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June 2010
swansea university
Higher efficient Power plant cycles and solar power plant
RESEARCH REPORT
arpit
7/3/2010
Student name :- Arpit Dubey Coordinator :- DR. R.S.Ransing Signature :- Student number :- 567569 Course :- MSc Mechanical Engineering Date :-
June 2010
Contents
Chapter 1 Introduction
1.1 - Introduction................................................................................................................4
1.2 - Classification of power plants....................................................................................6
1.3 – Review of thermodynamics cycles related to power plants.......................................7
1.4 – Classification of power cycle.....................................................................................8
Chapter 2 Vapour Power Cycle
2.1 - Rankine Cycle............................................................................................................9
2.2 – Organic Rankine Cycle..............................................................................................11
2.3 – Reheat Cycle..............................................................................................................12
2.4 – Regenerative Cycle....................................................................................................13
2.5 – Reheat Regenerative Cycle........................................................................................14
Chapter 3 Research on Improvement of Plants Efficiency
3.1 – Effect of Rotary Air Preheater on Efficiency of Power Plants..................................15
3.2 - Energy and exergy analysis of a steam power plant..................................................18
Chapter 4 Combined Cycle Gas Turbine (CCGT)
4.1 – Introduction...............................................................................................................19
4.2 – Construction and Working........................................................................................19
4.3 – Efficiency Of CCGT Plants......................................................................................20
Chapter 5 Research on Increase the Efficiency of Geothermal Power plants
5.1 – Introduction..............................................................................................................21
5.2 – Description...............................................................................................................21
5.3 – Result and Conclusion.............................................................................................22
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Chapter 6 Utilisation of solar energy in solar power plants
6.1 Introduction.....................................................................................................................23
6.2 Solar Thermal Power Technology...................................................................................24
6.3 Analytic modelling of a solar power plant with parabolic linear collectors....................26
6.4 Binary conversion cycles for concentrating solar power technology..............................28
7 Conclusions...........................................................................................................................30
8 References............................................................................................................................ 33
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Chapter -1 Introduction
1.1 Introduction
Thermal Power plants are the main source for production of electric power in the world and the
Thermal Efficiency of steam cycle is always an important matter in stream power plants. Even Small
increases in Thermal Efficiency can mean large savings regarding fuel requirements. Therefore,
every effort should be made to improve the Efficiency of steam power plants. Different Plants operate
on different steam cycle and each different cycle has a different Efficiency.
Nowadays combination of two steam cycles is very popular for increases in the efficiency of plants.
Additionally, the solar thermal plants and geo thermal power plants are a very good invention for
production of electric power.
In my dissertation, I am try to describe modified form of vapour power cycles (Rankine cycle, Reheat
and regenerative cycles), Combined cycle, gas power cycle, geo thermal power plants and solar
thermal power plants.
Combined cycle Gas turbine power plants (CCGT) are one of the most attractive power plants across
the world. Researchers and manufacturers in a number of countries are trying to develop the
combined cycle power plants with an efficiency of more than 60% .Presently the leading combined
cycle power plant manufacturers are capable of supplying can achieve efficiency varying from 57 to
60 at ISO condition. More and more new design of combined cycle power plants has been provided
recently.
The new facility features the world first installation of GE’S next generation gas turbine combined –
cycle technology, the h system. This technology is design to achieve 60% thermal efficiency when
operating on natural gas. This is a major mile stone for the global power industry. The practical
example of this technology is situated in Cardiff (Baglan bay power station) Wales UK. During the
recently completed testing period, the H System at Baglan Bay generated up to 530 MW at 44F for
the UK national grid. The H System was introduced at a rating of 480 MW operating on natural gas at
ISO conditions. Built by GE on land leased From BP, the Baglan Bay Power Station also features a
33-MW combined heat and power plant based on a GE LM2500 gas turbine. Now in Great Britain all
manufactures are going to develop combined cycle power plants.
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New Build Electricity Generating plants in great Britain
Station Name Owner Size(MW) Technology Type
Langage Centrica 890 CCGT
Immingham Conoco
Phillips(expansion from
730MW to 1180MW)
450 CCGT
Marchwood SSE and ESB
International
840 CCGT
Grain E. on UK 1275 CCGT
Staythorpe RWE npower 1650 CCGT
Uskmouth Severn power 800 CCGT
New Pembroke RWE npower 2000 CCGT
Drakelow E on 1220 CCGT
West Burton EDF 1270 CCGT
New Sutton
Bridge B
EDF 1260 CCGT
New Carrington Bridestones 380 CCGT
Barking Barking power 470 CCGT
Kingsnorth E on 1600 COAL
The amount of energy consumption is one of the most future problems for world .Population
increment, urbanization, industrializing, and technologic development result directly in increasing
energy consumption. The reserves of fossil fuels are getting depleted and combustion of fossil fuels
has a negative impact on our environment. This rapid growing trend brings about the crucial
environmental problem such as contamination and green house effect. Currently 80 % of electricity in
the world is approximately produced from fossil fuels (coal, petroleum, fuel oil, natural gas) where
20% of the electricity is come from different sources such as solar, hydraulic nuclear, wind
geothermal and biogas.
The three potential practical solutions to environmental problems are: Energy conservation
technologies, Renewable energy technologies and Cleaner technologies. Combined cycle is the one of
the best technology for energy conservation and one of the promising renewable energy sources is
solar energy for renewable energy technologies processed heat produced by solar collectors can
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contribute significantly to the conservation of conventional energy resources, reducing CO2 emission,
and delaying global warming. Thus the solar thermal power plant is also getting more and more
attention.
