during the cleaning of each chamber is registered in a control unit 27, where the measured pressure is compared to a preset value for the pressure for each chamber and where the control unit 27, based on a comparison between measured pressure and the preset value for reverse-air pressure, gives a signal to the suction fan 17 to increase or decrease the amount of air next time this chamber is to be cleaned. Figure 2 shows a second embodiment of the method according to the present invention. Figure 2 shows a vertical section through a bag house filter having three chambers. Parts in Figure 2 which are identical to parts in Figure 1 have the same reference numerals. The bag house filter shown on Figure 2 is identical to the bag house filter shown on Figure 1, except that the reverse-air pressure in each chamber 2,3,4 is measured by means of a common pressure transmitter 30 which is connected to the bottom hoppers 8,9,10 by means of pipes 31,32,33. The pipes 31,32,33 are equipped with valves 34,35,36 for opening and closing the pipes 31,32,33. In Figure 2 the chamber 3 is bei ng cleaned. The pressure in the bottom hopper 9 is measured as the valve 35 is in open position and the valves 34,36 are in closed position. In the same way as described in connection with the embodiment shown in Figure 1, the measured pressure is registered in the control unit 2 7 where the measured pressure is compared to a preset value of the reverse-air pressure and where the control unit unit gives a signal to the auction fam 17 to increase or decrease the amount of air the next time the chamber is to be cleaned. We Claim: 1. A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, in which bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned and in which each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber, the method comprising: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and; if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to the preset value. 2. A method as claimed in Claim 1, in which the pressure in each of the chambers during the reverse-air cleaning is measured by a pressure transmitter arranged in each chamber. 3. A method as claimed in Claim 1, in which the pressure in each of the chambers during the reverse-air cleaning is measured by means of one common pressure transmitter which is connected to all of the chambers by means of pipes and where one chamber at a time can be connected to the common pressure transmitter by opening and closing valves in the pipps. 4. A method as claimed in any of Claims 1 to 3, in which the preset values for the reverse-air pressure are the same for all chambers. 5. A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, substantially as herein described with reference to the accompany ing drawings -

Full Text

Method for regulating reverse-air in bag filters
The present invention relates to a method for regulating reverse-air pressure in bag filters.
The term "bag filters" as used herein includes all types of filters where the gas to be cleaned of solid particles passes through a filtering cloth. In these kinds of filters, the filter cloth is usually in the form of cylinder-shaped bags. The uncleaned gas is passed through the cloth in the filtering bags either by passing uncleaned gas into the bags and out through the filtering cloth whereby solid particles are retained on the inside of the filtering cloth, or, alternatively, by passing uncleaned gas through the filtering cloth from the outside of the bags whereby solid particles are retained on the outside of the filtering bags. In this specification, gas filters of the kind where uncleaned gas is passed into the filtering bags will be described, but it should be understood that the comments will also apply to all other types of bag filter.
Bag filters usually comprises a plurality of chambers where each chamber comprises a plurality of normally vertically arranged filtering bags. Uncleaned gas is passed into the bag and passes through the filtering cloth in the walls of the bag, while the solid particles are retained inside the bags. When the filter has been in operation for some time the solid particles must be removed from the bags. This is done by disconnecting the supply of uncleaned gas to the chamber to be cleaned, and the bags in the disconnected chamber are then cleaned by supplying cleaning gas in the opposite direction of the direction of the uncleaned gas. This method is called reverse-air cleaning.
The particulate material contained in the chamber

which is being cleaned will fall into a closed-bottom hopper situated below the chamber and is then transported through valves or the like to a storage silo by means of pneumatic transport or by some other means of transportation such as chain conveyers of other ways of mechanical transportation.
The reverse-air method for cleaning chambers uses a suction fan which is connected to the chamber to be cleaned after the supply of uncleaned gas to this chamber has been disconnected. The duration of running the suction fan for each chamber is relatively short, normally between 10 and 15 seconds. In conventional methods for regulating the pressure provided by the suction fan, the suction fan is set at a fixed value regardless of which of the chambers is to be cleaned. This is effected by keeping the conductor rail of the suction fan in a fixed position or by running the suction fan at a fixed number of revolutions per minute.
Those approaches, however, have a number of drawbacks and disadvantages. There is often a substantial physical distance between the chambers which are located closest to the suction fan and the chambers which are located furthest from the suction fan. As the settings for the suction fan is fixed the pressure provided by the suction fan will vary from chamber to chamber due to the different pressure drops in the pipes from the suction fan to each chamber. Further, new filtering bags will have a lower pressure drop than filtering bags which have been in operation for some time, and this will give a lower cleaning pressure in chambers having new filtering bags t ban in chambers having filtering bags which have been in use for some time. After some time in operation, it may al so be necessary to close some of the bags in one or more chambers due to leakages in the bags and in such cases,

