Method, device and computer program for monitoring and controlling a control valve

Abstract

The present invention relates to a method for monitoring and controlling a function of a control valve (10a to 10d) of a polymer production plant, as well as a device and a computer program for implementing the method. According to the method, a condition of the control valve (10a to 10d) is determined, the determined condition is compared with a threshold value for said condition thereby providing an indication of a potential risk for malfunction of the control valve (10a to 10d), and if a potential risk for malfunction is identified, a predetermined actuation signal is applied to the control valve (10a to 10d) thereby eliminating or reducing the potential risk for malfunction of the control valve (10a to 10d).

Description

[0001] METHOD, DEVICE AND COMPUTER PROGRAM FOR MONITORING AND CONTROLLING A CONTROL VALVE

[0002] The present invention relates to a method for monitoring and controlling a control valve of a polymer production plant, as well as a device and a computer program for implementing the method.

[0003] Background

[0004] In a polymer production plant control valves are used to take slurry / polymer powder out from polymer reactors (loop or gas phase reactor) and from different kinds of vessels. These control valves are typically regulated by level or pressure controllers. They can also be operated manually, for example, via a control panel of a control device / control system of the polymer production plant.

[0005] In this context WO 2021 / 1 15908 A1 relates to a system for producing polyolefin. The system comprises a gas phase reactor for polymerizing an olefin to obtain polymerization product having a first and a second outlet for continuously withdrawing polymerization product from the gas phase reactor. The system further comprises a first outlet tank in fluid communication with the first outlet via a first passage having a first valve means for controlling the flow of the first product stream in the first passage, a product receiver tank in fluid communication with the second outlet via a second passage, having a second valve means for controlling the flow of the second product stream in the second passage, and a control means in communication with the first valve means and the second valve means and arranged to control the operation of the first valve means and the second valve means so that flow in only one of the first passage and the second passage is allowed at a time.

[0006] Due to stable process conditions a control valve can remain in the same position for a long time, as no major changes in the valve position are required. In this case there is a risk of deposits building up on / in the valve, which lead to a reduction in flow rate through the valve, and in a worst case, to a plugging of the entire valve / pipe line. In particular, when using a ball valve for taking out polymer powder from reactors or vessels, the ball can fill with powder in a closed position. The technical problem underlying the invention is thus to improve reliability and durability of a control valve in a polymer production plant.

[0007] This problem is solved by the invention according to the independent claims. Further preferred developments are described by the dependent claims.

[0008] The invention causes an additional movement of the control valve which enables cleaning of the latter from deposits caused, for example, by polymer particles / polymer powder included in the process.

[0009] The present invention provides a method for monitoring and controlling a function of a control valve of a polymer production plant. In particular, a plurality of control valves mounted at / on / in different components of the polymer production plant may be monitored and controlled by the provided method.

[0010] The polymer production plant may comprise, for example, at least one loop reactor, at least one gas phase reactor, at least one product receiver vessel at least one purge vessel and / or at least one surge vessel, the different components being interconnected by respective pipes / lines. The at least one loop reactor may comprise one or more loops, in particular a plurality of loops, in which a slurry is circulated. The gas phase reactor may preferably be a fluid bed reactor. Any other type of gas phase reactor is also possible.

[0011] According to an embodiment, the control valve may be mounted at an outlet of a loop reactor, a gas phase reactor, a product receiver vessel, a purge vessel and / or a surge vessel of the polymer production plant. In particular, one or more control valves may be mounted at an outlet of the reactors and / or vessels. Most preferably, the control valve may be an outlet control valve of a polymerization loop reactor or a polymerization gas phase reactor.

[0012] According to a further embodiment, the control valve may be a ball valve or a butterfly valve. Any other valve type appropriate to continuously control a flow rate in a polymer production plant may also be possible. Preferably, the control valve may be a ball valve. A flow rate through the control valve may be in a range of 0 t / h to 200 t / h.

[0013] According to another embodiment, the control valve may be a continuously movable valve. In particular, the control valve can be moved continuously from a fully closed to a fully open state and vice versa. A pneumatic, hydraulic and / or electrical actuator may be used to actuate the control valve. Preferably, the control valve may be equipped with an electric drive / electric motor configured to adjust an opening / closing position of the valve.

