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Use of thermal analysis and Drop Tube Furnace (DTF) to evaluate the thermal efficiency of mineral coal, sugarcane bagasse and their mixtures

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Author(s):
Daniela Andresa Mortari
Total Authors: 1
Document type: Doctoral Thesis
Press: São Carlos.
Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
Defense date:
Examining board members:
Paula Cristina Garcia Manoel Crnkovic; Ivonete Ávila; Salvador Claro Neto; Josmar Davilson Pagliuso; Araí Augusta Bernárdez Pécora
Advisor: Paula Cristina Garcia Manoel Crnkovic
Abstract

This study evaluates the thermal behavior of sugar cane bagasse, two bituminous coals (CE 4500 and PSOC 1451) and blends composed of 75%coal/25%bagasse under 80%N2/20%O2 (conventional combustion), 80%CO2/20%O2 (oxy-fuel combustion simulation), 100% CO2, 100% N2 and 100% O2 atmospheres. The evaluations were conducted by means of ultimate analysis, Thermogravimetric analysis (TGA), Differential Thermal Analysis (DTA) and DTF (developed in this study) – which includes thermal decomposition profiles, determination of activation energy, evaluation of atmosphere and interaction effects on the blends, evaluation of SO2, CO2, NO e CO emissions, burning yield and residues analysis. The results show the high content of volatile matter in the bagasse leads to a high rate reaction during the thermal decomposition of the material in comparison to coals, hence, a higher intensity of exothermic events. Such a characteristic of the bagasse also influences the first step of the thermal decomposition and leads to a lower activation energy (Eα) (30 kJ mol-1) in comparison with the values obtained for coals (126 kJ mol-1 for CE 4500 and 100 kJ mol-1 for PSOC 1451). When N2 was replaced by CO2, the activation values obtained in the first step of the bagasse decomposition increased from 30 kJmol-1 to 170 kJ mol-1. However, an opposite effect was observed for both coals (E decreased from 200 to 130 kJ mol-1 for CE 4500 and from 100 to 75 kJ mol-1 for PSOC 1451). The difference was attributed to the volatile mechanism of the matter diffusivity during the thermal decomposition. The atmospheres applied did not affect the thermal decomposition behavior of the blends. Regarding the DTF results, under CO2 atmosphere, all materials showed lower NO emissions in comparison to air atmosphere - NO emissions were up to 34% lower than those in air atmosphere. However, the CO emissions were lower in the CO2 environment. No trend could be observed regarding SO2 emissions. The bagasse burning efficiency was 50% higher in air environment due to the easy ignition under such atmosphere. For coals, higher burning efficiency and lower activation values were achieved under CO2 atmosphere (8% higher). Regarding the study of synergism, the analytical techniques applied did not confirm the interaction between the materials. (AU)