Method, device and computer program for monitoring and controlling a concentrator device

Abstract

The present invention relates to a method for monitoring and controlling a concentrator device of a polymer production plant as well as a device and a computer program for implementing the method. The method comprises the steps of setting a threshold for a solids concentration of a slurry flowing through the bottom outlet (15) of the concentrator device (1) to prevent a plugging of the bottom outlet (15); determining the solids concentration of the slurry at the bottom outlet (15) of the concentrator device (1 ); adjusting a mass flow of the slurry flowing through the top outlet (20) of the concentrator device (1) to control the solids concentration of the slurry at the bottom outlet (15) based on the set threshold.

Description

[0001] Method, device and computer program for monitoring and controlling a concentrator device

[0002] The present invention relates to a method for monitoring and controlling a concentrator device 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 using the BORSTAR process as polymer production process, a concentrator device, in particular a hydrocyclone can be used to increase the solids concentration of slurry discharged from a loop reactor high above maximum solids concentration of the loop reactor . This reduces the loading of the heated product line and recovery system, leading to energy and cost savings.

[0005] The hydrocyclone may be fed with slurry downstream of a circulation pump in the loop reactor. A slurry or suspension is a heterogeneous mixture of solid particles dispersed in a liquid phase. The solid particles are usually solid polymer particles obtained by the polymerization process. The fluid phase usually comprises unreacted alpha-olefin monomer(s), and optionally a diluent, in particular a hydrocarbon diluent.

[0006] Inside the hydrocyclone the solid polymer particles are exposed to centrifugal forces and concentrated at the bottom thereof. A part of the hydrocyclone’s bottom flow (underflow) can be directed to the loop reactor’s continuous outlet and discharged to the product line, for example to a subsequent gas phase reactor. The remaining bottom flow as well as a top flow (overflow) of the hydrocyclone can be returned to the suction side of the circulation pump in the loop reactor.

[0007] In US 2010 / 121002 A1 an olefin polymerisation process is disclosed in which a slurry of olefin polymer is produced within a polymerisation zone, and a polymer slurry stream is withdrawn from the polymerisation zone and passed through a transfer line to a centrifugal concentrating device, which separates it into a solids-lean stream or streams each having a solids concentration less than that of the polymer slurry stream entering the concentrating device and a solids-rich stream or streams each having a solids concentration greater than that of the polymer slurry stream entering the concentrating device, wherein at least part of the solids-rich stream or streams is recycled back into the polymer slurry stream upstream of the concentrating device and downstream of the polymerisation zone.

[0008] US 2008 / 039597 A1 discloses a process and an apparatus for continuous polymerisation olefin monomers like ethylene and other monomers, wherein an olefin monomer is polymerised in slurry phase in an inert hydrocarbon diluent in at least one loop reactor. A polymer slurry is continuously withdrawn from the loop reactor and concentrated. The concentrated slurry is conducted to a flash unit in order to remove the remaining fluid phase, and gas obtained is compressed in a flash gas compressor before it is being fed to a distillation section.

[0009] However, too high concentration of solid particles at the bottom of the hydrocyclone can lead to immediate plugging of the pipe / line connected thereto and the hydrocyclone itself.

[0010] The technical problem underlying the invention is thus to improve reliability and durability of a concentrator device in a polymer production plant.

[0011] This problem is solved by the invention according to the independent claims. Further preferred developments are described by the dependent claims.

[0012] Disclosure of the invention

[0013] The present invention provides a method for monitoring and controlling a concentrator device of a polymer production plant, the concentrator device including an inlet, a top outlet and a bottom outlet.

[0014] The polymer production plant may in particular use the BORSTAR process as polymer production process / polymerization process.

[0015] The BORSTAR process, in which loop and gas phase reactors are coupled, is described, e.g., in WO 98 / 58975 A1 dealing with a preparation of propylene homopolymers and copolymers, which comprises polymerizing propylene optionally with comonomers in the presence of a catalyst at elevated temperature and pressure in at least one loop reactor and at least one gas phase reactor.

