Shut-off device for an ethylene production plant

Abstract

Shut-off device for an ethylene production plant with at least one slide plate (11) arranged concentrically in a plate basket (10) and connected to a slide rod (14) and a pipe bridge (12) which are each movable between guide plates (13) to shut off or open a line connected to pipe stubs (17) of the shut-off device by actuating the slide rod (14), wherein sealing seats (18, 19) are defined between the at least one slide plate (11) and / or the pipe bridge (12) on one side and the respective associated pipe stub (17) on the other side, against which the at least one slide plate (11) and the associated pipe stub (17) bear in the closed state of the shut-off device and the pipe bridge (12) and the associated pipe stub (17) bear in the open state of the shut-off device, characterized in thatthat the at least one slide plate (11) extends towards the respective associated pipe stub (17) and / or the pipe stub (17) extends towards the respective associated slide plate (11) or, depending on whether the pipe bridge (12) is in a closed or open state and / or the pipe bridge (12) extends towards the respective associated pipe stub (17) in the area of ​​the respective sealing seats (18, 19) and has / have at least one sealing ring receptacle in the form of a recess or hollow section for receiving at least one sealing ring, wherein the sealing ring can be detachably fastened in the sealing ring receptacle and the sealing ring is fastened in the sealing ring receptacle by means of at least three spot welds or a continuous weld seam, which are / are arranged evenly around a circumference of the sealing ring.

Description

The invention relates to a shut-off device, in particular a plate slide or double plate slide, for an ethylene production plant according to the preamble of claim 1 and to such a plant according to the preamble of claim 12 and to a method for operating such a plant according to the preamble of claim 13.Ethylene is produced by thermal cracking of long chain hydrocarbons, for example naphtha, using steam by the so-called steam cracking process. In this process, the hydrocarbon feedstock is mixed with steam, heated and introduced into a cracking furnace in which so-called "cracking" takes place.The raw gas emerging from the cracking furnace is passed with its fission products through a product main line, referred to as "main transfer line", into connected systems for further processing.During this production process, coke residues accumulate, reducing the free cross section of the conduits. In order to remove these disturbing residues, the plant must be decocked at intervals. For this purpose, the plant is switched from production operation to the so-called "decoking operation" and flushed with an air / steam mixture which, together with dissolved coke residues, is blown out via a decoking line, the so-called "Decake Line".During production operation, the decoking line is shut off by a first shut-off element and the transfer line is opened by a second shut-off element. In the decoking operation, conversely, the first shut-off element in the decoking line is opened and the second shut-off element in the transfer line is closed.In the course of a changeover process between the production operation and the decoking operation, a critical process phase usually occurs, in which a return flow of hydrocarbons via the second shut-off element in the transfer line must be avoided. This is achieved in that the two shut-off members in the transfer line and in the decoking line are actuated in a manner coordinated with one another. This results in good tightness and reliable opening and closing functions of the respective shut-off elements. Valves used for this purpose are usually slides, so-called split gas slides and decoking slides.So-called plate slides and in particular "double plate tube bridge slides", the basic principle of which is based on a technology developed by the applicant and which are also used as special fitting in other areas of the petrochemical industry, have proven particularly successful for use in ethylene production plants.One challenge with shut-off members of this type is, on the one hand, to produce a good sealing effect and, on the other hand, to enable as easy a movement as possible during opening and closing, so that the shut-off member or the slide can be actuated reliably and reliably. Different concepts are available for this purpose. Spring-loaded sealing seats are thus installed on the inner side of the pipe flanges, for example, which enable a defined sealing force to be precisely set on the slide plates or the pipe bridge. Sprung sealing seats are described, for example, in EP 2 241 792 A2 and DE 197 23 962 A1, which are likewise based on the applicant. EP 1 561 180 B1 likewise discloses a sealing seat which, under the action of an elastic element, bears against the periphery of a shut-off plate in the closed position and against a pipe bridge in the open position. These systems function excellently, but are very complicated in terms of their construction and require a high maintenance outlay.EP 13 76 000 A1 discloses sealing seats in the form of annular fluid cylinders which are connected