Title of Invention

"SWELL CONTROL IN SLURRY LOOP REACTOR."

Abstract The present invention discloses a method for controlling the onset and development of swelling in a slurry loop reactor by progressively diluting the reactor, the amount of dilution being driven by the amplitude of the fluctuations measured on some plant measurement.
Full Text WO 2005/082518 PCT/EP2005/050519
SWELL CONTROL IN SLURRY LOOP REACTOR.
The present invention relates to the field of polymerisation of olefin in a slurry loop reactor.
High density polyethylene (HDPE) was first produced by addition polymerization carried out in a liquid that was a solvent for the resulting polymer. That method was rapidly replaced by polymerisation under slurry conditions according to Ziegler or Phillips. More specifically slurry polymerisation was carried out continuously in a pipe loop reactor. A polymerization effluent is formed which is a slurry of particulate polymer solids suspended in a liquid medium, ordinarily the reaction diluent and unreacted monomer (see for Example US-A-2,285,721). It Is desirable to separate the polymer and the liquid medium comprising an inert diluent and unreacted monomers without exposing the liquid medium to contamination so that said liquid medium can be recycled to the polymerization zone with minimal or no purification. As described in US-A-3,152,872, a slurry of polymer and the liquid medium is collected in one or more settling legs of the slurry loop reactor from which the slurry is periodically discharged to a flash chamber thus operating in a batch-wise manner.
The mixture is flashod in order to remove the liquid medium from the polymer fluff. It is afterwards necessary to recompress the vaporized polymerization diluent to recondition and purify it.
Due to economical incentives, the reactor is generally pushed to its limits of operability. High concentration of monomer and optional comonomer, high temperature and high solid content are three important factors that allow to increase the kinetics of the polymerisation chemical reaction.
The power consumption of the circulation pump normally increases slowly with increasing solid content When any one of the three parameters just mentioned (monomer and optional comonomer concentration, temperature and solid content) increases above a certain level, depending upon the polymer characteristics and

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upon the reactor characteristics, it is additionally observed that the level of noise of this power consumption starts Increasing gradually and if not property controlled may provoke the safety shut-down of operations. This behaviour is known as the swelling phenomenon. The same type of behaviour can be observed on other plant control measurements such as, without limitation, the reactor temperature, the slurry density or the temperature change experienced by the cooling water circulating in all or a portion of the cooling jacket
In this description and In the context of slurry loop polymerisation, swelling is then defined as a phenomenon that is well known to the person in the art and is associated to the onset of a process instability characterised by rapid fluctuations, significantly larger than usual, in several process variables, the most perturbing of which being the pump power. The term rapid in this context means that successive peaks are separated by less than one minute. Whereas normal operations are performed with pump power fluctuating in a range of less than 10 kW, such range may increase by a factor of 10 when swelling is well established. Fluctuations in the pump power consumption are Important and if not controlled they can rapidly reach the safety threshold, thereby inducing automatic actions that may include operations shut-down thus ending the polymerisation process. The onset of instability is linked to the transgression of some process limitations associated with measurable process variables such as for example reactor temperature, monomer and/or comonomer concentrations and/or solids concentration in the reactor. Profitability of the plant is however also linked, among othor parameters, to those same variables but counter to the stability requirements. There is thus a strong economical incentive to work as close as possible to the multi-dimensional stability boundary with the risk that some natural process fluctuation initiates swelling instability.
Ways of controlling operations at high solids concentrations are known in the prior art For example,
EP-A-432555 provides a method for controlling the polymerisation process. This Is accomplished by establishing control signals which typify flow rate of diluent fluid required to;
(a) maintain a minimum velocity for the circulating reaction slurry;

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(b) maintain a maximum pressure head at a selected point in the reactor and
(c) maintain a maximum power level supplied to the circulating pump.
The one of signals (a), (b) and (c)above which requires the greatest flow rate of diluent fluid, is automatically selected to manipulate diluent flow.
Monomer concentration and reactor temperature are usually kept nominally constant to maintain the product quality in the narrow specification required. Increasing solids concentration generally improves the product quality as, at constant reactor throughput, the residence time in the reactor, defined as the mass of solids present in the reactor divided by the production, increases with increasing solids concentration.
It is indeed desired to increase the residence time in the reactor in order to maximize the contact time with the catalyst and to improve the granulometry of the final product. As the mass of solids present in the reactor is defined as the product of the reactor volume by the density of the slurry and by the solid content, and as the density of the slurry is increasing with the solid content, it is thus highly desirable to increase the solid content. Unfortunately, the most usual cause of swelling Is high solid content.
For all these reasons, it is desirable to operate the reactor at conditions that are as close as possible to the onset of swelling.
It is an object of the present invention to detect the onset of swelling
It is another object of the present invention to control and refrain the development of the swelling.
It is also an aim of the present invention to improve the catalyst productivity and therefore the reactor throughput.
It is a further object of the present invention to increase the solids concentration in the reactor or in the settling legs.

