Improved system and method for olefin polymerization

Abstract

The present application provides for improved systems and processes for olefin polymerisation, particularly wherein the slurry is conveyed from a reactor vessel to a product recovery system by at least one slurry withdrawal lines, particularly a plurality of slurry withdrawal lines, wherein a mass flow meter, particularly a single straight tube Coriolis type mass flow meter is provided on each of the at least one or plurality of slurry withdrawal lines, and particularly positioned upstream of the discharge valve, particularly the continuous take off (CTO) valve, of each individual flash line. Additionally, the position of the valve of each flash line of the plurality of flash lines is individually adjusted based on the mass flow and / or the slurry density measured by the (mass) flow meter of that individual flash line. Additionally, the heating of the flash line may be individually controlled based on the flow of the slurry measured by the flow meter of that individual flash line, and the temperature measured at the end of the flash line. Additionally, the transfer of preferably a diluent, and / or, optionally, a monomer and / or a catalyst to the reactor vessel is adjusted based on the slurry density measured by the mass flow meter.

Description

[0001] IMPROVED SYSTEM AND METHOD FOR OLEFIN POLYMERIZATION

[0002] FIELD

[0003] The present application is related to the field of olefin polymerization.

[0004] BACKGROUND

[0005] Polyolefins, such as polyethylene (PE) and polypropylene (PP) or copolymers thereof, are synthesized by polymerizing monomers, such as ethylene (CH2=CH2) and propylene (CH3CH=CH2). Because polyolefins are cheap, safe, stable to most environments and easy to be processed, they are useful in many applications and are available in multiple types with different properties and characteristics. For instance, PE can be classified into several types, such as but, not limited to, Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE), and High Density Polyethylene (HDPE). PP types include atactic polypropylene (aPP), syndiotactic polypropylene (sPP) and isotactic polypropylene (iPP).

[0006] Olefin polymerizations are frequently carried out under slurry conditions, with the produced polymer usually in a form of solid particles suspended in liquid medium. The liquid medium typically comprises unreacted monomer and, optionally, a reaction diluent, which is typically an inert hydrocarbon solvent. The polymerization reaction is often performed in a loop reactor or stirred tank reactor, using a monomer (such as ethylene or propylene), a catalyst, and optionally one or more of a diluent, an activating agent, one or more co-monomer(s), and hydrogen. Each of these components is typically provided to the reactor vessel by a feed system. For instance, in a loop reactor, the slurry is circulated continuously in the reactor with a pump to maintain efficient suspension of the polymer solid particles in the liquid medium. The slurry density is typically monitored via a nuclear (radioactive) densimeter, wherein the amount of radiation measured by the detector is dependent upon the shielding by the slurry in the pipe. The polymer slurry is typically discharged from the reactor via multiple outlets, through heated flash lines to a flash vessel or another unit or type of product recovery system, where most of the (optional) diluent and unreacted monomers are flashed off and recycled. Optionally, the product slurry may be fed to a second reactor, such as a second loop reactor, serially connected to the first reactor, such as a first loop reactor, wherein a second polymer fraction may be produced. Typically, when two reactors in series are employed in this manner, the resultant polymer product is a bimodal polymer product, which comprises a first polymer fraction produced in the first reactor and a second polymer fraction produced in the second reactor, and has a bimodal molecular weight distribution.After the polymer product is collected from the reactor and the hydrocarbon residues are removed, the polymer product is dried, additives can be added and finally the polymer may be mixed and pelletized.

[0007] The discharge of the slurry from the reactor, particularly into heated flash lines, is typically performed via multiple slurry discharge lines, each comprising a discharge valve, but which are controlled together. The continuous or discontinuous discharge flow control by the discharge valves is important for controlling the reactor pressure. The heated flash lines are typically equipped with a pressure transmitter just at the outlet of the discharge valve, such as a continuous take off valve or CTO valve, to monitor the correct functioning of the lines, and to detect possible blocking of the valve and fouling of the flash line. However, this method is not very reliable and precise. If the flow in the flash lines is too low or too high, the slurry going through the flash lines may not be heated sufficiently or may be overheated, respectively.

[0008] In addition, the density of the polymer slurry in the reactor is an important parameter of the olefin polymerization process. The slurry density is used as a measure for the amount of polymer inside the reactor. A higher solid content implies longer residence times, which corresponds to better catalyst productivities. However, a too high slurry density may cause instability in the circulation pump. Monitoring and controlling the slurry density is thus important for the operation of an olefin polymerization reactor. The slurry density is typically monitored via a nuclear (radioactive) densimeter, wherein the amount of radiation measured by the detector is dependent upon the shielding by the slurry in the pipe. However, this has multiple disadvantages. The use of radioactive sources in the nuclear densimeter poses potential health and safety hazards, requiring strict safety protocols during operation, maintenance and disposal. The accuracy of nuclear densimetry is influenced by slurry composition, particle size and temperature. Additionally, the system needs to be recalibrated periodically to account for the decay in the radioactive source.

[0009] There is thus a need in the art for improved methods and system for olefin polymerization, particularly for methods and systems for an improved monitoring and control of the polymerization reactor, such as the slurry density in the reactor, and of the lines for withdrawing the slurry from the reactor, for instance to a slurry treatment section.SUMMARY OF THE INVENTION

[0010] The inventors have surprisingly found that one or more of the above-mentioned drawbacks in the art can be overcome by the improved methods and system for olefin polymerization according to the present application, comprising

[0011] (i) providing a flow meter on each individual slurry withdrawal line or individual flash line of a plurality of slurry withdrawal lines or a plurality of flash lines, particularly a mass flow meter, more particularly a Coriolis type mass flow meter, even more particularly a single straight tube Coriolis type mass flow meter, and / or

[0012] (i) monitoring and controlling the slurry density using a mass flow meter, particularly a Coriolis type mass flow meter, more particularly a single straight tube Coriolis type mass flow meter, particularly wherein said mass flow meter is positioned on a slurry withdrawal line and is operably connected, such as via a control system, to the feed system of the reactor system. As the mass flow meter, particularly a Coriolis type mass flow meter, more particularly a single straight tube Coriolis type mass flow meter is used to monitor the density of the slurry, advantageously, the slurry density no longer has to be measured using a nuclear source and the nuclear (radioactive) densimeter can be replaced by said mass flow meter.

[0013] Preferably, the flow meter, particularly mass flow meter, is positioned upstream of the discharge valve, such as continuous take off valve, of each individual slurry withdrawal line and the flow meter, particularly mass flow meter, of each slurry withdrawal line is operably connected via a control system to the discharge valve on the same slurry withdrawal line. This allows for individually adjusting the position of the discharge valve, such as the CTO valve, on the same slurry withdrawal line at least in response to the monitored flow rate by the flow meter, and thus individually controlling the flow through each slurry line, while maintaining full control of the reaction conditions in the polymerization reactor.

[0014] Additionally, each slurry withdrawal line or flash line may be equipped with a temperature sensor, particularly positioned downstream of the line heater, and the control system may individually adjust the position of the discharge valve, such as the CTO valve, at least in response to the monitored flow rate by the flow meter, and further in response to the monitored temperature in an individual slurry withdrawal line. This allows fora better control of each flash line, including but not limited to a better temperature control, resulting in a better energy balance and improved energy savings, and lowering the risk of having liquid in the slurry treatment system (e.g. in the flash vessel). It also lowers the risk of overheating in a flash line leading to the fouling of the flash line.

[0015] A first aspect of the present application provides a reactor system comprising:a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0016] b / a plurality of slurry withdrawal lines, such as between 2 and 10 slurry withdrawal lines, wherein each slurry withdrawal line is adapted for removing a portion of the slurry from the reactor vessel via a slurry outlet; and

[0017] c / a slurry treatment system, particularly adapted for recovering the solid olefin polymer, wherein the plurality of slurry withdrawal lines is configured to provide the slurry from the reactor vessel to the slurry treatment system;

[0018] wherein each slurry withdrawal line comprises a discharge valve, wherein a position of the discharge valve between the fully closed position and the fully open position of the valve regulates the flow of the slurry through each slurry withdrawal line;

[0019] wherein each slurry withdrawal line further comprises a flow meter, wherein the flow meter of each slurry withdrawal line is operably connected via the control system to the discharge valve on the same slurry withdrawal line;

[0020] wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the slurry treatment system, wherein the first section of each slurry withdrawal line comprises the discharge valve and the flow meter, and wherein the second section of each slurry withdrawal line comprises a line heater and a temperature sensor, particularly positioned downstream of the line heater;

[0021] wherein the reactor system further comprises a control system for controlling the position of the discharge valves and the heating of the line heater, wherein the control system is configured for individually adjusting the position of the discharge valve and the heating of the line heater on the same slurry withdrawal line for each slurry withdrawal line of the plurality of slurry withdrawal lines at least in response to the monitored flow rate by the flow meter and an input signal received from the temperature sensor on the slurry withdrawal line.

[0022] In particular embodiments, the discharge valve on each slurry withdrawal line is a continuous take off valve (CTO valve), for continuously removing a portion of the slurry from the reactor vessel, or a product take off valve (PTO valve). The flow meter may be positioned upstream or downstream of the valve.

[0023] In particular embodiments, the flow meter on each slurry withdrawal line is a mass flow meter, particularly a Coriolis type mass flow meter, and wherein the control system is configured for individually adjusting the position of the CTO valve on the same slurry withdrawal line at least in response to the monitored mass flow rate by the mass flow meter. More in particular themass flow meter is a single straight tube Coriolis type mass flow meter, particularly wherein the diameter of the single straight tube Coriolis type mass flow meter differs at most 50% or at most 20% with the diameter of the slurry withdrawal line. In particular embodiments, the reactor system does not comprise a nuclear densimeter.

[0024] In particular embodiments, the reactor vessel is a pipe loop reactor, which defines a continuous flow path for a reaction mixture; a double loop reactor, comprising a first pipe loop reactor connected in series to a second pipe loop reactor, or a stirred-tank reactor, such as a continuous stirred-tank reactor (CSTR).

[0025] In particular embodiments, the reactor system further comprises:

[0026] a feed system for transferring at least an olefin monomer and a catalyst, or for transferring at least an olefin monomer, a catalyst and a diluent, to the reaction vessel, and wherein the flow meter, particularly mass flow meter, of a slurry withdrawal line is operably connected via a control system to the feed system. More in particular, the flow meter is a mass flow meter and is operably connected, via the control system, to the feed system, for adjusting the transfer of one or more of the olefin monomer and the catalyst, or for adjusting the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0027] Another, related aspect of the present application provides an olefin polymerisation process comprising the steps of:

[0028] (a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0029] (b) Withdrawing, particularly in a continuous manner, a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each slurry withdrawal line comprises a discharge valve, in particular a continuous take off (CTO) valve and a flow meter, and providing the slurry to a slurry treatment system, adapted for recovering the solid olefin polymer, wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises the discharge valve and the flow meter, wherein a position of the discharge valve between the fully closed position and the fully open position of the valve regulates the flow of the slurry through each slurry withdrawal line; and wherein the second section of each slurry withdrawal line comprises a line heater;(c) Monitoring the flow rate, particularly the mass flow, in an individual slurry withdrawal line of the plurality of slurry withdrawal line with a flow meter, particularly a mass flow meter, particularly positioned upstream of the discharge valve of the individual slurry withdrawal line and monitoring the temperature of an individual slurry withdrawal line of the plurality of slurry withdrawal lines by a temperature sensor, particularly positioned downstream of the line heater; and

[0030] (d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each discharge valve individually at least in response to the monitored flow in each individual slurry withdrawal line, particularly in response to the monitored mass flow in each individual slurry withdrawal line, and further in response to the monitored temperature in an individual slurry withdrawal line.

[0031] More in particular, the process further comprises the step of regulating the heating of the line heater of an individual slurry withdrawal line of the plurality of slurry withdrawal lines in response to at least the monitored temperature and the monitored flow rate, particularly mass flow, of that individual slurry withdrawal line, particularly by individually modulating a steam flow to each line heater or by individually modulating the slurry mass flow through each slurry withdrawal line.

[0032] In particular embodiments, the olefin monomer is a 1-alkene having up to 10 carbon atoms per molecule, particularly wherein the olefin monomer is ethylene, propylene, butene, pentene, hexene, octene, or a mixture thereof.

[0033] In particular embodiments, the process comprises further monitoring, such as in step (c), - the mass flow in an individual slurry withdrawal line of the plurality of slurry withdrawal lines with a Coriolis type mass flow meter, particularly a single straight tube Coriolis type mass flow meter; and / or

[0034] - the slurry density in an individual slurry withdrawal line with a Coriolis type mass flow meter, particularly a single straight tube Coriolis type mass flow meter; and / or

[0035] - the reaction pressure in the reactor vessel or the level of the slurry in the reactor vessel, particularly in a CSTR.

[0036] In certain embodiments, step (d) is performed further in response to the monitored reaction pressure, the monitored slurry level in the reactor vessel and / or the slurry density.DESCRIPTION OF THE FIGURES

[0037] The teaching of the application is illustrated by the following Figures which are to be considered as illustrative only and do not in any way limit the scope of the claims.

[0038] Figure 1 represents an embodiment of a system according to the present application.

