Tubular filter element and method for cleaning it

Abstract

Tubular filter element (1) comprising a) a clean-gas-side cylindrical internal volume with at least one clean-gas-side outlet, b) a lateral surface surrounding the internal volume designed as filter surfaces (9), c) Cleaning agent (7, 8, 10) for the outer surface, wherein the cleaning agent has a tubular cleaning lance (7) fixedly arranged coaxially in the cylindrical inner volume with several outlet openings (15) distributed axially over the axial extent of the filter surfaces into the inner volume, d) Closure devices (11) which have at least one outlet on the clean gas side and e) at least one cleaning valve (10) for a purge gas inlet in the tubular cleaning lance, characterized in that f) the closure means (11) shall comprise at least one hydraulic or pneumatic flow valve (17) without moving parts.

Description

[0001] The present invention relates to a tubular filter element according to the first claim and to a method for cleaning the tubular filter element exposed to a flow of raw gas according to claim 10.

[0002] The aforementioned tubular filter elements are known in particular in the form of cartridge filters or filter candles, in which the outer surface is formed by rigid, i.e., stiff and non-flexible filter surfaces, and preferably one end is open. The diameter-to-length ratio (L / D ratio) is typically greater than 25. They serve for dust separation, especially at high gas temperatures, for example in combustion processes (hot gas filtration, preferably above 500°C), and have diameters exceeding 100 mm with lengths up to 6 m. It is understood, however, that the method according to the invention is in principle applicable to all tubular or hollow cylindrical filter elements. For particle filtration at high temperatures, ceramic filter elements are used almost exclusively, with the exception of special metallic materials.

[0003] These tubular filter elements are typically exposed to a raw gas flow (i.e., a dust-laden gas) on the raw gas side. The raw gas penetrates the filter surfaces and enters the clean gas-side interior of the tubular filter elements, where it is discharged axially, preferably through only one open end of the filter element. Particle fractions from the raw gas typically separate onto the filter surfaces, leading to a gradual clogging of the filter elements with a so-called filter cake—a layer of compacted, often adhering, particle fractions—as the filtration time increases.

[0004] In the filtration of dust-laden gases, i.e., free-flowing and / or extremely fine dusts or particles, the particles already separated on the filter surfaces on the raw gas side are usually detached by cleaning through periodically recurring counter-currents or counter-current pulses and sediment into a dust collection chamber; however, some are also resuspended in the gas, i.e., finely distributed again in the raw gas space of the filter system.

[0005] DE 199 17 165 A1 describes, for example, a method for cleaning filter cartridges exposed to an external flow of raw gas. Each cartridge has a safety filter located downstream of it in the clean gas chamber, arranged in the clean gas chamber. This cleaning is achieved by backflushing the filter cartridge from the clean gas side. The purge gas flow required for backflushing, originating in the clean gas chamber behind the filter cartridge, is guided through the safety filter into or through the filter cartridge, while the safety filter is shut off from the exhaust air side. This shut-off is accomplished by a fluid-dynamic, pneumatic switch without moving parts. The flow path of this switch is alternately opened by the lower process pressure from the clean gas chamber and closed by the higher backflushing pressure. As the L / D ratio increases, the amount of gas that can effectively be introduced through the inlet cross-section decreases, so that the purge gas flow rate relative to the filter area steadily declines.

[0006] However, the effectiveness of cleaning decreases not only with the lateral extent of the filter surfaces, but also with an increasing length-to-diameter ratio of the tubular filter elements. This results in unevenly distributed cleaning gas flows and impulses across the filter surface areas, leading to locally insufficient cleaning of the dust adhering to the filter surfaces.

[0007] In conventional systems, the cleaning intensity is further limited by the speed of sound, which acts as the upper limit for the flow through the filter channels. Since the overpressure in filter cartridges, necessary for cleaning, is derived from the kinetic energy of the gas, it remains limited. Operational performance deteriorates further if the filters exhibit high resistance, for example, due to ingress of fine dust, high dust concentrations, or high filtration velocities. Clogged filters, especially those with a higher L / D ratio, often cannot be adequately cleared by blowing if the dust is highly adhesive.

[0008] DE 36 20 489 A1 proposes a method and apparatus for cleaning bag- and tube-shaped filter elements, in which a back pressure is briefly built up on the clean gas side of each filter element by injecting a cleaning gas via a blow lance, which removes the raw gas-side deposits on the filter element by means of a counterflow. Another relevant prior art is DE 10 2016 212 676 A1.