Some Best Solar Thermal Power Station in World
Station Name Location Size(MW) Technology Type
Solar millennium
Blythe
California 968 Solar trough
SAE solar one California 850 Stirling engine
Mojave solar park California 553 Parabolic trough
Solar project Florida 300 Parabolic trough
Solar power plant Mongolian desert
(China)
2000 Power tower
Huala pai valley
Sloar project
Arizona 340 Parabolic trough
New Pembroke RWE npower 2000 CCGT
Drakelow E on 1220 CCGT
West Burton EDF 1270 CCGT
New Sutton
Bridge B
EDF 1260 CCGT
New Carrington Bridestones 380 CCGT
Barking Barking power 470 CCGT
Kingsnorth E on 1600 COAL
1.2 Classification of Power Plants
Power Plant is an assembly of equipment which is used for generation of electrical energy. The main
equipment for the generation of electrical energy is generator. Steam power plants, Diesel power
plants, Gas turbine power plants, Nuclear power plant are called Thermal power Plants because
these convert heat into an electric energy. All Thermal power plants working on power cycle. Steam
power plants working on a stream cycle and gas power plant working on gas power cycle. (1) Now a
day combination of steam and gas cycle is very popular because of its higher thermal efficiency
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1.3 Review of Thermodynamics Cycles Related to Power Plants
Thermodynamics is science of many processes which deal with change of energy in useful work or
change of energy one form to another .Thermodynamics consists of principles that enable us to
understand and follow energy as it transformed from one form or state to the other.
The Zeroth law of thermodynamics was enunciated after the first law. It state that “when two systems
are in thermal equilibrium with a third system, then the two systems are also in thermal equilibrium
with one another”. Equilibrium implies the existence of a situation in which the system undergoes no
net charge, and there is no net transfer of heat between the bodies.
The first law of thermodynamics say that “Energy can neither be create nor destroyed through it can
be transferred from one form to another”. When one energy form is convert in to another, the total
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amount of energy remains constant. An example of this law is gasoline engine. In this engine the
chemical energy present in fuel is converted into a various forms including kinetic energy of motion,
potential energy, chemical energy in carbon dioxide, and water of the exhaust gas.
The second law of thermodynamics is an expression of universal principle of entropy (1). The second
law of thermodynamics may be defined in many ways but the two common statements given by
Kelvin – Planck and Clausius. According to Kelvin-Planck it is impossible to construct a heat engine,
working on a cyclic process, can convert whole of the heat supplied to it, into mechanical work.
According to Clausius it is impossible for a self acting machine, working in a cyclic process, to
transfer neat from a body at a lower temperature to a higher temperature without the aid of an external
agency. This means that it is impossible to make a transformation of energy resource who will be 100
percent efficient. Entropy is a measure of disorder, when entropy increases disorder increases.
The third law of thermodynamics is a statistical law of nature regarding entropy and the impossibility
of reaching absolute zero of temperature (1), which says that entropy of an ideal crystal at zero
degrees Kelvin is zero. It’s unattainable because it is the lower temperatures that can possible exist
and can only be approaches but not actually reached. This is not necessary for most thermodynamics
work, but is a reminder that like efficiency of an ideal engine, there are absolute limits in physics.
The steam power plants works on a modified rankine cycle and combined cycle. Regenerative cycle,
reheat cycle and the regenerative reheat cycle is a modify version of rankine cycle which is mostly
used in power plants for higher thermal efficiency and utilization of heat. In the case of I.C. Engines
(Diesel power plant) it works on Otto cycle, diesel cycle or dual cycle and in the case of gas turbine it
works on Brayton cycle, in the case of nuclear power plants it works on Einstein equation, as well as
on the basic principle of fission or fusion. However in the case of non-conventional energy generation
it is complicated and depends upon the type of system and the site location.
1.4 CLASSIFICATION OF POWER PLANT CYCLE
Power plants cycle generally divided in to the following groups
(1) Vapour power cycle
(2) Combine cycle
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Chapter -2 Vapour Power Cycle
2.1 Rankine Cycle
Introduction
The rankine cycle is a thermodynamic cycle which converts heat into a useful work. It is an ideal
cycle for comparing the performance of steam plants. It is a modified form of Carnot cycle, in which
condensation process is continued until the steam is condensed in water. This cycle generates about
80 percent of all electric power used throughout the world, including virtually all solar thermal,
biomass, coal and nuclear power plants.
Thermal Efficiency of Rankine Cycle:
Consider 1 kg of working fluid, and applying first law of flow system to various with the assumption
of neglecting change in potential and kinetic energy, so we can write,
δq - δw = dh
For process 2-3, δw = 0 (heat addition process), we can write
(δq )boiler = (dh )boiler = (h3 – h2)
For process 3-4, (δq) = 0 (adiabatic process)
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(δw )turbine = -(dh)turbine = (h3 – h4)
Similarly,
(δq )cond = (h1 – h4)
(δw )pmp = (h1 – h2)
(δw) net = (δw )turbine + (δw )pmp = (h3 - h4) + (h1 – h2) = (h3 – h4) - (h2 – h1)
Now Thermal efficiency = ηth = Net work / heat supplied = (δw) net / (δq) boiler
rankineη = ηth = (h3- h4 ) - (h2 – h1) / (h3 – h2) = area 122'341/areaa22'3ba
The pump work (δw) pump is negligible, because specific volume of water is very small.
