Combined Cycle Gas Turbine.ppt

Combined Cycle Gas TurbineAbbas A M Al Fardan
Combined Cycle Gas Turbine
What is the CCGT?
A combined cycle gas turbine power plant, frequently identified by CCGT shortcut, is essentially an electrical power plant in which a gas turbine and a steam turbine are used in combination to achieve greater efficiency than would be possible independently. The gas
turbine drives an electrical generator. The gas turbine exhaust is then used to produce steam in a heat exchanger (steam generator) to supply a steam turbine whose output provides the means to generate more electricity. However the Steam Turbine is not necessarily, in that case the plant produce electricity and industrial steam which can be used for heating or industrial purpose.
Basic Gas Turbine Information
Main Gas Turbine Manufactures:
Approximately Cost per MW – 0.7mln E
Efficiency approx 40% for gas turbine however in the CCGT plant the efficiency is 50-60% (even higher for cogenerated plant)
Low Green Gas Emission C02, NOx & SOx
Chepear comparing to other technology e.g. CCS
Lifetime 30-40 years
Natural Gas. Resources available in KSA
Synthetic Gas from coal.
Fuel Oil. Resources available in KSA
Biogas from forestry, domestic and agricultural waste.
Resources not available in KSA
Variable
CCGT
630
1200
Grid Code contains general conditions and rules for general application.
The specification and conditions for each application are adjust individually.
Those information are included in Grid Connection Offer & Agreement
between developer and Transmission Operator TSO.
Client (Requires connection) and TSO must implement Grid Code specification during each stages of the project, for project above 10MW
TSO may be disconnected or terminated the Grid Connection Agreement
if the Grid Code is not implemented by client.
The Implementation of the Grid Code may have significant impact on the cost of the Grid Connection
ESB Networks Electrical Safety Rules must be implemented
Small Infrastructures of the High Voltage Lines
Distance from Energy Load Centres (West Coast)
High Cost of Design and planning permission for Shallow Connection, significantly for OHL 220kV
Planning Restrictions regarding OHL Construction
Simple Cycle
Operate for Short / Variable Times
Designed for Quick Start-Up
Combined Cycle
Designed for Quick Start-Up
Typically Has Ability to Operate in SC Mode
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The energy contained in a flowing ideal gas is the sum of enthalpy and kinetic energy.
Pressurized gas can store or release energy. As it expands the pressure is converted to kinetic energy.
Principles of Operation
Link to picture
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Compressor
As air flows into the compressor, energy is transferred from its rotating blades to the air. Pressure and temperature of the air increase.
Most compressors operate in the range of 75% to 85% efficiency.
Combustor
The purpose of the combustor is to increase the energy stored in the compressor exhaust by raising its temperature.
Turbine
The turbine acts like the compressor in reverse with respect to energy transformation.
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Overall Energy Transformations (Thermal Efficiency)
Useful Work = Energy released in turbine minus energy absorbed by compressor.
The compressor requires typically approximately 50% of the energy released by the turbine.
Overall Thermal Efficiency =
Useful Work/Fuel Chemical Energy *100
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Combustion System
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Compressor
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Aero-derivatives
Higher Pressure Ratios and Firing Temperatures Result in Higher Power Output per Pound of Air Flow
Smaller Chilling/Cooling Systems Required
Compressor Inlet Temperature Has a Greater Impact on Output and Heat Rate
Benefits of Chilling/Cooling Systems are More Pronounced
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Prime Mover (Combustion Turbine)
Gas Turbine Exhaust used as the heat source for the
Steam Turbine cycle
Advantages:
Higher overall efficiency
Good cycling capabilities
Disadvantages
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The first question that should be answered is how does a combined cycle work.
A combined cycle plant generates power by the use of both steam and heated air. Air is drawn into the combustion turbine and compressed. The compressed air is heated, which forces it to expand and turn the rotor blades of the turbine. Since, the turbine, compressor, and generator share the same shaft, the energy imparted to the turbine also generates the mechanism for turning the generator, which generates electricity.
The remaining energy in the flue gas is exhausted from the combustion turbine as waste energy. The waste energy exhausted from the combustion turbine is channeled through the heat recovery steam generator (HRSG) and is absorbed by the heating surface to produce steam for generating power or for use in process applications.