[0009] Based on this, one object of the invention is to design the aforementioned method and the tubular filter element in such a way that reliable cleaning is ensured even with larger L / D ratios.

[0010] The problem is solved by a tubular filter element having the features of the first claim and by a method for cleaning the tubular filter element having the features of claim 10. Related dependent claims describe advantageous embodiments.

[0011] The basis for solving this problem is a conventional tubular filter element comprising a clean-gas-side cylindrical inner volume with at least one clean-gas-side outlet, a shell surface surrounding the inner volume designed as a filter surface, and cleaning agents for the shell surface. The method for cleaning a tubular filter element of the aforementioned type, subjected to a raw gas flow, with cleaning agents includes backflushing the filter element with a purge gas stream or pulse from the clean-gas side.

[0012] Building upon the aforementioned prior art, a device and a method are proposed in which the supply of purge gas is modified and, at the same time, outflow from the filter element via the inlet opening is effectively reduced. This significantly increases the cleaning efficiency, particularly of large-volume rigid, tubular filter elements. The key measures relate in particular to: - the purge gas supply to the filter elements into the filter element, so that a rapid pressure build-up with a sufficiently high purge gas volume is achievable, especially in very long, large-caliber filter elements (larger L / D ratio), as well as - the sealing devices that hydraulically separate the filter cartridge from the clean gas chamber for the cleaning period, thus preventing or minimizing a loss flow.

[0013] A key feature of the filter element is the cleaning agent, which comprises a tubular cleaning lance arranged coaxially within the cylindrical inner volume, with several outlet openings distributed axially across the filter surfaces. It also includes at least one cleaning valve for supplying purge gas to the tubular cleaning lance and a sealing device for the at least one clean gas-side outlet.

[0014] Distributed along the axial extent of the filter surfaces, the design of the tubular cleaning lance means that the outlet openings are arranged axially across the entire (tubular) surface, i.e., also radially across the circumference. This is the only way for the outlet openings to cover the entire filter surface along its entire axial extent, preferably simultaneously. For this purpose, the cleaning lance is fixed, i.e., rigidly and permanently installed in the filter cartridge, and therefore neither rotatable nor pivotable, and preferably not axially displaceable either. In a preferred embodiment, the cleaning lance also has no moving parts, i.e., none even within the tubular surface.

[0015] Preferably, the filter cartridge and the cleaning lance are arranged coaxially. Between the filter surfaces, i.e., the inner surfaces of the filter cartridge and the outer surface of the cleaning lance, a free internal volume of the filter cartridge extends, with an annular cross-section that preferably remains constant along its axial extent. This cross-section must be dimensioned with respect to flow resistance such that, during filtration, the clean gas flow from the inner filter surfaces passes axially past the sealing elements in the region of the filter cartridge head into a clean gas chamber. This requires low flow resistance, particularly in the axial direction, which is facilitated by an increasing distance between the inner surface of the filter cartridge and the outer surface of the cleaning lance, or by an increasing cross-sectional area.

[0016] On the other hand, a small internal volume of the candle promotes a rapid pressure build-up for cleaning the filter surfaces.

[0017] Preferably, the aforementioned distance is larger than the diameter of the cleaning lance or the cross-section of the free internal volume of the filter candle.

[0018] On the other hand, the aforementioned free internal volume of the filter cartridge serves as a gas buffer during cleaning of the filter surfaces. A purge gas flows from the outlet openings of the cleaning lance into the internal volume of the filter cartridge and distributes itself evenly across the filter surfaces. The flow resistance of the filter surfaces generates a back pressure within the internal volume of the filter cartridge, thus advantageously resulting in a preferably uniform pressure build-up across the entire filter surface. Sealed closures in the area of ​​the filter cartridge head prevent or reduce the outflow of the purge gas towards the cleanroom. The aim is to achieve a uniform cleaning efficiency across the entire axial extent of the filter cartridges and, consequently, a uniform back pressure within the internal volume of the filter cartridge.It should be noted that the static pressure of the cleaning gas flow in the cleaning lance, and thus the outflow velocity from the outlet openings along the lance, increases. To ensure a uniform pressure build-up across the axial extent of the filter cartridge's internal volume, it is proposed that the cleaning lance be designed not cylindrically, but conically tapered in the flow direction, or alternatively, that the cross-sections of the outlet openings be continuously reduced in the flow direction.

