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Gas Turbines Technology, Efficiency, and Performance by Donna J. Ciafone | PDF Free Download.
This book presents current research in the study of gas turbines from across the globe. Topics discussed include techno-economic evaluations of gas turbine repowering systems; in-service degradation of gas turbine nozzles and moving blades
The corrosion characteristics of titanium-based alloys and their degradation mechanisms optimization of a regenerative gas turbine power plant and a discussion of the fluid/solid coupled heat transfer problems in gas turbine applications.
Chapter 1 - This paper evaluates the thermodynamic and economic characteristics of newly proposed two gas turbine (GT) repowering systems together with those of a conventional GT repowering system.
A steam turbine (ST) power generation system (PGS), that uses the steam produced at a small scale refuse incineration plant treating 50 t/d of refuse, is taken as an example of a PGS to be repowered.
First, thermodynamic and economic characteristics of an ST PGS using the steam produced at a refuse incineration furnace (RIF) are evaluated, and it is shown that the net steam-to-electricity efficiency is low (12.4%), the generated net electric power is small (351 kW), and the system is economically infeasible. Second, a GT PGS with the use of a heat exchanger is adopted as a conventional repowering system (S-C).
In the S-C, GT exhaust gas is used to increase the steam temperature from the RIF for increasing generated power and improving the economics of the ST PGS. The optimal scale of the GT is estimated to be small (400 kW), the repowering efficiency of the S-C is 55.2%, and the S-C is economically feasible.
Third, to further improve repowering efficiency and CO2 reduction characteristics, a new repowering system referred to as S-P1 is proposed.
In the S-P1, saturated steam with relatively high pressure (SSHP) produced at the RIF is utilized as a main working fluid of a kind of GT, referred to as an H2O turbine.
The temperature of the SSHP is directly raised to a high temperature by burning fuel with the use of a combustor and is used to drive a generator connected to the H2O turbine.
Hence, the air is only required to burn the fuel, and thus required power for compressing the air becomes significantly small compared with the S-C.
Owing to the smallness of power consumed in an energy-consuming air compression process and the use of SSHP having larger heat energy compared with air as a working fluid, the efficiency of fuel use of the S-P1 is considered to be significantly improved.
It is estimated that repowering efficiency and the internal rate of return (IRR) is 71.2% and 8.33%, compared with those (55.2% and 7.16%) of the S-C, respectively. That is, the S-P1 is estimated to be superior to the S-C in these thermodynamic and economic indices.
Forth, a new repowering H2O turbine PGS referred to as S-P2, is also proposed to increase CO2 reduction characteristics of the S-P1.
The S-P2 is different from the S-P1 in the following points that the fuel is burnt by using pure oxygen instead of air and that the S-P2 can capture the generated CO2. It is estimated that the annual CO2 reduction amount is 2600 t-CO2, compared with those (1330 and 1403 t-CO2) of S-C and S-P1, respectively.
Finally, it is shown that the S-P2 is economically feasible if CO2 emission credit higher than 10 $/(t-CO2) is applied to the amount of captured CO2, not to the CO2 reduction amount.
Chapter 2 - In-service degradation of the gas turbine nozzles and moving blades are presented which is typical for gas turbines.
The qualitative evaluation of deterioration of a gas turbine nozzle and blade related to metal temperature and stress which are variable in different zones of these components during steady-state and high thermal transient loads is carried out.
This evaluation includes microstructural deterioration; volume fraction of carbides increment, grain coarse growing, degradation of γ´ due to elongation (rafting) and coalescence (coarse growing), coating deterioration due to oxidation mechanism and cracks formation.
The direct relationship between the degree of alloy deterioration and the metal temperature is confirmed. The stresses with a detrimental effect on the nozzle and blade were principal of thermal type, developed due to high-temperature gradients across the airfoil wall.
These generate thermal fatigue mechanism and high steady-state load leading to creep mechanism. The dense and continuous net of carbides reduces ductility and toughness of alloy and facilitates crack initiation and propagation.
The degradation of γ´ originates a reduced alloy creep lifetime and the degradation of the alloy (matrix γ) due to grain coarse growing originates a reduced alloy fatigue lifetime.
The application of effective methods of material deterioration evaluation can be used for practical lifetime prediction, just-in-time blades rehabilitation (rejuvenation), safe and cost-effective lifetime extension and to avoid a nozzle/blade catastrophic failure.
Chapter 3 - The present chapter describes the corrosion characteristics of titanium-based alloys, their degradation mechanisms specifically in the context of gas turbines used in aerospace applications.
In addition, life prediction modeling for titanium alloy components is a very important area of research and this aspect explained in detail including the results of the recently developed model.
This is followed by a brief description of efforts made by earlier researchers in the field to develop protective coatings for their protection and the necessity of development of novel coatings with significantly improved properties.
Subsequently, the chapter explains the efforts made in innovating, designing, and developing smart protective coatings with considerably improved oxidation and hot corrosion resistance for effective protection of titanium alloys used in gas turbine engine applications.
Finally, the advantages of developed smart coatings and the necessity of their use in modern gas turbine engines that allow the alloys to be used safely at higher temperatures, which not only would enhance the efficiency of gas-turbine engine-compressor sections but also their life span, has been stressed.
Chapter 4 - Optimization of an intercooler reheat regenerative gas turbine power plant combined (ICRHR) is presented in this chapter. The plant consists of eight components, namely LP and HP compressors; intercooler; regenerator; combustor; HP and LP turbines; and reheater.