[0014] The control valve may be electrically connected to a control device / control system of the polymer production plant which may control a position of the valve. The control valve may have / may be connected to a dedicated control unit, e.g. a pressure and / or level controller, which may be connected to a general control device / control system of the entire polymer production plant. In particular, the control device / control system of the polymer production plant may provide a closed loop control for each reactor, with the control valves serving as manipulated variables. Alternatively or in addition, the control valve may be directly connected to the general control system and actuated via a manual input into an operating interface.

[0015] For performing a polymerization process, the at least one loop reactor may be fed, e.g., with one or more monomers, a diluent and a catalyst forming a slurry which may be circulated in the at least one loop reactor by an electric pump, for example. Preferably, olefin monomers, like ethylene and optionally one or more alpha-olefin comonomers may be polymerized in the at least one loop reactor in a hydrocarbon diluent such as propane or isobutane in the presence of a catalyst, and optionally in the presence of hydrogen.

[0016] The at least one loop reactor may be operated at a temperature in a range of 60°C to 95°C and a pressure in a range of 30 bar to 70 bar, for example. The slurry may be withdrawn from the at least one loop reactor via an outlet control valve arranged at the loop reactor or in a pipe / line downstream thereof. In particular, the slurry may be withdrawn at a bottom of the at least one loop reactor where a high concentration or polymer particles is present. A pipe / line in which the outlet control valve of the loop reactor is disposed may typically have a diameter of 2” to 5”, for example.

[0017] The slurry withdrawn from the at least one loop reactor may be conducted to the at least one gas phase reactor, which may in particular be a fluid bed reactor. In the latter, a fluidized bed consisting of polymer particles can be kept in a fluidized state by drawing gases from an upper part of the gas phase reactor and passing them into a lower part thereof, for example by means of a compressor.

[0018] A discharge rate of polymer powder withdrawn from the at least one gas phase reactor may be adjusted by an outlet control valve such that a constant bed level during polymerization is maintained. Furthermore, the at least one gas phase reactor may comprise at least one further control valve for adjusting a pressure therein. The at least one gas phase reactor may be operated at a pressure in a range of 7 bar to 25 bar and a temperature of 70°C to 95°C, for example.

[0019] The discharged polymer powder may be directed to a purge vessel for degassing and then via a surge vessel to a dry end of the polymer production plant. Both vessels may be equipped with at least one outlet control valve for adjusting a discharge rate of polymer powder withdrawn therefrom.

[0020] It becomes clear that the outlet control valves of the various components of the polymer production plant are exposed to different environmental conditions (pressure, temperature) and that polymers in different aggregate states flow through them.

[0021] The method according to the invention takes these different operating conditions into account and therefore allows undisturbed operation of the polymer production plant over an entire polymerization process.

[0022] In a first step of the method a condition of the control valve is determined.

[0023] A condition of the control valve may be understood as a functional condition / aging condition thereof and may represent a probability of an expected valve malfunction / failure or give an indication thereof. The condition of the control valve is determined based on an operation time and / or an operation parameter of the control valve. It is also possible that a plurality of operation parameters to which the control valve is exposed, such as pressure and temperature inside the control valve, flow rate through the control valve etc., are considered for determining its condition.

[0024] The determined condition is then compared with a threshold value for said condition, thereby providing an indication of a potential risk for malfunction of the control valve.

[0025] In terms of operation time, one or more predetermined time periods may be set as threshold value(s) for said condition of the control valve. For example, 200 hours of operation of the control valve may be a first threshold value, 500 hours of operation of the control valve may be a second threshold value and so on. In particular, operation time and operation parameter(s) during the operation time may be taken into account for determining the condition of the control valve.

[0026] Alternatively or in addition, a flow rate through the control valve may be measured, e.g., with a coriolis measurement device at a fully open position of the valve, and a threshold value of the control valve may be determined by comparing the measured flow rate with a rated flow rate of the control valve. For example, a first threshold value for the flow rate of the control valve may be set to 90% of the rated flow rate, and a second threshold value may be set to 70% of the rated flow rate.

[0027] If one or more of the conditions of the control valve have reached one of their threshold values, for example, if the operation time has reached or exceeded the first threshold for operating time, a potential risk for malfunction of the control valve is identified.

