Student UniSIm AnneMueller

Power to PerformHoneywell Users Group 2008

Testing Automation Software With Dynamic Process Models

Anne Mueller

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Outline

• Introduction

• Creating the Dynamic Process Model

• Expanding the Model with UniSim Operations

• Connecting the DCS

• Conclusion and Outlook

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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

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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

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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

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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

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• 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

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• 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

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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

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– Insert pipe segment between units without pressure-flow relation or holdup (e.g. Tee or Mixer)

Holdup volume NOT modelled Holdup volume modelled

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• 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

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• 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

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• Temperature cross of hot and cold streams

• Desired temperature profile

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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

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• 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)

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• 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

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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

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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

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Preparing The DCS Connection

Pressure specification on boundary stream

Level control + switch

Transmitter

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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

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• 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

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• Successful loading indicated by the message

• Tags automatically added to MV-table

• Data now available over OPC

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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)

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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

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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

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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

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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?

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• 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

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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

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Signal interface hierarchy

Data from the model

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• Opening simulation starts the SoftPLC on the emulation PC

initialised

running

go online

(CPU accessible to PCS7)

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Connecting the DCS – Inside PCS7

• Model values visible in CFC plans in PCS 7 (test mode)

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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

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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

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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

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Thank you for your attention!

Student UniSIm AnneMueller

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