Therefore,
rankineη = ηth = (h3 - h4 ) / (h3 – h2) = area 122'341/areaa12'3ba (Neglecting pump work).
Note that the rankine cycle has a lower efficiency compared to corresponding Carnot cycle 2’-3-4-1’
with the same maximum and minimum temperatures. The reason is that the average temperature at
which heat is added in the rankine cycle lies between T2 and T1 2 and is thus less than the constant
temperature T12 at which heat is added to the Carnot cycle.
Reasons for considering Rankine Cycle as an ideal cycle for steam power plants
It is very difficult to build a pump that will handle a mixture of liquid and vapour at state 1’
(refer T-s diagram) and deliver saturated liquid at state 2’. It is much easier to completely
condense the vapour and handle only liquid in the pump.
In the rankine cycle, the vapour may be superheated at constant pressure from3 to 3” without
difficulty. In a Carnot cycle using superheated steam, the superheating will have to be done at
constant temperature along path 3-5.During this process, the pressure has to be dropped. This
means that heat is transferred to the vapour as it undergoes expansion doing work. This is
difficult to achieve in practice.
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2.2 Organic Rankine Cycle:-
Introduction
The Organic Rankine Cycle (ORC) is a promising process for conversion of low and medium
temperature heat to electricity. ORC process work like a Rankine steam power plants but uses as an
organic Woking fluid instead of water (2). The fluid allow to take low temperature for the low
temperature sources such as industrial waste heat, geothermal heat, solar pounds etc, and this low
temperature heat is converted in to a useful work. It is a very good recovery candidate.
Working
The working principal of the Organic Rankine Cycle is the same as that of the Rankine Cycle. The
working fluid is pumped in to a boiler where it is evaporated, after that evaporated vapour expands in
turbine and it finally re- condensed in condenser.
Different type of ORC cycle (2):-
(1) Based on shape of the saturated vapour line:-
(A) Fluid with bell-shaped coexistence curve.
(B) Fluid with bell-shaped co existence curve.
(2) Based on pressure:-
(A) Subcritical pressure cycle
(B) Super critical pressure cycle
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2.3 Reheat cycle:-
Introduction: -
Reheat cycle is the modification of rankine cycle. As my knowledge, efficiency of rankine cycle can
be improve by increasing the temperature and pressure of the steam entering in to the turbine but the
increase in the initially steam pressure increase the expansion ration and steam will become quite wet
at the end of expansion. So this difficulty may be overcome by heating of the steam. In this cycle
steam is extracted from a suitable point in the turbine and reheated generally to the original
temperature by flue gases. Reheating is generally used when the pressure is high .The various
advantages of reheating are as follows:
(1) It increases dryness fraction of steam at exhaust so that blade erosion due to impact of water
particles is reduced.
(2) It increases thermal efficiency.
(3) It increases the work done per kg of steam and these results in reduced size of boiler.
The disadvantages of reheating are as follows:
(1) Cost of plant is increased due to the reheater and its long connections.
(2) It increases condenser capacity due to increased dryness fraction
Working:-
In reheat cycle the expansion takes place in two turbines. The steam expands in the high
pressure turbine to some intermediate pressure, and then passed to the reheater where it is reheated at
constant pressure, usually to the original superheat pressure.
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If,
H1 = Total heat of steam at 1 H2 = Total heat of steam at 2
H3 = Total heat of steam at 3 H4 = Total heat of steam at 4
Hw4 = Total heat of water at 4
Efficiency = {(H1 – H2) + (H3 – H4)}/ {H1 + (H3 – H2) – Hw4}
2.4 Regenerative cycle:-
Introduction
We discussed about Rankine and Carnot cycles. The efficiency of Rankine cycle is less than that of
Carnot cycle, because in the rankine cycle, the heat is not added at the higher temperature as in done
in the case of Carnot cycle. This is achieved during regenerative cycle.
Working
The process of extracting steam from the turbine at certain points during its expansion and using this
steam for heating for feed water is known as Regeneration or Bleeding of steam. The arrangement of
bleeding the steam at two stages can see in this diagram.
Let,
m2 = Weight of bled steam at a per kg of feed water heated
m2 = Weight of bled steam at a per kg of feed water heated
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H1 = Enthalpies of steam and water in boiler
Hw1 = Enthalpies of steam and water in boiler
H2, H3 = Enthalpies of steam at points a and b
H4, Hw4 = Enthalpy of steam and water exhausted to hot well.
Work done in turbine per kg of feed water between entrance and a
= H1 – H2
Work done between a and b = (1 – m2)(H2 – H3)
Work done between b and exhaust = (1 – m2 – m3)(H3 – H4)
Total heat supplied per kg of feed water = H1 – Hw2
Efficiency ( ) η = Total work done/Total heat supplied
= {(H1 – H2) + (1 – m2)(H2 – H3) + (1 – m2 – m3)(H3 – H4)}/(H1 – Hw2)
2.5 Reheat Regenerative cycle:-
.
In steam power plants using high steam pressure reheat regenerative cycle is used. The thermal
efficiency of this cycle is higher than only reheat or regenerative cycle. This cycle is commonly used
to produce high pressure steam (90 kg/cm2) to increase the cycle efficiency.
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Chapter – 3 Research on Improvement of Plants Efficiency
3.1 Exergy Analysis on the irreversibility of the rotary air preheater
Introduction
Rotary air preheater (RAPH) is commonly used in thermal power plants and air conditioning systems
for conservation of energy. RAPH is also used as a key component of several industrial processes.