[0016] In the present case, a concentrator device is connected to a loop reactor used in the BORSTAR process, wherein the concentrator device may preferably be a hydrocyclone.

[0017] A hydrocyclone is a device to classify, separate or sort particles in a liquid suspension or slurry based on the ratio of their centripetal force to fluid resistance. This ratio is high for dense (where separation by density is required) and coarse (where separation by size is required) particles, and low for light and fine particles. Hydrocyclones also find application in the separation of liquids of different densities. A hydrocyclone may have a cylindrical section at the top where liquid suspension or slurry is being fed tangentially, and a conical base. The angle, and hence length of the conical section, plays a role in determining operating characteristics of a hydrocyclone. A use of a hydrocyclone in a polymerization process is described in WO 2017 / 097577 A1 , for example.

[0018] The inlet of the hydrocyclone may be connected to the loop reactor at a position downstream of a circulation pump. At this position, slurry can be continuously removed from the loop reactor and fed into the inlet of the hydrocyclone, where the concentration of the slurry takes place by effect of centrifugal forces. The hydrocyclone may divide the slurry flow into two streams, namely into an overflow, which is rich in liquid and mainly consists of hydrocarbon diluent separated from the slurry, and an underflow, which is rich in polymer and has a high concentration of solid particles.

[0019] The overflow may be recycled to the loop reactor via a top outlet of the hydrocyclone and the underflow may be withdrawn from the hydrocyclone via its bottom outlet. A part of the underflow can be fed into a production line of the polymer production plant and another part can be fed back into the loop reactor.

[0020] The method according to the invention enables to avoid a plugging of the hydrocyclone’s bottom outlet by adjusting / controlling the particle concentration / solids concentration at this position. In a first step of the method according to the invention, a threshold for a solids concentration of a slurry flowing through the bottom outlet of the concentrator device (underflow) is set to prevent a plugging thereof. The maximum solids concentration of the underflow is set by the limit of stable operation. If the solids concentration of the slurry is too high, the risk of plugging the underflow increases.

[0021] The threshold may be determined in advance, for example, by varying the solids concentration and determining a concentration at which the bottom outlet becomes blocked. Measuring devices and methods for determining the solids concentration are described below.

[0022] The threshold for the solids concentration of the underflow can be set to a value that corresponds to the concentration at which the bottom outlet is plugged. Alternatively, the threshold can be set to a value that is a predetermined amount lower than the solids concentration at plugging. For example, a threshold for the solids concentration of the underflow may be set to 55% - 62 % by volume.

[0023] The determined threshold may be set / stored, e.g., in a control device of the concentrator device. This control device may be a separate control unit or may be implemented in a general control device / control system of the polymer production plant. Any other controller suitable to control the concentrator device may also be used.

[0024] When the threshold is set, the solids concentration at the bottom outlet of the concentration device (solids concentration of the underflow) is determined.

[0025] To enable a concentration to be determined, the following steps may be carried out beforehand:

[0026] - feeding a slurry into the concentrator device via its inlet;

[0027] - withdrawing a first mass flow of the slurry (overflow) rich in liquid from the top outlet of the concentrator device,

[0028] - withdrawing a second mass flow of the slurry (underflow) rich in solids from the bottom outlet of the concentrator device. The solids concentration of the slurry and / or a parameter that correlates with the solids concentration is measured at the bottom outlet of the concentrator device. The solids concentration and / or a correlating parameter of the underflow are continuously measured during the polymer production process. The determined solids concentration is transmitted to the control device of the concentrator device.

