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A Study on the catalytic pyrolysis and combustion characteristics of Turkish lignite and co-processing effects with biomass under various ambient conditions

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2012
Abbasi Atibeh, Ehsan
In this study the catalytic pyrolysis and combustion characteristics of Turkish coal samples in O2/N2 and O2/CO2 (oxy-fuel conditions) ambient conditions were explored and the evolution of emissions during these tests was investigated using non-isothermal Thermo-gravimetric Analysis (TGA) technique combined with Fourier Transform Infrared (FTIR) spectroscopy. Potassium carbonate (K2CO3), calcium hydroxide (Ca(OH)2), iron (III) oxide (Fe2O3) and iron (III) chloride (FeCl3) were employed as precursors of catalysts to investigate the effects of potassium (K), calcium (Ca) and iron (Fe). Furthermore the effects of these catalysts on calorimetric tests of Turkish coal samples were investigated. TGA-FTIR pyrolysis tests were carried out in 100 % N2 and 100 % CO2 ambient conditions which are the main diluting gases in air and oxy-fuel conditions. Lignite pyrolysis tests revealed that the major difference between pyrolysis in these two ambient conditions was observed beyond 720 ˚C and Derivative Thermogravimetric (DTG) profiles experienced sharp peaks at 785 ˚C in pure CO2 cases which can be attributed to char-CO2 gasification reaction. Furthermore K2CO3 found to be the most effective catalyst in lignite char gasification reaction during pyrolysis tests in 100 % CO2. Combustion experiments were carried out in various oxygen concentrations from 21 % to 35 % in N2 and CO2 ambient conditions. Lignite combustion tests carried out in CO2 ambient revealed that in 30 % and 35 % oxygen concentrations, the relative active sequence of catalysts to the reaction rates of devolatilization can be described as Fe˃˃ K˃ Ca˃ Raw-form and Fe˃ Ca˃ Raw-form˃˃ K respectively. Furthermore K-based catalyst showed the best char reactivity due to its much higher reaction rates in all the oxygen concentrations. Emission profiles of CO2, CO, H2O, CH4, SOx, COS, NH3, NO and HCl evolved species were analyzed using Fourier Transform Infrared spectroscopy (FTIR) method for pyrolysis and combustion tests in both N2 and CO2 ambient conditions. A good correlation was seen in most of the combustion tests between the T2max (temperature of the maximum rate of weight loss in the devolatalization region of combustion) and TFG-max (temperature of the maximum flue gas emission) and also between