ISSN (Online) 2456 -1304

International Journal of Science, Engineering and Management (IJSEM)

Vol 4, Issue 3, March 2019

Investigations on the Critical Parameters of a 500

MW Utility Boiler
[1]
P. Subha Hency Jose, [2] G. Jims John Wessley, [3] R. Rajalakshmy
[1][3]
Department of Instrumentation Engineering, [2] Department of Aerospace Engineering
[1][2][3]
Karunya Institute of Technology and Sciences, Coimbatore, Tamil Nadu, India
[1]
hency20002000@karunya.edu, [2] jims_john@karunya.edu, [3]rajalakshmy@karunya.edu

Abstract: Electricity is the prime indicator of the economic growth and standard of living of the people in a nation. Generation of
power is mainly dependent on coal fired power plants throughout the world. Coal is known to be one of the most important natural
resources in the world. The surplus availability, extensive distribution and versatility of coal makes it a significant source of
electrical energy for all times. The major proportion of electric power is generated using coal rather than any other source of fuel.
It is cheaper than other fossil fuels but it is hard to be burnt. For power units operating on fossil fuel, the sole, prime, operating
cost is fuel. The fuel expenses account for about 50 - 60% of the cost of generating electricity. Hence, procuring fuel of lower
price is often a major challenge. Despite this and other environmental concerns, coal is still found to hold a major share of the
electrical energy consumption in future. Over 48% of the world’s electric power supply is obtained from thermal power plants. A
thermal power plant produces electrical power from fossil fuel, namely coal through several energy conversion processes, using
water as a working fluid. It comprises a boiler, turbine, electric generator and other auxiliary equipments each of which serve a
definite purpose. This paper deals with the mathematical model and the design aspects of the boiler and the system response when
it is subjected to many inputs.

Keywords: - Process control, Utility Boiler, Chien-Hrones-Reswick tuning, feed control

I. INTRODUCTION B. Economizer
A Fossil Fuel Power Unit (FFPU) is a multivariable They are located in the second pass of the boiler. An
dynamic system. The interchange of energy from chemical economizer is also a heat exchanger. The feed water before
to electrical in a FFPU is a complex process. Mathematical entering the boiler drum is sent to the economizer. The
model of this process enables operator to optimize the economizer increase the temperature of the feed water but
control of the actual plant and the designer to optimize the not beyond the boiling point of water. Feed water is
design of the future plants. preheated because if the water enters the furnace with it in
Controlling of main steam pressure and other vital normal rrom temperature, most of the heat produced in the
parameters of an Utility boiler during variations of the furnace will be utilized in rising the temperature of the feed
calorific value of coal fed into boiler furnace (fuel water thereby reducing the production of steam. This affects
switching) is quite complex. In this paper, classical Chien- the boiler efficiency. Hence an economizer is used to
Hrones-Reswick (CHR) tuning method is employed to study preheat te feed water. The flue gas is used to heat the feed
the performance of a 500 MW Utility boiler during fuel water.
switching fully taking care of the performance requirements C. Circulaion System
of Auto controls as indicated by plant owners .Instead of
It comprises of the boiler drum, down comer tubes and
choosing the controller parameters using trial and error
upriser(water walls) tubes. Sub cooled water from the
method or by soft computing techniques, CHR tuning
economizer, enters the boiler drum and flows through the
method has been judiciously applied to obtain the PID
down comer tubes by natural circulation and into the upriser
controller parameters from the open loop step response of
tubes which also are the water walls (furnace walls). The
the boiler.
feed water in the water walls is converted into steam and the
II. COMPONENTS OF THERMAL POWER PLANT water and steam mixture in the water walls reach the boiler
drum. The steam produced exists above the water level in
A. Feed Control Station the drum. Heat transfer takes place through direct radiation.
The feed control station consists of one low load valve At a given pressure, the temperature at which water reaches
(0 % to 30 % load) and two valves for full load conditions. boiling state is called saturation temperature. At saturation

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 ISSN (Online) 2456 -1304

International Journal of Science, Engineering and Management (IJSEM)