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It is yet another object of the present invention to increase the production of polymer in a slurry loop reactor.
Accordingly, the swelling is controlled by diluting the reactor medium, said dilution being triggered and controlled by the standard deviation or the variance or the fluctuation range or any other function monotonically related to the variance of a plant control measurement displaying an increasing fluctuation level when swelling occurs.
Contrary to EP-A-432555 that describes the manipulation of diluent fluid rate in order to avoid increase of actual pump power above a pre-determined threshold, the present invention does not aim at controlling the actual values of selected plant control measurements but at controlling the standard deviation of said selected plant control measurements. As can be seen on figure 1, swelling, as described here-above, starts developing without significant increase of the actual pump power. The objective of the present invention is to control incipient swelling at an early stage.
The plant control measurements are for example the pump power consumption, the reactor temperature, the slurry density or the temperature difference between the entering and exiting cooling liquid or any combination of such measurements.
List of Figures.
Figure 1 represents the pump power expressed in kW as a function of time expressed in hours for a loop reactor without by-pass during an uncontrolled swelling.
Figure 2 represents schematically the loop reactor (1) with a by-pass line (2) inserted between two points of the main loop. It also includes the settling legs (3).

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Figure 3 represents the pump power expressed in kW as a function of time expressed in hours for a loop reactor equipped with a by-pass line during an uncontrolled swelling.
Figure 4 represents the proposed processed signal used for controlling the dilution of the reactor in the case of the swelling corresponding to figure 3. The pump power is displayed on top to allow a better visualisation of the reaction time of the detection.
The pump power consumption in normal operating conditions is displayed on Figure 1 representing the pump power expressed in kW as a function of time expressed in hours. Typically the pump power consumption is of the order of 200 kW to 800 kW depending on the reactor size and shape and the standard deviation of the signal due to white noise is of the order of 1 to 10 kW. As the solid content increases, the ' pump power consumption increases very slowly keeping the same level of white noise. When swelling occurs, the standard deviation starts increasing and reaches progressively an unacceptable level causing the system to shut-off as seen on the same Figure 1.
Other plant control measurements like (but not limited to) the temperature of the reactor, the density of the slurry and the temperature change experienced by the cooling water circulating in all or a portion of the cooling jacket also all exhibit variations in the standard deviation that Increases with increasing solids concentration.
Surprisingly, it is found that this fluctuation increase is due to the superposition to the constant white noise of a unique signal characteristic of the reactor. The amplitude of said unique signal progressively increases during the swelling phenomenon.
Several parameters of the signal have been studied such as for example the standard deviation, or the variance, or the fluctuation range, or any other function monotonically related to the standard deviation. Usual mathematical signal treatments, such as for example deconvolution, frequency filtering, standard pattern recognition techniques may be applied to the signal before computation of the

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variance related detector, depending on the strength of the unique signal characteristic of the reactor just mentioned here above.
The swelling is controlled by diluting the reactor medium, thereby decreasing the solid content and the temperature.
As soon as the signal parameters of pump power consumption increase above a pre-determined threshold, the control loops of the reactor are modified in ordorto inject more diluent in the reactor. The amount of injected diluent increases progressively up to a new value that is typically twice larger than the starting value. A typical diluent is isobutane. This control scheme is tuned to keep the reactor just at the onset of swelling in order to maximise the solids concentration and thus the yield of the installation.
The present invention thus discloses a method for controlling the swelling that comprises the steps of:
a) providing a loop reactor, said reactor being optionally equipped with
one or more devices aimed at improving the homogeneity of the
circulating slurry;
b) measuring as a function of time, one or more plant control parameters
that displays an increasing level of fluctuation during swelling;
c) processing these measurements in real-time, including amplifying the
signal to noise ratio if required;
d) identifying in real-time the onset of swelling;
e) progressively diluting the reactor when the fluctuation level reaches a
pre-determined level.
The device aimed at improving the homogeneity of the circulating slurry can be a by-pass line wherein the circulating slurry has a different travel time than in the main line.

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The pre-detenmined level is defined as a percentage of the fluctuation level measured at low solid content. This percentage is of less than 300 %, preferably of less than 250%, most preferably of less than 180%.

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CLAIMS.
1. A method for controlling swelling in olefin polymerisation process, said
swelling being defined as a phenomenon that is associated to the onset of a
process instability characterised by rapid fluctuations, significantly larger than
usual, in several process variables, said method comprising the steps of:
a) providing a slurry loop reactor, said reactor being optionally equipped
with one or more devices aimed at improving the homogeneity of the
circulating slurry;
b) measuring, as a function of time, a plant control parameter that
displays an increasing level of fluctuation during swelling;
c) processing these measurements in real-time by mathematical signal
treatment in order to detect the onset of swelling;
d) progressively diluting the reactor when the fluctuation level reaches a
pre-determined level.

2. The method of claim 1 wherein the device aimed at improving the
homogeneity of the circulating slurry is a by-pass lino wherein the circulating
slurry has a different travel time than in the main line.
3. The method of claim 1 or claim 2 wherein the plant control parameter is the
pump power consumption, the reactor temperature, the slurry density or the
temperature change experienced by the cooling water when circulating in all
or in a portion of the cooling jacket
4. The method of claim 3 wherein the plant control parameter is the pump power
consumption.
5. The method of any one of the preceding claims wherein the processing of
step c) includes amplification of the signal to noise ratio.

