Dimensionamento e análise de um sistema experimental para recuperação de calor residual e condicionamento de ar para um motor de combustão interna de grande porte

Abstract

Thermoelectric plants with Internal Combustion Engine (ICE) are a significant part of the brazilian electricity generation. Most of these plants are installed in hot and humid regions, affecting engine performance negatively. Thus, it is interesting to analyse investment alternatives for intake air conditioning, in order to prevent load reduction (derating). Besides that, since most of these power plants are expected to dispatch sporadically, as peaking power plants, they were designed and built focusing on low investment cost, at the expense of its efficiency. Therefore, with these plants dispatching continuously due to a reduction in natural gas price and increasing draughts, opportunities for investments to install Waste Heat Recovery (WHR) systems to increase plant efficiency are surging. Therefore, a thermal system composed by an absorption chiller, fed by the engine residual heat, can produce cold water to condition intake air and, if possible, to provide further cooling to the engine cooling water, after the radiator. However, many configurations can be designed to accomplish this goal, thus a study must be done to determine the most viable option amongst them, financially and thermodynamically. This work aims to analyse, size and compare two configurations of a Waste Heat Recovery (WHR) thermal system for intake air conditioning purposes of a large ICE, with an economic feasibility study for each configuration based on real commercial proposals. A turbocharged internal combustion engine, model Wärtsilä 20V34SG, with 9 MW rated shaft power, installed at the Thermoelectric Power Plant Luiz Oscar Rodrigues de Melo (UTE LORM), in Linhares, Espírito Santo, is used as case study. A modelling of the thermal system integrated with engine is developed in Python, based on mass and energy balance from the Wärtsilä brochure and on a transient model developed separately in the GT-Power software, which also defines the maximum allowed engine’s power output. Heat exchanger, cooling tower and absorption chiller sizing are based on a period of 26 months considering distinct weather conditions which are extracted from a weather station’s record near the thermoelectric plant. Results showed that the configuration with cooling tower water aiding radiator cooling instead of cold water is the best financial option in every economic feasibility indicator. Nevertheless, as consequence, higher engine cooling water temperature should increase charge air temperature, possibly reducing engine efficiency and possibly increasing knocking occurrence.