ABSTRACT
This work is based on the application
of Cohen-Coon and Zeigler-Nichols tuning techniques using proportional (P),
proportional-integral (PI) and proportional-integral-derivative (PID)
controllers to the control of a reactive distillation process used for the
production of methyl oleate, which is a fatty acid methyl ester, produced from
the esterification reaction between oleic acid and methanol. The model used for
the study was obtained from literature and formulated in Simulink environment
of MATLAB. Before embarking on the control study, the open-loop dynamics of the
system was first studied by applying a step to its input variable. Furthermore,
the closed-loop dynamic simulation was accomplished by applying a step to the
set-point of the controlled variable of the system. From the results obtained,
it was discovered that the obtained model of the process was a stable one
because it was able to get settled within the simulation time considered. Also,
the closed-loop results obtained from the simulation revealed that the process
was successfully controlled using PID controllers tuned with the techniques
because they (the controllers) made the system to behave as it was desired,
even though there was a normal offset in the case of P-only controller.
CHAPTER ONE
1.0
INTRODUCTION
With the limited availability of
conventional petroleum diesel and, also, as a result of environmental concerns,
fatty acid methyl Ester, otherwise known as biodiesel, which is an alternative
fuel, is currently receiving attention in both academic and industrial
research. This material can be used to replace petroleum diesel without any
modification because their properties are similar (Simasatitkul et al., 2011;
Giwa et al., 2014; Giwa et al., 2015a; Giwa et al., 2015c). Biodiesel is
defined as the mono-alkyl esters of long chain fatty acids derived from oils
and fats by transesterification of vegetable oils using alcohol in presence of
catalyst that conforms to ASTM D-6159 specifications (Cherng-Yuan and Jung-Chi,
2010; Kapilan et al., 2009).
Biodiesel has similar fuel properties
to diesel and, therefore, it can be used as a substitute for diesel fuel,
either in neat form or in blends with petroleum diesel (Pasias et al., 2006).
The fuel has the following advantages over petroleum-based diesel: it is
renewable, carbon neutral, more rapidly biodegradable, less toxic, has a higher
flash point and low sulphur content. The use of straight vegetable oils (SVO)
in energy production processes has been studied, but in the last three decades,
renewed interest in biodiesel has re-instigated the research into vegetable
oils science and engineering which established that biodiesel is a possible
substitute or supplement to mineral diesel for engine and other applications.
There are different technologies
available for the production of biodiesel and many more are expected to emerge
in the near future. The most widely used method worldwide, however, remains
transesterification process to form an alkyl-ester of the fatty acid along with
glycerol as a by-product of the reaction. Various techniques of biodiesel
production are available today. These are catalytic (Lin et al., 2009;
Hou et al., 2007), enzymatic (Hama et al., 2008), reactive
distillation (Simasatitkul et al., 2011) and non-catalytic techniques
(Diasakou et al., 1998; Kusdiana and Saka, 2001; He et al.,
2007). Catalytic technique is commonly used in the industrial sectors.
The transesterification global
reaction process is normally a sequence of three consecutive reversible
reactions. The triglycerides are converted step by step in diglycerides,
monoglycerides and finally in glycerol. One fatty acid ester molecule is
produced at each step (Marchetti et al., 2007). The performance of the
transesterification is affected by multiple parameters, such as molar ratio of
alcohol:vegetable oil, type and quantity of catalyst, reaction time, reaction
temperature, feedstock properties and mixer intensity. Usually, an alcohol in
excess is used for driving the reaction equilibrium towards the product side.
This alcohol excess must be recovered in order to reutilize it and,
furthermore, purify the biodiesel. The alcohol recovery process is generally
carried out by distillation process, thus, the energy consumption, operating
costs, equipment number and the production time increase. This is the reason
why it is better to employ a novel process known as reactive distillation in
this production of biodiesel.
Reactive Distillation (RD) belongs to
the so-called “process-intensification technologies” (Michael Sakuth et al.
2003). It may be advantageous for liquid-phase reaction systems when the
reaction must be carried out with a large excess of one or more of the
reactants, when a reaction can be driven to completion by removal of one or
more of the products as they are formed, or when the product recovery or
by-product recycle scheme is complicated or made infeasible by azeotrope
formation (Perry et al., 1997).
