Waldyr Luiz Ribeiro Gallo

Choice of a reference state for exergetic analysis

The concepts of thermomechanical exergy, chemical exergy, restricted dead state, and unrestricted dead state are described. A detailed discussion is presented on identification of the reference state. The influence of commonly-used methods on evaluation of the overall exergy is analysed. The effect of using a standard reference state is compared with that for a reference state in which the composition is defined according to the problem under study. Finally the second-law efficiency is defined and discussed for general control volumes and closed systems.

Exergetic evaluation of a cogeneration system in a petrochemical complex

The purpose of this paper is the study of a real cogeneration system existing in a petrochemical complex. The total capacity of the plant is 200 MW of electrical power and 2100 t/h of steam for processes. This work presents the mass and energy balances of this cogeneration system. Exergy of each involved stream is calculated and the exergetic balance of each subsystem is presented, as well as of the global system, identifying where and why losses and irreversibility occur. Efficiencies based on the second law of thermodynamics are calculated for each subsystem and compared. Some conclusions regarding operational strategies are presented.

Effect of turbine-blade cooling on the hat (humid air turbine) cycle

We discuss the effects of turbine-blade cooling on HAT-cycle performance. The performance depends on the location for cooling by air bleeding; four possible locations have been explored. A parametric analysis was performed to verify pressure-ratio and turbine-inlet-temperature (TIT) effects. An exergetic analysis was used to clarify the differences between bleed-air point options and cycle-configuration choices.