to a pressure line. Annular sealing bodies are arranged in the fluid cylinders. The sealing bodies are pressed against the slide by means of a pneumatic pressure.A further disadvantage of these known systems, or shut-off members, is that the sealing seats there are subjected to very high wear and thus a maintenance of a good sealing effect over time and in particular also under the extreme reaction conditions in an ethylene production plant is problematic. Moreover, maintenance of these known systems for restoring or improving their tightness is possible only by replacing complete assemblies, such as the slide plate or the pipe bridge. Such a procedure is extremely complicated and expensive.The object of the invention is to provide a shut-off member which avoids the above-mentioned disadvantages and, in particular when used in an ethylene production plant, ensures a good and reliable sealing effect over a long period of time and also enables reliable operation and simple, cost-effective and reliable maintenance. In addition, the invention is also based on the object of specifying an ethylene production plant having such a shut-off element and a method for operating such an ethylene production plant.This object is achieved by a shut-off device according to claim 1, by an ethylene production plant according to claim 12 and by a method for operating such a plant according to claim 12.In particular, the object is achieved by a shut-off element, in particular a plate slide valve or a double plate slide valve, for an ethylene production plant, in particular a cracked gas slide valve or a decoking slide valve, having at least one slide plate which is arranged concentrically in a plate basket and is connected to a slide rod, and a pipe bridge which can be moved in each case between guide plates in order to shut off or open a line connected to pipe stubs of the shut-off element by actuating the slide rod, wherein sealing seats are defined between the at least one slide plate and / or the pipe bridge on the one side and the respectively associated pipe stub on the other side, said sealing seats being in contact with said sealing seats in the closed state of the shut-off element the at least one slide plate and the associated pipe stub and the associated pipe stub in the open state of the shut-off element, wherein the pipe bridge and the associated pipe stub are in contact with said sealing seatsthe at least one slide plate in the direction of the respectively associated pipe socket and / orthe pipe socket in the direction of the respectively assigned slide plate or, depending on whether the pipe bridge is in the closed or open state and / orthe pipe bridge in the direction of the respectively associated pipe socketin the region of the respective sealing seats, at least one sealing ring receptacle in the form of a recess or cutout for receiving at least one sealing ring has / have.An important aspect of the invention is to provide a valve which is useful as a slide valve or a double slide valve, particularly for an ethylene production plant. This can be, in particular, a cracked gas slide valve or a decoking slide valve. In the case of the shut-off device being designed as a double-plate slide, it has slide plates arranged concentrically in a plate basket and a pipe bridge which can be moved between guide plates for shutting off and opening a line by actuating a slide rod. Between the slide plates there is arranged an expanding element which is connected to the slide rod. The pipe bridge further comprises a compensator unit. The slide plates or the pipe bridge bear against sealing seats in the closed or open position.A further important point of the invention is that at least one sealing ring receptacle is provided in the region of the respective sealing seats. This sealing ring receptacle can be designed in the form of a recess or cutout which is suitable for receiving and detachably fastening at least one sealing ring.An important advantage of the invention is thus that the shut-off element according to the invention has sealing seats which are arranged in the form of sealing rings which are arranged on the slide plate and / or the pipe bridge and / or on its respective counterpiece, namely the respectively associated pipe socket, and are detachably fastened there.According to the invention, the sealing ring can be fastened detachably in the sealing ring receptacle. The essential advantage according to the invention associated therewith is thus that the respective sealing ring forming a tight seat can be replaced if necessary, i.e. in the event of wear, so that the present invention makes it possible to replace only the components ensuring the tightness of the shut-off member, namely the sealing ring or rings, the slide plate, pipe bridge or the pipe socket, without the need for a complete replacement of slide plate, pipe bridge or pipe socket and thus virtually the entire plate slide.Within the scope of the invention, it is possible that the replaceable sealing ring is arranged only concentrically around the circumference of the slide plate. Alternatively or additionally, the sealing ring can also be arranged on the side of the shut-off element opposite the slide plate, i.e. on the