This process is used under conditions of high temperature and significant pressure difference between
hot and cold gas streams. The usages of RAPH can be shown by the following two methods. In first
method, it is used to affect the heat transfer between the fluids by temporarily storing heat. (3)The
other method is that the regenerator surface of RAPH can be considered as being subjected to a
successive link of the hot and cold gas streams. Whenever heat transfers and work from one form to
another, there will be always a energy loss as a result. So in the real world this type of energy losses
cannot be recovered to its initial state without the aid of external process. In RAPH, the typical
energy losses are originated from three methods, in first method a heat transfer within finite
temperature differences, in second, mixing or splitting of the fluid streams, and in third, the friction
caused by fluid flow(3). The first two phenomena alter temperature distributions and the third one
influences pressure on each side of RAPH. The generation of exergy loss is either from heat transfer
through the temperature difference or by the fluid friction in the channels, which has been evaluated
by Bejan. Bejan has discovered the concept of entropy generation and suggested the technique, which
is used in the air preheater. This paper is focused on the identification and evaluation of every
parameter for irreversibility in RAPH. The dominants for expressed in the terms of entropy generation
and every other parameters, which are relate to it.
FIG: Systematic diagram of RAPH in Thermal Power Plant
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Methodology
In the methodology of RAPH, the entropy is obtained at each irreversible process of thermodynamics
and it is calculated and derived with uniform parameter of working fluids. The expression of entropy
is depends upon the following parameters(3) (i) cycling working medium fluid behaves as a perfect
gas with constant specific heat, (ii) RAPH is a adiabatic overall, (iii) leakage of fluids occurs at the
end of the RAPH only and the distribution can be expressed as a ratio, (iv) working fluid properties
are determined by average temperatures from inlet to outlet on each side, (v) a symmetrical balance of
RAPH is considered and (vi) pressure of working fluids after mixing at the end of RAPH, is at
atmospheric pressure.
The efficiency in the thermal process can be measured by estimating the irreversibility level acquires
within the heat transfer process. This irreversibility can be determined by using the entropy rate. To
get the higher values of entropy generation rate, there should be higher losses, due to heat transfer
irreversibility and fluid friction irreversibility.
To find the total entropy generation rate, in the RAPH can be expressed as in terms of
thermodynamics, is given by:
∑ ∆s=¿∆sQ+∆ s∆P+∆sH+∆sC+∆sff +∆sfd+∆ sO¿
Where ∑ ∆sis the total entropy generation rate in the air gas heat exchanging cycle, ∆ sQ is the
entropy generation rate by heat transfer between cold and hot fluid, ∆ s∆P is the entropy generation
rate by the pressure loss, ∆ sH and ∆ sC are the entropy generation rates produced by leakage or
mixing at hot and cold end of RAPH respectively, ∆ sff and ∆ sfd are entropy generation rates of
throttling and friction, ∆ sO is the entropy generation rates of the exhaust gas, emitted by to the
atmosphere. All of these generation rates in this equation represent the irreversibility process in air
gas thermodynamic cycle. This shows that the amounts of entropy generation rates are measure of the
quality level of the energy transfer. The irreversibility can be considered as a loss of certain potential
energy, due to its inherent characteristics.
The exergy for RAPH can be calculated by:
ew=T 0∑ ∆ s
Where T 0 is the ambient Temperature.
The fraction of exergy loss is given by the ratio of the total exergy loss to the input energy. This
fraction is termed as E, which is exergy efficiency. So E can be calculated by:
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E=T0
T 1/B−T 3∑ ∆ s
This function can be used to calculate the irreversibility, during the process of energy transfer in
RAPH.
Efficiency of Thermal Plant
The efficiency of thermal plant can be calculated by:
ŋ0=[1− (T 7−T 1 ) (1+X )BT1−BT3
]ŋv− B (1+X )T1 KR
(T 1−BT 3 ) (K−1 )CP[ a2
ŋ ff
( k−1 )/ k
+T 6 (a3
(1−k ) /k−1)T 1ŋ fd
]
Pressure Loss
The pressure loss can be calculated by (3):
∆ P=C f Reb
LDdl
ρw2
2
The effectiveness of RAPH:
ŋr=1−exp [−NTU (1−Cb ) ]
1−Cbexp [−NTU (1−Cb ) ] [1− 19C r
1.93 ]Result
The systematic diagram of a typical RAPH is shown in figure. After calculate the total entropy
generation∑ ∆s, we found that the contribution of each entropy generation rate totals the entropy
generation rate in the complete thermodynamic systems. The entropy generation rates are then
followed in such a descending order
∆ sQ>∆ s∆ P>∆sH>∆sC>∆ sff>∆sfd>∆sO
After comparing these entropies in the form of magnitude, we found that the first three entropy
generation rates are bigger than the remaining four. After that we calculated the exergy efficiency E,
Efficiency of thermal plant, Pressure Loss and the effectiveness of RAPH.
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3.2 Energy and exergy analysis of a steam power plant
Introduction:
This report concentrates on analyzing the systems of power generation which his very vital for
identifying the factors during energy generation so that its efficiency and deficiencies can be
measured & resources of energy can be utilised to their full capacities. It focuses on the exergy
analysis which evaluates the efficiency of physical components like machinery & equipments and the
process as well during various stages of energy conversion.(4) By this, the steps where efficiency has
been compromised, losses have occurred and the measure of the quality of energy generated can be
easily identified. Exergy analysis acts as an apparatus to underline clearly the factors owing to energy
losses to the external surroundings & the irreversibility happening during the process internally. The
site of the study is a Jordanian power plant (Al Hussein) that uses heavy fuel oil as its main resource.
