Sliding valve

Abstract

Sliding valve (20) for high temperature processes having: - a valve body (1), - a working fluid passage seat (3), - sliding guides (4) connected to the passage seat (3) and a movable shutter disc (5), configured to slide on the guides (4), - an actuator (7) connected to the body (1) and configured to generate the force necessary for moving the moving parts of the valve (20), and - a movable stem (6), interposed and rigidly connected to the actuator (7) by one end and to the shutter disc (5) on the other end, wherein the valve (20) is provided with a mobile wedge (8) interposed between the stem (6) and the disc (5), in which the contact between the stem (6) and the mobile wedge (8) is achieved by means of two corresponding frontal surfaces (61, 81) and the contact between the mobile wedge (8) and the disc (5) is achieved by means of respective inclined surfaces (82, 52).

Description

[0001] SLIDING VALVE

[0002] DESCRIPTION

[0003] Technical field of the invention

[0004] The present invention relates to a sliding valve for application in high-temperature processes requiring the control and shut-off of an evolving fluid. Specifically, the subject sliding valve is issuable for use in hydrocarbon refining plants. More specifically, such valve can be used for process control and / or shut-off in catalytic cracking plants.

[0005] Background Art

[0006] As is known, fluid catalytic cracking (FCC) is one of the most important conversion processes used in oil refineries. It is widely used to convert the high-boiling, high-molecular-weight hydrocarbon fraction of crude oil into higher-value products such as gasoline, olefin gases, and other similar products. Cracking of oil hydrocarbons, originally performed as thermal cracking, has now been almost completely replaced by catalytic cracking as it produces a greater quantity of higher-octane gasoline. Catalytic cracking also allows the production, as a by-product, of gaseous elements with a higher olefin content, which are also more important than those produced by thermal cracking.

[0007] Sliding valves play a vital role in controlling the flow of materials within the FCC reactor and regenerator. Thanks to their ability to operate under extreme temperature and pressure conditions, they ensure a safe and efficient process operation. Furthermore, their precise flow control iscrucial to maintaining the balance between the reactor and the regenerator, thus optimizing yield and quality of the final products.

[0008] In general, although the FCC field is the most developed application area and has the most extensive literature, this category of valves is particularly suited for use in chemical plants with complex cycles where the flow of fluids and gases must be regulated and controlled. Their reliability and durability are crucial to avoiding leaks, reducing downtime, and ensuring operational safety. The choice of material and design of sliding valves must be carefully considered to resist corrosion, erosion, and high temperatures typical of chemical processes.

[0009] For this type of application, but more generally for high-temperature processes, a prior art sliding valve is made of a discrete number of components that enable its operation. Among the main components are: - valve body, the main pressure-sealing element,

[0010] - passage seat support, connected to the valve body,

[0011] - fluid passage seat, directly connected to the support,

[0012] - sliding guides, mounted on the passage seat,

[0013] - disc, i.e. the moving element that slides on the guides, acting as a shutter, - stem, the element that connects the actuator to the shutter disc, - actuator, the element capable of generating the force necessary to move the stem and disc.

[0014] Sliding valves operate through the linear movement of the closing disc within the valve body. When the actuator is actuated, the disc slides along the guides, opening or closing the fluid passage. This movement can be modulated to precisely control the flow, or it can be used to completelyisolate a section of the plant. Due to the critical temperature conditions, the components described above must be coupled with precise dimensional tolerances and clearances.

[0015] An important issue in the management of process fluids in plants concerns the isolation of pressure chambers or well-defined piping sections. The valve must therefore have good sealing properties. In the FCC context, a similar type of valve is the shut-off valve. These have an operating principle very similar to sliding valves, with a stem moving a disc that slides on guides. Specifically, shut-off valves allow the disc's vertical clearances to be closed by raising the moving elements on an inclined surface or wedge. This same operating principle can be applied to a sliding valve, allowing the same unit to perform control and sealing functions.

[0016] The current design of sliding valves, similar to the operating principle of shut-off valves, involves the addition of wedges inside the valve.