pipe socket. In exceptional cases, provision of a respective sealing ring on the slide plate and on the pipe socket is also possible according to the invention. In an analogous manner, a sealing ring that can be exchanged according to the invention can also be arranged on the pipe bridge and / or the pipe socket interacting with the pipe bridge in the open state of the shut-off element.In the invention, the sealing ring is fastened in the sealing ring receptacle by means of at least three welding points which are arranged substantially uniformly around a, preferably outer, circumference of the slide plate. For this purpose, the sealing ring receptacle is formed as a recess which is formed, for example, in a rectangular shape in an edge of the slide plate facing the pipe socket. This stepped or step-shaped recess in the slide plate edge is suitable for receiving a sealing ring of complementary shape, which has such a shape that it can be fitted exactly into the stepped or step-shaped recess and terminates substantially flush with the surface of the slide plate facing the pipe socket or protrudes slightly beyond this surface.The sealing ring is fastened in the recess, as mentioned above, by means of welding points or a continuous weld seam, which are / is preferably arranged along the outer circumference of the slide plate, or of the sealing ring. According to the invention, the number of welding points is selected such that they are distributed uniformly over the circumference of the slide plate and ensure a secure fit and retention of the sealing ring in the recess. In order to release the sealing ring attached according to the invention from the slide plate again, it is only necessary to open the weld seam, for example by means of a welding torch or by means of flexging.In a manner analogous to the invention, the sealing ring can also be arranged in a correspondingly designed recess on the pipe socket assigned to the slide plate. The same applies to the attachment of the sealing ring to the pipe bridge. In this connection, it should be pointed out that instead of a recess in an edge of the respective component, it is also possible in principle to mount the sealing ring in a recess of the respective component, wherein this recess can be formed, for example, in the shape of a groove. In this case, the application of welding points or a welding seam in the sealing surface itself is necessary, wherein the respective welding is smoothed and optionally polished in this case after the fastening of the sealing ring in the recess.According to a further embodiment of the invention, the sealing ring can alternatively or additionally be screwed into the sealing ring receptacle, wherein the respective screw head is preferably countersunk in a respective counterbore hole provided in the sealing ring, so that the screw head does not protrude beyond the surface of the sealing ring, provided the screw is screwed in from the later sealing side.According to an alternative embodiment of the invention, the sealing ring can also be screwed on from its circumference. In this case, a screw is passed through a screw hole provided in the seal ring and disposed in the circumferential periphery of the seal ring, and is screwed and fixed laterally into the slide plate. In the case of such a lateral attachment of a fastening screw, it is not necessary to sink the screw head, since the respective screw head in this case does not project into the region of the sealing seat. In an analogous manner, the sealing ring can also be fixed according to the invention to the pipe socket and / or to the pipe bridge. In this connection, it should also be pointed out that, according to the invention, a multiplicity of fastening screws distributed substantially uniformly around the circumference of the respective sealing ring are used for fixing the sealing ring.A screw fastening of the sealing ring to the slide plate and / or the pipe socket and / or the pipe bridge is particularly advantageous in that such a screw fastening can be effected easily and, for replacing the sealing ring, can also be loosened again very easily.According to a further embodiment of the invention, the sealing ring in the sealing ring receptacle can alternatively or additionally also be glued with a high-temperature-resistant adhesive. Such an adhesion of the sealing ring in the sealing ring receptacle can be provided either, preferably over the entire surface, along the entire contact surface of the sealing ring with the slide plate and / or the pipe socket and / or the pipe bridge or only at points.Furthermore, according to the invention, the sealing ring can be composed of segments which are braced with respect to one another and with one another when the sealing ring is inserted into the sealing ring receptacle. According to the invention, the sealing ring can thus be configured, for example, in two parts, wherein each segment of the sealing ring is embodied in a semi-annular manner. These two segments are then inserted into the sealing ring receptacle from both sides towards each other and are clamped against each other, for example, by means of tangentially inserted screws or a clamping band.According to a particularly advantageous