[0028] In this context, a probability of a potential malfunction / failure may be presumed / estimated. For example, if the control valve has been in operation for 200 hours (first threshold value for operation time) at 70 bar and 95°C, a higher failure probability (second failure probability) may be presumed than if it has been in operation for 200 hours at 30 bar and 60°C (first failure probability). If a potential risk for malfunction of the control valve is identified, a predetermined actuation signal is applied to the control valve in a further step of the method. Depending on the predetermined actuation signal, the control valve performs a specific movement thereby the potential risk for malfunction of the control valve is eliminated or at least reduced. A potential risk for malfunction / failure may be indicated depending on the presumed / estimated probability thereof.

[0029] According to an embodiment, the predetermined actuation signal may be selected from a plurality of predetermined actuation signals depending on the condition of the control valve. The plurality of predetermined actuation signals may be determined in advance at different conditions of one or more control valves and stored in the control device / control system of the polymer production plant.

[0030] For example, a first predetermined actuation signal may be applied to a control valve when the latter has exceeded a first threshold value where a first failure probability is presumed (e.g. after the control valve has been operated for 200 hours at 30 bar and 60°C). Likewise, a second actuation signal may be applied to a control valve when it has exceeded a second threshold value where a second failure probability is presumed (e.g. after the control valve has been operated for 200 hours at 70 bar and 95°C). Here, the first predetermined actuation signal may cause the control valve to move less than the second predetermined actuation signal, as the first failure probability is lower than the second due to the lower load on the control valve.

[0031] The terms “first” and “second” are merely used to differentiate one condition / failure probability, predetermined actuation signal, etc. from another and shall not limit the number of conditions / failure probabilities, predetermined actuation signals etc. to two.

[0032] According to an embodiment, the predetermined actuation signal may be selected from a plurality of predetermined actuation signals depending on a mounting position of the control valve.

[0033] A mounting position of the control valve shall be understood as a location of the control valve in the polymer production plant where the respective control valve is arranged. For example, a control valve mounted at an outlet of a loop reactor may have a smaller size than a control valve mounted at an outlet of a purge vessel which may result in different actuation signals being required.

[0034] It is also possible that the predetermined actuation signal is selected from a plurality of predetermined actuation signals depending on a type of the valve (ball valve or butterfly valve), in a case where different types of valves are used in the polymer production plant.

[0035] The plurality of predetermined actuation signals may be determined in advance using a plurality of control valves (of different types) arranged at different positions in the polymer production plant. The predetermined actuation signals are again stored in the control device / control system of the polymer production plant, from which they may be selected when a specific control valve is in a respective condition. In particular, each control valve mounted at an outlet of a reactor or a vessel may have one or more independent actuation signals including different sequences of control pulses / pulse patterns.

[0036] For example, the control valve for adjusting the slurry removed from the at least one loop reactor may be applied with a different actuation signal than the control valve for controlling the discharge rate of polymer powder removed from the at least one gas phase reactor. In this way, the different environmental conditions of the valves included in the polymer production plant can be taken into account.

[0037] In particular, a plurality of actuation signals for each control valve may be stored in the control device / control system of the polymer production plant for different conditions of a respective control valve. In other words, for each defined condition of a control valve (e.g., the first and second condition described above) a particular actuation signal having a sequence of control pulses may be stored.

[0038] According to an embodiment, the predetermined actuation signal may be characterized by a pulse height, a pulse width and a number of pulses. The pulse height can be used, for example, to set a position of a valve ball or a valve plate of the control valve. Furthermore, a slope of the pulse high may determine a velocity with which the valve ball / valve plate is actuated to reach a desired position. The pulse width can be used, e.g., to define a dwell time of the valve ball / valve plate at said position. It is also possible that the pulse height increases continuously over the pulse width so that the desired position of the valve is reached at an end of the pulse. The number of pulses determines as to how often the valve ball or the valve disc is brought into the position defined by the pulse height.

[0039] The respective actuation signal for each control valve may be selected automatically depending on a condition thereof. Alternatively or in addition, an operator may select an actuation signal for a particular control valve via an input panel of the control device / control system. It is also possible, that the operator defines a new actuation signal including a specific sequence of control pulses and applies it to a respective control valve via the input panel.