where the number of bags in one or more chambers are fewer than normal, the pressure in these chambers will increase when the suction fan is operated with a fixed regulation. If the pressure in one or more chambers during the reverse -air cleaning becomes too high, there will be an increased risk of damage to the bags, for instance by destroying the connection between the bags and metal rings which are used
r
to hold the bags open during the reverse-air cleaning. The consumption of filtering gas can thus become high and the maintenance costs for the bag house filter will be increased. On the other hand, if the reverse-air pressure becomes too low in one or more of the chambers, the cleaning of the filter bags will not be adequate.
It is therefore an object of the present invention to provide a method which solves the above mentioned problems which exist in bag house filters which use a common suction fan for reverse-air cleaning.
According to the present invention, there is provided a method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, in which bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned and in which each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber, the method comprising: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and, if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to

the preset value.
Preferably, the pressure in each of the chambers during the reverse-air cleaning is measured by a pressure transmitter arranged in each chamber.
Alternatively, the pressure in each of the chambers during the reverse-air cleaning is measured by means of one common pressure transmitter which is connected to all of the chambers by means of pipes and where one chamber at a time can be connected to the common pressure transmitter by opening and closing valves in the pipes.
The preset values for the reverse-air pressure can be set individually for each chamber. It is, however, preferred to use the same preset value for the reverse-air pressure in all of the chambers.
By the method according to the present invention it will always be possible to obtain a substantially constant reverse-air pressure in each chamber corresponding to the preset pressure value. Even if one or more filtering bags in one chamber have to be closed, the reverse-air pressure in this chamber will not increase, but will be kept at the preset value. It is thus possible to avoid the reverse-air pressure in a chamber becoming so high that the remaining filtering bags are damaged or destroyed.
The invention also extends to apparatus suitable for carrying out the method of the invention.
The invention may be carried into practice in various ways and some embodiments will now be described by way of example, with reference to the accompanying drawings, in which:-
Figure 1 shows a bag house filter where the reverse-air pressure is regulated according to a first embodiment of the method of the present invention; and
Figure 2 shows a bag house filter where the reverse-air pressure is regulated according to a second embodiment

of the method of the present invention.
Figure 1 shows a vertical section through a bag house filter comprising three chambers. The filter building is indicated by reference number 1. For simplicity, three chambers 2,3,4 are shown, each containing one filtering bag 5,6,7. Each of the chambers 2,3,4 is equipped with a bottom hopper 8,9,10. The filtering bags 5,6,7 are suspended from the filtering building 1 at their upper ends and their open lower ends are connected to the bottom hoppers 8,9,10. The chamber 4 is shown in a disconnected state for the installment of a new filtering bag 7.
Gas which is to be cleaned is supplied through a main fan 2 8 to the chamber 2,3,4 via pipes 11,12,13 to the bottom hoppers 8,9,10. The pipes 11,12,13 are equipped with valves 14,15,16 for opening and closing the supply of uncleaned gas to the bottom hoppers 8,9,10, The valve 14 is open while the valves 15 and 16 are in the closed position . Uncleaned gas is thus supplied through the pipe 11 to the bottom hopper 28 for the chamber 2 and flows upwards through the filter in bag 5, then passes through the cloth in the filtering bag 5 and into the bag house building 1. Particles contained in the uncleaned gas are retained on the inside of the filtering bag 5.
A reverse-air suction fan 17 is connected to the bottom hoppers 8,9,10 via pipes 18,19,20. The pipes 18,10,20 are equipped with valves 21,22,23 for opening and closing the pipes 18,19,20. The outlet end of the suction fan 17 is connected to the pipe for uncleaned gas. The valves 21 and 23 are in the closed position and the valve 2 2 is in open position. This means that chamber 3 is being cleaned. During the cleaning, air is sucked from the outside of the filtering bag 6, through the bottom hopper 9 and via the suction fan 17 into the pipe for uncleaned gas. Solid particles retained on the inside of