[0017] During the final part of the disc closing stroke, the force transmitted by the actuator, via the stem, to the disc overcomes friction and ensures the valve moves up the wedges until they contact the seat above. This type of design features a flat-headed stem and two wedges on each of the guides.

[0018] Since the disc requires vertical movement, a relative movement is generated between the stem and the disc, resulting in high vertical friction forces. These vertical forces on the stem cause high bending moments and, consequently, equally high stresses. All of these conditions, in order for the stem to withstand these forces, require overall over-sizing of the latter and of all internal components.There is therefore a need to improve the sliding valve's sealing function, which is achieved by the vertical movement of the shutter disc.

[0019] Summary of the Invention

[0020] The purpose of the present invention is to provide a sliding valve that eliminates the drawbacks described above. Specifically, the valve according to the present invention includes an additional element placed between the disc and the stem, which acts as a movable wedge.

[0021] An advantage of this solution is the ability to transfer vertical friction forces to the movable wedge rather than to the stem.

[0022] According to the present invention, a sliding valve is described with the features set forth in the appended independent claim.

[0023] Further preferred and / or particularly advantageous embodiments of the invention are described according to the features set forth in the appended dependent claims.

[0024] Brief Description of the Drawings

[0025] The invention will now be described with reference to the annexed drawings, which illustrate several non-limiting embodiments, in which: - Figure 1 is an exploded view of a prior art sliding valve,

[0026] - Figure 2 is a detail of the sliding valve of Figure 1,

[0027] - Figure 3 is a partial view of a sliding valve according to a preferred embodiment of the present invention,

[0028] Figure 4 is a detail of the sliding valve of Figure 3,

[0029] Figure 5 is a first construction detail of the sliding valve of Figure 3, Figure 6 is a second construction detail of the sliding valve of Figure

[0030]

[0031] Figure 7 is a third construction detail of the sliding valve of Figure 3, and

[0032] Figure 8 is a graph illustrating the trend of the forces transmitted as a function of characteristic parameters of the present invention.

[0033] Detailed description

[0034] Referring to Figures 1 and 2, numeral 10 indicates a sliding valve as a whole. Valve 10 is a valve of a known type and therefore is not part of the present invention. However, its description is preliminary to that of the sliding valve according to the present invention.

[0035] The sliding valve 10 essentially comprises:

[0036] - a valve body 1. This is the main pressure-holding element, with a special shape that allows the accommodation of the internal components (fixed and moving ones). Depending on the type of process, it can be made of different types of steel or alloys to ensure suitable mechanical properties at operating temperatures;

[0037] - a support 2 for the working fluid passage seat. This component is connected and welded directly to the valve body or indirectly by means of an expansion cone. A fundamental feature of the support is the slot (gap) machined into it, which can have different shapes depending on the type of regulation desired. Support 2 is often coated with anti-abrasive cements or hard metal coatings to resist erosion and high temperatures;

[0038] - a working fluid passage seat 3. It is connected directly to support 2 by a leverage. It mirrors the gap in support 2 of the passage seat and is usually made of the same material and coated with the same cements or hard coatings. Its main role is to allow the guides to be mounted;- sliding guides 4, preferably in number of two. These are two mirror-image components connected directly to the passage seat 3 by a leverage. They feature teeth coated with a hard coating that allows the disc to slide and direct it throughout its travel. The guides 4 are carefully sized to withstand the forces transmitted by a shutter disc, essentially pressure differences and friction;

[0039] - a shutter disc 5. This is a mobile part that slides on the guides, acting as a shutter. By adjusting its position, it allows the opening to be partially closed and the flow to be regulated. Like the passage seat 3 and the passage seat support 2, the disc 5 is coated with anti-abrasive cements or hard coatings to resist the erosive flow. It has two teeth, also covered with a hard coating, which allow it to slide on the teeth of the guides 4. The disc 5 is carefully sized to withstand all the stresses caused by the valve's operating conditions and the dynamics of its movement;

[0040] - a stem 6, a long and slender element, interposed and rigidly connected to an actuator 7 at one end and to the shutter disc 5 at the other. Through the forces transmitted by the actuator 7, the stem 6 moves the disc, adjusting its position. It must withstand critical temperature conditions and tensile / compressive stresses, and is therefore made of steels or noble alloys;