[0040] In this way, an automatic movement of each control valve is carried out when the latter reaches a specific condition. Furthermore, an operator can initiate a movement of a control valve by applying a sequence of control pulses to the valve. This manual operation may be used, e.g., when the automatically chosen actuation signal has not sufficiently cleaned the valve from deposits. The latter may be detected e.g. by determining a flow rate through the valve when it is fully opened.

[0041] According to an embodiment, the predetermined actuation signal may be applied to the control valve when a polymerization process, is stopped or interrupted. For example, the predetermined actuation signal may be applied to the control valve when a depressurization is carried out in the polymer production plant or a reactor thereof. This ensures that the polymerization process is not disturbed by the additional actuation signal of a control valve. However, it is also possible that an actuation signal of a small height not causing an opening is applied to a control valve. For example, a ball valve mounted at the surge vessel and being in a closed state may have accumulated an amount of polymer powder in its opening. In order to remove the powder from the control valve during the polymerization process, a sequence of short control pulses with a low height can be applied, which do not cause the control valve to open. In this way, the control valve can be moved very quickly through a small angle, allowing the powder to be conveyed out of the opening.

[0042] The implementation of a method according to the invention in form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this results in particularly low costs, especially if an executing control device / control system is still used for other tasks and is therefore available anyway. Finally, a machine-readable storage medium is provided with a computer programme stored thereon as described above. Suitable storage media or data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as hard discs, flash memories, EEPROMs, DVDs, etc. It is also possible to download a programme via computer networks (Internet, Intranet, etc.). Such a download can be wired or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0043] The present invention allows easy maintenance of a plurality of control valves when installed in a polymer production plant by applying an additional actuation signal to them, whereby deposits that have formed during the polymerization process can be removed from the control valves. In this way it is possible to use only one type of control valves, e.g. only ball valves, for different tasks / functions in the production plant, which reduces effort and costs.

[0044] Brief description of the figures

[0045] Fig. 1 shows schematically and exemplarily a polymer production plant including a plurality of control valves at which a method according to the invention may be implemented.

[0046] Figs. 2a and 2b show schematically an example of a control valve which can be used in the polymer production plant disclosed in Fig. 1.

[0047] Figs. 3a to 3c show three different sequences of control pulses each forming an actuation signal according to an example of the present invention. Fig. 4 shows the gas phase reactor of Fig. 1 having an outlet control valve at which a method according to the invention may be implemented.

[0048] Examples

[0049] In the following, examples of the present invention are described in detail with reference to exemplary figures. In the figures, identical elements are provided with identical reference signs, so that a repeated description of the elements is omitted unless this is necessary.

[0050] Fig. 1 shows schematically and exemplarily a polymer production plant including a plurality of control valves 10a to 10d at which a method according to the invention may be implemented. The depicted simplified example of a polymer production plant comprises a loop reactor 20, a gas phase reactor 30, a product receiver vessel 40 and a purge vessel 50 which are connected via a plurality of not further specified pipes / lines. The pipes / lines are indicated by arrows whose direction show a flow direction of polymerization products.

[0051] For performing a polymerization process, the loop reactor 20 may be fed, with one or more monomers, a diluent and a catalyst (indicated by three arrows directed to the loop reactor 20) forming a slurry which may be circulated in the loop reactor 20 by an electric pump (not depicted). Preferably, olefin monomers, like ethylene and optionally one or more alpha-olefin comonomers maybe polymerized in the loop reactor 20 in a hydrocarbon diluent such as propane or isobutane in the presence of a catalyst, and optionally in the presence of hydrogen.

[0052] The loop reactor 20 may be operated at a temperature in a range of 60°C to 95°C and a pressure in a range of 30 bar to 70 bar, for example. The slurry is withdrawn from the loop reactor 20 via an outlet control valve 10a arranged in a not further specified pipe / line downstream the loop reactor 20. The slurry is withdrawn at a bottom of the loop reactor 20 where a high concentration or polymer particles is present. The pipe / line downstream the loop reactor 20, in which the control valve 10a is disposed, may typically have a diameter of 2” to 5”, for example.