[0029] To control the solids concentration at the bottom outlet of the concentrator device based on the set threshold, the first mass flow of the slurry flowing through the top outlet of the concentrator device (overflow) is adjusted such that the solids concentration of the underflow does not exceed the threshold. Alternatively or in addition, a ratio of the overflow to the underflow may be adjusted to keep the solids concentration of the underflow below the threshold. The respective adjustment may be carried out, e.g. by the control device of the concentrator device based on the determined solids concentration of the underflow. Adjusting the overflow shall mean that the entire first mass flow through the top outlet of the concentrator device having a liquid and solid content is adjusted.

[0030] The solids concentration of the overflow may be about 0 (or at least 0.001 ) to 5 % by volume. Thus, the solids concentration of the underflow can be increased by increasing the overflow and decreased by reducing the overflow. In other words, the overflow serves as manipulated value to adjust the solids concentration of the underflow to a value not exceeding the threshold.

[0031] The solids concentration of the slurry at the bottom outlet of the concentrator device is controlled to a target value which is less than or equal to the threshold. The target value is a value to which the solids concentration of the underflow is controlled in a closed loop control. The closed loop control is performed by the control device of the concentrator device.

[0032] In particular, the target value may be determined based on operating conditions of the polymer production plant. The operating conditions of the polymer production plant may depend on a type of polymer to be produced and may be, for example, feedstock of polymerization, composition of the slurry, temperature, pressure and / or flow rate in different reactors of the polymer production plant, in particular in the loop reactor to which the concentrator device is connected.

[0033] Depending on these operating parameters a risk for plugging at the bottom outlet of the concentrator device may vary so that different target values may be determined, e.g., for different types of polymers to be produced, that may be stored in the control device of the concentrator device. For example, the target values of the solids concentration of the underflow may be in a range of 50% to 60% by volume.

[0034] The solids concentration is determined from density measurements performed on the slurry. The density of the slurry is measured by a radioactive measuring device. It is also possible to measure the density of the slurry with a coriolis measuring device.

[0035] A radioactive measuring device / radiometric measurement may comprise a source that emits y-radiation, produced from a nuclear radioisotope, a vessel or container with process material under investigation, and a detector capable of detecting y-radiation. If there is no or little material in the pathway of the radiation beam, the radiation intensity will remain strong. If there is material in the pathway of the beam, its strength will be attenuated. The amount of radiation detected by the detector can be used to calculate the desired process value, such as density and mass flow.

[0036] A suitable radioactive measuring device for density measurements performed on the slurry in the concentrator device may be, for example, SENSseries LB 480 D distributed by Berthold Technologies GmbH.

[0037] A coriolis measuring device / coriolis mass flow meter measures mass through inertia. A liquid or gas flows through a tube which is being vibrated by a small actuator. This artificially introduces a coriolis acceleration into the flowing stream, which produces a measurable twisting force on the tube resulting in a phase shift. This twisting force is proportional to the mass and the meter measures mass flow by detecting the resulting angular momentum. Usually, the tube is anchored at two points and vibrated between these anchors. This configuration can be envisioned as vibrating a spring and mass assembly. Once placed in motion, a spring and mass assembly will vibrate at its resonant frequency, which is a function of the mass of that assembly. Since mass of the fluid is its density multiplied by its volume, the frequency of vibration can be also related to the density of the process fluid.

[0038] A suitable coriolis measuring device for density measurements performed on the slurry in the concentrator device may be, for example, Micro Motion (e.g. Elite Coriolis meter) distributed by Emerson Process Management. However, a radioactive measuring device is preferred for the density measurements described herein.

[0039] The solids concentration can be calculated from the measured density of the slurry according to formula (1 ) given in WO 2017 / 097577 A1. It is also possible for the radioactive measuring device and / or the coriolis measuring device to provide a value for the solids concentration directly.

[0040] According to an embodiment, the solids concentration of the slurry at the bottom outlet of the concentrator device may be controlled by determining a separation efficiency of the concentrator device. In particular, the target value to which the solids concentration is controlled may be determined as a tradeoff between maximum separation efficiency of the concentrator device and avoidance of plugging therein. For example, if a determined separation efficiency of the concentrator device falls below 95%, the target value of the solids concentration may be reduced e.g. within the above described range of 50% to 60% by volume. In this way, a stable production process can be maintained without compromising production efficiency.