[0041] - the actuator 7. This is the element capable of generating the force necessary to move the stem 6 and the disc 5. It can be of various types (electric, pneumatic, electro-hydraulic, manual) and is connected directly to the valve via a coupling flange.In order to create a seal between disc 5 and seat 3, each guide 4 is provided with a first wedge-shaped element 45, and disc 5 is provided, in its front portion, with a pair of second wedge-shaped elements 55. During the final part of the closing stroke of disc 5, the first 45 and second wedge-shaped elements 55 engage each other by means of respective oblique contact surfaces 46, 56. In this way, the shutter disc is pushed upward, that is, toward the passage seat 3, creating a seal by means of corresponding and second oblique surfaces 51, 31, with the oblique surface 51 belonging to disc 5 and the surface 31 belonging to the passage seat 3. Therefore, during the final part of the disc closing stroke, the force transmitted from actuator 7 to stem 6 and then to disc 5, allows the latter to overcome the friction force and ensure the rise on the wedges until they contact the seat above the passage seat 3.

[0042] With reference to Figures 3 and 4, a sliding valve 20 according to the present invention is provided, in addition to the components previously illustrated for valve 10 of Fig. 1, with an additional movable element, interposed between stem 6 and shutter disc 5 and configured to act as a mobile wedge 8. The movement is first transmitted from the stem 6 to the mobile wedge 8 via two corresponding front surfaces 61, 81, where surface 61 belongs to stem 6 and surface 81 belongs to the mobile wedge 8. Then the movement is transmitted from the mobile wedge 8 to the disc 5 via further, respectively inclined surfaces 82, 52, were surface 82 belongs to mobile wedge 8 and surface 52 belongs to disc 5. In this way, the mobile wedge 8 is able to withstand the vertical friction forces, without them impacting the stem 6. These forces, in fact, are counteracted by the guidesthat support the mobile wedge 8. Furthermore, the mobile wedge 8 is a squat element and therefore no significant bending moments are generated upon it. By operating in this way, it is not necessary to size the bending stem, resulting in smaller dimensions and savings in material.

[0043] The geometric characteristics of each element have a high impact on the push and pull performance of the disc, as well as on the vertical forces acting on the mobile wedge 8 and the guides 4. In particular, and with reference to Figures 5 to 7, the sizing of the characteristic angles a and P is very important.

[0044] The first angle a defines the inclination of the wedge-shaped elements 45 integrated into the sliding guides 4 and the wedge-shaped elements 55 integrated on the front portion of the disc 5. More precisely, angle a is the inclination angle of the respective oblique surfaces 46, 56 in contact between disc 5 and guides 4, as well as of the oblique surfaces 51, 31 respectively belonging to disc 5 and the passage seat 3, i.e. the surfaces that provide the seal between disc 5 and seat 3. This inclination allows the disc to move vertically until it contacts the overlying passage seat 3. The smaller the angle a, the less force required to move the disc both by pushing and pulling.

[0045] The second angle 3 defines the inclination of the mobile wedge 8 and the rear portion of the disc, i.e., the inclination of the inclined surfaces 82, 52 of contact between the mobile wedge 8 and disc 5, with surface 82 belonging to the mobile wedge 8 and surface 52 belonging to disc 5. The second angle 3, similar to the first angle a, allows the vertical movement of the disc 5 until it contacts the passage seat 3. The selection of this angle iscritical for correct sizing: this angle 0, in addition to acting directly on the pushing force, defines the portion of the vertical forces discharged directly onto the guides 4: the smaller the angle 0, the smaller the magnitude of the vertical forces directly transmitted onto the guides.

[0046] The values of these angles are reasonably evaluated based on the design conditions. The most impactful external factors are: temperature, pressure difference on the disc, and the friction coefficient of the contacting parts.

[0047] In particular, the lower limit of the first angle a is defined to prevent excessive wedging of the disc 5 between the guides 4 and the passage seat 3, thus avoiding difficulty in retracting the disc itself. It is therefore advisable to avoid angles less than 15-20°.

