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Power to PerformHoneywell Users Group 2008
Testing Automation Software With Dynamic Process Models
Anne Mueller
2
Outline
• Introduction
• Creating the Dynamic Process Model
• Expanding the Model with UniSim Operations
• Connecting the DCS
• Conclusion and Outlook
3
Personal Data
• Anne Mueller
• Studying Process Engineering at the Technical
University of Dresden, Germany, since 2004
• Project developed during work experience placement
at Linde-KCA-Dresden GmbH
• Supported by the Department of Process Automation
by Prof. Dr.-Ing. habil. Wolfgang Kloeden
4
Introduction
• Modern industrial plants are very complex and require extensive control schemes
• Control typically provided by a Distributed Control System (DCS)
• Dynamic process models allow the accurate prediction of plant behaviour for various process conditions
• The connection of both leads to a powerful means to test the implemented control algorithms of the DCS
• In this case, the control system PCS7 by Siemens is connected to a USD dynamic model
5
Introduction
• Ready-made solutions to connect a USD process model to common DCS already exist for Experion, SimC300, SimACE and more
• So far, no interface between UniSim Design and PCS7 available
• This work demonstrates the steps required to establish communication between the two systems
USD 370 Dynamics + USO R300
Simit 5.2.201 PCS7 6.1 SP1
6
Creating The Dynamic Process Model
Process: CO2-Purification and –Liquefaction
• Used to separate CO2 from flue gas
• Operating conditions up to 20 bar and between -50°C and 100°C
Two-stage Densification
Water Separation
Adsorptive Drying
Liquefaction (plate-fin HX)
Inert Gas Separation
7
Creating The Dynamic Process Model
• Components include CO2, O2, N2, Ar, CO, H2S, SO2, SO3, NO, NO2, H2O and NH3
• Peng-Robinson EOS recommend for cryogenic gas processes
• Dynamic model created from scratch with a steady state model as reference
• Inlet stream as starting point for the model
• Pressure-driven simulation pressure specifications on every boundary stream
8
Creating The Dynamic Process Model
• Piecewise addition of unit operations downstream integrator run after each new operation to update stream data
• Advantage: errors found immediately
• Disadvantage: separate steady-state calculation necessary for initial values for the distillation column
• Contains • 1 distillation column• 1 plate-fin heat exchanger• 3 adsorber• 4 compressors and 1 pump
• 7 vessels• 11 shell-and-tube heat
exchangers• about 180 transmitters and
control units
9
The Dynamic Process Model - Challenges
• Keeping numerical stability
– Process showed periodical oscillation
– Stability increased by changing the integrator time step from 0.5 s to 0.3 s
0.3 s 0.5 s 0.3 s
10
The Dynamic Process Model - Challenges
– Insert pipe segment between units without pressure-flow relation or holdup (e.g. Tee or Mixer)
Holdup volume NOT modelled Holdup volume modelled
11
The Dynamic Process Model - Challenges
• Modeling adsorber regeneration
– adsorber used for removing moisture
– USD adsorber model does not support regeneration
– spreadsheet and integrator logic used
counts adsorbed water
automatic switch of water split fraction when maximum capacity is reached
counts back to zero during regeneration
implementation of complicated adsorber control possible
12
The Dynamic Process Model - Challenges
• Parametrising the plate-fin heat exchanger
– Estimation of heat transfer coefficients (U)
– Difficult for mixed gas-liquid flow and condensation / vaporisation
– Assumption of constant U-value
– Only rough correlation for U on mass flow
– Experimental estimation by comparison with steady-state temperatures
– Results: UGas=20…80 W/m²K Ucond=2000…2800 W/m²K
– Problem with temperature crosses solved with new LMTD approach
8.0
ref
act
specact mm
UU
13
The Dynamic Process Model - Challenges
• Temperature cross of hot and cold streams
• Desired temperature profile
14
Setting Up The Control Scheme
• Control units necessary to keep desired process conditions, e.g. for plant pressure, levels and temperatures
• Dynamic model allows efficient controller tuning by monitoring the step response
• Different tuning rules used, e.g. Ziegler and Nichols
• Parameter testing possible
• Reduction of controller tuning time at startup
15
Setting Up The Control Scheme
• Step response of a pressure controller to identify the parameters of the system
Tg
Tw
Tu
Δx
Δy
Δxw
Su
gR KT
T6.0K
un T4T
(CHIEN, HRONES and RESWICK)
16
Setting Up The Control Scheme
• Using the stability limit to find controller parameters with Ziegler-Nichols
KR=5
KR=8
KR=1
0
KR=11
KR=11,8Kkr=11,
9KR=11,
5
Tkr
krR K45.0K
krn T85.0T
Kkr=11,9
17
Setting Up The Control Scheme
Level tap
= 0 – 100 %
• Focus on level taps
– used to observe level in certain boundaries
– level normalised to a desired scale
– scale depends on the scale of the transmitter
– provides input for level controller
18
Preparing The DCS Connection
