Multi-coalescence oily sewage treatment equipment adopting backwashing self-unfolding filter pipe

Abstract

The utility model discloses multi-coalescence oily sewage treatment equipment adopting a backwashing self-unfolding filter pipe, and relates to the technical field of oily sewage treatment, the multi-coalescence oily sewage treatment equipment is characterized in that a filtering tank is provided with an oil discharge port, a water discharge port and a liquid inlet, and is sequentially provided with a coarse filter, a fine filter and a fine filter from top to bottom; a filter tube outer support frame is sleeved on the periphery of the filter tube inner support frame, the filter element is sleeved on the filter tube inner support frame, a gap is reserved between the filter element and the outer support frame, the filter element is of a folding wedge-shaped structure, and a hoop is arranged on the periphery of the filter element; a filter pipe replacement port is formed in the filter tank, a water outlet is formed in the other corresponding side, the modified coalescence filter pipe is inserted into the filter tank from the filter pipe replacement port, and one end of the modified coalescence filter pipe is in butt joint with the water outlet; and the backwashing device comprises a backwashing pipe communicated with the water outlet. Therefore, the problems existing in existing oilfield produced water treatment are solved, the occupied area of equipment is reduced, the operation cost is reduced, the long-time and high-efficiency treatment requirements are met, and the oilfield produced water reinjection requirement is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oily sewage treatment, in particular to a multiple coalescence oily sewage treatment equipment adopting a backwashing self-unfolding filter pipe. BACKGROUND

[0002] Oily sewage is wastewater containing oil substances discharged in the industrial production process. The oil substances in the wastewater are in various states, such as floating oil, dispersed oil, emulsified oil and dissolved oil. For example, oil and gas exploitation produced water, oil and gas chemical industry electric dehydration cooling water, port discharge water and production and manufacturing mechanical processing discharge water. The oily sewage produced by oil and gas exploitation is huge, and the treatment of oilfield produced water mainly aims at oil removal and suspended solids removal, and the treated water is mainly used for reinjection.

[0003] There are various commonly used sewage treatment technologies:

[0004] 1. Sedimentation and oil removal tank (gravity, coarse granulation), which has the problems of large occupied area, long time consumption and low efficiency;

[0005] 2. Flocculation sedimentation, which has the problems of high operation cost, large amount of reagent and difficult sludge treatment;

[0006] 3. Biological method, which has the problems of large occupied area, long time consumption, strict temperature requirement and limited oil content;

[0007] 4. Filtration method (walnut shell, multi-layer filter material filter, etc.), which has the problems of complex equipment, short service life of filter material and limited oil content.

[0008] The existing oily sewage treatment technology has the following bottlenecks:

[0009] 1. In the late stage of oil and gas development, the water content of oil well produced liquid is increasing, and most of the sewage treatment systems are overloaded, which affects the treatment efficiency and effect, and the sewage quality does not meet the standard;

[0010] 2. The existing sewage treatment system has many stages, large occupied area and high operation cost.

[0011] Therefore, it is necessary to develop an oily sewage treatment equipment to reduce the occupied area, reduce the operation cost, ensure long-term high-efficiency treatment demand, realize oil removal and suspended solids removal of oilfield produced water, and meet the reinjection requirements. Content of the utility model

[0012] In order to solve the above problems, reduce the occupied area, reduce the operation cost, ensure long-term high-efficiency treatment demand, realize oil removal and suspended solids removal of oilfield produced water, and meet the reinjection requirements, the present application provides a multiple coalescence oily sewage treatment equipment adopting a backwashing self-unfolding filter pipe.

[0013] The multiple coalescence oily sewage treatment equipment provided by the application adopts the following technical scheme.

