analisis exergetico-ciclo combinado

7/28/2019 Analisis Exergetico-ciclo Combinado

1/28

Exergy analysis of a gas-turbinecombined-cycle power plantUniversidad de Cartagena Faculty of

Chemistry Engineering

Thermodynamic II


2/28

2

Content

IntroductionCombined Cycles features

Advantages of combined cycle

environmentalimplications

Power Plant Description

Gas turbineSteam turbine

Recovery boiler

Thermodynamics analysis

Combined Cycles features

Thermodynamic cycle of the.

Exergy

Hysys simulation


3/28

3

IntroductionStudies of engineering designs and exergy analyses for powergeneration systems are of scientific interest and also essential for the

efficient utilization of energy resources. For this reason, the exergyanalysis has drawn much attention by scientists and system designersin recent years. Some devoted their studies to component exergyanalyses and efficiency improvement; others concentrate on systemsdesign and analyses A computerized thermodynamic analyses of a gasturbine based combined cycle power plant (CCPP) fitted with a triplepressure HRSG and hot reheat foresees the efficiency reaching a value

Of 62%. the performance evaluation of a CCPP based only on the firstlaw of thermodynamics is not adequate, but the second law ofthermodynamics must be taken into consideration to get a betterevaluation. The principal processes which cause the destruction ofexergy in a power generation cycle are the combustion process, thesubsequent heating of the working fluid and the heat transfer in theheat exchangers For engineering and system design, gas turbines are

the main power producers in the CCPP, and great progress has beenmade in recent decades to enhance the efficiency of gas turbines. Onthe other hand, researchers also look for methods to improve thepower output and thermal efficiency of already installed gas turbines.System modifications can include cooling the compressor inlet air andpreheating of the fuel gas.


4/28

4

On the combined cycle is the combination of gas turbine, boiler and turbine ofsteam. With this basic scheme, the thermal energy of the exhaust gas turbineis exploited in the recovery boiler to generate steam to the turbine is driven ofsteam.

The basic idea of the combined cycle is the fact that the ejected gas turbinegas high energy content. This energy is used in the steam cycle. With this useof residual thermal energy of the gas cycle, you get a greater use of energyput into game and ultimately increase the overall thermal efficiency. This is amore rational use of energy, achieving energy efficiencies higher thanconventional thermal power plants.

Combined Cycles features


5/28

5

Environmental implications

The basic point is to mention an environmental study of these plants, basedall impacts that may occur in the surrounding environment are:

The justification for the project based on the need for electricity in the areawhere you want implemented, based on the obligation by law to install centralpower generation near the places of consumption.

Consider a range sufficient, considering the biological significance of some ofnatural areas surrounding the site.

Consider the effects of emissions as well as central visual impact of the caseon people living in a principal residence. Should also be taken into account thesame effects on people using the tourist infrastructure in the area near thepotential plant site.


6/28

6

Clearly specify whether the legal and technical incompatibilitiesexist for the installation of high-risk industries.

In the event that the installation of a central, consistent,environmental impact study must consider safety measuresshould be implemented.

It should detail the effects on species and habitats of priorityinterest included in the natural areas that are withinappropriate action.

Clarify the exact number of days that the plant will work withthe type of fuels that can be used and explain the emissions.

You must set the dispersion model of pollutants NOx and SO2for every time of year taking into account the prevailing winds,so that would ensure that no ecosystem exceeds the criticalload.

It should include methods of evaluation and control of thermaleffects in the discharge of effluents and effects on habitats andspecies located in the area of receiving waters. Also shouldinclude the evaluation and control of the effect of discharge ofeffluents.

Should be considered the effects on hydrology, wildlife, floraand landscape of the new pipes and water emission capture

and emission of waste.

