Determination of the NO_x precursors NH_3 and HCN in a Flash Pyrolysis Reactor

摘要

Coal combustion is characterized by several superimposed processes which influence each other. Heating the coal in an inert atmosphere ensures the examination of coal pyrolysis independently from other combustion steps. Therefore, a flash-pyrolysis reactor was developed to investigate the pyrolysis of pulverized coal under these conditions. The following relevant parameters were derived from typical modem coal fired plants: heating rate. (10~5 K/s), reactor temperature (<1500 deg C) and particle size distribution (<125 urn). The aim of the experiments was to determine the NH3- and HCN-yields after coal pyrolysis as well as the determination of the overall kinetic parameters, the yield factor as the quotient of high to proximate volatile matter, the fuel bound nitrogen distribution and the composition of the pyrolysis gas. The results obtained in the current investigations are of specific significance since they provide more detailed information than conventional coal analysis. The nitrogen distribution between the volatiles and fixed char is the key value in predicting the NO_x-formatlon behaviour of pulverized coal. Major intermediate species for the NO_x-formation are NH3 and HCN which are determined quantitatively among others by Mass-Spectroscopy. Despite similar proximate and ultimate analysis high volatile coals show a different pyrolysis behaviour. Especially characteristic parameters like the yield factor exceed standard values and the HCN-formation shows different conversion rates. At present mathematical pyrolysis models are not accurate enough to substitute experimental investigations. The results obtained contribute to the further development of detailed pyrolysis models.