Control system for ethylene polymerization reactor

• US 4,668,473 A
• Filed: 08/23/1985
• Issued: 05/26/1987
• Est. Priority Date: 04/25/1983
• Status: Expired due to Fees

• Current Assignee: Elsag International BV (ABB Limited)
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Agarwal, Suresh C.
• Primary Examiner(s): Lacey, David L.
• Application Number:
  US06/769,782
• Time in Patent Office: 641 Days
• Field of Search: 422/62, 422/109, 422/110, 422/111, 422/132, 422/134, 364/500, 364/496, 364/502, 364/557, 526/59-61, 526/64, 585/263, 585/401, 585/501, 585/950, 585/951
• US Class Current: 422/62
• CPC Class Codes: B01J 19/002 Avoiding undesirable reactions or side-effects, e.g. avoiding explosions, or improving the yield by suppressing side-reactions
• CPC Class Codes: B01J 19/0033 Optimalisation processes, i.e. processes with adaptive control systems adaptive control systems per se G05B13/00
• CPC Class Codes: B01J 2219/00054 Controlling or regulating the heat exchange system
• CPC Class Codes: B01J 2219/00058 Temperature measurement
• CPC Class Codes: B01J 2219/00069 Flow rate measurement
• CPC Class Codes: B01J 2219/00072 Mathematical modelling
• CPC Class Codes: B01J 2219/00164 controlling the flow
• CPC Class Codes: B01J 2219/00243 Mathematical modelling
• CPC Class Codes: B01J 2219/00261 Predicting runaway of the chemical reaction
• CPC Class Codes: C08F 10/00 Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
• CPC Class Codes: C08F 2/00 Processes of polymerisation
• CPC Class Codes: C08F 2/01 characterised by special features of the polymerisation apparatus used
• CPC Class Codes: C08F 2400/02 Control or adjustment of polymerization parameters

Abstract

A control apparatus for a tubular polymerization reactor having a feed line for a raw material to be polymerized, a cooling circuit for cooling the reactor with a flow of coolant and exit line for a product polymerization, comprises a quality sensor for sensing the actual quality of the product in the exit line, a quality controller for receiving a desired product quality set point and comparing it with the actual quality of the product to generate a desired temperature value for the reactor, temperature sensors for determining the maximum temperature of the reactor and a temperature controller for controlling the amount of coolant supplied to the reactor by the cooling circuit. The temperature controller compares the maximum temperature of the reactor with a desired temperature value therefor corresponding to the desired quantity to control the cooling circuit accordingly. A production rate controller is also provided which controls the rate of production by regulating the amount of raw material flow to the reactor as a function of the concentration of raw material in the exit line from the reactor. The amount of catalyst supplied to the feed line is regulated as a function of raw material concentration of the feed line or flow of raw material in the feed line. The control apparatus also optimizes the process by maximizing reactor temperature, catalyst flow rate, coolant flow rate, reactor exit temperature and maximum polymerization in the reactor.

Claims

1. A polymerization reactor comprising:

a feed line connected to an input of said reactor for transporting a raw material to be polymerized to the reactor;

cooling means for cooling the reactor including means for causing a flow of coolant to the reactor;

an exit line connected to an exit of said reactor for transporting a product of polymerization from the reactor;

a product separator connected in the exit line beyond said reactor for separating the product from the raw material;

quality sensing means positioned and arranged so as to sense the actual quality of the product in the exit line beyond said product separator;

quality controller means connected to said quality sensing means for receiving a desired product quality set point and comparing it with the actual quality of the product and generating a desired temperature value of the reactor;

temperature sensing means associated with the reactor and positioned and arranged to sense a representative temperature thereof;

temperature control means connected to said temperature sensing means and to said quality controller means for comparing the representative temperature of the reactor with the desired temperature value therefor to generate a coolant flow value, said temperature control means connected to the cooling means for controlling the coolant flow to the reactor in accordance with the coolant flow value;

a raw material flow regulator in the feed line for regulating an amount of raw material supplied to the reactor;

a raw material concentration sensor in the exit line between said reactor and said product separator for sensing an amount of raw material admixed with the product in the exit line; and

production rate controller means connected to said raw material concentration sensor and to said raw material flow regulator for receiving a desired production rate as a set point and comparing it with an actual production rate determined as a function of the raw material concentration therefor to generate a raw material feed flow rate value, said production rate controller means connected to said raw material flow regulator for regulating the amount of raw material supplied to the reactor in accordance with the raw material feed flow rate value.