[0041] The separation efficiency of the concentrator device may be determined, for example according to formula (2) of WO 2017 / 097577 A1 , as a ratio of a solids flowrate in the underflow to a solids flow rate in an inlet flow of the concentrator device. The solids flowrates of the inlet flow and the underflow may be determined, for example, by determining the respective mass flows with a coriolis measurement device and the respective solids concentration by a radioactive measuring device as described above.

[0042] According to an embodiment, the first mass flow of the slurry flowing though the top outlet (overflow) may be adjusted by a control valve. The control valve may be electrically connected, e.g., to the control device of the concentrator device which may automatically control a position of the control valve depending on the solids concentration of the underflow. For example, the control valve may receive a drive signal from the control device of the concentrator device, depending on a difference between the target value of the solids concentration of the underflow and the determined / measured solids concentration therein. By means of the drive signal a flow rate through the control valve may be adjusted for achieving the target value of the solids concentration of the underflow.

[0043] Additionally, the overflow may be measured, for example, by a coriolis measuring device as described above, so that the overflow through the control valve can also be controlled to a required value to achieve the target value of the solids concentration in the underflow. This subordinate control can improve the adjustment of the solids concentration of the underflow. Moreover, a solids concentration of the overflow may be determined by the coriolis measuring device and or a radioactive device, to gain additional information about the manipulated value for controlling the solids concentration of the underflow.

[0044] The control valve may be a continuously movable valve. In particular, the control valve may 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. The control valve may be a ball valve or a butterfly valve, for example.

[0045] According to an embodiment, the first mass flow of the slurry flowing though the top outlet (overflow) may be adjusted by an operator. For example, the operator may adjust the control valve via a manual input into an operating interface of the control device of the concentrator device. Alternatively or in addition, the control valve may allow a manual adjustment of the ball or the plate, e.g., via a square using a tool spanner. It is also possible, that the concentrator device has a bypass to the control valve adjusting the overflow, in which a manual valve (ball valve, gate valve, etc.) is arranged, which can be adjusted directly by the operator. To provide a feedback of the manual adjustment of the overflow to the operator, the control device of the of the concentrator device may include a display on which the determined solids concentration of the underflow is shown. According to an embodiment, the solids concentration of the slurry at the bottom outlet of the concentrator device may be controlled based on a solids concentration of the slurry at the inlet of the concentrator device (inlet flow).

[0046] In this case, the solids concentration of the inlet flow may also be determined, for example, using a radioactive measuring device and / or a coriolis measuring device as described above. In this context, a mass flow of the slurry entering the concentrator device (inlet flow) may also be measured by the radioactive measuring device and / or the coriolis measuring device. The inlet flow may have a solids concentration of 40% to 45% by volume, for example.

[0047] If the solids concentration of the inlet flow into the concentrator device is high, a risk for a potential plugging in the bottom outlet is increased. Therefore, less overflow may be drawn from the concentrator device to increase the diluent therein. Knowing the solids concentration of the inlet flow can improve an estimation of a potential plugging at the bottom outlet of the concentrator device, as it represents a further parameter that influences the solids concentration of the underflow. Therefore, it may be advantageous to control a ratio of solids concentration of the inlet flow to the solids concentration of the underflow.

[0048] 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.). Brief description of the figures

[0049] Fig. 1 shows schematically a configuration of a concentrator device designed as a hydrocyclone at which a method according to an embodiment of the invention may be performed.

[0050] Fig. 2 shows schematically another configuration of the concentrator device depicted in Fig. 1 at which a method according to another embodiment of the invention may be performed.

[0051] Examples

[0052] 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.

[0053] Fig. 1 shows schematically a configuration of a concentrator device 1 designed as a hydrocyclone 1 at which a method according to an embodiment of the invention may be performed.