[0053] The slurry withdrawn from the loop reactor 20 is conducted to the gas phase reactor 30 which in the present case is designed as fluid bed reactor 30. In the latter, a fluidized bed consisting of polymer particles can be kept in a fluidized state by drawing gases from an upper part of the gas phase reactor 30 and passing them through a circulation gas line 31 with a filter 35 into a lower part thereof, for example by means of a compressor (not depicted).

[0054] A discharge rate of polymer powder withdrawn from the gas phase reactor 30 may be adjusted by another outlet control valve 10b such that a constant bed level during polymerization is maintained. Furthermore, the gas phase reactor comprises a control valve 1 1 for adjusting a pressure therein. The gas phase reactor 30 may be operated at a pressure in a range of 7 bar to 25 bar and a temperature of 70°C to 95°C, for example.

[0055] The discharged polymer powder is then directed to a product receiver vessel 40 for degassing (indicated by an arrow pointing out of the product receiver vessel 40) and then via a purge vessel 50 to a dry end of the polymer production plant (not depicted). Both vessels 40, 50 are equipped with an outlet control valve 10c, 10d for adjusting a discharge rate of polymer powder withdrawn therefrom. The pipes / lines downstream the product receiver vessel 40 and the purge vessel 50, in which the outlet control valves 10c, 10d are disposed, may typically have a diameter of 12”, for example.

[0056] Figs. 2a and 2b show schematically an example of a control valve 10 which can be used as outlet control valve 10a to 10d in the polymer production plant disclosed in Fig. 1. In the depicted case, the control valve 10 is designed as ball valve 10.

[0057] In particular, Fig. 2a shows the ball valve 10 in a fully open position (indicated by a long arrow extending through an opening 1 a of a ball 1 of the control valve 10) and Fig. 2b shows the ball valve 10 in a fully closed position (indicated by the short arrow limited by the ball 1 ). The control valve 10 comprises a valve body 2 in which the ball 1 is disposed for adjusting a flow rate through the valve 10. The valve body 2 is fluidly connected to a pipe / line 6 at two opposite sites. The ball 1 is sealed against the valve body 2 by two seals 4 and rotated by an electric motor 5 via a stem 3. In particular, the electric motor 5 may be configured to continuously rotate the ball 1 from a fully closed position to a fully open position of the valve 10 and vice versa. In other words, the electric motor 5 may rotate the ball 1 from a position in which it completely closes the opening 1 a and prevents a flow rate in the pipe / line 6 from passing through the valve 10, to a position in which the ball 1 aligns its opening 1 a towards the pipe / line 6 so that a maximum flow rate can pass through the valve 10. Any position of the ball 1 between the fully closed and the fully open position may be set by the electric motor 5. In this context, the electric motor 5 may be electrically connected to a control device / control system (not depicted) of the polymer production plant which may control a position of the valve 10 e.g. according to its respective function.

[0058] The control device / control system may further be configured to apply an additional predetermined actuation signal to the control valve 10, which causes the latter to carry out an additional movement in order to remove deposits from an inside of the valve body 2.

[0059] If the ball valve 10 is held in a stable position for a longer period of time, for example to provide a stable discharge rate of the polymer powder removed from the gas phase reactor 30 during the polymerization process, deposits may accumulate, for example between the seals 4 and the ball 1 or in a part of the opening 1 a facing an inner surface of the valve body 2, if the valve is not fully open. In this case, the predetermined actuation signal may be applied to the ball valve 10, which then moves its ball 1 in a specific way for removing the deposits from the valve 10.

[0060] The predetermined actuation signal may be determined in advance and stored in the control device / control system of the polymer production plant. For example, a plurality of predetermined actuation signals may be determined for each of the control valves 10a to 10d depicted in Fig. 1 , which are arranged at different locations in the polymer production plant. The plurality of predetermined actuation signals may be determined at different conditions of the outlet control valves 10 a to 10d. Each actuation signal may comprise a sequence of control pulses / pulse pattern which may vary according to a location and a condition of the outlet control valves 10a to 10d.

[0061] For example, the outlet control valve 10a for adjusting the slurry removed from the loop reactor 20 may be applied with a different pulse pattern than the outlet control valve 10b for controlling the discharge flow of polymer powder removed from the gas phase reactor 30. In this way, the different environmental conditions of the outlet control valves 10a to 10d included in the polymer production plant can be taken into account.

