Facility for cleaning filters and method for operating a facility for cleaning filters

0001The invention relates to a system for cleaning filters, in particular from textile filter materials, comprising a compressor, by means of which a cleaning gas is compressible up to a cleaning pressure and can be directed into a pressure vessel, a cleaning tube being connected to the pressure vessel, Cleaning gas can be blown into a filter via nozzle openings, and a method for operating a system for cleaning filters.

0002The <patcit id="pcit0001" dnum="DE3939645"><text>DE 39 39 645</text></patcit> Discloses a dedusting system with tubular filter elements through which a raw gas flows, so that particles to be filtered can settle on the filter. In order to clean the filter elements, a backflushing purge gas is used at certain intervals, which flows through the filter from the purge side to the raw gas side, so that the dust is released from the outer side of the filter elements.

0003A filter element for such a cleaning installation is, for example, shown in FIG <patcit id="pcit0002" dnum="DE9103538"><text>DE 91 03 538</text></patcit> described.

0004In the case of such dedusting systems, the cleaning is carried out with a cleaning gas compressed to, for example, 6 bar, which is then blown in counter-rotating manner into the tubular filter elements. The compressed air surge required for cleaning is produced by the fact that the jet jet emerging from a nozzle with near sound velocity entrains secondary air from its environment. However, the generation of a high pressure and the throttling losses of the purge gas at the valves and the nozzles ensure a relatively high energy consumption. It must be taken into account that gases can be released in an orifice of a nozzle or a valve only up to the critical pressure, the Laval pressure, no matter how low the back pressure is lowered behind the mouth.

0005The <patcit id="pcit0003" dnum="US4465497A"><text>U.S. 4,465,497</text></patcit> Discloses a pneumatic system for cleaning filters, in which a cleaning gas can be blown onto a filter via a diaphragm valve. A plurality of diaphragm valves are fed via a common pressure chamber. The pressure chamber has, at the beginning of the cleaning process, according to an indication from the<patcit id="pcit0004" dnum="US4690166A"><text>U.S. 4,690,166</text></patcit>, Which is based on the same inventor, has a pressure of 5.5 bar (80psi). In the<patcit id="pcit0005" dnum="US4690166A"><text>U.S. 4,690,166</text></patcit> During the cleaning process, the pressure in the pressure chamber is reduced to approximately ambient pressure.

0006In the <patcit id="pcit0006" dnum="US6270732B"><text>US 6,270,732</text></patcit> Is disclosed to a filter system which will operate under reduced pressure. The purified gas is then discharged to the environment via a pump.

0007It is, therefore, an object of the present invention to provide a system for cleaning filters which allows for effective cleaning of the filters with low energy consumption.

0008This object is achieved by a system for cleaning filters with the features of claim 1 and a method with the features of claim 7.

0009According to the invention, for closing the cleaning tube connected to the pressure vessel, there is provided a diaphragm valve which operates in the mainly subcritical range in relation to the cleaning pressure of the compressor, via which the blowing of cleaning gas into the filter is controlled. As a result, throttling losses due to excessively small flow cross sections or too great pressure differences can be avoided. The diaphragm valve therefore operates mainly in the subcritical range and the flow cross sections are dimensioned such that only small throttle losses occur. In this case, a supercritical state should be permitted by a partially opened valve body. Only when the valve is fully open do subcritical conditions occur. As a result, the outlet pressure of the cleaning gas can also be lowered, Which reduces the energy expenditure for the compression of the cleaning gas. This makes it possible to generate the pressure and quantity of the cleaning gas as required. This ensures that a pressure of the cleaning gas is generated only to the extent necessary for the next cleaning process. In addition, short response times of the diaphragm valve can prevent further losses of compressed cleaning gas, so that the plant can be operated particularly efficiently.

0010Preferably, the pressure in the pressure vessel is controllable via a control depending on the required cleaning pressure on the cleaning tube.

0011The compressor can thereby supply the pressure vessel with compressed cleaning gas directly after each cleaning process so that only the counterpressure present in the pressure vessel acts on the compressor.

0012Furthermore, the degree of soiling of the filter can be detected via a pressure difference measurement, the length of the cleaning intervals being controllable as a function of the degree of contamination. As a result, the system for cleaning filters can be controlled in accordance with the requirements, ie the cleaning intervals can be lengthened with a smaller contamination of the filters and, in the case of heavier soiling, can also be shortened. Depending on the necessary length of the cleaning intervals, a controller can control the performance of the compressor for compressing the purge gas in the pressure vessel.

0013Preferably, the cleaning tube has a substantially constant flow cross-section. The cleaning tube can be bent or can also be tubular, whereby throttling losses are reduced or avoided by the constant flow cross-section.