embodiment of the invention, the sealing ring receptacle can in this case have one or more undercut(s) in which respective projections of the sealing ring engage and fix the sealing ring in an axial direction with respect to a flow direction, or of the pipe socket.According to the invention, the segments are designed overlapping one another, in particular in a direction axial to the pipe socket. In this way, both a good mutual fixing of the sealing ring segments and a good sealing effect can be ensured.Furthermore, according to the invention, the sealing ring has, on its side facing the respective sealing seat, armouring which extends in particular over optionally present counterbores. This armouring and / or the sealing ring itself also have, according to the invention, a hardened and / or polished sealing surface.An embodiment of the shut-off device is particularly effective and low-maintenance, in which a compensator unit arranged on the pipe bridge and the sealing seats each form a metal seal. This type of seal has proven particularly useful in the operation of ethylene production plants.Such a compensator unit may further have hardened sealing surfaces which abut the baffles. This reduces the wear of the pipe bridge during the opening and closing of the slide.It is also possible to provide an ethylene production plant having a cracking furnace which is operable in a production mode and a decoking mode. A first shut-off element according to the invention is arranged in a transfer line and a second shut-off element according to the invention is arranged in a decoking line. The first and second shut-off members according to the invention are reciprocally movable into an open and a closed position. The first and / or second shut-off element according to the invention can each be designed as a slide valve, or preferably a double slide valve, according to the preceding embodiments.A method for operating an ethylene production plant is also possible, in which, for decoking, a first shut-off element according to the invention is closed in a transfer line for cracking gas which is connected to a cracking furnace, and at the same time a second shut-off element according to the invention is opened in a decoking line which is connected to the transfer line. The first and / or second shut-off element according to the invention can each be designed as a slide valve, or preferably a double slide valve, according to the preceding embodiments.The invention is explained in more detail below with reference to the attached single schematic figure.The single FIGURE shows a section of a double-plate pipe bridge slide according to an exemplary embodiment of the invention. Such a slide valve is used in ethylene production equipment and is also referred to as a cracked gas slide valve or a decoking slide valve.The slide has a housing 23 which surrounds the internals located in the housing 23 in a fluid-tight manner. Connected, in particular welded, to the housing 23 are two pipe stubs 17 which are arranged on the slide at the front and at the rear in the flow direction. The pipe stubs 17 are flanged to corresponding lines (not shown) in the mounted state, for example a transfer line or a decoking line.The slide furthermore refers to a plate basket 10 in which slide plates 11 are inserted. The slide plates 11 are arranged concentrically and parallel to one another and close off the two pipe stubs 17 in the illustrated closed position. The slide plates 11 are loosely inserted into the plate basket 10 so that they can be moved in the axial direction, i.e. perpendicular to the surface of the slide plates 11. This is used to press the slide plates 11 in the closed position against the sealing seats 18, 19 provided on the housing 23, which sealing seats are formed by releasable sealing rings (not shown). For this purpose, an expanding element 15 is arranged between the two slide plates 11 and is connected to a slide rod 14. The slide rod 14 is mounted in a fluid-tight manner in the housing 23 and is movable in the longitudinal direction by a drive (not shown). The spreading member 15 has an inner wedge 20 which is arranged in an outer wedge 21 on the inner side of the slide plates 11. For centering the spreading element 15, a centering ball 22 is arranged between the jaws of the inner wedge 20.Upon actuation of the slide rod 14, the inner wedge 20 is moved into the outer wedge 21, whereby the two slide plates 11 are spread apart. The spreading movement presses the two slide plates against the sealing seats 18, 19, whereby a good sealing effect is achieved in the closed position of the slide.Below or next to the plate basket 10 there is arranged a pipe bridge 12 which, in the open position (not shown), is aligned with the two pipe stubs 17. The pipe bridge 12 is connected to the plate basket 10 so that these can be moved together with the plate basket 10 into the open or closed position by an actuation of the slide rod 14. For this purpose, the plate basket 10 and the pipe bridge 12 are moved between two guide plates 13 arranged in parallel.The pipe bridge 12 further comprises a compensator unit 16, the height of which determines the overall height of the pipe bridge 12. The compensator unit 16 has two