polymer apc

POLYETHYLENE APC (ADVANCED PROCESS

CONTROL)

June, 2014

REFERENCES

Beaumont PE Plant, BPEP

Production rate increase by a spectacular 20%

Temperature amplitudes reduced from +-3°C to +-0.5 °C

Grade transition automation reduced off-prime by 25%

ExxonMobil, Mont Belvieu, TX

Temperature amplitudes reduced from +-4°F to +-0.75 °F

Property control successfully installed inside Honeywell DCS

Mass balance control allowed fastest possible grade

transitions

Univation PE Plant, Baytown, TX

PiLIMS installed for laboratory

TC-TC tuning optimization successfully reduced temperature

swings 2

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POLYETHYLENE APC - BENEFITS

3-10% increase in production rate

20-50% reduction in product grade transition time

50-100% reduction in reactor temperature deviation

from setpoint

1-3 avoidance of shutdowns because of operator

error and/or smoother operation.

1-3 reduction in control problems due to online

analyzer failure

Smoother, more stable and safer plant operation

Euros 450,000 – 750,000 per year per reactor

savings demonstrated on gas phase PE reactors 3

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POLYMER APC (ADVANCED PROCESS

CONTROL) SUITE

Primary PID Control Improvement:

Reactor Temperature Control

Reactor Pressure Control

Reactor Bed Level Control

Gas Composition Control

Polymer online predictive models

Melt Index

Density

Polymer Property Control

Steady State

Product Grade Transition

Product Rate Maximization

Reactor Pressure Minimization

Extruder – Finishing/Compounding Maximization

Reactor-Finishing Integration

Online Analyzer Signal Validation

Online Dew-point and Enthalpy Calculations

Laboratory Information Management System

Rule-based Operator Advisory

Some applications

inside DCS and some

inside Computer

connected to DCS

using OPC

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REACTOR TEMPERATURE CONTROL

PE gas phase reactor temperature control is very

challenging.

Dynamics are open-loop unstable.

TC-TC cascade to slave tuning is sensitive and can

become oscillatory during grade transitions and

changes in operating conditions.

PiControl’s PITOPS product can simulate open-loop

unstable transfer function dynamics and calculate

optimal PID tuning parameters for the TC-TC

cascade.

100-300% reduction in temperature swings have

been successfully demonstrated.5

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Exothermic Open-loop Unstable Process

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TC-TC Cascade Challenging PID Control

TC-TC cascade control in exothermic reactors very challenging

Open-loop unstable response

Cannot characterize process model using conventional modeling theory

Using Pitops, fit a “pseudo-second-order-plus-delay model” to characterize the open-loop unstable dynamics

Model identification followed by controller simulation and optimization produces spectacular results.

Example of closed-loop identification (no step tests) to identify open-loop unstable dynamics followed by tuning optimization

Novel, unique and revolutionary! 7

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Slave Loop Cascade Loop

Dead Time 2.3 minutes 3.2 minutes

Process Gain 1.01 °C/% 0.595 °C/%

1st Time Constant 38.4 minutes 95.3 minutes

2nd Time Constant 0 minutes 9.1 minutes

Controller Gain (P) 9.25 0.33

Integral (I) 8 minutes 15 minutes

Derivative (D) 0 minutes 0 minutes

TC-TC Cascade Control Simulation

On Open-loop Unstable Process

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REACTOR TEMPERATURE CONTROL

IMPROVEMENT PROCEDURE

Analysis of closed-loop TC-TC master/slave data

Closed-loop transfer function identification

PID tuning optimum calculations

Download new TC tuning into DCS

Reduction in temperature swings from +- 1 to 3

degC to about ) 0.5-0.7 degC.

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POLYMER ONLINE PROPERTY PREDICTIVE

MODELS

Melt Index and Density Calculations based on

Temperature

Hydrogen Composition

Hexene or Butene Flowrate

Generate steady state predictive models based on

equation from license supplier.

Ln(MI) = F(T, H2/C2=, Cx/C2=)

Density = F(H2/C2=, Cx/C2=)

Use Pitops to incorporate dynamics (first-order

transfer function lag) to make the models dynamic.

Add correction every 2-4 hours based on laboratory

values of polymer samples.10

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POLYETHYLENE MASS BALANCE CONTROL

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POLYMER MODEL-BASED CONTROL SCHEMATIC1

2C

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APC FOR PROPERTY CONTROL

APC1

APC2

H2 Flow

Control

Operator

MI Setpoint

APC3

APC4

C4= Flow

Control

Operator

Density

Setpoint

MI

Model

Density

ModelPV PV

Process Signals

Lab Sample

Values

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Polymer Plants transition from one Product Grade

to another.

Need to store process and operating conditions for

each grade.

Need control scheme to automatically and optimally

transition from one grade to the other.

ReciCon software is targeted for such control

needs.

POLYETHYLENE PRODUCT GRADE TRANSITION

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PICONTROL’S RECICON SOFTWARE FOR POLYMER

GRADE TRANSITIONS

ReciCon is PiControl’s Advanced Control Software

Product with the following functions:

Recipe Database storing different operating zones

Automatic Transition to New Zone or Product

Automatic Unmeasured Disturbance Compensation

ReciCon is a Master (higher level) Supervisory-type

controller that sends Multivariable Setpoints to

downstream Slave Controllers.

ReciCon uses modern OPC communications

Runs with any DCS or PLC from any vendor.

15Copyright PiControl Solutions Company © 2014

ReciCon can be configured to provide top quality

control for all types of NONLINEAR processes.