Optimum pressure ratios across the compressors and the turbines are determined. Explicit relationships are derived for the network and the thermal efficiency of the plant through thermodynamic models of the components
Which are expressed as functions of total pressure drop within the cycle, the ratio of maximum temperature to a minimum temperature of the cycle, efficiencies of the turbines and the compressors, regenerator effectiveness, and overall pressure ratio of the system?
It is shown that the maximum thermal efficiency design has the advantages of higher efficiency, lower emissions, and smaller sizes of turbines and compressors, compared to the maximum work design.
Hence, the optimization of the power cycle is carried out by maximizing the thermal efficiency with respect to the overall pressure ratio.
The results are presented for the optimal pressure ratio and the corresponding maximum efficiency and the work output versus the ratio of the highest-to-lowest temperatures and the pressure drop factor.
Also, a typical comparison is made between the optimum design points of a regenerative gas turbine engine (RGT) and the ICRHR cycle in terms of the optimum pressure ratio, optimal thermal efficiency, and the corresponding work output under identical conditions.
Chapter 5 - It is shown in this chapter that to optimize a regenerative gas turbine power plant operating on the basis of an open Brayton cycle by maximization of work output, the first law
And second law efficiencies, and minimization of total entropy generation rate associated with the power cycle, as fundamental thermodynamic optimization objectives, means to find an optimal for an overall pressure ratio of the cycle.
The study accounts for components efficiencies and pressure drop throughout the cycle. It is found that at regenerator effectiveness of 50 percent, maximum work output, maximum 1st law efficiency, and minimum entropy generation are coincident
Though this value of the effectiveness is irrelevant from a practical perspective. However, in general, the optimization of any of these four objectives results in different design regimes.
It is shown that entropy generation is a basic requirement to drive a Brayton type heat engine, and it is incorrect to consider the Carnot efficiency as the upper limit of the 1st law efficiency of the plant.
The results indicate that a real engine must operate at a region imposed by maximum work output and maximum 1st law efficiency. In other words, the pressure ratio of the cycle must lie between pressure ratios obtained by maximization of the work output and maximization of the 1st law efficiency.
Furthermore, a criterion is established for the utilization of a regenerator, which leads to introduce the Critical Pressure Ratio beyond which employing a regenerator would be no longer useful.
For the regenerator effectiveness greater than 0.8, the 2nd law efficiency may be considered as a trade-off between the maximum work and maximum 1st law efficiency designs, given that for the regenerator effectiveness around 0.8, a design based on the 2nd law efficiency maximization would be almost equivalent to the maximum work output design.
Chapter 6 - Heat exchanger network (HEN) can be optimized using the stage-wise model of superstructure representation, as proposed by Yee and Grossmann. This model can be solved easily regarding both trivial problems and serious and complex industrial plants.
In this paper, the stage-wise model is extended to retrofits. The method using a stage-wise model is very general; it can be used in new designs as well as in existing process integration.
The methodology of the stage-wise model has been extended to retrofits and can be used to solve heat exchanger networks (HENs) easily and well enough, over a short time, and simultaneously.
Chapter 7 - An accurate prediction of metal temperatures is an important problem in aero-engine design and optimization. The coupled fluid/solid heat transfer computations are performed to predict the temperatures reached in the rotor/stator disc cavities.
An efficient finite element analysis/ computational fluid dynamics (FEA/CFD) thermal coupling technique has been developed and demonstrated. The thermal coupling is achieved by an iterative procedure between FEA and CFD calculations.
Communication between FEA and CFD calculations ensures continuity of temperature and heat flux. In the procedure, the FEA simulation is treated as unsteady for a given transient cycle.
To speed up the thermal coupling, steady CFD calculations are employed, considering that fluid flow timescales are much shorter than those for the solid heat conduction and therefore the influence of unsteadiness in fluid regions is negligible.
To facilitate the thermal coupling, the procedure is designed to allow a set of CFD models to be defined at key time points/intervals in the transient cycle and to be invoked during the coupling process at specified time points.
Test cases considered include rotor/stator disc cavity, free rotating disc, industrial low-pressure (LP) turbine and high-pressure (HP) compressor, with CFD modeling of the flow in the rotor and stator disc cavity, flow induced by the rotating disc, LP turbine disc cavity and the HP compressor drive cone cavity flows, respectively.
Good agreement of wall temperatures with the industrial rig test data was observed. The prediction methods and tools developed and improved can be used in order to automate aero-thermal analysis and to reduce engine design and testing costs.
Chapter 8 - Lately, the use of gas turbines following the deregulation of the electricity supply industry has become greater quickly. The motivation for modeling the gas turbines and their controllers is determinant to the interpreting of their impacts on distribution systems.
The model predictive control (MPC) is used to damp the oscillation when the power distribution system is subjected to a disturbance. MPC is selected because it can explicitly handle the nonlinearities, and constraints of many variables in a single control formulation.
The IEEE 13 node power distribution system is employed to demonstrate the effectiveness of MPC to damp the oscillations of gas turbines. Among fossil fuels, gas is the quickest, with a growth rate nearly double that of coal and oil.
The electricity generation field is the leading market for gas. The natural gas business has a great interaction with the electricity market in terms of fuel consumption and energy conversion.
On the other hand, the transmission and distribution activities are very similar to natural gas transportation through pipelines.
The power losses in gas and electric systems are compared. It is also demonstrated that the electricity system results in more convenient for longer distances of gas wells from the electricity consumption area.
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