ABSTRACT
The performance of the FCC units plays a major
role on the overall economics of refinery plants. Any improvement in operation
or control of FCC units will result in dramatic economic benefits. Present
studies are concerned with the general behaviour of the industrial FCC plant,
and have dealt with the modelling of the FCC units, which are very useful in
elucidating the main characteristics of these systems for better design,
operation, and control. Due to the large economic benefits, these trends make
the process control more challenging. There is now strong demand for advanced
control strategies with higher quality to meet the challenges imposed by the
growing technological and market competition.
Usually, the optimum operating conditions are
met where constraints are also active. As a consequence, it is important to
control FCCU as close as possible to the operating and equipment constraints
but without violating them.
This study reviews
differentcontrol approaches of the fluid catalytic cracking unitaimed to control the main variables of the unit and to demonstrate the
benefits of the control for the FCC unit.
TABLE
OF CONTENTS
Title Page i
Certification ii
Letter of Transmittal iii
Dedication iv
Acknowledgement v
Abstract vi
Table of Contents vii-viii
List of Tables ix
List of Figures x-xi
List of Symbols xii-xiii
CHAPTER
ONE INTRODUCTION
1.0 BACKGROUND
OF STUDY 1-5
1.1 AIM AND OBJECTIVES OF RESEARCH 5
1.2 SCOPE OF RESEARCH 5
1.3 SIGNIFICANCE OF RESEARCH 5-6
CHAPTER
TWO LIREATURE
REVIEW
2.0. THEORITICAL PRINCIPLES 7-8
2.1. HISTORY OF FLUID CATALYTIC CRACKING PROCESS 8-10
2.2. PROCESS DESCRIPTION 10-14
2.2.1
PREHEAT SYSTEMS 11
2.2.2
RISERS 11-12
2.2.3
REACTORS 11-13
2.2.4
REGENERATORS 13-14
2.2.5
FLUE GAS SYSTEM 14
2.3. FCC FEED CHARACTERISATION 14-16 2.3.1 Paraffin 15
2.3.2
Olefins 15
2.3.3
Naphthalene 15-16
2.3.4
Aromatics 16
CHAPTER
THREE MODEL
DEVELOPMENT
3.0 MODELLING OF FCCU 17-18
3.1
THE MODEL PREDICTIVE CONTROL SYSTEM FOR
THE FCCU 18-20
3.1.1 THE MATHEMATICAL MODEL 20-21
3.1.2 MODEL BASED PREDICTIVE CONTROL SYSTEM 21-22
3.2 DECOUPLING
CONTROL OF FCCU 22-24
3.2.1
THE DYNAMIC MODEL 24
3.2.2 SELECTION OF
LOOPS INTERACTION 24-27
3.2.3 DECOUPLING OF
INTERACTING LOOPS 27-29
3.3 MULTIVARIABLE
CONTROL 29-31
3.3.1
MULTIVARIABLE CONTROL CONFIGURATION DESIGN 31-35
CHAPTER
FOUR
RESULTS AND DISCUSSION 36-47
CHAPTER
FIVE
CONCLUSIONS AND RECOMMENDATIONS 48-50
LIST
OF TABLES
Table Title Page
3.1 The transfer functions of the simplified model
used by 21
implementation of the MBPC.
LIST
OF FIGURES
Figure
No. Title Page
1.1. Products
from typical barrel of crude oil 2
2.1.
Schematic of
the Fluid Catalytic Cracking Unit 10
3.1. The identification scheme 18
3.2.
The input-output informational
characterization 19
3.3.
The predictive control structure of the catalytic cracking process
22
3.4 Schematic
of Interaction for Controlled And Manipulated Variables 26
3.5 Schematic
of a fluid catalytic cracking unit with one closed loop 26
3.6 Block
Diagram of the control of a fluid catalytic cracking unit with decouplers
28
4.1 The dynamic evolution of the riser outlet temperature and regenerated
catalyst flow 37
when the controller set-point - Tr increases
4.2. The dynamic evolution of the regenerator temperature and air flow
rate when controller 38
set point -Treg1increases
4.3. The dynamic evolution of the riser outlet temperature and
regenerated catalyst flow 38
4.4. The evolution in time
of the regenerated catalysts temperature and air flow 39
when the feedstock increases
4.5 The dynamic evolution of the riser outlet temperature and regenerated
catalyst flow 39
when the temperature riser controller set point increases
4.6. The dynamic evolution of the regenerator temperature and air flow
trend when the 40
Temperature regenerator controller set point increases
4.7Simulated response of riser exit temperature under PI controller
without decoupler 42
4.8 Simulated response of the
regenerator temperature under PI controller without 43
decoupler
4.9 Simulated response of riser
exit temperature and under PI controller with decoupler 43
4.10 Simulated response of the regenerator
temperature under PI controller with decoupler 44
4.11 Step
identification for a FCC unit for control design purposes 46
4.12 Closed-loop
performance of three decentralized control configurations for a FCC unit 47
LIST
OF SYMBOLS
Cca: Catalytic coke on the catalyst
(mass%).