Its machinery includes 7 steam turbine and 2 gas turbine units operating at 1000% load. Properties of
the fuel & the process of turbine operation have been described diagrammatically.
Description:
Analysis of exergy is done to identify the highest level of capacity of a system to carry out productive
work. It is destructed in the system itself & its destruction acts as a scale of irreversibility. The
strategic points during the process where energy is lost, its magnitude & the source can be identified
by exergy analysis. With the carefully taken measurements of all the participating elements like Mass,
Energy, Pressure, Heat transfer, Losses, Machine components etc, the power station was analyzed.
The energy balance showed that the energy efficiency was low than others as it was based on the
lower heating value of fuel. It identified the location of the loss. The Study pinpointed the domination
of boiler in exergy destruction i.e. about 77%. The efficiency was lower which directly stressed the
need and scope of major improvements that can be made to prevent this loss. The effect of reference
environment i.e. (4) dead state was also examined and alterations were made in temperature &
pressure, the measurements were recorded but the boiler was still the major source of exergy
destruction. However the increase in temperature also increased the efficiency of condenser which
was attributed to the temperature difference between steam & cooling air.
Conclusion:
The energy & exergy analysis showed that condenser was the main source of losing energy to the
environment i.e. 66%. The energy loss of boiler was found to be 6% and the thermal efficiency was
calculated to be around 26%. The exergy analysis however showed that boiler was the main source of
exergy losses which was attributed to the chemical reaction in combustion chamber. The exergy
efficiency was around 25%. Preheating the combustion air and decreasing the fuel-air ration can be
considered to decrease this loss.
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June 2010
Chapter -4 Combined Cycle Gas Turbine (CCGT)
4.1 Introduction
Combined cycle Gas turbine power plants (CCGT) are one of the most attractive power plants across
the world. Researchers and manufacturers in a number of countries are trying to develop the
combined cycle power plants with an efficiency of more than 60 percent. One of the principal
reasons for the popularity of the combined cycle power plants is their high thermal
efficiency. Combined cycle plants with high thermal efficiencies. Combined cycle plants
can achieve these high efficiencies because much of the heat exhaust from the gas
turbine(s) is captured and used in the Rankine cycle portion of the plant. The heat from the
exhaust gases would normally be lost to the atmosphere in an open cycle gas turbine
Another reason for the popularity of combined cycle plant is that it requires less time for
their construction as compared to a conventional steam power plant of the same output.
Although it takes longer time to build a combined cycle plant than a simple gas turbine
plant. Natural gas is the most common fuel used by combined cycle gas turbine power
plants.
The main components of a Combined Cycle include the following:
Gas Turbine Diverter Damper Heat recovery Steam generator (HRSG)
Steam Turbine Feed water Pumps Condenser and Condensate Pumps
Cooling Tower etc
4.2 Construction and Working:-
A combined-cycle gas turbine power plant consists of one or more gas turbine generators
Equipped with heat recovery steam generators to capture heat from the gas turbine Exhaust. Steam
produced in the heat recovery steam generators powers a steam turbine Generator to produce
additional electric power. Use of the otherwise wasted heat in the Turbine exhaust gas results in high
thermal efficiency compared to other combustion based Technologies.
In this cycle a gas turbine is connected to a steam turbine via a boiler. The steam turbine cycle
makes use of much of the heat in the gas turbine exhaust gases. Thermodynamically, the
combined cycle can be represented by joining the high temperature Brayton cycle with the
moderate pressure and temperature Rankine cycle
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Gas Turbine cycle
Heat Rejected
Combined Cycle T-h Diagram
Steam Turbine cycle
June 2010
The area enclosed by the Rankine cycle is within the area that represents the heat rejected
from the Brayton cycle. Thus, the Rankine cycle area represents the heat energy that is
converted to useful mechanical energy that would other-wise be rejected to the atmosphere. A
large portion of the heat lost from the Brayton cycle is used in the Rankine cycle. A much
greater fraction of the heat added to the cycle is actually converted to useful mechanical
energy in the combined cycle than either the Brayton cycle or the Rankine cycle alone.
The Rankine cycle parameters (pressure and temperature) are selected to match the
temperature of the available gas turbine exhaust gases. Usually, the pressure and temperature
used in the Rankine cycle portion of the combined cycle plant are much lower than those used
in conventional Rankine cycle plants. The lower pressure and temperature are necessary
because the gas turbine exhaust gas, while very hot, is not nearly as hot as the flue gas
entering the convection pass of a conventional fuel fired boiler. The challenge in joining the
Brayton and Rankine cycles in a combined cycle plant is the degree of integration needed to
maximize efficiency at an economic cost.
4.3 Efficiency of CCGT plants
By combining both gas and steam cycles, high input temperatures and low output temperatures can be
achieved. The efficiency of the cycles adds, because they are powered by the same fuel source. So, a
combined cycle plant has a thermodynamic cycle that operates between the gas-turbine's high firing
temperature and the waste heat temperature from the condensers of the steam cycle. This large range
means that the Carnot efficiency of the cycle is high. The actual efficiency, while lower than this, is
still higher than that of either plant on its own. The actual efficiency achievable is a complex area.
