METHOD FOR CLEANING THE FILTER BAGS OF A BAG-FILTER INSTALLATION

Abstract: In a method for cleaning filter bags (9) in a bag-filter installation (1), in which the filter bags (9) are arranged in a plurality of rows and the dust content of the filtered gas is monitored by means of a monitoring unit (8), cleaning is carried out by blowing a pressure medium into the filter bags. The pressure medium is blown into the filter bags (9) row by row, the filter bags (9) in one and the same row being cleaned simultaneously, and the rows being successively cleaned at a time interval exceeding the time it takes for conveying the filtered gas from the cleaned row to the monitoring unit (8).

Description: METHOD FOR CLEANING THE FILTER BAGS OF A BAG-FILTER INSTALLATION This invention relates to a method for cleaning fil- ter bags in a dust-separating bag-filter installation for gas filtration, the filter bags being arranged in a plu¬ rality of rows of juxtaposed filter bags, and the dust content of the filtered gas being monitored by means of a monitoring unit, in which method cleaning is carried out by blowing a pressure medium into the filter bags. Large-size filter installations of this type usually comprise a plurality of chambers arranged in parallel and each housing a plurality of rows of filter bags. A gas from which dust is to be separated, is conducted through the chambers so as to be filtered and cleaned. The cleaned gas is drawn off from the filter installation through an outlet conduit which is common to all the chambers and in which a monitoring unit is provided. Usually, the monitoring unit is an opacimeter measuring the opacity of the outgoing cleaned gas in order to monitor its dust content. In one prior-art bag-filter installation, the filter bags are cleaned by blowing a pressure medium in the form of compressed-air pulses into the filter bags in a direction opposite to that of the gas when in the process of being filtered. The rows of filter bags are successive¬ ly cleaned, a compressed-air pulse being supplied simulta¬ neously to all the filter bags in a row in each chamber, thereby to release dust adhering to ' and within the walls of the filter bags during operation of the installation. For each compressed-air pulse, the monitoring unit records a minor increase in the dust content of the cleaned gas. Should one or more of the filter bags be damaged, the filtering capacity of the installation is impaired. When a compressed-air pulse is supplied to a row containing one or more defective filtered bags, the dust content of the filtered gas increases considerably, which is recorded by the monitoring unit. When this happens, the operator will know that the filter installation holds one or more defec¬ tive filter bags, but he will not know in which chamber the defective filter bag or bags are to be found. To obtain this information, the operator has to put one cham¬ ber at a time out of operation and infer, from the reac¬ tion of the monitoring unit, which chamber holds one or more defective filter bags. When the operator has estab¬ lished, or believes that he has established, which chamber holds one or more defective filter bags, he puts this chamber out of operation and opens it from the clean-gas side in order to locate the defective bag or bags causing the increase in dust emission. It goes without saying that this is a roundabout and time-consuming procedure. The object of the present inven¬ tion is, therefore, to provide a method for cleaning the filter bags of a bag-filter installation by means of a pressure medium, enabling simple and expedient identifi¬ cation of the row containing one or more defective filter bags. According to the invention, this object is achieved by a method which is of the type stated by way of intro¬ duction and which is characterised by blowing the pressure medium into the filter bags row by row, the filter bags in one and the same row being cleaned simultaneously, and the rows being successively cleaned at a time interval exceeding the time it takes for conveying the filtered gas from the cleaned row to the monitoring unit. Since the pressure medium is only blown into the filter bags in one row at a time (and not in one row in each chamber at a time) and since the time elapsing between the cleaning of successive rows is sufficient, for conveying the filtered gas from the last-cleaned row to the monitoring unit before the next row is cleaned, an emission peak recorded by the monitoring unit and exceed¬ ing by far a predetermined reference value corresponding to the emission peak obtained when cleaning a filter-bag row free from defects, can be linked to the row causing the emission peak and thus containing one or more defec¬ tive filter bags. As a result, the row holding one or more defective filter bags can be easily and expediently iden- tified. Then, the defective filter bag or bags are located and replaced or put out of operation by being plugged up. The invention will now be described in more detail with reference to the accompanying drawing, in which Fig. 1 is a schematic