[0054] The depicted the hydrocyclone 1 comprises an inlet 10, a top outlet 20 and a bottom outlet 15. The inlet 10 of the hydrocyclone 1 is connected to a loop reactor 2 at a position downstream of a circulation pump 2a. At this position, slurry circulating in the loop reactor 2 (indicated by a curved arrow) can be continuously removed therefrom and fed into the inlet 10 of the hydrocyclone 1 , where the concentration of the slurry takes place by effect of centrifugal forces. The hydrocyclone 1 divides the slurry flow into two streams, namely into an overflow (first mass flow), which is rich in liquid and mainly consists of hydrocarbon diluent separated from the slurry, and an underflow (second mass flow), which is rich in polymer and has a high concentration of solid particles.

[0055] The overflow may be recycled to the loop reactor 2 via the top outlet 20 of the hydrocyclone 1 and the underflow may be withdrawn from the hydrocyclone 1 via its bottom outlet 15. A part of the underflow is fed into a production line of a polymer production plant (not depicted) via a pipe / line 30 and another part is fed back into the loop reactor 2 via a further pipe / line 25. T o adjust an amount of overflow fed back to the loop reactor 2, a control valve 20a is arranged at the top outlet 20 of the hydrocyclone 1. A further control valve 30a is arranged in the pipe / line 30, to adjust an amount of underflow fed into the production line.

[0056] The control valves 20a, 30a may be continuously movable valves. In particular, the control valves 20a, 30a may be moved continuously from a fully closed to a fully open state and vice versa. Each control valve 20a, 30a may have pneumatic, hydraulic and / or electrical actuator. Preferably, the control valves 20a, 30a may be equipped with an electric drive / electric motor configured to adjust their opening / closing positions. The control valves 20a, 30a may be ball valves or butterfly valves, for example.

[0057] Furthermore a density measuring device 3a is disposed at the bottom outlet 15 of the hydrocyclone 1 , which may be radioactive measuring device 3a or a coriolis measuring device 3a.

[0058] To avoid a plugging of the hydrocyclone’s bottom outlet 15 a particle concentration / solids concentration is adjusted / controlled at this position. For this purpose, a threshold for a solids concentration of the slurry flowing through the bottom outlet 15 of the hydrocyclone 1 is set to prevent a plugging thereof. The threshold may be determined in advance, for example, by varying the solids concentration of the underflow and determining a concentration at which the bottom outlet 15 becomes blocked. The determined threshold may be stored in a control device (not depicted) of the hydrocyclone 1 .

[0059] When the threshold is set, the solids concentration at the bottom outlet 15 of the hydrocyclone 1 is determined. In the depicted example the solids concentration is determined based on a density of the second mass flow of the slurry flowing through the bottom outlet 15 (underflow) which is measured by the density measuring device 3a. It is also possible that the density measuring device 3a outputs the solids concentration of the underflow directly. The determined solids concentration may then be transmitted to the control device of the hydrocyclone 1. To control the solids concentration at the bottom outlet 15 of the hydrocyclone 1 , the first mass flow of the slurry flowing through the top outlet 20 of the hydrocyclone 1 (overflow) is adjusted such that the solids concentration of the underflow does not exceed the threshold. The solids concentration of the underflow can be increased by increasing the overflow and decreased by reducing the overflow.

[0060] In particular, the solids concentration of the underflow is controlled to a target value which may be less than or equal to the threshold. The target value may be a value to which the solids concentration of the underflow is controlled in a closed loop control by the control device of the hydrocyclone 1. It may be determined as a tradeoff between maximum separation efficiency of the hydrocyclone 1 and avoidance of plugging therein.

