04-06-2012, 10:51 AM
Modelling Study Of Supercritical Power Plant And Parameter Identification Using Genetic Algorithms
[attachment=24075]
Abstract
The paper aims to study the whole process
mathematical model for a supercritical coal-fired power
plant. The modeling procedure is based on thermodynamic
and engineering principles and the previously published
literatures. Model unknown parameters are identified using
Genetic Algorithms (GAs) with 600MW supercritical power
plant on-site measurement data. The identified parameters
are verified with different sets of measured plant data.
Although some assumptions are made in modeling process,
the supercritical coal-fired power plant model reported in the
paper can be used to simulate the main features of the real
plant once-through boiler operation and the simulation
results show the main variation trends of the process.
I .INTRODUCTION
The world is now facing the challenge of global
warming and environment protection. On the other hand,
the demand of electricity is growing rapidly due to
economic growth and increases in population. With the
consideration of environmental issues and sustainable
development in energy, renewable energy such as wind,
solar, and tidal wave should be only resources to be
explored in theory. But the growth in demand is also a
heavy factor in energy equations so the renewable energy
alone is not able to generate enough electricity to fill the
gap within a short time of period. Power generation using
fossil fuels is inevitable, especially, coal fired power
generation is found to be an unavoidable choice due to its
huge capacity and flexibility in load following ([1], [2]).
The conventional coal fired power plants have a huge
environmental impact and lower energy conversion
efficiencies. Any new coal fired power plants must be
cleaner compared with traditional power plants.
Supercritical power plants are the most suitable choice
with consideration of the factors in environmental
enhancement, higher energy efficiency and economic
growth. However, there has been an issue to be addressed
to adopt this technology in the UK because the dynamic
response and performance still require study for better
understanding supercritical plants in relation with
conventional subcritical plants, and the supercritical units
are considered by others to be unreliable in comparison
with subcritical units [3]. Therefore, the characteristics of
supercritical plants remain to be considered and
investigated. Supercritical boilers have to be once-through
type boilers because there is not distinction between water
and steam phases in supercritical process so there is no
need for drum to separate water steam mixture. Due to the
Omar Mohamed, Jihong Wang*, Shen Guo, Jianlin Wei are with the
School of Electronic, Electrical and Computer Engineering, the
University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
Bushra Al-Duri is with the School of Chemical Engineering, University
of Birmingham, Edgbaston, Birmingham B15 2TT, UK
* The author for correspondence.
Email: j.h.wang[at]bham.ac.uk
Proceedings of the World Congress on Engineering 2010 Vol II
WCE 2010, June 30 - July 2, 2010, London, U.K.
ISBN: 978-988-18210-7-2
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2010
absence of the drum, the once-through boilers have less
stored energy and faster response than the drum boiler
plants. However, there are several advantages of
supercritical power plants over traditional subcritical
plants include:
• Reduced fuel cost due to improved plant efficiency.
• Significant improvement of environment by reduction
in CO2 emissions.
• Plant costs less than subcritical technology costs and
other coal technologies.
• Can be fully integrated with appropriate CO2 capture
technology.
• Fast response due to load changes and high capacity
which make them suitable for base load operation, and
also for fast load demand following.
From the literature survey, it has been found that
several models have been reported with emphasis on
different aspects of the boiler characteristics. Studying the
response and control performance of once through
supercritical (SC) units began on 1958 when work was
started on a simulation of the Eddystone I unit of
Philadelphia Electric Company and the work was extended
for simulation of Bull run SC generation unit ([4], [5]).
Yutaka Suzuki et al. modelled a once through SC boiler in
order to improve the control system of an existing plant.
The model was based on nonlinear partial differential
equations, and the simulation results indicated that the
model is valid ([6]). Wataro Shinohara et al. (1996)
presented a simplified state space model for SC once
through boiler-turbine and designed a nonlinear controller
[7]. Pressure node model description was introduced by
Toshio Inoue et al. for power system frequency simulation
studies [8]. Intelligent techniques contributions have
yielded an excellent performance for modeling. Neural
network has the ability to model the SC power plant with
sufficiently accurate results if they are trained with
suitable data provided by operating unit [9]. However,
neural network performances are unsatisfactory to
simulate some emergency conditions of the plant because
NN method depends entirely on the data not on physical
laws. Simulation of SC boilers may be achieved either
theoretically based on physical laws or empirically based
on experimental work. In this paper, the proposed
mathematical model is based on thermodynamic principles
and the model parameters are identified according to a
600MW SC power plant operating currently in China. The
simulation results show that the model is trustable to
simulate the whole once-through mode of operation.