Vol 4, Issue 3, March 2019

temperature water boils and vapor formation takes place. During this situation, fluctuations in main steam pressure
Both steam and water remains at saturation temperature in and temperature is noticed even when the load on the plant
the drum. remains constant. These fluctuations are due to variations in
the calorific value of the fuel burnt and the phenomena is
D. Boiler Drum
often known as “ fuel switching” (though the terminology
The boiler drum is a horizontally mounted cylinder-with was earlier used to refer to change of coal source, now
both its ends enclosed by hemispherical structures. The it is also used to refer to wide variations in quality of coal
bottom side has number of holes, fitted with tubes which received from the same mine). The effect of changes in
join in a header that carries the down comer tubes. heating value of coal is given below:
Similarly, there are relatively smaller holes present fitted  As heating value changes, number of units (in
with tubes that join the steam header. Steam produced in the kilograms) of fuel required to achieve the same heat
riser tubes of the furnace, are joined to the steam header input changes.
through which steam is taken to the top portion of the boiler  If the heating value decreases by more than the excess
drum. There are tubes fitted on top of the drum which takes capacity of the pulverizers, then the pulverizers will
the steam out of the drum to the steam headers which in turn not be able to process enough coal for full-load
takes the steam to the superheaters. The Schematic diagram operation of the boiler.
of boiler furnace is given in Fig.1.
IV. MODEL OF THE BOILER
A nonlinear mathematical model developed and
validated for a 500 MW Unit available at Centre of
Excellence for Simulators, Corporate R&D, BHEL,
Hyderabad is considered for this research work. All the
subsystems covered in Section II had been modeled by
means of first principles approach. Conservation equations
for mass, energy and momentum have been considered.
Appropriate heat transfer and fluid flow correlations based
on collaborators data as well as data from Heat transfer and
Fluid Flow (HTFS) documents had been used. All the
subsystems mentioned were modeled based on equipment
performance curves as these are available with BHEL as
Original Equipment Manufacturer (OEM). The control
loops were synthesized based on ABB P13 hardware and all
the logics have been software emulated for integrating
control loops with integrated boiler model using various
subsystem models obtained as described above. From the
point of view of overall modeling and simulation of FFPUs,
the contributions of Kwatny et al. and Åström et al. (2000)
are noteworthy and their works include
Fig. 1. Schematic diagram of boiler furnace
 Mathematical equations for most of the sub systems,
 Integration of sub systems and
III. COAL QUALITY – FUEL SWITCHING  Simulation of integrated model for various
To take care of coal quality variation (specifically disturbances.
heating value of coal) , plant owners specify wide range of The model also includes, For a given coal history (elemental
coal for the design of boilers. Specifying wide range of composition), coal flow, secondary air flow, burner tilt and
coals for design of boiler will not allow the boiler the burner elevations, the Furnace model calculates the
manufacturer to select optimum equipment for the particular following:
power station. Due to coal property variations, the calorific  The flow and the flue gas temperature at the furnace
value (heating value) of coal from the same mine does not outlet plane.
remain the same, but varies randomly over an average value.  Heat transferred to water walls, platen super heaters,

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International Journal of Science, Engineering and Management (IJSEM)

Vol 4, Issue 3, March 2019

final super heaters and reheaters by direct radiation variations. In a FFPU, thermal stresses due to steam
 The heat transferred by convection and non-luminous pressure and temperature fluctuations are particularly
radiation to various heat exchangers such as platen, important. They are the critical process parameters in a
final and low temperature super heaters, reheaters, thermal power plant. Thick walled steam generator
economizer and air heaters and thereby the transient components undergo severe stress during quick startup,
variations in pressure, temperature of the inside fluid sudden and large variations and fuel property variations.
such as steam, water or air and metal temperature of Hence the authors have considered main steam pressure and
the heat exchanger. main steam temperature variations for the various studies
 Circulation system calculating the drum pressure and during fuel switching disturbances However while carrying
water level variations including the effects of swell and out the simulation studies, the data pertaining to other
shrink. controlled variations have also been collected but not
 Turbine and generator systems, condenser, low included in the paper, since the focus is on critical process
pressure and high pressure heaters, de-aerator, parameters. The main Control loops are
condensate pumps and boiler booster pumps  Drum Level Controller
These nonlinear mathematical models are significantly  Furnace Pressure controller
different in the following aspects from other models by  Super heater outlet temperature controller
Chien et al. (1958) and Mc Donald and Kwatny (1970).  Reheater temperature controller
 The radiative and convective modes of heat transfer  Master Pressure controller (Fuel flow controller, Total
have been regarded for all heat transfer surfaces. air flow controller with O2 bias)
 Heat transfer coefficients both on the gas side as well
as on the steam side have been continuously updated VII. SIMULATION
with changes in operating parameters. The dynamic simulation studies on the boiler for
 Heat transfer by direct radiation to water walls, panel variations in the calorific value of the coal have been carried
super heater, platen super heater, reheater sections and out and the performance has been analyzed. The results
the flue gas temperature at furnace outlet plane have obtained have been quiet encouraging and it proves the
been fairly detailed taking into account the burner tilt efficacy of the results obtained by CHR method of tuning.
and the mills in service (burners in service). The calorific value has been changed from 3300 KCal/Kg to
 As OEM of boilers, heat transfer correlations which 3700 Kcal/Kg. The variation in the critical parameters like
have been validated are used. Main Steam Pressure, Power, Primary Air Flow and
Secondary Air Flow are shown in Fig 1, 2, 3 and 4
V. MODEL VALIDATION respectively The PID Controller parameters employed for
The integrated model had been tested first as design this study is Kp = 2.0 , Ki = 60.0 Seconds , Kd = 120.0
specific (process variables like pressure, temperature and Seconds. The Performance Metrices considered are
flow for water, steam, flue gas at different nodes compared Overshoot and Undershoot and the result is portrayed in
with predicted design values and those obtained from Table 1.
models). The error had been less than 0.5 to 1.0%. After the
performance guarantee tests on the actual power plant,
steady state data for different loads had been collected and
the model had been tuned to plant specific. Further, over a
period of time, specific open loop tests had been conducted
to obtain the transient responses and the model had been
further fine-tuned for plant specific. The accuracy limits
during transient‟s zones are well within 5.0 % for wide
variety of disturbances.