[0039] Figure 2 represents another embodiment of a system according to the present application. Figure 3 represents another embodiment of a system according to the present application. Figure 4 represents another embodiment of a system according to the present application.

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] When describing the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0042] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0043] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while certain embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0044] The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of".

[0045] As used in the specification and the appended claims, the singular forms "a", "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0046] As used herein, the term “and / or” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of thelisted items can be employed. For example, if a list is described as comprising group A, B, and / or C, the list can comprise A alone, B alone, C alone, A and B in combination, A and C in combination, B and C in combination, or A, B, and C in combination.

[0047] The recitation of numerical ranges by endpoints includes all intervening values between the lower and upper endpoints, as well as the recited endpoints. Intervening values may be integers or, where applicable, fractions, i.e., more broadly any real numbers such as any rational numbers. For instance: 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements. The recitation of endpoints also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). This applies to numerical ranges irrespective of whether they are introduced by the expression “from... to...” or the expression “between... and...” or another expression. Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0048] As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.

[0049] As used herein, the term “about” is used to provide flexibility to a numerical value or range endpoint by providing that a given value may be “a little above” or “a little below” said value or endpoint, depending on the specific context. Unless otherwise stated, use of the term “about” in accordance with a specific number or numerical range should also be understood to provide support for such numerical terms or range without the term “about”. For example, the recitation of “about 30” should be construed as not only providing support for values a little above and a little below 30, but also for the actual numerical value of 30 as well.

[0050] The terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other sequences than described or illustrated herein.Reference in this specification may be made to methods that provide “improved” performance (e.g. increased or decreased results, depending on the context). It is to be understood that unless otherwise stated, such “improvement” is a measure of a benefit obtained based on a comparison to methods in the prior art. Furthermore, it is to be understood that the degree of improved performance may vary between disclosed embodiments and that no equality or consistency in the amount, degree, or realization of improved performance is to be assumed as universally applicable.

[0051] As used herein, the term “continuous” in the context of a system or process means a system or process that operates without interruption or cessation. For example, a continuous process to produce a polymer would be one where the reactants are continually introduced into one or more reactors and polymer product is continually withdrawn. By this it is meant herein that the reactors, when operating, are run in continuous mode, that is at least one feed stream is predominantly fed continuously to the reactor, while at least one polymer stream is predominantly withdrawn continuously.

[0052] As used herein, when a subscript is used herein following a carbon atom, the subscript refers to the number of carbon atoms that the named group or compound may contain. For instance, an aliphatic C2-C10 olefin refers to an olefin molecule having between 2 and 10 carbon atoms.

[0053] The inventors have generally developed improved systems and processes for olefin polymerisation, particularly for improving the monitoring and control of an olefin polymerisation system and process, more in particular by improving the individually monitoring and control of a plurality of slurry withdrawal lines, such as a plurality of flash lines, and / or by improving the monitoring and control of the slurry density.

[0054] Olefin polymerisation is well known in the art. As used in the different aspects and embodiments herein, the term “olefin polymerisation” generally refers to a process, particularly a continuous process, performed in a slurry phase, comprising the step of polymerizing an olefin monomer, optionally hydrogen or another chain transfer agent, optionally a comonomer, and optionally a diluent, in the presence of a least one catalyst, thereby obtaining a polyolefin. The term “olefin” is well known in the art, and refers herein to molecules composed of carbon and hydrogen, containing at least one carbon-carbon double bond. Particular preferred examples of olefin monomers are described below and include for instance ethylene and propylene.

[0055] Throughout the present application the terms “olefin polymer”, "polyolefin" and "polyolefin polymer" are used synonymously and interchangeably.The terms "slurry", "polymerization slurry", "polymer slurry" or “polyolefin slurry” are generally used synonymously and interchangeably, and, as used herein, refer to substantially a multiphase composition including at least polyolefin polymer solids and a liquid phase, wherein said liquid phase may comprise unreacted olefin monomers and optionally the diluent and comonomers. The slurry density is a measure of the amount of polymer in the slurry, or, stated differently, the solids concentration in the slurry, particularly the solids concentration in the reactor vessel.

[0056] As used in the different aspects and embodiments herein, the term “catalyst” refers to a substance that causes a change in the rate of a reaction without itself being consumed in the reaction. In the context of the present application, it is understood that at least part of the catalyst is removed from the reactor together with the polyolefin slurry. In the present application, it is particularly applicable to catalyst suitable for the polymerization reaction of olefin monomers (and optionally comonomers) to olefin polymers, i.e. olefin polymerization catalysts. Non-limiting examples of suitable catalysts include metallocene catalysts, Ziegler-Natta catalysts, or chromium catalysts, and they are well known to the skilled person. The term "metallocene catalyst" is used herein to describe any transition metal complexes consisting of metal atoms bonded to one or more ligands. The metallocene catalysts are compounds of Group IV transition metals of the Periodic Table such as titanium, zirconium, hafnium, etc., and have a coordinated structure with a metal compound and ligands composed of one or two groups of cyclopentadienyl, indenyl, fluorenyl or their derivatives. Use of metallocene catalysts in the polymerization of olefins has various advantages. Metallocene catalysts have high activities and are capable of preparing polymers with enhanced physical properties in comparison with the polymers prepared using Ziegler-Natta catalysts.

[0057] As used in the different aspects and embodiments herein, the term “comonomer” refers to a monomer which is suitable for being polymerized with the olefin monomer. The comonomer if present is typically a second olefin monomer that is different from the first olefin monomer and chosen such that it is suited for copolymerization with the first olefin monomer. Comonomers may comprise but are not limited to aliphatic C2-20, or preferably C2-C10 olefins. Examples of aliphatic olefins comonomers for polymerization according to the present invention include for instance ethylene, propylene, 1 -butene, 1 -pentene, 4-methyl-1 -pentene, 1 -hexene, 1 -octene, and 1 -decene.

[0058] Polymerization processes according to the invention include homopolymerization processes, such as resulting in polyethylene or polypropylene, as well as copolymerization processes. Examples of copolymers which can be prepared according to the invention include for instance random copolymers of propylene and ethylene, ethylene-butene copolymers, ethylene-hexenecopolymers, ethylene-octene copolymers, or heterophasic copolymers of propylene and ethylene.

[0059] As used in the different aspects and embodiments herein, the term “diluent” refers to any organic diluent, which does not dissolve the synthesized polyolefin. As used herein, the term “diluent” refers to diluents in a liquid or supercritical state, liquid at room temperature and preferably liquid under the pressure conditions in the loop reactor. Suitable diluents comprise but are not limited to hydrocarbon diluents such as aliphatic, cycloaliphatic, and aromatic hydrocarbon solvents, or halogenated versions of such solvents. Preferred solvents are C12 or lower, straight chain or branched chain, saturated hydrocarbons, C5 to C9 saturated alicyclic or aromatic hydrocarbons or C2 to Ce halogenated hydrocarbons. Non-limiting illustrative examples of solvents are propane, butane, isobutane, pentane, hexane, heptane, cyclopentane, cyclohexane, cycloheptane, methyl cyclopentane, methyl cyclohexane, isooctane, benzene, toluene, xylene, chloroform, chlorobenzenes, tetrachloroethylene, dichloroethane and trichloroethane, preferably isobutane or hexane.

[0060] The improved systems and processes for olefin polymerisation according to the present application comprise at least one of the following features (i) or (ii).

[0061] (i) A flow meter, particularly a mass flow meter, more particularly a Coriolis type mass flow meter, even more particularly a single straight tube Coriolis type mass flow meter, is provided on each individual slurry withdrawal line or individual flash line of a plurality of slurry withdrawal lines (or plurality of flash lines) of an olefin polymerization reactor system. In particular, the flow meter or mass flow meter as envisaged herein is positioned upstream of the discharge valve, particularly continuous take off (CTO) valve, of each individual slurry withdrawal line. The position of each discharge valve can be adjusted individually at least in response to the measured flow rate, particularly mass flow rate, in the individual slurry withdrawal line or individual flash line. This not only allows for a better control of the flow within each individual slurry withdrawal line of a plurality of slurry withdrawal lines (flash lines), thereby lowering the risk of valve blockage or line fouling, but also allows for a better control of the reactor conditions, particularly reactor pressure and slurry density, as well as a better control of the slurry withdrawal line (flash line) itself and the product recovery system, such as by avoiding the presence of liquid in the flash vessel of the product recovery system, and / or

[0062] (ii) a mass flow meter, particularly a Coriolis type mass flow meter, more particularly a single straight tube Coriolis type mass flow meter, is provided on a slurry withdrawal line of an olefin polymerization reactor system for measuring the slurry density. The mass flow meter is operably connected to at least a feed system of the olefin polymerization reactor system, for controlling the transfer of at least one of a diluent, a catalyst and / or a monomer to the reactorsystem, preferably the transfer of the diluent to the reactor system, at least in response to the measured slurry density by the mass flow meter, particularly the Coriolis type mass flow meter, more particularly the single straight tube Coriolis type mass flow meter.

[0063] As used herein, the expression “adjusting / adjustment of the position of a valve” and variants thereof is in the meaning that the valve is positionable between a fully open and a fully closed position. The flow rate through the line comprising the valve is varied as a function of the position of the valve, or stated differently, as a function of the valve’s degree of opening. Changing or adjustment of the valve position, i.e. its degree of opening, will increase or decrease the flow in a controlled manner.

[0064] The present invention is further detailed in the preferred statements (features), aspects and embodiments mentioned below. Each statement and embodiment of the invention so defined may be combined with any other statement and / or embodiment unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features or statements indicated as being preferred or advantageous. Hereto, the present invention is in particular captured by any one or any combination of one or more of the below numbered statements and embodiments, with any other aspect and / or embodiment.

[0065] Statement 1. A reactor system comprising:

[0066] a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0067] b / a plurality of slurry withdrawal lines, wherein each slurry withdrawal line is adapted for removing a portion of the slurry from the reactor vessel and wherein each slurry withdrawal line comprises a discharge valve, wherein a position of the discharge valve regulates the flow of the slurry through each slurry withdrawal line;

[0068] c / a control system for controlling the position of the discharge valves;

[0069] wherein each slurry withdrawal line further comprises a flow meter, wherein the flow meter of each slurry withdrawal line is operably connected via the control system to the discharge valve on the same slurry withdrawal line, and wherein the control system is configured for individually adjusting the position of the discharge valve on a slurry withdrawal line at least in response to the monitored flow in that slurry withdrawal line by the flow meter.

[0070] Statement 2. The reactor system according to statement 1 , wherein:(i) the flow meter is a mass flow meter or a volumetric flow meter;

[0071] (ii) the flow meter is positioned upstream or downstream of the discharge valve; and / or (iii) the discharge valve is a continuous take off (CTO) valve or a product take off (PTO) valve.

[0072] Statement 3. A reactor system according to statement 1 or 2 comprising:

[0073] a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst to produce a slurry comprising a solid olefin polymer in a liquid medium, particularly wherein the reactor vessel comprises a plurality of slurry outlets;

[0074] b / a plurality of slurry withdrawal lines, wherein each slurry withdrawal line is adapted for continuously removing a portion of the slurry from the reactor vessel via a slurry outlet and wherein each slurry withdrawal line comprises a continuous take off (CTO) valve, wherein a position of the CTO valve regulates the flow of the slurry through each slurry withdrawal line; c / a control system for controlling the position of the CTO valves;

[0075] wherein each slurry withdrawal line further comprises a mass flow meter, particularly upstream of the continuous take off valve, wherein the mass flow meter of each slurry withdrawal line is operably connected via the control system to the CTO valve on the same slurry withdrawal line, and wherein the control system is configured for individually adjusting the position of the CTO valve on the same slurry withdrawal line at least in response to the monitored mass flow by the mass flow meter, or at least in response to the reaction pressure and / or to the slurry level, and to the monitored mass flow by the mass flow meter.

[0076] Statement 4. The reactor system according to statement 2 or 3, wherein the mass flow meter is a Coriolis type flow meter.

[0077] Statement 5. The reactor system according to any one of statements 2 to 4, wherein the mass flow meter is a single straight tube Coriolis type mass flow meter.

[0078] Statement 6. The reactor system according to statement 5, wherein the diameter of the single straight tube Coriolis type mass flow meter differs at most 50%, at most 40%, at most 30%, at most 20% or at most 10% with the diameter of the slurry withdrawal line, more particularly wherein the diameter of the single straight tube Coriolis type mass flow meter has the same diameter as the slurry withdrawal line.

[0079] Statement 7. The reactor system according to any one of the previous statements, wherein the reactor system further comprises a feed system for transferring at least an olefin monomerand a catalyst, or for transferring at least an olefin monomer, a catalyst and a diluent, to the reactor vessel.

[0080] Statement 8. The reactor system according to statement 7, wherein at least one mass flow meter is operably connected, particularly via a control system, to the feed system, for adjusting the transfer of one or more of the olefin monomer and the catalyst, or for adjusting the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0081] Statement 9. The reactor system according to statement 8, wherein the feed system comprises at least an olefin monomer feed line for transferring the olefin monomer to the reactor vessel and a catalyst feed line for transferring the catalyst to the reactor vessel, or an olefin monomer feed line for transferring the olefin monomer to the reactor vessel, a catalyst feed line for transferring the catalyst to the reactor vessel and a diluent feed line for transferring the diluent to the reactor vessel, and wherein the mass flow meter is operably connected, particularly via the control system, to the olefin monomer feed line, to the catalyst feed line and / or to the diluent feed line, such as operably connected, particularly via the control system, to a valve on the olefin monomer feed line, to a valve on the catalyst feed line and / or to a valve on the diluent feed line.

