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Intelligent digital operations -incorporating deep process knowledge
within plant automation systemsChris Leingang | APAC 2019 | Manchester
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Evolution of a Digital Twin for a Steam Cracker
Pfeiffer, B.; Oppelt, M.; Leingang, C. (2019): Evolution of a
Digital Twin for a Steam Cracker
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Detailed
equipment design
Data analysis,
experiment
designConceptual
process design
Catalyst design
and analysis
Design of
operating policy
Process
optimisation
Control
design &
verification
Front-end
engineering design
(FEED)
Digital twin:
Health monitoring
Digital twin:
Soft-sensing
Digital twin:
Forecasting
Digital twin:
Real-time optimisation
D I G I T A L E N G I N E E R I N G D I G I T A L O P E R A T I O N SD I G I T A L R & D & D E S I G N
A single integrated modelling environment ACROSS the
PROCESS LIFECYCLE
Digital Design Digital Operation
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Digital Design
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Integrated engineering extend by detailed process
simulations
gPROMS
Steady state and
conceptual dynamic
simulationSIMIT SP
gPROMS
Dynamic simulation
„open loop“
PCS 7
HW and SW-Engineering
CMT based
SIMIT VC
Hardware configuration
Import
Automation interface
Control Module Type
based import
Templates
PCS 7 OS
manual engineering
gPROMS
Dynamic simulation
„closed loop“
DCS
Engineering
Lib
rary
Ma
pp
ing
PFD, P&ID
Customer Inputs
Specifications(description, equipment,
control loop definition, SFC
description, …)
Existing
Vision
Central repository of plant design
Single Version of Truth
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Overview of Ethylene Plant
Page 6
Raw materials
• Ethane, propane and/or naphtha
• Several steam crackers in
parallel
• Multi-stage separation process
with distillation columns, flash
tanks, coolers and similar units
Products
• Ethylene, propylene, methane,
hydrogen
• are used to produce
intermediates for polymers (e.g.
polyethylene), varnishings,
solvents or herbicides
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Steam Cracker
• Steam cracker: tubular reactor with numerous
coils, belongs to the most complex unit
operations in petrochemicals
• Educts are mixed with steam and heated to
temperatures of about 840°C
• Long-chain hydrocarbon molecules are
transformed in seconds by thermal cracking
• High throughput, high economic value → any
optimization potential has to be exploited!
Hydrocarbon (educts)
Process steam
TI
COT
Fuel gas
Air
TI
TMT
Cracked gas (product)
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Steam Cracker: Challenges
Hydrocarbon (educts)
Process steam
TI
COT
Fuel gas
Air
TI
TMT
Cracked gas (product)
Yield
• Depends on a lot of influencing factors →
multi-variable control problem
• Cannot be measured directly at cracker
outflow, but only in summary and with large
delay after cooldown
Severity
• Describes the actual degree of thermal
cracking, quantified by the ratio of certain
concentrations
• Not directly measurable either
→ Online estimation by soft sensor
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Steam Cracker: Challenges
Hydrocarbon (educts)
Process steam
TI
COT
Fuel gas
Air
TI
TMT
Cracked gas (product)
Coking
• Builds up at inside of coils
• Reduces heat transfer
• Reduces yield
• Planning of maintenance works → online
estimation of actual coking state
Pass-balancing
• Keep all coils (“passes”) at same COT („Coil
Outlet Temperature“) despite different state
of coking
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Page 10
Cracker Process Model
Rigorous dynamic model• Energy- and material balances for coil segments incl.
reaction kinetics and coking
• Real-time simulation, no FEM, no segmentation in radial
direction
• System of differential and algebraic equations (DAE) with
more than 10.000 equations
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Digital Operation –Application example ethylene
steam cracker
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Multi-Level Solution Concept
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DI PA SE&C SO SIM
Base Layer Automation and Advanced Process Control
Page 14
2. Gas-to-air ratio control: „GARC“
1. Ratio control educt feed and process steam
3. Model Predictive Control
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Multi-Level Solution Concept
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MPC 4x3
TMT
Ethylene
Throughput
Ratio Steam /
HydrocarbonCOT MV3
CV3:
Deadband
Conversion Rate
Ethane
CV1 MV1Feed Flow
Fuel Gas
CV4:
Deadband
MV2CV2Feed Flow
Hydrocarbon
Tasks to be solved by MPC
• Production: drive ethylene throughput to
specified setpoint
• Product quality: keep conversion rate
ethane (~ severity) at setpoint
• Limit coking: keep COT (Coil Outlet
Temperature) in specified range
• Safe plant operation: keep TMT (Tube
Metal Temperature) below critical upper
limit
• Find suitable combination of setpoints
for hydrocarbon feed, process steam and
fuel gas
MPC Concept
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Multi-Level Solution Concept
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RTO: Real-time Optimization of Overall Plant
Overall plant: • 7 steam cracker, therefrom
3 processing propane
3 processing ethane
1 processing a mixture
• Decision variables: COTs, ethane- and propane-feed into mix cracker
• Constraints: throughput limits of each unit, upper limit of recycling
flows
Real-time Optimization of Overall Plant –Gross Profit of plant operation: 834…896 M$/year
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Summary
Rigorous process model can be used
• at different levels of solution concept
• in all phases of plant lifecycle
Digital Twin
• Integration of several models and software
tools that up to now have been considered
isolated: online communication and common
data management
• Amortization along complete plant lifecycle,
including economic benefit in plant operation
phase
Digital twin for steam cracker
• Process model in gPROMS (PSE)
• Device model, coordination und PLC-
emulation in Simit simulation platform
• Base layer automation, MPC und operator
station in DCS SIMATIC PCS 7
• Soft sensor, run length prediction and
plantwide RTO in gPROMS
Solution concept and implementation in
software demonstrator are available for
discussions
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Chris Leingang
Siemens plc
RC-GB DI PA AE-PRM
Princess Road
Manchester M20 2UR, Großbritannien und Nordirland
Contact
siemens.com/PSE