Co-processing of Lignite with Corn Residues for Energy or Syngas Production Thermochemical Behavior and Kinetic Modeling

The combustion and carbon dioxide gasification behavior of lignite/corn cobs mixtures through thermal analysis experiments was investigated. A simple and accurate model was developed to provide and compare the kinetics of these processes. The characteristic parameters of combustion and gasification, such as decomposition temperature, reaction rate and reactivity, were correlated to the pore structure of the fuels, the composition of ash and mutual interactions between blend components. Combustion of fuels studied occurred in two distinct stages. The reactivity of corn cobs was much higher. When this material was blended with the lignite it improved its combustion efficiency and the mixture presented an additive behavior. The gasification process of chars took place between 750 °C and 950 °C. Corn cobs char exhibited a higher rate. The percentage of this material in the blend was quite low to influence the reactivity of the lignite. The independent parallel reactions model fitted the experimental results with a good accuracy. Activation energy values of combustion varied between 65 kJ/mol and 261 kJ/mol, while those of gasification were enhanced 136-395 kJ/mol, due to the higher thermal stability of chars. The similar thermochemical behavior of the fuels could be advantageous for their co-processing in existing lignite plants, offering economic and environmental benefits.