Cpa: Air specific heat (kcal/kg.oC).
Cpc: Catalyst Specific heat (kcal/kg.oC).
Cpf: Gasoil Specific heat (kcal/kg.oC).
Crc: Coke on the catalyst of the
regenerator (mass %).
Csc: Coke on the spent catalyst (mass %).
D12&D21: Decoupler
transfer function.
Fa: Air flow rate to regenerator
(kg/sec).
Frc: Catalyst flow rate to riser
(kg/sec).
Ftf: Total feed flow rate to
riser(kg/sec).
G(s): Transfer function.
ΔHcr: Heat of cracking reaction
(kcal/kg).
ΔHfv: Heat of vaporization of gasoil feed
(kcal/kg).
ΔHg: Heat of combustion of coke on
regenerator (kcal/kg).
K: Steady state gain.
K': closed-loop gain.
Kc: Controller gain.
Mg: Catalyst hold-up in the regenerator
(kg).
Mr: Catalyst hold-up in the reactor
vessel and riser (kg).
Qmp: feedstock
flow (kg/sec)
Rcb: Rate of coke burned in regenerator
(mass %/min.).
Rcf: Rate of coke formation (kg/min.).
Roc: Cracking reaction rate (kg/min.).
s: Laplace domain (1/sec).
Tfp: Feed temperature at riser entrance (oC).
Tg: Regenerator bed temperature (oC).
Tfp: Reactor bed temperature (oC).
Treg1: Regenerated catalyst temperature (oC)
Tr: Riser outlet temperature (oC)
t: Time domain (sec).
Greek letters
ρtf : Feed density (kg/m3).
τI : Time constant of integral controller
(min.)
λ : Relative gain.
CHAPTER ONE
1.0.INTRODUCTION
BACKGROUND OF STUDY
Public enterprises were established, to enhance Nigeria’s socio economic
development, especially after independence in 1960. The major concern in this
regard had been to accelerate development and economic self-reliance through
‘’economic nationalism.’’ Public enterprises thus reflect one of those
instruments by which government intervenes in economic development rather than
allow market forces to dictate the pace of development. According to Ayodele
(2004), Nigeria relied heavily upon public enterprises, up to the mid-1980s,
for the development, management and allocation of utilities and social
services. They were seen as major instruments not only for the mobilization and
allocation of public investment resources, employment generation and income
redistribution, but also for determining government finances and the
acceleration of overall economic development.
Adeyemo (2005), reflecting on Turkey, Mexico, India and Nigeria, noted
that the establishment of public enterprises was premised on what he considered
as obstacles to economic development in the post-independence states. It is
also instructive to note that in Nigeria like many developing countries, public
enterprises are used as employers of last resort. According to Hemming and Mansor
(1988), state owned enterprises enable governments to pursue goals of social
equity that the market ordinarily ignores. Similarly, Ugorji (1995) observed
that public enterprises had been established for political reasons. Many
government undertakings were used to provide jobs for constituents, political
allies, and friends. The location of public enterprises and the distribution of
government employment have further been defended on the need to maintain
.federal character and promote national integration.
Other factors that accelerated the growth of Nigeria’s public sector
were the indigenization policy of 1972 as enacted by the Nigerian Enterprises
Promotion Decree. It was designed to control the commanding heights of the
economy. The policy further provided the much needed legal basis for extensive
government participation in the ownership and control of significant sectors of
the economy. According to Adeyemo (2005), Nigerian public enterprises have come
under gross criticism in spite of the impetus given to them. Their problems
were so enormous that many Nigerians became greatly disillusioned. These
criticisms vary from the lack of productivity/profitability to reliance on
large government subsidies. Ogundipe (1986) once argued that between 1975 and 1985,
government capital investments in public enterprises totalled about 23billion
Naira. In addition to equity investments, government gave subsidies of N11.5
billion to various government enterprises. All these expenditures contributed
in no small measure to increase government expenditures and deficits.
Generally, public expectations from these enterprises were largely
unmet, despite the sizable proportion of public budgetary investible funds
which were being allocated to them. In addition, public enterprises suffered
from gross mismanagement and consequently resulted to inefficiency in the use
of productive capital, corruption and nepotism, which in turn weakened the
ability of government to carry out its functions efficiently. (World Bank
1991). However, given the financial impacts of the global economic crisis on
the Nigerian economy, the public sector- led development strategy became
unsustainable. This in turn propelled radical economic adjustments and reforms,
one of which is the emphasis on less of government in the production,
management and the allocation of resources in Nigeria. Consequently, Nwoye
(2010) stated that Privatization in Nigeria was formally introduced by the
Privatization and Commercialization Act of 1988, which later set up the Technical
Committee on Privatization and Commercialization (TCPC), chaired by Dr. Hamza
Zayyad, with a mandate to privatize 111 public enterprises and commercialize 34
others. The Federal Military Government promulgated the Bureau for Public
Enterprises Act of 1993, which repealed the 1988 Act and set up the Bureau for
Public Enterprises (BPE) to implement the privatization program in Nigeria. In
1999, the Federal Government enacted the Public Enterprise (Privatization and
Commercialization) Act, which created the National Council on Privatization
(NCP) chaired by the Vice President.