Compared to competitors, ReciCon provides far

simpler, extremely robust, far easier to maintain and

yet more powerful mechanism for NONLINEAR

control using its novel recipe-based sequence

control methodology.

NON-LINEAR CONTROL CAPABILITY

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Batch and semi-batch processes need Sequence Control

Logic.

Need to change operation from one zone to another as

function of time.

ReciCon provides convenient and valuable advanced

control capability on such processes.

Applications are abundant in Pharmaceutical Plants,

Chemical/Petrochemical Plants and Related Industries.

NEED FOR RECICON – BATCH, SEMI-BATCH &

SEQUENCED PROCESSES

Copyright PiControl Solutions Company © 2014 17

RECICON ARCHITECTURE OVERVIEW

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ReciCon

OPC

Connection

to DCS/PLC

Operator/

Engineer DCS/PLC

DatabaseConfigure

Data

Access

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SUMMARY OF HOW RECICON WORKS

• Specify different operating

zones

• Specify product grade zones

• Install ReciCon Database

• Define zone names

• Connect to DCS/PLC using

OPC

• Click on New Zone to transition

• ReciCon automatically moves

the plant to the New Zone

• Tune for appropriate speed of

transition

• Tune for Optimal Control

• Embedded Auto Bias

Correction ensures high level of

automation and Robustness 19

DATABASE VALUES

• ReciCon Database can include

hundreds of properties

corresponding to each ZONE.

• Transition from one zone to

another can comprise of tens,

even hundreds of independent

variables.

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ZONE TRANSITIONS & TRAJECTORY MOVES

20Zone 10

Zone 2

Zone 3

Zone 4

Zone 5

Zone 6

Zone 7

Zone 8

Zone 9

Zone 1

Zone 11

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RECICON USER INTERFACE

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ReciCon Polyethylene Gas Phase Reactor Controls

Current Grade = X113 New Grade = Y659

Transition Start Time = July 07 2013 17:35

Current Time = July 07 2013 17:07

Process Conditions

X113 Current Y659

Temperature 88.2 88.7 91.5

H2 Ratio 17.7 18.2 31.9

Comon Ratio 0.15 0.149 0.12

Diluent 11.2 11.7 11.2

START

HOLD

ABORT

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PRODUCTION RATE MAXIMIZATION

Build Cascade PIDs connected to Low Constraint Override Selector Scheme.

Slave PID is Catalyst Feed

Masters control the following controlled variables (CVs): Production Rate

Cooling Limit on External Heat Exchanger

Downstream Extruder and Bin Constraints

Any other licensor recommended constraints

Scientifically calculate: Dynamics between Catalyst Feed and all CVs using Pitops closed-

loop identification.

PID tuning for all masters using Pitops PID optimization.

Production Rate Maximization Scheme can increase production rate by 3-10%.

Performance using this approach has been demonstrated to be superior to DMC, NLC and other competitor approaches.

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PRODUCTION RATE MAXIMIZATION

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REACTOR PRESSURE OPTIMIZATION

Needlessly higher reactor pressure reduces

operating efficiency.

Needlessly high ethylene partial pressure causes

excessive ethylene losses to flare.

Lower than optimal ethylene partial pressure can

reduce catalyst activity and increase catalyst

consumption.

Reactor pressure dynamics are slow and complex

and the PID tuning numbers after optimization have

been seen to be radically different from initial,

obvious tuning parameters.

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EXTRUDER MAXIMIZATION AND INTEGRATING

REACTOR WITH EXTRUDER

Every extruder has typical constraints that can cause a trip (shutdown):

High temperature

High Pressure

High Amps/Power

Others –depending on make of extruder

Polymer APC comprising of all constraint relationships with the extruder feed will maximize extruder production rate.

Another control scheme can be designed to connect reactor production with extruder rates.

Key to success is the scientific calculation of dynamics and PID tuning parameters using Pitops. 25

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PILIMS – LABORATORY INFORMATION

MANAGEMENT SYSTEM

PiLIMSLaboratory

Information

Management

System

OPC

Server

Connection

Lab

Technician

entering

Lab Data

DCS/PLC

and

Plant Data

Historian

Remote

Located

Laboratory

Computer

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ONLINE DEW-POINT CALCULATION

Dew-point calculation is important in many gas-

phase polymer reactors.

Low temperature at inlet can cause condensing of

vapor and the droplets of liquid can cause problems

in the cooler and compressor feeding the reactor.

PiControl can offer a complete OPC-based custom

online calculation package that will calculate the

dew-point every minute based on the gas phase

molar composition, gas temperature using rigorous

chemical engineering thermodynamics. Calculation

will be based on activity, fugacity and enthalpies. 33

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OPERATOR RULE-BASED ADVISORY

Polymer plant is complex, difficult to operate

Operator can make mistakes – too much going on.

PiControl uses dedicated PLC connected to DCS to generate smart rules to advise, assist and help the operator.

For example: H2 flow control on for > 30 min, but reactor H2 mole% composition not increasing during startup –message: “Check H2 manual valve may be closed/blinded”.

Smart messages, no annoying audible sound.

Help both new and experienced operators.

Average prevent 1-3 bad mistakes/shutdowns per year.

Everything can be nicely programmed on PLC connected to DCS.

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CONTACT

If you have any questions, please contact

Yazzoom BVBA

Managing Director: Dr. Ir. Ing. Jan Verhasselt

Email: [email protected]

Mobile: +32 486 31 68 09

Office: Derbystraat 381 9051 Ghent (SDW) Belgium

Yazzoom is the exclusive value-added distributor of

Houston, TX, USA based PiControl Solutions’

products and services in Western Europe

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mailto:[email protected]

polymer apc

Engineering