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
CopyrightPiControlSolutionsCompany©2014

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

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
4

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

Exothermic Open-loop Unstable Process
6

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

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
8

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.
9

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

POLYETHYLENE MASS BALANCE CONTROL
11

POLYMER MODEL-BASED CONTROL SCHEMATIC
12CopyrightPiControlSolutionsCompany©2014

APC FOR PROPERTY CONTROL
APC1
APC2
H2 Flow
Control
Operator
MI Setpoint
APC3
APC4
C4= Flow
Control
Operator
Density
Setpoint
MI
Model
Density
Model
PV PV
Process Signals
Lab Sample
Values
13

 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
14

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
16

 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
18
ReciCon
OPC
Connection
to DCS/PLC
Operator/
Engineer DCS/PLC
Database
Configure
Data
Access

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.

ZONE TRANSITIONS & TRAJECTORY MOVES
20
Zone 10
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
Zone 9
Zone 1
Zone 11

RECICON USER INTERFACE
21
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

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.
22

PRODUCTION RATE MAXIMIZATION
23

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.
24

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

SIGNAL VALIDATION:
ANALYZER SIGNAL SPIKES

SIGNAL VALIDATION:
SPIKE REJECTION LOGIC

SIGNAL VALIDATION:
FROZEN VALUE CHECK

PILIMS – LABORATORY INFORMATION
MANAGEMENT SYSTEM
PiLIMS
Laboratory
Information
Management
System
OPC
Server
Connection
Lab
Technician
entering
Lab Data
DCS/PLC
and
Plant Data
Historian
Remote
Located
Laboratory
Computer
29

PILIMS OPERATOR DATA INTERFACE
30

OPC- SUCCESS - DATA DOWNLOAD STATUS
31

LABEL PRINT FUNCTION
32

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

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.
34

CONTACT
If you have any questions, please contact
Yazzoom BVBA
Managing Director: Dr. Ir. Ing. Jan Verhasselt
Email: jan.verhasselt@yazzoom.com
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
35

Polymer APC

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