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June 2010
Chapter - 5 Research on Increase the Efficiency of Geothermal
Power plants
5.1 Introduction
Now a day geothermal power plant is a very important part of the world renewable source of energy
due to its attractive cost and reliability, New Zealand country is one of them. About 70% of New
Zealand electricity comes from renewable sources. Electricity demand in New Zealand is growing at a
rate of about 1.3% per year. Projection suggest that approximate 3900MW of additional capacity
between could be required between 2005 and 2030. (5) New Zealand tries to increase the proportion
of electricity generation from renewable energy sources to 90% by 2050.
Geothermal power plants provide base load generation for New Zealand Therefore; these plants are
very importance to New Zealand power supply system. This paper is deal with study investigates
increase in efficiency by incorporating a water- augmented air- cooled system. A theoretical analysis
including modelling and simulation of a typical plant using local weather data is presented (5). The
Rotokawa binary cycle geothermal plant is taken as a test case and compared against other base load
options. The improved summer hot-day performance is compared to other peak load options as well
as policy implications are presented.
5.2 Description
Electricity production from the geothermal power cycle is affected by ambient conditions .The
ambient temperature is the most significant ambient parameter to plant performance.
Binary cycle plants have ability to utilise low temperature sources and very cost effective when source
temperature are below 175°C .This power plants is a combination of direct steam turbine and
bottoming cycles.
Binary cycle geothermal plants can have a combination of direct steam turbine and bottoming cycles.
The bottoming cycles can utilise low temperature brine resources and exhaust steam from the steam
turbine by using a volatile hydrocarbon i.e. pentane, as the working fluid.
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Current geothermal power plant designs simply use induced draft air- cooled condensers to reject heat
from the condensing working fluid after the power extraction through a turbine. With air-cooled
condensers, the temperature of the ambient air would determine the heat-sink temperature, and thus
the plant efficiency. If heat were to be rejected to air from a water-augmented air-cooled system, the
effective ambient temperature would be reduced, depending on other site parameters such as relative
humidity, air pressure and elevation using water for cooling from rivers or lakes.
5.3 Result and conclusion
After this research, result presented that the efficiency of geothermal power plants can be improve
use air cooled condensers (5)This investigation showed that the performance of some of these plants
could be improved by using a water-augmented air-cooled system for the air-cooled condensers. The
conclusion of this analysis suggests that policies to optimise generation efficiency should be
considered as well as development of further resources. These steps could help New Zealand to
advance further its stated goals of sustainable development, the current goal of 90% renewable
generation.
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Chapter- 6 Utilisation of solar energy in solar power plants
6.1 Introduction
Solar thermal power generation utilizes the sun as a source of heat which can be exploited by
concentrating that heat and using it to drive a heat engine to produce power. As such, solar thermal
power generation is much more closely related to traditional forms of power generation based on
fossil fuel combustion which also rely on heat engines to convert heat into electrical energy
Producing electricity from the energy in the sun’s rays is a straightforward process: direct solar
radiation can be concentrated and collected by a range of Concentrating Solar Power (CSP)
technologies to provide medium- to high temperature heat. This heat is then used to operate a
conventional power cycle, (6) for example through a steam turbine or a Stirling engine. Solar heat
collected during the day can also be stored in liquid or solid media such as molten salts, ceramics, and
concrete or, in the future, phase-changing salt mixtures. At night, it can be extracted from the storage
medium thereby continuing turbine operation.
Solar thermal power plants designed for solar-only generation are ideally suited to satisfying summer
noon peak loads in wealthy countries with significant cooling demands(6), such as Spain and
California. Thermal energy storage systems are capable of expanding the operation time of solar
thermal plants even up to base-load operation.
For example, in Spain the 50 MWe AndaSol plants are designed with six to 12 hours thermal storage,
increasing annual availability by about 1,000 to 2,500 hours. During the market introduction phase of
the technology, hybrid plant concepts which back up the solar output by fossil cofiring are likely to be
the favoured option, as in commercially operating parabolic trough SEGS plants in California where
some fossil fuel is used in case of lower radiation intensity to secure reliable peak-load supply.
Also, Integrated Solar- Combined Cycle (ISCC) plants for mid- to base-load operation are best suited
to this introduction phase. Combined generation of heat and power by CSP has particularly promising
potential, as the high-value solar energy input is used to the best possible efficiency,(6) exceeding
85%. Process heat from combined generation can be used for industrial applications, district cooling
or sea water desalination. Current CSP technologies include parabolic trough power plants, solar
power towers, and parabolic dish engines. Parabolic trough plants with an installed capacity of 354
MW have been in commercial operation for many years in the California Mojave desert, whilst solar
towers and dish engines have been tested successfully in a series of demonstration projects.
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June 2010
Solar thermal power generation utilizes the sun as a source of heat which can be exploited by
concentrating that heat and using it to drive a heat engine to produce power. As such, solar thermal
power generation is much more closely related to traditional forms of power generation based on
fossil fuel combustion which also rely on heat engines to convert heat into electrical energy.
6.2 Solar Thermal Power Technologies
Solar thermal power plants, often also called Concentrating Solar Power (CSP) plants, produce
electricity in much the same way as conventional power stations. The difference is that they obtain
their energy input by concentrating solar radiation and converting it to high-temperature steam or gas
to drive a turbine or motor engine. Four main elements are required: a concentrator, a receiver, some
form of transport media or storage, and power conversion. Many different types of systems are
possible, including combinations with other renewable and non-renewable technologies, but the three
most promising solar thermal technologies are:
(1) Central receiver or solar tower
A circular array of heliostats (large individually tracking mirrors) is used to concentrate sunlight on to
a central receiver mounted at the top of a tower. A heat-transfer medium in this central receiver
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June 2010
absorbs the highly concentrated radiation reflected by the heliostats and converts it into thermal
energy to be used for the subsequent generation of superheated steam for turbine operation. To date,
the heat transfer media demonstrated include water/steam, molten salts, liquid sodium and air. If
pressurised gas or air is used at very high temperatures of about 1,000°C or more as the heat transfer
medium, it can even be used to directly replace natural gas in a gas turbine, thus making use of the
excellent cycle (60% and more) of modern gas and steam combined cycles.