[0048] The upper limit of the first angle a is defined relative to the increase in pushing force. With a fixed angle 0, as the angle a increases, the thrust also increases, up to a point where vertical movement becomes impossible. Figure 8 illustrates the pushing trend as a varies for two angles P defined with pi>p2. The upper limit of the first angle a is therefore evaluated relative to the second angle 0. In any case, the choice falls on angles a slightly greater than the wedging values. It can therefore be concluded that the value of the first angle a is between 15° and 25°.

[0049] The upper limit of the second angle p is calculated so that the vertical resultant of the forces transmitted to the guides is non-zero and directed downward. This is to ensure that the movable wedge always remains in contact with the guides. The lower limit of the angle P is chosen so that the vertical force transmitted to the guides is not too high. The calculations areperformed considering the value of the friction coefficient between the contact surfaces. For high-temperature applications and friction coefficients between 0.4 and 0.7, the value of the angle 0 is between 40 and 60 degrees.

[0050] In addition to the embodiments of the invention, as described above, it is to be understood that numerous further variations exist. It should also be understood that the aforementioned embodiments are merely exemplary and do not limit the scope of the invention, nor its applications, nor its possible configurations. On the contrary, although the above description makes it possible for a skilled craftsman to realize the present invention at least according to one exemplary configuration, it should be understood that numerous variations of the described components are conceivable, without departing from the scope of the invention, as defined in the appended claims, interpreted literally and / or according to their legal equivalents.

Claims

CLAIMS1. Sliding valve (20) for high temperature processes requiring the control and interception of an evolving fluid, the valve (20) comprising:- a valve body (1),- a working fluid passage seat (3) connected to a relative support (2) in turn connected to the body (1),- sliding guides (4) connected to the passage seat (3) and a movable shutter disc (5), configured to slide on the guides (4) and to throttle the working fluid, wherein each guide (4) is provided with a first wedge-shaped element (45) and the disc (5) is provided, in its front portion, with a pair of second wedge-shaped elements (55),- an actuator (7) connected to the body (1) and configured to generate the force necessary for moving the moving parts of the valve (20), and- a movable stem (6), interposed and rigidly connected to the actuator (7) by one end and to the shutter disc (5) on the other end, the valve (20) being characterized in that it comprises a mobile wedge (8) interposed between the stem (6) and the disc (5), in which the contact between the stem (6) and the mobile wedge (8) is achieved by means of two corresponding frontal surfaces (61, 81) and the contact between the mobile wedge (8) and the disc (5) is achieved by means of respective inclined surfaces (82, 52).

2. Valve (20) according to claim 1, wherein the first wedge-shaped elements (45) and the second wedge-shaped elements (55) engage each other by means of respective first oblique contact surfaces (46, 56).

3. Valve (20) according to claim 2, wherein the first wedge-shaped elements (45) and the second wedge-shaped elements (55) are configured to push the shutter disc (5) towards the passage seat (3), so that the disc (5) is in contact with the passage seat (3) to provide a seal to the passage of the working fluid.

4. Valve (20) according to claim 3, wherein the disc (5) and seat (3) are in contact by means of corresponding second oblique surfaces (51, 31).

5. Valve (20) according to claim 4, wherein the first oblique surfaces (46, 56) of contact between the disc (5) and the guides (4) and the second oblique surfaces (51, 31) respectively belonging to the disc (5) and to the passage seat (3) have an inclination (a), wherein as the inclination (a) decreases, the force required to move the disc (5) both in pushing and pulling is reduced.

6. Valve (20) according to claim 5, wherein the value of the inclination (a) is between 15° and 25°.

7. Valve (20) according to anyone of the preceding claims, wherein the inclined surfaces (82, 52) of contact between the mobile wedge (8) and the disc (5) have an inclination (p), wherein as the inclination (p) decreases, the amount of the vertical forces transmitted directly onto the guides is reduced.

8. Valve (20) according to claim 7, wherein the value of the inclination (p) is between 40° and 60° for a value of the friction coefficient, between the inclined surfaces (82, 52) of contact of the mobile wedge (8) and the disc (5), comprises between 0.4 and 0.7.

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