Effects of water/steam injection on the thermoeconomic performance and emissions of gas turbines and their optimization

Rapidly growing demand for gas turbines promotes research on their performance improvement and reducing their exhaust pollutants. Even small increments in net work or cycle efficiency and small changes in pollutant emissions have become significant concerns for both new designs and cycle modifications. To fulfill these requirements an accurate performance evaluation method which enables to see the effects on the exhaust gas composition is an important necessity. Such methods with chemical equilibrium approximation which depends on the exact gas composition inside the combustion chamber have been demonstrated by previous authors and proved accuracy for reciprocating engines but none has been proposed for gas turbines in the available literature. To fill this gap, a precise thermoenvironomic performance evaluation approach for gas turbine cycles which enables economic and environmental aspects to be considered simultaneously, is presented in this work. This approach provides more accurate results than present methods which assume constant specific heats and complete combustion and can be applied to all gas turbine cycles for any type fuel. Additionally, equilibrium exhaust species and flame temperature obtained can directly be used for the estimation of non-equilibrium exhaust pollutants using existing chemical kinetic or semi-empirical correlations. With all its capabilities, this approach enables to combine the key objectives of a gas turbine engine design: performance, emission and cost optimization by providing an accurate method that depends on the equilibrium exhaust species. Chapter 1 gives detailed information about gas turbines, especially about steam/water injection technique, its constrains, alternative NOx control methods and a literature review. In Chapter 2, chemical equilibrium routines of Olikara and Borman is modified to simulate steam/water injected, double fuel, EGR - reheat combustion model which will be used in the following chapters to calculate exhaust gas properties precisely and consequently performance of the steam/water injected gas turbine cycles. In Chapter 3, a STIG cycle with steam injection is modeled and analyzed to show the capabilities of the presented approach. Later on, performance of this cycle is evaluated for varying steam injection, as well as equivalence and pressure ratios, taking irreversibilities and pressure losses into account and effects of each parameter on the net work and thermal efficiency are demonstrated. A full thermoenvironomic analysis is conducted. Steam injection effects on the non-equilibrium NOx and CO emissions and environmental damage costs, also fuel and investment costs are also presented. In the following chapters, 4, 5 and 6, RSTIG, ISTIG and RHSTIG cycles are aslo modelled using the presented approach. Steam injection effects on all those cycles are analyzed and thermoenvironomic performance is also presented and optimization potentials are discussed. Chapter 7 introduces the potential requirements of steam generation in steam injected gas turbine systems and puts forward a practical HRSG design for steam injected gas turbines which is used for thermo-economic evaluation of steam injected gas turbine cycles. Chapter 8 presents a verification of the model in comparison to a real steam injected gas turbine with intercooling and reheat. The study is concluded in Chapter 9 in which the key findings of the study are stressed. Weather the future technological improvements to gas turbines are likely to make steam injected cycles more or less attractive is discussed. Examples for further capabilities of the model for gas turbine analysis of different scope are also mentioned.