2. An apparatus according to claim 1, wherein said temperature sensing means includes a plurality of temperature detectors throughout said polymerization reactor connected to a maximum temperature unit which is constructed so as to sense a maximum temperature of the reactor which forms the representative temperature thereof.

3. An apparatus according to claim 1, wherein said quality sensing means is a raw material concentration sensor which is constructed so as to sense a concentration of raw material in the exit line as a measure of actual product quality.

4. An apparatus according to claim 1, including at least one return line connected between said separator and the feed line for returning raw material to the feed line, a second raw material flow regulator in said at least one return line and flow summing means connected to said first mentioned and second raw material flow regulators for determining a total amount of raw material supplied to the feed line, said flow summing means connected to said production rate controller means for providing said production rate controller means with a total flow value for raw material to the feed line.

5. An apparatus according to claim 4, including catalyst supply means connected to at least one point of the feed line for supplying a catalyst at a selected catalyst flow rate to the feed line, catalyst controller means connected to said catalyst supply means and to said flow summing means for controlling said catalyst supply means in accordance with a total flow of raw material to the feed line.

6. An apparatus according to claim 5, wherein said production rate controller means, said quality controller means and said catalyst controller means are contained with a control computer, said temperature sensing means comprising a plurality of temperature sensors connected to the reactor for sensing temperatures along the reactor, an input temperature sensor connected to the feed line for sensing the temperature of raw material to the reactor and an output temperature sensor connected to the exit line for sensing the temperature of material in the exit line, said temperature sensing means further including a maximum temperature block for determining the maximum temperature of the reactor, said maximum temperature block incorporated in said control computer, said flow summing means including a flow transmitter in the feed line and the at least one return line, and means for combining flow values incorporated into said control computer, said control computer including a unit conversion block for receiving signals from said temperture sensors and flow transmitters and signals from said raw material concentration sensor and said product quality sensor, a continuous running average block connected to said maximum temperature block and said unit conversion block for periodically sampling signals from said unit conversion block and maximum temperature block, and optimization block connected to said continuous running average block for receiving the sampled signals and receiving the desired product quality set point, a process model including parameters for variables of the polymerization process in the reactor connected to said optimization block so that said optimization block generates values corresponding to maximum reactor temperature, maximum coolant flow rate, maximum total catalyst flow rate and maximum production of the reactor corresponding to optimal conditions therefor, said optimization block connected to said production rate controller means for applying the maximum production rate value thereto to control said raw material flow regulator means said optimization block connected to said catalyst controller means for applying said maximum catalyst flow rate thereto to control the amount of catalyst added to the feed line.

7. An apparatus according to claim 6, wherein said control computer includes a limit checking block connected to said unit conversion block, said continuous running average block, said maximum temperature block and said optimization block for checking limits of values therefrom and generating an alarm signal upon diversion of signals from said limits therefor.

8. A tubular olefin polymerization reactor comprising:

a feed line connected to an input of said reactor for transporting olefin to be polymerized to the reactor, with at least one compressor therein for compressing the olefin;

an exit line connected to an exit of said reactor for transporting a product of polymerization from the reactor, with a separator for separating polymerized product from the olefin with at least one return line connected to the feed line before said at least one compressor for returning separated olefin to the feed line upstream of the at least one compressor;

a first flow transmitter in the feed line for sensing flow of olefin to the reactor;

at least one second flow transmitter in the return line for sensing flow of olefin returned from the separator;

an olefin flow valve in the feed line for controlling the flow of olefin to the reactor;

