THERMODYNAMIC ANALYSIS OF GAS TURBINE COGENERATION SYSTEM INTEGRATED WITH IAC AND STIG

Abstract

With a high back-work ratio and a high exhaust temperature, the simple cycle gas-turbine generation system usually has a low generation-efficiency especially when the ambient temperature is hot. The exhaust gases of a gas turbine carry a significant amount of thermal energy that is usually expelled to the atmosphere without taking any further part in the power generation process. The low grade thermal energy can however be put to beneficial use. To recover the very high temperature of exhaust gases (around 500˚C) from simple cycle gas turbine generation sets (GENSETs), a heat recovery steam generator (HRSG) is often used and steam is generated. The generated steam can be either used for many useful processes (heating, drying, separation etc.) or used back in the power generation system for enhancing power generation capacity and efficiency. Among many technologies to improve the efficiency of a simple cycle gas turbine, inlet air cooling (IAC) and steam injection gas turbine (STIG) are considered the best ways to modify an existing simple cycle unit without major destruction to its original integrity. These attractive features can use the steam generated in the HRSG to improve the power generation capacity and efficiency. The objective of the present work is to explore the utilization of the exhaust gases of a gas turbine plant. In this study, a 7B Frame GENSET was considered as base unit and IAC & STIG features have been sequentially analyzed after system retrofitting with the concept of cogeneration without steam injection, cogeneration with steam injection and cogeneration with IAC & process steam cycle. The present study is to evaluate the system performance parameters (first-law and second-law efficiency, power-to-heat ratio, COP, fuel-air ratio, steam injection ratio, compressor work, turbine work and net power output) in different cases after system retrofitting. For the simulation of power generation system, a computer program has been developed in Engineering Equation Solver (EES) software and validated with the data available in the literature. Parametric study has been performed using combined first and second law approach to investigate the effects of compressor air inlet temperature and pressure of steam on first and second law efficiency, power-to-heat ratio, fuel-air ratio, steam injection ratio and exergy destruction in the system components.