0014For rapid control of the diaphragm valve, this is preferably connected to a ventilatable line on the side remote from the pressure vessel. Furthermore, the diaphragm valve can be connected, on the side remote from the pressure vessel, to a pressurized auxiliary reservoir via a line so that the diaphragm valve can be selectively vented or closed quickly. For the effective switching of the diaphragm valve, a 3-2-way valve is preferably provided, which is connected to a first connection for venting with a container to ambient pressure and is connected with a second connection to the additional reservoir for pressurizing the membrane valve with compressed cleaning gas.

0015According to the invention, a cleaning pressure between 2 bar to 4 bar, in particular between 2 bar and 3.5 bar, is provided in the pressure vessel. As a result, the system can be operated with significantly lower pressure in the pressure vessel than with conventional cleaning systems. This reduces the energy consumption of the compressor to supply the pressure vessel. The pressure in the pressure vessel during a cleaning process may drop by up to 2.5 bar, which corresponds to the pressure amplitude in the pressure vessel, and then be recharged to the original cleaning pressure by the compressor.

0016In order to reduce compressed air consumption, it is also advantageous if the opening time of the diaphragm valve is relatively short, as a result of which losses of cleaning gas are avoided, which arise as long as the pressure in the cleaning tube has not yet reached the level required for cleaning.

0017The invention is explained in more detail below with reference to an exemplary embodiment with reference to the attached drawings. Show it:<dl id="dl0001"><dt>FIG</dt><dd>4 is a schematic view of a system according to the invention for cleaning filters;</dd><dt>FIG</dt><dd>A pneumatic circuit diagram for operating the <figref idrefs="f0001">FIG</figref>;</dd><dt>FIG</dt><dd>A pressure-time diagram over a cleaning cycle;</dd><dt>FIG</dt><dd>A pressure-time diagram over a purge cycle with a slowly closing diaphragm valve, and FIG</dd><dt>FIG</dt><dd>A pressure-time diagram of the pressure vessel.</dd></dl>

0018A system 1 for cleaning a filter is arranged on a filter container 2, which has an inlet 3 for raw gas, which flows into a filter chamber 4. A plurality of tubular filter elements 5 are arranged in the filter chamber 4, the raw gas being passed through, so that the filtered crude gas can then leave the filter chamber 4 as a pure gas through an outlet 6. The individual filter elements 5 are suspended from an intermediate wall 7 in the filter chamber 4 and are mounted on a tubular holder 8.

0019In order to clean the individual filter elements 5 at certain intervals, a cleaning tube 9 is arranged above the filter elements 5, on which nozzles 10 directed toward an upper opening of the filter elements 5 are provided. By means of the nozzles 10, cleaning gas can be blown into the tubular filter elements 5, so that dust particles deposited on the filter elements 5 due to the short-term change in the direction of flow drop down into a funnel 11 at the end of which a rotary valve sluice 12 is arranged.

0020Other arrangements of pressure vessels, cleaning pipes, nozzles, as well as filter elements are conceivable.

0021The cleaning pipe 9 for blowing in a cleaning gas is fed via a pressure vessel 13, which is supplied with a pressurized cleaning gas via a compressor 14. In order to control a cleaning process, a control unit 15 is provided which, via lines 16 and 17, detects the pressure in the pressure vessel 13 and in the filter chamber 4 on the raw gas side and the pure-body side. The controller 15 can also detect further parameters via sensors.

0022In <figref idrefs="f0002">FIG</figref> A circuit diagram of the system according to the invention for cleaning the filter elements 5 is shown, the cleaning tube 9 being shown only in one end section. The cleaning tube 9 can be closed on the face side via a diaphragm valve 20. The diaphragm valve 20 comprises a valve body 21, which can be pressed against the cleaning tube 9 on the end side in order to close it. The valve body 21 is annularly surrounded by an elastic diaphragm 23 which is arranged on the pressure container 13 in the region of a recess 22. At the outer circumference, the membrane 23 is fixed to the pressure vessel 13 via a cover 30. The cover 30 comprises a connection 31 which connects a control chamber, which is formed between the diaphragm 23 and the cover 30, via a line 32 to a 3-2-way valve 33. The 3-2-way valve can connect the line 32 to a vent line 35 so that the pressure in the control chamber drops and the diaphragm valve 20 with the valve body 21 lifts off from the end of the cleaning tube 9. This opens the opening of the cleaning tube 9 toward the pressure chamber 13, and a cleaning gas arranged in the pressure chamber 13 can flow into the cleaning tube 9.

0023The 3-2-way valve 33 is connected with a further line 36 to an additional accumulator 37, which is fed via a line 38 from the compressor 14. If the connection of the line 32 to the vent line 35 is now closed via the filter control 15, which is connected to a control line 34 to the 3-2-way valve 33, the connection from the additional storage 37 opens via the line 36 and 32 to the control chamber At port 31. The diaphragm valve 20 is moved back into the closed position by raising the pressure in the control chamber, and the valve body 21 is pressed against the end of the cleaning pipe 9. *** "

0024The compressor 14 is connected to the pressure vessel 13 via a line 39 and can supply both the pressure vessel 13 and the additional reservoir 37 with a pressurized gas. A valve 40 or 41 for shutting off the line is arranged in the line 38 to the additional reservoir 37 as well as in the line 39.