[0062] A predetermined actuation signal for a particular outlet control valve 10a to 10d of the polymer production plant may then be selected depending on its condition. A condition of an outlet control valve 10a to 10d may be understood as a functional condition / aging condition thereof and may represent a probability of an expected valve malfunction / failure or give an indication thereof.

[0063] The respective actuation signal for each outlet control valve 10a to 10d may be selected automatically by the control device / control system of the polymer production plant. Alternatively or in addition, an operator (not depicted) may select an actuation signal for a particular outlet control valve 10a to 10d via an input panel (not depicted) of the control device / control system. It is also possible that the operator defines a new actuation signal including a specific sequence of control pulses and applies it to a respective outlet control valve 10a to 10d via the input panel.

[0064] In particular, the predetermined actuation signal may be applied to an outlet control valve 10a to 10d when the polymerization process is stopped or interrupted. For example, the actuation signal may be applied to the respective outlet control valve 10a to 10d when a depressurization is carried out in the polymer production plant or a reactor 20, 30 thereof. This ensures that the polymerization process is not disturbed by the additional actuation signal applied to the outlet control valve 10a to 10d.

[0065] However, the ball valve 10 depicted in Fig. 2 may also be designed in such a way that between an end position of the stem 3 rotated by the electric motor 5 and a position in which the ball 1 begins to release the opening 1 a, there is a dead travel by which the ball 1 can be moved without any effects on the polymerization process. This means, for example, that during a polymerization process the ball 1 may be repeatedly rotated through a small angle corresponding to the dead travel, to generate a plurality of impulses which may cause the polymer powder accumulated in the opening 1 a of the ball 1 to be removed therefrom. This makes it possible to move the ball valve 10 for removing deposits thereon even while the polymer production plant is in operation.

[0066] Figs. 3a to 3c show three different sequences of control pulses 300, 301 302, each forming an actuation signal 300, 301 , 302 according to an example of the present invention. The depicted actuation signals 300, 301 , 302 may be applied to the ball valve 10 depicted in Fig. 2, which in turn can be used as outlet control valve 10a to 10d in the polymer production plant shown in Fig. 1. In particular, the actuation signals 300, 301 , 302 may be used for operating the electric motor 5 of the ball valve 10.

[0067] In the present case, the electric motor 5 may rotate the ball 1 via the stem 3 about 90° to fully open the valve 10. A position of the ball 1 may be a function of a height hA_v of a control pulse 300, 301 302. When a control pulse 300, 301 302 is switched off, the ball 1 may rotate back to the closed position of the valve 10.

[0068] Each of the depicted actuation signals 300, 301 , 302, is characterized by a pulse height hA_v, a pulse width (time period) AtA_v and a number of pulses. The maximum pulse height hA_vmax is set to 100%, whereby the ball 1 may be rotated by 90° so that an area of its opening may be fully released.

[0069] The actuation signal 300 depicted in Fig. 3a comprises two control pulses 300a, 300b, both of which reach a pulse height hA_v of 50%, which may correspond to a rotation angle of the ball 1 of 45°. In this position, the ball 1 may, for example, release half of the area of its opening 1 a. The 50% pulse height hA_v is reached during a time period AtA_v. A pause Atp is defined between the two control pulses 300a, 300b, during which the ball 1 is in the closed state. In the present case, the pause Atp is shorter than the duration of each pulse 300a, 300b. The actuation signal 301 depicted in Fig. 3b also comprises two control pulses 301 a, 301 b, a first control pulse 301 a having a pulse height hA_v of 50% and a second control pulse 301 b having a pulse height hA_v of 100%. The 50% pulse height hA_v is again reached during the time period AtA_v and the 100% pulse height hA_v is reached during a time period of 2AtA_v. This means that a velocity with which the ball 1 is rotated is constant for both control pulses 301 a, 301 b.

[0070] The actuation signals 300 and 301 may be applied to the ball valve 10 when the polymerization process in the polymer production plant or in a reactor 20, 30 thereof is stopped or interrupted, as the actuation signals 300, 301 would cause a half or full opening of the valve 10 and thus lead to an undesired flow rate during the polymerization process.