VI. CONTROL LOOPS IN BOILER

For the boiler-turbine control system, the central task is
to adjust the output power to meet system demand while
minimizing unwanted steam pressure and temperature

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 ISSN (Online) 2456 -1304

International Journal of Science, Engineering and Management (IJSEM)

Vol 4, Issue 3, March 2019

Table 1 Performance Metrices for the critical

parameters of a 500 MW Utility Boiler when subjected
to coal variation disturbances
Maxim Final
S. Steady Maximu
um Settle
N Variable Flow m Under
Oversh d
o. Value shoot
oot value
Main
stream
1 170.3 5.66 - 170.3
Pressure in
ata
Power in
2 500 16.6 - 500 Fig 3. Variation in Power
MW
SA Total
3 (Tonnes/Hr 1050 166 38 1163
)
PA Total
4 (Tonnes/Hr 550 - 17 522
)

VIII. RESULTS AND DISCUSSION

The validated model was simulated for a atep change in
the calorific value of coal and the simulation results are
shown in Fig 2 to 5
Fig 4. Secondary Air Flow

Fig 5. Primary Air Flow

The steady state value of Main Steam Pressure, Power,

Secondary and Primary Air Flow are 170.3 ata, 500MW,
Fig 2. Variation in Main Steam Pressure 1200 tonnes/hr and 520 tonnes/hr. A change in the calorific
value of the fuel was given from 3300 Kcal/ Kg to 3700
Kcal/Kg at 150 secs. Because of the fuel switching
disturbance, there are variations in the critical parameters of
the boiler. The PID controller is so efficient that it brings the
variations to the steady state after few seconds. This shows

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International Journal of Science, Engineering and Management (IJSEM)

Vol 4, Issue 3, March 2019

the efficacy of the PID Controller employed in the control evaluate the PID controller constants for controlling the critical
process parameters of a 500 MW steam generator in a thermal
system of the thermal power plant. power plant during fuel switching”, Journal of Electrical
Engineering, Vol.16, 4th Edition, 299-309.
IX. CONCLUSION 11. Angeline Rajathi, P.Subha Hency Jose (2017), “Implementation
From the response given in Figures 2, 3, 4, 5 and Table of Adaptive Neuro Fuzzy inference System for Electro
Coagulation Process to treat Dye WasteWater”, Indian Journal
1, it is evident that the process parameter settle within the of Environmental Protection, Vol.37, No.7, July 2017, pp 568-
operating points inspite of the variations in the input side of 572
the boiler (calorific value of the coal changes). The 12. P. Subha Hency Jims, J. Jayakumar, S. Dharmalingam (2017),
„Application of classical step response method to determine the
controller that is designed using the CHR method of tuning PID controller parameters for a 500 MW steam generator in a
of PID controller suits well for the input side disturbances Thermal Power Plant‟, Pak. J. Biotechnol. Vol. 14 (Special Issue
and it is proved in the complex process which is the 500 II) Pp. 242-245
13. P. Subha Hency Jims, S. Dharmalingam, G. Jims John
MW Utility boiler. Wessley(2017),‟ An improved method to control the critical
parameters of a Multivariable Control System‟ IOP conf. Series:
ACKNOWLEDGEMENT Materials Science and Engineering 247 (2017) 012006
The authors would like to thank the authorities of BHEL, DOI:10.1088/1757-899X/247/1/012006
14. R. Krishnaraj, G. Jims John Wessley, P. Subha Hency Jose,
Hyderabad and the Karunya Institute of Technology and Davidson Dharmaraj, “On-design and off-design simulation of
Sciences for the support and encouragement rendered. the performance of a Micro Turbofan Engine using LabVIEW
and GSP”, International Journal of Pure and Applied
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