Estudo da influência da composição do carvão e dos requisitos operacionais na combustão em caldeiras usando balanço de massa

Abstract

The combustion process is responsible for more than 80% of the energy used by man, passing through almost all sectors of a society, whether in any part of the world, despite the degree of development. In Brazil, it is estimated that more than 75% of the energy used in the country comes from the burning of coal, firewood, petroleum derivatives, charcoal and biomass, that is, by combustion processes. The inconvenience of using these processes is air pollution, a topic that has been widely researched in recent decades and is characterized as a factor of great relevance in the search for the preservation of the environment and in the execution of sustainable development, as its effects affect human health, ecosystems and materials in many ways. The first step to better use this form of energy conversion is to understand how the combustion process takes place, which variables can be changed, aiming at efficiency and reduction in the emission of pollutants. In this work, the influence of the type of coal and operating conditions on the combustion process was studied, through the elaboration of a mass balance model and also through the comparison of real values measured in a pulverized-coal-fired power plant. The emissions of SO2 and NOx pollutants were analyzed as a function of coal composition and individual variations of the excess air coefficient were also tested, thus observing the influence of this variable on CO and NOx emissions. Through the analysis of the composition of the coals, it was examined that the SO2 emission is directly proportional to the sulfur content of the coal. In the tests, it was noticed that excess air exerts a small influence on the formation of total NOx from coal combustion, and an increase in this variable decreases the emission of NOx. Regarding CO emission, there was a more considerable decrease of this pollutant when the excess air was increased. Comparing the results of the analysis of the combustion gases measured in the industrial plant with the values calculated by the model, a good agreement was verified, making it useful for the analysis of different combustion scenarios.