Plant Efficiency ~ 58-60 percent
Biggest losses are mechanical input to the compressor and heat in the exhaust
Steam Turbine output
More with duct-firing
up to 750 MW for 3 on 1 configuration
Up to 520 MW for 2 on 1 configuration
Construction time about 24 months
Engineering time 80k to 130k labor hours
Engineering duration about 12 months
Capital Cost ($900-$1100/kW)
Two (2) versus Three (3) Pressure Designs
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Correlating Efficiency to Heat Rate (British Units)
h= 3412/(Heat Rate) --> 3412/h = Heat Rate*
Simple cycle – 3412/.44 = 7,757 Btu/Kwh*
Combined cycle – 3412/.58 = 5,884 Btu/Kwh*
Correlating Efficiency to Heat Rate (SI Units)
h= 3600/(Heat Rate) --> 3600/h = Heat Rate*
Simple cycle – 3600/.44 = 8,182 KJ/Kwh*
Combined cycle – 3600/.58 = 6,207 KJ/Kwh*
Practical Values
Simple cycle 7FA (new and clean) 10,860 Btu/Kwh (11,457 KJ/Kwh)
Combined cycle 2x1 7FA (new and clean) 6,218 Btu/Kwh (6,560 KJ/Kwh)
*Gross LHV basis
Load (Base, Peak, or Part)
Compressor Inlet Temperature
Exhaust Pressure Drop
Steam or Water Injection Rate
Used for either power augmentation or NOx control
Relative Humidity
A Cogeneration Plant
Power generation facility that also provides thermal energy (steam) to a thermal host.
Typical thermal hosts
paper mills,
chemical plants,
refineries, etc…
potentially any user that uses large quantities of steam on a continuous basis.
Good applications for combined cycle plants
Require both steam and electrical power
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Combustion Turbine (CT/CTG)
Steam Generator (Boiler/HRSG)
Steam Turbine (ST/STG)
Heat Rejection Equipment
Electrical Equipment
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Electricity Basics
Electricity can be either direct current (DC) or alternating current (AC)
In AC current, the voltage and current fluctuate up and down 60 times per second in North America and 50 times per second in the rest of the world
The power (W) in a DC current is equal to current (amps) x voltage (volts): P=VI
The power in an AC current is equal to the product of the root mean square (RMS) of the fluctuating current and voltage if the current and voltage are exactly in phase (exactly tracking each other):
P=Vrms x Irms
The standard electricity distribution system consists of 3 wires with the current in each wire offset by 1/3 of a cycle from the others, as shown in the next figure
Electricity demand continuously varies, and power utilities have to match this variation as closely as they can by varying their power production. The following distinctions are made:
Base_load power plants: these are plants that run steadily at full load, with output equal to the typical minimum electricity demand during the year. Plants (such as coal or nuclear) that cost a lot to build but are cheap to operate (having low fuel costs) are good choices
Peaking powerp lants: these are plants that can go from an off state to full power within an hour or so, and which can be scheduled based on anticipated variation in demand (natural gas turbines or diesel engines would be a common choice)
Spinning reserve: these are plants that are on but running at part load – this permits them to rapidly (within a minute) vary their output, but at the cost of lower efficiency (and so requires greater fuel use in the case of fossil fuel power plants).
Electricity from Fossil Fuels
Fuel cells
Full load efficiency
Auxiliary energy use
Source: Hoffert et al (2002, Science 298, 981-987)
The upper limit to the possible efficiency of a power plant is given by the Carnot efficiency:
η = (Tin-Tout)/Tin
So, the hotter the steam supplied to the steam turbine, the greater the efficiency.
Hotter steam requires greater pressure, which requires stronger steel and thicker walls.