[0082] Statement 10. The reactor system according to any one of statements 1 to 9, wherein the reactor vessel is a pipe loop reactor, which defines a continuous flow path for a reaction mixture.

[0083] Statement 11. The reactor system according to any one of statements 1 to 9, wherein the reactor vessel is a double loop reactor, comprising a first pipe loop reactor connected in series to a second pipe loop reactor.

[0084] Statement 12. The reactor system according to statement 11, wherein the first pipe loop reactor is connected to the second pipe loop reactor via a plurality of slurry withdrawal lines.

[0085] Statement 13. The reactor system according to any one of statements 1 to 9, wherein the reactor vessel is a stirred-tank reactor, particularly a continuous stirred-tank reactor (CSTR).

[0086] Statement 14. The reactor system according to any one of statements 2 to 13, wherein the CTO valve is a V-ball valve.Statement 15. The reactor system according to any one of statements 1 to 14, wherein the plurality of slurry withdrawal lines comprises between 2 and 10 slurry withdrawal lines, particularly between 2 and 8 or between 2 and 6 slurry withdrawal lines.

[0087] Statement 16. The reactor system according to any one of statements 1 to 15, further comprising a slurry treatment system, particularly adapted for recovering the solid olefin polymer.

[0088] Statement 17. The reactor system according to statement 16, wherein the plurality of slurry withdrawal lines is configured to provide the slurry from the reactor vessel to the slurry treatment system.

[0089] Statement 18. The reactor system according to statement 16 or 17, wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises the discharge valve, particularly the continuous take off (CTO) valve, and the flow meter, particularly mass flow meter, wherein a position of the discharge valve, particularly CTO valve, regulates the flow of the slurry through each slurry withdrawal line; and wherein the second section of each slurry withdrawal line comprises a line heater.

[0090] Statement 19. The reactor system according to statement 18, wherein the second section of each slurry withdrawal line comprises a temperature sensor, particularly positioned downstream of the line heater; and wherein the control system is further configured to receive an input signal from the temperature sensor of each slurry withdrawal line.

[0091] Statement 20. The reactor system according to statement 19, wherein the temperature sensor is a temperature contact probe or a flush mounted temperature probe.

[0092] Statement 21. The reactor system according to statement 19 or 20, wherein the control system is further configured to control the heating of the line heater of each slurry withdrawal line individually at least in response to the input signal received from the temperature sensor on the slurry withdrawal line.Statement 22. The reactor system according to any one of statements 18 to 21, wherein the line heater is configured to be heated by steam.

[0093] Statement 23. A reactor system comprising:

[0094] - a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst, or polymerizing at least one olefin monomer in the presence of a catalyst and a diluent, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0095] - a feed system for transferring at least the olefin monomer and the catalyst, or for transferring at least the olefin monomer, the catalyst and the diluent, to the reactor vessel; and

[0096] - at least one slurry withdrawal line, adapted for removing a portion of the slurry from the reactor vessel;

[0097] wherein the at least one slurry withdrawal line comprises a mass flow meter for monitoring the slurry density, wherein the mass flow meter is operably connected, particularly, via a control system, to the feed system, for adjusting the transfer of one or more of the olefin monomer and the catalyst, or for adjusting the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0098] Statement 24. The reactor system according to statement 23, wherein the mass flow meter is a Coriolis type mass flow meter or a single straight tube Coriolis type mass flow meter.

[0099] Statement 25. The reactor system according to statement 24, wherein the diameter of the single straight tube Coriolis type mass flow meter differs at most 50%, particularly at most 40%, at most 30%, at most 20% or at most 10% with the diameter of the slurry withdrawal line.

[0100] Statement 26. The reactor system according to any one of statements 23 to 25, wherein the feed system comprises at least an olefin monomer feed line for transferring the olefin monomer to the reactor vessel and a catalyst feed line for transferring the catalyst to the reactor vessel, or an olefin monomer feed line for transferring the olefin monomer to the reactor vessel, a catalyst feed line for transferring the catalyst to the reactor vessel and a diluent feed line for transferring the diluent to the reactor vessel, and wherein the mass flow meter is operably connected, particularly via a control system, to the olefin monomer feed line, to the catalyst feed line and / or to the diluent feed line, such as operably connected, particularly via the control system, to a valve on the olefin monomer feed line, to a valve on the catalyst feed line and / or to a valve on the diluent feed line.Statement 27. The reactor system according to statement 26, wherein the mass flow meter is operably connected via the control system to the diluent feed line, particularly to the valve on the diluent feed line.

[0101] Statement 28. The reactor system according to any one statements 23 to 27, wherein:

[0102] - the reactor vessel is a pipe loop reactor, which defines a continuous flow path for a reaction mixture,

[0103] - wherein the reactor vessel is a double loop reactor, comprising a first pipe loop reactor connected in series to a second pipe loop reactor via the at least one slurry withdrawal line, or

[0104] - wherein the reactor vessel is a stirred-tank reactor, particularly a continuous stirred-tank reactor (CSTR).

[0105] Statement 29. The reactor system according to any one of statements 23 to 28, further comprising a slurry treatment system, particularly adapted for recovering the solid olefin polymer, wherein the at least one slurry withdrawal line is configured to provide the slurry from the reactor vessel to the slurry treatment system, and

[0106] wherein the at least one slurry withdrawal line comprises a first section, which is connected to the reactor vessel, and a second section, downstream of the first section, and connected to the slurry treatment system; wherein the first section comprises a discharge valve and the mass flow meter, wherein a position of the discharge valve regulates the flow of the slurry through the at least one slurry withdrawal line; and wherein the second section of the at least one slurry withdrawal line comprises a line heater, particularly wherein the second section of the at least one slurry withdrawal line comprises a temperature sensor, such as a temperature contact probe or a flush mounted temperature probe, particularly positioned downstream of the line heater;

[0107] wherein the control system is further configured to receive an input signal from the temperature sensor and the mass flow meter of the at least one slurry withdrawal line; and

[0108] wherein the control system is further configured to modulating the flow in the at least one slurry withdrawal line by adjusting the position of the discharge valve at least in response to the monitored mass flow and / or to the monitored temperature in the at least one slurry withdrawal line and / or to the monitored reaction pressure.

[0109] Statement 30. The reactor system according to any one of the previous statements, wherein the reactor system does not comprise a nuclear densimeter.Statement 31. An olefin polymerisation process comprising the steps of:

[0110] (a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0111] (b) Withdrawing a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each slurry withdrawal line comprises a discharge valve and a flow meter;

[0112] (c) Monitoring the mass flow rate or volumetric flow rate in an individual slurry withdrawal line of the plurality of slurry withdrawal line with the flow meter; and

[0113] (d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each discharge valve individually at least in response to the monitored mass flow rate or monitored volumetric flow rate in each individual slurry withdrawal line.

[0114] Statement 32. An olefin polymerisation process according to statement 31, comprising the steps of:

[0115] (a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0116] (b) Continuously withdrawing a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each slurry withdrawal line comprises a continuous take off (CTO) valve and a mass flow meter, particularly positioned upstream of the CTO valve of the individual slurry withdrawal line;

[0117] (c) Monitoring the mass flow rate in an individual slurry withdrawal line of the plurality of slurry withdrawal line with the mass flow meter; and

[0118] (d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each CTO valve individually at least in response to the monitored mass flow rate in each individual slurry withdrawal line.

[0119] Statement 33. The process according to statements 31 or 32, further comprising monitoring the reaction pressure in the reactor vessel or monitoring the level of the slurry in the reactor vessel, particularly in a CSTR reactor vessel, and wherein step (d) is performed further in response to the monitored reaction pressure or to the monitored slurry level.Statement 34. The process according to any one of statements 31 to 33, wherein step (a) comprises transferring at least one olefin monomer and a catalyst, or transferring at least one olefin monomer, a diluent and a catalyst, from a feed system to the reactor vessel.

[0120] Statement 35. The process according to any one of statements 32 to 34, wherein the mass flow meter is a Coriolis type flow meter.

[0121] Statement 36. The process according to statement 35, wherein the mass flow meter is a single straight tube Coriolis type mass flow meter.

[0122] Statement 37. The process according to statement 36, wherein the diameter of the single straight tube Coriolis type mass flow meter differs at most 50%, at most 40%, at most 30%, at most 20% or at most 10% with the diameter of the slurry withdrawal line, more particularly wherein the diameter of the single straight tube Coriolis type mass flow meter has the same diameter as the slurry withdrawal line.

[0123] Statement 38. The process according to any one of statements 35 to 37, wherein step (c) further comprises monitoring the slurry density by the mass flow meter.

[0124] Statement 39. The process according to statement 38, wherein in step (a) the olefin monomer, the catalyst and the diluent are transferred to the reactor vessel by a monomer feed line, a catalyst feed line and a diluent feed line, respectively, and wherein the process further comprises a step (e) of modulating the transfer of the olefin monomer and / or the catalyst, or modulating the transfer of one or more of the olefin monomer, the catalyst and / or the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter, particularly comprising adjusting the position of a valve positioned on an olefin monomer feed line, a catalyst feed line and / or a diluent feed line.

[0125] Statement 40. The process according to any one of statements 31 to 39, wherein step (b) comprises providing the slurry to a slurry treatment system, particularly adapted for recovering the solid olefin polymer.

[0126] Statement 41. The process according to statement 40, wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises the discharge valve,particularly the continuous take off (CTO) valve, and the flow meter, particularly the mass flow meter, wherein a position of the discharge valve, particularly the CTO valve, regulates the flow of the slurry through each slurry withdrawal line; and wherein the second section of each slurry withdrawal line comprises a line heater.

[0127] Statement 42. The process according to statement 41, further comprising the step of monitoring the temperature of an individual slurry withdrawal line of the plurality of slurry withdrawal lines by a temperature sensor, particularly positioned downstream of the line heater, and wherein step (d) is performed further in response to the monitored temperature in an individual slurry withdrawal line.

[0128] Statement 43. The process according to statement 42, further comprising the step of regulating the heating of the line heater of an individual slurry withdrawal line of the plurality of slurry withdrawal lines in response to at least the monitored temperature and the monitored flow rate, particularly the monitored mass flow rate, of that individual slurry withdrawal line, particularly by individually modulating a steam flow to each line heater, or by individually adapting the slurry mass flow through each slurry withdrawal line.

[0129] Statement 44. The process according to any one of statements 31 to 43, wherein the process is a method of controlling the polymerization process according to any one statements 31 to 43, wherein a target total flow rate of the slurry out of the reactor vessel is controlled by the reaction pressure or the slurry level in the reactor vessel, and wherein the individual flow rate of the slurry in an individual slurry withdrawal line is based on the target total flow rate of the slurry divided by the number of active discharge valves, particularly active CTO valves, of the plurality of slurry withdrawal lines, and wherein the position of each individual discharge valve, particularly CTO valve, on the plurality of slurry withdrawal lines is adjusted in response to the monitored flow rate, particularly mass flow rate, in each of the slurry withdrawal lines in order to reach the target total flow rate.

[0130] Statement 45. An olefin polymerisation process comprising the steps of:

[0131] (a1) transferring at least an olefin monomer and a catalyst, or transferring at least an olefin monomer, a catalyst and a diluent, from a feed system to a reactor vessel;

[0132] (a2) polymerizing, in the reactor vessel, at least the olefin monomer in the presence of the catalyst or polymerizing at least the olefin monomer in the presence of the catalyst and the diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;(b) withdrawing, particularly continuously withdrawing, a portion of the slurry from the reactor vessel through at least one slurry withdrawal line;

[0133] (o’) monitoring the slurry density in the at least one slurry withdrawal line with a mass flow meter, particularly a Coriolis type flow mater, and

[0134] (d’) modulating the transfer of the olefin monomer and / or the catalyst, or modulating the transfer of one or more of the olefin monomer, the catalyst and / or the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0135] Statement 46. The process according to statement 45, wherein the mass flow meter is a single straight tube Coriolis type mass flow meter.

[0136] Statement 47. The process according to statement 45 or 46, wherein in step (a1) the olefin monomer, the catalyst and the diluent are transferred to the reactor vessel by a monomer feed line, a catalyst feed line and a diluent feed line, respectively, and wherein step (d’) comprises adjusting the position of a valve positioned on an olefin monomer feed line, a catalyst feed line and / or a diluent feed line.

[0137] Statement 48. The process according to statement 47, wherein step (d’) comprises adjusting the position of the valve on the diluent feed line.