Environmental implications


7/28

7

With respect to emissions from a plant of this type and in relation to aconventional power station, the advantages offered by these plants are:

The main advantage of combined cycle plants is to reduce emissionssolid and gaseous waste today compared with the most advanced coal

plants. The emission of CO2, the main responsible of the greenhouse effect in the

atmosphere is reduced by 10% and 25% of the issue of a pulverized coalboiler

The concentration of NO2 with the designs of existing plants can be keptbelow 200 mg NO2/m3.

Environmental advantages ofcombined cycle


8/28

8

Advantages of combined Cycles High thermal efficiency through the application of two

thermodynamic cycles complementary and explained later.

A transfer of heat by the gas turbine can be used in asimple and efficient.

Working fluids air and water readily available, inexpensive,and nontoxic

The combined cycle thermal efficiency is higher than anyother system of conventional power generation.

Flexible charging cycle, combined cycle systems provideflexibility in the operation at base load and average load withdaily start the gas turbine combined cycle multi-axisconfiguration can be started quickly. Combined cycle plantsalso provide efficient operation at part load, particularly incombined cycle systems of multiple gas turbines.

Short Installation Time: combined cycle plants can be

installed and made operational in less time than conventionalsteam plants. This is basically due to packing of the maincomponents in the factory. The phased installation of theplant, where gas turbines are installed and operating in simplecycle during installation of the equipment of the steam cycle,allows users to generate power and start entering from the

first year after the date of order .


9/28

9

Advantages of combined Cycles

> High availability and reliability: The high reliability of operationis the result of evolutionary design development that improvesparts and components and build quality programs. Highavailability is achieved through the development of the entireoperation and maintenance practices, which fall mainly on the

user. The manufacturer's experience and recommendationsalso contribute to high availability.

> Lower operation and maintenance.

> High efficiency with small increments of capacity: Gas turbinesare manufactured and designed in discrete sizes. This allowsfor a phased installation of the same.


10/28

10

Combined Cycle (Brayton & Rankine Cycles)

STEAM TURBINEGAS TURBINE


11/28

11

For the utilization of the exhaust gas turbine, a boiler is usedheat recovery. This team receives hot gases from the turbine, usingenergy to generate steam. This is achieved by harnessing the energy integralfuel, with a high overall efficiency of the installation. The size and characteristics ofthe recovery boiler depend on the one hand the flow, temperature andcomposition of the gas turbine and the other, the flow rate and steam conditions isdesired to produce.

Recovery boiler


12/28

12

Thermodynamics analysis

Thermodynamics studies the transformation of heat intomechanical work, and transformations inverse of mechanical work

into heat. The first principle of thermodynamics is essentially astatement of the law of conservation of energy. This principle isfundamental but enough, since all the energy is equally withoutregard to quality or degradation during a transformation.Thermodynamic system is defined, that portion of the physicalworld (set of field or region of space) under study.

The mechanical work is completely transformed into thermalenergy while the reverse is not entirely possible. That is where theprocessing is done in reverse, part of the thermal energy istransformed into work. The first principle makes no distinctionbetween different types of energy and therefore does not havethis limitation within the meaning of the transformation.

To complement the first principle, it is postulated the second lawof thermodynamics. This principle shows, among other things,that energy has quality and therefore a some ability to producework. this is the problem of thermal energy conversion workdifferently in the transformation of work into heat energy.


13/28

13

Enthalpy and entropy

In the process at constant pressure, isobars, the work associatedwith a change in volume V1 to V2

According to the equation of state of ideal gases:

The enthalpy change of an ideal gas is then as:


14/28

14


The terms of the second member of this equation are based solelyon the temperature For ideal gases. Therefore, the enthalpy of an

ideal gas of course will depend solely on the temperature. As theheat capacity at constant pressure is defined as:

To obtain the enthalpy at different temperatures, we define areference temperature to be given a reference value of theenthalpy, this value is added to the value of the variation enthalpywith the temperature obtained


15/28

15


The Clausius inequality. It states that when a system performsany closed cyclic process, the sum of all terms Q/T on the

frontier of for each differential evolution system is always lessthan or equal to zero. This inequality applies equally to cyclessystems to non-cyclic systems at steady state. This inequality isbecomes an equality only when the process is internallyreversible, being less than zero in the if applied to irreversibleprocesses internally for any closed system

The entropy in the case of a non-cyclic process for a systeminternally reversible closed is defined as:


16/28

16

Exergy

Exergy is defined as the maximum useful work that can beobtained from the combined system-environment when the

system passes from a given state to the dead state.