II. MATHEMATICAL MODEL OF THE PLANT
A. Plant description
The unit of a once-through supercritical 600MW
power plant is selected for the modelling study. The
schematic view of the boiler is shown in Fig.1. Water from
the feedwater heater is heated in the economizer before
entering the superheating stages through the waterwall.
The superheater consists of three sections which are low
temperature superheater, platen superheater, and final
stage superheater. The main steam outlet temperature is
about 571Cº at the steady state and a pressure is 25.5 MPa.
There are 2 reheating sections in the boiler for reheating
the reduced thermal energy steam exhausted from the high
pressure turbine. The inlet temperature of the reheater is
309 Cº and the outlet temperature is nearly 571 Cº and
average pressure is 4.16MPa. The reheated steam is used
to energize the intermediate pressure turbine. Finally, the
mechanical power is generated through multi-stage
turbines to provide an adequate expansion of the steam
through the turbine and subsequently high thermal
efficiency of the plant.
Fig.1. schematic view of the plant
B. Assumptions
Assumptions which are stated to simplify the process
should be logically acceptable and sufficient to transfer the
model from its complex physical state to simple
mathematical state. A great attention should be taken for
the choice of assumptions because some assumptions
result in over-simplification and nonrelaistic system. For
successful mathematical modeling, the following general
assumptions are made:
• Fluid properties are uniform at any cross section, and
the fluid flow in the boiler tubes is one-phase flow.
• In the heat exchanger, the pipes for each heat
exchanger are lumped together to form one pipe.
• Only one control volume is considered in the
waterwall.
• The dynamic behaviour of the air and gas pressure is
neglected.
• Only the change in internal energy is considered, the
deviations or changes of kinetic energy and potential
energy of fluid are neglected.
[attachment=24075]
Abstract
The paper aims to study the whole process
mathematical model for a supercritical coal-fired power
plant. The modeling procedure is based on thermodynamic
and engineering principles and the previously published
literatures. Model unknown parameters are identified using
Genetic Algorithms (GAs) with 600MW supercritical power
plant on-site measurement data. The identified parameters
are verified with different sets of measured plant data.
Although some assumptions are made in modeling process,
the supercritical coal-fired power plant model reported in the
paper can be used to simulate the main features of the real
plant once-through boiler operation and the simulation
results show the main variation trends of the process.
I .INTRODUCTION
The world is now facing the challenge of global
warming and environment protection. On the other hand,
the demand of electricity is growing rapidly due to
economic growth and increases in population. With the
consideration of environmental issues and sustainable
development in energy, renewable energy such as wind,
solar, and tidal wave should be only resources to be
explored in theory. But the growth in demand is also a
heavy factor in energy equations so the renewable energy
alone is not able to generate enough electricity to fill the
gap within a short time of period. Power generation using
fossil fuels is inevitable, especially, coal fired power
generation is found to be an unavoidable choice due to its
huge capacity and flexibility in load following ([1], [2]).
The conventional coal fired power plants have a huge
environmental impact and lower energy conversion
efficiencies. Any new coal fired power plants must be
cleaner compared with traditional power plants.
Supercritical power plants are the most suitable choice
with consideration of the factors in environmental
enhancement, higher energy efficiency and economic
growth. However, there has been an issue to be addressed
to adopt this technology in the UK because the dynamic
response and performance still require study for better
understanding supercritical plants in relation with
conventional subcritical plants, and the supercritical units
are considered by others to be unreliable in comparison
with subcritical units [3]. Therefore, the characteristics of
supercritical plants remain to be considered and
investigated. Supercritical boilers have to be once-through
type boilers because there is not distinction between water
and steam phases in supercritical process so there is no
need for drum to separate water steam mixture. Due to the
Omar Mohamed, Jihong Wang*, Shen Guo, Jianlin Wei are with the
School of Electronic, Electrical and Computer Engineering, the
University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
Bushra Al-Duri is with the School of Chemical Engineering, University
of Birmingham, Edgbaston, Birmingham B15 2TT, UK
* The author for correspondence.