so there is a practical limit to the achievable Carnot efficiency (and actual efficiencies are even lower)
Typical: 590ºC, 35% efficiency
This is an alternative advanced coal power plant concept
Rather than burning pulverized solid coal, the coal is heated to 1000ºC or so at high pressure in (ideally) pure oxygen
This turns the coal into a gas that is then used in a gas turbine, with heat in the turbine exhaust used to make steam that is then used in a steam turbine
Efficiencies of ~ 50% are expected, but are much lower at present
Simple-cycle power generation
Combined-cycle power generation
Has a compressor, combustor, and turbine proper
Because hot gases rather than steam are produced, it is not restricted in temperature by the rapid increase in steam pressure with temperature
Thus, the operating temperature is around 1200ºC
Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)
Efficiency of generating electricity using natural gas
One might expect a high efficiency from the gas turbine, due to the high input temperature (and the resulting looser Carnot limit)
However, about half the output from the turbine has to be used to compress the air that is fed into it
Thus, the overall efficiency is only about 35% in modern gas turbines
Efficiency and cost of a simple-cycle gas turbine with and without water injection
Due to the afore-mentioned high operating temperature of the gas turbine, the temperature of the exhaust gases is sufficiently hot that it can be used to either:
Make steam and generate more electricity in a steam turbine (this gives combined cycle power generation). Or:
provide steam for some industrial process that can use the heat, or to supply steam for district heating (this gives simple cycle cogeneration)
Source: Williams (1989, Electricity: Efficient End-Use and New Generation Technologies and Their Planning Implications, Lund University Press)
The energy can be cascaded even further, as follows:
Gas turbine → steam turbine → useful heat as steam from the steam turbine (combined cycle cogeneration), or
Gas turbine → steam turbine → steam → hot water (also combined cycle cogeneration), or
Gas turbine → steam → hot water
Source: Malik (1997, M. Eng Thesis, U of Toronto)
State-of-the-art natural gas combined-cycle (NGCC) systems have electricity generation efficiencies of 55-60%, compared to a typical efficiency of 35% for single-cycle turbines
However, NGCC systems are economical only in sizes of 25-30 MW or greater, so for smaller applications, only the less efficient simple-cycle systems are used
Thus, a number of techniques are being developed to boost the electrical efficiency of simple gas turbines to 42-43%, with one technique maybe reaching 54-57%
In cogeneration applications, the overall efficiency (counting both electricity and useful heat) depends on how much of the waste heat can be put to use. However, overall efficiencies of 90% or better have been achieved
These have pistons that go back and forth (reciprocate)
Normally they use diesel fuel – so these are the diesel generators normally used for backup or emergency purposes
However, they can also be fuelled with natural gas, with efficiencies as high as 45%
These are electrochemical devices – they generate electricity through chemical reactions at two metal plates – an anode and a cathode
Thus, they are not limited to the Carnot efficiency
Operating temperatures range from 120ºC to 1000ºC, depending on the type of fuel cell
All fuel cells require a hydrogen-rich gas as input, which can be made by processing natural gas or (in the case of high-temperature fuel cells) coal inside the fuel cells
Fuel cells (continued)
Electricity generation efficiencies using natural gas of 40-50% are possible, and 90% overall efficiency can be obtained if there is a use for waste heat
In the high-T fuel cells, the exhaust is hot enough that it can be used to make steam that can be used in a steam turbine to make more electricity
An electrical efficiency of 70% should be possible in this way – about twice that of a typical coal-fired.
to each other to form a fuel cell stack.
Cross section of
a single fuel cell.
United Technologies Company 200-kW phosphoric acid fuel cell that uses natural gas as a fuel.
Source: www.utcfuelcells.com
Electrical efficiency vs. load
Summarizing the preceding slides and other information,
Natural gas combined-cycle has the highest full-load efficiency (55-60%) and holds its efficiency well at part load
Reciprocating engines have intermediate full-load efficiencies (40-45%) and load their efficiencies well at part load
Gas turbines and micro-turbines have low full-load efficiencies (typically 25-35%, but ranging from 16% to 43%) and experience a substantial drop at part load
Fuel cells using natural gas have intermediate full-load efficiency (40-45%) but this efficiency increases at part load
Pulverized coal power plant with state-of-the-art pollution controls: $1200-1400/kW
Natural gas combined cycle: $400-600/kW in mature markets, $600-900/kW in most developing countries
Reciprocating engines: $600-1200/kW
Fuel cells: $3000-5000/kW
Cogeneration is the simultaneous production of electricity and useful heat – basically, take the waste heat from electricity generation and put it to some useful purpose. Two possible uses are to feed the heat into a district heating system, and to supply it to an industrial process
Impact of withdrawing useful heat on the production of electricity
Ratio of electricity to heat production
Temperature at which heat is supplied
Electrical, thermal and overall efficiencies
Marginal efficiency of electricity generation
Four efficiencies for cogeneration:
The electrical efficiency – the amount of electricity produced divided by the fuel use (later I’ll need to call this the direct electrical efficiency)
The thermal efficiency –
the amount of useful heat provided divided __by the fuel use
The overall efficiency – the sum of the of two
The effective or marginal efficiency of electricity generation – explained later
Impact of withdrawing heat
In simple-cycle cogeneration, capturing some of the heat in the hot gas exhaust does not reduce the production of electricity, but the electrical production is already low
In cogeneration with steam turbines, the withdrawal of steam from the turbine at a higher temperature than would otherwise be the case reduces the electricity production
The higher the temperature at which we want to take heat, the more that electricity production is reduced
Example of the tradeoff between production of useful heat and loss of electricity production
using steam turbine cogeneration
Source: Bolland and Undrum (1999, Greenhouse Gas Control Technologies, 125-130, Elsevier Science, New York)
Thus, to maximize the electricity production, we want to be able to make use of heat at the lowest possible temperature.