[0138] Statement 49. The process according to any one of statements 45 to 48, wherein step (b) comprises providing the slurry to a slurry treatment system, particularly adapted for recovering the solid olefin polymer, by the at least one slurry withdrawal line,

[0139] wherein the at least one slurry withdrawal line comprises a first section, which is connected to the reactor vessel, and a second section, downstream of the first section, and connected to the slurry treatment system; wherein the first section comprises a discharge valve and the mass flow meter, wherein a position of the discharge valve regulates the flow of the slurry through the at least one slurry withdrawal line; and wherein the second section comprises a line heater,

[0140] wherein step (o’) of the process further comprises monitoring the mass flow in the at least one slurry withdrawal line by the mass flow meter, and / or monitoring the temperature of the slurry in the at least one slurry withdrawal line by a temperature sensor, particularly positioned downstream of the line heater, and / or monitoring the reaction pressure or slurry level in the reactor vessel; and

[0141] wherein step (d’) of the process further comprises modulating the flow in the at least one slurry withdrawal line at least in response to the monitored mass flow and / or to the monitoredtemperature in the slurry withdrawal line and / or to the monitored reaction pressure and / or to the monitored slurry level in the reactor vessel.

[0142] Statement 50. The process according to statement 49, further comprising the step of regulating the heating of the line heater of the at least one slurry withdrawal line in response to at least the monitored temperature and / or the monitored mass flow in the at least one slurry withdrawal line, particularly by modulating the steam flow to the line heater.

[0143] Statement 51. The process according to any one of statements 31 to 50, wherein the reactor vessel is a pipe loop reactor, which defines a continuous flow path for a reaction mixture.

[0144] Statement 52. The process according to any one of statements 31 to 50, wherein the reactor vessel is a double loop reactor, comprising a first pipe loop reactor connected in series to a second pipe loop reactor, particularly wherein the first pipe loop reactor is connected to the second pipe loop reactor via at least one slurry withdrawal line, particularly via a plurality of slurry withdrawal lines.

[0145] Statement 53. The process according to any one of statements 31 to 50, wherein the reactor vessel is a stirred-tank reactor, particularly a continuous stirred-tank reactor (CSTR).

[0146] Statement 54. The process according to any one of statements 31 to 53, wherein the olefin monomer is a 1 -alkene having up to 10 carbon atoms per molecule, particularly up to 8 carbon atoms per molecule, or a mixture thereof, particularly wherein the olefin monomer is ethylene, propylene, butene, pentene, hexene, octene, or a mixture thereof.

[0147] Statement 55. The process according to statement 54, wherein the olefin monomer is ethylene and / or propylene.

[0148] Statement 56. The process according to any one of statements 31 to 55, wherein the diluent, when present, is isobutane, propane, n-pentane, i-pentane, neopentane, n-hexane, or a mixture thereof, particularly wherein the diluent is isobutane; and / or wherein the comonomer, when present, is ethylene, propylene, 1 -butene, 1 -pentene, 4-methyl-1 -pentene, 1 -hexene, 1-octene, and 1 -decene, or a mixture thereof.A first aspect of the present application provides for a reactor system comprising:

[0149] a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst, or polymerizing at least one olefin monomer in the presence of a catalyst and diluent, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0150] b / a plurality of slurry withdrawal lines, wherein each slurry withdrawal line is adapted for removing a portion of the slurry from the reactor vessel and wherein each slurry withdrawal line comprises a discharge valve, wherein a position of the discharge valve regulates the flow of the slurry through each slurry withdrawal line;

[0151] c / a control system for controlling the position of the discharge valves;

[0152] wherein each slurry withdrawal line further comprises a flow meter, wherein the flow meter of each slurry withdrawal line is operably connected via the control system to the discharge valve on the same slurry withdrawal line, and wherein the control system is configured for individually adjusting the position of the discharge valve on a slurry withdrawal line at least in response to the monitored flow in that slurry withdrawal line by the flow meter.

[0153] Each slurry withdrawal line comprises a discharge valve. The position of the discharge valve, i.e. its degree of opening, regulates the flow of the slurry through the individual slurry withdrawal line and the valve position between a fully closed position and a fully open position may be regulated by a control system in response to the reaction pressure in the reactor vessel or in response to the slurry level in the reactor vessel, particularly in case when the reactor vessel is a CSTR. In particular embodiments, the discharge valve is a continuous take off valve, used interchangeably herein with the term “CTO valve”. A CTO valve is designed for continuous removal of slurry from the reactor vessel. In particular embodiments, the CTO valve is a V-ball valve. In particular, a position of the CTO valve regulates the flow of the slurry through the individual slurry withdrawal line. For instance, the position of the CTO valve may be regulated by a control system in response to the reaction pressure measured in the reactor vessel by a pressure sensor, or in response to the slurry level measured in the (CSTR) reactor vessel by a level sensor, and in response to the measured flow, particularly mass flow, in the individual slurry withdrawal line. The discharge valve may also be a product take-off valve, used interchangeably herein with the term “PTO valve”. A PTO valve is particularly designed for intermittent removal of slurry from the reactor vessel, and may operate in a cyclic manner, with opening and closing of the valve based on the reactor conditions (product accumulation, etc.).

[0154] Additionally, each slurry withdrawal line comprises a flow meter for determining the flow rate of the slurry flowing in the withdrawal line. The flow meter may be positioned upstream ordownstream of the discharge valve. Preferably, the flow meter is positioned upstream of the discharge valve. The flow meter may be a volumetric flow meter, such as an ultrasonic flow meter. An ultrasonic flow meter uses sound waves to determine the velocity of the fluid, from which the volumetric flow rate can be calculated.

[0155] In particular embodiments, the flow meter is a mass flow meter. Preferably, the mass flow meter is a Coriolis type flow meter. More preferably, the mass flow meter is a single straight tube Coriolis type mass flow meter. In certain embodiments, the diameter of the single straight tube Coriolis type mass flow meter differs at most 50%, at most 40%, at most 30%, at most 20% or at most 10% with the diameter of the slurry withdrawal line, more particularly wherein the diameter of the single straight tube Coriolis type mass flow meter has the same diameter as the slurry withdrawal line. Advantageously, a single straight tube Coriolis type mass flow meter allows to measure the mass flow directly and accurately, particularly allows to measure simultaneously the slurry density and mass flow of the slurry in the slurry withdrawal line directly and accurately. Indeed, as the slurry in the slurry withdrawal line has similar or even essentially the same properties as the slurry at the outlet of the reactor vessel, monitoring the density of the slurry in the slurry withdrawal line, particularly between the reactor vessel outlet and a discharge valve positioned on the slurry withdrawal lines, allows to monitor the density of the slurry in the reactor vessel. The mass flow measurement is not sensitive to flow disturbances or vibrations. The single straight tube Coriolis type mass flow meter is a compact system, with a reduced risk of blockage, and thus with a minimal impact on the process. Furthermore, the mass flow meter as considered herein also measures the slurry density, thereby allowing to replace the nuclear based densimetry that is often used in slurry polyolefin polymerization processes and systems. Accordingly, in certain embodiments, the reactor system does not comprise a nuclear densimeter.

[0156] In particularly preferred embodiments, the reactor system comprises:

[0157] a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst, or polymerizing at least one olefin monomer in the presence of a catalyst and diluent, to produce a slurry comprising a solid olefin polymer in a liquid medium, particularly wherein the reactor vessel comprises a plurality of slurry outlets;

[0158] b / a plurality of slurry withdrawal lines, wherein each slurry withdrawal line is adapted for continuously removing a portion of the slurry from the reactor vessel, particularly via a slurry outlet of the plurality of slurry outlets and wherein each slurry withdrawal line comprises a continuous take off (CTO) valve, wherein a position of the CTO valve regulates the flow of the slurry through each slurry withdrawal line;c / a control system for controlling the position of the CTO valves;

[0159] wherein each slurry withdrawal line further comprises a mass flow meter, particularly a Coriolis type flow meter, more particularly a single straight tube Coriolis type mass flow meter upstream of the continuous take off valve, wherein the mass flow meter of each slurry withdrawal line is operably connected via the control system to the CTO valve on the same slurry withdrawal line, and wherein the control system is configured for individually adjusting the position of the CTO valve on the same slurry withdrawal line at least in response to the monitored mass flow by the mass flow meter.

[0160] In particular embodiments, the reactor system further comprises a feed system for transferring at least an olefin monomer and a catalyst (as described elsewhere herein), or for transferring at least an olefin monomer, a catalyst and a diluent (as described elsewhere herein), to the reaction vessel.

[0161] A further, related aspect of the present application provides for a reactor system comprising: a’ / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst, or polymerizing at least one olefin monomer in the presence of a catalyst and a diluent, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0162] b7 a feed system for transferring at least the olefin monomer and the catalyst, or for transferring at least the olefin monomer, the catalyst and the diluent, to the reactor vessel; and c7 a slurry withdrawal line, adapted for removing a portion of the slurry from the reactor vessel; wherein the slurry withdrawal line comprises a mass flow meter for monitoring the slurry density, particularly a Coriolis type mass flow meter or a single straight tube Coriolis type mass as described elsewhere herein, wherein the mass flow meter is operably connected, particularly via a control system, to the feed system, for adjusting the transfer of the olefin monomer or the catalyst, or for adjusting the transfer of one or more of, preferably one of, the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0163] In particular embodiments, the reactor vessel of the reactor system is in the form of a loop reactor, which defines a continuous flow path for a reaction mixture and wherein polymerisation is typically carried out in a circulating turbulent flow. As used in the different aspects and embodiments herein, the term “pipe loop reactor”, “loop reactor” or “slurry loop reactor” is well known to the skilled person and generally refers to a closed-circuit reactor vessel with a tubular configuration. The loop reactor generally comprises a long pipe or tube, arranged in a closed loop, thus forming a continuous flow path for the reaction mixture. A loopreactor typically comprises a plurality of interconnected pipe segments, particularly a plurality of vertical pipe segments that are interconnected by smooth bends or interconnected by horizontal pipe segments with smooth elbows between a horizontal and a vertical pipe segment, together forming a loop. Segments of the loop reactor may be provided with cooling jackets, for extracting polymerization heat. The polymerization slurry is typically circulated within the loop reactor by means of a motive device, such as a pump or a motor-driven impeller.

[0164] In certain embodiments, the reactor vessel is a stirred-tank reactor, particularly a continuous stirred-tank reactor (CSTR), as known to the skilled person. Briefly, as used in the different aspects and embodiments herein, a stirred-tank reactor, such as a CSTR, comprises an enclosed reactor vessel, such as a substantially cylindrical enclosed tank, with an inlet port for introducing reactants and an outlet port for the extraction of the reaction product stream. The reactor tank includes an internal agitator, typically driven by a motor, which facilitates mixing of reactants, which typically also maintains a turbulent flow regime, and which ensures a homogenous reaction mixture throughout the reactor tank. The reactor tank is often equipped with one or more heat exchange elements, such as jackets or internal coils.

[0165] The reactor vessel may be connected in parallel or in series to one or more further reactor vessels. In particular, a first loop reactor may be connected in parallel or in series to a second loop reactor, thereby forming a "double loop" reactor. In particular, as used in the different aspects and embodiments herein, a “double loop reactor” refers to two, or at least two, single loop reactors which are coupled in series, wherein the content of a first single loop reactor after completion of the polymerization reaction is fed, particularly via at least one transfer line, to a second single loop reactor.

[0166] In the context of the present application, a portion of the slurry comprising the polymer product is withdrawn, particularly in a continuous manner, from the reactor vessel by a slurry withdrawal line via a reactor outlet, particularly by one or more (i.e. at least one) slurry withdrawal lines via one or more reactor outlets. In particular embodiments, the reactor vessel comprises a plurality of slurry outlets, and the slurry comprising the polymer product is withdrawn from one or more reactors present in the reactor system by a plurality of slurry withdrawal lines, each connected to an outlet of the plurality of slurry outlets of a reactor vessel. The term “slurry withdrawal line” as used herein generally refers to an elongated pipe or tube connected to an outlet of the reactor vessel and adapted for conveying the slurry out of the reactor vessel, in particular to a second reactor vessel or to a product recovery system.In particular embodiments, a portion of the slurry is continuously removed from the reactor vessel via a slurry outlet of the plurality of slurry outlets and a slurry withdrawal line of the plurality of slurry withdrawal lines. In particular embodiments, the at least one slurry withdrawal line comprises a discharge valve, as described elsewhere herein, wherein a position of the discharge valve regulates the flow of the slurry through the slurry withdrawal line.

[0167] When the reactor system comprises a plurality of slurry withdrawal lines, for each slurry withdrawal line of the plurality of slurry withdrawal lines, the flow meter as described elsewhere herein, in particular the mass flow meter, more in particular the Coriolis type flow meter or the single straight tube Coriolis type mass flow meter, is positioned upstream or downstream of the discharge valve, preferably continuous take off valve, preferably is positioned between a slurry outlet of the reactor vessel and the discharge valve.

[0168] The flow meter, particularly mass flow meter as described elsewhere herein, of each slurry withdrawal line is operably connected via a control system to the valve on the same slurry withdrawal line. More in particular, the control system is configured for individually adjusting the position of each discharge valve, particularly of each CTO valve, of the plurality of slurry withdrawal lines at least in response to the monitored (mass) flow in each individual slurry withdrawal line. The position of the valve of an individual slurry withdrawal line will thus be adjusted via the control system at least in response to the (mass) flow measured in the same individual slurry withdrawal line by the flow meter, particularly mass flow meter, as described herein, positioned on the same individual slurry withdrawal line. Advantageously, this allows a better control of both the overall flow of the slurry out of the reactor vessel and the control of the reactor pressure, or the slurry level in the reactor vessel, particularly in case of a CSTR reactor vessel, as well as the flow in an individual slurry withdrawal line, thus reducing the risk for fouling and / or blockage of a slurry withdrawal line.