[0061] The first mass flow of the slurry flowing though the top outlet 20 is adjusted by the control valve 20a to bring the solids concentration of the underflow to the target value. The control valve 20a may be electrically connected to the control device of the hydrocyclone 1 which may automatically control a position of the control valve 20a depending on the solids concentration of the underflow. For example, the control valve 20a may receive a drive signal from the control device of the hydrocyclone 1 , depending on a difference between the target value of the solids concentration of the underflow and the determined / measured solids concentration therein. By means of the drive signal a flow rate through the control valve 20a may be adjusted for achieving the target value of the solids concentration of the underflow.

[0062] Fig. 2 shows schematically another configuration of the hydrocyclone 1 depicted in Fig. 1 at which a method according to another embodiment of the invention may be performed.

[0063] The configuration depicted in Fig. 2 differs from that in Fig. 1 only in that two further measuring devices 3b, 3c are included therein, which are arranged at the inlet 10 and the top outlet 20 of the hydrocyclone 1. The measuring devices 3b, 3c may be radioactive measuring devices and / or coriolis measuring devices being able to measure a mass flow and a density / solids concentration of the slurry entering / exiting the hydrocyclone 1 The measuring device 3b at the inlet 10 allows for considering a solids concentration of the inlet flow when adjusting the overflow by the control valve 20a, in order to bring the solids concentration of the underflow to the target value. If the solids concentration of the inlet flow is high, a risk for a potential plugging in the bottom outlet 15 of the hydrocyclone 1 is increased.

[0064] Therefore, less overflow may be drawn from the hydrocyclone 1 in this case to increase the diluent therein.

[0065] The measuring device 3a arranged at the top outlet 20 of the hydrocyclone 1 can be used for determining a mass flow and a solids concentration of the overflow, which means that the overflow through the control valve 20a can also be controlled to a required value to achieve the target value of the solids concentration in the underflow. This subordinate control can improve the adjustment of the solids concentration of the underflow.

[0066] Summarizing the above, it becomes clear from the described examples that the claimed method is apt to improve a reliability and durability of a concentrator device in a polymer production plant by monitoring and controlling a solids concentration of a mass flow through a bottom outlet thereof.

Claims

Claims1 . A method for monitoring and controlling a concentrator device (1 ) of a polymer production plant, the concentrator device (1 ) including an inlet (10), a top outlet (20) and a bottom outlet (15), the method comprising the steps of:- setting a threshold for a solids concentration of a slurry flowing through the bottom outlet (15) of the concentrator device (1 ) to prevent a plugging of the bottom outlet (15);- determining the solids concentration of the slurry at the bottom outlet (15) of the concentrator device (1 );- adjusting a mass flow of the slurry flowing through the top outlet (20) of the concentrator device (1 ) to control the solids concentration of the slurry at the bottom outlet (15) based on the set threshold, wherein. the density of the slurry is continuously measured at the bottom outlet (15) of the concentrator device (1 ) using a radioactive measuring device (3a, 3b, 3c) to determine the solids concentration, and the determined solids concentration is transmitted to a control device of the concentrator device (1 ), and wherein- the solids concentration of the slurry at the bottom outlet (15) of the concentrator device (1 ) is controlled in a closed loop control by the control device to a target value which is less than or equal to the threshold.

2. The method according to claim 1 , wherein the solids concentration of the slurry at the bottom outlet (15) of the concentrator device (1 ) is controlled based on a solids concentration of the slurry at the inlet (10) of the concentrator device (1 ).

3. The method according to claim 1 or 2, wherein the solids concentration of the slurry at the bottom outlet (15) of the concentrator device (1 ) is controlled by determining a separation efficiency of the concentrator device (1 ).

4. The method according to any one of the preceding claims, wherein the mass flow of the slurry flowing though the top outlet (20) is adjusted by a control valve (20a).

5. The method according to any one of the preceding claims, wherein the mass flow of the slurry flowing though the top outlet (20) is adjusted by an operator.

6. The method according to claim 1 , wherein the target value is determined based on operating conditions of the polymer production plant.

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

8. 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 6.

9. A computer-readable data carrier having stored thereon the computer program product of claim 8.

Images