THE CHARACTERISTIC AND EVOLUTION OF NITROGEN FUNCTIONAL GROUPS IN COAL AND SEWAGE SLUDGE DURING THEIR CO-COMBUSTION

摘要

X-ray photoelectron spectroscopy was used to investigate the characteristic and evolution of nitrogen in mixtures of bituminous coal and sewage sludge (SS) and their chars during isothermal combustion. Five groups of mixtures, in which the mass percent α of SS were 0，10%，20%，30% and 100% respectively, were detected at different burn off ratio βof 0, 30%,50%, 70% and 100%. Important conclusions were obtained from experiment as follows: The nitrogen in the coal existed in the forms of pyridine (N-6), pyrrol (N-5), quaternary nitrogen (N-Q) and nitrogen oxides (N-O). N-5 decreased during mono-combustion while N-6 and N-Q increased at the beginning and decreased with the process. The opposite tendency of N-O was observed. Nitrogen in SS was mainly nitryl（-NO2）, nitrate（NO3 -）and ammonium（NH4 +）. -NO2 declined at first and rose up at last while NO3 - and NH4 ＋ presented in opposite characteristic. Nitrogen in the mixtures resulted from the accumulation of that in coal and SS respectively. N-5 detected was much lower than the estimated value in original mixtures, which may be ascribed to the adhesion of SS on coal surface. The transformation of each functional group during co-combustion were correlated with that during mono-combustion of coal and SS and no obvious interactions was observed, which demonstrated that combustion of nitrogen in mixtures both kept their own characteristics in the process of reaction. The tendency of N-6，N-5，N-Q/NH4 + and N-O/-NO2 were in accordance with coal while that of NO3 - was similar to SS.