[0169] In certain embodiments, the flow meter, particularly mass flow meter as described elsewhere herein, of a slurry withdrawal line may be operably connected via a control system to the feed system. Preferably, the mass flow meter as described herein may also monitor the slurry density, and the controller is further configured for adjusting the transfer of one or more of the olefin monomer, the diluent and / or the catalyst, particularly for adjusting the transfer of at least the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter, in particular the Coriolis type flow meter, more in particular the single straight tube Coriolis type mass flow meter. Stated differently, the mass flow meter on the at least one slurry withdrawal line or on the plurality of slurry withdrawal lines is not only operably connected to the discharge valve, particularly CTO valve, on the same slurry withdrawal line,to control the flow of the slurry through the slurry withdrawal line at least in response to the mass flow measured by the mass flow meter, but is also operably connected to the feed system to control the flow one or more of the olefin monomer, the diluent and / or the catalyst, at least in response to the measured slurry density. Advantageously, this way, the production process and the operation of the reactor system can be better optimized and controlled.

[0170] The at least one slurry withdrawal line or the plurality of slurry withdrawal lines may convey the slurry from the reactor vessel to a slurry treatment system or product recovery system, or to a second reactor vessel.

[0171] As used herein, the product recovery system or polymer recovery system generally refers to a system configured to separate the solid olefin polymer from the remainder of the reaction mixture or slurry, particularly from the liquid components in the slurry, such as unreacted monomer, and comonomer and / or diluent, if present. In certain embodiments, the product recovery system comprises one or more flash vessels, for flashing (evaporating) liquid in the slurry to vapour, thereby retaining the polymer solids. The evaporated liquid is recovered and these non-polymer liquid components are typically recycled to the reactor system. The flash vessel may be a single-stage or a multiple stage flash vessel.

[0172] When the at least one slurry withdrawal line or the plurality of slurry withdrawal lines conveys the slurry to a product recovery system, the slurry withdrawal lines are also referred to herein as flash lines or heated flash lines. In particular, as used in the different aspects and embodiments herein, the term “flash line” refers to a slurry withdrawal line comprising a segment adapted to be heated, or, more particularly, an elongated pipe or tube comprising a jacketed pipe or tube segment, the interior of which may be heated indirectly by running a heating medium through the jacket.

[0173] When the plurality of slurry withdrawal lines conveys the slurry to a second reactor vessel, the slurry withdrawal lines are also referred to herein as slurry transfer lines or transfer lines. In certain embodiments, the reactor system comprises between 2 and 10 slurry withdrawal lines, such as between 2 and 10 flash lines and / or between 2 and 10 transfer lines, particularly between 2 and 8 or between 2 and 6 slurry withdrawal lines, such as between 2 and 8 or between 2 and 6 flash lines and / or between 2 and 8 or between 2 and 6 transfer lines. It is understood that not all slurry withdrawal lines need to be active when the reactor system is in operation. The plurality of slurry withdrawal lines may comprise an inactive slurry withdrawal line or one or more inactive slurry withdrawal lines.

[0174] In particular embodiments, the reactor vessel in the reactor system is a double loop reactor, comprising a first pipe loop reactor connected in series to a second pipe loop reactor. Inparticular, the first pipe loop reactor is connected to the second pipe loop reactor via a single transfer line or via at least one transfer line (i.e. via at least one first slurry withdrawal line), such as via a single transfer line, or, particularly via a first plurality of slurry withdrawal lines or transfer lines, and the second pipe loop reactor is connected to a product recovery system via at least one flash line (i.e. via at least one second slurry withdrawal line), such as via a single flash line, or, particularly via a second plurality of slurry withdrawal lines or flash lines. It is understood that each transfer line of the at least one transfer line and each flash line of the at least one flash line may be provided with the mass flow meter, in particular the Coriolis type flow meter, more in particular the single straight tube Coriolis type mass flow meter as described elsewhere herein. More in particular, it is understood that each line of the first plurality of slurry withdrawal lines and each line of the second plurality of withdrawal lines may be provided with the (mass) flow meter, in particular the Coriolis type flow meter, more in particular the single straight tube Coriolis type mass flow meter as described elsewhere herein. Furthermore, the second plurality of slurry withdrawal lines (flash lines) comprises a discharge valve, particularly a CTO valve as described elsewhere herein, whereas the single transfer line or the first plurality of slurry withdrawal lines may or may not comprise a discharge valve.

[0175] In particular, when the reactor system comprises a plurality of slurry withdrawal lines, the flow meter, particularly the mass flow meter as described elsewhere herein, particularly positioned upstream of the discharge valve of each line of at least the second plurality of the slurry withdrawal lines, is operably connected via the control system to the discharge valve, particularly CTO valve, on the same slurry withdrawal line of at least the second plurality of the slurry withdrawal lines, wherein the control system is configured for individually adjusting the position of the discharge valve on the same slurry withdrawal line at least in response to the monitored (mass) flow by the flow meter, particularly mass flow meter as described elsewhere herein, and preferably in response to the reaction pressure measured by a pressure sensor in the reactor. Advantageously, this allows a better control of both the overall flow of the slurry out of the reactor vessel and the control of the reactor pressure, as well as the flow in an individual slurry withdrawal line, thus reducing the risk for fouling and / or blockage of a slurry withdrawal line. Particularly when the reactor vessel is a CSTR, the control system may preferably be configured for individually adjusting the position of the discharge valve on the same slurry withdrawal line at least in response to the monitored (mass) flow by the flow meter, particularly mass flow meter as described elsewhere herein, and preferably in response to the slurry level measured by a level sensor in the reactor.In certain embodiments, the at least one slurry withdrawal line provided with the mass flow meter, particularly the Coriolis type mass flow meter, more particularly the straight bore Coriolis type mass flow meter as described elsewhere herein corresponds to the at least one slurry transfer line connecting a first reactor vessel, particularly a first loop reactor, to a second reactor vessel, particularly a second loop reactor, thereby particularly forming the double loop reactor.

[0176] Accordingly, in certain embodiments, the reactor system comprises

[0177] (a’) a first reactor vessel adapted for performing a first slurry olefin polymerization process as described elsewhere herein, connected via at least one slurry transfer line to a second reactor vessel, wherein said second reactor vessel is preferably also adapted for performing a second slurry olefin polymerization process. Preferably, the first and second reactor vessels are loop reactors;

[0178] b7 a first feed system for transferring at least the olefin monomer and the catalyst, or for transferring at least the olefin monomer, the catalyst and the diluent, to the first reactor vessel; and

[0179] c7 at least one slurry transfer line, adapted for transferring a portion of the slurry from the first reactor vessel to the second reactor vessel, particularly in a continuous manner; wherein the at least one slurry transfer line comprises a mass flow meter for monitoring the slurry density of the slurry in the first reactor vessel, as described elsewhere herein, and, optionally, a discharge valve, particularly a CTO valve, wherein the mass flow meter is operably connected, particularly via a control system, to the first feed system, for adjusting the transfer of the olefin monomer or the catalyst, or for adjusting the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the first reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0180] In particular embodiments, the at least one slurry transfer line comprises a discharge valve, particularly positioned downstream of the mass flow meter. The position of the discharge valve regulates the flow of the slurry through the at least one slurry transfer line and the valve position may be regulated by a control system in response to the reaction pressure in the first reactor vessel, or, particularly in case of a CSTR reactor vessel, in response to the slurry level in the reactor vessel, and, preferably, also in response to the mass flow measured by the mass flow meter in the individual slurry transfer line.

[0181] In particular embodiments, the reactor system further comprises a product recovery system or a polymer recovery system adapted for recovering the solid olefin polymer from the reaction mixture, wherein the at least one slurry withdrawal line is configured to provide the slurry from the reactor vessel to the product recovery system. In more particular embodiments, the reactorsystem further comprises a product recovery system or a polymer recovery system adapted for recovering the solid olefin polymer from the reaction mixture, wherein the plurality of slurry withdrawal lines (flash lines) is configured to provide the slurry from the reactor vessel to the product recovery system. In the context of the present application, each flash line of the at least one flash line or of the plurality of flash lines comprises a first section, which is connected to the reactor vessel - via a slurry outlet, and a second section, downstream of the first section, and connected to the product recovery system.

[0182] More in particular, the first section of each slurry withdrawal line or flash line is connected to a slurry outlet of the reactor vessel, and the second section is positioned, downstream of the first section, and connected to the product recovery system, wherein the first section of each slurry withdrawal line comprises the discharge valve, particularly continuous take off (CTO) valve, and the flow meter, particularly mass flow meter as described elsewhere herein, particularly positioned upstream of the CTO valve, wherein a position of the discharge valve regulates the flow of the slurry through each slurry withdrawal line (flash line); and wherein the second section of each slurry withdrawal line or flash line comprises a line heater. In certain embodiments, the line heater is configured to be heated by steam. It is understood that the liquid medium of the polymer slurry is vaporized in the flash line utilizing the heat supplied by the line heater.

[0183] Preferably, the second section of each slurry withdrawal line or flash line comprises a temperature sensor, particularly positioned downstream of the line heater and upstream of the product recovery system, particularly for measuring the temperature of the composition in the slurry withdrawal line (flash line) exiting the heated section thereof. In particular embodiments, the temperature sensor is a temperature contact probe or a flush mounted temperature probe. The control system of the reactor system may be further configured to receive an input signal from the temperature sensor of each slurry withdrawal line (flash line). Advantageously, monitoring the temperature measured at the end of the flash line, prior to entering the product recovery system, allows a more reliable and precise monitoring of the correct functioning of each flash line and earlier detection of problems on the flash line, particularly compared to a pressure-based monitoring system. Preferably, each flash line further comprises control means for adjusting the temperature within the flash line, such as means for modulating a steam flow to each line heater, as known by the skilled person.

[0184] Additionally, the control system may be further configured to:

[0185] - control the heating of the line heater of each slurry withdrawal line individually at least in response to the input signal received from the temperature sensor on the individual slurry withdrawal line of the plurality of slurry withdrawal lines, i.e. the measured temperature of the individual slurry withdrawal line downstream of the line heater, and preferably also in responseto the monitored flow rate or mass flow rate by the flow meter as described elsewhere herein and / or

[0186] - adjust the position of the discharge valve, particularly CTO valve, on the same slurry withdrawal line at least in response to the monitored flow rate or mass flow by the flow meter as described elsewhere herein and to the measured temperature of the same slurry withdrawal line exiting the heated section thereof.

[0187] Advantageously, combining the (mass) flow measurement and, optionally, the slurry density measurement, at the beginning of a slurry withdrawal line, for each slurry withdrawal line of a plurality of slurry withdrawal lines, by a flow meter or mass flow meter as described elsewhere herein, and the temperature measurement at the end of a slurry withdrawal line, for each slurry withdrawal line of a plurality of slurry withdrawal lines, and subsequently controlling the heating of the line heater and / or the flow of the slurry through that slurry withdrawal line based thereupon, allows for a highly specific and individualised control of the olefin polymerization and recovery process in general, and the operation of each individual flash line in particular. More in particular, the individualized control of the heating and the mass flow in each slurry withdrawal line of a plurality of slurry withdrawal lines (flash lines) results in an optimized operation of each individual slurry withdrawal line (flash line), which goes hand in hand with a lower energy consumption and an optimized polyolefin production.

[0188] In certain embodiments, the mass flow meter as described elsewhere herein is operably connected to the discharge valve, particularly CTO valve, on the same flash line, wherein the control system is configured for individually adjusting the position of the discharge valve, particularly CTO valve, on the same flash line at least in response to the monitored mass flow by the mass flow meter, and preferably in response to the reactor pressure measured by a pressure sensor in the reactor vessel, or, particularly in case when the reactor vessel is a CSTR reactor vessel, in response to the slurry level in the reactor vessel measured by a level sensor. In addition, the mass flow meter as described elsewhere herein is preferably also operably connected via a control system to the feed system, to control the flow one or more of the olefin monomer, the diluent and / or the catalyst, at least in response to the measured slurry density. Advantageously, this allows a better control of both the slurry density as well as the overall flow of the slurry out of the reactor vessel and the control of the reactor pressure or slurry level, as well as the flow in an individual flash line of the at least one flash lines, such as in an individual flash line of a plurality of flash lines, thus reducing the risk for fouling and / or blockage of a slurry withdrawal line / flash line.The different components and reactants of the olefin polymerization process, i.e. at least an olefin monomer and a catalyst, and, optionally, a diluent, a comonomer and / or a chain transfer agent (e.g. hydrogen) are typically provided to the reactor vessel by a feed system as known in the art. In particular, the feed system comprises an olefin monomer feed line for transferring the olefin monomer to the reactor vessel, a catalyst feed line for transferring the catalyst to the reactor vessel, and, optionally a diluent feed line, a comonomer feed line and / or a chain transfer agent feed line, for transferring the diluent, the comonomer and the chain transfer agent, respectively, to the reactor vessel. In particular embodiments, each feed line comprises a valve for controlling the transfer of the respective component or reactant to the reactor vessel.