the filtering bag 6 will fall down into the bottom hopper 9 during the reverse-air cleaning and are removed therefore through valves or chain conveyers in a conventional way.
In accordance with the present invention, pressure transmitters 24,25,26 are arranged in each chamber 2,3,4 for measuring the pressure during the cleaning of the chambers. The pressure measured during the cleaning of each chamber is registered in a control unit 27, where the measured pressure is compared to a preset value for the pressure for each chamber and where the control unit 27, based on a comparison between measured pressure and the preset value for reverse-air pressure, gives a signal to the suction fan 17 to increase or decrease the amount of air next time this chamber is to be cleaned.
Figure 2 shows a second embodiment of the method according to the present invention. Figure 2 shows a vertical section through a bag house filter having three chambers. Parts in Figure 2 which are identical to parts in Figure 1 have the same reference numerals. The bag house filter shown on Figure 2 is identical to the bag house filter shown on Figure 1, except that the reverse-air pressure in each chamber 2,3,4 is measured by means of a common pressure transmitter 30 which is connected to the bottom hoppers 8,9,10 by means of pipes 31,32,33. The pipes 31,32,33 are equipped with valves 34,35,36 for opening and closing the pipes 31,32,33. In Figure 2 the chamber 3 is bei ng cleaned. The pressure in the bottom hopper 9 is measured as the valve 35 is in open position and the valves 34,36 are in closed position.
In the same way as described in connection with the embodiment shown in Figure 1, the measured pressure is registered in the control unit 2 7 where the measured pressure is compared to a preset value of the reverse-air

pressure and where the control unit unit gives a signal to the auction fam 17 to increase or decrease the amount of air the next time the chamber is to be cleaned.

We Claim:
1. A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, in which bag house filters comprise a plurality of chambers, and each chamber comprises a plurality of filtering bags, in which a suction fan is connected to the chamber which is to be cleaned and in which each chamber is equipped with means for measuring the air pressure during the cleaning of the chamber, the method comprising: measuring the pressure in the chambers and registering the measured pressure when the chambers are cleaned; comparing the pressure measured during the cleaning of a chamber with a preset value from the pressure in that chamber; and; if the measured pressure deviates from the preset value for that chamber, changing the settings for the suction fan for that chamber during the next reverse-air cleaning of that chamber, in order to obtain a pressure which is closer to or equal to the preset value.
2. A method as claimed in Claim 1, in which the pressure in each of the chambers during the reverse-air cleaning is measured by a pressure transmitter arranged in each chamber.
3. A method as claimed in Claim 1, in which the pressure in each of the chambers during the reverse-air cleaning is measured by means of one common pressure transmitter which is connected to all of the chambers by means of pipes and where one chamber at a time can be connected to the common pressure transmitter by opening and closing valves in the pipps.
4. A method as claimed in any of Claims 1 to 3, in which

the preset values for the reverse-air pressure are the same for all chambers.
5. A method for regulating the pressure in bag house filters which are cleaned by the reverse-air method, substantially as herein described with reference to the accompany ing drawings -

Documents:

2715-mas-1998-abstract.pdf

2715-mas-1998-claims filed.pdf

2715-mas-1998-claims granted.pdf

2715-mas-1998-correspondnece-others.pdf

2715-mas-1998-correspondnece-po.pdf

2715-mas-1998-description(complete)filed.pdf

2715-mas-1998-description(complete)granted.pdf

2715-mas-1998-drawings.pdf

2715-mas-1998-form 1.pdf

2715-mas-1998-form 19.pdf

2715-mas-1998-form 26.pdf

2715-mas-1998-form 3.pdf

2715-mas-1998-form 4.pdf

2715-mas-1998-form 5.pdf

2715-mas-1998-other documents.pdf

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Patent Number

212458

Indian Patent Application Number

2715/MAS/1998

PG Journal Number

07/2008

Publication Date

15-Feb-2008

Grant Date

03-Dec-2007

Date of Filing

02-Dec-1998

Name of Patentee

ELKEM ASA

Applicant Address

HOFFSVEIEN 65B, 0377 OSLO,

Inventors:

#	Inventor's Name	Inventor's Address
1	SVEIN FILTLESTAD	SOMMERRROGATA 10, 4630 KRISTIANSAND,

PCT International Classification Number

B 01 D 29/66

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19975645	1997-12-04	Norway