STATEMENT
OF PROBLEMS
The concept of
privatization poses its own challenges. In this context, it is apposite to
examine the objectives of privatization. In the words of Guislain, defining
privatization objectives is an important exercise that should be undertaken as
early as possible. Many privatization programs have foundered when clear
objectives were lacking or where conflicting objectives were simultaneously
pursued. The definition of objectives is not an easy task, however, and it is
made no easier by the multiplicity of possible objectives and actors with
different, often conflicting interests.
According to Adesanmi (2011), the government, set up the Bureau of
Public Enterprise (BPE) to privatise and commercialise, as the case may be,
public enterprises with the objective of reducing or eliminate the drain on
public treasury. It also seek to reducing corruption, modernise technology,
strengthen domestic capital markets, promote efficiency and better management,
reduce debt burden and fiscal deficit, resolve massive pension funding
problems, broaden the base of ownership of business. Others include generating
funds for the treasury, promoting governance, attracting foreign involvement
and attract back flight capital. Whether the BPE has met and realised these
objectives is a matter that is open for debate. This paper attempted to assess
the operation of the privatization scheme in Nigeria, determined its level of
performance/productivity. It also proffered objective solutions for the
amelioration of gaps.
Microeconomic theory predicts that incentive
and contracting problems create inefficiencies stemming from public ownership,
given that managers of state-owned enterprises pursue objectives that differ
from those of private firms and face less monitoring. Not only are the
managers’ objectives distorted, but the budget constraints they face are also
softened. Empirical evidence shows a robust corroboration of this theoretical
implication in several countries. How true is this for Africa? The study will
also appraise the nature of the contracts between these firms and government in
the pre and post-reform period and show how the contracts address three
interrelated problems: information asymmetry, incentives and commitment.
OBJECTIVES OF THE STUDY
a) To
understand the extent and pattern of privatization
b) To
establish the results of privatization in Nigeria.
c) To establish whether privatization has improved the performance of
enterprises as anticipated.
d) To
outline policy lessons that can be learned from the privatization exercise.
RESEARCH QUESTIONS
To
have an in-depth knowledge of this study, the following research questions will
be considered:
a) What
is the extent and pattern of privatization in Nigeria?
b) What
has been the result of privatization over-time in Nigeria?
c) Has
privatization improved the performance of enterprises as anticipated?
d) What
are the policy lessons that can be learned from the privatization program?
RESEARCH HYPOTHESIS(S)
H1: There
is a relationship between privatization and productivity of formerly state
owned companies
H0: There
is no relationship between privatization and productivity of formerly state owned
companies
H2: There
is a relationship between government management of companies and the
performance of such companies
H0: There
is no relationship between government management of companies and the
performance of such companies
DATA SOURCES AND SCOPE OF WORK
For
this study, we will be taking a very close look as formerly public enterprises
that have been transferred to private individuals or corporations. The study
will engage the assessment of former employees as well as the public to
evaluate the performance of the firms now and before. Previous studies have
shown that the measure to understand the impact of privatization is to use the
return on shares, equity and asset approach. This method will also be implored,
but more to it will be the perception and profitability of these new
organizations. The study will also focus on the decrease in government
expenditure in businesses and how these funds have been redirected to providing
basic amenities for the populace. As a basis of scoping, we will be taking a
look into organizations like NITEL, PHCN, among others.
RESEARCH DESIGN
Data for this thesis will be collected using a quantitative,
survey-based methodology. This approach is important when causal relationships
among the underlying theoretical constructs need to be examined.
Self-administered questionnaires are considered to be the most appropriate tool
as well as interviews. Most importantly, this method is quick, inexpensive,
efficient, and can be administered to a large sample (McCelland, 1994;
Churchill, 1995, Sekaran, 2000; Zikmund, 2003). To ensure that the questions
are clearly understood and there is no ambiguity among them, a pre-test will be
conducted.
Respondents will be selected to conduct the study. Descriptive analysis
for the entire sample will be performed using SPSS (Statistical Package for the
Social Sciences).
In this study, where
relationships are being established, two statistical methods will be used to
analyze, interpret, and test data related to the study. Sample percentage (SP)
arranged in tables will be used to analyze respondent’s bio-data and hypothesis
of the study will be tested by the use of Pearson's Coefficient of correlation.
The analysis of data and testing of hypothesis will be based on the responses
obtained through interview and questionnaire administered.
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