If the heat is to be provided to buildings, that means having well insulated buildings that can be kept warm with radiators that are not very hot
The alternative to cogeneration is the separate production of heat and electricity. The effective efficiency in generating electricity is the amount of electrical energy produced divided by the extra fuel used to produce electricity along with heat compared to the amount of fuel that would be used in producing heat alone. The extra amount of fuel required in turn depends on the efficiency with which we would have otherwise have produced heat with a boiler or furnace.
For example, suppose that we have a cogeneration system with an electrical efficiency of 25% and an overall efficiency of 80%. Then, the thermal efficiency is 80%-25%=55% - we get 55 units of useful heat from the 100 units of fuel. If the alternative for heating is a furnace at 80% efficiency, we would have required 68.75 units of fuel to produce the 55 units of heat. Thus, the extra fuel use in cogeneration is 100-68.75=31.25 units, and the effective electricity generation efficiency is 25/31.25=80%. I call this the marginal efficiency, because it is based on looking at things on the margin (this is a concept from economics).
With a little algebra, it can be shown that the marginal efficiency is given by
nmarginal = nel/(1-nth/nb)
where nel and nth are the electrical and thermal efficiencies of the cogeneration system, and nb is the efficiency of the boiler or furnace that would otherwise be used for heating
(ηel = efficiency of the alternative, central power plant for electricity generation)
Key points
For a given thermal efficiency, the effective electrical efficiency is higher the higher the direct electrical efficiency
However, very high effective electrical efficiencies can be achieved even with low direct electrical efficiencies if the thermal efficiency is high – that is, if we can make use of most of the waste heat
To get a high thermal efficiency requires being able to make use of low-temperature heat (at 50-60ºC), as well as making use of higher temperature heat
Electricity:heat ratio
Because the marginal electricity generation efficiency in cogeneration is generally much higher than the efficiency of a dedicated central powerplant, there is a substantial reduction in the amount of fuel used to generate electricity when cogeneration is used
Thus, we would like to displace as much inefficient central electricity generation as possible when cogeneration is used to supply a given heating requirement
This in turn requires that the electricity-to-heat production ratio in cogeneration be as large as possible
(Remember – none of the gains that we’ve talked about occur if we can’t use the waste heat produced by cogeneration)
Figure 3.17 Dependence of overall savings through cogeneration on the electricity:heat ratio and on the central powerplant efficiency, assuming a 90% overall efficiency for cogeneration and 90% efficiency for the alternative heating system
Capital cost, interest rate, lifespan
Fuel cost (impact of depends on efficiency)
Fixed and variable operation & maintenance costs
Baseload vs peaking costs
Amount of backup capacity
Amortization of capital cost:
where CRF = i /(1-(1+i)-N) is the cost recovery factor
_i = interest rate
8760 is the number of hours in a year
CF= capacity factor (annual average output as a fraction of capacity)
Fuel contribution to the final cost:
Cfuel ($/GJ) x 0.0036 (GJ/kWh) / efficiency
The cost of electricity from less efficient power plants will be more sensitive to the cost of fuel than the cost of electricity from efficient power plants, but more efficient power plants will tend to have greater capital cost
Pulverized coal: $1200-1400/kW,η= 0.45-0.48
$1150-1400/kW hoped for, future
NGCC: $400-600/kW, η = 0.55-0.60
Reciprocating engine: $600-1200/kW,η=0.40-0.46
Micro-turbine: $1800-2600/kW, η= 0.23-0.27
$1000-1500/kW hoped for, future
Cost of heat from boilers, electricity with or without cogeneration, and heat from cogeneration
and from natural gas (at $10/GJ)
Water requirements
Most thermal power plants use water to cool the condenser of a steam turbine and for other, minor, purposes
There are two approaches:
a once-through cooling system
a recirculating system in a cooling tower
Water use by power generation represents the largest or second largest use of water in most countries (with irrigation sometimes being a larger use)
