ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
MODIFICATIONS OF STEAM POWER PLANT INTO
COMBINED CYCLE BY INTRODUCING LNG AS FUEL
Akhil Mohandas1, Subin Thomas2 , Akul Vijay N3, Gokul V H4,Jithin Martin5, Shyam
Kumar S6 , Tom M Pynadath7, Vimal Kumar8, Rafin T A9
1-7(B-Tech student, Mechanical Department, Nirmala College of Engineering, Thrissur, Kerala, India)
8(Senior Engineer, Petrochemical Division, FACT, Udyogamandal, Ernakulam, Kerala, India)
9(Assistant Professor, Mechanical Department, Nirmala College of Engineering, Thrissur, Kerala, India)
ABSTRACT: The aim of the presented paper is to understand the latest trends in the
steam power plant which works on the simple Rankine cycle.Steam power plants suffer from
limited efficiencies and consequential dominance of fuel prices on generation costs.
Combined cycles, however, exploit the waste heat from exhaust gases to boost power output,
resulting in overall efficiencies around 50%, which are significantly above those of steam
power plants. The underlying idea to write this paper is to study the possibilities of
installation of gas turbine with heat recovery steam generator for the required power and
steam production, hence determine numerically the cost of power production, steam
production, and profit of the company.
KEYWORDS: Rankine cycle; Brayton cycle; Cogeneration; Reheat
ABBREVATIONS: LNG: Liquefied Natural Gas
order to overcome these disadvantages and
make economical, we proposed our guide
to use the possibilities of a single gas
turbine with heat recovery steam generator
instead of steam turbines. The gas turbine
works on the basis of Brayton cycle. The
fuel required for running gas turbine is
LNG (Liquefied Natural Gas). Gas turbine
with heat recovery steam generator is a
form of highly efficient energy generation
technology that combines a gas fired
turbine with a heat recovery steam
generator. The power plant is generates
heat. The design uses a gas turbine to
create power and then recover the resulting
waste heat to produce steam.
1. INTRODUCTION
In a steam power plant, power and steam
production is done with the help of steam
turbines, which works on the basis of
simple Rankine cycle. We observe that the
use of steam power plant is uneconomical ,
because it has a lot of disadvantages such
as variable heat losses, efficiency is only
35 to 40% and high cost to operate. In a
combined cycle power plant (CCPP), or
combined cycle gas turbine (CCGT) plant,
a gas turbine generator generates
electricity and heat in the exhaust is used
to make steam, which in turn drives a
steam turbine to generate additional
electricity. This last step enhances the
efficiency of electricity generation. In
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
2. LITERATURE SURVEY
I.
II.
Najjar&Akyurt (1994) reviewed
various types of combined cycles,
including repowering, integrated
gasification and other advanced
systems. According to this study:
1). Combined cycles boost power
output and efficiency to levels that
are considerably above those of
steam
power
plants
2).
Repowering, when converting an
existing steam plant to combined
cycle, offers savings in capital cost
as compared to new construction
3).
Combined
cycle,
when
integrated with coal gasification,
holds promise in converting coal
into electric power in an efficient,
economical and environmentally
acceptable manner 4). The airbottoming
cycle
(ABC),
chemically recuperated gas turbine,
compressed air energy storage
(CAES) and compressed air storage
humidification (CASH) are among
advanced concepts with promise
for combined cycle applications.
Khaliq & Kaushik (2004) carried
an improved second-law analysis
of the combined power-cycle with
reheat and showed the importance
of the parameters examined. The
analysis has included the energy
destruction in the components of
the cycle and an assessment of the
effects
of
pressure
ratio;
temperature ratio and number of
reheat stages on the cycle
performance. The energy balance
or second-law approach presented
facilitates
the
design
and
III.
IV.
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optimization of complex cycles by
pinpointing and quantifying the
losses. By placing reheat in the
expansion process, significant
increases in specific power output
and efficiency were obtained. The
gains are substantial for one and
two reheats, but progressively
smaller for subsequent stages.