Email: j.h.wang[at]bham.ac.uk
Proceedings of the World Congress on Engineering 2010 Vol II
WCE 2010, June 30 - July 2, 2010, London, U.K.
ISBN: 978-988-18210-7-2
ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)
WCE 2010
absence of the drum, the once-through boilers have less
stored energy and faster response than the drum boiler
plants. However, there are several advantages of
supercritical power plants over traditional subcritical
plants include:
• Reduced fuel cost due to improved plant efficiency.
• Significant improvement of environment by reduction
in CO2 emissions.
• Plant costs less than subcritical technology costs and
other coal technologies.
• Can be fully integrated with appropriate CO2 capture
technology.
• Fast response due to load changes and high capacity
which make them suitable for base load operation, and
also for fast load demand following.
From the literature survey, it has been found that
several models have been reported with emphasis on
different aspects of the boiler characteristics. Studying the
response and control performance of once through
supercritical (SC) units began on 1958 when work was
started on a simulation of the Eddystone I unit of
Philadelphia Electric Company and the work was extended
for simulation of Bull run SC generation unit ([4], [5]).
Yutaka Suzuki et al. modelled a once through SC boiler in
order to improve the control system of an existing plant.
The model was based on nonlinear partial differential
equations, and the simulation results indicated that the
model is valid ([6]). Wataro Shinohara et al. (1996)
presented a simplified state space model for SC once
through boiler-turbine and designed a nonlinear controller
[7]. Pressure node model description was introduced by
Toshio Inoue et al. for power system frequency simulation
studies [8]. Intelligent techniques contributions have
yielded an excellent performance for modeling. Neural
network has the ability to model the SC power plant with
sufficiently accurate results if they are trained with
suitable data provided by operating unit [9]. However,
neural network performances are unsatisfactory to
simulate some emergency conditions of the plant because
NN method depends entirely on the data not on physical
laws. Simulation of SC boilers may be achieved either
theoretically based on physical laws or empirically based
on experimental work. In this paper, the proposed
mathematical model is based on thermodynamic principles
and the model parameters are identified according to a
600MW SC power plant operating currently in China. The
simulation results show that the model is trustable to
simulate the whole once-through mode of operation.
II. MATHEMATICAL MODEL OF THE PLANT
A. Plant description
The unit of a once-through supercritical 600MW
power plant is selected for the modelling study. The
schematic view of the boiler is shown in Fig.1. Water from
the feedwater heater is heated in the economizer before
entering the superheating stages through the waterwall.
The superheater consists of three sections which are low
temperature superheater, platen superheater, and final
stage superheater. The main steam outlet temperature is
about 571Cº at the steady state and a pressure is 25.5 MPa.
There are 2 reheating sections in the boiler for reheating
the reduced thermal energy steam exhausted from the high
pressure turbine. The inlet temperature of the reheater is
309 Cº and the outlet temperature is nearly 571 Cº and
average pressure is 4.16MPa. The reheated steam is used
to energize the intermediate pressure turbine. Finally, the
mechanical power is generated through multi-stage
turbines to provide an adequate expansion of the steam
through the turbine and subsequently high thermal
efficiency of the plant.
Fig.1. schematic view of the plant
B. Assumptions
Assumptions which are stated to simplify the process
should be logically acceptable and sufficient to transfer the
model from its complex physical state to simple
mathematical state. A great attention should be taken for
the choice of assumptions because some assumptions
result in over-simplification and nonrelaistic system. For
successful mathematical modeling, the following general
assumptions are made:
• Fluid properties are uniform at any cross section, and
the fluid flow in the boiler tubes is one-phase flow.
• In the heat exchanger, the pipes for each heat
exchanger are lumped together to form one pipe.
• Only one control volume is considered in the
waterwall.
• The dynamic behaviour of the air and gas pressure is
neglected.
• Only the change in internal energy is considered, the
deviations or changes of kinetic energy and potential
energy of fluid are neglected.