In once-through systems, the water is returned to the source (but at a warmer temperature). Large volumes of water are needed – not available in arid regions
In a recirculating systems, water that has removed heat from the condenser is sprayed through a cooling tower, where it is cooled by evaporation, then returns to the condenser
This consumes water, but the amount that is withdrawn from the water source (lakes, rivers or groundwater) is smaller than in once-through systems
Steam turbines (as in coal power plants)
Once through: 80-190 liters withdrawn per kWh of __generated electricity, ~ 1 liter / kWh consumed
Recirculating: 1-3 liters/kWh withdrawn
~ 0.4 liters/kWh consumed
Bottom line:
More efficient power plants, such as natural gas combined cycle power plants, use less water per kWh of generated electricity than less efficient power plants
The water requirements can be a constraining factor in arid regions
It is possible to use air rather than water to cool the condenser, but then the efficiency drops
Overview
First Practical Turbine – 1884, C. Parsons
First Power Plant – 7.5 kw – 1890
Reaction, Impulse and Velocity-Compounded
Reheat Steam – 1930’s
Last 100 years Turbine is the key element in generating electricity
Turbines run Generators, Pumps, Fans, etc.
Today up to 1,500 MW
Energy Transfer
Reaction Turbines
Newton’s third law of motion – For every action there is an equal and opposite reaction.
Narrowing Steam Path
Narrowing Steam Path
Steam Turbine Fundamentals
Impulse Turbines
Reaction – Impulse Comparison
Velocity-Compounded Turbine
Velocity compounding is a form of staging which by dividing the work load over several stages results in improved efficiency and a smaller diameter for the blade wheels due to a reduction in Ideal blade speed per stage.
P =
1
V
Turbine Components - Blades
Turbine Diaphragms
Steam Turbine Casing
Turbine Rotor
Turbine Types
Straight HP
Tandem HP
Tandem LP
Turbine – Multiple Sets
Overview
Reheat
Turbine Design - Basics
Materials
Blades
17-4 PH steel (+ Ti)
A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in 1884.
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Because the turbine generates rotary motion, it is particularly suited to be used to drive an
electrical generator – about 90% of all electricity generation in the United States, is by use of steam turbines. The steam turbine is a form of
heat engine that derives much of its improvement
in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal
reversible process.
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Further the steam turbine is based upon Rankine cycle
An ideal Rankine cycle operates between pressures of 30 kPa and 6 MPa. The temperature of the steam at the inlet of the turbine is 550°C. Find the net work for the cycle and the thermal efficiency.
Wnet=Wturbine-Wpump OR Qin-Qout
Thermal efficiency hth=Wnet/Qin
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Ideal Rankine Cycle
This cycle follows the idea of the Carnot cycle but can be
practically implemented.
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According to action of steam
(a) Impulse turbine
(b) Reaction turbine
Axial flow turbine
Radial flow turbine
Single stage turbine
Multi stage turbine
Single cylinder turbine
Double cylinder turbine
Three cylinder turbine
(a) Low pressure turbine
(b) Medium pressure turbine.
(c) High pressure turbine
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The common types of steam turbine are
1. Impulse Turbine.
2. Reaction Turbine.
The main difference between these two turbines lies in the way of expanding the steam while it moves through them.
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Simple impulse Turbine.
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Reaction Turbine
In this type of turbine, there is a gradual pressure drop and takes place continuously over the fixed and moving blades. The rotation of the shaft and drum, which carrying the blades is the result of both impulse and reactive force in the steam. The reaction turbine consist of a row of stationary blades and the following row of moving blades.
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When the steam expands over the blades there is gradual increase in volume and decrease in pressure. But the velocity decreases in the moving blades and increases in fixed blades with change of direction.