Manuel Valdés (2003) shows a
possible way to achieve a thermo
economic
optimization
of
combined cycle gas turbine
(CCGT) power plants. The
optimization has been done using a
genetic algorithm, which has been
tuned applying it to a single
pressure CCGT power plant. Once
tuned, the optimization algorithm
has been used to evaluate more
complex plants, with two and three
pressure levels in the heat recovery
steam
generator
(HRSG).The
variables considered for the
optimization
were
the
thermodynamic parameters that
establish the configuration of the
HRSG. Two different objective
functions are proposed: one
minimizes the cost of production
per unit of output and the other
maximizes the annual cash flow.
The results obtained with both
functions are compared in order to
find the better optimization
strategy.
Bartnik&Ryszard (2011) in their
book “Conversion of Coal-Fired
Power Plant to Cogeneration and
Combined-Cycle” presents the
methodology,
calculation
procedures and tools used to
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
support enterprise planning for
adapting
power
stations
to
cogeneration and combined-cycle
forms. They alsoanalyse the
optimum selection of the structure
of heat exchangers in a 370 MW
power block, the structure of heat
recovery steam generators and gas
turbines. Conversion of Coal-Fired
Power Plant to Cogeneration and
Combined-Cycle also addresses the
problems of converting existing
power plants to dual-fuel gas-steam
combined-cycle
technologies
coupled with parallel systems.
3. THE EXISTING SYSTEM
Fig.1.Schematic Diagram Showing the Simple Steam Cycle in a Power Plant.
The schematic diagram Fig.1. Shows a
simple steam cycle which works on the
basis of simple Rankine cycle. It consists
of a boiler, steam turbine, generator,
deaerator, pumps, condenser, a source and
sink
Power and steam production is
done with the help of steam turbines. In
boiler superheated steam is generated.
Steam expands in steam turbine which
drives a generator. The cooling water
circuit is modelled by sink and cooling
water pump. The fuel in the furnace may
be furnace oil or coal. It produces an
electrical power Pel of 36448.00 KW. The
mass flow rate of steam through the
system is 450kg/s and the enthalpy is
3273.23kJ/kg. The simple steam cycle is
less economical because it has a lot of
disadvantages such as variables heat
losses, less efficiency and higher cost of
operation.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
4. THE PROPOSED SYSTEM
Fig.2. Schematic Diagram Showing Combine Power Plant with Gas Turbine.
Inorder to overcome the disadvantages of
steam power plant we propose a combined
cycle power plant with gas turbine which
is shown in Fig.2. The above schematic
diagram shows a combine cycle power
plant with a gas turbine producing an
electrical power Pel of 36448.00 KW. The
mass flow rate of steam through the
system is 79.544 kg/s . We can infer that
for the same electrical power the steam
production rate is more for a combined.
Also the mechanical efficiency and exergy
efficiency is more. So the heat loss is less
as well the losses in the whole system is
less when compared to the simple steam
cycle. Combined cycles boost power
output and efficiency to levels that are
considerably above those of steam power
plants.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
6. RESULTS AND DISCUSSION
Graph.1. Effect of temperature and entropy of a simple steam turbine power plant system .
Graph 2. Effect of temperature and entropy of a combined cycle power plant with gas turbine
system.
The graphs 1 and 2 show the variation of
enthalpy at various temperatures in a steam
cycle and a combined cycle power plant.
When we compare the cycles obtained we
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
found that the superheated temperature for
combined cycle is 450.4°C while the
superheated temperature for simple cycle
is 448°C. This shows the superheated
temperature is more for combined cycle
than simple cycle. So heat loss is less in a
combined cycle than simple steam cycle.
The entropy at the superheated stage for
simple steam cycle is 6.55KJ/KgK and that
of combined cycle is 6.925KJ/KgK.
Therefore the efficiency of a combined
cycle is better compared to a simple cycle.
.
Table1 showing different percentage exergy efficiency, losses and exergy transmitted from
various equipments in a simple steam power plant.