olefin flow controller means connected to said olefin flow valve for controlling the rate of olefin supplied through the feed line;

an olefin concentration sensor connected to the exit line between the reactor and the separator for determining the concentration of olefin left in a mixture of olefin and polymerization product from the reactor;

production rate controller means connected to the olefin concentration sensor for receiving a desired production rate set point, said production rate controller means connected to said olefin flow controller means for controlling olefin flow rate in the feed line;

a product quality sensor connected to the feed line beyond the separator for sensing the actual quality of product from the separator;

quality controller means for receiving a desired quality set point, connected to said product quality sensor for comparing the actual product quality with the desired product quality and generating a desired temperature set point;

flow means connected to the reactor for supplying the reactor with a flow of coolant;

coolant flow controller means connected to said coolant flow means;

temperature controller means connected to said quality controller means for receiving the desired temperature set point;

maximum temperature sensing means connected to the reactor positioned and arranged for determining the maximum temperature thereof, said maximum temperature sensing means connected to said temperature controller means, said temperature controller means constructed so as to compare the maximum temperature with the desired temperature set point to control said coolant flow controller means for establishing the desired temperature of the desired temperature set point in the reactor to avoid overcooling of the reactor and fouling of the reactor by polymerization product;

catalyst flow means connected to at least one point on the feed line for supplying a flow of catalyst to the feed line; and

catalyst controller means connected to the first and second flow transmitters and connected to said catalyst flow means for regulating flow of catalyst to the feed line as a function of olefin flow to the feed line.

9. A tubular olefin polymerization reactor comprising:

a feed line connected to an inlet of said reactor for transporting olefin to be polymerized to the reactor;

an exit line connected to an outlet of said reactor for transporting a product of polymerization from the reactor;

a separator on the exit line for separating polymerization product from olefin;

at least one olefin return line connected between the separator and the feed line for returning olefin to the feed line;

at least one compressor on the feed line for compressing olefin to be supplied to the reactor;

a first flow transmitter on the feed line;

a second flow transmitter on the at least one olefin return line;

an olefin flow valve on the feed line for regulating flow of olefin to the reactor;

olefin flow controller means connected to said olefin flow valve for control thereof;

an olefin concentration sensor connected to the exit line before the separator for determining the concentration of olefin left in a mixture of olefin and polymerization product from the reactor;

production rate controller means connected to the olefin concentration sensor for receiving a desired production rate set point, said production rate controller means connected to said olefin flow controller means for controlling olefin flow rate in the feed line;

catalyst supply means including a catalyst flow valve connected to the feed line for supplying catalyst to the feed line;

catalyst flow controller means connected to said catalyst flow valve for control thereof;

a first temperature sensor in the feed line before the reactor, a second temperature sensor in the exit line between the reactor and the separator and a plurality of third temperature sensors connected to the reactor;

a product quality sensor connected to the feed line beyond the separator for sensing product quality from the separator; and

a control computer connected over analog to digital converters to each of said sensors and transmitters, and over digital to analog converters to each of said controller means, said control computer including means for optimizing once through polymer production in the reactor by maximizing permitted maximum temperature values for the reactor, coolant flow values for the reactor, catalyst flow values for the reactor and quality values for the reactor.

10. A polymerization reactor comprising:

a feed line connected to an inlet of said reactor for transporting a raw material to be polymerized to the reactor;

an exit line connected to an outlet of said reactor for transporting a product of polymerization from the reactor;

a product separator connected in the exit line beyond said reactor for separating the product from the raw material;

raw material flow regulator means in the feed line for regulating an amount of raw material supplied to the reactor;

a raw material concentration sensor in the exit line before said product separator for sensing an amount of raw material admixed with product in the exit line; and

production rate controller means connected to said raw material concentration sensor and to said raw material flow regulator means for receiving a desired production rate as a set point and comparing it with an actual production rate determined as a function of the raw material concentration therefor to generate a raw material feed flow rate value, said production rate controller means connected to said raw material flow regulator means for regulating the amount of raw material supplied to the reactor in accordance with the raw material feed flow rate value.