(2) Parabolic trough technology:-
Parabolic trough-shaped mirror reflectors are used to concentrate sunlight on to thermally efficient
receiver tubes placed in the trough’s focal line. A thermal transfer fluid, such as synthetic thermal oil,
is circulated in these tubes. Heated to approximately 400°C by the concentrated sun’s rays, this oil is
then pumped through a series of heat exchangers to produce superheated steam. The steam is
converted to electrical energy in a conventional steam turbine generator, which can either be part of a
conventional steam cycle or integrated into a combined steam and gas turbine cycle.
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June 2010
(3) Parabolic dish
A parabolic dish-shaped reflector is used to concentrate sunlight on to a receiver located at the focal
point of the dish. The concentrated beam radiation is absorbed into the receiver to heat a fluid or gas
(air) to approximately 750°C. This fluid or gas is then used to generate electricity in a small piston or
Stirling engine or a micro turbine, attached to the receiver.
6.3 Analytic modelling of a solar power plant with parabolic linear
collectors
Introduction
In present, the solar technology is used as a conversion system of thermal to electric energy, which is
based on the parabolic reflectors with linear focus phenomenon. This type of technology can be
deliver electric energy at a peak efficiency of 24%, which is a highest rate between several
commercial solar technologies. By using this technology, we can achieve higher efficiency and top
temperature of the thermodynamic cycle (400®C) at low cost. These type of solar plant needs a large
field of concentrating collectors, a power block that converts thermal into mechanical and then
electrical energy, an interface between the collector field and the power block integrated by a set of
heat exchanges where water is preheated, evaporated and the generated steam superheated.
In this paper we used collector’s field of 800m long, where a large temperature difference is
established, makes it necessary to consider the variation of heat-loss coefficient with temperature. For
this technique, there are two processes are considered, (i) the energy transfer between the thermal
fluid, circulating along the absorbers of the collector’s field and water or water vapour, (ii) the
thermodynamics cycle of water vapour fluid.
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Modelling the solar power plant
FIG: Energy balance of a thermal solar plant
A flow diagram of a typical solar plant is shown in figure. The figure shows that the incident solar
radiation on the collector’s field ( I coll Acoll) propagates along the parabolic mirror and is converted
into absorbed power¿¿, where (I coll)shows the direct irradiance, incident at right angles to the
aperture plane and (Acoll) the aperture area of collector. (7) The difference between the incident and
absorbed power is given by (I coll Acoll−Q|¿|¿). The absorbed power is converted into thermal power (
Qu) and thermal losses (Qloss). The transfer process of heat between the thermal fluid and water,
results in total heat water vapour of a thermodynamic system, which is converted into mechanical
power in conversion block. After that, mechanical power is then converted into electric power.
RESULT
In this paper author developed an analytical model of a power station. This model is a combination of
two subsystems, which are the solar collector’s field and the power station. The power cycle is
considered as endo-reversible, irreversibility. The system described by analytic model, which shows
the existence of a maximum efficiency of thermodynamic cycle.
The efficiency of the solar radiation into thermal energy is calculated by (7):
ŋ st=Qu
I coll Acoll
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6.4 Binary conversion cycles for concentrating solar power technology
Introduction: -
Temperature potential of concentrated solar energy is much higher than used by standard conversion
cycles. Solar receivers are in development phase and are used as a reference standard. Binary alkali-
metal steam cycles are more efficient than any other means (8), but they need some more
investigation. The aim of this paper is to compare the performance of the advance conversion cycles
with the conventional cycles. The conventional cycles taken are:- convention steam cycle , closed gas
(helium) cycle , combined gas-steam cycle.
Description: -
To investigate further about binary cycles we will concentrate on following points, these are:-
Low temperature binary cycle- this cycle is at a maximum temperature equal to that of steam,
can dramatically reduce the most evident thermodynamic imperfection of steam cycle. An avg
temperature of the heat input from the primary source that is much lower than the top
temperature.
High temperature binary cycle- In this case a two loop indirect cycle is used, because it is
flexible and reliable. In this cycle pressure drops and pressure levels are freely selected, the
inlet-outlet temperature difference is optimized (8).
Turbine design- There are some main characteristics of the Alkali-metal turbines like inlet
pressure is limited (below 4.0-0.6 bar) , limited expansion works, limited expansion ratios,
large exhaust volume flows , poor vapour quality. Because of the above characteristics the
alkali-metal turbines rotate at low rpm.
Materials- Refractory metals (niobium, molybdenum, and tantalum) are preferable. At higher
temperature lithium is mainly used as transfer fluid. Mild steel and pure nickel exhibits a
good resistance.
Heat storage:- heat storage are of three types:-
o Molten salt storage: - molten salt (nitrite, nitrate) is used for receiver cooling.
Maximum temperature is up to 5500 C.
o Latent heat storage:- more effective than sensible heat storage. Salt mixtures of ca, Mg,
Na, K etc. are used; the temperature range is from 750 to 12500 C.