[0014] The multiple coalescence oily sewage treatment equipment adopting the backwashing self-expanding filter pipe comprises:

[0015] The filter tank is provided with an oil discharge port at the top, and is provided with a liquid inlet, and the filter tank is sequentially provided with a coarse filter, a fine filter and a fine filter from top to bottom below the liquid inlet;

[0016] The coarse filter comprises a wire mesh;

[0017] The fine filter comprises a modified coalescence filter pipe, the modified coalescence filter pipe comprises a filter core support frame and a filter core, the filter core support frame comprises an inner filter pipe support frame, an outer filter pipe support frame is sleeved on the periphery of the inner filter pipe support frame, and the filter core is sleeved on the inner filter pipe support frame; the filter core is made of a fiber material, the filter core has a folded wedge structure, and a clamp is arranged on the periphery of the filter core;

[0018] A filter pipe replacement opening is arranged on the filter tank, and a water outlet is arranged on the other side of the filter tank corresponding to the filter pipe replacement opening; the modified coalescence filter pipe is inserted into the filter tank from the filter pipe replacement opening, and one end of the modified coalescence filter pipe is arranged in opposite connection with the water outlet;

[0019] The backwashing device comprises a backwashing pipe in communication with the water outlet.

[0020] By adopting the above technical scheme, the coarse filter, the fine filter and the fine filter are sequentially arranged in the filter tank from top to bottom, so that multiple oily sewage can be filtered step by step, which is beneficial to reduce the probability of filter blockage and improve the service life. The filter core has a folded wedge structure and can be arranged in the filter core support frame. During forward filtration, the filter core can be self-tightened and densified under the action of pressure, so as to ensure the filtering effect of the filter core. During reverse flushing, the filter core can expand, the diameter becomes larger, and the folded surface is opened, which is more conducive to the desorption of oil droplets and impurities contained in the filter core and is conducive to improving the backwashing effect. The modified coalescence filter pipe is integrally inserted into the filter tank, can be quickly plugged in and out and replaced outside the filter tank, does not need to enter the inside of the tank body, the operation space is not limited, and safety accidents in the tank can be avoided.

[0021] Optionally, the filter pipe replacement opening comprises an opening A formed in the filter tank, a first-end pipe is arranged at the opening A, a door plate is flange-connected to the end of the first-end pipe, and a door plate handle is arranged on the door plate.

[0022] By adopting the above technical scheme, the door plate handle is arranged, the door plate is convenient to take and operate, the door plate is flange-connected, the installation mode is simple and reliable, and the sealing performance is good.

[0023] Optionally, one end of the outer support frame of the filter tube is provided with a ring baffle, the tail end flange of the male joint is clamped between the inner support frame of the filter tube and the ring baffle, and a sealing ring groove is formed on the outer surface of the head end of the male joint.

[0024] Optionally, the water outlet comprises an opening B formed on the filter tank, an end pipe is arranged at the opening B, an end plate is connected to the end flange of the end pipe, the water outlet connecting pipe penetrates through the end plate, and a female joint matched with the male joint is arranged at the inner end of the water outlet connecting pipe.

[0025] By adopting the above technical scheme, the male joint and the female joint are arranged, which is conducive to improving the convenience of connection, and conducive to realizing the quick plugging and replacement of the modified coalescence filter tube, and the installation sealing performance is good.

[0026] Optionally, the other end of the outer support frame of the filter tube is provided with a circular baffle, and the circular baffle abuts against the other end of the inner support frame of the filter tube and the filter core.

[0027] Optionally, a baffle handle is arranged on the circular baffle.

[0028] By adopting the above technical scheme, the baffle handle is arranged, which facilitates the replacement operation of the modified coalescence filter tube.

[0029] Optionally, the modified coalescence filter tubes in the filter tank are distributed in a radial manner.

[0030] By adopting the above technical scheme, the distribution form can arrange multiple modified coalescence filter tubes, which is conducive to improving the treatment efficiency of oily sewage.

[0031] Optionally, the modified coalescence filter tubes in the filter tank are arranged in parallel.

[0032] By adopting the above technical scheme, the distribution form can arrange multiple modified coalescence filter tubes, which is conducive to improving the treatment efficiency of oily sewage.