It is more advantageous than a
conventional process with separate reaction and separation sections owing to
the following advantages that include low reduced investment and operating
costs as a result of increased yield of a reversible reaction that is due to
the separation of the desired product from the reaction mixture (PĂ©rez-Correa
et al., 2008; Giwa and Giwa, 2015), high conversion, improved selectivity, low
energy consumption, ability to carry out difficult separations and avoidance of
azeotropes (Jana and Adari, 2009; Giwa, 2012; Giwa and Giwa, 2012; Giwa and
Giwa, 2015).
The RD process has less separation
steps, produces no waste salt streams as water is the only by-product, and
could use a part of the produced biodiesel as source of energy. The low
residence time of the liquid phase inside the RD column (20–60 min) requires a
highly active catalyst. A RD column has some hydraulic constrains that limit the
maximum residence time. In addition, the production rate is increased when the
residence time is short (Anton et al., 2006). However, no mixing devices are
used in distillation columns and typically any moving part is avoided in
chemical industry due to the increased energy consumption and higher
maintenance costs. (Anton et al., 2006).
Model can be defined scientifically as
"A mathematical or physical system, obeying certain specified conditions,
whose behaviour is used to understand a physical, biological, or social system
to which it is analogous in some way." A working definition of process
model is a set of equations (including the necessary input data to solve the
equations) that allows us to predict the behaviour of a chemical process. Models
play a very important role in control-system design. Models can be used to
simulate expected process behaviour with a proposed control system. Also,
models are often "embedded" in the controller itself; in effect the
controller can use a process model to anticipate the effect of a control
action.
The term process dynamics refers to
unsteady-state (or transient) process behaviour. By contrast, most of the
chemical engineers’ curricula emphasize steady-state and equilibrium conditions
such courses as material and energy balance, thermodynamics, and transport
phenomena. But process dynamics are also very important. Transient operation
occurs during important situations such as start-ups and shut-downs, un-usual
process disturbances, planned transitions from one product grade to another.
The primary objective of process
control is to maintain a process at the desire operation conditions safely and
efficiently, while satisfying environmental and product quality requirements.
The subject of process control is concerned on how to achieve these goals. In
large-scale, integrated processing plants such as oil refineries or ethylene
plants, thousands of process variables such as compositions, temperatures and
pressures are measured and must be controlled. In order to design a controller,
then, we need to know whether an increase in the manipulated input increases or
decreases the process output variable; that is, we need to know whether the
process gain is positive or negative.
In recent years the performance
requirements for process plants have become increasingly difficult to satisfy.
Stronger competition, tougher environmental and safety regulations, and rapidly
changing economic conditions have been key factors in tightening product
quality specification. A further complication is that modern plants have become
more difficult to operate because of the trend towards complex and high
integrated processes. For such plant, it is difficult to prevent disturbances
from propagating from one unit to other interconnected units.
In view of the increased emphasis
placed on safe, efficient plant operation, it is only natural that the subject
process control has been increasingly important in recent years. Without
computer-based process control systems it would be impossible to operate modern
plants safely and profitably while satisfying products quality and
environmental requirements. Thus, it is important chemical engineers to have an
understanding of both the theory and practice of control.
1.1 Aim
This research project is aimed at
applying proportional-integral-derivative control to the control of a process
used for the production of a fatty acid methyl ester.
1.2 Problem Statement
One of the problems facing chemical
process industries producing fatty acid methyl ester is low purity, in terms of
mole fraction, of the desired product. There is the need to look for a way to
tackle this problem so that the future of biodiesel can be guaranteed.
1.3 Justification
The successful completion of this
project will provide a control algorithm that can be used to handle any fatty
acid methyl ester reactive distillation process for the purpose of obtaining
high mole fraction of the desired FAME.
TOPIC: PID CONTROL OF A FATTY ACID METHYL ESTER REACTIVE DISTILLATION PROCESS
Chapters: 1 - 5
Delivery: Email
Delivery: Email
Number of Pages: 95
Price: 3000 NGN
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