[0019] The closure means of a first embodiment preferably comprise at least one check valve, i.e., a closure means that is advantageously operable and switchable solely by the prevailing flow conditions and not actively by an actuator. Preferably, the closure means has two switching positions: a closed position as the first switching position and a flow-through position as the second switching position. The two switching positions are further preferably without an intermediate position, i.e., they can be switched discretely back and forth.

[0020] The closure means of a second embodiment comprise at least one hydraulic or pneumatic flow control valve without moving parts, which in turn reduces the probability of wear and failure. The proposed hydraulic or pneumatic flow control valve preferably consists of porous materials such as foams, metal fibers, fabrics or other fibrous materials, granular ceramics or sintered metals with a continuous pore system with cross-sections of a few hundred micrometers (preferably 50, 100 or 200 micrometers up to 300, 500 or 1000 micrometers), i.e., a material that offers flow resistance to the fluid as it passes through. The flow resistance increases with the volume flow rate, preferably disproportionately, but does not result in either a complete closure or unrestricted flow. In this respect, the two switching positions of this embodiment also differ from those of the first embodiment.The closed position inherently allows a minimal residual flow, while the open position, also inherently, presents a residual resistance to the flow. The two switching positions are preferably not, or only to a limited extent, discretely switchable back and forth, but rather change continuously between the two aforementioned switching positions.

[0021] It is particularly advantageous if, in an embodiment of the second design, the flow in the porous material changes with increasing fluid volume flow, for example from laminar to turbulent, whereby the flow resistance increases significantly. At a minimum, however, the hydraulic or pneumatic flow valve preferably has a lower permeability than the at least one filter surface, i.e., any overpressure that arises in the filter element during cleaning of the aforementioned tubular filter element with cleaning agents is preferably dissipated via the filter surface.

[0022] The aforementioned closure means of the first two embodiments preferably have a response threshold to a closure position which lies at a pressure gradient between 30 and 250 Pa or a flow velocity of 2.5 cm / sec.

[0023] The sealing means of a third embodiment preferably comprise at least one mechanically, electromechanically, and / or pneumatically actuated shut-off valve, i.e., an actively actuated valve, preferably with two switchable positions, i.e., a closed and a flow-through position. The pneumatic shut-off valve is not a check valve in the sense of the aforementioned first embodiment, in which backflow, for example, acts directly on the valve flaps and deflects them from the flow-through position to the closed position, but rather a valve whose permeability can be adjusted and switched via a pneumatic actuator. In contrast to the aforementioned flow control valve, this enables complete sealing. Unlike the aforementioned check valve, this valve can be activated even before backflow begins.Preferably, the mechanically, electromechanically or pneumatically actuated shut-off valve is functionally coupled with the at least one cleaning valve for a purge gas inlet, i.e., it is preferably activated immediately upon introduction of the cleaning fluid into the purge gas inlet and not only upon introduction into the filter element.

[0024] One design of the cleaning lance involves aligning the outlet openings from the tubular cleaning lance axially and radially distributed within its internal volume. This advantageously ensures that the purge gas flow or pulse exiting the lance directly approaches and then flows through the filter surfaces from the inside.

[0025] Preferably, the openings are designed as flow deflectors, i.e., they preferably have deflection plate areas, which can be achieved, for example, during manufacturing by means of tabs bent into the interior of the cleaning lance. This design is particularly suitable when an initially axial flow in the cleaning lance must be deflected radially towards the filter surfaces at the exit with only a small pressure loss.

[0026] As the pressure drop of the flow increases upon exiting the cleaning lance, it is proposed to design the openings as nozzle structures. The axial flow is not deflected by flow deflection surfaces, but rather accumulates in front of the openings, where it expands and is directed onto the filter surfaces as purge gas flows newly aligned by these openings.

[0027] The filter surfaces of the filter element preferably consist of an open-pore ceramic or an open-pore metal, preferably Si3N4, ZrO2, SiC, Al2O3, spinel or sintered metals.

[0028] A key feature of the method for cleaning the aforementioned tubular filter element with cleaning agents is that the purge gas flow or pulse, preferably under positive pressure and preferably consisting of a gas mixture or dried / superheated steam, is introduced through an opening of a purge valve into a tubular purge lance fixed coaxially within the cylindrical inner volume. The gas is then directed through the filter surfaces via several outlet openings of the purge lance distributed axially along the filter surface area, and the sealing means for the at least one clean gas-side outlet are closed. To reduce condensation, the purge gas flow, preferably the purge gas flow impacting the filter surfaces, has a temperature equal to the system temperature.