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6. The method of any one of the preceding claims wherein the dilution is
triggered and controlled by any one or more of the standard deviation, or the
variance, or the fluctuation range or any other function monotonically related
to the variance of a plant control measurement, said plant measurement
displaying an increasing fluctuation level when swelling occurs.
7. The method of claim 6 wherein the progressive dilution is carried out by
progressively increasing the amount of diluent injected in the reactor.
8. The method of any one of the preceding claims wherein the pre-determined
level of fluctuation, defined as a percentage of tho fluctuation level measured
at low solid content, is of less than 300 %.
9. The method of claim 8 wherein the pre-determined level of fluctuation is of
less than 180%.

The present invention discloses a method for controlling the onset and development of swelling in a slurry loop reactor by progressively diluting the reactor, the amount of dilution being driven by the amplitude of the fluctuations measured on some plant measurement.

Documents:

02023-kolnp-2006 abstract.pdf

02023-kolnp-2006 assignment.pdf

02023-kolnp-2006 claims.pdf

02023-kolnp-2006 correspondence others.pdf

02023-kolnp-2006 description (complete).pdf

02023-kolnp-2006 drawings.pdf

02023-kolnp-2006 form-1.pdf

02023-kolnp-2006 form-3.pdf

02023-kolnp-2006 form-5.pdf

02023-kolnp-2006 international publication.pdf

02023-kolnp-2006 international search report.pdf

02023-kolnp-2006 pct form.pdf

02023-kolnp-2006 priority document.pdf

02023-kolnp-2006-abstract-1.1.pdf

02023-kolnp-2006-claims-1.1.pdf

02023-kolnp-2006-correspondence others-1.1.pdf

02023-kolnp-2006-drawings-1.1.pdf

02023-kolnp-2006-priority document-1.1.pdf

2023-KOLNP-2006-(08-01-2013)-AMANDED PAGES OF SPECIFICATION.pdf

2023-KOLNP-2006-(08-01-2013)-ANNEXURE TO FORM 3.pdf

2023-KOLNP-2006-(08-01-2013)-CORRESPONDENCE.pdf

2023-KOLNP-2006-(08-01-2013)-DRAWINGS.pdf

2023-KOLNP-2006-(08-01-2013)-FORM-1.pdf

2023-KOLNP-2006-(08-01-2013)-FORM-2.pdf

2023-KOLNP-2006-(08-01-2013)-OTHERS.pdf

2023-KOLNP-2006-(08-01-2013)-PETITION UNDER RULE 137.pdf

2023-KOLNP-2006-ASSIGNMENT.pdf

2023-KOLNP-2006-CORRESPONDENCE.pdf

2023-KOLNP-2006-EXAMINATION REPORT.pdf

2023-kolnp-2006-form 18.pdf

2023-KOLNP-2006-GPA.pdf

2023-KOLNP-2006-GRANTED-ABSTRACT.pdf

2023-KOLNP-2006-GRANTED-CLAIMS.pdf

2023-KOLNP-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

2023-KOLNP-2006-GRANTED-DRAWINGS.pdf

2023-KOLNP-2006-GRANTED-FORM 1.pdf

2023-KOLNP-2006-GRANTED-FORM 2.pdf

2023-KOLNP-2006-GRANTED-FORM 3.pdf

2023-KOLNP-2006-GRANTED-FORM 5.pdf

2023-KOLNP-2006-GRANTED-SPECIFICATION-COMPLETE.pdf

2023-KOLNP-2006-INTERNATIONAL PUBLICATION.pdf

2023-KOLNP-2006-INTERNATIONAL SEARCH REPORT & OTHERS.pdf

2023-KOLNP-2006-OTHERS.pdf

2023-KOLNP-2006-PETITION UNDER RULE 137 1.1.pdf

2023-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

abstract-02023-kolnp-2006.jpg


Patent Number 255891
Indian Patent Application Number 2023/KOLNP/2006
PG Journal Number 14/2013
Publication Date 05-Apr-2013
Grant Date 28-Mar-2013
Date of Filing 18-Jul-2006
Name of Patentee TOTAL PETROCHEMICALS RESEARCH FELLUY
Applicant Address ZONE INDUSTRIELLE C, B-7181 SENEFFE (FELUY)
Inventors:
# Inventor's Name Inventor's Address
1 FOUARGE LOUIS SLEUTELPASSTRAAT, 4, B-1700 DILBEEK
2 VAN DER AUWERA MARC PARLAAN 48, B-3080 TERVUREN
3 VAN DEN BRANDE FRANS HOLLANDSE TUIN 10/2, B-2640 MORTSEL
4 LEWALLE ANDRE AVENUE JEANNE, 19, BTE 17, B-1050 BRUXELLERS
PCT International Classification Number B01J19/00 ,B01J19/18
PCT International Application Number PCT/EP2005/050519
PCT International Filing date 2005-02-08
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 04100573.7 2004-02-13 EUROPEAN UNION