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June 2010
o Liquid metal sensible heat:- It is proposed as optimum solutions for a space power
station because in this charging and discharging of storage system is very simple and
rapid. Heat is stored in lithium fluoride (LiF) , lithium acts as a heat transfer agent.
Results:-
The results of this study are:-
The temperature potential of solar resource is much higher than usual steam cycle.
The best efficiency is expected from solar combined cycle (gas+steam turbine) with reference
to conventional fossil fired plants.
Due to a better match of temperature for heat exchange between top and bottom cycles alkali-
metal top cycles are intrinsically more efficient.
Experimentally data shows that stainless steel is an adequate material for a potassium system
up to 800-8500C.
For efficient binary cycle turbine diameters should be large.
The sun’s radiation is the source of high temperature for top cycles.
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7-Conclusion
World is facing problem regarding precious use of conventional and non- conventional source of
energy.
Power plant is a main source for electric power generation. 80 % of electricity in the world generated
by Thermal power plants because of its advantages.
Advantages:-
They can located very conveniently to the near the load centres.
Does not require shielding like required in nuclear power plant.
Method of power production is easy as comparison to other power plants method.
Transmition cost is reduced as they can be setup near to the industries.
The portion of steam generated can be used as process steam for use full work.
Steam engines and turbines can work under 25% of over load capacity.
Able to respond changing loads without difficulty.
It’s also having some disadvantages.
Disadvantages:-
Large amount of water required.
Great difficulties experiences in coal handling and disposal of ash.
Maintenance and operation costs are high.
With increase in pressure and temperature, the cost of plant increase.
Troubles from smoke and heat from the plant.
These Thermal power plants works on a different vapour power cycle. Carnot cycle and Rankine
cycle are the two basic vapour power cycles for power plants. Carnot cycle have a higher thermal
efficiency as comparison to Rankine cycle but it is impossible to make power plant on Carnot cycle
because of its disadvantage which I disused in my dissertation. In other hand the efficiency of
Rankine cycle is very low. Modify ranking cycle and combined cycle is very useful solution for this
problem. Now a day combined cycle Gas turbine power plants (CCGT) are one of the most attractive
power plants across the world. It’s have a following advantages.
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June 2010
It has a higher Thermal efficient approximate 55% to 60%.
Low pollution is a crucial advantage of combined cycle plants that burn natural gas natural
gas. The low pollution permits the plants to be near enough to a city to be used for district
heating and cooling.
Higher fuel efficiency.
The capital cost of building a combined cycle unit are about two – third the capital cost of a
comparable coal plant.
Reduced emission and fuel consumption.
Reduced need to long distance electricity transmission.
The amount of energy consumption is one of the most future problems for world .Population
increment, urbanization, industrializing, and technologic development result directly in increasing
energy consumption. The reserves of fossil fuels are getting depleted and combustion of fossil fuels
has a negative impact on our environment. This rapid growing trend brings about the crucial
environmental problem such as contamination and green house effect. Currently 80 % of electricity in
the world is approximately produced from fossil fuels (coal, petroleum, fuel oil, natural gas) where
20% of the electricity is come from different sources such as solar, hydraulic nuclear, wind
geothermal and biogas. The three potential practical solutions to environmental problems are: Energy
conservation technologies, Renewable energy technologies and Cleaner technologies. and one of the
promising renewable energy sources is solar energy for renewable energy technologies processed heat
produced by solar collectors can contribute significantly to the conservation of conventional energy
resources, reducing CO2 emission, and delaying global warming. Thus the solar thermal power plant
is also getting more and more attention. Current solar thermal power technologies are distinguished
in the way they concentrate solar radiation, such as, (a) parabolic trough systems, (b) solar tower
systems and (c) solar dish systems. The direct radiation is concentrated using reflectors and the energy
concentrated in this way is transformed into steam, which is used to drive conventional electricity
generators. Comparison of this technology is
parabolic trough systems solar tower systems solar dish systems
Application Grid-connected plants, mid- to high processHeat
Grid-connected plants, high temperature process heat
Stand-alone, small off-grid power systems or clustered to larger grid connected dish parks
Advantages • Commercially available – over 12 billion kWh of
• Good mid-term prospects for high
• Very high conversion efficiencies –
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June 2010
operational experience;operating temperature potential up to 500°C (400°C commercially proven)• Commercially proven annual netplant efficiency of 14% (solar radiationto net electric output)• Commercially proven investment andoperating costs• Modularity• Best land-use factor of all solartechnologies• Lowest materials demand• Hybrid concept proven• Storage capability
conversion efficiencies, operating temperature potential beyond1,000°C (565°C proven at 10 MW scale)• Storage at high temperatures• Hybrid operation possible
peak solar to net electric conversionover 30%• Modularity• Hybrid operation possible• Operational experience of first demonstration projects
Disadvantages • The use of oil-based heat transfermedia restricts operatingtemperatures today to 400°C,resulting in only moderate steamqualities
• Projected annual performance values,investment and operating costs stillneed to be proven in commercialoperation
• Reliability needs to be improved• Projected cost goals of massproduction still need to be achieved
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June 2010
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8. Gianfranco Angelino a, Costante Invernizzi “Binary conversion cycles for concentrating solar
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10. Butti, Ken; Perlin, John (1981). A Golden Thread (2500 Years of Solar Architecture and
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15. http://www.claverton-energy.com/the-difference-between-lcv-and-hcv-or-lower-and-higher-
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right-or-wrong-definition.html
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