[0033] Optionally, the wire mesh comprises a metal wire mesh, the inner wall of the filter tank is provided with a first convex ring, the edge of the metal wire mesh is lapped on the first convex ring, and the metal wire mesh is connected with the first convex ring through bolts.

[0034] By adopting the above technical scheme, the bolt connection mode is simple and reliable, the metal wire mesh can perform primary rough filtration on the oily sewage, and can coalesce large-particle dispersed oil, so that the large-particle dispersed oil coalesces together and floats above the water surface.

[0035] Optionally, the fine filter includes particulate filter material, and the inner wall of the filter tank is provided with a second convex ring and a third convex ring at intervals. The edge of the particulate filter material overlaps on the third convex ring, and a pressure plate is provided on the top of the particulate filter material. The pressure plate is connected to the third convex ring by bolts.

[0036] In summary, this application includes at least the following beneficial effects:

[0037] 1. The filter tank of this application is equipped with a coarse filter, a fine filter, and a high-precision filter arranged sequentially from top to bottom. This allows for the filtration of oily wastewater at different stages, reducing the probability of filter clogging and extending its service life. The filter element has a folded wedge structure with circumferential water inlet and internal outlet. During forward filtration, the filter element tightens and densifies under water pressure, adsorbing fine oil droplets and intercepting suspended solids (SS). During backwashing, due to the gap between the filter element and the external support frame, the filter element can expand in the reverse direction, opening the folds to release the intercepted SS and desorb the adsorbed oil droplets and initial scale layer, resulting in more thorough cleaning and a longer service life. To enable the filter element to expand in the reverse direction during backwashing, a high-intensity water wash or a "gas explosion + water flushing" backwashing method is required. The treatment equipment of this application is small in size, reducing the footprint, and has low operating costs, ensuring long-term high-efficiency treatment needs, achieving oil and suspended solids removal from oilfield produced water, and meeting reinjection requirements.

[0038] 2. The modified coalescing filter tube of this application is placed near the bottom of the filter tank, and can be quickly inserted and removed from the outside of the filter tank for replacement without entering the tank. This allows for unrestricted operation and avoids safety accidents inside the tank. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the filtration process of a multi-stage coalescing oily wastewater treatment device that uses a backwashed self-expanding filter tube.

[0041] Figure 2 This is a schematic diagram of the backwashing process of a multi-coalescing oily wastewater treatment equipment that uses a backwashing self-expanding filter tube.

[0042] Figure 3 This is a schematic diagram of the modified coalescing filter tube structure.

[0043] Figure 4 yes Figure 3 A magnified schematic diagram of part A in the middle.

[0044] Figure 5 is a filter core structure schematic diagram.

[0045] Figure 6 is a multiple coalescence oily sewage treatment equipment structure schematic diagram of example two using the backwashing self-expanding filter tube.

[0046] Figure 7 is a modified coalescence filter tube distribution schematic diagram of example two.

[0047] Figure 8 is a multiple coalescence oily sewage treatment equipment structure schematic diagram of example three using the backwashing self-expanding filter tube.

[0048] Figure 9 is a modified coalescence filter tube distribution schematic diagram of example three.

[0049] BRIEF DESCRIPTION OF DRAWINGS: 1, liquid inlet; 2, oil outlet; 3, coarse filter; 4, fine filter; 5, fine filter; 6, filter core; 7, filter tube inner support frame; 8, filter tube outer support frame; 9, ring baffle; 10, round baffle; 11, clamp; 12, male joint; 13, sealing ring; 14, baffle handle; 15, water outlet; 16, head tube; 17, door plate; 18, door plate handle; 19, tail tube; 20, tail plate; 21, water outlet connecting pipe; 22, female joint; 23, backwashing drainage port. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0051] The following will be described in detail with reference to the drawings in the embodiments of the present application. Figures 1 to 9 The present application will be further described in detail.

[0052] The embodiments of the present application disclose a multiple coalescence oily sewage treatment equipment using backwashing self-expanding filter tube.

[0053] Embodiment one

[0054] With reference to Figures 1 to 5 , the multiple coalescence oily sewage treatment equipment using backwashing self-expanding filter tube comprises: a filter tank.