0025The operation of the system for cleaning the filter elements 5 can be carried out in such a way that a largely constant cleaning pressure of between 2.5 bar and 3.5 bar is generated in the pressure vessel 13 as well as in the additional reservoir 37, for example about 2.8 bar. If a cleaning operation is now initiated, a cleaning gas flows out of the control space between the cover 30 and the diaphragm 20 via the vent line 35 to open the diaphragm valve 20. The cleaning gas then flows out of the pressure container 13 into the cleaning tube 9, the flow cross sections and the pressure conditions being such that the flow takes place in the subcritical range.

0026Subsequently, cleaning gas is blown into the filter elements 5 from the pressure container 13 via the cleaning tube 9 and the nozzles 10. Pre-critical flow conditions also prevail at the nozzles 10, which can be influenced indirectly via the cleaning pressure in the pressure vessel 13 or the flow cross sections at the nozzles 10.

0027The diaphragm valve 20 can now be closed again by closing the 3-2-way valve 33, the line 32 and the control chamber adjacent to the diaphragm valve 20 then being pressurized via the additional reservoir 37. The opening and closing of the diaphragm valve 20 can take place in a very short period of time, for example less than 0.2 s, in particular less than 0.15 s, so that the flow losses are kept low.

0028In <figref idrefs="f0002">FIG</figref> The pneumatic circuit diagram of the system is only shown schematically. The 3-2-way valve 33 can be arranged directly on the cover 30 to minimize the volume of the line 32 and to ensure a fast response time of the diaphragm valve 20. [ Furthermore, further valves and control lines can be provided in order to ensure the function of the system. The controller 15 can detect the pressure in all the lines.

0029In <figref idrefs="f0003">FIG</figref> A pressure-time diagram of a cleaning operation is shown. After a timeout of 0.05 s, the diaphragm valve is opened so that the pressure in the cleaning tube 9 rises briefly from 0 bar (ambient pressure) to 2 bar. By opening the diaphragm valve 20, the cleaning gas flows out of the pressure vessel 13 into the cleaning tube 9, so that the pressure in the pressure vessel 13 decreases, starting from 2.8 bar to about 2 bar. The pressure amplitude during a cleaning operation can be in a range between 0.5 bar and 2.5 bar. Then, the diaphragm valve 20 is closed abruptly, and the initial pressure of 0 bar (ambient pressure) is established in the cleaning tube 9. The pressure vessel 13 must now be filled again from 2 bar to 2.8 bar via the compressor 14.

0030Since the cleaning gas must first be produced only against the residual pressure in the pressure vessel 13 after cleaning and until the cleaning pressure has been reached it is only generated against the pressure currently present in the pressure vessel 13, which saves considerable electrical energy. The energy consumption of the compressor 13 is strongly dependent on the counterpressure or pressure ratio. The necessary cleaning pressure is varied by the filter controller and adapted to the operating conditions of the filter system.

0031<figref idrefs="f0004">FIG</figref> 10 shows a pressure-time diagram over a cleaning cycle with an overall long opening time. Before the solenoid valve is closed, the pressure in the cleaning tube has already fallen below the level necessary for its effectiveness. The pressure amplitude in the cleaning tube 9 remains as high as 2.4 bar at the diaphragm valve<figref idrefs="f0003">FIG</figref>, However, the pressure drop in the pressure vessel 13 is substantial at around 2 bar. When looking at the closing behavior, one sees a flat falling curve, which in turn represents a high loss due to ineffective cleaning gas. In addition, it can be seen that due to the low flow losses on the diaphragm valve, the pressure in the compressed-air accumulator 13 and in the cleaning tube 9 is almost identical when the diaphragm valve is closed. By analogue measurement of the pressure in the pressure vessel and the processing of the pressure in the control it is possible to close the diaphragm valve in time and to prevent the loss of cleaning gas.

0032In <figref idrefs="f0005">FIG</figref> An example of a pressure-time diagram of the pressure vessel is shown at the beginning of several cleaning cycles. The production of the compressed air during the first filling process takes approx. 295 s. After cleaning, the pre-pressure in the compressed-air accumulator drops by approx. 0.85 bar to 1.95 bar. The production of the pressure consumed per cleaning takes about 75 s. This is the minimum time between two cleaning operations.

0033The filter system can detect the degree of contamination or clogging on the filter elements 5 by means of differential pressure measurement. Depending on the degree of clogging, the controller can determine the length of the pause time between the individual cleaning operations, for example, by controlling the power of the compressor. The minimum time between two cleaning operations is therefore equal to the time that the compressor 13 needs to increase the pressure of the cleaning gas up to the desired cleaning pressure. The compressor 13 can then be operated at a constant speed for a certain degree of soiling. Furthermore, the maximum pressure in the compressed-air accumulator can also be controlled via the control.