When the system is in thermal and mechanical imbalance in thereference room, the maximum work that can be done to reachequilibrium with the environment is called thermomechanicalexergy or exergy physics. In the event that there is only a

chemical imbalance in the environment, the maximum workthat can be done to reach equilibrium with the environmentis called chemical exergy. The sum of these twointernal exergy is the irreversibility rates of the system. There aretwo types of exergy, the former due to the kinetic energy ofthe system is calculated assuming that it is open and due to thepotential energy of the system, ie its position in a field of forces.

In the systems under study, the latter two tend tobe negligible because of its small value compared to thosepreviously mentioned.


17/28

17

Calculation of exergy

Exergy of a closed system

To determine the usable energy of the system,

ideally enough to carry the dead state through theprocess desired reversible. The exergy of the system will:

Be

The exergy change is:

The mathematical expression of the change in availability, whenthe system undergoes a process elemental is


18/28

18

18


Applying the first and second law of thermodynamics, whereSi entropy created in the system due to the irreversibility of

the process, which is only zero when the process is reversible.

It follows that:


19/28

19

19


Exergy in an open system.

As in the dead state potential and kinetic energies are zero, useful

work is obtained, if we represent the specific exergy b:

Defining the role of Darrieus as:

The specific exergy or exergy per unit mass of the stream takesthe following form:

The kinetic energy and potential are fully convertible into usefulwork. The values of these irreversibility rates are negligible inmost cases against the internal exergy.

The internal exergy subdivided into physical and chemicalexergy exergy:


20/28

20

20


The expression of the ideal gas physical exergy is:

The expression of the ideal-gas chemical exergy is:


21/28

21

21

Exergetic efficiency

The usefulness of the energy contained in a

system described by exergy. Sincetechnically we areinterested in a system is its ability to produce work, it makesmuch more sense from an economic standpoint, calculateyields exergy instead of energy.

exergetic=exergy obtained/exergy supplied


22/28

22

22

Exergy of a stream

> Means to determine the degree of imbalance of the

substance to the environment.>The environmental parameters are:

To Ambient temperature.

Po Ambient pressure.

Moo Molar chemical potetial (absolute)


23/28

23

23

Calculation of the exergy of the stream

E = h ho To (S- So) + (Mo Moo)PM

Gases and vapors:dh = Cp(T)dT + Q + v(p po)ds = Cp(T) dT/T

Incompressible substances in closed systems:( v constant y Q= 0)dh = Cp(T)dT + vdpds = Cp(T)dT/T

Chemicals in physical equilibrium with the environment:Eq = (Mo Moo)PM


24/28

24

24

Calculation of exergy for flows of watervapor

E = Cp(T-To) + r + v(p-po) To ( CpLnT/To + r/Te )

E = Cp {(T-To) ToLnT/To} + v(p-po) + r(1 To/Te)

E = Cp(T-To) + v(p-po) ToCpLnT/To

E = Cp {(T-To) ToLnT/To } + v(p-po)

E = Cp [(T-To) ToCpLnT/To] R To ln p / po

R y Cp - J / K Kg

Calculation of the exergy of the water

Calculation of exergy from gas streams


25/28

25

25

Thermodynamic efficiency devices,equipment and processes

Turbine with an inlet and an outlet

Turbine bypass with one input and two outputs


26/28

26

26


Compressor


27/28

27

27


Heat exchanger


28/28

28

28


Gas turbine unit

analisis exergetico-ciclo combinado

Documents