[0029] The invention is explained in more detail with reference to further exemplary embodiments, the following figures, and descriptions. All features shown and their combinations are not limited to these exemplary embodiments and their configurations. Rather, they are intended to be considered representative of further possible configurations that are not explicitly shown as exemplary embodiments. The figures in each case are shown as examples. Fig. 1 a basic sectional view of the filter element with coaxially arranged cleaning lance in this during normal operation (filtration mode), Fig. 2 a basic cross-sectional view of the filter element according to Fig. 1 in cleaning mode (cleaning mode), Fig. 3 a basic sectional view of a second embodiment of the filter element with a cleaning lance and flow valve arranged coaxially in it as a sealing means as well as Fig. 4 a basic sectional view of a third embodiment of the filter element with a cleaning lance arranged coaxially in it and an actuator, in the example electromechanically controllable shut-off valve as a sealing means.

[0030] The figures schematically depict tubular filter elements 1, which are inserted into a partition 2 between a raw gas chamber 3 and a clean gas chamber 4. A ceramic filter candle 5, preferably open on one side towards the clean gas chamber 4, is inserted into the partition 2 from above as a tubular filter element with a shell surface designed as filter surfaces 9. The gas stream 6 to be cleaned passes through the filter element from below (see figure). Fig. 1) through which water flows. Conventional filter systems have several filter candles arranged in rows or clusters in the form of filter batteries, which are not shown in detail, but for which the new method is also intended and for which the filter candle 5 shown in the figures is considered representative.

[0031] Preferably, a tubular cleaning lance 7 is arranged immovably coaxially within the filter candle 5. In the figures, this lance is closed at the bottom and has a plurality of outlet openings on its outer surface 8, which preferably point radially towards the inner surfaces of the filter surfaces 9 (which are also outer surfaces) of the filter candles. As shown, the cleaning lance is connected at its open end to a purge gas valve 10 (purge gas supply) for a cleaning agent (purge gas).

[0032] Furthermore, sealing means 11 are provided in the transition between filter element 1 and the clean gas chamber 4, i.e. downstream of the gas stream 13 to be cleaned, behind or in the filter candle 5.

[0033] Fig. 1 and Fig. Figure 2 schematically shows a first embodiment of these closure devices with check valves 12 (corresponding to the aforementioned first embodiment, preferably comprising at least one check valve), which in normal operation (filtration mode) are in a Fig. In the open position shown in Figure 1, a flow of cleaned flue gas into the clean gas chamber is permitted. The check valves are preferably spring-mounted (in the example, on the inside of the cleaning lance 7) so that, in the unloaded state, they remain as shown in Figure 1. Fig. 1 shown are open and only closed with an increasing flow 13 from the filter element 1 towards the clean gas chamber 4, moved against the spring action, i.e. into a second in Fig. 2. The closed state shown is transferred.

[0034] Flow 13 occurs when the closure devices are open, i.e., set to allow passage, during normal filter operation according to Fig. 1, in which gas flows to be cleaned 6 flow through the filter surfaces 9 into the filter element 1 and are directed as a flow 13 axially past the sealing means 11 into the clean gas chamber 4.

[0035] In the cleaning operation according to Fig. 2. In contrast, a purge gas flow 14 is introduced from the feed 10 into the cleaning lance 7. Via the openings 15 in the cleaning lance, the purge gas flow 14 is directed as purge gas flows or pulses 16 into the interior of the filter element 1 towards the filter surfaces, penetrates them and thus reaches the raw gas chamber 3. With increasing dynamic pressure in front of the filter surfaces in the filter element, the purge gas flows are increasingly diverted past the check valves 12 towards the clean gas chamber 4 when the closure devices are open, whereby the check valves close from a certain flow velocity or volume flow rate or with increasing pressure gradient.

[0036] Purge gas flows are preferably continuous, while purge gas pulses flow discontinuously. Compared to purge gas flows, purge gas pulses lead to cleaning-promoting effects on the one hand and a lower tendency for back pressure on the other.

[0037] Fig. Figure 3 represents, in a general sectional view, the aforementioned second embodiment of the closure means. The structure and function of the filter element 1 with the cleaning lance 7 arranged coaxially within it correspond to that of the one in Fig. 1 of the illustrated embodiment. Instead of the check valves, the illustrated embodiment has a pneumatic flow valve 17 of the aforementioned type and function as a closing means 11, for example as shown coaxially in the clean gas chamber 4 aligned with the filter element 1.

