dynamic simulation and chemical engineering

Dynamic Simulation and Chemical Engineering Based on the presentation in the 3rd Pan-Hellenic... Dynamic Simulation and Chemical Engineering1 SUMMARY In dynamic simulation, natural

Dynamic Simulation and

Chemical Engineering

Based on the presentation in the 3rd Pan-Hellenic

DOCUMENT HISTORY

This document is based on the presentation of Kyriakopoulou, D., Poulou, S and Atha-nassiou, V in the 3rd Pan-Hellenic Chemical Engineering Conference 31 May - 2 June

2001

For comments on this document please contact Dr Vassilis Harismiadis

(V.Harismiadis@hyperion.com.cy)

OWNERSHIP

This document, the concepts, ideas, designs and commercial offers included therein are

the sole property of Hyperion Systems Engineering Ltd

Copyright © 2006, Hyperion Systems Engineering, All rights reserved

Dynamic Simulation and Chemical Engineering

1 SUMMARY

In dynamic simulation, natural and chemical phenomena are expressed with algebraic and differential equations based on engineering principles The mathematical models created are used for analysing how process behaviour varies with time For the typical case of a process industry, we describe/model the plant subunits and their regulatory control The relevant equations are solved repeatedly in the time domain and the values of tempera-ture, pressure, flow and composition as well as the valve openings and the process control system output are calculated at every point of interest Thus, the interactions between the process subunits can become obvious Further, the process reaction to disturbances (such

as feed variation, instruments failure or change of operation strategy) can be fully investi-gated

2 INTRODUCTION

Many of the operations in the Process Industry are naturally dynamic, such as the start-up and shutdown of a unit, the changeover from one product to another, the operation of batch reactors or adsorption/regeneration trains etc Actually, it is practically impossible for

a process unit to operate under strictly constant conditions (steady state) On the other hand, the industrial process units are becoming increasingly complex with applications of new technologies that include thermal integration, modern process design and advanced process control systems The units are required to operate non-stop for longer periods of time at optimal conditions The need for flexibility, regarding processes or equipment, con-tinuously increases It is, further, well known that big and fast changes in the plant operat-ing conditions should be avoided, since the effects of movoperat-ing from one operational region

to another can be unanticipated and possibly dangerous Thus, one need to be aware of the danger zones and when these occur

In brief, the behaviour of the process unit on the whole is not a simple sum of the plant’s subunits actions Safety, environmental, and economic factors highlight the importance of understanding the design and operating of the plant, as well as the sufficient training of the plant personnel at a time of an ever-increasing worldwide need for highly qualified and ca-pable operators Dynamic simulation is the only economically effective solution to these needs, since it yields a lot more information than what traditional steady state simulation offers This is because dynamic simulation allows us to study a plant’s behaviour in a wide

range of operation conditions, like during start-up or shutdown Further, it can incorporate algorithms describing the process unit safety or regulatory control philosophy Thus, it is possible to use a dynamic model for the investigation and improved understanding of the unit's behaviour based on design or operational data

3 APPLICATIONS OF DYNAMIC SIMULATION

The dynamic simulation applications in the process industry can be used for a variety of purposes These include the following

In today’s world, where the developed regions face massive retirements

of their work force and where the regions in-development face a skills shortage, dynamic proc-ess models integrated with the plant’s Distrib-uted Control Systems (DCS) can be used to capture, maintain and de-velop existing operating skills Among others, a fully deployed operator training system can be used to:

• Offer plant operators an improved understanding of the unit operation and handling

• Familiarize the operators to the process design and the control systems, while empha-sizing the interactions between the two

• Demonstrate the use and explain the advantages of advanced process control

• Control and verify the operators’ actions

• Practice without the presence of an instructor (stand-alone tool)

A dynamic model of a process unit can be use to optimise operations Some typical exam-ples are:

• Creating, testing and verifying procedures for the safe start-up and shutdown of the process or for the minimisation of time that plant equipment stays out of operation

Dynamic Simulation and Chemical Engineering

• Finding ways to move the plant operation to equally feasible and safe but more

profit-able conditions

• Addition of new process lines, before or after start up, for improved plant controllability

during transients

The process design can be relatively easily modified and troubleshot with a dynamic

simu-lator

• Technical assessment of alter-native design solutions

• Dynamic studies: Analysis of controllability, de-bottlenecking, depressurising, feed differentia-tion effects etc

• Determination of characteristic equipment parameters (instru-ment minimum sampling time or permissible noise levels, control-ler tuning parameters, control valves characteristics etc.)

• Compressor performance verifi-cation and avoiding compressor surge

• Effects to plant controllability due to equipment modifications

• Rapid assessment of alternative solutions to what-if scenarios

• Achievement of optimal plant conditions, after

an unanticipated change

• Incident investigation and procedures for fu-ture prevention

• Estimation of functional parameters for instru-mentation

3.5 Safety and Environmental Issues

• Exhaustive testing of plant procedures and detection of unfavourable conditions (e.g explosive/toxic mixtures, for-mation and deposition of hy-drates etc.) due to transients or malfunctions

• Verification of depressurising procedures

• Verification of DCS and emer-gency shutdown system con-trol loops and sequences

4 REFERENCES

[1] Nisenfeld A E., 1982 Principles of Operation and Control, ISA, Monograph Series 3 [2] AspenTech Modelling Philosophy, 1998 AspenTech Ltd

[3] Gas Injection Plant, 1997 SAST Ltd

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