• Basic dynamic model ready and tuned
• Addition of all DCS tags besides the controller, i.e. transmitters for pressure, temperature, flow and composition as well as switches and state transmitters
• Making tag values available to external devices
19
Preparing The DCS Connection
Pressure specification on boundary stream
Level control + switch
Transmitter
20
UniSim Operations
USD Model
OPC Server Control System
OPC Client
• OPC (OLE for Process Control) – communication standard of real-time plant data between control devices from different manufacturers
• UniSim Operations provides an advanced operator training solution plus capabilities for control system checkout
• Only the OPC-Server is used for the project
Expanding The Model With UniSim Operations
21
Expanding The Model With UniSim Operations
• Create a reference text file with desired tags for OPC access
UsdTags.dat
• Maintain a certain folder structure
• Load the dynamic model into UniSim Operations
22
Expanding The Model With UniSim Operations
• Successful loading indicated by the message
• Tags automatically added to MV-table
• Data now available over OPC
23
Testing the OPC-connection
• Test with a free OPC-client from Rockwell Software International (RSI)
• All values can be read
• Analogue values can be written by the OPC-client
Writing error occurs with digital values (states)
24
Connecting the DCS - Software
• PCS 7: Distributed Control System by Siemens
– handles all automation and controlling tasks
– OPC-client NOT included
• Simit: platform for running and testing S7-applications
– includes process simulation library
– includes Emulation Platform to emulate the automation hardware
– equipped with an optional OPC-Client package
„bridge“ between USD model and PCS 7
25
Connecting the DCS - Structure
• DCS structure:
• Automation hardware emulated as SoftPLC on a PC with the Simit Emulation Platform
• Same performance and S7-code as real AS
• Signal communication between dynamic model and DCS
SIMATIC PCS 7 Engineering Station
Automation System (AS)
Field Device
Field Device
Field DeviceSoftware Hardware
SIMATIC PCS 7 Engineering Station
SIMIT SoftPLCUSD Model
OPCOPC
26
Connecting the DCS – Test Network
• Test-network on three virtual machines
SIMIT Controller + Emulation Platform
USD Model
WinnCC Server WinnCC Client
PCS7 Simatic Manager DCS
Ethernet Switch
SIMIT
Emulation Platform
SoftPLC (AS)
Emulation PCInstructor Station
Operator + Engineering Station
USO
27
Connecting the DCS – Platform Configurator
• Setting up a new project with the platform configurator
Basis for overall connection
• Specifying all network resources (IP-address, shared folder, etc.)
• Specifying the distribution of the resources On which computer?
28
Connecting the DCS – Platform Configurator
• Import PCS 7 hardware configuration SoftPLC emulation
• Specify communication connections (to SoftPLC, to operator interface (WinCC), to USD model)
• Generate emulation environment
Simit project file with signal interface automatically generated
• Contains all tags from the DCS
Tag names in the model must equal the DCS tags
Do NOT use spaces in tag names
29
Connecting the DCS – Platform Configurator
30
Connecting the DCS – Inside Simit
• Import the generated Simit project
• Already contains the signal interface (connection between emulation and USD model)
• Additions necessary (Insert Coupling )
– Data link to emulation
– OPC-Client
(Activate „Take signals from plans“)
• Compile Simit project
Start simulation
31
Connecting the DCS – Inside Simit
Signal interface hierarchy
Data from the model
32
Connecting the DCS – Inside Simit
• Opening simulation starts the SoftPLC on the emulation PC
initialised
running
go online
(CPU accessible to PCS7)
33
Connecting the DCS – Inside PCS7
• Model values visible in CFC plans in PCS 7 (test mode)
34
Connecting the DCS - Summary
• Communication successfully established
USD Model
Process Values
USD Model
Controller Output
PCS 7
SoftPLC
CFC - Plan
SimitAnalogue / Binary - Switch
SimitAnalogue / Binary - Switch
OPC
OPC
WinCC
Operator Interface
TCP/IP
TCP/IP
35
Conclusion and Outlook
• UniSim Operations together with Simit allows the connection of a UniSim Design Dynamics model and the control system PCS 7
• Proof given by model values in PCS 7 CFC-plans
• Signal interface easy to generate with Simit
• Difficulties:
– Failure to communicate digital values
Cause apparently in USO OPC-server
– Connection to operator interface inside PCS 7 not established
(no effect on model – DCS interaction)
– Creating UsdTags.dat reference file is time-consuming
36
Conclusion and Outlook
• Possible uses:
– Testing the control system
– First estimates for controller parameters
– Operator training with the real DCS
Reduce time and cost of startup
Increase safety and stability of the plant
• latest USO release R320+ already includes an interface to Siemens PCS7 Simit
37
Thank you for your attention!
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