[0071] The actuation signal 302 depicted in Fig. 3b comprises a plurality of small control pulses 302a to 306o, more precisely fifteen control pulses 302a to 306o having a pulse height hA_v of 10% and a pulse width of 1 / 5 AtA. The low pulse height hA_v may result in a small rotation angle which may not release the opening 1 a of the ball 1 . Thus, the actuation signal 302 may be applied to the ball valve 10 during operation of the polymer production plant.

[0072] Fig. 4 shows the gas phase reactor 30 of Fig. 1 having an outlet control valve 10b, at which a method according to the invention may be implemented.

[0073] The structure of the gas phase reactor 30 is equal to that shown in Fig. 1 , wherein means for adjusting the control valve 11 regulating the pressure in the gas phase reactor 30 are additionally depicted. In particular, a flow rate of gas withdrawn from the gas phase reactor 30 and directed to a flare (not depicted) is controlled by a two different flow controllers 100a, 100b, for example, one determining a volumetric flow rate and the other determining a mass flow rate of the gas. A stilling volume 210 is arranged between a not further specified pipe / line through which the gas is directed to the flare and the flow controllers 100a, 100b, which allows for determining an averaged flow rate. In a calculation element 101 , a minimum is selected from the determined flow rates, based on which the control valve 11 is regulated. For depressurizing the gas phase reactor 30 a gas flow to the flare may be controlled to a value of 120 t / h by the two flow controllers 100a, 100b. The value may vary depending on the specific design of the polymer production plant. During or after the depressurizing of the gas phase reactor 30 a predetermined actuation signal, such as those shown in Figs. 3a and 3b may be applied to the outlet control valve 10b. In this way the outlet control valve 10b can be moved for removing deposits thereon without disturbing the polymerization process.

Claims

Claims1. A method for monitoring and controlling a function of a control valve (10, 10a to 10d) of a polymer production plant, comprising the steps:- determining a condition of the control valve (10, 10a to 10d);- comparing the determined condition with a threshold value for said condition thereby providing an indication of a potential risk for malfunction of the control valve (10, 10a to 10d), and if a potential risk for malfunction is identified,- applying a predetermined actuation signal (300, 301 , 302) to the control valve (10, 10a to 10d), thereby eliminating or reducing the potential risk for malfunction of the control valve (10, 10a to 10d), wherein the condition of the control valve (10, 10a to 10d) is determined based on an operation time and / or an operation parameter thereof.

2. The method according to claim 1 , wherein the predetermined actuation signal (300, 301 , 302) is selected from a plurality of predetermined actuation signals (300, 301 , 302) depending on a mounting position of the control valve (10, 10a to 10d).

3. The method according to claim 1 or 2, wherein the predetermined actuation signal (300, 301 , 302) is selected from a plurality of predetermined actuation signals (300, 301 , 302) depending on the condition of the control valve (10, 10a to 10d).

4. The method according to any one of the preceding claims, wherein the predetermined actuation signal (300, 301 , 302) is characterized by a pulse height (hA_v), a pulse width (AtA_v) and a number of pulses.

5. The method according to any one of the preceding claims, wherein the predetermined actuation signal (300, 301 , 302) is applied to the control valve (10, 10a to 10d) when a production process is stopped or interrupted.

6. The method according to any one of the preceding claims, wherein the control valve (10, 10a to 10d) is a continuously movable valve.

7. The method according to any one of the preceding claims, wherein the control valve (10, 10a to 10d) is a ball valve (10) or a butterfly valve.

8. The method according to any one of the preceding claims, wherein the control valve (10, 10a to 10d) is mounted at an outlet of a reactor (20, 30), a purge vessel (50), a surge vessel, and / or a product receiver vessel (40) of the polymer production plant.

9. The method according to any one of the preceding claims, wherein the control valve (10, 10a to 10d) is an outlet control valve (10a, 10b) of a polymerization loop reactor (20) or a polymerization gas phase reactor (30).

10. A data processing device comprising a processor configured to perform all steps of a method according to any one of the preceding claims.

11. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out all steps of a method according to any one of the claims 1 to 9.

12. A computer-readable data carrier having stored thereon the computer program product of claim 11 .

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