[0055] The liquid inlet 1 is arranged at a position close to the top of the filter tank, and the liquid inlet 1 is provided with a shunt pipe for injecting oil-containing sewage into the filter tank.

[0056] The filter tank is sequentially provided with a coarse filter 3, a fine filter 4 and a fine filter 5 from top to bottom below the liquid inlet 1.

[0057] The coarse filter 3 comprises a wire mesh, which can be a metal wire mesh, and is made of 1-2 layers of duplex steel wire mesh or a porous membrane. The coarse filter 3 is arranged at the top of the tank body and mainly coalesces large-particle dispersed oil, so that the large-particle dispersed oil coalesces together and then floats above the water surface. A first protruding ring is arranged on the inner wall of the filter tank, the edge of the metal wire mesh is lapped on the first protruding ring, and the metal wire mesh is connected with the first protruding ring through bolts. The bolt connection is simple and reliable.

[0058] The fine filter 4 comprises a granular filter material, which can filter small-particle impurities and coalesce small-particle oil droplets into large-particle dispersed oil, so that the particle size of the oil droplets is increased and the oil droplets can gradually float up. Second and third protruding rings are arranged on the inner wall of the filter tank in an interval. The edge of the granular filter material is lapped on the third protruding ring, and a pressing plate is arranged at the top of the granular filter material. The edge of the pressing plate is connected with the third protruding ring through bolts, and the granular filter material is pressed on the third protruding ring by the pressing plate.

[0059] The fine filter 5 comprises a modified coalescence filter tube, which comprises a filter core support frame and a filter core 6.

[0060] The filter core support frame comprises an inner filter tube support frame 7, an outer filter tube support frame 8, a ring baffle 9 and a circular baffle 10. The inner filter tube support frame 7 and the outer filter tube support frame 8 are both cylindrical metal welded frames, and the outer filter tube support frame 8 is sleeved on the periphery of the inner filter tube support frame 7.

[0061] The filter core 6 is made of a fiber material and has a folded wedge structure. The filter core 6 is sleeved on the inner filter tube support frame 7, and a clamp 11 is arranged on the periphery of the filter core 6. The clamp 11 is limited on the inner filter tube support frame 7, and the clamp 11 clamps the filter core 6, so that the filter core 6 cannot fall off.

[0062] The fiber material of the filter core 6 is a modified fiber material made of super-hydrophilic and oil-wet materials, which can realize oil coalescence and SS filtration. 1. The material has a three-dimensional network structure and a curved channel pore structure, which can greatly increase the collision and interception probability of oil droplets and suspended solids in the fluid in the pore structure. 2. Compared with the previous stage, the oil-wetness of the filter tube composite material of the later stage is stronger, and in addition to the coalescence effect, it also has an interception effect on free oil in the final effluent. 3. The ultra-fine fiber filter core 6 also has a demulsification function.

[0063] The ring baffle 9 is connected with one end of the outer support frame 8 of the filter tube by bolts, the flange at the tail end of the male joint 12 is clamped between the inner support frame 7 of the filter tube and the ring baffle 9, a sealing ring groove is formed on the outer surface of the head end of the male joint 12, and a sealing ring 13 is arranged in the sealing ring groove. The circular baffle 10 is connected with the other end of the outer support frame 8 of the filter tube by bolts, and the circular baffle 10 abuts against the other end of the inner support frame 7 of the filter tube and the filter core 6.

[0064] A baffle handle 14 is arranged on the circular baffle 10.

[0065] The modified coalescence filter tube is inserted into the filter tank, a filter tube replacement opening is arranged on the filter tank, the other side of the filter tank corresponding to the filter tube replacement opening is provided with a water outlet 15, the modified coalescence filter tube is inserted into the filter tank from the filter tube replacement opening, and the male joint 12 at one end of the modified coalescence filter tube is arranged opposite to the water outlet 15.