[0189] In particular, the slurry density in the reactor vessel is monitored by a mass flow meter, particularly a Coriolis type mass flow meter, more in particular a straight bore Coriolis type mass flow meter as envisaged herein, provided on at least one slurry withdrawal line or on each line of a plurality of slurry withdrawal lines, and which is operably connected, particularly via a control system, to the feed system. As the slurry density is a measure for the amount of polymer in the reactor vessel, or, stated differently, of the solid content in the reactor vessel, modulating the different feed streams in response to the monitored slurry density, particularly via the valves on the different feed lines, will impact the polymerization process and thus the solid content in the reactor.

[0190] In preferred embodiments, particularly when the olefin polymerization process is a polyethylene polymerization process, the slurry density is controlled by adjusting the feed of the diluent, which is comprised in the liquid medium. A higher amount of diluent results in a lower slurry density and vice versa. More in particular, the mass flow meter, particularly the Coriolis type mass flow meter, more in particular the straight bore Coriolis type mass flow meter as envisaged herein, provided on the at least one slurry withdrawal line or on each line of a plurality of slurry withdrawal lines, is operably connected, particularly via a control system, to the diluent feed line, particularly to a valve on the diluent feed line, wherein a position of said valve regulates the flow or transfer of the diluent to the reactor vessel.

[0191] Accordingly, in particular embodiments, the reactor system comprises

[0192] a’ / a reactor vessel, adapted for performing a slurry polyethylene polymerization process at a reaction pressure, said process comprising polymerizing at least ethylene in the presence of a catalyst and a diluent, to produce a slurry comprising a solid polyethylene polymer in a liquid medium;

[0193] b7 a feed system for transferring at least ethylene, the catalyst and the diluent, to the reactor vessel; andc7 at least one slurry withdrawal line or a plurality of slurry withdrawal lines, adapted for removing a portion of the slurry from the reactor vessel;

[0194] wherein the at least one slurry withdrawal line comprises a mass flow meter, as described elsewhere herein, for monitoring the slurry density, wherein the mass flow meter is operably connected, particularly via a control system, to the feed system, for adjusting the transfer of at least the diluent to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0195] Alternatively, for instance when the polymerization process occurs in absence of a diluent, such as when the olefin polymerization process is a polypropylene polymerization process, the slurry density may be controlled by adjusting the feed of monomer, which makes up the liquid medium, and / or by adjusting the feed of catalyst. A higher amount of catalyst will result in higher amounts of polyolefin polymers, and thus a higher solid content, and vice versa. More in particular, the mass flow meter, particularly the Coriolis type mass flow meter, more in particular the straight bore Coriolis type mass flow meter as envisaged herein, provided on the at least one slurry withdrawal line or on each line of a plurality of slurry withdrawal lines, is operably connected, particularly via a control system, to the monomer feed line and / or to the catalyst feed line, particularly to a valve on the monomer feed line and / or to a valve on the catalyst feed line, wherein a position of said valve(s) regulate(s) the flow or transfer of the monomer and / or catalyst to the reactor vessel.

[0196] Accordingly, in particular embodiments, the reactor system comprises

[0197] a’ / a reactor vessel, adapted for performing a slurry polypropylene polymerization process at a reaction pressure, said process comprising polymerizing at least propylene in the presence of a catalyst, to produce a slurry comprising a solid polypropylene polymer in a liquid medium; b7 a feed system for transferring at least propylene and the catalyst to the reactor vessel; and c7 at least one slurry withdrawal line or a plurality of slurry withdrawal lines, adapted for removing a portion of the slurry from the reactor vessel;

[0198] wherein the at least one slurry withdrawal line comprises a mass flow meter, as described elsewhere herein, for monitoring the slurry density, wherein the mass flow meter is operably connected, particularly via a control system, to the feed system, for adjusting the transfer of at least propylene and / or the catalyst to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0199] A second aspect of the present application provides an olefin polymerisation process comprising the steps of:(a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0200] (b) Withdrawing, preferably in a continuous manner, a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each individual slurry withdrawal line comprises a discharge valve and a flow meter, wherein a position of the discharge valve regulates the flow of the slurry through the individual slurry withdrawal line;

[0201] (c) Monitoring the mass flow rate or the volumetric flow rate in an individual slurry withdrawal line of the plurality of slurry withdrawal line with the flow meter; and

[0202] (d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each discharge valve individually at least in response to the monitored mass flow rate or monitored volumetric flow rate in each individual slurry withdrawal line.

[0203] In particular embodiments, each slurry withdrawal line comprises a discharge valve. The position of the discharge valve regulates the flow of the slurry through the individual slurry withdrawal line and the valve position may be regulated by a control system in response to the reaction pressure in the reactor vessel. In particular embodiments, the discharge valve is a continuous take off valve (CTO valve) or a product take off valve (PTO valve) as described elsewhere herein. Preferably, the discharge valve is a CTO valve which allows for the continuous removal of slurry from the reactor vessel in step (b).

[0204] Additionally, each slurry withdrawal line comprises a flow meter for determining the flow rate of the slurry flowing in the withdrawal line. The flow meter may be positioned upstream or downstream of the discharge valve. Preferably, the flow meter is positioned upstream of the discharge valve. Preferably, each slurry withdrawal line comprises a mass flow meter. Preferably, the mass flow meter is a Coriolis type flow meter and, more preferably, a single straight tube Coriolis type mass flow meter, as described elsewhere herein. In certain embodiments, the diameter of the single straight tube Coriolis type mass flow meter differs at most 50%, at most 40%, at most 30%, at most 20% or at most 10% with the diameter of the slurry withdrawal line, more particularly wherein the diameter of the single straight tube Coriolis type mass flow meter has the same diameter as the slurry withdrawal line. In particular embodiments, each mass flow meter on an individual slurry withdrawal line of the plurality of slurry withdrawal lines is operably connected to each CTO valve on the same individual slurry withdrawal line, particularly via a control system, allowing to individually adjust the position of each CTO valve, and hence, the flow of slurry through each individual slurry withdrawal line. Individually adjusting the position of the discharge valve, particularly the CTO valve of eachslurry withdrawal line of the plurality of slurry withdrawal lines at least in response to the mass flow measured in each individual slurry withdrawal line by the mass flow meter as described herein, positioned on the same individual slurry withdrawal line, allows a better control of both the overall flow of the slurry out of the reactor vessel and the control of the reaction pressure and reaction conditions, as well as the flow in an individual slurry withdrawal line, thus reducing the risk for fouling and / or blockage of a slurry withdrawal line.

[0205] In particularly preferred embodiments, the olefin polymerisation process comprises the steps of:

[0206] (a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0207] (b) Continuously withdrawing a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each slurry withdrawal line comprises a continuous take off (CTO) valve, such as a V-ball valve;

[0208] (c) Monitoring the mass flow in an individual slurry withdrawal line of the plurality of slurry withdrawal line with a mass flow meter as described elsewhere herein, particularly positioned upstream of the CTO valve of the individual slurry withdrawal line; and

[0209] (d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each CTO valve individually at least in response to the monitored mass flow in each individual slurry withdrawal line.

[0210] A further, related aspect of the present application provides an olefin polymerisation process comprising the steps of:

[0211] (aT) transferring at least an olefin monomer and a catalyst, or transferring at least an olefin monomer, a catalyst and a diluent, from a feed system to a reactor vessel;

[0212] (a2’) polymerizing, in the reactor vessel, at least the olefin monomer in the presence of the catalyst or polymerizing at least the olefin monomer in the presence of the catalyst and the diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;

[0213] (b’) withdrawing, particularly continuously withdrawing, a portion of the slurry from the reactor vessel through at least one slurry withdrawal line;

[0214] (o’) monitoring the slurry density in the at least one slurry withdrawal line with a mass flow meter, particularly a Coriolis type flow meter, and(d’) modulating, particularly via a control system, the transfer of the olefin monomer or the catalyst, or modulating the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

[0215] Advantageously, the slurry density no longer has to be measured using a nuclear source as in prior art polymerization systems and processes. Stated differently, in certain embodiments, the slurry density in the polymerization reaction according to the present application is not or no longer monitored by a nuclear (radioactive) densimeter. Preferably, the mass flow meter is a Coriolis type flow meter and, more preferably, a single straight tube Coriolis type mass flow meter, as described elsewhere herein.

[0216] According to the polymerization process of the present application, particularly in step (a) or step (aT) of the polymerization process of the present application, a reaction mixture in the form of a slurry is particularly prepared by feeding reactants to a reactor vessel, particularly a loop reactor, a double loop reactor or a CSTR as described elsewhere herein, to produce a polyolefin polymer or polyolefin copolymer slurry. Said reactants include at least one olefin monomer and a catalyst, or at least one olefin monomer, a diluent and a catalyst, and optionally one or more of hydrogen or other additives and one or more co-monomers, as described elsewhere herein. Said reactants are typically conveyed from a suitable feed system to the reactor vessel. In particular, the feed system comprises an olefin monomer feed line for transferring the olefin monomer to the reactor vessel, a catalyst feed line for transferring the catalyst to the reactor vessel, and, optionally a diluent feed line, a comonomer feed line and / or a chain transfer agent feed line, for transferring the diluent, the comonomer and the chain transfer agent, respectively, to the reactor vessel. In particular embodiments, each feed line comprises a valve for controlling the transfer of the respective component or reactant to the reactor vessel.

[0217] In particular embodiments, the olefin monomer is a 1-alkene having up to 10 carbon atoms per molecule, particularly up to 8 carbon atoms per molecule, or a mixture thereof. More in particular, the olefin monomer is ethylene, propylene, butene, pentene, hexene, octene, or a mixture thereof. A particularly preferred olefin monomer is ethylene and / or propylene. The diluent, when present, is preferably isobutane, propane, n-pentane, i-pentane, neopentane, n-hexane, or a mixture thereof, more preferably is isobutane.

[0218] In particular embodiments, for the synthesis of polyethylene polymers or copolymers, the reactants include ethylene (as monomer), a diluent and a catalyst, and optionally hydrogenand / or a comonomer. Suitable diluents are well known in the art and include hydrocarbons which are inert and liquid under reaction conditions, as discussed above. Non-limiting examples include isobutane, propane, n-pentane, i-pentane, neopentane and n-hexane. In particular embodiments, the reactants include ethylene (as monomer), isobutane (as diluent) and a catalyst, and optionally hydrogen and / or a comonomer.

[0219] In particular embodiments, for the synthesis of polypropylene polymers or copolymers, the reactants include propylene (as monomer) and a catalyst, and optionally hydrogen and / or a comonomer. Often, no diluent is present, with propylene acting both as the olefin monomer and as the liquid medium for the polymer slurry.

[0220] In certain embodiments, the polymerization step (a) or (a2’) may be performed at a temperature from 20 °C to 125 °C, preferably from 40 °C to 110 °C, more preferably from 40 °C to 100 °C and most preferably from 50 °C to 100 °C. In certain embodiments, particularly when performing the polymerization step in a loop reactor, the polymerization step (a) or step (a2’) may be performed at a reaction pressure from about 20 bar to about 100 bar, preferably from about 30 bar to about 50 bar, and more preferably from about 37 bar to about 45 bar. In other embodiments, particularly when performing the polymerization step in a CSTR reactor vessel, the polymerization step (a) or step (a2’) may be performed at a reaction pressure from about 5 bar to about 10 bar.

[0221] In certain embodiments, the process, particularly step (c), further comprises monitoring the slurry density by the mass flow meter, particularly by the Coriolis type flow meter, more in particular by the single straight tube Coriolis type mass flow meter. Advantageously, the slurry density no longer has to be measured using a nuclear source as in prior art polymerization systems and processes. Stated differently, in certain embodiments, the polymerization reaction according to the present application, particularly the slurry density in the reaction vessel is not or no longer monitored by a nuclear (radioactive) densimeter.

[0222] Additionally, the mass flow meters of the plurality of slurry withdrawal lines may be operably connected to the feed system, particularly via a control system. Accordingly, in certain embodiments, step (a) of the polymerization process according to the present invention comprises transferring the olefin monomer and the catalyst, or the olefin monomer, the catalyst and the diluent, to the reaction vessel, and the process further comprises adjusting the transfer or the flow of one or more of the olefin monomer, the catalyst and the diluent to the reactor vessel, particularly adjusting the transfer of at least the diluent to the reaction vessel, at leastin response to the monitored slurry density by the mass flow meter. Advantageously, this way, the polymerization process is better optimized and controlled.

[0223] In particular embodiments, step (c) or step (o’) may further comprise monitoring other process parameters. More in particular, these measured parameters are provided as input signals to a control system.

[0224] In certain embodiments, the polymerization process according to the present application further comprises, in step (c) or step (o’) monitoring the reaction pressure in the reactor vessel or, particularly in case of a CSTR reactor vessel, monitoring the slurry level in the reactor vessel. Additionally, step (d) or step (d’) may be performed further in response to the monitored reactor pressure or the monitored slurry level.

