Characteristic and evolution of sulfur functionalities in coal and sewage sludge during combustion

X-ray photoelectron spectroscopy was used to investigate the forms and the evolution of sulfur in a bituminous coal, a sewage sludge(SS) and their chars at different bum off ratio (0, 30%, 50%, 70% and 100%) during isothermal combustion. Samples were dried at 105 degrees C and ground into fine powder, and passed through a 120 mesh screen. Chars were prepared at the temperature of 850 degrees C under the environment of N-2 and O-2 (N-2:O-2=80:20) in a tube furnace reactor. Important conclusions were obtained from experiment as follows: The sulfur in the coal mainly existed in the forms of mercaptan(SI), sulfide(S2), thiophene(S3),sulfoxide(S4), sulfone(S5) and sulfate(S6). With the process of combustion, the contents of S1 and S2 decreased while that of S3 and S5 presented in the tendency of increasing in early stage and decreasing in terminal stage. S4 ascended in whole combustion period. Small amount of S6 was detected and the fluctuant characteristic of it was observed. The tendency of S1, S2, S5 and S6 in sewage sludge was consistent with that in coal, however, S4 decreased in the end of combustion. The evolution of S3 in sewage sludge was opposite to that of coal.