Table 2 showing different percentage exergy efficiency, losses and exergy transmitted from
various equipments in a combined cycle power plant.
From the above tables 1 and 2 we can infer
that the losses in steam power plant are
more compared to that of the combined
cycle power plant. Also we can conclude
that the heat converted into work is more
in combined cycle power plant compared
to the steam power plant. We can also
infer from the above tables that the
efficiency of a combined cycle power plant
is more compared to that of the steam
power plant. This is because steam can be
produced from waste heat of the exhaust,
and injected into the air delivered by the
compressor or into the combustor, thus
increasing the electrical output of the gas
turbine in a combined cycle.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
Table 4 Shows gross and net efficiencies
of a combined steam power plant.
Table 3 Shows gross and net efficiencies
of a simple steam power plant.
From the above tables 3 and 4 we can infer
that net energy for simple steam cycle is
31.539% while that for combined cycle is
47.756%. The net exergy for simple steam
cycle is 30.221% while that for combined
cycle is 45.672%. Therefore energy and
exergy produced in a combined cycle
power plant is more compared to the steam
power plant. Also we can conclude that the
gross efficency of a combined cycle power
plant is better compared to the steam
power plant. This is also same in case of
net
efficiencies.
Thus
dramatic
improvements in efficiency at all loads i.e.
better efficiency.




7. MERITS OF COMBINED
CYCLE



Simple-cycle gas turbines that are
designed for power generation have
often been used when natural gas
or distillate fuels can be burned
economically.
Steam can be produced from waste
heat of the exhaust, and injected
into the air delivered by the

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compressor or into the combustor,
thus increasing the electrical output
of the gas turbine.
Dramatic
improvements
in
efficiency at all loads i.e. better
efficiency.
Improved operating reliability.
New modifications can be added at
low-cost to existing power
facilities.
Modifying can greatly enhance the
efficiency to levels comparable
with those of plants originally
constructed as fully-fired combined
cycle economic analyses reveal that
significant fuel savings justify the
capital investment.
Cooling requirement of the
combined cycle is much lower than
the normal steam turbine power
plant having same capacity output.
It has high ratio of power output to
the area occupied. Therefore for
designing a combined cycle plant
space requirement is not a concern.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016

all the faculties of the department of
mechanical engineering, Nirmala College
of Engineering. Authors are thankful to
Petrochemical
Division,
FACT
Udyogamandal
for their support and
guidance.
Combined cycle power plant is
more suitable for rapid start and
shutdown than the steam power
plants. Therefore these plants
accept load variations quickly and
help in maintaining the stability in
the electric grid.
REFERENCE
8. CONCLUSION
I.
Combined cycle generation system
features high thermal efficiency, low
installed cost, fuel flexibility with a wide
range of gas and liquid fuels, low
operation and maintenance costs, operating
flexibility at base, mid-range and daily
start, high reliability and availability, short
installation times and high efficiency in
small capacity increments .
II.
III.
In particular:
1. Combined cycles boost power output
and efficiency to levels that are
considerably above those of steam power
plants.
2. Repowering, when converting an
existing steam plant to combined cycle,
offers savings in capital cost as compared
to new construction.
IV.
3. Combined cycle, when integrated with
coal gasification, holds promise in
converting coal into electric power in an
efficient, economical and environmentally
acceptable manner.
V.
ACKNOWLEDGEMENT
This paper is the outcome of hard work
with the help and cooperation from many
sources. We express our gratitude and
sincere thanks to college management and
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engine”, Heat Recovery Systems
& CHP Vol. 14, No. 2, pp. 93-103,
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&
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Kaushik,
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and
Antonio
Rovira,
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Thermoeconomic optimization of
combined cycle gas turbine power
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economic
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thermodynamic
relationships”, Applied Thermal
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April 2011, Pages 852-871.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-4, Issue-2, March 2016
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79–197.
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Prasad “Comparative performance
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