[0225] In particular embodiments, step (d) further comprises monitoring the reaction pressure in the reactor vessel, and / or monitoring the level of the slurry in case of CSTR, and / or monitoring the temperature in the at least one flash line, particularly downstream of the line heater, and step (e) further comprises modulating, particularly individually modulating, particularly via a control system, the flow of the slurry through the at least one slurry withdrawal line, such as by adjusting the position of the discharge valve, particularly CTO valve, on the at least one slurry withdrawal line, at least in response to the monitored reaction pressure, the monitored slurry level (in case of CSTR) and / or the monitored mass flow and / or temperature in the at least one slurry withdrawal line. This way, a more complete control of the olefin polymerization process is obtained. More in particular, it allows a better control of both the reaction conditions (slurry density) and the reactor pressure (reaction pressure) or reactor level (in case of CSTR), as well as the overall flow of the slurry out of the reactor vessel and the flow in an individual slurry withdrawal line, thus reducing the risk for fouling and / or blockage of a slurry withdrawal line.

[0226] In particular embodiments, the monitoring of the mass flow and particularly also the slurry density by the mass flow meter as described elsewhere herein, particularly the Coriolis type flow meter, more in particular by the single straight tube Coriolis type mass flow meter, in step (c) or step (o’), has a central role in the monitoring and the control of the polymerisation process in general, and the reaction conditions in the reactor vessel in particular. Indeed, the mass flow meter as described herein allows to monitor both the individual flowthrough a slurry withdrawal line of the plurality of slurry withdrawal lines and the slurry density. These measurements, combined with the measurements of the reaction pressure or reactor level (particularly in case of a CSTR reactor vessel), may be provided as input signals to a control system, and subsequently the polymerization process and the reaction conditions in thereactor vessel can be controlled by adjusting the transfer of one or more compounds from the feed system to the reactor vessel, in particular by adjusting the transfer of at least the diluent from the feed system to the reactor vessel, and by adjusting the position of the individual CTO valves on each slurry withdrawal line, and hence the flow of slurry in the individual slurry withdrawal line out of the reactor vessel. Advantageously, by providing a mass flow meter on the individual slurry withdrawal lines, a single type of instrument can be used to control both the feed system, and hence, the conditions in the reactor vessel, as well as the flow exiting the reactor vessel, in particular the flow and conditions in the individual slurry withdrawal lines, particularly the flow and conditions in the individual flash lines.

[0227] Accordingly, in particular embodiments, the process according to the present application is a method of controlling a polymerization process according to the present application, wherein a target total flow rate of the slurry out of the reactor vessel is controlled or determined by the reaction pressure and wherein the individual flow rate of the slurry in an individual slurry withdrawal line is based on the target total flow rate of the slurry divided by the number of active CTO valves of the plurality of slurry withdrawal lines, and wherein the position of each individual CTO valve is adjusted in response to the monitored mass flow rate of the slurry, and preferably also in response to the monitored temperature of the flash line, in each of the slurry withdrawal lines in order to reach the target total flow rate and target temperature, and, additionally, wherein the feed rate of at least the diluent, and optionally the other components from the feed system to the reactor vessel is adjusted at least in response to the monitored slurry density and to the reactor pressure (or the slurry level, particular in case of a CSTR reactor vessel).

[0228] In step (b) or step (b’), the slurry is typically provided to a slurry treatment system or a product recovery system, adapted for recovering the solid olefin polymer from the polymer slurry, as described elsewhere herein. The slurry may also be provided to a second reactor vessel, such as in a double loop reactor setup comprising a first loop reactor connected in series to a second loop reactor.

[0229] In particular embodiments, step (b) comprises providing the slurry to a product recovery system as described elsewhere herein via the plurality of slurry withdrawal lines, also referred to as flash lines, wherein each slurry withdrawal line (flash line) comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises the discharge valve, particularly the continuous take off (CTO)valve, and the flow meter, particularly the mass flow meter as described elsewhere herein, and wherein the second section of each slurry withdrawal line comprises a line heater, adapted for heating the slurry conveyed through each slurry withdrawal line (flash line).

[0230] In particular embodiments, the polymerization process further comprises the step of monitoring the temperature of an individual slurry withdrawal line (flash line) of the plurality of slurry withdrawal lines (flash lines) by a temperature sensor, particularly positioned downstream of the line heater, and wherein step (d) is performed further in response to the monitored temperature in an individual slurry withdrawal line.

[0231] Additionally, the polymerization process may further comprise the step of regulating the heating of the line heater of an individual slurry withdrawal line of the plurality of slurry withdrawal lines in response to at least the monitored temperature and the monitored mass flow of that individual slurry withdrawal line, particularly by individually modulating a steam flow to each line heater.

[0232] In particular embodiments, the polymerization process according to the present application comprises the steps of:

[0233] (a) Polymerizing, in a loop reactor or a double loop reactor as described elsewhere herein, at least one olefin monomer, such as propylene, in the presence of a catalyst or at least one olefin monomer, such as ethylene, in the presence of a catalyst and a diluent, such as isobutane, at a reaction pressure, to produce a slurry comprising a solid olefin polymer, such as a propylene or ethylene polymer or copolymer, in a liquid medium;

[0234] (b) Continuously withdrawing a portion of the slurry from the loop or double loop reactor through a plurality of slurry withdrawal lines to a product recovery system, wherein each slurry withdrawal line comprises a first section, connected to the loop or double loop reactor, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises a continuous take off (CTO) valve and a mass flow meter, particularly a Coriolis type flow meter, more in particular a single straight tube Coriolis type mass flow meter, positioned upstream of the CTO valve, and wherein the second section of each slurry withdrawal line comprises a line heater, adapted for heating the slurry conveyed through each slurry withdrawal line;

[0235] (c) Monitoring the mass flow in an individual slurry withdrawal line of the plurality of slurry withdrawal line with a mass flow meter, positioned upstream of the CTO valve of the individual slurry withdrawal line; and, preferably, monitoring the slurry density with the mass flow meter; and / or monitoring the reaction pressure in the loop or double loop reactor and / or monitoring the temperature of the composition in the slurry withdrawal line downstream of the line heater;(d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each CTO valve individually at least in response to the monitored mass flow in each individual slurry withdrawal line, to the monitored slurry density, to the monitored reaction pressure or to the monitored temperature in each slurry withdrawal line downstream of the line heater. Additionally, the transfer of at least the diluent, and optionally the transfer of the olefin monomer and / or catalyst, may be adjusted at least in response to the monitored slurry density, or optionally also in response to the mass flow in each individual slurry withdrawal line, or to the monitored reaction pressure. Additionally, the heating of the line heater of each slurry withdrawal line may be individually modulated, such as by modulating the transfer of steam to the line heater, at least in response to the monitored mass flow in each individual slurry withdrawal line and to the monitored temperature in each slurry withdrawal line downstream of the line heater.

[0236] Advantageously, combining the mass flow measurement at the beginning of a slurry withdrawal line, for each slurry withdrawal line of a plurality of slurry withdrawal lines, by a mass flow meter as described elsewhere herein, and the temperature measurement at the end of a slurry withdrawal line, downstream of the line heater, for each slurry withdrawal line of a plurality of slurry withdrawal lines, and subsequently controlling the heating of the line heater and / or the flow of the slurry through that slurry withdrawal line, allows for a highly specific and individualised control of the olefin polymerization and recovery process in general, and the operation of each individual flash line in particular. More in particular, the individualized control of the heating and the mass flow in each slurry withdrawal line of a plurality of slurry withdrawal lines (flash lines) results in an optimized operation of each individual slurry withdrawal line (flash line), which goes hand in hand with a lower energy consumption and an optimized polyolefin production.

[0237] In particular embodiments, in step (d’), the transfer of the olefin monomer or the catalyst, or the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel is modulated by modulating the flow of olefin monomer in the olefin monomer feed line, the flow of catalyst in the catalyst feed line and / or the flow of diluent in the diluent feed line, particularly by adjusting the position of a valve on the olefin monomer feed line, the catalyst feed line and / or the diluent feed line.

[0238] In particular embodiments, when the olefin polymerization process is a polyethylene polymerization process, in step (d’), the slurry density is preferably controlled by adjusting the feed of the diluent, which is comprised in the liquid medium. A higher amount of diluent resultsin a lower slurry density and vice versa. More in particular, the mass flow meter, particularly the Coriolis type mass flow meter, more in particular the straight bore Coriolis type mass flow meter as envisaged herein, provided on the at least one slurry withdrawal line, is operably connected, particularly via a control system, to the diluent feed line, particularly to a valve on the diluent feed line, wherein a position of said valve regulates the flow or transfer of the diluent to the reactor vessel.

[0239] Accordingly, in particular embodiments, the olefin polymerisation process is a polyethylene polymerisation process, comprising the steps of:

[0240] (aT) transferring at least ethylene, a diluent, and a catalyst, to a reactor vessel, particularly to a loop reactor;

[0241] (a2’) polymerizing, in the reactor vessel, at least ethylene in the presence of the catalyst and the diluent, at a reaction pressure, to produce a slurry comprising a solid polyethylene polymer in a liquid medium;

[0242] (b’) withdrawing, particularly continuously withdrawing, a portion of the slurry from the reactor vessel through at least one slurry withdrawal line;

[0243] (o’) monitoring the slurry density in the at least one slurry withdrawal line with a mass flow meter, particularly a Coriolis type flow meter, more particularly a single straight bore Coriolis type flow meter, as described elsewhere herein,

[0244] (d’) modulating, particularly via a control system, the transfer of the diluent to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter, and, optionally,

[0245] (e’) monitoring the mass flow in the at least one slurry withdrawal line by the mass flow meter, monitoring the temperature of the slurry in the at least one slurry withdrawal line by a temperature sensor, particularly positioned downstream of the line heater, and monitoring the reactor pressure in the reaction vessel or, particularly in case of a CSTR reactor vessel, monitoring the slurry level; and modulating the flow in the at least one slurry withdrawal line at least in response to the monitored mass flow and / or to the monitored temperature in the slurry withdrawal line and / or to the monitored reaction pressure and / or to the monitored slurry level.

[0246] Alternatively, for instance when the polymerization process occurs in absence of a diluent, such as when the olefin polymerization process is a polypropylene polymerization process, the slurry density may be controlled, in step (d’) by adjusting the feed of monomer, which makes up the liquid medium, and / or by adjusting the feed of catalyst. A higher amount of catalyst will result in higher amounts of polyolefin polymers, and thus a higher solid content, and vice versa. More in particular, the mass flow meter, particularly the Coriolis type mass flow meter, more in particular the straight bore Coriolis type mass flow meter as envisagedherein, provided on the at least one slurry withdrawal line, is operably connected, particularly via a control system, to the monomer feed line and / or to the catalyst feed line, particularly to a valve on the monomer feed line and / or to a valve on the catalyst feed line, wherein a position of said valve(s) regulate(s) the flow or transfer of the monomer and / or catalyst to the reactor vessel.

[0247] Accordingly, in particular embodiments, the olefin polymerisation process is a polypropylene polymerisation process, comprising the steps of:

[0248] (aT) transferring at least propylene and a catalyst, to a reactor vessel, particularly to a loop reactor;

[0249] (a2’) polymerizing, in the reactor vessel, at least propylene in the presence of the catalyst, at a reaction pressure, to produce a slurry comprising a solid polypropylene polymer in a liquid medium;

[0250] (b’) withdrawing, particularly continuously withdrawing, a portion of the slurry from the reactor vessel through at least one slurry withdrawal line;

[0251] (o’) monitoring the slurry density in the at least one slurry withdrawal line with a mass flow meter, particularly a Coriolis type flow meter, more particularly a single straight bore Coriolis type flow meter, as described elsewhere herein, and

[0252] (d’) modulating, particularly via a control system, the transfer of the catalyst and / or the propylene, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter; and, optionally,

[0253] (e’) monitoring the mass flow in the at least one slurry withdrawal line by the mass flow meter, monitoring the temperature of the slurry in the at least one slurry withdrawal line by a temperature sensor, particularly positioned downstream of the line heater, and monitoring the reactor pressure in the reaction vessel or, particularly in case of a CSTR reactor vessel, monitoring the slurry level; and modulating the flow in the at least one slurry withdrawal line at least in response to the monitored mass flow and / or to the monitored temperature in the slurry withdrawal line and / or to the monitored reaction pressure and / or to the monitored slurry level. Additionally, the polymerization process may further comprise the step of regulating the heating of the line heater of the at least one flash line, in response to at least the monitored temperature and the monitored mass flow in the at least one flash line, such as by individually modulating a steam flow to the line heater on the at least one flash line. Advantageously, the control of the heating and the mass flow in the at least one flash line, particularly the individual control of a plurality of flash lines, results in an optimized operation of the at least one flash line, which goes hand in hand with a lower energy consumption and an optimized polyolefin production.EXAMPLARY EMBODIMENTS

[0254] The embodiments described herein are further illustrated by the following non-limiting examples.