[0066] The filter tube replacement opening comprises an opening A formed on the filter tank, and a head-end pipe 16 is communicated at the opening A. A flange at an end of the head-end pipe 16 is connected with a door plate 17, the door plate 17 is connected with the flange at the end of the head-end pipe 16 by bolts, and a sealing gasket is arranged therebetween. A door plate handle 18 is arranged on the door plate 17. The bolt connection mode is simple and reliable, the door plate 17 is easy to disassemble, and the installation and disassembly of the fine filter tube are facilitated.

[0067] The water outlet 15 comprises an opening B formed on the filter tank, and a tail-end pipe 19 is communicated at the opening B. A flange at an end of the tail-end pipe 19 is connected with a tail-end plate 20, and a water outlet connecting pipe 21 penetrates through the tail-end plate 20. A female joint 22 is threadedly connected with an inner end of the water outlet connecting pipe 21. After the modified coalescence filter tube is inserted into the filter tank, the male joint 12 at one end of the modified coalescence filter tube is inserted into the female joint 22, so that the modified coalescence filter tube is connected with the water outlet connecting pipe 21.

[0068] The oil-containing wastewater treatment equipment of the application further comprises a backwashing device, and the backwashing device comprises a backwashing pipe communicated with the water outlet connecting pipe 21. When backwashing is needed, the modified coalescence filter tube can be backwashed by using the water outlet connecting pipe 21. A backwashing water outlet 23 is arranged at the top of the filter tank.

[0069] Oil substances in wastewater are in various states, such as floating oil, dispersed oil, emulsified oil and dissolved oil. The oil-containing wastewater enters the filter tank, and a series of coalescence, filtration and sedimentation are performed in the filter tank. The wastewater in the filter tank is sequentially arranged from top to bottom as water, oil-water mixture and oil. The floating oil is gradually floated and discharged from the oil discharge port 2. The dispersed oil and the emulsified oil are subjected to coalescence, the oil droplet size is gradually increased, and finally the oil is also discharged from the oil discharge port 2.

[0070] The filter tank is sequentially provided with a coarse filter 3, a fine filter 4 and a fine filter 5 from top to bottom, so that the oil-containing wastewater can be filtered in stages, which is beneficial to reducing the probability of filter blockage and improving the service life.

[0071] The filter core 6 is a folded wedge structure, water enters from the circumference, and water is discharged from the inner cavity. When filtering in the positive direction, the filter core 6 is self-tightened and densified under the action of water pressure, adsorbs small oil droplets, and intercepts SS. The filter core 6 leaves a gap with the outer support frame 8. When backwashing, the filter core 6 can be reversely expanded, the folded surface is opened, the intercepted SS is released, the adsorbed oil droplets and the initial layer of scale are desorbed, and the cleaning is more thorough, and the service life is longer. In order to make the filter core 6 reversely expand during backwashing, a higher strength water washing or a backwashing mode of "gas explosion + water flushing" needs to be used. The treatment equipment of the application has small volume, reduces the occupied area, has low operation cost, guarantees long-time high-efficiency treatment demand, realizes oilfield produced water oil removal and suspended solids removal, and meets the reinjection requirements.

[0072] The modified coalescence filter pipe is placed at a position close to the bottom of the filter tank, can be integrally quickly plugged and replaced outside the filter tank, does not need to enter the inside of the tank body, has no limited space operation, and avoids the occurrence of safety accidents in the tank.

[0073] Example Two

[0074] With reference to Figure 6 , 7 , the modified coalescence filter pipes in the filter tank are radially distributed in a plurality of ways. The radial distribution type is suitable for occasions with large treatment capacity and large tank body diameter. The modified coalescence filter pipes are radially and uniformly distributed on the circumference to ensure that water can be uniformly collected on the large-diameter circular section. The water discharged from the modified coalescence filter pipes is collected in a center pipe at the center, and the arrangement is simple and convenient to connect externally.

