Thermodynamic and Energy Study of a Regenerator in Gas Turbine Cycle and Optimization of Performances

Thermodynamic and Energy Study of a Regenerator in Gas Turbine Cycle and Optimization of Performances

Saria Abed (National Engineering School of Gabes (ENIG), University of Gabès, Gabès, Tunisia), Taher Khir (National Engineering School of Gabes (ENIG), University of Gabès, Gabès, Tunisia) and Ammar Ben Brahim (National Engineering School of Gabes (ENIG), University of Gabès, Gabès, Tunisia)
Copyright: © 2016 |Pages: 20
DOI: 10.4018/IJEOE.2016040102
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Abstract

In this paper, thermodynamic study of simple and regenerative gas turbine cycles is exhibited. Firstly, thermodynamic models for both cycles are defined; thermal efficiencies of both cycles are determined, the overall heat transfer coefficient through the heat exchanger is calculated in order to determinate its performances and parametric study is carried out to investigate the effects of compressor inlet temperature, turbine inlet temperature and compressor pressure ratio on the parameters that measure cycles' performance. Subsequently, numerical optimization is established through EES software to determinate operating conditions. The results of parametric study have shown a significant impact of operating parameters on the performance of the cycle. According to this study, the regeneration technique improves the thermal efficiency by 10%. The studied regenerator has an important effectiveness (˜ 82%) which improves the heat transfer exchange; also a high compressor pressure ratio and an important combustion temperature can increase thermal efficiency.
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1. Introduction

The gas turbines are energy systems used to convert thermal energy into mechanical energy (on the basis of thermodynamic transformations). This mechanical energy is obtained directly from the kinetic energy of the gases produced by the combustion of a hydrocarbon (oil, fuel gas ...), undergoing expansion in a turbine. The oxidant is usually ambient air; it is generally compressed before entering the combustion chamber, using a rotary compressor driven by the same shaft as the turbine (Y.S.H. Najjar, 1987).

These thermodynamic machines have known a phenomenal development and a growth since its first successful development in 1930 (Claire M, 2006). The first gas turbine built in the 1940s and even the 1950s had low thermal efficiency of approximately 17% due to low efficiencies of compressors and turbines and bass turbine inlet temperatures because of metallurgical limitations of materials forming the turbine components. It is used in many different sectors such as energy production, oil, gas processing plants, aviation as well as domestic applications and small industries (L. Langston, 1996).

The simple cycle turbine known Brayton gas cycle is composed of a compressor, combustion chamber and a gas turbine which is mounted on the same axis with the compressor (Y.S.H. Najjar & M.S. Ismail, 1990). There are two forms: closed cycle and open cycle (H. Cohen et al., 1987). For the open cycle, the outlet gas from turbine is rejected to a chimney to be released into the atmosphere. An energy recovery at the output of the turbine it is nevertheless possible that will improve performance of the cycle (Filippo de Monte & Paolo Rosa, 2007; Mehrwan P. Boyce, 2006). The closed cycle has the same elements shown in the previous cycle plus a heat exchanger for cooling the gas from the turbine before being introduced back into the compressor. Although this cycle shows less polluting gas recycling, there is a possibility to reach the mechanical elements of the cycle (Filippo de Monte & Paolo Rosa, 2007; Mehrwan P. Boyce, 2006).

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