Combustion Behavior and Kinetics of Turkish Lignite Blended with Biomass/Magnesite Dust

Abstract

The effect of blending on the combustion behavior of a Turkish lignite blended with biomass or magnesite dust using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared spectrometer (FTIR) under air atmosphere has been investigated. The lignite used in this study is Tunçbilek lignite (TL), which is blended with two biomasses, olive residue (OR) and almond shell (AS), and the inorganic industrial waste, magnesite dust (MD). The blends are composed of various weight fractions of fuels, with a constant weight fraction of molasses (1% by weight) as a binding agent. TGA weight loss trends are used to obtain characteristic temperatures and to define weight conversion stages. Experimental results show three distinct stages of conversion during combustion of biomass fuels and two stages for lignite. Burnout temperature increases and the combustibility index decreases for lignite when blended with molasses. On the other hand, blending of biomass with lignite results in approximately 4°C lower ignition temperatures and an increase in combustibility index and reactivity. FTIR results of biomass blend combustion indicate a positive effect in reducing the CO and SOx emissions when blended with lignite. Magnesite dust addition causes a decrease in gaseous emissions for all blending ratios having the maximum reduction at 1% by weight of magnesite. Moreover, kinetic parameters (apparent activation energy, pre-exponential factor) for each fuel are obtained using a model-fitting method (Coats-Redfern). Addition of biomass/magnesite dust to the lignite caused a decrease in apparent activation energy. Specifically, apparent activation energy of lignite decreases from 15.6 to 81.6 kJ·mol−1 by adding molasses and reaches approximately 2 kJ·mol−1 by adding 7% by weight of olive residue and almond shell, respectively.