Akademik Veri Yönetim Sistemi
FUEL, cilt.115, ss.841-849, 2014 (SCI-Expanded)
The catalytic pyrolysis and combustion characteristics of low calorific value Turkish lignite in various ambient conditions were explored and the evolution of gases during pyrolysis tests was examined using a Thermogravimetric Analyzer coupled with a Fourier Transform Infrared spectrometer (TGA-FTIR). Potassium carbonate (K2CO3), calcium hydroxide (Ca(OH)(2)) and iron (III) oxide (Fe2O3) were employed as precursors of the catalysts and compared to the Raw-form (no catalyst added) to investigate the effects of potassium (K), calcium (Ca) and iron (Fe) on pyrolysis and combustion. Pyrolysis tests were carried out in 100% N-2 and 100% CO2 ambient conditions which are the main diluting gases in air and oxy-fuel combustion. These experiments revealed that the major difference between pyrolysis in these two ambient conditions was observed above 720 degrees C and DTG (Derivative Thermogravimetric) profiles experienced sharp peaks at 785 degrees C in 100% CO2 which can be attributed to a char-CO2 gasification reaction. Furthermore, K2CO3 was found to be the most effective catalyst in the char gasification reaction during pyrolysis tests in 100% CO2. Combustion experiments were carried out in various oxygen concentrations from 21% to 35% O-2 in N-2 and CO2 ambient conditions. Combustion tests carried out in O-2/CO2 ambient conditions revealed that for 30% and 35% O-2, 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, potassium catalyst had the best char reactivity due to its much higher reaction rates for all oxygen concentrations. The burnout temperature (T-b) also experienced a significant drop in the case of the K-based catalyst. Finally, emission profiles of the evolved gases, CO2, CO, H2O, SOx and COS, were analyzed during pyrolysis tests in both N-2 and CO2 ambient conditions using the FTIR method. (C) 2013 Elsevier Ltd. All rights reserved.