Because of the pressure drops in each stage, the number of stages required in a reaction turbine is much greater than in a impulse turbine of same capacity.
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The compounding is the way of reducing the wheel or
rotor speed of the turbine to optimum value. It may be defined as the process of arranging the expansion of steam or the utilization of kinetic energy or both in several rings.
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1.Velocity Compounding
2.Pressure Compounding
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Velocity Compounding:
There are a number of moving blades separated by rings of fixed blades. All the moving blades are keyed on a common shaft. When the steam passed through the nozzles where it is expanded to condenser pressure, it's Velocity becomes very high. This high velocity steam then passes through a series of moving and fixed blades
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These are the rings of moving blades which are keyed on a same shaft in series, are separated by the rings of fixed nozzles.
The steam at boiler pressure enters the first set of nozzles and expanded partially. The kinetic energy of the steam thus obtained is absorbed by moving blades.
The steam is then expanded partially in second set of nozzles where it's pressure again falls and the velocity increase the kinetic energy so obtained is absorbed by second ring of moving blades.
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This method of compounding is the combination of two previously discussed methods. The total drop in steam pressure is divided into stages and the velocity obtained in each stage is also compounded. The rings of nozzles are fixed at the beginning of each stage and pressure remains constant during each stage as shown in figure.
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These types include condensing, non-condensing, reheat, extraction and induction.
Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.
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Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.
Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.
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These arrangements include single casing, tandem compound and cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator.
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Casing or shaft arrangements
A two-flow turbine rotor. The steam enters in the middle of the shaft, and exits at each end, balancing the axial force.
The moving steam imparts both a tangential and axial thrust on the turbine shaft, but the axial thrust in a simple turbine is unopposed. To maintain the correct rotor position and balancing, this force must be counteracted by an opposing force.
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An ideal steam turbine is considered to be an isentropic process, or constant entropy process, in which the entropy of the steam entering the turbine is equal to the entropy of the steam leaving the turbine
No steam turbine is truly isentropic, however, with typical isentropic efficiencies ranging from 20–90% based on the application of the turbine.
The interior of a turbine comprises several sets of blades, or buckets as they are more commonly referred to. One set of stationary blades is connected to the casing and one set of rotating blades is connected to the shaft.
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Schematic diagram outlining the difference between an impulse and a reaction turbine
To maximize turbine efficiency the steam is expanded, doing work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as either impulse or reaction turbines.
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An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which is converted into shaft rotation by the bucket-like shaped rotor blades, as the steam jet changes direction.
A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage. As the steam flows through the nozzle its pressure falls from inlet pressure to the exit pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this high ratio of expansion of steam, the steam leaves the nozzle with a very high velocity.
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In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor.
Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades.
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When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also, a turning gear is engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion.
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Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade breaking away from the rotor at high velocity and being ejected directly through the casing. To minimize risk it is essential that the turbine be very well balanced and turned with dry steam - that is, superheated steam with a minimal liquid water content.
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To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine. Modern designs are sufficiently refined that problems with turbines are rare and maintenance requirements are relatively small.
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A force is created on the blades due to the pressure of the vapor on the blades causing them to move. A generator or other such device can be placed on the shaft, and the energy that was in the vapor can now be stored and used.
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To measure how well a turbine is performing we can look at its isentropic efficiency. This compares the actual performance of the turbine with the performance that would be achieved by an ideal, isentropic, turbine. When calculating this efficiency, heat lost to the surroundings is assumed to be zero.
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The isentropic efficiency is found by dividing the actual work by the ideal work.
where
h1 is the specific enthalpy at state one
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COMPRESSOR
TURBINE
COMBUSTOR
GENERATOR
1512 10-13-2004 23:27:31 file=C:\Tflow13\MYFILES\3P 0 70.gtp
Net Power 95959 kW
p[psia], T[F], M[kpph], Steam Properties: Thermoflow - STQUIK
4.717 m
V4
AC,FC = Air & Fuel compressor
HE = Heat exchanger
and micro-turbine
0.0
0.5
1.0
1.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Boiler efficiency = 0.8
Boiler efficiency = 0.9
Heat cost
0
2
4
6
8
10
12
14
MOVING
BLADE
NOZZLE
FIXED
BLADE
MOVING
BLADE

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Combined Cycle Gas Turbine.ppt