[0038] The aforementioned third embodiment of the closure means represents Fig. 4. Here too, the structure and function of the filter element 1 with the cleaning lance 7 arranged coaxially within it corresponds to that of the one in Fig. Figure 1 illustrates the embodiment. The closure means 11 comprise a mechanically actuated, in this example electromechanically actuated, closure valve 18, which preferably closes the clean gas-side outlet 19 (passage between filter element 1 and clean gas chamber 4) around the cleaning lance 7 from the outside, similar to an optical aperture. Shown as an example are closure lamellae 20 inserted into the partition 2 between a raw gas chamber 3 and a clean gas chamber 4, as well as a schematic representation of the actuators 21 required for adjustment. Reference symbol list: 1 filter element 2 partition wall 3 Raw gas room 4 Clean gas room 5 filter candle 6 Gas flow 7 Cleaning lance 8 Cleaning lance casing area 9 filter area 10 Purge gas valve 11 Sealing agents 12 check valves 13 Current 14 Purge gas flow 15 openings 16 Purge gas flow or pulse 17 Flow valve 18 actuated shut-off valves 19 clean gas side outlet 20 locking lamellae 21 Actuator

Claims

Tubular filter element (1) comprising: a) a clean gas-side cylindrical inner volume with at least one clean gas-side outlet; b) a shell surface surrounding the inner volume designed as filter surfaces (9); c) cleaning means (7, 8, 10) for the shell surface, wherein the cleaning means comprises a tubular cleaning lance (7) fixedly arranged coaxially in the cylindrical inner volume with several outlet openings (15) distributed axially over the axial extent of the filter surfaces into the inner volume; d) closure means (11) having at least one clean gas-side outlet; and e) at least one cleaning valve (10) for a purge gas inlet in the tubular cleaning lance, characterized in that f) the closure means (11) comprise at least one hydraulic or pneumatic flow valve (17) without moving parts. Tubular filter element according to claim 1, characterized in that the closure means comprise at least one check valve (12). Tubular filter element according to claim 1 or 2, characterized in that the at least one hydraulic or pneumatic flow valve (17) consists of porous materials such as foams, metal fibers, fabrics or other fibrous materials, granular ceramics or sintered metals with a continuous pore system with cross-sections of a few hundred µm. Tubular filter element according to one of the preceding claims, characterized in that the at least one hydraulic or pneumatic flow valve (17) has a lower permeability than the at least one filter surface. Tubular filter element according to one of the preceding claims, characterized in that the closing means (11) has a response threshold to a closing position which is at a pressure gradient between 30 and 250 Pa or a flow velocity of 2.5 cm / sec. Tubular filter element according to one of the preceding claims, characterized in that the closing means comprise a mechanically, electromechanically or pneumatically controllable closing valve (18, 20, 21). Tubular filter element according to claim 6, characterized in that the mechanically, electromechanically or pneumatically controllable shut-off valve (18, 20, 21) is functionally coupled with the at least one cleaning valve (10) for a purge gas inlet. Tubular filter element according to one of the preceding claims, characterized in that the outlet openings from the tubular cleaning lance (7) are distributed axially and radially on it and directed into the inner volume. Tubular filter element according to one of the preceding claims, characterized in that the filter surfaces (9) consist of Si3N4, ZrO2, SiC, Al2O3, spinel or sintered metals. Method for cleaning a tubular filter element (1) exposed to a flow of raw gas with cleaning agents (11) according to one of the preceding claims by backflushing the filter element with a purge gas flow or pulse (16) from the clean gas side, characterized in that the purge gas flow or pulse is introduced through an opening of a cleaning valve (10) into a tubular cleaning lance (7) arranged coaxially in the cylindrical inner volume and is directed through the inner volume and the filter surfaces (9) via several outlet openings (15) of the cleaning lance arranged axially over the axial extent of the filter surfaces, and the closing means (11) for the at least one clean gas-side outlet (19) are closed from the inner volume. Method according to claim 10, characterized in that the purge gas flow or pulse (16) is carried out under overpressure. Method according to claim 10 or 11, characterized in that the purge gas stream or pulse (16) consists of a gas mixture or dried / superheated steam. Method according to one of claims 10 to 12, characterized in that the purge gas flow or pulse has a temperature equal to the system temperature.

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