[0075] Example Three

[0076] With reference to Figure 8 , 9 , the modified coalescence filter pipes in the filter tank are parallelly distributed in a plurality of ways. The parallel distribution type is suitable for occasions with small treatment capacity and small tank body diameter. The parallel distribution of the modified coalescence filter pipes facilitates the arrangement on one side of the tank body, does not need to reserve operation space for replacing the modified coalescence filter pipes on the circumference, and is more convenient for replacing the modified coalescence filter pipes and more compact in equipment.

[0077] In the description of the utility model, it is understood that the terms "bottom", "top", "one end", "the other end", "the first end", "the other side" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the utility model. In the description of the utility model, unless otherwise specified and limited, it is necessary to explain that the term "connection" should be understood broadly, for example, it can be mechanical connection or electrical connection, and can be the communication between two elements, can be directly connected, or indirectly connected through an intermediate medium, and for ordinary skilled persons in the art, the specific meaning of the above-mentioned term can be understood according to the specific situation.

[0078] The above is only a preferred embodiment of the utility model, and is not used to limit the utility model, and any modification, equivalent replacement, improvement and the like made within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A multi-stage coalescing oily wastewater treatment device employing backwashing self-expanding filter tubes, characterized in that, include: The filter tank has an oil drain port at the top and a liquid inlet at the top. Inside the filter tank below the liquid inlet, a coarse filter, a fine filter, and a fine filter are arranged sequentially from top to bottom. The coarse filter includes a wire mesh; The fine filter includes a modified coalescing filter tube, which includes a filter element support frame and a filter element. The filter element support frame includes an inner support frame and an outer support frame. The filter element is fitted on the inner support frame, with a gap between the filter element and the outer support frame. The filter element is made of fiber material and has a folded wedge structure. A clamp is provided around the filter element. A filter tube replacement port is provided on the filter tank, and an outlet is provided on the other side of the filter tank corresponding to the filter tube replacement port. The modified coalescing filter tube is inserted into the filter tank through the filter tube replacement port, and one end of the modified coalescing filter tube is connected to the outlet. A backwashing device, the backwashing device including a backwashing pipe connected to a water outlet.

2. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 1, characterized in that, The filter tube replacement port includes an opening A on the filter tank, a head tube is provided at the opening A, a door panel is connected to the end flange of the head tube, and a door panel handle is provided on the door panel.

3. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 1, characterized in that, One end of the outer support frame of the filter tube is provided with an annular baffle. The tail flange of the male connector is clamped between the inner support frame of the filter tube and the annular baffle. The outer surface of the first end of the male connector has a sealing annular groove, and a sealing ring is provided in the sealing annular groove.

4. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 3, characterized in that, The water outlet includes an opening B on the filter tank, an end pipe is provided at the opening B, an end plate is connected to the end flange of the end pipe, a water outlet connection pipe passes through the end plate, and a female connector that mates with the male connector is provided at the inner end of the water outlet connection pipe.

5. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 3, characterized in that, A circular baffle is provided at the other end of the outer support frame of the filter tube, and the circular baffle abuts against the other end of the inner support frame and the filter element of the filter tube.

6. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube according to claim 5, characterized in that, The circular baffle is equipped with a baffle handle.

7. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 1, characterized in that, The modified coalescing filter tubes inside the filter canister are arranged radially in several shapes.

8. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube as described in claim 1, characterized in that, Several modified coalescing filter tubes are arranged in parallel inside the filter tank.

9. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube according to claim 1, characterized in that, The wire mesh includes a metal wire mesh, and the inner wall of the filter tank is provided with a first protruding ring. The edge of the metal wire mesh overlaps the first protruding ring, and the metal wire mesh is connected to the first protruding ring by bolts.

10. The multi-stage coalescing oily wastewater treatment equipment using a backwashed self-expanding filter tube according to claim 1, characterized in that, The fine filter includes particulate filter material. The inner wall of the filter tank is provided with a second convex ring and a third convex ring at intervals. The edge of the particulate filter material overlaps on the third convex ring. A pressure plate is provided on the top of the particulate filter material. The pressure plate is connected to the third convex ring by bolts.

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