OXY-COMBUSTION OF CHAR FROM FAST PYROLYSIS PRODUCED IN CO_2 AND N_2 ATMOSPHERES

摘要

One of the clean coal technologies with potential promise of carbon dioxide reduction from power plant is oxy-combustion. This technology is advantageous for retrofitting existing units from conventional combustion to oxy-combustion. Differences between air and oxy gases composition lead to different combustion process behavior. The basic parameters in oxy and air combustion are different, among them are: fluid dynamics, ignition, heat release and heat transfer rates. That is why it is necessary to study behaviour of the pulverized solid fuels in oxy-combustion processes. The oxy-fuel combustion environment affects both on coal pyrolysis and char combustion; hence effects of oxy-fuel atmosphere on those processes still need to be studied. Significant influence on both these processes have CO_2 and H_2O gasification reactions and the homogenous water shift reactions. The investigations of this work compare results performed under air conditions i.e. devolatilization in nitrogen and char combustion in air with results performed in oxy-fuel conditions. For the experimental investigations high volatile lignite with various moisture content was used. Results of the pyrolysis experiments have given information about the gas composition including N-fuel species in gas phase and the total and fractional mass loss of C, H, N. In addition, the solid phase (char) was characterized by ultimate, SEM and by mercury porosimetry technique. With the remaining char fractions obtained in N_2 and CO_2 environment, additional combustion tests under air and oxy-fuel conditions have been performed. A major focus of the investigations was to determine the impact of moisture content in lignites on the composition of pyrolitic gas and comparison of NO_x emission from raw lignite and char combustion.