compensator rings 24, 25 which are arranged concentrically and spaced apart from one another in the axial direction. A compensator shaft 28 is arranged between the two compensator rings 24, 25. In the present exemplary embodiment, this is formed in multiple corrugations. Single-wave compensator waves are likewise possible, in particular in the case of smaller nominal widths.The compensator shaft 28 includes an inner pipe portion 26 and an outer pipe portion 27 which are arranged coaxially. The inner pipe section 26 is aligned with the inner surfaces of the sealing rings 24, 25 detachably fastened according to the invention, so that a substantially smooth flow passage through the pipe bridge is ensured.The height of the compensator unit 16 or of the pipe bridge 12 is measured from the sealing surface of one compensator ring 24 to the sealing surface of the other compensator ring 25. The height of the compensator unit 16 has an excess in relation to the clear distance between the sealing seats 18, 19, which is in a range from 0.5 mm to 1.60 mm. This overdimension ensures that the compensator unit 16 or the pipe bridge 12 is pressed with a sufficiently high sealing force against the sealing seats 18, 19 in the open position of the slide.In the case where the sealing force decreases with increasing operating time, a plurality of Belleville spring columns are provided on the outside of the compensator unit 16. For example, 3, 4, 5 or 6 disk spring columns can be arranged distributed on the outer circumference of the compensator unit 16. The prestress of the disk spring columns, specifically the prestress path, is 1 mm to 4 mm per column. Each Belleville spring column may include 8 to 12 Belleville springs.The number of the disk spring column in or the number of disk springs per column depends on the nominal width of the slide.List of reference characters10 Plate cage 11 Slide plates 12 Pipe bridge 13 Guide plates 14 Slide rod 15 Expansion element 15 16 Compensator unit 17 Pipe socket 18 Sealing seat 19 Sealing seat 20 Inner wedge 21 Outer wedge 22 Centering ball 23 Housing 24 Compensator ring 25 Compensator ring 26 Inner pipe section 27 Outer pipe section 28 Compensator shaft

Claims

Shut-off element for an ethylene production plant, having at least one slide plate (11) which is arranged concentrically in a plate basket (10) and is connected to a slide rod (14), and a pipe bridge (12) which can be moved in each case between guide plates (13) in order to shut off or open a line connected to pipe stubs (17) of the shut-off element by actuating the slide rod (14), wherein sealing seats (18, 19) are defined between the at least one slide plate (11) and / or the pipe bridge (12) on the one side and the respectively associated pipe stub (17) on the other side, the at least one slide plate (11) and the associated pipe stub (17) bearing against said sealing seats in the closed state of the shut-off element and the pipe bridge (12) and the associated pipe stub (17) bearing against said sealing seats in the open state of the shut-off element, characterized in that, the at least one slide plate (11) in the direction of the respectively assigned pipe socket (17) and / or the pipe socket (17) in the direction of the respectively assigned slide plate (11) or, depending on whether the closed or open state of the pipe bridge (12) and / or the pipe bridge (12) in the direction of the respectively assigned pipe socket (17) in the region of the respective sealing seats (18, 19) has / have at least one sealing ring receptacle in the form of a recess or cutout for receiving at least one sealing ring, wherein the sealing ring can be detachably fastened in the sealing ring receptacle and the sealing ring is fastened in the sealing ring receptacle by means of at least three welding points or a continuous welding seam which are / is arranged uniformly around a circumference of the sealing ring.Shut-off member according to one of the preceding claims 1, characterized in that the sealing ring is screwed into the sealing ring receptacle.Shut-off member according to Claim 2, characterized in that the sealing ring has a countersunk hole for countersunk a respective screw head.Shut-off member according to one of the preceding claims 2 to 3, characterised in that the sealing ring is glued in the sealing ring receptacle.Shut-off member according to one of the preceding claims, characterized in that the sealing ring is composed of segments which are braced with respect to one another in the state in which they are inserted into the sealing ring receptacle.Shut-off member according to claim 5, characterised in that the sealing ring receptacle has an undercut in which a protrusion of the sealing ring engages.Shut-off member according to one of the preceding claims 5 to 6, characterised in that the segments are formed overlapping one another.Shut-off member according to one of the preceding claims, characterized in that the sealing ring has armouring on its side facing the respective sealing seat (18, 19).Shut-off element according to Claim 8, characterized in that the armouring and / or the sealing ring has / have hardened and / or polished sealing surface(s).

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