Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Coal to Liquid facility, Sasol, Secunda operates as a train of processes. Disturbances
and capacity restrictions can occur throughout the plant and the throughput
fluctuates whenever disturbances occur. When capacity restrictions occur in a subplant
and more substances enter the sub-plant than can be processed, the extra substances
are flared or dumped and therefore lost. To reduce losses and extra costs and
to maximise the throughput of the whole plant, supervisory control is implemented over
the whole plant system.
Each process in the process train is controlled with regulatory controllers and the overall
process is then controlled with a supervisory controller. These two sets of controllers
operate in two different layers of control, with the regulatory controllers the faster inner
layer. The supervisory control is the outer layer of the two control layers. The
supervisory controller takes over the work of the human operator by deciding on the
changes in total throughput as well as the set points for each individual process. These
set points for each process are then followed with the regulatory controllers. For the
regulatory control of the system, different control methods are investigated and compared.
The different control methods that are looked at are PI control, Linearised State
Feedback control, Fuzzy Logic control and Model Reference Adaptive Control.
After an investigation into the various control methods Fuzzy Logic control was chosen
for the regulatory as well as the supervisory control levels. Fuzzy Logic control is a rule
based control method. Fuzzy variables are everyday terms such as very slow or nearly
full. These terms are easy to understand by the operator and multi-variable control is
possible with Fuzzy Logic control without an accurate mathematical representation of
the system. These facts made Fuzzy Logic control ideal for this implementation.
To improve the profit of the Coal to Liquid facility the throughput was maximised. The
combination of regulatory and supervisory controllers minimised losses and rejected
disturbances. This resulted in a smoother output with maximum profit. / AFRIKAANSE OPSOMMING: Die Steenkool-na-Olie fasiliteit, Sasol, Secunda funksioneer as ’n trein van prosesse.
Versteurings en kapasiteit beperkings kan deur die hele aanleg voorkom en die deurset
wissel voortdurend wanneer versteurings voorkom. Wanneer kapasiteit beperkings
voorkom in ’n aanleg en meer stowwe word in die aanleg ingestuur as wat dit kan
verwerk, word die ekstra stowwe gestort en dit gaan verlore. Om verliese en kostes
te verminder en om die deurset van die hele aanleg te vergroot, is oorhoofse beheer
geïmplementeer oor die hele stelsel.
Elke proses in die trein van chemiese prosesse word beheer met regulerende beheerders.
Die totale proses word dan beheer met ’n oorhoofse beheerder. Hierdie twee
tipes beheerders funksioneer in twee lae van beheer met die regulerende beheerders
die vinniger binneste laag. Die oorhoofse beheerder vorm die buitenste laag van die
twee beheer lae en neem die werk van die menslike operateur oor deur die veranderinge
in die totale deurset, sowel as die stelpunte vir elke afsonderlike proses, te
bepaal. Hierdie stelpunte vir elke proses word dan met die regulerende beheerders gevolg.
Verskillende beheer metodes is ondersoek vir die regulerende beheer van die stelsel.
Die verskillende beheer metodes waarna gekyk word, is PI beheer, Geliniariseerde
Toestands Terugvoer beheer, Wasige Logiese beheer en Model Verwysing Aanpassende
beheer.
Na ’n ondersoek na die verskillende beheer metodes is Wasige Logiese beheer gekies
vir die regulerende asook die oorhoofse beheer. Wasige Logiese beheer is ’n reël
gebasseerde beheer metode. Wasige Logika veranderlikes is alledaagse terme soos
baie stadig of byna vol. Hierdie terme is maklik om te verstaan deur die operateur.
Meervoudige-veranderlike beheer is moontlik met Wasige Logiese beheer sonder ’n
akkurate wiskundige voorstelling van die stelsel. Hierdie feite maak Wasige Logiese
beheer ideaal vir hierdie doel.
Om die wins van die Steenkool-na-Olie fasiliteit te verbeter, is die deurset gemaksimeer.
Die kombinasie van regulerende- en toesighoudende beheerders beperk verliese en
verwerp versteurings. Dit lei tot ’n gladder uitset en ’n maksimum wins.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5218 |
| Date | 12 1900 |
| Creators | Gryffenberg, Jolandi |
| Contributors | Steyn, W. H., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 104 p. : ill. |
| Rights | University of Stellenbosch |
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