[0255] Figure 1 schematically represents an embodiment of a polyolefin polymerization reaction system, particularly for the production of polyethylene, according to the present application. The reactor system (100) comprises a double loop reactor comprising a first loop reactor (110) and a second loop reactor (115). Each loop reactor comprises a plurality of interconnected pipes and the vertical sections of the pipe segments are preferably provided with cooling jackets. Each loop reactor is connected to a feed system (150, 155) for supplying the monomer, e.g. ethylene, diluent, polymerization catalyst and optionally hydrogen or other additives and olefin co-monomers to the first and / or second loop reactor (110, 115) to form a polymerization slurry in the reactor. In particular, when polymerizing ethylene, in the presence of a suspension of catalyst in diluent, said diluent having low solubility for the polymer, the polymer is produced in the form of solid particles, insoluble in the diluent. The polymerization slurry is circulated continuously, for instance with a pump or with a motor-driven impeller disposed within the reactor (111, 112). In the present embodiment, the polymer slurry produced in the first loop reactor (110) is transferred to the second loop reactor (115) via a slurry transfer line (113). The polyolefin slurry, e.g. the polyethylene slurry consisting of the reactants and polyethylene powder, is withdrawn from the second loop reactor (115) via multiple slurry withdrawal lines (120a, 120b, 120c), also referred to as flash lines, to a product recovery system. Each slurry withdrawal line (120a, 120b, 120c) comprises a straight bore Coriolis-type mass flow meter (140a, 140b, 140c) a continuous take off valve (CTO valve) (130a, 130b, 130c) and an in-line flash heater (160a, 160b, 160c), wherein heat is provided by steam. Downstream of each in-line flash heater a temperature sensor (170a, 170b, 170c) is positioned. A control system monitors the pressure in the dual loop reactor and the mass flow through each slurry withdrawal line, and controls the position of each individual CTO valve of each slurry withdrawal line based on the measured parameters. Additionally, the control system monitors the temperature of the individual slurry withdrawal line and controls the steam flow and / or the flow of the slurry (by controlling the position of each individual CTO valve of each slurry withdrawal line) based on the measured parameters.

[0256] Figure 2 schematically represents an alternative embodiment of a polyolefin polymerization reaction system, particularly for the production of polyethylene, according to the present application. The reactor system (200) comprises a CST reactor (210), connected to a feed system (250) for supplying the monomer (e.g. ethylene), diluent, polymerization catalyst andoptionally hydrogen or other additives and olefin co-monomers to the reactor (210) to form a polymerization slurry in the reactor. The CSTR comprises an internal agitator driven by a motor (211) for mixing the reaction slurry. The polyolefin slurry, e.g. the polyethylene slurry consisting of the reactants and polyethylene powder, is withdrawn from the CSTR via multiple slurry withdrawal lines (220a, 220b, 220c), also referred to as flash lines, to a product recovery system. Each slurry withdrawal line (220a, 220b, 220c) comprises a straight bore Coriolis-type mass flow meter (240a, 240b, 240c), a continuous take off valve (CTO valve) (230a, 230b, 230c) and an in-line flash heater (260a, 260b, 260c). In the in-line heater, steam is used to heat the slurry in the flash line. Downstream of each in-line flash heater, a temperature sensor (270a, 270b, 270c) is positioned. A control system monitors the level in the CSTR and the mass flow through each slurry withdrawal line, and controls the position of each individual CTO valve of each slurry withdrawal line based on the measured parameters, thereby individually controlling the mass flow through each individual slurry withdrawal line. Additionally, the control system monitors the temperature of the individual slurry withdrawal line and controls the steam flow and / or the flow of the slurry (by controlling the position of each individual CTO valve of each slurry withdrawal line) based on the measured parameters.

[0257] Figure 3 schematically represents an embodiment of a polyolefin polymerization reaction system, particularly for the production of polyethylene, according to the present application. The reactor system (300) comprises a loop reactor (310), comprising a plurality of interconnected pipes. The vertical sections of the pipe segments are preferably provided with cooling jackets. The loop reactor (310) is connected to a feed system (350) for supplying the monomer, e.g. ethylene, diluent, polymerization catalyst, and, optionally, hydrogen or other additives and olefin co-monomers to the loop reactor (310) to form a polymerization slurry in the reactor. In particular, when polymerizing ethylene, in the presence of a suspension of catalyst in diluent, said diluent having low solubility for the polymer, the polymer is produced in the form of solid particles, insoluble in the diluent. The polymerization slurry is circulated continuously, for instance with a motor-driven impeller (315) disposed within the reactor. The polyolefin slurry, e.g. the polyethylene slurry consisting of the reactants and polyethylene powder, is withdrawn from the loop reactor (310) via a slurry withdrawal line (320) and may be provided to a second reactor or to a polymer recovery system. The slurry withdrawal line (320) comprises a straight bore Coriolis-type mass flow meter (330) for measuring the density of the polyolefin slurry withdrawn from the reactor. Advantageously, this makes a nuclear based densimeter in the reactor vessel obsolete. The slurry density, and preferably the reactor pressure, is further monitored by a control system, which particularly controls the addition of diluent to the reactor via a valve (340) on the diluent feed line.Figure 4 schematically represents an alternative embodiment of a polyolefin polymerization reaction system, particularly for the production of polyethylene, according to the present application. The reactor system (400) comprises a CST reactor (410), connected to a feed system (450) for supplying the monomer (e.g. ethylene), diluent, polymerization catalyst and optionally hydrogen or other additives and olefin co-monomers to the reactor (410) to form a polymerization slurry in the reactor. In particular, when polymerizing ethylene, in the presence of a suspension of catalyst in diluent, said diluent having low solubility for the polymer, the polymer is produced in the form of solid particles, insoluble in the diluent. The CSTR (410) comprises an internal agitator driven by a motor (411) for mixing the reaction slurry. The polyolefin slurry, e.g. the polyethylene slurry consisting of the unreacted reactants and polyethylene powder, is withdrawn from the CST reactor (410) via a slurry withdrawal line (420) and may be provided to a second reactor or to a polymer recovery system. The slurry withdrawal line (420) comprises a straight bore Coriolis-type mass flow meter (430) for measuring the density of the polyolefin slurry withdrawn from the reactor. The slurry density, and preferably also the level in the CST reactor, is further monitored by a control system, which particularly controls the addition of diluent to the reactor via a valve (440) on the diluent feed line.

Claims

CLAIMS1. A reactor system comprising:a / a reactor vessel, adapted for performing a slurry olefin polymerization process at a reaction pressure, said process comprising polymerizing at least one olefin monomer in the presence of a catalyst to produce a slurry comprising a solid olefin polymer in a liquid medium;b / a plurality of slurry withdrawal lines, such as between 2 and 10 slurry withdrawal lines, wherein each slurry withdrawal line is adapted for removing a portion of the slurry from the reactor vessel via a slurry outlet; andc / a slurry treatment system, particularly adapted for recovering the solid olefin polymer, wherein the plurality of slurry withdrawal lines is configured to provide the slurry from the reactor vessel to the slurry treatment system;wherein each slurry withdrawal line comprises a discharge valve, wherein a position of the discharge valve between the fully closed position and the fully open position of the valve regulates the flow of the slurry through each slurry withdrawal line;wherein each slurry withdrawal line further comprises a flow meter, wherein the flow meter of each slurry withdrawal line is operably connected via the control system to the discharge valve on the same slurry withdrawal line;wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the slurry treatment system, wherein the first section of each slurry withdrawal line comprises the discharge valve and the flow meter, and wherein the second section of each slurry withdrawal line comprises a line heater and a temperature sensor;wherein the reactor system further comprises a control system for controlling the position of the discharge valves and the heating of the line heater, wherein the control system is configured for individually adjusting the position of the discharge valve and the heating of the line heater on the same slurry withdrawal line for each slurry withdrawal line of the plurality of slurry withdrawal lines at least in response to the monitored flow rate by the flow meter and an input signal received from the temperature sensor on the slurry withdrawal line.

2. The reactor system according to claim 1, wherein:- the discharge valve on each slurry withdrawal line is a continuous take off valve (CTO valve) for continuously removing a portion of the slurry from the reactor vessel; and / orthe flow meter on each slurry withdrawal line is a mass flow meter, particularly a Coriolis type mass flow meter, positioned upstream of the discharge valve, and wherein the control systemis configured for individually adjusting the position of the CTO valve on the same slurry withdrawal line at least in response to the monitored mass flow rate by the mass flow meter.

3. The reactor system according to claim 2, wherein the mass flow meter is a single straight tube Coriolis type mass flow meter, particularly wherein the diameter of the single straight tube Coriolis type mass flow meter differs at most 50% or at most 20% with the diameter of the slurry withdrawal line.

4. The reactor system according to any one of claims 1 to 3, wherein the reactor system further comprises a feed system for transferring at least an olefin monomer and a catalyst, or for transferring at least an olefin monomer, a catalyst and a diluent, to the reaction vessel, and wherein the flow meter, particularly mass flow meter, of a slurry withdrawal line is operably connected via a control system to the feed system.

5. The reactor system according to claim 4, wherein the flow meter is a mass flow meter and is operably connected, via the control system, to the feed system, for adjusting the transfer of one or more of the olefin monomer and the catalyst, or for adjusting the transfer of one or more of the olefin monomer, the catalyst and the diluent, to the reaction vessel, at least in response to the monitored slurry density by the mass flow meter.

6. The reactor system according to any one claims 1 to 5, wherein the reactor vessel is a pipe loop reactor, which defines a continuous flow path for a reaction mixture, wherein the reactor vessel is a double loop reactor, or wherein the reactor vessel is a stirred-tank reactor, particularly a continuous stirred-tank reactor (CSTR).

7. The reactor system according to any one of claims 1 to 6, wherein the flow meter is positioned upstream of the discharge valve on each slurry withdrawal line of the plurality of slurry withdrawal lines.

8. The reactor system according to claim 7, wherein the temperature sensor, such as a temperature contact probe or a flush mounted temperature probe, is positioned downstream of the line heater on each slurry withdrawal line of the plurality of slurry withdrawal lines.

9. An olefin polymerisation process comprising the steps of:(a) Polymerizing, in a reactor vessel, at least one olefin monomer in the presence of a catalyst or at least one olefin monomer in the presence of a catalyst and a diluent, at a reaction pressure, to produce a slurry comprising a solid olefin polymer in a liquid medium;(b) withdrawing, particularly in a continuous manner, a portion of the slurry from the reactor vessel through a plurality of slurry withdrawal lines, wherein each slurry withdrawal line comprises a discharge valve, in particular a continuous take off (CTO) valve and a flow meter, and providing the slurry to a slurry treatment system, adapted for recovering the solid olefin polymer, wherein each slurry withdrawal line comprises a first section, which is connected to a slurry outlet of the reactor vessel, and a second section, downstream of the first section, and connected to the product recovery system; wherein the first section of each slurry withdrawal line comprises the discharge valve and the flow meter, wherein a position of the discharge valve between the fully closed position and the fully open position of the valve regulates the flow of the slurry through each slurry withdrawal line; and wherein the second section of each slurry withdrawal line comprises a line heater;(c) Monitoring the flow rate, particularly the mass flow, in an individual slurry withdrawal line of the plurality of slurry withdrawal line with a flow meter, particularly a mass flow meter, particularly positioned upstream of the discharge valve of the individual slurry withdrawal line and monitoring the temperature of an individual slurry withdrawal line of the plurality of slurry withdrawal lines by a temperature sensor, particularly positioned downstream of the line heater; and(d) Individually modulating the flow of the slurry through each individual slurry withdrawal line of the plurality of slurry withdrawal lines by adjusting the position of each discharge valve individually at least in response to the monitored flow in each individual slurry withdrawal line, particularly in response to the monitored mass flow in each individual slurry withdrawal line, and further in response to the monitored temperature in an individual slurry withdrawal line.

10. The process according to claim 9, wherein step (c) comprises monitoring the mass flow and, optionally, the slurry density, in an individual slurry withdrawal line of the plurality of slurry withdrawal lines with a Coriolis type mass flow meter, particularly a single straight tube Coriolis type mass flow meter.

11. The process according to claim 10 or 11, further comprising monitoring the reaction pressure or the slurry level in the reactor vessel, and wherein step (d) is performed further in response to the monitored reaction pressure or slurry level.

12. The process according to any one of claims 9 to 11, further comprising the step of regulating the heating of the line heater of an individual slurry withdrawal line of the plurality of slurry withdrawal lines in response to at least the monitored temperature and the monitored flow rate, particularly mass flow, of that individual slurry withdrawal line.

13. The process according to claim 12, wherein regulating the heating of an individual slurry withdrawal line of the plurality of slurry withdrawal lines is performed by individually modulating a steam flow to each line heater or by individually modulating the slurry mass flow through each slurry withdrawal line.

14. The process according to any one of claims 9 to 13, wherein the olefin monomer is a 1-alkene having up to 10 carbon atoms per molecule, particularly wherein the olefin monomer is ethylene, propylene, butene, pentene, hexene, octene, or a mixture thereof, more particularly wherein the olefin monomer is ethylene and / or propylene; and / or wherein the diluent, when present, is isobutane, propane, n-pentane, i-pentane, neopentane, n-hexane, or a mixture thereof.

15. The process according to any one of claims 9 to 14, wherein the process is a method of controlling the olefin polymerization process, wherein a target total flow rate of the slurry out of the reactor vessel is determined by the reaction pressure or the slurry level in the reactor vessel, and wherein the individual flow rate of the slurry in an individual slurry withdrawal line is based on the target total flow rate of the slurry divided by the number of active discharge valves, particularly active CTO valves, of the plurality of slurry withdrawal lines, and wherein the position of each individual discharge valve, particularly CTO valve, is adjusted in response to the monitored mass flow rate in each of the slurry withdrawal lines in order to reach the target total flow rate.

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