plan view showing a bag-filter installation in which the inventive method can be imple¬ mented; and Fig. 2 is a partial side view showing a unit used in the installation of Fig. 1 for supplying compressed-air pulses. The bag-filter installation 1 shown in Fig. 1 con¬ sists of four identical chambers 2a, 2b, 2c and 2d which are arranged in parallel and through which a gas polluted by dust is conducted in order to be filtered. The polluted gas is introduced into the chambers 2a, 2b, 2c and 2d through inlet conduits 3a, 3b, 3c and 3d, respectively. Via shut-off registers 4a, 4b, 4c and 4d, the inlet con¬ duits 3a, 3b, 3c and 3d, respectively, are connected to a common main conduit 5 for polluted gas. The filtered gas is drawn off from the chambers 2a, 2b, 2c and 2d through outlet conduits 6a, 6b, 6c and 6d, respectively. The out¬ let conduits 6a, 6b, 6c and 6d are connected to a common main conduit 7 for filtered gas. An opacimeter 8 continuously monitoring the dust con¬ tent of the filtered gas is arranged in the main conduit 7. Each chamber 2a-2d contains a plurality of vertical filter bags 9 arranged in a plurality of rows of juxta¬ posed filter bags. The filter bags 9 are so arranged that the "bag openings" face upwards. In the embodiment shown in Fig. 1, each chamber 2a-2d holds seven parallel rows each comprising five filter bags 9. It should here be observed that the chambers in modern filter installations contain a few hundred filter bags and that the embodiment shown in Fig. 1 comprising a very restricted number of filter bags merely is intended as an illustration of the inventive idea. Furthermore, each chamber 2a-2d has a unit provided above the filter bags 9 in each row for supplying com¬ pressed-air pulses to the filter bags. Each such unit is made up of a tube 10 extending in parallel with the respective rows of filter bags 9 and having a plurality of tubular connections 11 (five in the illustrated embo¬ diment) which project downwards and each are located straight above the "bag opening" of a filter bag 9. Each tube 10 is closed at one end and connected, at. the other end and via a normally closed valve device 13, to a com- pressed-air chamber 12 common to all the tubes in one and the same chamber 2a-2d. The valve device 13 may be of the type described in W091/19922. The valve device 13 can be temporarily opened in order to establish communication between the compressed-air chamber 12 and the tube 10, thus supplying, via the tube and its tubular connections 11, a compressed-air pulse to each of the filter bags 9 in the row below the tube. Such a compressed-air pulse is then used to clean the filter bags 9 in known manner by releasing dust adhering to and within the walls of the filter bags 9 during operation of the installation. It will be appreciated that, in Fig. 1, the chambers 2b and 2d are shown with roofs, the chamber 2c is shown without any roof, and the chamber 2a is shown without any roof or any units for supplying compresssed-air pulses. When the filter bags 9 of the bag-filter installation are to be cleaned, the tubes 10 are connected one at a time and in a predetermined order to the respective com¬ pressed-air chambers 12 via the respective valve devices 13 in order to supply a compressed-air pulse to each of the filter bags 9 in the row below the tube at issue. The valve devices 13 are controlled in such a manner that the time elapsing between the cleaning of two successive rows in the predetermined order is sufficient for conveying the filtered gas from the last-cleaned row to the monitoring unit 8 before the subsequent row is cleaned. When the monitoring unit 8 records an increase in the dust content of the filtered gas exceeding a predeter¬ mined reference value, which is much higher than the value obtained when cleaning a row of filter bags free from defects, the row causing this increase in the dust con¬ tent, and thus containing one or more defective filter bags, can be identified with certainty. Thus, the operator will know at once in which chamber and in which row the defective filter bag or bags are to be found.

Claims: CLAIM A method for cleaning filter bags ( 9 ) in a dust- separating bag-filter installation (1) for gas filtra¬ tion, the filter bags being arranged in a plurality of rows of juxtaposed filter bags, and the dust content of the filtered gas being monitored by means of a monitor¬ ing unit (8), in which method cleaning is carried out by blowing a pressure medium into the filter bags, c h a r a c t e r i s e d by blowing the pressure medium into the filter bags (9) row by row, the filter bags (9) in one and the same row being cleaned simultaneously, and the rows being successively cleaned at a time interval exceeding the time it takes for conveying the filtered gas from the cleaned row to the monitoring unit ( 8 ) .

Inventors: LINDAU LEIF, WIKTORSSON ANDERS, LINDAU, LEIF, WIKTORSSON, ANDERS
Applicants: FLAEKT AB, LINDAU LEIF, WIKTORSSON ANDERS, ABB FLAEKT AB, LINDAU, LEIF, WIKTORSSON, ANDERS
Application year: 1993
Main classification: B01D46
IPC codes: B01D46