Dynamical modelling of a biphasic separator for hydrocarbon field
M. Zelmat, M. Kidouche, A.Habbi
Laboratory of Applied Automation
University of Boumerdès 35000, Algeria,
zelmat_mimoun@yahoo.com
Abstract - A great number of today’s problems are
brought about by present day technology and
environmental process which are highly complex as
separator (process of separation) used in hydrocarbon
fields. Since the separation process unrolls inside a
block of separation, it is necessarily that the model
takes in the account the dimension of the separator
and the physical properties of the composites to be
separated. This paper deals with the problem of
finding a moderately complex model of the separator
that may capture the key dynamical properties of the
physical plant.
Keywords : Hydrocarbons, system dynamics, twophase
separation, transfer function
I. INTRODUCTION
In hydrocarbon fields, static processes such as biphasic
separators are still of substantial interest. The composites,
liquid and gas, are separated inside a block of separation
and water which is often produced is removed from the
mixture liquid-gas simultaneously. Because of the
complicated dynamics of the biphasic separator, stringent
requirements are imposed on the control systems that may
be designed to achieve good performances in terms of
commands tracking, disturbances rejection and plant
safety. Since the correct separation process can only
be described by nonlinear differential equations with time
varying parameters, it is necessary that we focus on the
development of a moderately complex model that
captures well the key dynamical properties of the physical
plant. On the issue of the separator control system design,
many conventional controllers have been suggested.
However, regarding the complexity of the separator
dynamic behaviour, the conventional controllers are less
effective in practice and very sensitive to parameter
variations. The need for simultaneous controlling of the
strongly interacting variables of the biphasic separator
system makes the separator control system design an ideal
application for knowledge-based control. Hence, because
of the limitations of the conventional control theory,
alternative approaches have been suggested and
implemented for many industrial applications. To date,
fuzzy logic is considered as an alternative approach to
conventional control techniques for industrial complex
control systems. Fuzzy logic is one of the most useful
approaches for utilizing the qualitative knowledge of a
system to design a controller [Takagi and Sugeno, 1985].
It represents a means of both collecting human knowledge
and expertise and dealing with uncertainties in the process
control. Therefore, despite the fact that much progress has
been made in successfully applying fuzzy logic control to
industrial control systems, it has become evident that
many basic issues remain to be further addressed. Thus,
we find it much more interesting to start first with a
quantitative model development for the separation process
to see in what way fuzzy logic approach may be applied
for biphasic separator control system design. The
resulting mathematical model will be used to validate
future works on fuzzy modelling and control of the
biphasic separator system.
II. MATHEMATICAL MODEL
In order to provide a better understanding about the
separation process, it is necessary to focus, first, on the
quantitative description of the dynamic behaviour of the
biphasic separator. The mathematical model is built upon
physical principles with taking into account the empirical
parameters that describe well the key properties of the
separator in a specified operating range. Since the
separation process unrolls inside a block of separation, it
is necessary that the model takes into account the
dimension of the separator and the physical properties of
the composites to be separated. Therefore, to develop a
mathematical model, we must define the principal
physical constants such as the physical properties of the
charge and the dimension of the separator. Thus, the
necessary steps for a system model development
emphasize the fact that the biphasic separation process
(liquid-gas) unrolls inside the separator of cylindrical
form in vertical or horizontal position (fig. 1). The
mixture flow (liquid-gas) at the input of the separator
constitutes its charge. The separator has two principal
output, one for the gas and the other for the liquid. To
have a correct separation of (liquid-gas), we should
maintain the pressure and the interface level at some
determined values. It is important to notice that there
exists a various approaches to construct the model of the
separator, and every scheme is constructed for a specified
use, which must be stable at working conditions.
Its stability analysis is studied with respect to various
perturbations (externals conditions). For this, the
dynamical model should take in the account the externals
and internals factors that act on the separator. Thus the
model is represented by differential equations that
describe the internal parameters variations in function of
the externals ones. The complexity of these equations
depends on the assigned goal of the model wanted.
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